TRANSMISSION OF POWER BY ALTERNA TING CURRENT 383 



live force in loop CA , provided the conductors are symmetrically 

 spaced. 



In the three-phase case, therefore, the reactance per conductor 

 is found by equation (85), page 381, or by consulting the tables, 

 page 465. The distance between the centers of conductors is 

 used for D. 



Example. A three-phase line consists of three 0000 solid conductors 

 placed at the corners of an equilateral triangle, 4 ft. on a side. Find the 

 reactance drop per conductor per mile when a 25-cycle alternating current 

 of 120 amp. flows in the conductors. 



X = 2r25(80 + 741 log, '^JIQ~ 6 ohms. 



= 157(80 + 741 X 2.32) lO" 8 

 = 157 X 1800 X 10~ 6 = 0.282 ohm. 

 The voltage drop 



V = 120 X 0.282 = 33.8 volte. Ans. 



Instead of calculating the reactance X, it may first be found 

 in Appendix I, page 465, for 60 cycles per second, its value being 

 0.677 ohm. The 25-cycle reactance is 25/60 of this value, and 

 is equal to 0.282 ohm. 



160. Transmission Line Capacitance; Single-phase. If a 

 direct-current voltage be applied to a transmission line under no- 

 load conditions, no current flows 

 after the first few moments, except 

 the almost negligible leakage cur- 

 rent. It an alternating voltage be 

 applied to a transmission line, consid- 

 erable current may flow, even if there 

 I" no appreciable leakage and no 



connected load. This current is the 



'ling current of t he line, and leads 

 the voltage by almost 90. The line PM. 347, i .i.-tr-.-tatu -flux bo- 

 acts as a condenser, t he conductors 



tin- plates and the air the dielectric. Each conductor 

 becomes charged, first positively and then ly, which 



re>ult> in an altrrnatiim current. 



This is illiMrai.-d 1,\ \'\^. :U7. which shows conductors A and tt 

 of a siimlc-phasc line. At the instant shown, conductor A is 

 po>itivr and conductor tt is negative. The electrostatic flux 



