[Electric engineering.] . the line is3,000 volts. Calculate the current in each line. Ans. amperes. 3. 5,000 incandescent lamps are supplied with current from a single-phase alternator, having a frequency of 125, over a distance of 3 loss in the line is to be limited to 10 per cent, of the power deliv-ered and the pressure at the end of the line is to be 3,000 volts. Allow60 watts for each lamp supplied and calculate (a) the size of the linewire; (b) the current in the line; (c) the volts drop in the line; (d) the (a) 126,720 cir. mils, or aboutNo. 00 B. & S. (b) amperes.
[Electric engineering.] . the line is3,000 volts. Calculate the current in each line. Ans. amperes. 3. 5,000 incandescent lamps are supplied with current from a single-phase alternator, having a frequency of 125, over a distance of 3 loss in the line is to be limited to 10 per cent, of the power deliv-ered and the pressure at the end of the line is to be 3,000 volts. Allow60 watts for each lamp supplied and calculate (a) the size of the linewire; (b) the current in the line; (c) the volts drop in the line; (d) the (a) 126,720 cir. mils, or aboutNo. 00 B. & S. (b) amperes.(0 576 volts. L (d) 3,576 volts. voltage at the generator. Ans POWER MEASUREMENT. DIRECT-CURRENT CIRCUITS. 93. It has been shown that the power in watts supplied toany direct-current circuit may be obtained by multiplying thecurrent by the E. M. F. across the lines. For example, inFig. 34, we may, at any time, obtain the watts supplied tothe motor M by multiplying the reading given by the 80 ELECTRIC TRANSMISSION. 14. Fig. 34. ammeter A by that given by the voltmeter V. The num-ber of watts so obtained represents the rate at which work is being done at the in-stant the readings aretaken. It must be re-membered that thewatt is a unit of elec-trical power, not work,and expresses rate ofdoing work. The elec-trical unit of work isthe joule, and whenwork is done at the rateof 1 joule per second,1 watt is combining the volt-meter and ammeter wecan make an instru-ment the indicationsof which will be equal to the product of the current andvoltage, and thus indicate the watts directly. Such aninstrument is calledan indicating wattme-ter. Fig. 35 shows aWeston wattmeter ofthe kind referred principle on whichthis wattmeter oper-ates will be understoodby referring to Fig. stationary coils,consisting of a fewturns of heavy wire,as indicated by a, a,are mounted side byside, and a small coil b, consisting of a large number of turnsof fine wire, is mounted between the
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