Project Gutenberg's Electricity for the farm, by Frederick Irving Anderson
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Title: Electricity for the farm
Light, heat and power by inexpensive methods from the water
wheel or farm engine
Author: Frederick Irving Anderson
Release Date: November 14, 2008 [EBook #27257]
Language: English
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ELECTRICITY FOR THE FARM
THE MACMILLAN COMPANY
NEW YORK · BOSTON · CHICAGO · DALLAS
ATLANTA · SAN FRANCISCO
MACMILLAN & CO., Limited
LONDON · BOMBAY · CALCUTTA · MELBOURNE
THE MACMILLAN CO. OF CANADA, Ltd.
TORONTO
[Illustration: Even the tiny trout brook becomes a thing of utility
as well as of joy
(_Courtesy of the Fitz Water Wheel Company, Hanover, Pa._)]
ELECTRICITY FOR
THE FARM
LIGHT, HEAT AND POWER BY INEXPENSIVE
METHODS FROM THE WATER
WHEEL OR FARM ENGINE
BY
FREDERICK IRVING ANDERSON
AUTHOR OF "THE FARMER OF TO-MORROW," ETC., ETC.
New York
THE MACMILLAN COMPANY
1915
_All rights reserved_
Copyright, 1915
By THE CURTIS PUBLISHING COMPANY
The Country Gentleman
Copyright, 1915
By THE MACMILLAN COMPANY
Set up and electrotyped. Published April, 1915.
PREFACE
This book is designed primarily to give the farmer a practical working
knowledge of electricity for use as light, heat, and power on the
farm. The electric generator, the dynamo, is explained in detail; and
there are chapters on electric transmission and house-wiring, by which
the farm mechanic is enabled to install his own plant without the aid
and expense of an expert.
With modern appliances, within the means of the average farmer, the
generation of electricity, with its unique conveniences, becomes
automatic, provided some dependable source of power is to be had--such
as a water wheel, gasoline (or other form of internal combustion)
engine, or the ordinary windmill. The water wheel is the ideal prime
mover for the dynamo in isolated plants. Since water-power is running
to waste on tens of thousands of our farms throughout the country,
several chapters are devoted to this phase of the subject: these
include descriptions and working diagrams of weirs and other simple
devices for measuring the flow of streams; there are tables and
formulas by which any one, with a knowledge of simple arithmetic, may
determine the power to be had from falling water under given
conditions; and in addition, there are diagrams showing in general the
method of construction of dams, bulkheads, races, flumes, etc., from
materials usually to be found on a farm. The tiny unconsidered brook
that waters the farm pasture frequently possesses power enough to
supply the farmstead with clean, cool, safe light in place of the
dangerous, inconvenient oil lamp; a small stream capable of developing
from twenty-five to fifty horsepower will supply a farmer (at
practically no expense beyond the original cost of installation) not
only with light, but with power for even the heavier farm operations,
as threshing; and in addition will do the washing, ironing, and
cooking, and at the same time keep the house warm in the coldest
weather. Less than one horsepower of energy will light the farmstead;
less than five horsepower of energy will provide light and small
power, and take the drudgery out of the kitchen.
For those not fortunate enough to possess water-power which can be
developed, there are chapters on the use of the farm gasoline engine
and windmill, in connection with the modern storage battery, as
sources of electric current.
It is desired to make acknowledgment for illustrations and assistance
in gathering material for the book, to the editors of _The Country
Gentleman_, Philadelphia, Pa.; The Crocker-Wheeler Company, Ampere, N.
J.; The General Electric Company, Schenectady, N. Y.; the Weston
Electrical Instrument Company, of Newark, N. J.; The Chase Turbine
Manufacturing Company, Orange, Mass.; the C. P. Bradway Machine Works,
West Stafford, Conn.; The Pelton Water Wheel Company, San Francisco
and New York; the Ward Leonard Manufacturing Company, Bronxville, N.
Y.; The Fairbanks, Morse Company, Chicago; and the Fitz Water Wheel
Company, Hanover, Pa.
TABLE OF CONTENTS
PAGE
INTRODUCTION xvii
PART I
WATER-POWER
CHAPTER I
A WORKING PLANT
The "agriculturist"--An old chair factory--A neighbor's
home-coming--The idle wheel in commission again--Light,
heat and power for nothing--Advantages
of electricity 3
CHAPTER II
A LITTLE PROSPECTING
Small amount of water required for an electric
plant--Exploring, on a dull day--A rough and ready
weir--What a little water will do--The water wheel
and the dynamo--Electricity consumed the instant
it is produced--The price of the average small
plant, not counting labor 22
CHAPTER III
HOW TO MEASURE WATER-POWER
What is a horsepower?--How the Carthaginians
manufactured horsepower--All that goes up must come
down--How the sun lifts water up for us to
use--Water the ideal power for generating
electricity--The weir--Table for estimating
flow of streams with a weir--Another method of
measuring--Figuring water horsepower--The size
of the wheel--What head is required--Quantity of
water necessary 32
CHAPTER IV
THE WATER WHEEL AND HOW TO INSTALL IT
Different types of water wheels--The impulse and the
reaction wheels--The impulse wheel adapted to
high heads and small amount of water--Pipe lines--Table
of resistance in pipes--Advantages and disadvantages
of the impulse wheel--Other forms
of impulse wheels--The reaction turbine, suited to
low heads and large quantity of water--Its advantages
and limitations--Developing a water-power
project: the dam; the race; the flume; the penstock;
and the tailrace--Water rights for the farmer 56
PART II
ELECTRICITY
CHAPTER V
THE DYNAMO; WHAT IT DOES, AND HOW
Electricity compared to the heat and light of the
Sun--The simple dynamo--The amount of electric energy
a dynamo will generate--The modern dynamo--Measuring
power in terms of electricity--The volt--The
ampere--The ohm--The watt and the kilowatt--Ohm's
Law of the electric circuit, and some
examples of its application--Direct current, and
alternating current--Three types of direct-current
dynamos: series, shunt, and compound 89
CHAPTER VI
WHAT SIZE PLANT TO INSTALL
The farmer's wife his partner--Little and big
plants--Limiting factors--Fluctuations in water
supply--The average plant--The actual plant--Amount
of current required for various operations--Standard
voltage--A specimen allowance for electric
light--Heating and cooking by electricity--Electric
power: the electric motor 121
CHAPTER VII
TRANSMISSION LINES
Copper wire--Setting of poles--Loss of power in
transmission--Ohm's Law and examples of how it is
used in figuring size of wire--Copper-wire
tables--Examples of transmission lines--When to
use high voltages--Over-compounding a dynamo to
overcome transmission loss 153
CHAPTER VIII
WIRING THE HOUSE
The insurance code--Different kinds of wiring
described--Wooden moulding cheap and effective--The
distributing panel--Branch circuits--Protecting the
circuits--The use of porcelain tubes and other
insulating devices--Putting up chandeliers and
wall-brackets--"Multiple" connections--How to connect
a wall switch--Special wiring required for heat and
power circuits--Knob and cleat wiring, its advantages
and disadvantages 172
CHAPTER IX
THE ELECTRIC PLANT AT WORK
Direct-connected generating sets--Belt drive--The
switchboard--Governors and voltage regulators--Methods
of achieving constant pressure at all loads:
Over-compounding the dynamo; A system of resistances
(a home-made electric radiator); Regulating
voltage by means of the rheostat--Automatic
devices--Putting the plant in operation 192
PART III
GASOLINE ENGINES, WINDMILLS, ETC.
THE STORAGE BATTERIES
CHAPTER X
GASOLINE ENGINE PLANTS
The standard voltage set--Two-cycle and four-cycle
gasoline engines--Horsepower, and fuel
consumption--Efficiency of small engines and
generators--Cost of operating a one-kilowatt plant 217
CHAPTER XI
THE STORAGE BATTERY
What a storage battery does--The lead battery and the
Edison battery--Economy of tungsten lamps for
storage batteries--The low-voltage battery for
electric light--How to figure the capacity of a
battery--Table of light requirements for a farm
house--Watt-hours and lamp-hours--The cost of storage
battery current--How to charge a storage
battery--Care of storage batteries 229
CHAPTER XII
BATTERY CHARGING DEVICES
The automatic plant most desirable--How an automobile
lighting and starting system works--How the same
results can be achieved in house lighting, by means
of automatic devices--Plants without automatic
regulation--Care necessary--The use of heating devices
on storage battery current--Portable batteries--An
electricity "route"--Automobile power for
lighting a few lamps 250
ILLUSTRATIONS
Even the tiny trout brook becomes a thing of utility as
well as of joy _Frontispiece_
Farm labor and materials built this crib and stone dam 17
Measuring a small stream with a weir 23
Efficient modern adaptations of the archaic undershot
and overshot water wheels 59
A direct-current dynamo or motor, showing details of
construction 92
Details of voltmeter or ammeter 128
Instantaneous photograph of high-pressure water jet being
quenched by buckets of a tangential wheel 194
A tangential wheel, and a dynamo keyed to the same
shaft--the ideal method for generating electricity 194
A rough-and-ready farm electric plant, supplying two
farms with light, heat and power; and a Ward
Leonard-type circuit breaker for charging storage
batteries 244
INTRODUCTION
The sight of a dozen or so fat young horses and mares feeding and
frolicking on the wild range of the Southwest would probably inspire
the average farmer as an awful example of horsepower running to waste.
If, by some miracle, he came on such a sight in his own pastures, he
would probably consume much time practising the impossible art of
"creasing" the wild creatures with a rifle bullet--after the style of
Kit Carson and other free rovers of the old prairies when they were in
need of a new mount. He would probably spend uncounted hours behind
the barn learning to throw a lariat; and one fine day he would sally
forth to capture a horsepower or two--and, once captured, he would use
strength and strategy breaking the wild beast to harness. A single
horsepower--animal--will do the work of lifting 23,000 pounds one foot
in one minute, providing the animal is young, and sound, and is fed
12 quarts of oats and 10 or 15 pounds of hay a day, and is given a
chance to rest 16 hours out of 24--providing also it has a dentist to
take care of its teeth occasionally, and a blacksmith chiropodist to
keep it in shoes. On the hoof, this horsepower is worth about
$200--unless the farmer is looking for something fancy in the way of
drafters, when he will have to go as high as $400 for a big fellow.
And after 10 or 15 years, the farmer would look around for another
horse, because an animal grows old.
This animal horsepower isn't a very efficient horsepower. In fact, it
is less than three-fourths of an actual horsepower, as engineers use
the term. A real horsepower will do the work of lifting 33,000 pounds
one foot in one minute--or 550 pounds one foot in one second. Burn a
pint of gasoline, with 14 pounds of air, in a gasoline engine, and the
engine will supply one 33,000-pound horsepower for an hour. The
gasoline will cost about 2 cents, and the air is supplied free. If it
was the air that cost two cents a pound, instead of the gasoline, the
automobile industry would undoubtedly stop where it began some fifteen
years ago. It is human nature, however, to grumble over this two
cents.
Yet the average farmer who would get excited if sound young chunks and
drafters were running wild across his pastures, is not inspired by any
similar desire of possession and mastery by the sight of a brook, or a
rivulet that waters his meadows. This brook or river is flowing down
hill to the sea. Every 4,000 gallons that falls one foot in one
minute; every 400 gallons that falls 10 feet in one minute; or every
40 gallons that falls 100 feet in one minute, means the power of one
horse going to waste--not the $200 flesh-and-blood kind that can lift
only 23,000 pounds a foot a minute--but the 33,000 foot-pound kind.
Thousands of farms have small streams in their very dooryard, capable
of developing five, ten, twenty, fifty horsepower twenty-four hours a
day, for the greater part of the year. Within a quarter of a mile of
the great majority of farms (outside of the dry lands themselves)
there are such streams. Only a small fraction of one per cent of them
have been put to work, made to pay their passage from the hills to the
sea.
The United States government geological survey engineers recently made
an estimate of the waterfalls capable of developing 1,000 horsepower
and over, that are running to waste, unused, in this country. They
estimated that there is available, every second of the day and night,
some 30,000,000 horsepower, in dry weather--and twice this during the
eight wet months of the year. The waterfall capable of giving up 1,000
horsepower in energy is not the subject of these chapters. It is the
small streams--the brooks, the creeks, the rivulets--which feed the
1,000 horsepower torrents, make them possible, that are of interest to
the farmer. These small streams thread every township, every county,
seeking the easiest way to the main valleys where they come together
in great rivers.
What profitable crop on your farm removes the least plant food? A
bee-farmer enters his honey for the prize in this contest. Another
farmer maintains that his ice-crop is the winner. But electricity
generated from falling water of a brook meandering across one's acres,
comes nearer to the correct answer of how to make something out of
nothing. It merely utilizes the wasted energy of water rolling down
hill--the weight of water, the pulling power of gravity. Water is
still water, after it has run through a turbine wheel to turn an
electric generator. It is still wet; it is there for watering the
stock; and a few rods further down stream, where it drops five or ten
feet again, it can be made to do the same work over again--and over
and over again as long as it continues to fall, on its journey to the
sea. The city of Los Angeles has a municipal water plant, generating
200,000 horsepower of electricity, in which the water is used three
times in its fall of 6,000 feet; and in the end, where it runs out of
the race in the valley, it is sold for irrigation.
One water-horsepower will furnish light for the average farm; five
water-horsepower will furnish light and power, and do the ironing and
baking. The cost of installing a plant of five water-horsepower should
not exceed the cost of one sound young horse, the $200 kind--under
conditions which are to be found on thousands of farms and farm
communities in the East, the Central West, and the Pacific States.
This electrical horsepower will work 24 hours a day, winter and
summer, and the farmer would not have to grow oats and hay for it on
land that might better be used in growing food for human beings. It
would not become "aged" at the end of ten or fifteen years, and the
expense of maintenance would be practically nothing after the first
cost of installation. It would require only water as food--waste
water. Two hundred and fifty cubic feet of water a minute, falling ten
feet, will supply the average farm with all the conveniences of
electricity. This is a very modest creek--the kind of brook or creek
that is ignored by the man who would think time well spent in putting
in a week capturing a wild horse, if a miracle should send such a
beast within reach. And the task of harnessing and breaking this
water-horsepower is much more simple and less dangerous than the task
of breaking a colt to harness.
PART I
WATER-POWER
ELECTRICITY FOR THE FARM
CHAPTER I
A WORKING PLANT
The "agriculturist"--An old chair factory--A neighbor's
home-coming--The idle wheel in commission again--Light, heat and
power for nothing--Advantages of electricity.
Let us take an actual instance of one man who did go ahead and find
out by experience just how intricate and just how simple a thing
electricity from farm water-power is. This man's name was Perkins, or,
we will call him that, in relating this story.
Perkins was what some people call, not a farmer, but an
"agriculturist,"--that is, he was a back-to-the-land man. He had been
born and raised on a farm. He knew that you must harness a horse on
the left side, milk a cow on the right, that wagon nuts tighten the
way the wheel rims, and that a fresh egg will not float.
He had a farm that would grow enough clover to fill the average dairy
if he fed it lime; he had a boy coming to school age; and both he and
his wife wanted to get back to the country. They had their little
savings, and they wanted, first of all, to take a vacation, getting
acquainted with their farm. They hadn't taken a vacation in fifteen
years.
He moved in, late in the summer, and started out to get acquainted
with his neighbors, as well as his land. This was in the New England
hills. Water courses cut through everywhere. In regard to its
bountiful water supply, the neighborhood had much in common with all
the states east of the Mississippi, along the Atlantic seaboard, in
the lake region of the central west, and in the Pacific States. With
this difference; the water courses in his neighborhood had once been
of economic importance.
A mountain river flowed down his valley. Up and down the valley one
met ramshackle mills, fallen into decay. Many years ago before
railroads came, before it was easy to haul coal from place to place
to make steam, these little mills were centers of thriving industries,
which depended on the power of falling water to make turned articles,
spin cotton, and so forth. Then the railroads came, and it was easy to
haul coal to make steam. And the same railroads that hauled the coal
to make steam, were there to haul away the articles manufactured by
steam power. So in time the little manufacturing plants on the river
back in the hills quit business and moved to railroad stations. Then
New England, from being a manufacturing community made up of many
small isolated water plants, came to be a community made up of huge
arteries and laterals of smoke stacks that fringed the railroads.
Where the railroad happened to follow a river course--as the
Connecticut River--the water-power plants remained; but the little
plants back in the hills were wiped off the map--because steam power
with railroads at the front door proved cheaper than water-power with
railroads ten miles away.
One night Perkins came in late from a long drive with his next-door
neighbor. He had learned the first rule of courtesy in the country,
which is to unhitch his own side of the horse and help back the buggy
into the shed. They stumbled around in the barn putting up the horse,
and getting down hay and grain for it, by the light of an oil lantern,
which was set on the floor in a place convenient to be kicked over. He
went inside and took supper by the light of a smoky smelly oil lamp,
that filled the room full of dark corners; and when supper was over,
the farmwife groped about in the cellar putting things away by the
light of a candle.
The next day his neighbor was grinding cider at his ramshackle water
mill--one of the operations for which a week must be set aside every
fall. Perkins sat on a log and listened to the crunch-crunch of the
apples in the chute, and the drip of the frothy yellow liquid that
fell into waiting buckets.
"How much power have you got here?" he asked.
"Thirty or forty horsepower, I guess."
"What do you do with it, besides grinding cider to pickle your
neighbors' digestion with?"
"Nothing much. I've got a planer and a moulding machine in there, to
work up jags of lumber occasionally. That's all. This mill was a
chair-factory in my grandfather's day, back in 1830."
"Do you use it thirty days in a year?"
"No; not half that."
"What are you going to do with it this winter?"
"Nothing; I keep the gate open and the wheel turning, so it won't
freeze, but nothing else. I am going to take the family to Texas to
visit my wife's folks for three months. We've worked hard enough to
take a vacation."
"Will you rent me the mill while you are gone?"
"Go ahead; you can have it for nothing, if you will watch the ice."
"All right; let me know when you come back and I'll drive to town and
bring you home."
* * * * *
Three months went by, and one day in February the city man, in
response to a letter, hitched up and drove to town to bring his
neighbor back home. It was four o'clock in the afternoon when they
started out, and it was six--dark--when they turned the bend in the
road to the farm house. They helped the wife and children out, with
their baggage, and as Perkins opened the door of the house, he reached
up on the wall and turned something that clicked sharply.
Instantly light sprang from everywhere. In the barn-yard a street lamp
with an 18-inch reflector illuminated all under it for a space of 100
feet with bright white rays of light. Another street lamp hung over
the watering trough. The barn doors and windows burst forth in light.
There was not a dark corner to be found anywhere. In the house it was
the same. Perkins led the amazed procession from room to room of the
house they had shut up for the winter. On the wall in the hall
outside of every room was a button which he pushed, and the room
became as light as day before they entered. The cellar door, in
opening, automatically lighted a lamp illuminating that cavern as it
had never been lighted before since the day a house was built over it.
Needless to say, the farmer and his family were reduced to a state of
speechlessness.
"How the deuce did you do it?" finally articulated the farmer.
"I put your idle water wheel to work," said Perkins; and then,
satisfied with this exhibition, he put them back in the sleigh and
drove to his home, where his wife had supper waiting.
While the men were putting up the team in the electric lighted barn,
the farmwife went into the kitchen. Her hostess was cooking supper on
an electric stove. It looked like a city gas range and it cooked all
their meals, and did the baking besides. A hot-water tank stood
against the wall, not connected to anything hot, apparently. But it
was scalding hot, by virtue of a little electric water heater the size
of a quart tin can, connected at the bottom. Twenty-four hours a day
the water wheel pumped electricity into that "can," so that hot water
was to be had at any hour simply by turning a faucet. In the laundry
there was an electric pump that kept the tank in the attic filled
automatically. When the level of water in this tank fell to a certain
point, a float operated a switch that started the pump; and when the
water level reached a certain height, the same float stopped the pump.
A small motor, the size of a medium Hubbard squash operated a washing
machine and wringer on wash days. This same motor was a
man-of-all-work for this house, for, when called on, it turned the
separator, ground and polished knives and silverware, spun the sewing
machine, and worked the vacuum cleaner.
Over the dining room table hung the same hanging shade of old days,
but the oil lamp itself was gone. In its place was a 100-watt
tungsten lamp whose rays made the white table cloth fairly glisten.
The wires carrying electricity to this lamp were threaded through the
chains reaching to the ceiling, and one had to look twice to see where
the current came from. In the sitting room, a cluster of electric
bulbs glowed from a fancy wicker work basket that hung from the
ceiling. The housewife had made use of what she had throughout the
house. Old-fashioned candle-shades sat like cocked hats astride
electric bulbs. There is little heat to an electric bulb for the
reason that the white-hot wire that gives the light is made to burn in
high vacuum, which transmits heat very slowly. The housewife had taken
advantage of this fact and from every corner gleamed lights dressed in
fancy designs of tissue paper and silk.
"Now we will talk business," said Perkins when supper was over and
they had lighted their pipes.
The returned native looked dubious. His New England training had
warned him long ago that one cannot expect to get something for
nothing, and he felt sure there was a joker in this affair.
"How much do I owe you?" he asked.
"Nothing," said Perkins. "You furnish the water-power with your idle
wheel, and I furnish the electric installation. This is only a small
plant I have put in, but it gives us enough electricity to go around,
with a margin for emergencies. I have taken the liberty of wiring your
house and your horse-barn and cow-barn and your barn-yard. Altogether,
I suppose you have 30 lights about the place, and during these long
winter days you will keep most of them going from 3 to 5 hours a night
and 2 or 3 hours in the early morning. If you were in town, those
lights would cost you about 12 cents an hour, at the commercial rate
of electricity. Say 60 cents a day--eighteen dollars a month. That
isn't a very big electric light bill for some people I know in
town--and they consider themselves lucky to have the privilege of
buying electricity at that rate. Your wheel is running all winter to
prevent ice from forming and smashing it. It might just as well be
spinning the dynamo.
"If you think it worth while," continued Perkins,--"this $18 worth of
light you have on tap night and morning, or any hour of the day,--we
will say the account is settled. That is, of course, if you will give
me the use of half the electricity that your idle wheel is grinding
out with my second-hand dynamo. We have about eight electrical
horsepower on our wires, without overloading the machine. Next spring
I am going to stock up this place; and I think about the first thing I
do, when my dairy is running, will be to put in a milking machine and
let electricity do the milking for me. It will also fill my silo,
grind my mowing-machine knives, saw my wood, and keep water running in
my barn. You will probably want to do the same.
"But what it does for us men in the barn and barn-yard, isn't to be
compared to what it does for the women in the house. When my wife
wants a hot oven she presses a button. When she wants to put the
'fire' out, she presses another. That's all there is to it. No heat,
no smoke, no ashes. The same with ironing--and washing. No oil lamps
to fill, no wicks to trim, no chimneys to wash, no kerosene to kick
over and start a fire."
"You say the current you have put in my house would cost me about $18
a month, in town."
"Yes, about that. Making electricity from coal costs money."
"What does it cost here?"
"Practically nothing. Your river, that has been running to waste ever
since your grandfather gave up making chairs, does the work. There is
nothing about a dynamo to wear out, except the bearings, and these can
be replaced once every five or ten years for a trifle. The machine
needs to be oiled and cared for--fill the oil cups about once in three
days. Your water wheel needs the same attention. That's all there is
to it. You can figure the cost of your current yourself--just about
the cost of the lubricating oil you use--and the cost of the time you
give it--about the same time you give to any piece of good machinery,
from a sulky plow to a cream separator."
This is a true story. This electric plant, where Perkins furnishes the
electric end, and his neighbor the water-power, has been running now
for two years, grinding out electricity for the two places twenty-four
hours a day. Perkins was not an electrical engineer. He was just a
plain intelligent American citizen who found sufficient knowledge in
books to enable him to install and operate this plant. Frequently he
is away for long periods, but his neighbor (who has lost his original
terror of electricity) takes care of the plant. In fact, this farmer
has given a lot of study to the thing, through curiosity, until he
knows fully as much about it now as his city neighbor.
He had the usual idea, at the start, that a current strong enough to
light a 100 candlepower lamp would kick like a mule if a man happened
to get behind it. He watched the city man handle bare wires and
finally he plucked up courage to do it himself.
It was a 110-volt current, the pressure used in our cities for
domestic lighting. The funny part about it was, the farmer could not
feel it at all at first. His fingers were calloused and no current
could pass through them. Finally he sandpapered his fingers and tried
it again. Then he was able to get the "tickle" of 110 volts. It wasn't
so deadly after all--about the strength of a weak medical battery,
with which every one is familiar. A current of 110 volts cannot do any
harm to the human body unless contact is made over a very large
surface, which is impossible unless a man goes to a lot of trouble to
make such a contact. A current of 220 volts pressure--the pressure
used in cities for motors--has a little more "kick" to it, but still
is not uncomfortable. When the pressure rises to 500 volts (the
pressure used in trolley wires for street cars), it begins to be
dangerous. But there is no reason why a farm plant should be over 110
volts, under usual conditions; engineers have decided on this pressure
as the best adapted to domestic use, and manufacturers who turn out
the numerous electrical devices, such as irons, toasters, massage
machines, etc., fit their standard instruments to this voltage.
[Illustration: Farm labor and materials built this crib and stone
dam]
As to the cost of this co-operative plant--it was in the neighborhood
of $200. As we have said, it provided eight electrical horsepower on
tap at any hour of the day or night--enough for the two farms, and a
surplus for neighbors, if they wished to string lines and make use of
it.
The dynamo, a direct-current machine, 110 volts pressure, and what is
known in the trade as "compound,"--that is, a machine that maintains a
constant pressure automatically and does not require an attendant--was
picked up second-hand, through a newspaper "ad" and cost $90. The
switchboard, a make-shift affair, not very handsome, but just as
serviceable as if it were made of marble, cost less than $25 all told.
The transmission wire cost $19 a hundred pounds; it is of copper, and
covered with weatherproofed tape. Perkins bought a 50-cent book on
house-wiring, and did the wiring himself, the way the book told him
to, a simple operation. For fixtures, as we have said, his wife
devised fancy shades out of Mexican baskets, tissue paper, and silk,
in which are hidden electric globes that glow like fire-flies at the
pressing of a button. The lamps themselves are mostly old-style carbon
lamps, which can be bought at 16 cents each retail. In his living room
and dining room he used the new-style tungsten lamps instead of
old-style carbon. These cost 30 cents each. Incandescent lamps are
rated for 1,000 hours useful life. The advantage of tungsten lights is
that they give three times as much light for the same expenditure of
current as carbon lights. This is a big advantage in the city, where
current is costly; but it is not so much of an advantage in the
country where a farmer has plenty of water-power--because his current
costs him practically nothing, and he can afford to be wasteful of it
to save money in lamps. Another advantage he has over his city cousin:
In town, an incandescent lamp is thrown away after it has been used
1,000 hours because after that it gives only 80% of the light it did
when new--quite an item when one is paying for current. The experience
of Perkins and his neighbor in their coöperative plant has been that
they have excess light anyway, and if a few bulbs fall off a fifth in
efficiency, it is not noticeable. As a matter of fact most of their
bulbs have been in use without replacing for the two years the plant
has been in operation. The lamps are on the wall or the ceiling, out
of the way, not liable to be broken; so the actual expense in
replacing lamps is less than for lamp chimneys in the old days.
Insurance companies recognize that a large percentage of farm fires
comes from the use of kerosene; for this reason, they are willing to
make special rates for farm homes lighted by electricity. They
prescribe certain rules for wiring a house, and they insist that their
agent inspect and pass such wiring before current is turned on. Once
the wiring is passed, the advantage is all in favor of the farmer
with electricity over the farmer with kerosene. The National Board of
Fire Underwriters is sufficiently logical in its demands, and powerful
enough, so that manufacturers who turn out the necessary fittings find
no sale for devices that do not conform to insurance standards.
Therefore it is difficult to go wrong in wiring a house.
Finally, as to the added value a water-power electric plant adds to
the selling price of a farm. Let the farmer answer this question for
himself. If he can advertise his farm for sale, with a paragraph
running: "Hydroelectric plant on the premises, furnishing electricity
for light, heat, and power"--what do you suppose a wide-awake
purchaser would be willing to pay for that? Perkins and his neighbor
believe that $1,000 is a very modest estimate added by their electric
plant to both places. And they talk of doing still more. They use only
a quarter of the power of the water that is running to waste through
the wheel. They are figuring on installing a larger dynamo, of say 30
electrical horse-power, which will provide clean, dry, safe heat for
their houses even on the coldest days in winter. When they have done
this, they will consider that they are really putting their small
river to work.
CHAPTER II
A LITTLE PROSPECTING
Small amount of water required for an electric plant--Exploring, on
a dull day--A rough and ready weir--What a little water will
do--The water wheel and the dynamo--Electricity consumed the
instant it is produced--The price of the average small plant, not
counting labor.
The average farmer makes the mistake of considering that one must have
a river of some size to develop power of any practical use. On your
next free day do a little prospecting. We have already said that 250
cubic feet of water falling 10 feet a minute will provide light, heat
and small motor power for the average farm. A single water horsepower
will generate enough electricity to provide light for the house and
barn. But let us take five horsepower as a desirable minimum in this
instance.
[Illustration: Measuring a small stream with a weir]
In your neighborhood there is a creek three or four feet wide,
toiling along day by day, at its task of watering your fields. Find a
wide board a little longer than the width of this creek you have
scorned. Set it upright across the stream between the banks, so that
no water flows around the ends or under it. It should be high enough
to set the water back to a dead level for a few feet upstream, before
it overflows. Cut a gate in this board, say three feet wide and ten
inches deep, or according to the size of a stream. Cut this gate from
the top, so that all the water of the stream will flow through the
opening, and still maintain a level for several feet back of the
board.
This is what engineers call a weir, a handy contrivance for measuring
the flow of small streams. Experts have figured out an elaborate
system of tables as to weirs. All we need to do now, in this rough
survey, is to figure out the number of square inches of water flowing
through this opening and falling on the other side. With a rule,
measure the depth of the overflowing water, from the bottom of the
opening to the top of the dead level of the water behind the board.
Multiply this depth by the width of the opening, which will give the
square inches of water escaping. For every square inch of this water
escaping, engineers tell us that stream is capable of delivering,
roughly, one cubic foot of water a minute.
Thus, if the water is 8 inches deep in an opening 32 inches wide, then
the number of cubic feet this stream is delivering each minute is 8
times 32, or 256 cubic feet a minute. So, a stream 32 inches wide,
with a uniform depth of 8 inches running through our weir is capable
of supplying the demands of the average farm in terms of electricity.
Providing, of course, that the lay of the land is such that this water
can be made to fall 10 feet into a water wheel.
Go upstream and make a rough survey of the fall. In the majority of
instances (unless this is some sluggish stream in a flat prairie) it
will be found feasible to divert the stream from its main channel by
means of a race--an artificial channel--and to convey it to a not
far-distant spot where the necessary fall can be had at an angle of
about 30 degrees from horizontal.
If you find there is _twice_ as much water as you need for the amount
of power you require, a five-foot fall will give the same result. Or,
if there is only _one-half_ as much water as the 250 cubic feet
specified, you can still obtain your theoretical five horsepower if
the means are at hand for providing a fall of twenty feet instead of
ten. Do not make the very common mistake of figuring that a stream is
delivering a cubic foot a minute to each square inch of weir opening,
simply because it _fills_ a certain opening. It is the excess water,
falling _over_ the opening, after the stream has set back to a
permanent dead level, that is to be measured.
This farmer who spends an idle day measuring the flow of his brook
with a notched board, may say here: "This is all very well. This is
the spring of the year, when my brook is flowing at high-water mark.
What am I going to do in the dry months of summer, when there are not
250 cubic feet of water escaping every minute?"
There are several answers to this question, which will be taken up in
detail in subsequent chapters. Here, let us say, even if this brook
does flow in sufficient volume only 8 months in a year--the dark
months, by the way,--is not electricity and the many benefits it
provides worth having eight months in the year? My garden provides
fresh vegetables four months a year. Because it withers and dies and
lies covered with snow during the winter, is that any reason why I
should not plow and manure and plant my garden when spring comes
again?
A water wheel, the modern turbine, is a circular fan with curved iron
blades, revolving in an iron case. Water, forced through the blades of
this fan by its own weight, causes the wheel to revolve on its axis;
and the fan, in turn causes a shaft fitted with pulleys to revolve.
The water, by giving the iron-bladed fan a turning movement as it
rushes through, imparts to it mechanical power. The shaft set in
motion by means of this mechanical power is, in turn, belted to the
pulley of a dynamo. This dynamo consists, first, of a shaft on which
is placed a spool, wound in a curious way, with many turns of
insulated copper wire. This spool revolves freely in an air space
surrounded by electric magnets. The spool does not touch these
magnets. It is so nicely balanced that the weight of a finger will
turn it. Yet, when it is revolved by water-power at a predetermined
speed--say 1,500 revolutions a minute--it generates electricity,
transforms the mechanical power of the water wheel into another form
of energy--a form of energy which can be carried for long distances on
copper wires, which can, by touching a button, be itself converted
into light, or heat, or back into mechanical energy again.
If two wires be led from opposite sides of this revolving spool, and
an electric lamp be connected from one to the other wire, the lamp
will be lighted--will grow white hot,--hence _incandescent light_.
The instant this lamp is turned on, the revolving spool feels a
stress, the magnets by which it is surrounded begin to pull back on
it. The power of the water wheel, however, overcomes this pull. If one
hundred lights be turned on, the backward pull of the magnets
surrounding the spool will be one hundred times as strong as for one
light. For every ounce of electrical energy used in light or heat or
power, the dynamo will require a like ounce of mechanical power from
the water wheel which drives it.
The story is told of a canny Scotch engineer, who, in the first days
of dynamos, not so very long ago, scoffed at the suggestion that such
a spool, spinning in free air, in well lubricated bearings, could
bring his big Corliss steam engine to a stop. Yet he saw it done
simply by belting this "spool," a dynamo, to his engine and asking the
dynamo for more power in terms of light than his steam could deliver
in terms of mechanical power to overcome the pull of the magnets.
Electricity must be consumed the instant it is generated (except in
rare instances where small amounts are accumulated in storage
batteries by a chemical process). The pressure of a button, or the
throw of a switch causes the dynamo instantly to respond with just
enough energy to do the work asked of it, always in proportion to the
amount required. Having this in mind, it is rather curious to think of
electricity as being an article of export, an item in international
trade. Yet in 1913 hydro-electric companies in Canada "exported" by
means of wires, to this country over 772,000,000 kilowatt-hours (over
one billion horsepower hours) of electricity for use in factories near
the boundary line.
This 250 cubic feet of water per minute then, which the farmer has
measured by means of his notched board, will transform by means of its
falling weight mechanical power into a like amount of electrical
power--less friction losses, which may amount to as much as 60% in
very small machines, and 15% in larger plants. That is, the brook
which has been draining your pastures for uncounted ages contains the
potential power of 3 and 4 young horses--with this difference: that it
works 24 hours a day, runs on forever, and requires no oats or hay.
And the cost of such an electric plant, which is ample for the needs
of the average farm, _is in most cases less than the price of a good
farm horse_--the $200 kind--not counting labor of installation.
It is the purpose of these chapters to awaken the farmer to the
possibilities of such small water-power as he or his community may
possess; to show that the generating of electricity is a very simple
operation, and that the maintenance and care of such a plant is within
the mechanical ability of any American farmer or farm boy; and to show
that electricity itself is far from being the dangerous death-dealing
"fluid" of popular imagination. Electricity must be studied; and then
it becomes an obedient, tireless servant. During the past decade or
two, mathematical wizards have studied electricity, explored its
atoms, reduced it to simple arithmetic--and although they cannot yet
tell us _why_ it is generated, they tell us _how_. It is with this
simple arithmetic, and the necessary manual operations that we have to
do here.
CHAPTER III
HOW TO MEASURE WATER-POWER
What is a horsepower?--How the Carthaginians manufactured
horsepower--All that goes up must come down--How the sun lifts
water up for us to use--Water the ideal power for generating
electricity--The weir--Table for estimating flow of streams, with a
weir--Another method of measuring--Figuring water horsepower--The
size of the wheel--What head is required--Quantity of water
necessary.
If a man were off in the woods and needed a horsepower of energy to
work for him, he could generate it by lifting 550 pounds of stone or
wood, or whatnot, one foot off the ground, and letting it fall back in
the space of one second. As a man possesses capacity for work equal to
one-fifth horsepower, it would take him five seconds to do the work of
lifting the weight up that the weight itself accomplished in falling
down. All that goes up must come down; and by a nice balance of
physical laws, a falling body hits the ground with precisely the same
force as is required to lift it to the height from which it falls.
The Carthaginians, and other ancients (who were deep in the woods as
regards mechanical knowledge) had their slaves carry huge stones to
the top of the city wall; and the stones were placed in convenient
positions to be tipped over on the heads of any besieging army that
happened along. Thus by concentrating the energy of many slaves in one
batch of stones, the warriors of that day were enabled to deliver
"horsepower" in one mass where it would do the most good. The farmer
who makes use of the energy of falling water to generate electricity
for light, heat, and power does the same thing--he makes use of the
capacity for work stored in water in being lifted to a certain height.
As in the case of the gasoline engine, which burns 14 pounds of air
for every pound of gasoline, the engineer of the water-power plant
does not have to concern himself with the question of how this
natural source of energy happened to be in a handy place for him to
make use of it.
The sun, shining on the ocean, and turning water into vapor by its
heat has already lifted it up for him. This vapor floating in the air
and blown about by winds, becomes chilled from one cause or another,
gives up its heat, turns back into water, and falls as rain. This
rain, falling on land five, ten, a hundred, a thousand, or ten
thousand feet above the sea level, begins to run back to the sea,
picking out the easiest road and cutting a channel that we call a
brook, a stream, or a river. Our farm lands are covered to an average
depth of about three feet a year with water, every gallon of which has
stored in it the energy expended by the heat of the sun in lifting it
to the height where it is found.
The farmer, prospecting on his land for water-power, locates a spot on
a stream which he calls Supply; and another spot a few feet down hill
near the same stream, which he calls Power. Every gallon of water that
falls between these two points, and is made to escape through the
revolving blades of a water wheel is capable of work in terms of
foot-pounds--an amount of work that is directly proportional to the
_quantity_ of water, and to the _distance_ in feet which it falls to
reach the wheel--_pounds_ and _feet_.
_The Efficient Water Wheel_
And it is a very efficient form of work, too. In fact it is one of the
most efficient forms of mechanical energy known--and one of the
easiest controlled. A modern water wheel uses 85 per cent of the total
capacity for work imparted to falling water by gravity, and delivers
it as rotary motion. Compare this water wheel efficiency with other
forms of mechanical power in common use: Whereas a water wheel uses 85
per cent of the energy of its water supply, and wastes only 15 per
cent, a gasoline engine reverses the table, and delivers only 15 per
cent of the energy in gasoline and wastes 85 per cent--and it is
rather a high-class gasoline engine that can deliver even 15 per cent;
a steam engine, on the other hand, uses about 17 per cent of the
energy in the coal under its boilers and passes the rest up the
chimney as waste heat and smoke.
There is still another advantage possessed by water-power over its two
rivals, steam and gas: It gives the most even flow of power. A gas
engine "kicks" a wheel round in a circle, by means of successive
explosions in its cylinders. A reciprocating steam engine "kicks" a
wheel round in a circle by means of steam expanding first in one
direction, then in another. A water wheel, on the other hand, is made
to revolve by means of the pressure of water--by the constant force of
gravity, itself--weight. Weight is something that does not vary from
minute to minute, or from one fraction of a second to another. It is
always the same. A square inch of water pressing on the blades of a
water wheel weights ten, twenty, a hundred pounds, according to the
height of the pipe conveying that water from the source of supply, to
the wheel. So long as this column of water is maintained at a fixed
height, the power it delivers to the wheel does not vary by so much as
the weight of a feather.
This property of falling water makes it the ideal power for generating
electricity. Electricity generated from mechanical power depends on
constant speed for steady pressure--since the electric current, when
analyzed, is merely a succession of pulsations through a wire, like
waves beating against a sea wall. Water-power delivers these waves at
a constant speed, so that electric lights made from water-power do not
flicker and jump like the flame of a lantern in a gusty wind. On the
other hand, to accomplish the same thing with steam or gasoline
requires an especially constructed engine.
_The Simple Weir_
Since a steady flow of water, and a constant head, bring about this
ideal condition in the water wheel, the first problem that faces the
farmer prospector is to determine the amount of water which his stream
is capable of delivering. This is always measured, for convenience,
in _cubic feet per minute_. (A cubic foot of water weighs 62.5 pounds,
and contains 7-1/2 gallons.) This measurement is obtained in several
ways, among which probably the use of a weir is the simplest and most
accurate, for small streams.
A weir is, in effect, merely a temporary dam set across the stream in
such a manner as to form a small pond; and to enable one to measure
the water escaping from this pond.
It may be likened to the overflow pipe of a horse trough which is
being fed from a spring. To measure the flow of water from such a
spring, all that is necessary is to measure the water escaping through
the overflow when the water in the trough has attained a permanent
level.
[Illustration: Detail of home-made weir]
[Illustration: Cross-section of weir]
The diagrams show the cross-section and detail of a typical weir,
which can be put together in a few minutes with the aid of a saw and
hammer. The cross-section shows that the lower edge of the slot
through which the water of the temporary pond is made to escape, is
cut on a bevel, with its sharp edge upstream. The wing on each side of
the opening is for the purpose of preventing the stream from narrowing
as it flows through the opening, and thus upsetting the calculations.
This weir should be set directly across the flow of the stream,
perfectly level, and upright. It should be so imbedded in the banks,
and in the bottom of the stream, that no water can escape, except
through the opening cut for that purpose. It will require a little
experimenting with a rough model to determine just how wide and how
deep this opening should be. It should be large enough to prevent
water flowing over the top of the board; and it should be small
enough to cause a still-water pond to form for several feet behind the
weir. Keep in mind the idea of the overflowing water trough when
building your weir. The stream, running down from a higher level
behind, should be emptying into a still-water pond, which in turn
should be emptying itself through the aperture in the board at the
same rate as the stream is keeping the pond full.
Your weir should be fashioned with the idea of some permanency so that
a number of measurements may be taken, extending over a period of
time--thus enabling the prospector to make a reliable estimate not
only of the amount of water flowing at any one time, but of its
fluctuations.
Under expert supervision, this simple weir is an exact
contrivance--exact enough, in fact, for the finest calculations
required in engineering work. To find out how many cubic feet of water
the stream is delivering at any moment, all that is necessary is to
measure its depth where it flows through the opening. There are
instruments, like the hook-gauge, which are designed to measure this
depth with accuracy up to one-thousandth of an inch. An ordinary foot
rule, or a folding rule, will give results sufficiently accurate for
the water prospector in this instance. The depth should be measured
not at the opening itself, but a short distance back of the opening,
where the water is setting at a dead level and is moving very slowly.
With this weir, every square inch of water flowing through the opening
indicates roughly one cubic foot of water a minute. Thus if the
opening is 10 inches wide and the water flowing through it is 5 inches
deep, the number of cubic feet a minute the stream is delivering is 10
× 5 = 50 square inches = 50 cubic feet a minute. This is a very small
stream; yet, if it could be made to fall through a water wheel 10 feet
below a pond or reservoir, it would exert a continuous pressure of
30,000 pounds per minute on the blades of the wheel--nearly one
theoretical horsepower.
This estimate of one cubic foot to each square inch is a very rough
approximation. Engineers have developed many complicated formulas for
determining the flow of water through weirs, taking into account fine
variations that the farm prospector need not heed. The so-called
Francis formula, developed by a long series of actual experiments at
Lowell, Mass., in 1852 by Mr. James B. Francis, with weirs 10 feet
long and 5 feet 2 inches high, is standard for these calculations and
is expressed (for those who desire to use it for special purposes) as
follows:
Q = 3.33 L H^(3/2) or, Q = 3.33 L H sqrt(H),
in which Q means _quantity_ of water in cubic feet per second, L is
length of opening, in feet; and H is height of opening in feet.
The following table is figured according to the Francis formula, and
gives the discharge in cubic feet per minute, for openings one inch
wide:
TABLE OF WEIRS
Inches 0 1/4 1/2 3/4
1 0.403 0.563 0.740 0.966
2 1.141 1.360 1.593 1.838
3 2.094 2.361 2.639 2.927
4 3.225 3.531 3.848 4.173
5 4.506 4.849 5.200 5.558
6 5.925 6.298 6.681 7.071
7 7.465 7.869 8.280 8.697
8 9.121 9.552 9.990 10.427
9 10.884 11.340 11.804 12.272
10 12.747 13.228 13.716 14.208
11 14.707 15.211 15.721 16.236
12 16.757 17.283 17.816 18.352
13 18.895 19.445 19.996 20.558
14 21.116 21.684 22.258 22.835
15 23.418 24.007 24.600 25.195
16 25.800 26.406 27.019 27.634
17 28.256 28.881 29.512 30.145
18 30.785 31.429 32.075 32.733
Thus, let us say, our weir has an opening 30 inches wide, and the
water overflows through the opening at a uniform depth of 6-1/4
inches, when measured a few inches behind the board at a point before
the overflow curve begins. Run down the first column on the left to
"6", and cross over to the second column to the right, headed "1/4".
This gives the number of cubic feet per minute for this depth one inch
wide, as 6.298. Since the weir is 30 inches wide, multiply 6.298 × 30
= 188.94--or, say, 189 cubic feet per minute.
Once the weir is set, it is the work of but a moment to find out the
quantity of water a stream is delivering, simply by referring to the
above table.
_Another Method of Measuring a Stream_
Weirs are for use in small streams. For larger streams, where the
construction of a weir would be difficult, the U. S. Geological Survey
engineers recommend the following simple method:
Choose a place where the channel is straight for 100 or 200 feet, and
has a nearly constant depth and width; lay off on the bank a line 50
or 100 feet in length. Throw small chips into the stream, and measure
the time in seconds they take to travel the distance laid off on the
bank. This gives the surface velocity of the water. Multiply the
average of several such tests by 0.80, which will give very nearly the
mean velocity. Then it is necessary to find the cross-section of the
flowing water (its average depth multiplied by width), and this
number, in square feet, multiplied by the velocity in feet per second,
will give the number of cubic feet the stream is delivering each
second. Multiplied by 60 gives cubic feet a minute.
_Figuring a Stream's Horsepower_
By one of the above simple methods, the problem of _Quantity_ can
easily be determined. The next problem is to determine what _Head_ can
be obtained. _Head_ is the distance in feet the water may be made to
fall, from the Source of Supply, to the water wheel itself. The power
of water is directly proportional to _head_, just as it is directly
proportional to _quantity_. Thus the typical weir measured above was
30 inches wide and 6-1/4 deep, giving 189 cubic feet of water a
minute--_Quantity._ Since such a stream is of common occurrence on
thousands of farms, let us analyze briefly its possibilities for
power: One hundred and eighty-nine cubic feet of water weighs 189 ×
62.5 pounds = 11,812.5 pounds. Drop this weight one foot, and we have
11,812.5 foot-pounds. Drop it 3 feet and we have 11,812 × 3 =
35,437.5 foot-pounds. Since 33,000 foot-pounds exerted in one minute
is one horsepower, we have here a little more than one horsepower. For
simplicity let us call it a horsepower.
[Illustration: Detail of a water-power plant, showing setting of
wheel, and dynamo connection]
Now, since the work to be had from this water varies directly with
_quantity_ and _head_, it is obvious that a stream _one-half_ as big
falling _twice_ as far, would still give one horsepower at the wheel;
or, a stream of 189 cubic feet a minute falling _ten times_ as far, 30
feet, would give _ten times_ the power, or _ten_ horsepower; a stream
falling _one hundred times_ as far would give _one hundred_
horsepower. Thus small quantities of water falling great distances, or
large quantities of water falling small distances may accomplish the
same results. From this it will be seen, that the simple formula for
determining the theoretical horsepower of any stream, in which
Quantity and Head are known, is as follows:
Cu. Ft.
per Feet
minute × head × 62.5
(A) Theoretical Horsepower = ----------------------
33,000
_As an example, let us say that we have a stream whose weir
measurement shows it capable of delivering 376 cubic feet a minute,
with a head (determined by survey) of 13 feet 6 inches. What is the
horsepower of this stream?_
Answer:
Cu. ft. p. m. head pounds
376 × 13.5 × 62.5
H.P. = ----------------------------- = 9.614 horsepower
33,000
This is _theoretical horsepower_. To determine the _actual_ horsepower
that can be counted on, in practice, it is customary, with small water
wheels, to figure 25 per cent loss through friction, etc. In this
instance, the actual horsepower would then be 7.2.
_The Size of the Wheel_
Water wheels are not rated by horsepower by manufacturers, because the
same wheel might develop one horsepower or one hundred horsepower, or
even a thousand horsepower, according to the conditions under which
it is used. With a given supply of water, the head, in feet,
determines the size of wheel necessary. The farther a stream of water
falls, the smaller the pipe necessary to carry a given number of
gallons past a given point in a given time.
A small wheel, under 10 × 13.5 ft. head, would give the same power
with the above 376 cubic feet of water a minute, as a large wheel
would with 10 × 376 cubic feet, under a 13.5 foot head.
This is due to the _acceleration of gravity_ on falling bodies. A
rifle bullet shot into the air with a muzzle velocity of 3,000 feet a
second begins to diminish its speed instantly on leaving the muzzle,
and continues to diminish in speed at the fixed rate of 32.16 feet a
second, until it finally comes to a stop, and starts to descend. Then,
again, its speed accelerates at the rate of 32.16 feet a second, until
on striking the earth it has attained the velocity at which it left
the muzzle of the rifle, less loss due to friction.
The acceleration of gravity affects falling water in the same manner
as it affects a falling bullet. At any one second, during its course
of fall, it is traveling at a rate 32.16 feet a second in excess of
its speed the previous second.
In figuring the size wheel necessary under given conditions or to
determine the power of water with a given nozzle opening, it is
necessary to take this into account. The table on page 51 gives
velocity per second of falling water, ignoring the friction of the
pipe, in heads from 5 to 1000 feet.
The scientific formula from which the table is computed is expressed
as follows, for those of a mathematical turn of mind:
Velocity (ft. per sec.) = sqrt(2gh); or, velocity is equal to the
square root of the product (g = 32.16,--times head in feet, multiplied
by 2).
SPOUTING VELOCITY OF WATER, IN FEET PER SECOND, IN HEADS
OF FROM 5 TO 1,000 FEET
Head Velocity
5 17.9
6 19.7
7 21.2
8 22.7
9 24.1
10 25.4
11 26.6
11.5 27.2
12 27.8
12.5 28.4
13 28.9
13.5 29.5
14 30.0
14.5 30.5
15 31.3
15.5 31.6
16 32.1
16.5 32.6
17 33.1
17.5 33.6
18 34.0
18.5 34.5
19 35.0
19.5 35.4
20 35.9
20.5 36.3
21 36.8
21.5 37.2
22 37.6
22.5 38.1
23 38.5
23.5 38.9
24 39.3
24.5 39.7
25 40.1
26 40.9
27 41.7
28 42.5
29 43.2
30 43.9
31 44.7
32 45.4
33 46.1
34 46.7
35 47.4
36 48.1
37 48.8
38 49.5
39 50.1
40 50.7
41 51.3
42 52.0
43 52.6
44 53.2
45 53.8
46 54.4
47 55.0
48 55.6
49 56.2
50 56.7
55 59.5
60 62.1
65 64.7
70 67.1
75 69.5
80 71.8
85 74.0
90 76.1
95 78.2
100 80.3
200 114.0
300 139.0
400 160.0
500 179.0
1000 254.0
_In the above example, we found that 376 cubic feet of water a minute,
under 13.5 feet head, would deliver 7.2 actual horsepower. Question:
What size wheel would it be necessary to install under such
conditions?_
By referring to the table of velocity above, (or by using the
formula), we find that water under a head of 13.5 feet, has a spouting
velocity of 29.5 feet a second. This means that a solid stream of
water 29.5 feet long would pass through the wheel in one second. _What
should be the diameter of such a stream, to make its cubical contents
376 cubic feet a minute or 376/60 = 6.27 cubic feet a second?_ The
following formula should be used to determine this:
144 × cu. ft. per second
(B) Sq. Inches of wheel = --------------------------
Velocity in ft. per sec.
Substituting values, in the above instance, we have:
Answer: Sq. Inches of wheel =
144 × 6.27 (Cu. Ft. Sec.)
--------------------------- = 30.6 sq. in.
29.5 (Vel. in feet.)
That is, a wheel capable of using 30.6 square inches of water would
meet these conditions.
_What Head is Required_
Let us attack the problem of water-power in another way. _A farmer
wishes to install a water wheel that will deliver 10 horsepower on the
shaft, and he finds his stream delivers 400 cubic feet of water a
minute. How many feet fall is required?_ Formula:
33,000 × horsepower required
(C) Head in feet = ------------------------------
Cu. Ft. per minute × 62.5
Since a theoretical horsepower is only 75 per cent efficient, he would
require 10 × 4/3 = 13.33 theoretical horsepower of water, in this
instance. Substituting the values of the problem in the formula, we
have:
33,000 × 13.33
Answer: Head = ---------------- = 17.6 feet fall required.
400 × 62.5
_What capacity of wheel would this prospect (400 cubic feet of water a
minute falling 17.6 feet, and developing 13.33 horsepower) require?_
By referring to the table of velocities, we find that the velocity for
17.5 feet head (nearly) is 33.6 feet a second. Four hundred feet of
water a minute is 400/60 = 6.67 cu. ft. a second. Substituting these
values, in formula (B) then, we have:
Answer: Capacity of wheel =
144 × 6.67
---------- = 28.6 square inches of water.
33.6
_Quantity of Water_
Let us take still another problem which the prospector may be called
on to solve: _A man finds that he can conveniently get a fall of 27
feet. He desires 20 actual horsepower. What quantity of water will be
necessary, and what capacity wheel?_
Twenty actual horsepower will be 20 × 4/3 = 26.67 theoretical
horsepower. Formula:
33,000 × Hp. required
(D) Cubic feet per minute = ---------------------
(Head in feet × 62.5)
Substituting values, then, we have:
Cu. ft. per minute =
33,000 × 26.67
-------------- = 521.5 cubic feet a minute.
27 × 62.5
A head of 27 feet would give this stream a velocity of 41.7 feet a
second, and, from formula (B) we find that the capacity of the wheel
should be 30 square inches.
It is well to remember that the square inches of wheel capacity does
not refer to the size of pipe conveying water from the head to the
wheel, but merely to the actual nozzle capacity provided by the wheel
itself. In small installations of low head, such as above a penstock
at least six times the nozzle capacity should be used, to avoid losing
effective head from friction. Thus, with a nozzle of 30 square inches,
the penstock or pipe should be 180 square inches, or nearly 14 inches
square inside measurement. A larger penstock would be still better.
CHAPTER IV
THE WATER WHEEL AND HOW TO INSTALL IT
Different types of water wheels--The impulse and reaction
wheels--The impulse wheel adapted to high heads and small amount of
water--Pipe lines--Table of resistance in pipes--Advantages and
disadvantages of the impulse wheel--Other forms of impulse
wheels--The reaction turbine, suited to low heads and large
quantity of water--Its advantages and limitations--Developing a
water-power project: the dam; the race; the flume; the penstock;
and the tailrace--Water rights for the farmer.
In general, there are two types of water wheels, the _impulse_ wheel
and the _reaction_ wheel. Both are called turbines, although the name
belongs, more properly, to the reaction wheel alone.
Impulse wheels derive their power from the _momentum_ of falling
water. Reaction wheels derive their power from the _momentum and
pressure_ of falling water. The old-fashioned _undershot_, _overshot_,
and _breast_ wheels are familiar to all as examples of impulse
wheels. Water wheels of this class revolve in the air, with the energy
of the water exerted on one face of their buckets. On the other hand,
reaction wheels are enclosed in water-tight cases, either of metal or
of wood, and the buckets are entirely surrounded by water.
The old-fashioned undershot, overshot, and breast wheels were not very
efficient; they wasted about 75 per cent of the power applied to them.
A modern impulse wheel, on the other hand, operates at an efficiency
of 80 per cent and over. The loss is mainly through friction and
leakage, and cannot be eliminated altogether. The modern reaction
wheel, called the _turbine_, attains an equal efficiency. Individual
conditions govern the type of wheel to be selected.
_The Impulse, or Tangential Water Wheel_
The modern impulse, or tangential wheel (so called because the driving
stream of water strikes the wheel at a tangent) is best adapted to
situations where the amount of water is limited, and the head is
large. Thus, a mountain brook supplying only seven cubic feet of water
a minute--a stream less than two-and-a-half inches deep flowing over a
weir with an opening three inches wide--would develop two actual
horsepower, under a head of 200 feet--not an unusual head to be found
in the hill country. Under a head of one thousand feet, a stream
furnishing 352.6 cubic feet of water a minute would develop 534.01
horsepower at the nozzle.
Ordinarily these wheels are not used under heads of less than 20 feet.
A wheel of this type, six feet in diameter, would develop six
horsepower, with 188 cubic feet of water a minute and 20-foot head.
The great majority of impulse wheels are used under heads of 100 feet
and over. In this country the greatest head in use is slightly over
2,100 feet, although in Switzerland there is one plant utilizing a
head of over 5,000 feet.
[Illustration: Runner of Pelton wheel, showing peculiar shape of the
buckets]
[Illustration: The Fitz overshoot wheel
Efficient Modern Adaptations of the Archaic Undershot and Overshot
Water Wheels]
The old-fashioned impulse wheels were inefficient because of the fact
that their buckets were not constructed scientifically, and much of
the force of the water was lost at the moment of impact. The impulse
wheel of to-day, however, has buckets which so completely absorb the
momentum of water issuing from a nozzle, that the water falls into the
tailrace with practically no velocity. When it is remembered that the
nozzle pressure under a 2,250-foot head is nearly 1,000 pounds to the
square inch, and that water issues from this nozzle with a velocity of
23,000 feet a minute, the scientific precision of this type of bucket
can be appreciated.
A typical bucket for such a wheel is shaped like an open clam shell,
the central line which cuts the stream of water into halves being
ground to a sharp edge. The curves which absorb the momentum of the
water are figured mathematically and in practice become polished like
mirrors. So great is the eroding action of water, under great
heads--especially when it contains sand or silt--that it is
occasionally necessary to replace these buckets. For this reason the
larger wheels consist merely of a spider of iron or steel, with each
bucket bolted separately to its circumference, so that it can be
removed and replaced easily. Usually only one nozzle is provided; but
in order to use this wheel under low heads--down to 10 feet--a number
of nozzles are used, sometimes five, where the water supply is
plentiful.
The wheel is keyed to a horizontal shaft running in babbited bearings,
and this same shaft is used for driving the generator, either by
direct connection, or by means of pulleys and a belt. The wheel may be
mounted on a home-made timber base, or on an iron frame. It takes up
very little room, especially when it is so set that the nozzle can be
mounted under the flooring. The wheel itself is enclosed, above the
floor, in a wooden box, or a casing made of cast or sheet iron, which
should be water-tight.
Since these wheels are usually operated under great heads, the problem
of regulating their water supply requires special consideration. A
gate is always provided at the upper, or intake end, where the water
pipe leaves the flume. Since the pressure reaches 1,000 pounds the
square inch and more, there would be danger of bursting the pipe if
the water were suddenly shut off at the nozzle itself. For this reason
it is necessary to use a needle valve, similar to that in an ordinary
garden hose nozzle; and by such a valve the amount of water may be
regulated to a nicety. Where the head is so great that even such a
valve could not be used safely, provision is made to deflect the
nozzle. These wheels have a speed variation amounting to as much as 25
per cent from no-load to full load, in generating electricity, and
since the speed of the prime mover--the water wheel--is reflected
directly in the voltage or pressure of electricity delivered, the
wheel must be provided with some form of automatic governor. This
consists usually of two centrifugal balls, similar to those used in
governing steam engines; these are connected by means of gears to the
needle valve or the deflector.
As the demand for farm water-powers in our hill sections becomes more
general, the tangential type of water wheel will come into common use
for small plants. At present it is most familiar in the great
commercial installations of the Far West, working under enormous
heads. These wheels are to be had in the market ranging in size from
six inches to six feet and over. Wheels ranging in size from six
inches to twenty-four inches are called water motors, and are to be
had in the market, new, for $30 for the smallest size, and $275 for
the largest. Above three feet in diameter, the list prices will run
from $200 for a 3-foot wheel to $800 for a 6-foot wheel. Where one has
a surplus of water, it is possible to install a multiple nozzle wheel,
under heads of from 10 to 100 feet, the cost for 18-inch wheels of
this pattern running from $150 to $180 list, and for 24-inch wheels
from $200 to $250. A 24-inch wheel, with a 10-foot head would give
1.19 horsepower, enough for lighting the home, and using an electric
iron. Under a 100-foot head this same wheel would provide 25.9
horsepower, to meet the requirements of a bigger-than-average farm
plant.
_The Pipe Line_
The principal items of cost in installing an impulse wheel are in
connection with the pipe line, and the governor. In small heads, that
is, under 100 feet, the expense of pipe line is low. Frequently,
however, the governor will cost more than the water motor itself,
although cheaper, yet efficient, makes are now being put on the market
to meet this objection. In a later chapter, we will take up in detail
the question of governing the water wheel, and voltage regulation, and
will attempt to show how this expense may be practically eliminated by
the farmer.
To secure large heads, it is usually necessary to run a pipe line many
hundreds (and in many cases, many thousands) of feet from the flume to
the water wheel. Water flowing through pipes is subject to loss of
head, by friction, and for this reason the larger the pipe the less
the friction loss. Under no circumstances is it recommended to use a
pipe of less than two inches in diameter, even for the smallest water
motors; and with a two-inch pipe, the run should not exceed 200 feet.
Where heavy-pressure mains, such as those of municipal or commercial
water systems, are available, the problem of both water supply and
head becomes very simple. Merely ascertain the pressure of the water
in the mains _when flowing_, determine the amount of power required
(as illustrated in a succeeding chapter of this book), and install the
proper water motor with a suitably sized pipe.
Where one has his own water supply, however, and it is necessary to
lay pipe to secure the requisite fall, the problem is more difficult.
Friction in pipes acts in the same way as cutting down the head a
proportional amount; and by cutting down the head, your water motor
loses power in direct proportion to the number of feet head lost. This
head, obtained by subtracting friction and other losses from the
surveyed head, is called the _effective head_, and determines the
amount of power delivered at the nozzle.
The tables on pages 66-67 show the friction loss in pipes up to 12
inches in diameter, according to the amount of water, and the length
of pipe.
In this example it is seen that a 240-foot static head is reduced by
friction to 230.1 feet effective head. By referring to the table we
find the wheel fitting these conditions has a nozzle so small that it
cuts down the rate of flow of water in the big pipe to 4.4 feet a
second, and permits the flow of only 207 cubic feet of water a minute.
The actual horsepower of this tube and nozzle, then, can be figured by
applying formula (A), Chapter III, allowing 80 per cent for the
efficiency of the wheel. Thus:
Actual horsepower =
207 × 230.1 × 62.5
------------------ = 90.21 × .80 = 72.168 Hp.
33,000
To calculate what the horsepower of this tube 12 inches in diameter
and 900 feet long, would be without a nozzle, under a head of 240
feet, introduces a new element of friction losses, which is too
complicated to figure here. Such a condition would not be met with in
actual practice, in any event. The largest nozzles used, even in the
jumbo plants of the Far West, rarely exceed 10 inches in diameter; and
the pipe conveying water to such a nozzle is upwards of eight feet in
diameter.
PIPE FRICTION TABLES
INDICATING THE CALCULATED LOSS OF HEAD DUE TO FRICTION IN RIVETED
STEEL PIPE WITH VARIOUS WATER QUANTITIES AND VELOCITIES
[Courtesy of the Pelton Water Wheel Company]
Heavy-faced figures = Loss of head in feet for each one thousand
feet of pipe. Light-faced figures = Water quantity in cubic feet per
minute.
--------+-------------------------------------------------------------------------------------------+
Pipe | Velocity in Feet per Second |
Diameter+------+------+------+------+------+------+------+------+------+------+------+------+-------+
| 2.0 | 2.2 | 2.4 | 2.6 | 2.8 | 3.0 | 3.2 | 3.4 | 3.6 | 3.8 | 4.0 | 4.2 | 4.4 |
--------+------+------+------+------+------+------+------+------+------+------+------+------+-------+
|=17.1=|=20.0=|=25.6=|=28.3=|=32.0=|=37.3=|=40.9=|=45.8=|=50.4=|=56.0=|=62.3=|=68.1=|=74.9= |
3" | 5.9 | 6.5 | 7.1 | 7.7 | 8.3 | 8.9 | 9.4 | 10.0 | 10.6 | 11.2 | 11.8 | 12.4 | 13.0 |
|=11.0=|=13.0=|=15.0=|=17.3=|=20.2=|=23.2=|=26.2=|=29.6=|=33.0=|=36.5=|=41.0=|=45.4=|=49.2= |
4" | 10.5 | 11.5 | 12.6 | 13.6 | 14.7 | 15.7 | 16.8 | 17.8 | 18.8 | 19.9 | 21.0 | 22.0 | 23.0 |
| =7.7=| =9.4=|=11.0=|=12.9=|=14.9=|=16.9=|=19.5=|=21.6=|=24.0=|=27.0=|=29.8=|=32.9=|=36.0= |
5" | 16.4 | 18.0 | 19.6 | 21.2 | 22.9 | 24.5 | 26.1 | 27.8 | 29.5 | 31.0 | 32.7 | 34.3 | 36.0 |
| =6.0=| =7.2=| =8.6=| =9.9=|=11.7=|=13.0=|=14.6=|=16.6=|=19.0=|=21.5=|=23.4=|=25.5=|=27.8= |
6" | 23.5 | 25.9 | 28.2 | 30.6 | 32.9 | 35.3 | 37.7 | 40.0 | 42.4 | 44.7 | 47.1 | 49.5 | 51.8 |
| =4.9 | =6.9=| =7.0=| =8.1=| =9.3=|=10.6=|=12.0=|=13.6=|=15.2=|=17.0=|=19.0=|=21.0=|=23.0= |
7" | 32.0 | 35.3 | 38.5 | 41.7 | 44.9 | 48.1 | 51.3 | 54.5 | 57.7 | 60.9 | 64.1 | 67.3 | 70.5 |
| =4.0=| =4.9=| =6.0=| =6.9=| =7.8=| =9.1=|=10.0=|=10.2=|=13.0=|=14.4=|=15.9=|=17.2=|=19.2= |
8" | 41.9 | 46.1 | 50.2 | 54.4 | 58.6 | 62.8 | 67.0 | 71.2 | 75.4 | 79.6 | 83.7 | 87.9 | 92.1 |
| =3.4=| =4.2=| =5.1=| =5.9=| =6.7=| =7.7=| =8.9=| =9.8=|=11.0=|=12.2=|=13.8=|=15.0=|=16.0= |
9" | 53.0 | 58.3 | 63.6 | 68.9 | 74.2 | 79.5 | 84.8 | 90.1 | 95.4 |101 |106 |111 |116 |
| =2.9=| =3.7=| =4.4=| =5.1=| =5.9=| =6.7=| =7.5=| =8.6=| =9.5=|=10.6=|=12.1=|=13.1=|=14.1= |
10" | 65.4 | 72.0 | 78.5 | 85.1 | 91.6 | 98.2 |105 |111 |118 |124 |131 |137 |144 |
| =2.6=| =3.2=| =3.8=| =4.4=| =5.1=| =5.9=| =6.6=| =7.5=| =8.4=| =9.5=|=10.3=|=10.1=|=12.5= |
11" | 79 | 87 | 95 |103 |111 |119 |127 |134 |142 |150 |158 |166 |174 |
|=2.36=| =2.9=| =3.4=| =3.9=| =4.5=| =5.2=| =5.9=| =6.7=| =7.5=| =8.5=| =9.4=|=10.0=|=11.0= |
12" |94 |103 |113 |122 |132 |141 |151 |160 |169 |179 |188 |198 |207 |
--------+------+------+------+------+------+------+------+------+------+------+------+------+-------+
--------+------+------+------+------+-------+-------+-------+-------+-------+-------+-------+-------+
| 4.6 | 4.8 | 5.0 | 5.2 | 5.4 | 5.6 | 5.8 | 6.0 | 7.0 | 8.0 | 9.0 | 10.0 |
--------+------+------+------+------+-------+-------+-------+-------+-------+-------+-------+-------+
|=78.1=|=82.0=|=89.5=|=98.9=|=105.0=|=113.2=|=120.8=|=130.0=|=162.8=|=216.0=|=270.= |=323.= |
3" | 13.6 | 14.2 | 14.8 | 15.3 | 15.9 | 16.5 | 17.1 | 17.7 | 20.6 | 23.5 | 26.5 | 29.5 |
|=52.3=|=57.0=|=61.5=|=68.0=| =72.5=| =78.2=| =83.1=| =89.5=|=121.= |=155.= |=198.= |=242.= |
4" | 24.1 | 25.1 | 26.2 | 27.2 | 28.3 | 29.3 | 30.4 | 31.5 | 36.6 | 41.9 | 47.2 | 52.4 |
|=39.2=|=42.3=|=46.0=|=49.8=| =53.5=| =58.0=| =62.0=| =67.0=| =89.= |=118.= |=148.= |=182.= |
5" | 37.6 | 39.2 | 40.9 | 42.5 | 44.1 | 45.8 | 47.5 | 49.1 | 57.1 | 65.4 | 73.7 | 82.0 |
|=30.6=|=33.1=|=35.6=|=39.0=| =41.6=| =44.6=| =48.0=| =51.6=| =69.0=| =89.0=|=114.= |=140.= |
6" | 54.1 | 56.5 | 58.9 | 61.2 | 63.6 | 65.9 | 68.3 | 70.7 | 82.4 | 94.3 | 106 | 118 |
|=25.1=|=27.3=|=29.5=|=32.0=| =34.5=| =37.1=| =40.0=| =43.0=| =58.0=| =75.0=| =95.0=|=116.= |
7" | 73.7 | 76.9 | 80.2 | 83.3 | 86.6 | 89.8 | 93.0 | 96.2 | 112 | 128 | 145 | 161 |
|=20.0=|=22.5=|=24.9=|=27.0=| =28.8=| =30.6=| =32.8=| =35.5=| =47.5=| =61.2=| =78.6=| =95.1=|
8" | 96.3 |101 |105 |109 | 113 | 117 | 121 | 125 | 146 | 168 | 189 | 210 |
|=17.1=|=19.2=|=21.0=|=22.9=| =24.6=| =26.2=| =28.0=| =30.1=| =40.1=| =52.1=| =66.6=| =82.0=|
9" |122 |127 |132 |138 | 143 | 148 | 154 | 159 | 185 | 212 | 238 | 265 |
|=14.8=|=16.7=|=17.9=|=19.9=| =21.0=| =22.7=| =24.3=| =25.9=| =34.8=| =45.9=| =58.0=| =70.1=|
10" |150 |157 |163 |170 | 177 | 183 | 190 | 196 | 229 | 261 | 295 | 327 |
|=13.0=|=14.7=|=15.9=|=17.1=| =18.2=| =20.1=| =21.3=| =22.6=| =30.7=| =40.0=| =50.8=| =62.0=|
11" |182 |190 |198 |206 | 214 | 222 | 229 | 237 | 277 | 316 | 356 | 396 |
|=11.6=|=13.0=|=14.0=|=15.1=| =16.1=| =17.8=| =19.1=| =20.2=| =27.1=| =35.9=| =45.4=| =55.9=|
12" |217 |226 |235 |245 | 254 | 264 | 273 | 283 | 330 | 377 | 425 | 472 |
--------+---------+----------+------+-------+-------+-------+-------+-------+-------+-------+-------+
EXAMPLE
Assume the surveyed head as 240 feet, the water quantity as 207
cubic feet per minute and a pipe line 12 inches in diameter 900 feet
long. To ascertain the friction loss, refer to column of pipe
diameter and follow across the column for 12 inches diameter to the
quantity, 207 cubic feet per minute. The heavy-faced figures above
207 indicate that the loss per 1000 feet of pipe length is 11 feet.
Therefore, since the pipe in the example is 900 feet long, the loss
will be
11.' × 900/1000 or 9.9 feet, and the effective head will be
240' - 9.9' = 230.1'
Steel tubing for supply pipes, from 3 to 12 inches in diameter is
listed at from 20 cents to $1.50 a foot, according to the diameter and
thickness of the material. Discounts on these prices will vary from 25
to 50 per cent. The farmer can cut down the cost of this pipe by
conveying his supply water from its natural source to a pond, by means
of an open race, or a wooden flume. An ingenious mechanic can even
construct his own pipe out of wood, though figuring labor and
materials, it is doubtful if anything would be saved over a riveted
steel pipe, purchased at the regular price. This pipe, leading from
the pond, or forebay, to the water wheel, should be kept as short as
possible; at the same time, the fall should not be too sharp. An angle
of 30° will be found very satisfactory, although pipe is frequently
laid at angles up to 50°.
_Other Types of Impulse Wheels_
In recent years more efficient forms of the old-fashioned overshoot,
pitch-back breast, and undershoot wheels have been developed, by
substituting steel or other metal for wood, and altering the shape of
the buckets to make better use of the power of falling water.
In some forms of overshoot wheels, an efficiency of over 90 per cent
is claimed by manufacturers; and this type offers the additional
advantage of utilizing small quantities of water, as well as being
efficient under varying quantities of water. They utilize the falling
weight of water, although by giving the water momentum at the point of
delivery, by means of the proper fall, impulse too is utilized in some
measure. The modern steel overshoot wheel receives water in its
buckets from a spout set a few degrees back of dead center; and its
buckets are so shaped that the water is retained a full
half-revolution of the wheel. The old-style overshoot wheel was
inefficient principally because the buckets began emptying themselves
at the end of a quarter-revolution. Another advantage claimed for
these wheels over the old style is that, being made of thin metal,
their buckets attain the temperature of the water itself, thus
reducing the danger of freezing to a minimum. They are manufactured in
sizes from 6 feet in diameter to upwards of fifty feet; and with
buckets of from 6 inches to 10 feet in width. In practice it is usual
to deliver water to the buckets by means of a trough or pipe, through
a suitable spout and gate, at a point two feet above the crown of the
wheel. For this reason, the diameter of the wheel corresponds very
closely to the head in feet.
_The Reaction Turbine_
The reaction turbine is best adapted to low heads, with a large supply
of water. It is not advisable, under ordinary circumstances, to use it
under heads exceeding 100 feet, as its speed is then excessive. It
may be used under falls as low as two feet. Five thousand cubic feet
of water a minute would give approximately 14 actual horsepower under
such a head. A sluggish creek that flows in large volume could thus be
utilized for power with the reaction turbine, whereas it would be
useless with an impulse wheel. Falls of from five to fifteen feet are
to be found on thousands of farm streams, and the reaction turbine is
admirably adapted to them.
Reaction turbines consist of an iron "runner" which is in effect a
rotary fan, the pressure and momentum of the column of water pressing
on the slanted blades giving it motion and power. These wheels are
manufactured in a great variety of forms and sizes; and are to be
purchased either as the runner (set in bearings) alone, or as a runner
enclosed in an iron case. In case the runner alone is purchased, the
owner must enclose it, either with iron or wood. They vary in price
according to size, and the means by which the flow of water is
controlled. A simple 12-inch reaction turbine wheel, such as would be
suitable for many power plants can be had for $75. A twelve-inch
wheel, using 18 or 20 square inches of water, would generate about
7-1/2 horsepower under a 20-foot head, with 268 cubic feet of water a
minute. Under a 30-foot head, and with 330 cubic feet of water such a
wheel will give 14 horsepower. A 36-inch wheel, under a 5-foot head,
would use 2,000 cubic feet of water, and give 14 horsepower. Under a
30-foot head, this same wheel, using 4,900 cubic feet of water a
minute, would develop over 200 horsepower. If the farmer is confronted
by the situation of a great deal of water and small head, a large
wheel would be necessary. Thus he could secure 35 horsepower with only
a 3-foot head, providing his water supply is equal to the draft of
8,300 cubic feet a minute.
From these sample figures, it will be seen that the reaction turbine
will meet the requirements of widely varying conditions up to, say a
head of 100 feet. The farmer prospector should measure first the
quantity of water to be depended on, and then the number of feet fall
to be had. The higher the fall, with certain limits, the smaller the
expense of installation, and the less water required. When he has
determined _quantity_ and _head_, the catalogue of a reputable
manufacturer will supply him with what information is necessary to
decide on the style and size wheel he should install. In the older
settled communities, especially in New England, a farmer should be
able to pick up a second-hand turbine, at half the price asked for a
new one; and since these wheels do not depreciate rapidly, it would
serve his purpose as well, in most cases, as a new one.
[Illustration: A typical vertical turbine]
Reaction turbines may be either horizontal or vertical. If they are
vertical, it is necessary to connect them to the main shaft by means
of a set of bevel gears. These gears should be substantially large,
and if the teeth are of hard wood (set in such a manner that they can
be replaced when worn) they will be found more satisfactory than if of
cast or cut metal.
[Illustration: Two wheels on a horizontal shaft
(Courtesy of the C. P. Bradway Company, West Stafford, Conn.)]
The horizontal turbine is keyed to its shaft, like the impulse wheel,
so that the wheel shaft itself is used for driving, without gears or a
quarter-turn belt. (The latter is to be avoided, wherever possible.)
There are many forms of horizontal turbines; they are to be had of the
duplex type, that is, two wheels on one shaft. These are arranged so
that either wheel may be run separately, or both together, thus
permitting one to take advantage of the seasonal fluctuation in water
supply. A convenient form of these wheels includes draft tubes, by
which the wheel may be set several feet above the tailrace, and the
advantage of this additional fall still be preserved. In this case the
draft tube must be airtight so as to form suction, when filled with
escaping water, and should be proportioned to the size of the wheel.
Theoretically these draft tubes might be 34 feet long, but in practice
it has been found that they should not exceed 10 or 12 feet under
ordinary circumstances. They permit the wheel to be installed on the
main floor of the power station, with the escape below, instead of
being set just above the tailrace level itself, as is the case when
draft tubes are not used.
Reaction turbines when working under a variable load require water
governors (like impulse wheels) although where the supply of water is
large, and the proportion of power between water wheel and dynamo is
liberal--say two to one, or more--this necessity is greatly reduced.
Reaction wheels as a rule govern themselves better than impulse
wheels, due both to the fact that they use more water, and that they
operate in a small airtight case. The centrifugal ball governor is the
type usually used with reaction wheels as well as with impulse wheels.
This subject will be discussed more fully later.
_Installing a Power Plant_
In developing a power prospect, the dam itself is usually not the site
of the power plant. In fact, because of danger from flood water and
ice, it is better to locate it in a more protected spot, leading the
water to the wheel by means of a race and flume.
[Illustration: Bird's-eye view of a developed water-power plant]
A typical crib dam, filled with stone, is shown in section in the
diagram, and the half-tone illustration shows such a dam in course of
construction. The first bed of timbers should be laid on hard-pan or
solid rock in the bed of the stream parallel to its flow. The second
course, across the stream, is then begun, being spiked home by means
of rods cut to length and sharpened by the local blacksmith, from
3/4-inch Norway iron. Hemlock logs are suitable for building the crib;
and as the timbers are finally laid, it should be filled in and made
solid with boulders. This filling in should proceed section by
section, as the planking goes forward, otherwise there will be no
escape for the water of the stream, until it rises and spills over
the top timbers. The planking should be of two-inch chestnut, spiked
home with 60 penny wire spikes. When the last section of the crib is
filled with boulders and the water rises, the remaining planks may be
spiked home with the aid of an iron pipe in which to drive the spike
by means of a plunger of iron long enough to reach above the level of
the water. When the planking is completed, the dam should be well
gravelled, to within a foot or two of its crest. Such dams are
substantial, easily made with the aid of unskilled labor, and the
materials are to be had on the average farm with the exception of the
hardware.
[Illustration: Cross-section of a rock and timber dam]
This dam forms a pond from which the race draws its supply of water
for the wheel. It also serves as a spillway over which the surplus
water escapes. The race should enter the pond at some convenient
point, and should be protected at or near its point of entrance by a
bulkhead containing a gate, so that the supply of water may be cut off
from the race and wheel readily. The lay of the land will determine
the length and course of the race. The object of the race is to secure
the required head by carrying a portion of the available water to a
point where it can escape, by a fall of say 30° to the tailrace. It
may be feasible to carry the race in a line almost at right angles to
the stream itself, or, again, it may be necessary to parallel the
stream. If the lay of the land is favorable, the race may be dug to a
distance of a rod or so inshore, and then be permitted to cut its own
course along the bank, preventing the water escaping back to the river
or brook before the site of the power plant is reached, by building
suitable retaining embankments. The race should be of ample size for
conveying the water required without too much friction. It should end
in a flume constructed stoutly of timbers. It is from this flume that
the penstock draws water for the wheel. When the wheel gate is closed
the water in the mill pond behind the dam, and in the flume itself
should maintain an approximate level. Any surplus flow is permitted to
escape over flushboards in the flume; these same flushboards maintain
a constant head when the wheel is in operation by carrying off what
little surplus water the race delivers from the pond.
[Illustration: Detail of bulkhead gate]
At some point in the race or flume, the flow should be protected from
leaves and other trash by means of a rack. This rack is best made of
1/4 or 1/2-inch battens from 1-1/2 to 3 inches in width, bolted
together on their flat faces and separated a distance equal to the
thickness of the battens by means of iron washers. This rack will
accumulate leaves and trash, varying with the time of year and should
be kept clean, so as not to cut down the supply of water needed by the
wheel.
The penstock, or pipe conveying water from the flume to the wheel,
should be constructed of liberal size, and substantially, of two-inch
chestnut planking, with joints caulked with oakum, and the whole well
bound together to resist the pressure of the water. Means should be
provided near the bottom for an opening through which to remove any
obstructions that may by accident pass by the rack. Many wheels have
plates provided in their cases for this purpose.
The tailrace should be provided with enough fall to carry the escaping
water back to the main stream, without backing up on the wheel itself
and thus cutting down the head.
It is impossible to make any estimates of the cost of such a
water-power plant. The labor required will in most instances be
supplied by the farmer himself, his sons, and his help, during times
when farm operations are slack.
_Water Rights of the Farmer_
The farmer owns the bed of every stream not navigable, lying within
the boundary lines of the farm; and his right to divert and make use
of the water of such streams is determined in most states by common
law. In the dry-land states where water is scarce and is valuable for
irrigation, a special set of statutes has sprung up with the
development of irrigation in this country.
A stream on the farm is either public or private; its being navigable
or "floatable" (suitable for floating logs) determining which. Water
rights are termed in law "riparian" rights, and land is riparian only
when water flows over it or along its borders.
Green (Law for the American Farmer) says:
"Water is the common and equal property of every one through whose
land it flows, and the right of each land-owner to use and consume it
without destroying, or unreasonably impairing the rights of others, is
the same. An owner of land bordering on a running stream has the right
to have its waters flow naturally, and none can lawfully divert them
without his consent. Each riparian proprietor has an equal right with
all the others to have the stream flow in its natural way without
substantial reduction in volume, or deterioration in quality, subject
to a proper and reasonable use of its waters for domestic,
agricultural and manufacturing purposes, and he is entitled to use it
himself for such purposes, but in doing so must not substantially
injure others. In addition to the right of drawing water for the
purposes just mentioned, a riparian proprietor, if he duly regards the
rights of others, and does not unreasonably deplete the supply, has
also the right to take the water for some other proper uses."
Thus, the farmer who seeks to develop water-power from a stream
flowing across his own land, has the right to divert such a stream
from its natural channel--providing it is not a navigable or floatable
stream--but in so doing, he must return it to its own channel for
lower riparian owners. The generation of water-power does not pollute
the water, nor does it diminish the water in quantity, therefore the
farmer is infringing on no other owner's rights in using the water for
such a purpose.
When a stream is a dividing line between two farms, as is frequently
the case, each proprietor owns to the middle of the stream and
controls its banks. Therefore to erect a dam across such a private
stream and divert all or a part of the water for power purposes,
requires the consent of the neighboring owner. The owner of the dam is
responsible for damage due to flooding, to upstream riparian owners.
PART II
ELECTRICITY
CHAPTER V
THE DYNAMO; WHAT IT DOES, AND HOW
Electricity compared to the heat and light of the Sun--The simple
dynamo--The amount of electric energy a dynamo will generate--The
modern dynamo--Measuring power in terms of electricity--The
volt--The ampere--The ohm--The watt and the kilowatt--Ohm's Law of
the electric circuit, and some examples of its application--Direct
current, and alternating current--Three types of direct-current
dynamos: series, shunt, and compound.
What a farmer really does in generating electricity from water that
would otherwise run to waste in his brook, is to install a private Sun
of his own--which is on duty not merely in daylight, but twenty-four
hours a day; a private Sun which is under such simple control that it
shines or provides heat and power, when and where wanted, simply by
touching a button.
This is not a mere fanciful statement. When you come to look into it
you find that electricity actually is the life-giving power of the
Sun's rays, so transformed that it can be handily conveyed from place
to place by means of wires, and controlled by mechanical devices as
simple as the spigot that drains a cask.
Nature has the habit of traveling in circles. Sometimes these circles
are so big that the part of them we see looks like a straight line,
but it is not. Even parallel lines, according to the mathematicians,
"meet in infinity." Take the instance of the water wheel which the
farmer has installed under the fall of his brook. The power which
turns the wheel has the strength of many horses. It is there in a
handy place for use, because the Sun brought it there. The Sun, by its
heat, lifted the water from sea-level, to the pond where we find
it--and we cannot get any more power out of this water by means of a
turbine using its pressure and momentum in falling, than the Sun
itself expended in raising the water against the force of gravity.
Once we have installed the wheel to change the energy of falling water
into mechanical power, the task of the dynamo is to turn this
mechanical power into another mode of motion--electricity. And the
task of electricity is to change this mode of motion back into the
original heat and light of the Sun--which started the circle in the
beginning.
Astronomers refer to the Sun as "he" and "him" and they spell his name
with a capital letter, to show that he occupies the center of our
small neighborhood of the universe at all times.
_Magnets and Magnetism_
The dynamo is a mechanical engine, like the steam engine, the water
turbine or the gas engine; and it converts the mechanical motion of
the driven wheel into electrical motion, with the aid of a magnet.
Many scientists say that the full circle of energy that keeps the
world spinning, grows crops, and paints the sky with the Aurora
Borealis, begins and ends with magnetism--that the sun's rays are
magnetic rays. Magnetism is the force that keeps the compass needle
pointing north and south. Take a steel rod and hold it along the
north and south line, slightly inclined towards the earth, and strike
it a sharp blow with a hammer, and it becomes a magnet--feeble, it is
true, but still a magnet.
Take a wire connected with a common dry battery and hold a compass
needle under it and the needle will immediately turn around and point
directly across the wire, showing that the wire possesses magnetism
encircling it in invisible lines, stronger than the magnetism of the
earth.
[Illustration: (_Courtesy of the Crocker-Wheeler Company_)
A direct-current dynamo or motor, showing details of construction]
Insulate this wire by covering it with cotton thread, and wind it
closely on a spool. Connect the two loose ends to a dry battery, and
you will find that you have multiplied the magnetic strength of a
single loop of wire by the number of turns on the spool--concentrated
all the magnetism of the length of that wire into a small space. Put
an iron core in the middle of this spool and the magnet seems still
more powerful. Lines of force which otherwise would escape in great
circles into space, are now concentrated in the iron. The iron core
is a magnet. Shut off the current from the battery and the iron is
still a magnet--weak, true, but it will always retain a small portion
of its magnetism. Soft iron retains very little of its magnetism. Hard
steel retains a great deal, and for this reason steel is used for
permanent magnets, of the horseshoe type so familiar.
_A Simple Dynamo_
A dynamo consists, first, of a number of such magnets, wound with
insulated wire. Their iron cores point towards the center of a circle
like the spokes of a wheel; and their curved inner faces form a circle
in which a spool, wound with wire in another way, may be spun by the
water wheel.
Now take a piece of copper wire and make a loop of it. Pass one side
of this loop in front of an electric magnet.
As the wire you hold in your hands passes the iron face of the magnet,
a wave of energy that is called electricity flows around this loop at
the rate of 186,000 miles a second--the same speed as light comes to
us from the sun. As you move the wire away from the magnet, a second
wave starts through the wire, flowing in the opposite direction. You
can prove this by holding a compass needle under the wire and see it
wag first in one direction, then in another.
[Illustration: A wire "cutting" the lines of force of an
electro-magnet]
This is a simple dynamo. A wire "cutting" the invisible lines of
force, that a magnet is spraying out into the air, becomes
"electrified." Why this is true, no one has ever been able to explain.
The amount of electricity--its capacity for work--which you have
generated with the magnet and wire, does not depend alone on the
pulling power of that simple magnet. Let us say the magnet is very
weak--has not enough power to lift one ounce of iron. Nevertheless,
if you possessed the strength of Hercules, and could pass that wire
through the field of force of the magnet many thousands of times a
second, you would generate enough electricity in the wire to cause the
wire to melt in your hands from heat.
[Illustration: Cross-section of an armature revolving in its field]
[Illustration: Forms of annealed steel discs used in armature
construction]
This experiment gives the theory of the dynamo. Instead of passing
only one wire through the field of force of a magnet, we have hundreds
bound lengthwise on a revolving drum called an armature. Instead of
one magnetic pole in a dynamo we have two, or four, or twenty
according to the work the machine is designed for--always in pairs, a
North pole next to a South pole, so that the lines of force may flow
out of one and into another, instead of escaping in the surrounding
air. If you could see these lines of force, they would appear in
countless numbers issuing from each pole face of the field magnets,
pressing against the revolving drum like hair brush bristles--trying
to hold it back. This drum, in practice, is built up of discs of
annealed steel, and the wires extending lengthwise on its face are
held in place by slots to prevent them from flying off when the drum
is whirled at high speed. The drum does not touch the face of the
magnets, but revolves in an air space. If we give the electric
impulses generated in these wires a chance to flow in a circuit--flow
out of one end of the wires, and in at the other, the drum will
require more and more power to turn it, in proportion to the amount of
electricity we permit to flow. Thus, if one electric light is turned
on, the drum will press back with a certain strength on the water
wheel; if one hundred lights are turned on it will press back one
hundred times as much. Providing there is enough power in the water
wheel to continue turning the drum at its predetermined speed, the
dynamo will keep on giving more and more electricity if asked to,
until it finally destroys itself by fire. You cannot take more power,
in terms of electricity, out of a dynamo that you put into it, in
terms of mechanical motion. In fact, to insure flexibility and
constant speed at all loads, it is customary to provide twice as much
water wheel, or engine, power as the electrical rating of the dynamo.
[Illustration: An armature partly wound, showing slots and commutator]
We have seen that a water wheel is 85 per cent efficient under ideal
conditions. A dynamo's efficiency in translating mechanical motion
into electricity, varies with the type of machine and its size. The
largest machines attain as high as 90 per cent efficiency; the
smallest ones run as low as 40 per cent.
_Measuring Electric Power_
The amount of electricity any given dynamo can generate depends,
generally speaking, on two factors, i. e., (1) the power of the water
wheel, or other mechanical engine that turns the armature; and (2) the
size (carrying capacity) of the wires on this drum.
Strength, of electricity, is measured in _amperes_. An ampere of
electricity is the unit of the rate of flow and may be likened to a
gallon of water per minute.
In surveying for water-power, in Chapter III, we found that the
number of gallons or cubic feet of water alone did not determine the
amount of power. We found that the number of gallons or cubic feet
multiplied by the distance in feet it falls in a given time, was the
determining factor--pounds (quantity) multiplied by feet per
second--(velocity).
[Illustration: Showing the analogy of water to volts and amperes of
electricity]
The same is true in figuring the power of electricity. We multiply the
_amperes_ by the number of electric impulses that are created in the
wire in the course of one second. The unit of velocity, or pressure of
the electric current is called a _volt_. Voltage is the pressure which
causes electricity to flow. A volt may be likened to the velocity in
feet per second of water in falling past a certain point. If you
think a moment you will see that this has nothing to do with quantity.
A pin-hole stream of water under 40 pounds pressure has the same
velocity as water coming from a nozzle as big as a barrel, under the
same pressure. So with electricity under the pressure of one volt or
one hundred volts.
One volt is said to consist of a succession of impulses caused by _one
wire cutting 100,000,000 lines of magnetic force in one second_. Thus,
if the strength of a magnet consisted of one line of force, to create
the pressure of one volt we would have to "cut" that line of force
100,000,000 times a second, with one wire; or 100,000 times a second
with one thousand wires. Or, if a magnet could be made with
100,000,000 lines of force, a single wire cutting those lines once in
a second would create one volt pressure. In actual practice, field
magnets of dynamos are worked at densities up to and over 100,000
lines of force to the square inch, and armatures contain several
hundred conductors to "cut" these magnetic lines. The voltage then
depends on the speed at which the armature is driven. In machines for
isolated plants, it will be found that the speed varies from 400
revolutions per minute, to 1,800, according to the design of dynamo
used.
[Illustration: Pressure determines volume of flow in a given time]
Multiplying amperes (strength) by volts (pressure), gives us _watts_
(power). Seven hundred and forty-six watts of electrical energy is
equal to one horsepower of mechanical energy--will do the same work.
Thus an electric current under a pressure of 100 volts, and a density
of 7.46 amperes, is one horsepower; as is 74.6 amperes, at 10 volts
pressure; or 746 amperes at one volt pressure. For convenience (as a
watt is a small quantity) electricity is measured in _kilowatts_, or
1,000 watts. Since 746 watts is one horsepower, 1,000 watts or one
kilowatt is 1.34 horsepower. The work of such a current for one hour
is called a _kilowatt-hour_, and in our cities, where electricity is
generated from steam, the retail price of a kilowatt-hour varies from
10 to 15 cents.
Now as to how electricity may be controlled, so that a dynamo will not
burn itself up when it begins to generate.
Again we come back to the analogy of water. The amount of water that
passes through a pipe in any given time, depends on the size of the
pipe, if the pressure is maintained uniform. In other words the
_resistance_ of the pipe to the flow of water determines the amount.
If the pipe be the size of a pin-hole, a very small amount of water
will escape. If the pipe is as big around as a barrel, a large amount
will force its way through. So with electricity. Resistance,
introduced in the electric circuit, controls the amount of current
that flows. A wire as fine as a hair will permit only a small quantity
to pass, under a given pressure. A wire as big as one's thumb will
permit a correspondingly greater quantity to pass, the pressure
remaining the same. The unit of electrical resistance is called the
_ohm_--named after a man, as are all electrical units.
_Ohm's Law_
The _ohm_ is that amount of _resistance_ that will permit the passage
of _one ampere_, under the pressure of _one volt_. It would take two
volts to force two amperes through one ohm; or 100 volts to force 100
amperes through the resistance of one ohm. From this we have Ohm's
Law, a simple formula which is the beginning and end of all electric
computations the farmer will have to make in installing his
water-power electric plant. Ohm's Law tells us that the density of
current (amperes) that can pass through a given resistance in ohms (a
wire, a lamp, or an electric stove) equals _volts_ divided by
_ohms_--or _pressure_ divided by _resistance_. This formula may be
written in three ways, thus:
C = E/R, or R = E/C or, E = C × R. Or to express the same thing in
words, _current_ equals _volts_ divided by _ohms_; _ohms_ equals
_volts_ divided by _current_; or _volts_ equals _current_ multiplied
by _ohms_. So, with any two of these three determining factors known,
we can find the third. As we have said, this simple law is the
beginning and end of ordinary calculations as to electric current, and
it should be thoroughly understood by any farmer who essays to be his
own electrical engineer. Once understood and applied, the problem of
the control of the electric current becomes simple a b c.
_Examples of Ohm's Law_
Let us illustrate its application by an example. The water wheel is
started and is spinning the dynamo at its rated speed, say 1,500
r.p.m. Two heavy wires, leading from brushes which collect electricity
from the revolving armature, are led, by suitable insulated supports
to the switchboard, and fastened there. They do not touch each other.
Dynamo mains must not be permitted to touch each other _under any
conditions_. They are separated by say four inches of air. Dry air is
a very poor conductor of electricity. Let us say, for the example,
that dry air has a resistance to the flow of an electric current, of
1,000,000 ohms to the inch--that would be 4,000,000 ohms. How much
electricity is being permitted to escape from the armature of this
110-volt dynamo, when the mains are separated by four inches of dry
air? Apply Ohm's law, C equals E divided by R. E, in this case is 110;
R is 4,000,000; therefore C (amperes) equals 110/4,000,000--an
infinitesimal amount--about .0000277 ampere.
Let us say that instead of separating these two mains by air we
separated them by the human body--that a man took hold of the bare
wires, one in each hand. The resistance of the human body varies from
5,000 to 10,000 ohms. In that case C (amperes) equals 110/5,000, or
110/10,000--about 1/50th, or 1/100th of an ampere. This illustrates
why an electric current of 110 volts pressure is not fatal to human
beings, under ordinary circumstances. The body offers too much
resistance. But, if the volts were 1,100 instead of the usual 110 used
in commercial and private plants for domestic use, the value of C, by
this formula at 5,000 ohms, would be nearly 1/5th ampere. To drive
1/5th ampere of electricity through the human body would be fatal in
many instances. The higher the voltage, the more dangerous the
current. In large water-power installations in the Far West, where the
current must be transmitted over long distances to the spot where it
is to be used, it is occasionally generated at a pressure of 150,000
volts. Needless to say, contact with such wires means instant death.
Before being used for commercial or domestic purposes, in such cases,
the voltage is "stepped down" to safe pressures--to 110, or to 220, or
to 550 volts--always depending on the use made of it.
Now, if instead of interposing four inches of air, or the human body,
between the mains of our 110-volt dynamo, we connected an incandescent
lamp across the mains, how much electricity would flow from the
generator? An incandescent lamp consists of a vacuum bulb of glass, in
which is mounted a slender thread of carbonized fibre, or fine
tungsten wire. To complete a circuit, the current must flow through
this wire or filament. In flowing through it, the electric current
turns the wire or filament white hot--incandescent--and thus turns
electricity back into light, with a small loss in heat. In an ordinary
16 candlepower carbon lamp, the resistance of this filament is 220
ohms. Therefore the amount of current that a 110-volt generator can
force through that filament is 110/220, or 1/2 ampere.
[Illustration: Armature and field coils of a direct current dynamo]
One hundred lamps would provide 100 paths of 220 ohms resistance each
to carry current, and the amount required to light 100 such lamps
would be 100 × 1/2 or 50 amperes. Every electrical device--a lamp, a
stove, an iron, a motor, etc.,--must, by regulations of the Fire
Underwriters' Board be plainly marked with the voltage of the current
for which it is designed and the amount of current it will consume.
This is usually done by indicating its capacity in watts, which as we
have seen, means volts times amperes, and from this one can figure
ohms, by the above formulas.
_A Short Circuit_
We said a few paragraphs back that under no conditions must two bare
wires leading from electric mains be permitted to touch each other,
without some form of resistance being interposed in the form of lamps,
or other devices. Let us see what would happen if two such bare wires
did touch each other. Our dynamo as we discover by reading its plate,
is rated to deliver 50 amperes, let us say, at 110 volts pressure.
Modern dynamos are rated liberally, and can stand 100% overload for
short periods of time, without dangerous overheating. Let us say that
the mains conveying current from the armature to the switchboard are
five feet long, and of No. 2 B. & S. gauge copper wire, a size which
will carry 50 amperes without heating appreciably. The resistance of
this 10 feet of No. 2 copper wire, is, as we find by consulting a wire
table, .001560 ohms. If we touch the ends of these two five-foot wires
together, we instantly open a clear path for the flow of electric
current, limited only by the carrying capacity of the wire and the
back pressure of .001560 ohms resistance. Using Ohm's Law, C equals E
divided by R, we find that C (amperes) equals 110/.001560 or _70,515
amperes_!
[Illustration: A direct current dynamo]
Unless this dynamo were properly protected, the effect of such a
catastrophe would be immediate and probably irreparable. In effect, it
would be suddenly exerting a force of nearly 10,000 horsepower against
the little 10 horsepower water wheel that is driving this dynamo. The
mildest thing that could happen would be to melt the feed-wire or to
snap the driving belt, in which latter case the dynamo would come to a
stop. If by any chance the little water wheel was given a chance to
maintain itself against the blow for an instant, the dynamo, rated at
50 amperes, would do its best to deliver the 70,515 amperes you called
for--and the result would be a puff of smoke, and a ruined dynamo.
This is called a "short circuit"--one of the first "don'ts" in
handling electricity.
As a matter of fact every dynamo is protected against such a calamity
by means of safety devices, which will be described in a later
chapter--because no matter how careful a person may be, a partial
short circuit is apt to occur. Happily, guarding against its
disastrous effects is one of the simplest problems in connection with
the electric plant.
_Direct Current and Alternating Current_
When one has mastered the simple Ohm's Law of the electric circuit,
the next step is to determine what type of electrical generator is
best suited to the requirements of a farm plant.
In the first place, electric current is divided into two classes of
interest here--_alternating_, and _direct_.
We have seen that when a wire is moved through the field of a magnet,
there is induced in it two pulsations--first in one direction, then in
another. This is an _alternating_ current, so called because it
changes its direction. If, with our armature containing hundreds of
wires to "cut" the lines of force of a group of magnets, we connected
the beginning of each wire with one copper ring, and the end of each
wire with another copper ring, we would have what is called an
_alternating-current_ dynamo. Simply by pressing a strap of flexible
copper against each revolving copper ring, we would gather the sum of
the current of these conductors. Its course would be represented by
the curved line in the diagram, one loop on each side of the middle
line (which represents time) would be a _cycle_. The number of
_cycles_ to the second depends on the speed of the armature; in
ordinary practice it is usually twenty-five or sixty. Alternating
current has many advantages, which however, do not concern us here.
Except under very rare conditions, a farmer installing his own plant
should not use this type of machine.
[Illustration: Diagram of alternating and direct current]
If, however, instead of gathering all the current with brushes bearing
on two copper rings, we collected all the current traveling in one
direction, on one set of brushes--and all the current traveling in the
other direction on another set of brushes,--we would straighten out
this current, make it all travel in one direction. Then we would have
a _direct current_. A direct current dynamo, the type generally used
in private plants, does this. Instead of having two copper rings for
collecting the current, it has a single ring, made up of segments of
copper bound together, but insulated from each other, one segment for
each set of conductors on the armature. This ring of many segments, is
called a _commutator_, because it commutates, or changes, the
direction of the electric impulses, and delivers them all in one
direction. In effect, it is like the connecting rod of a steam engine
that straightens out the back-and-forth motion of the piston in the
steam cylinder and delivers the motion to a wheel running in one
direction.
Such a current, flowing through a coil of wire would make a magnet,
one end of which would always be the north end, and the other end the
south end. An alternating current, on the other hand, flowing through
a coil of wire, would make a magnet that changed its poles with each
half-cycle. It would no sooner begin to pull another magnet to it,
than it would change about and push the other magnet away from it, and
so on, as long as it continued to flow. This is one reason why a
direct current dynamo is used for small plants. Alternating current
will light the same lamps and heat the same irons as a direct current;
but for electric power it requires a different type of motor.
_Types of Direct Current Dynamos_
Just as electrical generators are divided into two classes,
alternating and direct, so direct current machines are divided into
three classes, according to the manner in which their output, in
amperes and volts, is regulated. They differ as to the manner in which
their field magnets (in whose field of force the armature spins) are
excited, or made magnetic. They are called _series_, _shunt_, and
_compound_ machines.
_The Series Dynamo_
By referring to the diagram, it will be seen that the current of a
_series_ dynamo issues from the armature mains, and passes through the
coils of the field magnets before passing into the external circuit to
do its work. The residual magnetism, or the magnetism left in the
iron cores of the field magnets from its last charge, provides the
initial excitation, when the machine is started. As the resistance of
the external circuit is lowered, by turning on more and more lights,
more and more current flows from the armature, through the field
magnets. Each time the resistance is lowered, therefore, the current
passing through the field magnets becomes more dense in amperes, and
makes the field magnets correspondingly stronger.
We have seen that the voltage depends on the number of lines of
magnetic force cut by the armature conductors in a given time. If the
speed remains constant then, and the magnets grow stronger and
stronger, the voltage will rise in a straight line. When no current is
drawn, it is 0; at full load, it may be 100 volts, or 500, or 1,000
according to the machine. This type of machine is used only in street
lighting, in cities, with the lights connected in "series," or one
after another on the same wire, the last lamp finally returning the
wire to the machine to complete the circuit. This type of dynamo has
gained the name for itself of "mankiller," as its voltage becomes
enormous at full load. It is unsuitable, in every respect, for the
farm plant. Its field coils consist of a few turns of very heavy wire,
enough to carry all the current of the external circuit, without
heating.
[Illustration: Connections of a series dynamo]
_The Shunt Dynamo_
The shunt dynamo, on the other hand, has field coils connected
directly _across_ the circuit, from one wire to another, instead of in
"series." These coils consist of a great many turns of very fine wire,
thus introducing _resistance_ into the circuit, which limits the
amount of current (amperes) that can be forced through them at any
given voltage. As a shunt dynamo is brought up to its rated speed, its
voltage gradually rises until a condition of balance occurs between
the field coils and the armature. There it remains constant. When
resistance on the external circuit is lowered, by means of turning on
lamps or other devices, the current from the armature increases in
working power, by increasing its amperes. Its voltage remains
stationary; and, since the resistance of its field coils never
changes, the magnets do not vary in strength.
[Illustration: Connections of a shunt dynamo]
The objection to this type of machine for a farm plant is that, in
practice, the armature begins to exercise a de-magnetizing effect on
the field magnets after a certain point is reached--weakens them;
consequently the voltage begins to fall. The voltage of a shunt dynamo
begins to fall after half-load is reached; and at full load, it has
fallen possibly 20 per cent. A rheostat, or resistance box on the
switchboard, makes it possible to cut out or switch in additional
resistance in the field coils, thus varying the strength of the field
coils, within a limit of say 15 per cent, to keep the voltage
constant. This, however, requires a constant attendance on the
machine. If the voltage were set right for 10 lights, the lights would
grow dim when 50 lights were turned on; and if it were adjusted for 50
lights, the voltage would be too high for only ten lights--would cause
them to "burn out."
Shunt dynamos are used for charging storage batteries, and are
satisfactory for direct service only when an attendant is constantly
at hand to regulate them.
_The Compound Dynamo_
The ideal between these two conditions would be a compromise, which
included the characteristics of both _series_ and _shunt_ effects.
That is exactly what the _compound_ dynamo effects.
A compound dynamo is a shunt dynamo with just enough series turns on
its field coils, to counteract the de-magnetizing effect of the
armature at full load. A machine can be designed to make the voltage
rise gradually, or swiftly, by combining the two systems. For country
homes, the best combination is a machine that will keep the voltage
constant from no load to full load. A so-called _flat-compounded_
machine does this. In actual practice, this voltage rises slightly at
the half-load line--only two or three volts, which will not damage the
lamps in a 110-volt circuit.
The compound dynamo is therefore self-regulating, and requires no
attention, except as to lubrication, and the incidental care given to
any piece of machinery. Any shunt dynamo can be made into a compound
dynamo, by winding a few turns of heavy insulated wire around the
shunt coils, and connecting them in "series" with the external
circuit. How many turns are necessary depends on conditions. Three or
four turns to each coil usually are sufficient for "flat compounding."
If the generating plant is a long distance from the farm house where
the light, heat, and power are to be used, the voltage drops at full
load, due to resistance of the transmission wires. To overcome this,
enough turns can be wound on top of the shunt coils to cause the
voltage to rise at the switchboard, but remain stationary at the spot
where the current is used. The usual so-called flat-compounded dynamo,
turned out by manufacturers, provides for constant voltage at the
switchboard. Such a dynamo is eminently fitted for the farm electric
plant. Any other type of machine is bound to cause constant trouble
and annoyance.
[Illustration: Connections of a compound dynamo]
CHAPTER VI
WHAT SIZE PLANT TO INSTALL
The farmer's wife his partner--Little and big plants--Limiting
factors--Fluctuations in water supply--The average plant--The
actual plant--Amount of current required for various
operations--Standard voltage--A specimen allowance for electric
light--Heating and cooking by electricity--Electric power: the
electric motor.
The farmer's wife becomes his partner when he has concluded the
preliminary measurements and surveys for building his water-power
electric plant. Now the question is, how big a plant is necessary, or
how small a plant can he get along with. Electricity may be used for a
multitude of purposes on the farm, in its sphere of furnishing
portable light, heat and power; but when this multitude of uses has
been enumerated, it will be found that the wife shares in the benefits
no less than the farmer himself. The greatest dividend of all,
whether dividends are counted in dollars or happiness, is that
electricity takes the drudgery out of housework. Here, the work of the
farmer himself ends when he has brought electricity to the house, just
as his share in housework ends when he has brought in the kerosene,
and filled the woodbox. Of the light and heat, she will use the lion's
share; and for the power, she will discover heretofore undreamed-of
uses. So she must be a full partner when it comes to deciding how much
electricity they need.
How much electricity, in terms of light, heat, and power, will the
farmer and his wife have use for? How big a plant should be installed
to meet the needs of keeping house and running the farm?
The answer hangs mainly on how much water-power there is available,
through all the seasons of the year, with which to generate
electricity. Beyond that, it is merely a question of the farmer's
pocketbook. How much money does he care to spend? Electricity is a
cumulative "poison." The more one uses it, the more he wants to use
it. After a plant has been in operation a year, the family have
discovered uses for electricity which they did not think of in the
beginning. For this reason, it is well to put in a plant larger than
the needs of the moment seem to require. An electrical horsepower or
two one way or another will not greatly change the first cost, and you
will always find use for any excess.
Once for all, to settle the question of water-power, the water wheel
should be twice the normal capacity of the dynamo it drives, in terms
of power. This allows for overload, which is bound to occur
occasionally; and it also insures smooth running, easy governing, and
the highest efficiency. Since the electric current, once the plant is
installed, will cost practically nothing, the farmer can afford to
ignore the power going to waste, and consider only how to get the best
service.
_The Two Extremes_
The amount of water to be had to be turned into electricity, will vary
with location, and with the season. It may be only enough, the
greater part of the year, for a "toy" plant--a very practical toy, by
the way--one that will keep half a dozen lights burning in the house
and barn at one time; under some conditions water may be so scarce
that it must be stored for three or four days to get enough power to
charge a storage battery for these six or eight lights. A one-quarter,
or a one-half kilowatt electrical generator, with a one horsepower (or
smaller) wheel, will light a farmstead very satisfactorily--much
better than kerosene lamps.
On the other hand, the driving power of your wheel may be sufficient
to furnish 50 or 100 lights for the house, barn, and out-buildings,
and barn-yard and drives; to provide ample current for irons,
toasters, vacuum cleaners, electric fans, etc.; to do all the cooking
and baking and keep the kitchen boiler hot; and to heat the house in
the coldest weather with a dry clean heat that does not vitiate the
air, with no ashes, smoke or dust or woodchopping--nothing but an
electric switch to turn on and off; and to provide power for motors
ranging from tiny ones to run the sewing machine, to one of 15
horsepower to do the threshing. A plant capable of developing from 30
to 50 kilowatts of electricity, and requiring from 50 to 100
horsepower at the water wheel, would do all this, depending on the
size of the farmstead. One hundred horsepower is a very small water
project, in a commercial way; and there are thousands of farms
possessing streams of this capacity.
_Fluctuations in Water Supply_
It would be only during the winter months that such a plant would be
driven to its full capacity; and since water is normally plentiful
during these months, the problem of power would be greatly simplified.
The heaviest draft on such a plant in summer would be during
harvesting; otherwise it would be confined to light, small power for
routine work, and cooking. Thus, a plant capable of meeting all the
ordinary requirements of the four dry months of summer, when water is
apt to be scarce, doubles or quadruples its capacity during the
winter months, to meet the necessities of heat for the house.
A dynamo requires only as much power to drive it, at any given time,
as is being used in terms of electricity. There is some small loss
through friction, of course, but aside from this the power required of
the prime mover (the water wheel) is always in proportion to the
amount of current flowing. When water is scarce, and the demands for
current for heating are low, it is good practice to close a portion of
the buckets of the turbine wheel with wooden blocks provided for this
purpose. It is necessary to keep the speed of the dynamo uniform under
all water conditions; and where there is a great fluctuation between
high and low water periods, it is frequently necessary to have a
separate set of pulleys for full gate and for half-gate. The head must
remain the same, under all conditions. Changing the gate is in effect
choking or opening the nozzle supplying the wheel, to cut down or
increase its consumption of water.
_The Average Plant_
It will be the exceptional plant, however, among the hundreds of
thousands to be had on our farms, which will banish not only the oil
lamp and kitchen stove, but all coal or wood burning stoves as
well--which will heat the house in below-zero weather, and provide
power for the heavier operations of the farm. Also, on the other hand,
it will be the exceptional plant whose capacity is limited to
furnishing a half-dozen lights and no more.
A happy medium between these two conditions is the plant large enough
to supply between five and ten electrical horsepower, in all seasons.
Such a plant will meet the needs of the average farm, outside of
winter heating and large power operations, and will provide an excess
on which to draw in emergencies, or to pass round to one's neighbors.
It is such a plant that we refer to when we say that (not counting
labor) its cost, under ordinary conditions should not greatly exceed
the price of one sound young horse for farm work.
Since the plant we described briefly in the first chapter, meets the
requirements of this "average plant" let us inquire a little more
fully into its installation, maintenance, and cost.
_An Actual Plant_
In this instance, the water-power was already installed, running to
waste, in fact. The wheel consists of the so-called thirty-six inch
vertical turbine, using 185 square inches of water, under a 14-foot
head. Water is supplied to this wheel by a wooden penstock 33 inches
square, inside measurements, and sloping at an angle of 30° from the
flume to the wheel.
[Illustration: Details of voltmeter or ammeter]
This wheel, under a 14-foot head, takes 2,312 cubic feet of water a
minute; and it develops 46.98 actual horsepower (as may be figured by
using the formulas of Chapter III). The water supply is provided by a
small mountain river. The dam is 10 feet high, and the race, which
feeds the flume from the mill pond is 75 yards long. The race has two
spillways, one near the dam, and the second at the flume itself, to
maintain an even head of water at all times.
_Half-Gate_
Since the water supply varies with the seasons, it has been found
practical to run the wheel at half-gate--that is, with the gate only
half-open. A set of bevel gears work the main shaft, which runs at
approximately 200 revolutions per minute; and the dynamo is worked up
to its required speed of 1,500 revolutions per minute through a
countershaft.
The dynamo is a modern four-pole machine, compound-wound, with a rated
output of 46 amperes, at 125 volts--in other words a dynamo of 5.75
kilowatts capacity, or 7.7 electrical horsepower. At full load this
dynamo would require a driving power of 10 horsepower, counting it as
75 per cent efficient; and, to conform to our rule of two water
horsepower to one electrical horsepower, the wheel should be capable
of developing 20 horsepower. As a matter of fact, in this particular
instance, shutting down the wheel to half-gate more than halves the
rated power of the wheel, and little more than 15 horsepower is
available. This allowance has proved ample, under all conditions met
with, in this plant.
The dynamo is mounted on a firm floor foundation; and it is belted
from the countershaft by an endless belt running diagonally. A
horizontal belt drive is the best. Vertical drive should be avoided
wherever possible.
_The Switchboard_
The switchboard originally consisted of a wooden frame on which were
screwed ordinary asbestos shingles, and the instruments were mounted
on these. Later, a sheet of electric insulating fibre was substituted,
for look's sake. The main requisite is something substantial--and
fireproof. The switchboard instruments consist of a voltmeter, with a
range of from 0 to 150 volts; an ammeter, with a range, 0 to 75
amperes; a field regulating rheostat (which came with the dynamo); a
main switch, with cartridge fuses protecting the machine against a
draft of current over 60 amperes; and two line switches for the two
owners, one fuse at 20 amperes, and the other at 40 amperes. Electric
fuses are either cartridges or plugs, enclosing lead wire of a size
corresponding to their rating. All the current of the line they
protect passes through this lead wire. If the current drawn exceeds
the capacity of the lead wire, it melts from the heat, and thus opens
the circuit, and cuts off the current.
[Illustration: A switchboard and its connections: _G._ Dynamo; _A._
Shunt field coils; _B._ Series coils; _DD._ Fuses; _FF._ Main switch;
_F._ Field switch; _C._ Ammeter; _V._ Voltmeter; _E._ Lamp; _R._
Rheostat. Dotted lines show connections on back of board]
_Items of Cost_
This water wheel would cost $250 new. There is a duplicate in the
neighborhood bought at second-hand, for $125. The dynamo cost $90,
and was picked up second-hand in New York City. New it would cost
$150. The voltmeter cost $7, and the ammeter $10; and the switches and
fuses could be had for $5. A wheel one-half the size, using one-half
the amount of water at full gate, would do the work required, and the
cost would be correspondingly less.
_Capacity_
This plant supplies two farms with electric light. One farm (that of
the owner of the wheel) has 30 lamps, of 16 candlepower each, and two
barn-yard lamps of 92 candlepower each. His wife has an electric iron
and an electric water heater. Needless to say, all these lamps, and
the iron and water heater are not in use at one time.
[Illustration: Carbon Lamps Gem Type (1/4 scale)]
The partner who owns the electric part of the plant has 30 lamps in
his house and barn, many of them being 25 watt tungsten, which give
more light for less power, but cost more to buy. They are not all in
use at one time, though (since the current costs nothing) the
inclination is to turn them on at night and let them burn. In his
kitchen he has an electric range, and a water heater for the 40 gallon
boiler. In addition to this he has all sorts of appliances,--irons,
toasters, grills, a vacuum cleaner, a vibrator, etc. Naturally all
these appliances are not in use at one time, else the draft on the
plant would be such as to "blow" the fuses. For instance, all the
baking is done in daylight; and when the oven is used after dark, they
are careful to turn off all lights not needed. An ideal plant, of
course, would be a plant big enough to take care of the sum of lamps
and handy devices used at one time.
To make this plant ideal, (for, being an actual affair, it has
developed some short-comings, with the extension of the use of
electricity) it would require a dynamo whose capacity can be figured,
from the following:
Watts
15 carbon lamps, 16 candlepower, @60 watts each 900
10 tungsten lamps, 20 candlepower, @25 watts each 250
2 tungsten lamps, 92 candlepower, @100 watts each 200
Water heater, continuous service 800
Toaster, occasional service 600
Iron, occasional service 400
Oven-baking, roasting, etc 2,000
2 stove plates @1,000 watts each 2,000
1 stove plate 400
Vacuum cleaner, occasional service 200
Vibrator, occasional service 100
Small water heater, quart capacity 400
Small motor, 1/4 horsepower, occasional 250
Motor, 1/2 hp, pumping water, etc 500
Electric fan, occasional service 100
-------
Total current, one house 9,100
30 carbon lamps, 16 candlepower, @60 1,800
2 lamps, 100 watt tungsten 200
Electric iron 400
Small water or milk heater 600
-------
Total current, 2nd house 3,000
1st house 9,100
-------
12,100
Thus, in this plant, if every electrical device were turned on at
once, the demand on the dynamo would be for 12.1 kilowatts, or an
overload of over 100 per cent. The main-switch fuse, being for 60
amperes, would "blow" or melt, and cut off all current for the
moment. To repair the damage would be merely the work of a second--and
at a cost of a few cents--simply insert a new fuse, of which there
must be a supply on hand at all times. Or, if either owner exceeded
his capacity, the line fuses (one for 20 amperes, and the other for 40
amperes) would instantly cut off all current from the greedy one.
[Illustration: 25 and 40 watt Mazda tungsten lamps (1/4 scale)]
_Lessons From This Plant_
The story of this plant illustrates two things which the farmer and
his wife must take into account when they are figuring how much
electricity they require. First, it illustrates how one uses more and
more current, as he finds it so serviceable and labor-saving, and at
the same time free. The electric range and the water boiler, in the
above instance, were later acquisitions not counted on in figuring the
original installation. Second, it illustrates, that while the normal
load of this generator is _5.75_ kilowatts, one does not have to limit
the electrical conveniences in the home to this amount. True, he
cannot use more electricity than his plant will produce _at any one
time_,--but it is only by a stretch of the imagination that one may
conceive the necessity of using them all at once. Ironing, baking, and
the use of small power are usually limited to daylight hours when no
lights are burning.
As a matter of fact, this plant has proved satisfactory in every way;
and only on one or two occasions have fuses been "blown", and then it
was due to carelessness. A modern dynamo is rated liberally. It will
stand an overload of as much as 100 per cent for a short time--half an
hour or so. The danger from overloading is from heating. When the
machine grows too hot for the hand, it is beginning to char its
insulation, to continue which, of course would ruin it. The best plant
is that which works under one-half or three-quarters load, under
normal demands.
_Standard Voltage_
We are assuming the farmer's plant to be, in 99 cases out of 100, the
standard 110-volt, direct current type. Such a plant allows for at
least a 10 per cent regulation, in voltage, up or down the scale;
supplies for this voltage are to be had without delay in even the more
remote parts of the country, and (being sold in greater volume) they
are cheaper than those for other voltages.
There are two general exceptions to this rule as to 110-volt plants:
(1) If the plant is located at a distance greater than a quarter of a
mile from the house, it will be found cheaper (in cost of transmission
line, as will be shown later) to adopt the 220-volt plant; (2), If the
water supply is so meagre that it must be stored for many hours at a
time, and then used for charging storage batteries, it will be found
most economical to use a 30-volt plant. A storage battery is made up
of cells of approximately 2 volts each; and, since more than 55 such
cells would be required for a 110-volt installation, its cost would
be prohibitive, with many farmers.
So we will assume that this plant is a 110-volt plant, to be run
without storage battery. It will be well to make a chart, dividing the
farm requirements into three heads--light, heat, and power.
_Light_
[Illustration: 60 and 100 watt Mazda tungsten lamp. These lamps may be
had in sizes from 10 to 500 watts (1/4 scale)]
[Illustration: The lamp of the future. A 1000 watt Mazda nitrogen
lamp, giving 2000 candlepower (1/4 scale)]
Light is obtained by means of incandescent lamps. There are two styles
in common use, the carbon and the tungsten lamp. It requires 3.5 to 4
watts of electricity to produce one candlepower in a carbon lamp. It
requires from 1 to 1.25 watt to produce one candlepower in the
tungsten lamp. The new nitrogen lamp, not yet in general use, requires
only 1/2 watt to the candlepower. Since tungsten lamps give three
times the light of the carbon lamp, they are the most economical to
use in the city or town where one is paying for commercial current.
But, in the country where water-power furnishes current for nothing,
it will be found most economical to use the carbon lamp, since its
cost at retail is 16 cents, as compared with 30 cents for a
corresponding size in tungsten. A 60 watt carbon lamp, of 16
candlepower; or a 25 watt tungsten lamp, of 20 candlepower, are the
sizes to use. In hanging lamps, as over the dining room table, a 100
watt tungsten lamp, costing 70 cents, and giving 92 candlepower light
is very desirable; and for lighting the barn-yard, these 100 watt
tungsten lamps should be used. For reading lamps, the tungsten style,
of 40 or 60 watt capacity, will be found best. Otherwise, in all
locations use the cheaper carbon lamp. Both styles have a rated life
of 1,000 hours, after which they begin to fall off in efficiency. Here
again, the farmer need not worry over lack of highest efficiency, as a
lamp giving only 80 per cent of its rated candlepower is still
serviceable when he is not paying for the current. With care not to
use them at voltages beyond their ratings, lamps will last for years.
_A Specimen Light Allowance_
Below is a typical table of lights for a large farm house, the barns
and barn-yard. It is given merely as a guide, to be varied for each
individual case:
Watts
Kitchen, 2 lights @60 watts 120
Dining room, 1 light, tungsten 100
Living room, table lamp with 3 tungstens @40 120
Living room, 2 wall fixtures, 4 lamps @60 watts 240
Parlor, same as living room 360
Pantry, 1 hanging lamp 60
Cellar, one portable lamp 60
Woodshed, 1 hanging lamp 60
2 bedrooms, 2 lights each @ 60 240
2 bed rooms, 1 light each @60 120
Bathroom, 1 "turn-down" light, @60 60
Hall, downstairs, 2 lights @60 120
Hall, upstairs, 1 light 60
Attic, 1 light 60
Porch, 1 light 60
Barn and barn-yard:
Barn-yard entrance, 1 tungsten 100
Watering trough, 1 " 100
Front gate, 1 " 100
Horse barn, 4 lights @60 240
Cow barn, 4 lights @60 240
Pig house, 1 light 60
Hay barn, 2 lights, @60 120
-------
Total for farmstead 2,800
This provides for 44 lights, an extremely liberal allowance. How many
of these lights will be burning at any one time? Probably not one-half
of them; yet the ideal plant is that which permits all fixtures to be
in service at one time on the rare occasions when necessary. Thus, for
lighting only, 2,800 watts maximum service would require a 4 kilowatt
generator, and 10 water horsepower, on the liberal rating of two to
one. A 3 kilowatt generator would take care of these lights, with a 30
per cent overload (which is not excessive) for maximum service. The
above liberal allowance of lights may be cut in two, or four--or even
eight--and still throw a kerosene lamp in shadow. It all depends on
the number of lights one wants burning at one time; and the power of
the water wheel.
If the 36 carbon lights in the above table were replaced by 25 watt
tungsten lights, the saving in power would be 35 watts each, or 1,260
watts, nearly two electrical horsepower; while the added first cost
would be 14 cents a light, or $5.04. A generator of 2 kilowatt
capacity would take care of all these lights then, with 460 watts to
spare.
_Heating_
Electric heating and cooking is in its infancy, due to the prohibitive
cost of commercial current in our cities. Here the farmer has the
advantage again, with his cheap current.
For heating the house, it is calculated that 2 watts is required for
each cubic foot of air space in a room, during ordinary winter
weather. Thus, a room 10 × 12, and 8 feet high, would contain 960
cubic feet, and would require 1,820 watts energy to heat it in cold
weather. Five such rooms would require 9.1 kilowatts; and 10 such
rooms, or their equivalent, would require 18.2 kilowatts.
Electric heating devices are divided into two classes: (1) those which
can be used on lamp circuits, _and do not draw more than 660 watts
each_; and (2) those which draw more than 660, therefore _require
special wiring_. The capacity of these devices is approximately as
follows:
Lamp circuit devices: Watts
Electric iron 400 to 660
Toaster 350 to 660
Vacuum cleaner 200 to 400
Grill 400 to 660
Small water heater 400 to 660
Hot plates 400 to 660
Lamp circuit devices:
Coffee percolator 400 to 660
Chafing dish 400 to 660
Electric fan 100 to 250
Special circuit devices:
Hot water boiler heater 800 to 1,200
Small ovens 660 to 1,200
Range ovens 1,200 to 3,000
Range, hot plates 400 to 1,300
Radiators (small) 750 to 1,500
Radiators (large) 1,500 to 6,000
The only device in the above list which is connected continuously, is
the hot water boiler, and this can be credited with at least one
electrical horsepower 24 hours a day. It is a small contrivance, not
much bigger than a quart can, attached to the back of the kitchen
boiler, and it keeps the water hot throughout the house at all hours.
Its cost will vary with the make, ranging from $8 to $15; and since it
is one of the real blessings of the farm kitchen and bathroom, it
should be included in all installations where power permits. Electric
radiators will be used 24 hours a day in winter, and not at all in
summer. They are portable, and can be moved from room to room, and
only such rooms as are in actual use need be heated. The other devices
are for intermittent service, many of them (like the iron) for only a
few hours each week.
The grill, chafing dish, coffee percolator, etc., which are used on
the dining room table while the family is at meals, each draw an
equivalent of from 6 to 10 carbon lights. By keeping this in view and
turning off spare lights, one can have the use of them, with even a
small plant. Thus, a one kilowatt plant permits the use of any one of
these lamp circuit devices at a time, with a few lights in addition.
_Power_
Electric power is to be had through motors. A direct current dynamo
and a direct current motor are identical in construction. That is, a
motor becomes a generator if belted to power; and a generator becomes
a motor, if connected to electric mains. This is best illustrated by
citing the instance of a trans-continental railroad which crosses the
Bitter Root Mountains by means of electric power. Running 200 miles up
a 2 per cent grade, it is drawn by its motors. Coasting 200 miles
down the 2 per cent grade on the other side of the mountains, its
motors become generators. They act as brakes, and at the same time
they pump the power of the coasting weight of this train back into the
wires to help a train coming up the other side of the mountains.
[Illustration: Connections of shunt motor and starting rheostat]
Just as there are three types of direct current generators, so there
are three types of direct current motors: _series_, _shunt_, and
_compound_, with features already explained in the case of generators.
Motors are rated by horsepower, and generators are rated by kilowatts.
Thus a one kilowatt generator has a capacity of 1,000 watts; as a
motor, it would be rated as 1000/746 horsepower, or 1.34 horsepower.
Their efficiency varies with their size, ranging from 40 to 60 per
cent in very small motors, and up to 95 per cent in very large ones.
The following table may be taken as a guide in calculating the power
required by motors, on 110-volt circuits:
1/4 Horsepower 2-1/2 amperes, or 275 watts
1/2 hp 4-1/2 amperes, or 500 watts
1 hp 9 amperes, or 990 watts
2 hp 17 amperes, or 1.97 kilowatts
3 hp 26 amperes, or 2.86 kilowatts
5 hp 40 amperes, or 4.40 kilowatts
7-1/2 hp 60 amperes, or 6.60 kilowatts
10 hp 76 amperes, or 8.36 kilowatts
15 hp 112 amperes, or 12.32 kilowatts
An electric motor, in operation, actually generates electricity, which
it pushes back into the line as a counter-electromotive-force. The
strength of this counter force, in volts, depends on the motor's
speed, the same as if it were running as a dynamo. For this reason,
when a motor is started, and before it comes up to speed, there would
be a rush of current from the line, with nothing to hold it back, and
the motor would be burned out unless some means were provided to
protect it for the moment. This is done by means of a starting
rheostat, similar to the regulating rheostat on the dynamo
switchboard. This resistance box is connected in "series" with the
armature, in the case of shunt and compound motors; and with the
entire motor circuit in the case of a series machine.
A _series_ motor has a powerful starting torque, and adjusts its speed
to the load. It is used almost altogether in street cars. It can be
used in stump pulling, or derrick work, such as using a hay fork. It
must always be operated under load, otherwise, it would increase in
speed until it tore itself to pieces through mechanical strain. The
ingenious farmer who puts together an electric plow, with the mains
following behind on a reel, will use a series motor.
A _shunt_ motor should be used in all situations where a fairly
uniform speed under load is required, such as separating, in milking
machines, running a lathe, an ensilage cutter, vacuum cleaners,
grinders, etc.
The _compound_ motor has the characteristics of the series and shunt
motors, giving an increased starting torque, and a more nearly
constant speed under varying loads than the shunt motor, since the
latter drops off slightly in speed with increasing load.
_Flexible Power_
An electric motor is an extremely satisfactory form of power because
it is so flexible. Thus, one may use a five horsepower motor for a one
horsepower task, and the motor will use only one electrical horsepower
in current--just enough to overcome the task imposed on it. For this
reason, a large-sized motor may be used for any operation, from one
requiring small power, up to its full capacity. It will take an
overload, the same as a dynamo. In other words it is "eager" for any
task imposed on it; therefore it must be protected by fuses, or it
will consume itself, if too big an overload is imposed on it.
A one horsepower shunt or compound motor is very serviceable for
routine farm operations, such as operating the separator, the churn,
the milking machine, grinder, pump, and other small power jobs. Motors
of 1/4 horsepower are handy in the kitchen, for grinding knives,
polishing silver, etc., and can be used also for vacuum cleaners, and
running the sewing machine. For the larger operations, motors will
vary from three horsepower for cutting ensilage, to fifteen horsepower
for threshing. They can be mounted on trucks and conveyed from one
point to another, being fed current from the mains by means of
suitable wires wound on reels.
Remember, in estimating the size of your plant for light, heat, and
power, that it does not have to be big enough to use all the devices
at one time. Also remember, that two water horsepower to one
electrical horsepower is a very liberal allowance; and that a
generator working under one-half or two-thirds capacity at normal
loads will require less attention than a machine constantly being
worked above its capacity. Therefore, let your generator be of liberal
size, because the difference in cost between a 5 and 10 kilowatt
machine is not in proportion to their capacity. In fact (especially
among second-hand machines), the difference in cost is very small. The
mere fact that the generator is of 110 electrical horsepower capacity
does not require a turbine of 20 horsepower. The chances are that
(unless you wish to heat your house and do large power jobs) you will
not use more than 3 to 5 electrical horsepower normally; therefore an
allowance of 10 water horsepower, in this case, would be ample. A
plant used simply for lighting the house and barn, for irons, and
toasters, and one horsepower motors, need not exceed 2 or 2-1/2
kilowatts for the generator, and 5 or 6 horsepower for the turbine
wheel. Normally it would not use one-half this capacity.
CHAPTER VII
TRANSMISSION LINES
Copper wire--Setting of poles--Loss of power in transmission--Ohm's
Law and examples of how it is used in figuring size of
wire--Copper-wire tables--Examples of transmission lines--When to
use high voltages--Over-compounding a dynamo to overcome
transmission loss.
Having determined on the location of the farm water-power electric
plant, and its capacity, in terms of electricity, there remains the
wiring, for the transmission line, and the house and barn.
For transmission lines, copper wire covered with waterproof braid--the
so-called weatherproof wire of the trade--is used. Under no
circumstances should a wire smaller than No. 8, B. & S. gauge be used
for this purpose, as it would not be strong enough mechanically. The
poles should be of chestnut or cedar, 25 feet long, and set four feet
in the ground. Where it is necessary to follow highways, they should
be set on the fence line; and in crossing public highways, the
ordinance of your own town must guide you. Some towns prescribe a
height of 19 feet above the road, others 27 feet, some 30. Direct
current, such as is advised for farm installations, under ordinary
circumstances, does not affect telephone wires, and therefore
transmission lines may be strung on telephone poles. Poles are set at
an average distance of 8 rods; they are set inclined outward on
corners. Sometimes it is necessary to brace them with guy wires or
wooden braces. Glass insulators are used to fasten the wires to the
cross-arms of the poles, and the tie-wires used for this purpose must
be the same size as the main wire and carry the same insulation.
_Size of Wire for Transmission_
To determine the size of the transmission wires will require knowledge
of the strength of current (in amperes) to be carried, and the
distance in feet. In transmission, the electric current is again
analogous to water flowing in pipes. It is subject to resistance,
which cuts down the amount of current (in watts) delivered.
[Illustration: Bringing wires into the house or barn]
The loss in transmission is primarily measured in volts; and since the
capacity of an electric current for work equals the _volts_ multiplied
by _amperes_, which gives _watts_, every volt lost reduces the working
capacity of the current by so much. This loss is referred to by
electrical engineers as the "C^2R loss," which is another way of
saying that the loss is equal to the _square of the current in
amperes_, multiplied by _ohms_ resistance. Thus, if the amperes
carried is 10, and the ohms resistance of the line is 5, then the loss
in watts to convey that current would be (10 × 10) × 5, or 500 watts,
nearly a horsepower.
The pressure of _one volt_ (as we have seen in another chapter) is
sufficient to force _one ampere_, through a resistance of _one ohm_.
Such a current would have no capacity for work, since its pressure
would be consumed in the mere act of transmission.
If, however, the pressure were _110 volts_, and the current _one
ampere_, and the resistance _one ohm_, the effective pressure after
transmission would be 110-1, or 109 volts.
To force a 110-volt current of _50 amperes_ through the resistance of
_one ohm_, would require the expenditure of _50 volts_ pressure. Its
capacity for work, after transmission, would be 110-50, or _60 volts,
× 50 amperes_, or 3,000 watts. As this current consisted of _110 ×
50_, or 5,500 watts at the point of starting, the loss would be 2,500
watts, or about 45 per cent. It is bad engineering to allow more than
10 per cent loss in transmission.
There are two ways of keeping this loss down. One is by increasing
the size of the transmission wires, thus cutting down the resistance
in ohms; the other way is by raising the voltage, thus cutting down
the per cent loss. For instance, suppose the pressure was 1,100 volts,
instead of 110 volts. Five amperes at 1,100 volts pressure, gives the
same number of watts, power, as 50 amperes, at 110 volts pressure.
Therefore it would be necessary to carry only 5 amperes, at this rate.
The loss would be 5 volts, or less than 1/2 of 1 per cent, as compared
with 45 per cent with 110 volts.
[Illustration: Splicing transmission wire]
In large generating stations, where individual dynamos frequently
generate as much as 20,000 horsepower, and the current must be
transmitted over several hundred miles of territory, the voltage is
frequently as high as 150,000, with the amperes reduced in proportion.
Then the voltage is lowered to a suitable rate, and the amperage
raised in proportion, by special machinery, at the point of use.
It is the principle of the C^2R loss, which the farmer must apply in
determining the size of wire he is to use in transmitting his current
from the generator switchboard to his house or barn. The wire table on
page 159, together with the formula to be used in connection with it,
reduce the calculations necessary to simple arithmetic. In this table
the resistance of the various sizes of wire is computed from the fact
that a wire of pure copper 1 foot long, and 1/1000 inch in diameter
(equal to one circular mill) offers a resistance of 10.6 ohms to the
foot. The principle of the C^2R loss is founded on Ohm's Law, which is
explained in Chapter V.
The formula by which the size of transmission wire is determined, for
any given distance, and a given number of amperes, is as follows:
Distance ft. one way × 22 × No. of amperes circular
------------------------------------------ = mills.
Number of volts lost
In other words, multiply the _distance in feet_ from mill to house by
22, and multiply this product by the _number of amperes_ to be
carried. Then divide the product by the _number of volts_ to be lost;
and the result will be the diameter of the wire required _in circular
mills_. By referring to the table above, the B. & S. gauge of the wire
necessary for transmission, can be found from the nearest
corresponding number under the second column, entitled "circular mills
area."
COPPER WIRE TABLE
--------+----------+-----------+-----------+-----------+------------
| | _Area in | _(R) Ohms | |
_B.& S. | _Feet | circular | per 1,000 | _Feet | _(R) Ohms
Gauge_ | per Lb._ | mills_ | feet_ | per Ohm_ | per pound_
--------+----------+-----------+-----------+-----------+------------
0000 | 1.561 | 211,600 | .04904 | 20,392.90 | .00007653
000 | 1.969 | 167,805 | .06184 | 16,172.10 | .00012169
00 | 2.482 | 133,079 | .07797 | 12,825.40 | .00019438
0 | 3.130 | 105,534 | .09829 | 10,176.40 | .00030734
1 | 3.947 | 83,694 | .12398 | 8,066.00 | .00048920
2 | 4.977 | 66,373 | .15633 | 6,396.70 | .00077784
3 | 6.276 | 52,634 | .19714 | 5,072.50 | .00123700
4 | 7.914 | 41,742 | .24858 | 4,022.90 | .00196660
5 | 9.980 | 33,102 | .31346 | 3,190.20 | .00312730
6 | 12.58 | 26,250 | .39528 | 2,529.90 | .00497280
7 | 15.87 | 20,816 | .49845 | 2,006.20 | .00790780
8 | 20.01 | 16,509 | .62840 | 1,591.10 | .01257190
9 | 25.23 | 13,094 | .79242 | 1,262.00 | .01998530
10 | 31.82 | 10,381 | .99948 | 1,000.50 | .03178460
11 | 40.12 | 8,234.0 | 1.26020 | 793.56 | .05054130
12 | 50.59 | 6,529.9 | 1.58900 | 629.32 | .08036410
13 | 63.79 | 5,178.4 | 2.00370 | 499.06 | .12778800
14 | 80.44 | 4,106.8 | 2.52660 | 395.79 | .20318000
15 | 101.4 | 3,256.7 | 3.18600 | 313.87 | .32307900
16 | 127.9 | 2,582.9 | 4.01760 | 248.90 | .51373700
17 | 161.3 | 2,048.2 | 5.06600 | 197.39 | .81683900
18 | 203.4 | 1,624.3 | 6.38800 | 156.54 | 1.29876400
--------+----------+-----------+-----------+-----------+------------
CARRYING CAPACITY OF WIRES AND WEIGHT
-----------+-------------------+--------------------+--------------------
| _Weight 1,000 ft. | _Carrying capacity | _Carrying capacity
_B. & S. | Weatherproof | Weatherproof | rubber cov.
Gauge No._ | (Pounds)_ | (Amperes)_ | (Amperes)_
-----------+-------------------+--------------------+--------------------
0000 | 800 | 312 | 175
000 | 666 | 262 | 145
00 | 500 | 220 | 120
0 | 363 | 185 | 100
1 | 313 | 156 | 95
2 | 250 | 131 | 70
3 | 200 | 110 | 60
4 | 144 | 92 | 50
5 | 125 | 77 | 45
6 | 105 | 65 | 35
7 | 87 | 55 | 30
8 | 69 | 46 | 25
10 | 50 | 32 | 20
12 | 31 | 23 | 15
14 | 22 | 16 | 10
16 | 14 | 8 | 5
18 | 11 | 5 | 3
-----------+-------------------+--------------------+--------------------
Since two wires are required for electrical transmission, the above
formula is made simple by counting the distance only one way, in feet,
and doubling the resistance constant, 10.6, which, for convenience is
taken as 22, instead of 21.2.
_Examples of Transmission Lines_
As an example, let us say that Farmer Jones has installed a
water-power electric plant on his brook, _200 yards distant_ from his
house. The generator is a 5 kilowatt machine, capable of producing _45
amperes_ at _110 volts pressure_. He has a 3 horsepower motor, drawing
26 amperes at full load; he has 20 lights of varying capacities,
requiring 1,200 watts, or 10 amperes when all on; and his wife uses
irons, toasters, etc., which amount to another 9 or 10 amperes--say 45
altogether. The chances are that he will never use all of the
apparatus at one time; but for flexibility, and his own satisfaction
in not having to stop to think if he is overloading his wires, he
would like to be able to draw the full _45 amperes_ if he wishes to.
He is willing to allow _5 per cent loss_ in transmission. _What size
wires will be necessary, and what will they cost?_ Substituting these
values in the above formula, the result is:
Answer: 600 × 22 × 45
------------- = 108,000 circular mills.
5.5
[Illustration: Transmission wire on glass insulator]
Referring to the table, No. 0 wire is 105,534 circular mills, and is
near enough; so this wire would be used. It would require 1,200 feet,
which would weigh, by the second table, 435.6 pounds. At 19 cents a
pound, it would cost $82.76.
Farmer Jones says this is more money than he cares to spend for
transmission. As a matter of fact, he says, he never uses his motor
except in the daytime, when his lights are not burning; so the maximum
load on his line at any one time would be _26 amperes_, not 45. _What
size wire would he use in this instance?_
Substituting 26 for 45 in the equation, the result is 61,300 circular
mills, which corresponds to No. 2 wire. It would cost $57.00.
Now, if Farmer Jones, in an emergency, wished to use his motor at the
same time he was using all his lights and his wife was ironing and
making toast--in other words, if he wanted to use the _45 amperes_
capacity of his dynamo, _how many volts would he lose?_ To get this
answer, we change the formula about, until it reads as follows:
Distance in feet × 22 × amperes
--------------------------------- = Number of volts lost
circular mills
Substituting values, we have, in this case, 600 × 22 × 45/66,373 (No.
2) = 9 volts, nearly, less than 10 per cent. This is a very efficient
line, under the circumstances. Now if he is willing to lose 10 per
cent on _half-load_, instead of full load, he can save still more
money in line wire. In that case (as you can find by applying the
formula again), he could use No. 5 wire, at a cost of $28.50. He would
lose 11 volts pressure drawing 26 amperes; and he would lose 18 volts
pressure drawing 45 amperes, if by any chance he wished to use full
load.
In actual practice, this dynamo would be regulated, by means of the
field resistance, to register 110 plus 11 volts, or 121 volts at the
switchboard to make up for the loss at half-load. At full load, his
voltage at the end of the line would be 121 minus 18, or 103 volts;
his motor would run a shade slower, at this voltage, and his lights
would be slightly dimmer. He would probably not notice the difference.
If he did, he could walk over to his generating station, and raise
the voltage a further 7 volts by turning the rheostat handle another
notch.
[Illustration: A barn-yard light]
Thousands of plants can be located within 100 feet of the house. If
Farmer Jones could do this, he could use No. 8 wire, costing $2.62.
The drop in pressure would be 5.99 volts at full load--so small it
could be ignored entirely. In this case the voltmeter should be made
to read 116 volts at the switchboard, by means of the rheostat.
If, on the other hand, this plant were 1,000 feet away from the house
and the loss 10 volts the size wire would be
1,000 × 22 × 45
--------------- = 99,000 circular mills;
10
a No. 0 wire comes nearest to this figure, and its cost, for 2,000
feet, at 19 cents a pound, would be $137.94. A No. 0000 wire, costing
$294.00, would give a 5 per cent drop at full load. In this case, the
cost of transmission can be reduced to a much lower figure, by
allowing a bigger drop at half-load, with regulation at the
switchboard. Thus, a No. 2 wire here, costing but $95, would be
satisfactory in every way. The loss at half-load would be about 9
volts, and the rheostat would be set permanently for 119 or 120 volts.
A modern dynamo can be regulated in voltage by over 25 per cent in
either direction, without harm, if care is taken not to overload it.
_Benefit of Higher Voltages_
If Farmer Jones' plant is a half of a mile away from the house, he
faces a more serious proposition in the way of transmission. Say he
wishes to transmit 26 amperes with a loss of 10 volts. What size wire
will be necessary?
2640 × 22 × 26
Thus: -------------- = 151,000 circular mills.
10
A No. 000 wire is nearest this size, and 5,280 feet of it would cost
over $650.00. This cost would be prohibitive. If, however, he
installed a 220-volt dynamo--at no increase in cost--then he would
have to transmit only a half of 26 amperes, or 13 amperes, and he
could allow 22 volts loss, counting 10 per cent. In this case, the
problem would work out as follows:
2640 × 22 × 13
-------------- = 34,320 circular mills,
22
or approximately a No. 5 wire which, at 19 cents a pound, would cost
$120.65.
Install a 550-volt generator, instead of a 220-volt machine and the
amperes necessary would be cut to 5.2, and the volts lost would be
raised to 55. In this case a No. 12 wire would carry the current; but
since it would not be strong enough for stringing on poles, a No. 8
wire would be used, costing about $63.
It will be readily seen from these examples how voltage influences the
efficiency of transmission. Current generated at a pressure in excess
of 550 volts is not to be recommended for farm plants unless an expert
is in charge. A safer rule is not to exceed 220 volts, for while 550
volts is not necessarily deadly, it is dangerous. When one goes into
higher voltages, it is necessary to change the type of dynamo to
_alternating current_, so that the current can be transformed to safe
voltages at the point where it is used. Since only the occasional farm
plant requires a high-tension system, the details of such a plant will
not be gone into here.
In transmitting the electric current over miles of territory,
engineers are accustomed to figure 1,000 volts for each mile. Since
this is a deadly pressure, it should not be handled by any one not an
expert, which, in this case, the farmer is not.
_Over-Compounding the Generator_
One can absorb the loss in transmission frequently, by
over-compounding the machine. In describing the compound machine, in
Chapter Five, it is shown that the usual compound dynamo on the market
is the so-called flat-compounded type. In such a dynamo, the voltage
remains constant at the switchboard, from no load to full load,
allowing for a slight curve which need not be taken into account.
Now, by adding a few more turns to the series wires on the field coils
of such a dynamo, a machine is to be had which gradually raises its
voltage as the load comes on in increasing volume. Thus, one could
secure such a machine, which would begin generating at 110 volts, and
would gradually rise to 150 at full load. Yet the voltage would remain
constant at the point of use, the excess being absorbed in
transmission. A machine of this type can be made to respond to any
required rise in voltage.
As an example of how to take advantage of this very valuable fact, let
us take an instance:
Say that Farmer Jones has a transmission line 1,000 feet long strung
with No. 7 copper wire. This 2,000 feet of wire would introduce a
resistance of one ohm in the circuit. That is, every ampere of current
drawn at his house would cause the working voltage there to fall one
volt. If he drew 26 amperes, the voltage would fall, at the house, 26
volts. If his switchboard voltage was set at say 120, the voltage at
his house, at 26 amperes of load, would fall to 94 volts, which would
cause his lights to dim considerably. It would be a very
unsatisfactory transmission line, with a flat-compounded dynamo.
On the other hand, if his dynamo was over-compounded 25 per cent--that
is, if it gained 28 volts from no load to full load, the system would
be perfect. In this case, the dynamo would be operated at 110 volts
pressure at the switchboard with no load. At full load the voltmeter
would indicate 110 plus 26, or 136 volts. The one or two lights burned
at the power plant would be subject to a severe strain; but the 50 or
100 lights burned at the house and barn would burn at constant
voltage, which is very economical for lamps.
The task of over-compounding a dynamo can be done by any trained
electrician. The farmer himself, if he progresses far enough in his
study of electricity, can do it. It is necessary to remove the top or
"series" winding from the field coils. Count the number of turns of
this wire to each spool. Then procure some identical wire in town and
begin experimenting. Say you found four turns of field wire to each
spool. Now wind on five, or six, being careful to wind it in the same
direction as the coils you removed and connect it in the same way. If
this additional number of turns does not raise the voltage enough, in
actual practice, when the dynamo is running from no load to full load,
add another turn or two. With patience, the task can be done by any
careful mechanic. The danger is in not winding the coils the same way
as before, and getting the connections wrong. To prevent this mistake,
make a chart of the "series" coils as you take them off.
To make the task of over-compounding your own dynamo even more simple,
write to the manufacturers, giving style and factory number of your
machine. Tell them how much voltage rise you wish to secure, and ask
them how many turns of "series" wire should be wound on each spool in
place of the old "series" coil. They could tell you exactly, since
they have mathematical diagrams of each machine they make.
Avoid overloading an over-compounded machine. Since its voltage is
raised automatically, its output in watts is increased a similar
amount at the switchboard, and, for a given resistance, its output in
amperes would be increased the same amount, as can be ascertained by
applying Ohm's Law. Your ammeter is the best guide. Your machine is
built to stand a certain number of amperes, and this should not be
exceeded in general practice.
CHAPTER VIII
WIRING THE HOUSE
The insurance code--Different kinds of wiring described--Wooden
moulding cheap and effective--The distributing panel--Branch
circuits--Protecting the circuits--The use of porcelain tubes and
other insulating devices--Putting up chandeliers and wall
brackets--"Multiple" connections--How to connect a wall
switch--Special wiring required for heat and power circuits--Knob
and cleat wiring, its advantages and drawbacks.
The task of wiring your house is a simple one, with well-defined rules
prescribed by your insurance company. Electricity, properly installed,
is much safer than oil lamps--so much so indeed that insurance
companies are ready to quote especial rates. But they require that the
wiring be done in accordance with rules laid down by their experts,
who form a powerful organization known as the National Board of Fire
Underwriters. Ask your insurance agent for a copy of the code rules.
Danger of fire from an electric current comes from the "short
circuit," partial or complete; and it is against this danger that the
rules guard one. The amount of electricity flowing through a short
circuit is limited only by the fuse protecting that line; and since
there is no substance known that can withstand the heat of the
electric arc, short circuits must be guarded against. Happily the
current is so easily controlled that the fire hazard is eliminated
entirely--something which cannot be done with oil lamps.
In house-wiring for farm plants, the wire should be rubber-covered,
and not smaller than No. 14 B. & S. gauge. This is the wire to use on
all lamp circuits. It costs about $0.85 cents per 100 feet. There are
four kinds of wiring permitted, under the insurance code:
(1) _Flexible armoured cable_: This consists of two-wire cable,
protected with a covering of flexible steel. It is installed out of
sight between the walls, and provides suitable outlets for lamps,
etc., by means of metal boxes set flush with the plaster. It is
easily installed in a house being built, but requires much tearing
down of plaster for an old house. Since its expense prohibits it in
the average farm house, this system will not be described in detail
here.
(2) _Rigid and flexible conduit_: As the name implies this system
consists of iron pipe, in connection with flexible conduit, run
between the walls. It differs from the above system, in that the pipes
with their fittings and outlet boxes are installed first, and the
wires are then "fished" through them. Duplex wires--the two wires of
the circuit woven in one braid--are used; and a liberal amount of
soapstone, and occasionally kerosene, are used to make the wires slip
easily into place. This is the most expensive system, and the best;
but it is difficult to install it in an old house without tearing down
a good deal of plaster. It has the advantage of being absolutely
waterproof and fireproof.
(3) _Wooden moulding_: This is simply moulding, providing two
raceways for the insulated wires to run in, and covered with a
capping. It is nailed or screwed firmly to the wall, on top of the
plaster; and when the wires have been installed in their respective
slots and the capping tacked on, the moulding is given a coat of paint
to make it in harmony with the other moulding in the room. This system
is cheap, safe, and easily installed, and will be described in detail
here.
[Illustration: Detail of wooden moulding]
(4) _Open wiring_: In open wiring, the wires are stretched from one
support to another (such as beams) and held by means of porcelain
cleats, or knobs. It is the simplest to install; but it has the
objection of leaving the wires unprotected, and is ugly. It is very
satisfactory in barns or out-buildings however.
_The Distributing Panel_
The first point to consider in wiring a house with wooden moulding is
the distribution board. It should be located centrally, on the wall
near the ceiling, so as to be out of ordinary reach. It consists of a
panel of wood--though fireproof material is better--firmly screwed to
the wall, and containing in a row, the porcelain cut-outs, as shown in
the cut, from which the various branch circuits are to be led. Each
cut-out provides for two branch circuits; and each branch contains
receptacles for two plug fuses. These fuses should be of 6 amperes
each. The Insurance Code limits the amount of electricity that may be
drawn on any branch lamp circuit to 660 watts; and these fuses protect
the circuit from drafts beyond this amount.
[Illustration: Porcelain cut-out and plug fuse]
The mains, leading from the entrance switch, as shown in the diagram,
to the panel board, should be of the same size as the transmission
wire itself, and rubber-covered. These mains terminate at the
distributing board. They are connected to the terminals of the
cut-outs by means of heavy brass screws.
_Wire Joints_
[Illustration: Examples of cleat and knob wiring, 1, 2, 3; wire
joints, 4; flexible armoured conductor, 5]
The branch circuits are, as has been said, of No. 14 rubber-covered
wire, running concealed in wooden moulding. All joints or splices in
this wire are made, as shown in the illustration, by first scraping
the wires bright, and fastening them stoutly together. This joint is
then soldered, to make the connection electrically perfect. Soft
solder is used, with ordinary soldering salts. There are several
compounds on the market, consisting of soft solder in powder form,
ready-mixed with flux. Coat the wire joint with this paste and apply
the flame of an alcohol lamp. The soldered joint is then covered with
rubber tape, and over this ordinary friction tape is wound on. A neat
joint should not be larger than the diameter of the wire before
insulation is removed.
_Branch Circuits_
First, make a diagram of your rooms and indicate where you wish lamps,
or outlets for other purposes. Since wooden moulding can be run across
ceilings, and up or down walls, lamps may be located in places where
they are out of the way. In planning the circuit, remember that you
will want many outlets in handy places on the walls, from which
portable cords will convey current to table lamps, to electric irons
and toasters and other handy devices which can be used on the lamp
circuit. These outlets are made of porcelain, in two pieces. One
piece is merely a continuation of the moulding itself; and the other
is a cap to connect permanently to the end of the lamp or iron cord,
which may be snapped into place in a second. Since there are a great
many designs of separable current taps on the market, it is well to
select one design and stick to it throughout the house, so that any
device can be connected to any outlet.
The code permits 660 watts on each circuit. This would allow 12 lamps
of 55 watts each. It is well to limit any one circuit to 6 lamps; this
will give leeway for the use of small stoves, irons, toasters, etc.
without overloading the circuit and causing a fuse to blow.
Having installed your distributing board, with its cut-outs, figure
out the course of your first branch circuit. Let us say it will
provide lights and outlets for the dining room and living room. It
will be necessary to run the wires through the partitions or floors in
several places. For this purpose porcelain tubes should be used,
costing one to three cents each. Knock holes in the plaster at the
determined point, insert the tubes so they project 3/4 inch on each
side, and fill up the ragged edge of the hole neatly with plaster.
[Illustration: The distributing panel]
When all the tubes have been set in place, begin laying the moulding.
Run it in a straight line, on the wall against the ceiling wherever
possible, mitering the joints neatly. Whenever it is necessary to
change the run from the ceiling to the wall and a miter cannot be
made, the wires should be protected in passing from one slot to the
other by being enclosed in non-metallic flexible conduit, called
circular loom.
In running wooden moulding, avoid brick walls liable to sweat or draw
dampness; keep away from places where the heat of a stove might
destroy the rubber insulation of the wires; do not pass nearer than
six inches to water pipes when possible--and when it is necessary to
pass nearer than this, the wooden moulding should pass above the pipe,
not below it, with at least an inch of air space intervening, thus
avoiding dampness from sweating of pipes.
[Illustration: Snap switch connections]
Places where chandeliers or wall bracket lamps are to be installed
permanently are fitted with wooden terminal blocks, which fit over
the moulding and flush with the plaster. These, after holes have been
bored in them for the wires, and the wires drawn through, should be
screwed firmly to the wall or ceiling, always choosing a joist or beam
for support. Then a crow's-foot, or tripod of iron, tapped and
threaded for iron pipe, is screwed to the terminal block. The iron
pipe of the chandelier or wall bracket is then screwed home in this
crow's-foot.
Do not begin stringing wires until all the moulding of the circuit has
been laid. Then thread the wires through the wall or floor tubes and
lay them in their respective slots. If trouble be found making them
stay in place before the capping is put on, small tacks may be driven
into the moulding beside them to hold them. When a terminal block is
reached, a loop is made of each wire, through the hole cut in the
block, if the circuit is to continue in the same direction. If it is
to end there, the two wires are drawn through taut, and cut off at a
length of 5 or 6 inches. These end wires, or loops, are then scraped
bare and spliced to the two wires coming out of the chandelier or
wall bracket. This joint is then soldered and covered with tape, and
the shell of the chandelier is screwed into place, covering the joint.
[Illustration: Detail of wooden moulding]
If the moulding is run along the walls flush with the ceiling, as is
usual, a branch is made for a wall light, or wall tap, by means of a
porcelain "T," or branch-block, which provides the means for running
the circuit at right angles to itself without letting the wires come
in contact with each other where they cross. Separable current taps
should be installed in handy places on all circuits, so that small
heating devices may be used without removing the lamps from their
sockets. The two wires are bared for half an inch where they run
through these current taps, and are fastened by means of brass screws.
_"Multiple" Connections_
All electric devices for this installation--lamps, irons, vacuum
cleaners, motors--must be connected _across_ the circuit--that is,
bridged, from one wire to the other. This is called _multiple_, or
shunt connection. There is only one exception to it, in wiring the
house. That one exception is installing a wall switch, the ordinary
snap switch. Since this wall switch, is, in effect, merely an
instrument, which opens or closes a circuit, it should be connected to
only one wire, which is cut to provide two ends for the screw
connections in the switch. When a moulding branch is run down from the
ceiling to some convenient spot for a snap switch (with which to turn
the lights of a room on or off), a porcelain "T" is not used. All that
is necessary to do is to loop the bottom wire of the circuit down
through the branch moulding, and connect it to the switch at a
terminal block, or porcelain base.
In wiring lamp fixtures, No. 14 rubber-covered wire will usually prove
too large. For this purpose, No. 18 may be used, with one lamp to each
loop. Hanging lamps may not be supported by electric lamp cord itself,
if there is more than one lamp in the cluster, because the weight is
apt to break the electrical connections. In such a case, the lamp
should be supported by a chain, and the twisted cord conveying current
to the electric bulbs, is woven in the links of the chain. For the
pantry, kitchen, woodshed, barn, etc., a single hanging lamp may be
suspended from a fielding rosette, as shown in the cut, provided a
single knot is tied inside both the rosette and the lamp socket, to
make it secure. This makes a very cheap fixture. The rosette of
porcelain will cost 15 cents; the lamp socket 20 cents, and the lamp
cord suspending the lamp and carrying the current will cost 1-1/2
cents a foot; while a tin shade will cost another 15 cents.
[Illustration: Detail of simple hanging lamp supported by rosette]
_Official Inspection_
In all communities, your insurance agent must inspect and pass your
wiring before you are permitted to throw the main switch and turn on
the electricity. Frequently they require that the moulding be left
uncapped, until they have inspected it. If you have more than 660
watts in lamps to a circuit; if your joints are not soldered and well
taped; if the moulding is used in any concealed or damp place, the
agent is liable to condemn your work and refuse permission to turn on
the electricity. However the rules are so clearly defined that it is
difficult to go wrong; and a farmer who does his own wiring and takes
pride in its appearance is more apt to be right than a professional
electrician who is careless at his task. After the work has been
passed, tack on the moulding capping, with brads, and paint the
moulding to match the woodwork.
Wooden moulding wiring is perfectly satisfactory if properly
installed. It is forbidden in many large cities, because of the
liability of careless workmanship. It should never be installed in
damp places, or out of sight. If the work is well done, the system
leaves nothing to be desired; and it has the additional advantage of
being cheap, and easily done by any farmer who can use carpenter
tools. Farmers with moulding machinery can make their own moulding.
The code prescribes it shall be of straight-grained wood; that the
raceways for the wires shall be separated by a tongue of wood one-half
inch wide; and that the backing shall be at least 3/8 inch thick. It
must be covered, inside and out, with at least two coats of
moisture-repellant paint. It can be had ready-made for about 2 cents a
foot.
_Special Heating Circuits_
If one plans using electricity for heavy-duty stoves, such as ranges
and radiators, it is necessary to install a separate heating circuit.
This is the best procedure in any event, even when the devices are all
small and suited to lamp circuits. The wire used can be determined by
referring to the table for carrying capacity, under the column headed
"rubber-covered." A stove or range drawing 40 amperes, would require a
No. 4 wire, in moulding. A good plan is to run the heating circuit
through the basement, attaching it to the rafters by means of
porcelain knobs. Branches can then be run up through the floor to
places where outlets are desired. Such a branch circuit should carry
fuses suitable to the allowed carrying capacity of the wire.
_Knob and Cleat Wiring_
Knob and cleat wiring, such as is used extensively for barns and
out-buildings, requires little explanation. The wires should not be
closer than 2-1/2 inches in open places, and a wider space is better.
The wires should be drawn taut, and supported by cleats or knobs at
least every four feet. In case of branch circuits, one wire must be
protected from the other it passes by means of a porcelain tube. It
should never be used in damp places, and should be kept clear of dust
and litter, and protected from abrasion.
[Illustration: Knob and cleat wiring]
Knob and tube wiring is frequently used in houses, being concealed
between walls or flooring. In this case, the separate wires are
stretched on adjoining beams or rafters, and porcelain tubes are used,
in passing through cross beams. For a ceiling or wall outlet, a
spliced branch is passed through the plaster by means of porcelain
tubes or flexible loom.
Wires from the house to the barn should be uniform with transmission
wires. At the point of entry to buildings they must be at least six
inches apart, and must take the form of the "drop loop" as shown in
the illustration. A double-pole entrance switch must be provided,
opening downward, with a double-pole fuse. In passing over buildings
wires must not come closer than 7 feet to flat roofs, or one foot to a
ridge roof. Feed-wires for electric motors should be determined from
the table of safe carrying capacities, and should be of liberal size.
CHAPTER IX
THE ELECTRIC PLANT AT WORK
Direct-connected generating sets--Belt drive--The
switchboard--Governors and voltage regulators--Methods of achieving
constant pressure at all loads: Over-compounding the dynamo; A
system of resistances; (A home-made electric radiator); Regulating
voltage by means of the rheostat--Automatic devices--Putting the
plant in operation.
Dynamos may be connected to water wheels either by means of a belt, or
the armature may spin on the same shaft as the water wheel itself. The
latter is by far the more desirable way, as it eliminates the loss of
power through shafting and belting, and does away altogether
with the belts themselves as a source of trouble. An installation
with the water wheel and armature on the same shaft is called a
"direct-connected set" and is of almost universal use in large power
plants.
To be able to use such a direct-connected set, the dynamo must be
designed to develop its full voltage when run at a speed identical
with that of the water wheel. That is, if the dynamo is wound to be
run at a speed of 800 revolutions per minute, it must be driven by a
water wheel which runs at this speed and can be governed within narrow
limits. Small impulse wheels running under great heads attain high
speed, and for such wheels it is possible to obtain a suitable dynamo
at low cost. For instance, a 12-inch impulse wheel, running under a
200-foot head will develop 6-3/4 horsepower when running at a speed of
875 revolutions per minute. A dynamo for direct coupling to such a
wheel should have a rated speed within 5 per cent of 875 r.p.m.; and,
as generators of this speed are to be had from the stock of almost all
manufacturers, there would be no extra charge.
When it comes to the larger wheels, however, of the impulse type, or
to turbines operating under their usual head the question becomes a
little more difficult. In such cases, the speed of the water wheel
will vary from 150 revolutions per minute, to 400, which is slow
speed for a small dynamo. As a general rule, the higher the speed of a
dynamo, the lower the cost; because, to lower the speed for a given
voltage, it is necessary either to increase the number of conductors
on the armature, or to increase the number of field coils, or both.
That means a larger machine, and a corresponding increase in cost.
In practice, in large plants, with alternating-current machines it has
become usual to mount the field magnets on the shaft, and build the
armature as a stationary ring in whose air space the field coils
revolve. This simplifies the construction of slow-speed, large-output
dynamos. Such a machine, however, is not to be had for the modest
isolated plant of the farmer with his small water-power.
[Illustration: Instantaneous photograph of high-pressure water jet
being quenched by buckets of a tangential wheel]
[Illustration: A tangential wheel, and a dynamo keyed to the same
shaft--the ideal method for generating electricity. The centrifugal
governor is included on the same base]
Dynamos can be designed for almost any waterwheel speed, and, among
small manufacturers especially, there is a disposition to furnish
these special machines at little advance in price over their stock
machines. Frequently it is merely a matter of changing the winding on
a stock machine. The farmer himself, in many cases, can re-wind an old
dynamo to fit the speed requirements of a direct-connected drive if
the difference is not too great. All that would be necessary to
effect this change would be to get the necessary winding data from the
manufacturer himself, and proceed with the winding. This data would
give the gauge of wire and the number of turns required for each spool
of the field magnets; and the gauge of wire and number of turns
required for each slot in the armature. The average boy who has
studied electricity (and there is something about electricity that
makes it closer to the boy's heart than his pet dog) could do this
work. The advantages of direct drive are so many that it should be
used wherever possible.
When direct drive cannot be had, a belt must be used, either from a
main shaft, or a countershaft. The belt must be of liberal size, and
must be of the "endless" variety--with a scarfed joint. Leather belt
lacing, or even the better grades of wire lacing, unless very
carefully used, will prove unsatisfactory. The dynamo feels every
variation in speed, and this is reflected in the lights. There is
nothing quite so annoying as flickering lights. Usually this can be
traced to the belt connections. Leather lacing forms a knot which
causes the lights to flicker at each revolution of the belt. The
endless belt does away with this trouble. Most dynamos are provided
with sliding bases, by which the machine can be moved one way or
another a few inches, to take up slack in the belt. To take advantage
of this, the belt must be run in a horizontal line, or nearly so.
Vertical belting is to be avoided.
The dynamo is mounted on a wooden base, in a dry location where it is
protected from the weather, or dampness from any source. It must be
mounted firmly, to prevent vibration when running up to speed; and the
switchboard should occupy a place within easy reach. Wires running
from the dynamo to the switchboard should be protected from injury,
and must be of ample size to carry the full current of the machine
without heating. A neat way is to carry them down through the flooring
through porcelain tubes, thence to a point where they can be brought
up at the back of the switchboard. If there is any danger of injury to
these mains they may be enclosed in iron pipe. Keep the wires out of
sight as much as possible, and make all connections on the back of the
switchboard.
_The Switchboard_
[Illustration: Connecting switchboard instruments]
The switchboard is constructed of some fireproof material, preferably
slate or marble. When the cost of this material is an item to
consider, build a substantial wooden frame for your switchboard. You
can then screw asbestos shingles to this to hold the various
instruments and with a little care such a switchboard can be made to
look business-like, and it is fully as serviceable as the more
expensive kind. The switchboard instruments have already been
described briefly. They consist of a voltmeter (to measure voltage);
an ammeter (to measure the strength of the current drawn, in amperes),
a rheostat (to regulate the voltage of the machine to suit the
individual requirements); and the usual switches and fuses. The main
switch should be so wired that when open it will throw all the current
off the line, but still leave the field coils, the voltmeter, and the
switchboard lamp in circuit. The main-switch fuses should have a
capacity about 50 per cent in excess of the full load of the dynamo.
If the machine is rated for 50 amperes, 75-ampere fuses should be
installed. This permits throwing on an overload in an emergency; and
at the same time guards against a short circuit. If the capacity of
the machine is under 30 amperes, plug fuses, costing 3 cents each, can
be used. If it is above this capacity, cartridge fuses, costing a
little more, are required. A supply of these fuses should be kept
handy at all times.
_Governors and Voltage Regulators_
[Illustration: A centrifugal governor (Courtesy of the C. P. Bradway
Company, West Stafford, Conn.)]
The necessity for water wheel governors will vary with conditions. As
a general rule, it may be said that reaction turbines working under a
low head with a large quantity of water do not require as much
governing as the impulse wheel, working under high heads with small
quantities of water. When governing is necessary at all, it is because
the prime mover varies in speed from no load to full load. Planning
one's plant with a liberal allowance of power--two water horsepower to
one electrical horsepower is liberal--reduces the necessity of
governors to a minimum. As an instance of this, the plant described
in some detail in Chapters One and Six of this volume, runs without a
governor.
However, a surplus of water-power is not usual. Generally plants are
designed within narrow limits; and then the need of a governor becomes
immediately apparent. There are many designs of governors on the
market, the cheapest being of the centrifugal type, in which a pair of
whirling balls are connected to the water wheel gate by means of
gears, and open or close the gate as the speed lowers or rises.
Constant speed is necessary because voltage is directly dependent on
speed. If the speed falls 25 per cent, the voltage falls likewise; and
a plant with the voltage varying between such limits would be a
constant source of annoyance, as well as expense for burned-out lamps.
Since constant voltage is the result aimed at by the use of a
governor, the same result can be attained in other ways, several of
which will be explained here briefly.
_Over-Compounding_
(1) Over-compounding the dynamo. This is simple and cheap, if one buys
the right dynamo in the first instance; or if he can do the
over-compounding himself, by the method described in the concluding
paragraphs of Chapter Seven. If it is found that the speed of the
water wheel drops 25 per cent between no load and full load, a dynamo
with field coils over-compounded to this extent would give a fairly
constant regulation. If you are buying a special dynamo for direct
drive, your manufacturer can supply you with a machine that will
maintain constant voltage under the normal variations in speed of your
wheel.
_A System of Resistances_
(2) Constant load systems. This system provides that the dynamo shall
be delivering a fixed amount of current at all times, under which
circumstances the water wheel would not require regulation, as the
demands on it would not vary from minute to minute or hour to hour.
This system is very simply arranged. It consists of having a set of
"resistances" to throw into the circuit, in proportion to the amount
of current used.
Let us say, as an example, that a 50-ampere generator is used at a
pressure of 110 volts; and that it is desirable to work this plant at
80 per cent load, or 40 amperes current draft. When all the lights or
appliances were in use, there would be no outside "resistance" in the
circuit. When none of the lights or appliances were in use (as would
be the case for many hours during the day) it would be necessary to
consume this amount of current in some other way--to _waste it_. A
resistance permitting 40 amperes of current to flow, would be
necessary. Of what size should this resistance be?
The answer is had by applying Ohm's Law, explained in Chapter Five.
The Law in this case, would be read R = E/C. Therefore, in this case R
= 110/40 = 2-3/4 ohms resistance, would be required, switched across
the mains, to keep the dynamo delivering its normal load.
The cheapest form of this resistance would be iron wire. In place of
iron wire, German silver wire could be used. German silver wire is to
be had cheaply, and is manufactured in two grades, 18% and 30%, with a
resistance respectively 18 and 30 times that of copper for the same
gauge. Nichrome wire has a resistance 60 times that of copper; and
manganin wire has a resistance 65 times that of copper, of the same
gauge.
First figure the number of feet of copper wire suitable for the
purpose. Allowing 500 circular mills for each ampere, the gauge of the
wire should be 40 × 500 = 20,000 circular mills, or approximately No.
7 B. & S. gauge. How many feet of No. 7 copper wire would give a
resistance of 2-3/4 ohms? Referring to the copper wire table, we find
that it requires 2006.2 of No. 7 wire to make one ohm. Then 2-3/4 ohms
would require 5,517 feet.
Since 30 per cent German silver wire is approximately 30 times the
resistance of copper, a No. 7 German silver wire, for this purpose,
would be 1/30 the length of the copper wire, or 186 feet. If nichrome
wire were used, it would be 1/60th the length of copper for the same
gauge, or 93 feet. This resistance wire can be wound in spirals and
made to occupy a very small space. As long as it is connected in
circuit, the energy of the dynamo otherwise consumed as light would be
wasted as heat. This heat could be utilized in the hot water boiler or
stove when the lights were turned off.
In actual practice, however, the resistance necessary to keep the
dynamo up to full load permanently, would not be furnished by one set
of resistance coils. Each lamp circuit would have a set of resistance
coils of its own. A double-throw switch would turn off the lamps and
turn on the resistance coils, or _vice versa_.
Let us say a lamp circuit consisted of 6 carbon lamps, of 16
candlepower each. It would consume 6 × 1/2 ampere, or 3 amperes of
current, and interpose a resistance of 36.6 ohms--say 37 ohms. Three
amperes would require a wire of at least 1,500 circular mills in area
for safety. This corresponds to a No. 18 wire. A No. 18 copper wire
interposes a resistance of one ohm, for each 156.5 feet length. For 37
ohms, 5,790 feet would be required, for copper wire, which of course
would be impractical. Dividing by 30 gives 193 feet for 30% German
silver wire; and dividing by 60 gives 96 feet of nichrome wire of the
same gauge.
It is simple to figure each circuit in this way and to construct
resistance units for each switch. Since the resistance units develop
considerable heat, they must be enclosed and protected.
_A Home-made Stove or Radiator_
While we are on the subject of resistance coils it might be well here
to describe how to make stoves for cooking, and radiators for heating
the house, at small expense. These stoves consist merely of
resistances which turn hot--a dull red--when the current is turned on.
Iron wire, German silver wire, or the various trade brands of
resistance wire, of which nichrome, calido, and manganin are samples,
can be used. In buying this wire, procure the table of resistance and
carrying capacity from the manufacturers. From this table you can make
your own radiators to keep the house warm in winter. Iron wire has the
disadvantage of oxidizing when heated to redness, so that it goes to
pieces after prolonged use. It is cheap, however, and much used for
resistance in electrical work.
Let us say we wish to heat a bathroom, a room 6 × 8, and 8 feet
high--that is a room containing 384 cubic feet of air space. Allowing
2 watts for each cubic foot, we would require 768 watts of current, or
practically 7 amperes at 110 volts. What resistance would be required
to limit the current to this amount? Apply Ohm's Law, as before, and
we have R equals E divided by C, or R equals 110 divided by 7, which
is 15.7 ohms. Forty-two feet of No. 20 German silver wire would emit
this amount of heat and limit the current output to 7 amperes. In the
Far West, it is quite common, in the outlying district, to find
electric radiators made out of iron pipe covered with asbestos, on
which the requisite amount of iron wire is wound and made secure. This
pipe is mounted in a metal frame. Or the frame may consist of two
pipes containing heating elements; and a switch, in this case, is so
arranged that either one or two heating elements may be used at one
time, according to the weather. An ingenious mechanic can construct
such a radiator, experimenting with the aid of an ammeter to ascertain
the length of wire required for any given stove.
_Regulating Voltage at Switchboards_
The voltage of any given machine may be regulated, within wide limits,
by means of the field rheostat on the switchboard.
A dynamo with a rated speed of 1,500 revolutions per minute, for 110
volts, will actually attain this voltage at as low as 1,200 r.p.m. if
all the regulating resistance be cut out. You can test this fact with
your own machine by cutting out the resistance from the shunt field
entirely, and starting the machine slowly, increasing its speed
gradually, until the voltmeter needle registers 110 volts. Then
measure the speed. It will be far below the rated speed of your
machine.
If, on the other hand, the speed of such a machine runs up to 2,500 or
over--that is, an excess of 67%--the voltage would rise
proportionally, unless extra resistance was cut in. By cutting in such
resistance--by the simple expedient of turning the rheostat handle on
the switchboard,--the field coils are so weakened that the voltage is
kept at the desired point in spite of the excessive speed of the
machine. Excessive speeds are to be avoided, as a rule, because of
mechanical strain. But within a wide range, the switchboard rheostat
can be used for voltage regulation.
As it would be a source of continual annoyance to have to run to the
switchboard every time the load of the machine was varied greatly this
plan would not be practical for the isolated plant, unless the
rheostat could be installed,--with a voltmeter--in one's kitchen.
This could be done simply by running a small third wire from the
switchboard to the house. Then, when the lights became dim from
excessive load, a turn of the handle would bring them back to the
proper voltage; and when they flared up and burned too bright, a turn
of the handle in the opposite direction would remedy matters. By this
simple arrangement, any member of the family could attend to voltage
regulation with a minimum of bother.
_Automatic Devices_
There are several automatic devices for voltage regulation at the
switchboard on the market. These consist usually of vibrator magnets
or solenoids, in which the strength of the current, varying with
different speeds, reacts in such a way as to regulate field
resistance. Such voltage regulators can be had for $40 or less, and
are thoroughly reliable.
* * * * *
To sum up the discussion of governors and voltage regulators: If you
can allow a liberal proportion of water-power, and avoid crowding
your dynamo, the chances are you will not need a governor for the
ordinary reaction turbine wheel. Start your plant, and let it run for
a few days or a few weeks without a governor, or regulator. Then if
you find the operation is unsatisfactory, decide for yourself which of
the above systems is best adapted for your conditions. Economy as well
as convenience will affect your decision. The plant which is most
nearly automatic is the best; but by taking a little trouble and
giving extra attention, a great many dollars may be saved in extras.
_Starting the Dynamo_
You are now ready to put your plant in operation. Your dynamo has been
mounted on a wooden foundation, and belted to the countershaft, by
means of an endless belt.
See that the oil cups are filled. Then throw off the main switch and
the field switch at the switchboard; open the water gate slowly, and
occasionally test the speed of the dynamo. When it comes up to rated
speed, say 1,500 per minute, let it run for a few minutes, to be sure
everything is all right.
Having assured yourself that the mechanical details are all right, now
look at the voltmeter. It is probably indicating a few volts pressure,
from 4 to 8 or 10 perhaps. This pressure is due to the residual
magnetism in the field cores, as the field coils are not yet
connected. If by any chance, the needle does not register, or is now
back of 0, try changing about the connections or the voltmeter on the
back of the switchboard.
Now snap on the field switch. Instantly the needle will begin to move
forward, though slowly; and it will stop. Turn the rheostat handle
gradually; as you advance it, the voltmeter needle will advance.
Finally you will come to a point where the needle will indicate 110
volts.
If you have designed your transmission line for a drop of 5 volts at
half-load, advance the rheostat handle still further, until the
needle points to 115 volts. Let the machine run this way for some
time. When assured all is right, throw on the main switch, and turn on
the light at the switchboard. Then go to the house and gradually turn
on lights. Come back and inspect the dynamo as the load increases. It
should not run hot, nor even very warm, up to full load. Its brushes
should not spark, though a little sparking will do no harm.
Your plant is now ready to deliver current up to the capacity of its
fuses. See that it does not lack good lubricating oil, and do not let
its commutator get dirty. The commutator should assume a glossy
chocolate brown color. If it becomes dirty, or the brushes spark
badly, hold a piece of fine sandpaper against it. Never use emery
paper! If, after years of service, it becomes roughened by wear, have
it turned down in a lathe. Occasionally, every few weeks, say, take
the brushes out and clean them with a cloth. They will wear out in the
course of time and can be replaced for a few cents each. The bearings
may need replacing after several years' continuous use.
Otherwise your electric plant will take care of itself. Keep it up to
speed, and keep it clean and well oiled. Never shut it down unless you
have to. In practice, dynamos run week after week, year after year,
without stopping. This one, so long as you keep it running true to
form, will deliver light, heat and power to you for nothing, which
your city cousin pays for at the rate of 10 cents a kilowatt-hour.
PART III
GASOLINE ENGINES, WINDMILLS, ETC. THE STORAGE BATTERIES
CHAPTER X
GASOLINE ENGINE PLANTS
The standard voltage set--Two-cycle and four-cycle gasoline
engines--Horsepower, and fuel consumption--Efficiency of small
engines and generators--Cost of operating a one-kilowatt plant.
Electricity is of so much value in farm operations, as well as in the
farm house, that the farmer who is not fortunate enough to possess
water-power of his own, or to live in a community where a coöperative
hydro-electric plant may be established, should not deny himself its
many conveniences. In place of the water wheel to turn the dynamo,
there is the gasoline engine (or other forms of internal combustion
engine using oil, gas, or alcohol as fuel); in many districts where
steam engines are used for logging or other operations, electricity
may be generated as a by-product; and almost any windmill capable of
pumping water can be made to generate enough electricity for lighting
the farm house at small expense.
The great advantage of water-power is that the expense of
maintenance--once the plant is installed--is practically nothing. This
advantage is offset in some measure by the fact that other forms of
power, gas, steam, or windmills, are already installed, in many
instances and that their judicious use in generating electricity does
not impair their usefulness for the other farm operations for which
they were originally purchased. In recent years gasoline engines have
come into general use on farms as a cheap dependable source of power
for all operations; and windmills date from the earliest times. They
may be installed and maintained cheaply, solely for generating
electricity, if desired. Steam engines, however, require so much care
and expert attention that their use for farm electric plants is not to
be advised, except under conditions where a small portion of their
power can be used to make electricity as a by-product.
There are two types of gasoline engine electric plants suitable for
the farm, in general use:
First: The Standard Voltage Set, in which the engine and dynamo are
mounted on one base, and the engine is kept running when current is
required for any purpose. These sets are usually of the 110-volt type,
and all standard appliances, such as irons, toasters, motors, etc.,
may be used in connection with them. Since the electricity is drawn
directly from the dynamo itself, without a storage battery, it is
necessary that these engines be efficient and governed as to speed
within a five per cent variation from no load to full load.
Second: Storage Battery Sets, in which the dynamo is run only a few
hours each week, and the electricity thus generated is "stored" by
chemical means, in storage batteries, for use when required. Since, in
this case, the current is drawn from the battery, instead of the
dynamo, when used for lighting or other purposes, it is not necessary
that a special type of engine be used to insure constant speed.
_The Standard Voltage Set_
In response to a general demand, the first type (the direct-connected
standard voltage set) has been developed to a high state of efficiency
recently, and is to be had in a great variety of sizes (ranging from
one-quarter kilowatt to 25 kilowatts and over) from many
manufacturers.
The principle of the gasoline engine as motive power is so familiar to
the average farmer that it needs but a brief description here.
Gasoline or other fuel (oil, gas, or alcohol) is transformed into
vapor, mixed with air in correct proportions, and drawn into the
engine cylinder and there exploded by means of a properly-timed
electric spark.
Internal combustion engines are of two general types--four-cycle and
two-cycle. The former is by far the more common. In a four-cycle
engine the piston must travel twice up and down in each cylinder, to
deliver one power stroke. This results in one power impulse in each
cylinder every two revolutions of the crank shaft. On its first down
stroke, the piston sucks in gas. On its first up stroke, it compresses
the gas. At the height of this stroke, the gas is exploded by means of
the electric spark and the piston is driven down, on its power stroke.
The fourth stroke is called the scavening stroke, and expels the
burned gas. This completes the cycle.
A one-cylinder engine of the ordinary four-cycle type has one power
stroke for every two revolutions of the fly wheel. A two-cylinder
engine has one power stroke for one revolution of the fly wheel; and a
four-cylinder engine has two power strokes to each revolution. The
greater the number of cylinders, the more even the flow of power. In
automobiles six cylinders are common, and in the last year or two,
eight-cylinder engines began appearing on the market in large numbers.
A twelve-cylinder engine is the prospect for the immediate future.
Since the dynamo that is to supply electric current direct to lamps
requires a steady flow of power, the single-cylinder gas or gasoline
engine of the four-cycle type is not satisfactory as a rule. The
lights will flicker with every other revolution of the fly wheel. This
would be of no importance if the current was being used to charge a
storage battery--and right here lies the reason why a cheaper engine
may be used in connection with a storage battery than when the dynamo
supplies the current direct for lighting.
A two-cylinder engine is more even in its flow of power and a
four-cylinder engine still better. For this reason, standard voltage
generating sets without battery are usually of two or four cylinders
when of the four-cycle type. When a single-cylinder engine is used, it
should be of the two-cycle type. In the two-cycle engine, there is one
power stroke to each up-and-down journey of the piston. This effect is
produced by having inlet and exhaust ports in the crank case, so
arranged that, when the piston arrives at the bottom of the power
stroke, the waste gases are pushed out, and fresh gas drawn in before
the up stroke begins.
For direct lighting, the engine must be governed so as not to vary
more than five per cent in speed between no load and full load. There
are many makes on the market which advertise a speed variation of
three per cent under normal loads. Governors are usually of the
centrifugal ball type, integral with the fly wheel, regulating the
amount of gas and air supplied to the cylinders in accordance with the
speed. Thus, if such an engine began to slow down because of increase
in load, the centrifugal balls would come closer together, and open
the throttle, thus supplying more gas and air and increasing the
speed. If the speed became excessive, due to sudden shutting off of
lights, the centrifugal balls would fly farther apart, and the
throttle would close until the speed was again adjusted to the load.
These direct-connected standard voltage sets are as a rule fitted with
the 110-volt, direct current, compound type of dynamo, the duplicate
in every respect of the machine described in previous chapters for
water-power plants. They are practically automatic in operation and
will run for hours without attention, except as to oil and gasoline
supply. They may be installed in the woodshed or cellar without
annoyance due to noise or vibration. It is necessary to start them, of
course, when light or power is desired, and to stop them when no
current is being drawn. There have appeared several makes on the
market in which starting and stopping are automatic. Storage batteries
are used in connection with these latter plants for starting the
engine. When a light is turned on, or current is drawn for any
purpose, an automatic switch turns the dynamo into a motor, and it
starts the engine by means of the current stored in the battery.
Instantly the engine has come up to speed, the motor becomes a dynamo
again and begins to deliver current. When the last light is turned
off, the engine stops automatically.
Since the installation of a direct-connected standard voltage plant of
this type is similar in every respect, except as to motive power, to
the hydro-electric plant, its cost, with this single exception, is the
same. The same lamps, wire, and devices are used.
With gasoline power, the cost of the engine offsets the cost of the
water wheel. The engine is more expensive than the ordinary gasoline
engine; but even this item of cost is offset by the cost of labor and
materials used in installing a water wheel.
The expense of maintenance is limited to gasoline and oil.
Depreciation enters in both cases; and though it may be more rapid
with a gasoline engine than a water wheel, that item will not be
considered here. The cost of lubricating oil is inconsiderable. It
will require, when operated at from one-half load to full load,
approximately one pint of gasoline to each horsepower hour. When
operated at less than half-load, its efficiency lowers. Thus, for a
quarter-load, an average engine of this type may require three pints
of gasoline for each horsepower hour. For this reason it is well, in
installing such a plant, to have it of such size that it will be
operating on at least three-fourths load under normal draft of
current. Norman H. Schneider, in his book "Low Voltage Electric
Lighting," gives the following table of proportions between the engine
and dynamo:
Actual watts Actual Horsepower Nearest engine size
150 .5 1/2
225 .7 3/4
300 .86 1
450 1.12 1-1/4
600 1.5 1-1/2
750 1.7 1-3/4
1000 2.3 2-1/2
2000 4.5 5
4000 9.0 10
This table is figured for an efficiency of only 40 per cent for the
smaller generators, and 60 per cent for the larger. In machines from 5
to 25 kilowatts, the efficiency will run considerably higher.
To determine the expense of operating a one-kilowatt gasoline
generator set of this type, as to gasoline consumption, we can assume
at full load that the gasoline engine is delivering 2-1/2 horsepower,
and consuming, let us say, 1-1/4 pint of gasoline for each horsepower
hour (to make allowance for lower efficiency in small engines). That
would be 3.125 pints of gasoline per hour. Allowing a ten per cent
loss of current in wiring, we have 900 watts of electricity to use,
for this expenditure of gasoline. This would light 900 ÷ 25 = 36 lamps
of 25 watts each, a liberal allowance for house and barn, and
permitting the use of small cooking devices and other conveniences
when part of the lights were not in use. With gasoline selling at 12
cents a gallon, the use of this plant for an hour at full capacity
would cost $0.047. Your city cousin pays 9 cents for the same current
on a basis of 10 cents per kilowatt-hour; and in smaller towns where
the rate is 15 cents, he would pay 13-1/2 cents.
Running this plant at only half-load--that is, using only 18 lights,
or their equivalent--would reduce the price to about 3 cents an
hour--since the efficiency decreases with smaller load. It is
customary to figure an average of 3-1/2 hours a day throughout the
year, for all lights. On this basis the cost of gasoline for this
one-kilowatt plant would be 16-1/2 cents a day for full load, and
approximately 10-1/2 cents a day for half-load. This is extremely
favorable, as compared with the cost of electric current in our cities
and towns, at the commercial rate, especially when one considers that
light and power are to be had at any place or at any time on the farm
simply by starting the engine. A smaller plant, operating at less cost
for fuel, would furnish ample light for most farms; but it is well to
remember in this connection plants smaller than one kilowatt are
practical for light only, since electric irons, toasters, etc., draw
from 400 to 660 watts each. Obviously a plant of 300 watts capacity
would not permit the use of these instruments, although it would
furnish 10 or 12 lamps of 25 watts each.
CHAPTER XI
THE STORAGE BATTERY
What a storage battery does--The lead battery and the Edison
battery--Economy of tungsten lamps for storage batteries--The
low-voltage battery for electric light--How to figure the capacity
of a battery--Table of light requirements for a farm
house--Watt-hours and lamp-hours--The cost of storage battery
current--How to charge a storage battery--Care of storage
batteries.
For the man who has a small supply of water to run a water wheel a few
hours at a time, or who wishes to store electricity while he is doing
routine jobs with a gasoline engine or other source of power, the
storage battery solves the problem. The storage battery may be likened
to a tank of water which is drawn on when water is needed, and which
must be re-filled when empty. A storage battery, or accumulator is a
device in which a chemical action is set up when an electric current
is passed through it. This is called _charging_. When such a battery
is charged, it has the property of giving off an electric current by
means of a reversed chemical action when a circuit is provided,
through a lamp or other connection. This reversed action is called
_discharging_. Such a battery will discharge nearly as much current as
is required originally to bring about the first chemical action.
There are two common types of storage battery--the lead accumulator,
made up of lead plates (alternately positive and negative); and the
two-metal accumulator, of which the Edison battery is a
representative, made up of alternate plates of iron and nickel. In the
lead accumulator, the "positive" plate may be recognized by its brown
color when charging, while the "negative" plate is usually light gray,
or leaden in color. The action of the charging current is to form
oxides of lead in the plates; the action of the discharging current is
to reduce the oxides to metallic lead again. This process can be
repeated over and over again during the life of the battery.
Because of the cost of the batteries themselves, it is possible (from
the viewpoint of the farmer and the size of his pocketbook) to store
only a relatively small amount of electric current. For this reason,
the storage battery was little used for private plants, where expense
is a considerable item, up to a few years ago. Carbon lamps require
from 3-1/2 to 4 watts for each candlepower of light they give out; and
a lead battery capable of storing enough electricity to supply the
average farm house with light by means of carbon lamps for three or
four days at a time without recharging, proved too costly for private
use.
_The Tungsten Lamp_
With the advent of the new tungsten lamp, however, reducing the
current requirements for light by two-thirds, the storage battery
immediately came into its own, and is now of general use.
Since incandescent lamps were first invented scientists have been
trying to find some metal of high fusion to use in place of the carbon
filament of the ordinary lamp. The higher the fusing point of this
filament of wire, the more economical would be the light. Edison
sought, thirty years ago, for just the qualities now found in tungsten
metal. Tungsten metal was first used for incandescent lamps in the
form of a paste, squirted into the shape of a thread. This proved too
fragile. Later investigators devised means of drawing tungsten into
wire; and it is tungsten wire that is now used so generally in
lighting. A tungsten lamp has an average efficiency of 1-1/4 watts per
candlepower, compared with 3-1/2 to 4 watts of the old-style carbon
lamp. In larger sizes the efficiency is as low as .9 watt per
candlepower; and only recently it has been found that if inert
nitrogen gas is used in the glass bulb, instead of using a high vacuum
as is the general practice, the efficiency of the lamp becomes still
higher, approaching .5 watt for each candlepower in large lamps. This
new nitrogen lamp is not yet being manufactured in small domestic
sizes, though it will undoubtedly be put on the market in those sizes
in the near future.
[Illustration: The Fairbanks Morse oil engine storage battery set]
The tungsten lamp, requiring only one-third as much electric current
as the carbon lamp, for the same amount of light, reduces the size
(and the cost) of the storage battery in the same degree, thus
bringing the storage battery within the means of the farmer. Some idea
of the power that may be put into a small storage battery is to be had
from the fact that a storage battery of only 6 volts pressure, such as
is used in self-starters on automobiles, will turn a motor and crank a
heavy six-cylinder engine; or it will run the automobile, without
gasoline, for a mile or more with its own accumulated store of
electric current.
_The Low Voltage Battery_
The 30-volt storage battery has become standard for small lighting
plants, since the introduction of the tungsten lamp. Although the
voltage of each separate cell of this battery registers 2.5 volts when
fully charged, it falls to approximately 2 volts per cell immediately
discharging begins. For this reason, it is customary to figure the
working pressure of each cell at 2 volts. This means that a 30-volt
battery should consist of at least 15 cells. Since, however, the
voltage falls below 2 for each cell, as discharging proceeds, it is
usual to include one additional cell for regulating purposes. Thus,
the ordinary 30-volt storage battery consists of 16 cells, the last
cell in the line remaining idle until the lamps begin to dim, when it
is switched in by means of a simple arrangement of connections. This
maintains a uniform pressure of 30 volts from the beginning to the end
of the charge, at the lamp socket.
We saw in earlier chapters that the 110-volt current is the most
satisfactory, under all conditions, where the current is to be used
for heating and small power, as well as light. But a storage battery
of 110 volts would require at least 55 cells, which would make it too
expensive for ordinary farm use. As a 30-volt current is just as
satisfactory for electric light, this type has become established, in
connection with the battery, and it is used for electric lighting
only, as a general rule.
Batteries are rated first, as to voltage; second, as to their capacity
in ampere hours--that is, the number of amperes that may be drawn from
them in a given number of hours. Thus, a battery rated at 60 ampere
hours would give 60 amperes, at 30 volts pressure, for one hour; 30
amperes for 2 hours; 15 amperes for 4 hours; 7-1/2 amperes for 8
hours; 3-3/4 amperes for 16 hours; etc., etc. In practice, a battery
should not be discharged faster than its 8-hour rate. Thus, a
60-ampere hour battery should not be drawn on at a greater rate than
7-1/2 amperes per hour.
This 8-hour rate also determines the rate at which a battery should
be re-charged, once it is exhausted. Thus, this battery should be
charged at the rate of 7-1/2 amperes for 8 hours, with another hour
added to make up for losses that are bound to occur. A battery of
120-ampere hour capacity should be charged for 8 or 9 hours at the
rate of 120 ÷ 8, or 15 amperes, etc.
To determine the size of battery necessary for any particular
instance, it is necessary first to decide on the number of lamps
required, and their capacity. Thirty-volt lamps are to be had in the
market in sizes of 10, 15 and 20 watts; they yield respectively 8, 12,
and 16 candlepower each. Of these the 20-watt lamp is the most
satisfactory for the living rooms; lamps of 10 or 15 watts may be used
for the halls, the bathroom and the bedrooms. At 30 volts pressure
these lamps would require a current of the following density in
amperes:
Candle
Power 30-volt lamp Amperes
8 10 watts 0.33
12 15 watts 0.50
16 20 watts 0.67
Let us assume, as an example, that Farmer Brown will use 20-watt
lamps in his kitchen, dining room, and sitting room; and 10-watt lamps
in the halls, bathroom, and bedrooms. His requirements may be figured
either in lamp hours or in watt-hours. Since he is using two sizes of
lamps, it will be simpler to figure his requirements in watt-hours.
Thus:
Number Size of Hours Watt-
Room of lamps lamps burned hours
Kitchen 1 20 4 80
Dining room 2 20 2 80
Sitting room 3 20 4 240
(3) Bedrooms 1 (each) 10 1 30
Bathroom 1 10 2 20
(2) Halls 1 (each) 10 4 80
Pantry 1 10 1 10
Cellar 1 10 1 10
----
Total 550
Since amperes equal watts divided by volts, the number of ampere hours
required in this case each night would be 550 ÷ 30 = 18.3 ampere
hours; or approximately 4-1/2 amperes per hour for 4 hours.
Say it is convenient to charge this battery every fourth day. This
would require a battery of 4 × 18.3 ampere hours, or 73.2 ampere
hours. The nearest size on the market is the 80-ampere hour battery,
which would be the one to use for this installation.
To charge this battery would require a dynamo capable of delivering 10
amperes of current for 9 hours. The generator should be of 45 volts
pressure (allowing 2-1/2 volts in the generator for each 2 volts of
battery) and the capacity of the generator would therefore be 450
watts. This would require a 1-1/4 horsepower gasoline engine. At 1-1/4
pints of gasoline for each horsepower, nine hours work of this engine
would consume 14 pints of gasoline--or say 16 pints, or two gallons.
At 12 cents a gallon for gasoline, lighting your house with this
battery would cost 24 cents for four days, or 6 cents a day. Your city
cousin, using commercial current, would pay 5-1/2 cents a day for the
same amount of current at 10 cents a kilowatt-hour; or 8-1/4 cents at
a 15-cent rate. If the battery is charged by the farm gasoline engine
at the same time it is doing its other work, the cost would be still
less, as the extra gasoline required would be small.
This figure does not take into account depreciation of battery and
engine. The average farmer is too apt to overlook this factor in
figuring the cost of machinery of all kinds, and for that reason is
unprepared when the time comes to replace worn-out machinery. The
dynamo and switchboard should last a lifetime with ordinary care, so
there is no depreciation charge against them. The storage battery, a
30-volt, 80-ampere hour installation, should not cost in excess of
$100; and, if it is necessary to buy a gasoline engine, a 1-1/4
horsepower engine can be had for $50 or less according to the type.
Storage batteries of the lead type are sold under a two-years'
guarantee--which does not mean that their life is limited to that
length of time. With good care they may last as long as 10 years; with
poor care it may be necessary to throw them away at the end of a year.
The engine should be serviceable for at least 10 years, with ordinary
replacements; and the storage battery may last from 6 to 10 years,
with occasional renewal of parts. If it were necessary to duplicate
both at the end of ten years, this would make a carrying charge of
$1.25 a month for depreciation, which must be added to the cost of
light.
_Figuring by Lamp Hours_
If all the lamps are to be of the same size--either ten, fifteen, or
twenty watts, the light requirements of a farm house can be figured
readily by lamp hours. In that event, the foregoing table would read
as follows:
Lamp hours
Kitchen, 1 lamp, 4 hours 4
Sitting room, 3 lamps, 4 hours each 12
Dining room, 2 lamps, 2 hours each 4
Bedrooms, 3 lamps, 1 hour each 3
Halls, 2 lamps, 4 hours each 8
Bathroom, 1 lamp, 2 hours 2
Pantry and cellar, 2 lamps, 1 hour each 2
To determine the ampere hours from this table, multiply the total
number of lamp hours by the current in amperes required for each lamp.
As 10, 15, and 20-watt tungsten lamps require .33, .50 and .67
amperes, respectively at 30 volts pressure, the above requirements in
ampere hours would be 12, 17-1/2, or 24 ampere hours, according to the
size of lamp chosen. This gives the average current consumption for
one night. If it is desired to charge the battery twice a week on the
average, multiply the number of lamp hours by 4, to get the size of
battery required.
The foregoing illustration is not intended to indicate average light
requirements for farms, but is given merely to show how a farmer may
figure his own requirements. In some instances, it will be necessary
to install a battery of 120 or more ampere hours, whereas a battery of
40 or 60 ampere hours would be quite serviceable in other instances.
It all depends on how much light you wish to use and are willing to
pay for, because with a storage battery the cost of electric light is
directly in proportion to the number of lights used.
As a general rule, a larger generator and engine are required for a
larger battery--although it is possible to charge a large battery
with a small generator and engine by taking more time for the
operation.
_How to Charge a Storage Battery_
Direct current only can be used for charging storage batteries. In the
rare instance of alternating current only being available, it must be
converted into direct current by any one of the many mechanical,
chemical, or electrical devices on the market--that is, the
alternating current must be straightened out, to flow always in one
direction.
A shunt-wound dynamo must be used; else, when the voltage of the
battery rises too high, it may "back up" and turn the dynamo as a
motor, causing considerable damage. If a compound dynamo is already
installed, or if it is desired to use such a machine for charging
storage batteries, it can be done simply by disconnecting the series
windings on the field coils, thus turning the machine into a shunt
dynamo.
The voltage of the dynamo should be approximately 50 per cent above
the working pressure of the battery. For this reason 45-volt machines
are usually used for 30 or 32-volt batteries. Higher voltages may be
used, if convenient. Thus a 110-volt dynamo may be used to charge a
single 2-volt cell if necessary, although it is not advisable.
_Direction of Current_
Electricity flows from the positive to the negative terminal. A
charging current must be so connected that the negative wire of the
dynamo is always connected to the negative terminal of the battery,
and the positive wire to the positive terminal. As the polarity is
always marked on the battery, there is little danger of making a
mistake in this particular.
When the storage battery is charged, and one begins to use its
accumulation of energy, the current comes out in the opposite
direction from which it entered in charging. In this respect, a
storage battery is like a clock spring, which is wound up in one
direction, and unwinds itself in the other. With all storage battery
outfits, an ammeter (or current measure) is supplied with zero at the
center. When the battery is being charged, the indicating needle
points in one direction in proportion to the strength of the current
flowing in; and when the battery is being discharged, the needle
points in the opposite direction, in proportion to the strength of the
current flowing out.
Sometimes one is at loss, in setting about to connect a battery and
generator, to know which is the positive and which the negative wire
of the generator. A very simple test is as follows:
Start the generator and bring it up to speed. Connect some form of
resistance in "series" with the mains. A lamp in an ordinary lamp
socket will do very well for this resistance. Dip the two ends of the
wire (one coming from the generator, the other through the lamp) into
a cup of water, in which a pinch of salt is dissolved. Bring them
almost together and hold them there. Almost instantly, one wire will
begin to turn bright, and give off bubbles. The wire which turns
bright and gives off bubbles is the _negative_ wire. The other is the
positive.
[Illustration: A rough-and-ready farm electric plant, supplying two
farms with light, heat and power; and a Ward Leonard-type
circuit-breaker for charging storage batteries]
_Care of Battery_
Since specific directions are furnished with all storage batteries, it
is not necessary to go into the details of their care here. Storage
battery plants are usually shipped with all connections made, or
plainly indicated. All that is necessary is to fill the batteries with
the acid solution, according to directions, and start the engine. If
the engine is fitted with a governor, and the switchboard is of the
automatic type, all the care necessary in charging is to start the
engine. In fact, many makes utilize the dynamo as a "self-starter" for
the engine, so that all that is necessary to start charging is to
throw a switch which starts the engine. When the battery is fully
charged, the engine is stopped automatically.
The "electrolyte" or solution in which the plates of the lead battery
are immersed, is sulphuric acid, diluted with water in the proportion
of one part of acid to five of water, by volume.
The specific gravity of ordinary commercial sulphuric acid is 1.835.
Since its strength is apt to vary, however, it is best to mix the
electrolyte with the aid of the hydrometer furnished with the battery.
The hydrometer is a sealed glass tube, with a graduated scale somewhat
resembling a thermometer. The height at which it floats in any given
solution depends on the density of the solution. It should indicate
approximately 1.15 for a storage battery electrolyte before charging.
It should not be over 1.15--or 1,150 if your hydrometer reads in
thousandths.
Only pure water should be used. Distilled water is the best, but fresh
clean rain water is permissible. Never under any circumstances use
hydrant water, as it contains impurities which will injure the
battery, probably put it out of commission before its first charge.
_Pour the acid into the water._ Never under any circumstances pour the
water into the acid, else an explosion may occur from the heat
developed. Mix the electrolyte in a stone crock, or glass container,
stirring with a glass rod, and testing from time to time with a
hydrometer. Let it stand until cool and then pour it into the battery
jars, filling them to 1/2 inch above the top of the plates.
Then begin charging. The first charge will probably take a longer time
than subsequent charges. If the installation is of the automatic type,
all that is necessary is to start the engine. If it is not of the
automatic type, proceed as follows:
First be sure all connections are right. Then start the engine and
bring the dynamo up to its rated speed. Adjust the voltage to the
pressure specified. Then throw the switch connecting generator to
battery. Watch the ammeter. It should register in amperes, one-eighth
of the ampere-hour capacity of the battery, as already explained. If
it registers too high, reduce the voltage of the generator slightly,
by means of the field rheostat connected to the generator. This will
also reduce the amperes flowing. If too low, raise the voltage until
the amperes register correctly. Continue the charging operation until
the cells begin to give off gas freely; or until the specific gravity
of the electrolyte, measured by the hydrometer, stands at 1.24. Your
battery is now fully charged. Throw the switch over to the service
line, and your accumulator is ready to furnish light if you turn on
your lamps.
Occasionally add distilled water to the cells, to make up for
evaporation. It is seldom necessary to add acid, as this does not
evaporate. If the battery is kept fully charged, it will not freeze
even when the thermometer is well below zero.
A storage battery should be installed as near the house as
possible--in the house, if possible. Since its current capacity is
small, transmission losses must be reduced to a minimum.
In wiring the house for storage battery service, the same rules apply
as with standard voltage. Not more than 6 amperes should be used on
any single branch circuit. With low voltage batteries (from 12 volts
to 32 volts) it is well to use No. 10 or No. 12 B. & S. gauge
rubber-covered wire, instead of the usual No. 14 used with standard
voltage. The extra expense will be only a few cents for each circuit,
and precious volts will be saved in distribution of the current.
CHAPTER XII
BATTERY CHARGING DEVICES
The automatic plant most desirable--How an automobile lighting and
starting system works--How the same results can be achieved in
house lighting, by means of automatic devices--Plants without
automatic regulation--Care necessary--The use of heating devices on
storage battery current--Portable batteries--An electricity
"route"--Automobile power for lighting a few lamps.
The water-power electric plants described in preceding chapters are
practically automatic in operation. This is very desirable, as such
plants require the minimum of care. It is possible to attain this same
end with a storage battery plant.
Automatic maintenance approaches a high degree of perfection in the
electric starting and lighting device on a modern automobile. In this
case, a small dynamo geared to the main shaft is running whenever the
engine is running. It is always ready to "pump" electricity into the
storage battery when needed. An electric magnet, wound in a peculiar
manner, automatically cuts off the charging current from the dynamo,
when the battery is "full;" and the same magnet, or "regulator,"
permits the current to flow into the battery when needed. The
principle is the same as in the familiar plumbing trap, which
constantly maintains a given level of water in a tank, no matter how
much water may be drawn from the tank. The result, in the case of the
automobile battery, is that the battery is always kept fully charged;
for no sooner does the "level" of electricity begin to drop (when used
for starting or lighting) than the generator begins to charge. This is
very desirable in more ways than one. In the first place, the energy
of the battery is always the same; and in the second place, the mere
fact that the battery is always kept fully charged gives it a long
life.
The same result can be achieved in storage battery plants for house
lighting, where the source of power is a gasoline or other engine
engaged normally in other work. Then your electric current becomes
merely a by-product of some other operation.
Take a typical instance where such a plant would be feasible: Farmer
Brown has a five horsepower gasoline engine--an ordinary farm engine
for which he paid probably $75 or $100. Electric light furnished
direct from such an engine would be intolerable because of its
constant flickering. This five horsepower engine is installed in the
milk room of the dairy, and is belted to a countershaft. This
countershaft is belted to the vacuum pump for the milking machine, and
to the separator, and to a water pump, any one of which may be thrown
into service by means of a tight-and-loose pulley. This countershaft
is also belted to a small dynamo, which runs whenever the engine is
running. The milking machine, the separator, and the water pump
require that the gasoline engine be run on the average three hours
each day.
The dynamo is connected by wires to the house storage battery through
a properly designed switchboard. The "brains" of this switchboard is
a little automatic device (called a regulator or a circuit breaker),
which opens and shuts according to the amount of current stored in the
battery and the strength of the current from the generator. When the
battery is "full," this regulator is "open" and permits no current to
flow. Then the dynamo is running idle, and the amount of power it
absorbs from the gasoline engine is negligible. When the "level" of
electricity in the battery falls, due to drawing current for light,
the regulator is "shut," that is, the dynamo and battery are
connected, and current flows into the battery.
These automatic instruments go still farther in their brainy work.
They do not permit the dynamo to charge the battery when the voltage
falls below a fixed point, due to the engine slowing down; neither do
they permit the dynamo current to flow when the voltage gets too high
due to sudden speeding up of the engine.
Necessarily, an instrument which will take care of a battery in this
way, is intricate in construction. That is not an argument against it
however. A watch is intricate, but so long as we continue to wind it
at stated intervals, it keeps time. So with this storage battery
plant: so long as Farmer Brown starts his engine to do his farm chores
every day, his by-product of electricity is stored automatically.
Such installations are not expensive. A storage battery capable of
lighting 8 tungsten lamps, of 16 candlepower each, continuously for 8
hours (or fewer lamps for a longer time); a switchboard containing all
the required regulating instruments; and a dynamo of suitable size,
can be had for from $250 to $300. All that is necessary to put such a
plant in operation, is to belt the dynamo to the gasoline engine so
that it will run at proper speed; and to connect the wires from dynamo
to switchboard, and thence to the house service. The dynamo required
for the above plant delivers 10 amperes at 45 volts pressure, or 10 ×
45 = 450 watts. A gasoline, gas, or oil engine, or a windmill of
1-1/2 horsepower furnishes all the power needed. If the farmer uses
his engine daily, or every other day, for other purposes, the cost of
power will be practically negligible. With this system electric lights
are available at any time day or night; and when the gasoline engine
is in service daily for routine farm chores, the battery will never
run low.
This system is especially desirable where one uses a windmill for
power. The speed of the windmill is constantly fluctuating, so much so
in fact that it could not be used for electric light without a storage
battery. But when equipped with a regulator on the switchboard which
permits the current to flow only when the battery needs it, and then
only when the speed of the windmill is correct, the problem of turning
wind power into electric light is solved.
* * * * *
If the farmer does not desire to go to the additional expense of
automatic regulation, there are cheaper plants, requiring attention
for charging. These plants are identical with those described above,
except they have no regulators. With these plants, when the battery
runs low (as is indicated by dimming of the lights) it is necessary to
start the engine, bring it up to speed, adjust the dynamo voltage to
the proper pressure, and throw a switch to charge the battery. For
such plants it is customary to run the engine to charge the battery
twice a week. It is necessary to run the engine from 8 to 10 hours to
fully charge the discharged battery. When the battery approaches full
charge, the fact is evidenced by so-called "gassing" or giving off of
bubbles. Another way to determine if the battery is fully charged is
by means of the voltmeter, as the volts slowly rise to the proper
point during the process of charging. A third way, and probably the
most reliable is by the use of the hydrometer. The voltage of each
cell when fully charged should be 2.5; it should never be discharged
below 1.75 volts. Many storage battery electric light plants on the
market are provided with a simple and inexpensive circuit breaker,
which automatically cuts off the current and stops the engine when the
battery is charged. The current is then thrown from the dynamo to the
house service by an automatic switch. If such a circuit breaker is not
included, it is necessary to throw the switch by hand when charging is
begun or ended.
Since the principal item of first cost, as well as depreciation, in a
storage battery electric light plant is the storage battery itself,
the smallest battery commensurate with needs is selected. Since the
amount of current stored by these batteries is relatively small,
electric irons and heating devices such as may be used freely on a
direct-connected plant without a battery, are rather expensive
luxuries. For instance, an electric iron drawing 400 watts an hour
while in use, requires as much energy as 20 tungsten lamps of 16
candlepower each burning for the same length of time. Its rate of
current consumption would be over 13 amperes, at 30 volts; which would
require a larger battery than needed for light in the average farm
home.
The use to which electricity from a storage battery is put, however,
is wholly a matter of expense involved; and if one is willing to pay
for these rather expensive luxuries, there is no reason why he should
not have them. Heating, in any form, by electricity, requires a large
amount of current proportionally. As a matter of fact, there is less
heat to be had in thermal units from a horsepower-hour of electricity
than from three ounces of coal. When one is generating current from
water-power, or even direct from gasoline or oil, this is not an
argument against electric heating devices. But it becomes a very
serious consideration when one is installing a storage battery as the
source of current, because of the high initial cost, and depreciation
of such a battery.
Farmers who limit the use of their storage battery plants to lighting
will get the best service.
_Portable Batteries_
Abroad it is becoming quite common for power companies to deliver
storage batteries fully charged, and call for them when discharged.
Without a stretch of the imagination, we can imagine an ingenious
farmer possessing a water-power electric plant building up a thriving
business among his less fortunate neighbors, with an "electricity"
route. It could be made quite as paying as a milk route.
[Illustration: Connections for charging storage batteries on 110-volt
mains]
Many communities have water or steam power at a distance too great to
transmit 110-volt current by wire economically; and because of lack of
expert supervision, they do not care to risk using current at a
pressure of 500 volts or higher, because of its danger to human life.
In such a case it would be quite feasible for families to wire their
houses, and carry their batteries to the generating plant two or
three times a week to be charged. There are a number of portable
batteries on the market suitable for such service, at voltages ranging
from 6 to 32 volts. The best results would be obtained by having two
batteries, leaving one to be charged while the other was in use; and
if the generating station was located at the creamery or feed mill,
where the farmer calls regularly, the trouble would be reduced to a
minimum.
Such a battery would necessarily be small, and of the sealed type,
similar to those used in automobiles. It could be used merely for
reading lamps--or it could be used for general lighting, according to
the expense the farmer is willing to incur for batteries.
An ordinary storage battery used in automobile ignition and lighting
systems is of the 6-volt, 60-ampere type, called in trade a "6-60."
Lamps can be had for these batteries ranging in sizes from 2
candlepower to 25 candlepower. A lamp of 15 candlepower, drawing 2-1/2
amperes, is used for automobile headlights, and, as any one knows
after an experience of meeting a headlight on a dark road, they give a
great deal of light. A "6-60" battery keeps one of these lamps running
for 24 hours, or two lamps running 12 hours. A minimum of wiring would
be required to install such a battery for the reading lights in the
sitting room, and for a hanging light in the dining room. The
customary gates for charging these batteries in a large city is 10
cents; but in a country plant it could be made less.
To charge such a battery on a 110-volt direct current, it is necessary
to install some means of limiting the amount of current, or in other
words, the charging rate. This charging rate, for 8 hours should be,
as we have seen, one-eighth of the ampere-hour capacity of the
battery. Thus a "6-60" battery would require a 7-1/2 ampere current.
Connecting two such batteries in "series" (that is, the negative pole
of one battery to the positive pole of the second) would make a
12-volt battery. Ten or twelve such batteries could be connected in
"series," and a 110-volt direct current generator would charge them in
8 hours at a 7-1/2 ampere rate.
The diagram on page 259 shows the connections for charging on a
110-volt circuit.
An ordinary 16-candlepower carbon lamp is of 220 ohms resistance, and
(by Ohm's Law, C equals E divided by R) permits 1/2 ampere of current
to flow. By connecting 15 such lamps across the mains, in parallel,
the required 7-1/2 amperes of current would be flowing from the
generator through the lamps, and back again. Connect the battery in
"series" at any point on either of the two mains, between the lamps
and the generator, being careful to connect the positive end to the
positive pole of the battery, and _vice versa_.
Lamps are the cheapest form of resistance; but in case they are not
available, any other form of resistance can be used. Iron wire wound
in spirals can be used, or any of the many makes of special resistance
wire on the market. First it is necessary to determine the amount of
resistance required.
We have just seen that the charging rate of a 60-ampere hour battery
is 7-1/2 amperes. Applying Ohm's Law here, we find that ohms
resistance equals volts divided by amperes, or R = 110/7.5 = 14.67
ohms. With a 220-volt current, the ohms resistance required in series
with the storage battery of this size would be 29.33 ohms.
_Automobile Power for Lighting_
There are many ingenious ways by which an automobile may be utilized
to furnish electric light for the home. The simplest is to run wires
direct from the storage battery of the self-starting system, to the
house or barn, in such a way that the current may be used for reading
lamps in the sitting room. By a judicious use of the current in this
way, the normal operation of the automobile in the daytime will keep
the battery charged for use of the night lamps, and if care is used,
such a plan should not affect the life of the battery. Care should be
used also, in this regard, not to discharge the battery too low to
prevent its utilizing its function of starting the car when it was
desired to use the car. However, if the battery were discharged below
its starting capacity, by any peradventure, the car could be started
by the old-fashioned cranking method.
Using an automobile lighting system for house lighting implies that
the car be stored in a garage near the house or barn; as this battery
is too low in voltage to permit transmitting the current any distance.
One hundred feet, with liberal sized transmission wires is probably
the limit.
That such a system is feasible is amply proved by an occurrence
recently reported in the daily papers. A doctor summoned to a remote
farm house found that an immediate operation was necessary to save the
patient's life. There was no light available, except a small kerosene
lamp which was worse than nothing. The surgeon took a headlight off
his car, strung a pair of wires through a window, and instantly had at
his command a light of the necessary intensity.
Another manner in which an automobile engine may be used for house
lighting is to let it serve as the charging power of a separate
storage battery. The engine can be belted to the generator, in such a
case, by means of the fly wheel. Or a form of friction drive can be
devised, by means of which the rear wheels (jacked up off the floor)
may supply the necessary motive power. In such a case it would be
necessary to make allowance for the differential in the rear axle, so
that the power developed by the engine would be delivered to the
friction drive.
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Transcriber's Notes:
The square root symbol is indicated by sqrt(..)
Exponents are indicated by ^
Bold in a table is indicated by =..=
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