TRANSMISSION LINES. 351 



would be 



E l 20,000 -+ 1/3 = 1 1,550 volts (see Fig. 298). 



The electromotive force between mains at the generating sta- 

 tion is to be 23,000 volts. Therefore, 



= 23,000 volts H- !/3 = 13,280 volts (see Fig. 298). 



Further specifications: P= 1,000 kilowatts, cos 0=o.8 5, 

 frequency = 60 cycles per second, distance = 30 miles, distance 

 apart of wires = 2 1 inches. 



From these data we find /= 34 amperes, and r' = 50.9 ohms. 

 Therefore, approximately, a number 5 wire is required. The 

 reactance x of a 3O-mile double line of number 5 wires, 21 inches 

 apart center to center, at 60 cycles per second, is 



;tr = 41.2 ohms 



which substituted in equation (i) gives 



r 46. 5 ohms 



so that a wire between number 4 and number 5 would give the 

 prescribed line drop. 



162. Interference of separate alternating-current transmission 

 lines. When a telephone line is near an alternating-current 

 transmission line, an alternating current may be produced in the 

 telephone line in three ways, as follows : (a) By magnetic induc- 

 tion, that is the alternating current line may act like the primary 

 and the telephone line like the secondary of a transformer ; (&) 

 By electrostatic induction. The alternating current transmission 

 wires are repeatedly charged and discharged with the alternations 

 of the electromotive force, and the telephone wires are repeatedly 

 charged and discharged " by influence," that is, the positive 

 charge on the alternating-current wires draws a negative charge 

 into the telephone wires from the ground, and a negative charge 

 on the alternating current wires draws a positive charge into the 

 telephone wires from the ground. This charging and discharging 

 of the telephone wires produces an alternating current in the 

 telephone line ; (c) By leakage. If the alternating- current line 



