[Electric engineering.] . mos, so few thatit is not worth while considering such systems. Practically 30 ELECTRIC TRANSMISSION. 14 all the current is distributed at constant potential and, inAmerica, compound-wound dynamos are generally used. The motors used inconnection with suchconstant-potential sys-tems are generally ofthe shunt type, if usedfor ordinary stationarywork, such as drivingmachinery. If used forrailway work, hoisting,mine haulage, etc., theyare of the series some kinds of spe-cial work, such as run-ning printing presses,elevators, etc., com-pound-wound motorsare used,
[Electric engineering.] . mos, so few thatit is not worth while considering such systems. Practically 30 ELECTRIC TRANSMISSION. 14 all the current is distributed at constant potential and, inAmerica, compound-wound dynamos are generally used. The motors used inconnection with suchconstant-potential sys-tems are generally ofthe shunt type, if usedfor ordinary stationarywork, such as drivingmachinery. If used forrailway work, hoisting,mine haulage, etc., theyare of the series some kinds of spe-cial work, such as run-ning printing presses,elevators, etc., com-pound-wound motorsare used, but such mo-tors are few in num-ber compared with theothers. 35. Simple Power-Transmission System. About the simplest pos-sible system of electric-power transmission isthat shown in Fig. we have a com-pound-wound dynamoShunt Wound j[ driven by means ofan engine not dynamo sends acurrent through themotor B by means offig. li. the lines M, M. The dynamo is driven at a constant speed and its series winding. Motor § 14 ELECTRIC TRANSMISSION. 31 is adjusted so that the pressure at the terminals of thedynamo rises slightly as the current increases, due to theincrease of the load on the motor. This slight rise in volt-age is to make up for the loss in pressure in the line, aswill be explained later. The pressure at the motor as awhole, however, remains nearly constant, no matter whatload the motor may be carrying, but the current suppliedincreases as the load is increased. Of course, lamps couldalso be operated on the same system, although it is advi-sable to have separate circuits for the lamps and motorswhenever possible, because if the load on the motor fluctu-ates, it is apt to cause variations in the lights. When bothlights and motors are operated, such a system would probablyuse a pressure of 110 volts at the receiving end of the circuit;if used for power alone, a pressure of 250 or 500 volts would beemployed. It should be mentioned that when the receivingend
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