Electricity for the farm Part 5

A typical crib dam, filled with stone, is shown in section in the diagram, and the half-tone ill.u.s.tration 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.

[Ill.u.s.tration: 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 insh.o.r.e, 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.

[Ill.u.s.tration: 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 acc.u.mulate 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 oak.u.m, 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 pa.s.s 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 ent.i.tled 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 quant.i.ty, 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 s.h.i.+nes or provides heat and power, when and where wanted, simply by touching a b.u.t.ton.

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 compa.s.s 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 compa.s.s 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.

[Ill.u.s.tration: (_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 s.p.a.ce. 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 s.p.a.ce, 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. Pa.s.s one side of this loop in front of an electric magnet.

As the wire you hold in your hands pa.s.ses 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 compa.s.s needle under the wire and see it wag first in one direction, then in another.

[Ill.u.s.tration: 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 pa.s.s 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.

[Ill.u.s.tration: Cross-section of an armature revolving in its field]

[Ill.u.s.tration: Forms of annealed steel discs used in armature construction]

This experiment gives the theory of the dynamo. Instead of pa.s.sing 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 s.p.a.ce. 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.

[Ill.u.s.tration: 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_