Throughout the western part of the United States much use is made of water power for generating purposes. Power-houses are situated in the bottom of ravines and are operating under heads of water as great as 2,000 feet. The famous Colgate plant on the Yuba River has transmitted power 253 miles, one of the longest power transmissions in the world. Al though the cost of water is small compared with the cost of coal, still the cost of electric power generated from water is not much cheaper than when generated from coal. This is due to the fact that the initial investment in a water-power plant is much greater than in a steam plant of the same magnitude. Much capital must be spent in the contruction of expensive dams, waterways and pipe lines.
Transformers.— One of the greatest ad vantages of electrical energy over other forms of energy is its flexibility. It may be generated in one place, and its pressure may be trans formed from a low voltage to a high voltage. The electrical energy in this form may be trans mitted to a distant place where the reverse transforming process occurs. The higher the voltage under which power is transmitted the smaller need he the cross-section of the trans mission line. A stationary static transformer operating upon the principle of induction is all that is essential to transform alternating cur rents, but with direct current transformation, it is necessary to employ rotating apparatus.
In principle the transformer is a sort of modernized induction coil. Its essential parts are a core of laminated sheet-iron, wound with two coils of copper wire, one coil consisting of a great many turns of fine wire, and the other of a few turns of coarse wire. If the fine wire coil is connected to the line, a current at a much lower pressure can be drawn from the other coil, or secondary, as it is called. If the connec tions are reversed, and the fine wire coil be used for the secondary, a current at a greatly in creased pressure is generated. Thus the trans former can be used either to °step up" or °step down' the pressure, and the ratio of transfor mation depends upon the ratio of the number of turns in the two coils. For instance, if we have an 1,100-volt current that we wish to use for lighting incandescent lamps at 110 volts, we simply use a transformer having a primary coil of 500 turns and a secondary coil of 50 turns.
Transformers have been built for operation on circuits having voltages as high as 150,000 volts. For experimental purposes apparatus for much higher voltages has been developed. At the Pittsfield works of the General Electric Company, located in the Berkshire Hills of Massachusetts, the majority of transformers used in the United States are constructed. This plant was at one time the Stanley Electric Man ufacturing Company operated by William Stan ley, one of the pioneers in the development of transformers and long distance electric power transmitting.
At the Pittsfield works 6,000 hands are em ployed. Here elaborate testing equipment is provided for testing transformers and for re search work. In figs. 7, 8 and 9 are shown three types of transformer in general use in the United States.
Without the transformer, long distance elec tric power transmission would be practically impossible. Therefore, with the development of the alternating current system of distribu tion, the use of the transformer has become very extensive. As the voltage and size of trans
formers have been increased, extensive develop ment has been necessary to overcome the prob lems involved.
In the early development of the transformer air was used generally for cooling the windings. With the advent of oil as an insulating and cool ing medium, the possibilities of the transformer were extended. With the increase in demand for large transformers several forms of tanks for radiating the heat produced in the trans former were developed. For transformers cooled by the air, circulating around the tank, corrugated tanks or tanks with external radia tors were used to increase the amount of sur face exposed. For larger sizes of transformers cooling coils were submerged in the oil and water passed through the coil, thus dissipating the heat. In this way larger output was ob tained with a smaller floor space. Transform ers have been built in sizes up to 25,000 Icv-a.— such transformers being cooled by means of water passing through cooling coils as indicated above.
It is not considered good engineering prac tice in the United States to use direct current for transmission purposes. Alternating current is used for this purpose and direct current is employed for distribution. Several machines have been designed which will transform direct current from one voltage to another voltage. They are termed motor-generators, dynamotors and boosters. A motor-generator consists of a motor and a generator coupled together upon one shaft. The speed of the motor may be va ried, which will correspondingly alter the vol tage generated by the dynamo. A dynamotor consists of two armature windings upon the _ _ same core, rotating in one field. The armature has two commutators, one at each end of the shaft. This type of machine has practically no armature reaction and therefore has a small tendency toward sparking. The main disad vantage of this machine is that it is impossible to vary the field strength for purposes of regu lation without correspondingly altering the vol tage of the dynamo. A booster is a machine used extensively to raise the potential of rail way feeders. Its armature is usually placed in series with the feeder and driven by some ex ternal source of energy. When its field coils are in seri - with the line, it is series booster, arid when the field coils arc connected in multiple it is called a shunt booster. The capacity in watts of a booster is determined by the product of the feeder current into the max imum change of voltage which it causes.
The simplest protecting device con sists of a fuse. Fuses are made in many forms. The link fuse is made in strips, or as wire of an alloy possessing a low melting point. When the current strength exceeds a certain limit, the heat developed in the fuse by the pre-- ire over coming the resistance i the flbt! is S' ficient to melt it and interrupt the service.
Circuit Where heavy currents have to be interrupted an electromagnetic de vice termed a circuit breaker is employed. This device consists of an electromagnet of low re sistance placed in series with the circuit. When the current in the circuit exceeds the normal amount, the magnet attracts an armature which releases a catch, and allows a spring to open the switch governing the circuit.