400 



ELECTRICAL ENGINEERING 



258. Voltage and Frequency. Voltages up to 110,000 volts 

 are now in use for the transmission of large amounts of power over 

 long distances. 



Power is usually generated and transmitted at either 25 cycles 

 or 60 cycles. With 25 cycles the reactance drop in the line is 

 less than with 60 cycles and therefore the voltage regulation is 

 better. In the case of very long high-voltage lines the increased 

 charging current at the higher frequency may counteract the 

 larger reactance drop of voltage. Where power is required for 

 lighting 60 cycles is necessary unless frequency chargers are in- 

 stalled. 



259. Spacing of Conductors. The distance between the con- 

 ductors of a transmission line depends both on the voltage and 

 also on certain points in the mechanical design, such as the ma- 

 terial of the conductor, length of span and the amount of sag al- 

 lowed. The curve in Fig. 374 gives approximately the relation 

 between the spacing of the conductors and the voltage. 



120 



1 100 



10 20 



30 40 50 60 70 

 Ktlovolts between Lines 



100 110 



FIG. 374. Standard spacings. 



260. Single-phase Transmission Line. (1) A single-phase 

 transmission line, Fig. 375, delivers 5100 kilowatts to a receiver 

 circuit at 60,000 volts. If the power factor of the load is 85 per 

 cent, find the generator voltage. 



r = resistance of the line = 20 ohms. 

 x = reactance of the line = 50 ohms. 

 The power delivered to the receiver circuit is 



P = El cos = 5,100,000 watts, 

 where E = 60,000 is the receiver voltage 



and cos $ = 0.85 is the power factor; 



