TRANSMISSION OF POWER HY ALTERNATING CURRENT 389 



Example. It is desired to deliver 4,000 kw., single-phase, at a distance of 

 25 miles, the load voltage being 33,000 volts, 60 cycles, and the power-factor 

 of tin- load bring 0.85. The conductors are spaced 4 ft. apart. The line loss 

 shall not exceed 10 per cent, of the power delivered. Determine: ^/'thesi/i- 

 of conductor; (6) the resistance drop per conductor; (c) the reactance drop 

 p. -r conductor; (d) the voltage at the sending end; (e) the line regulation. 

 Neglect capacitive effects. 



(a) The line loss = 4,000 X 0.10 = 400 kw. = 400,000 watts. 

 The loss per conductor = 400,000/2 = 200,000 watts. 



The current / = 



1*R' = (142.5)*#' = 200,000 watts. 



R' = 200,000/ (142.5) 2 = 9.85 ohms. 

 Res. (per mile) = 9.85/25 = 0.394 ohm. 



From Appendix H, page 464, the wire having the next lowest resistance 

 per mile is 000 A.W.G., the resistance of which is 0.333 ohm per mile. 



Ans. 

 (6) Total resistance per conductor 



72 = 25 X 0.333 = 8.34 ohms. 

 IR = 142.5 X 8.34 = 1188 volts. 



(c) From Appendix I, page 465, for 000 conductor and 48-in. spacing, 

 the reactance per conductor is 0.692 ohm per mile. 



Total reactance per conductor, X = 25 X 0.692 = 17.3 ohms. Ans. 

 The reactance drop 



IX = 142.5 X 17.3 = 2,470 volts. Ans. 



(d) Applying equation (90), using volts to neutral (E R = 16,500 volts), 

 cos 9 = 0.85 6 = 31.8 sin e = 0.527 



= \/(16,500 X 0.85 + 1188)' + (16,500 xT.527 + 2470) 

 = V(15,220) + (11,170)' = V357 X 10 == 18,900 volts, 



The volt.-me at the generator = 2 X 18,900 = 37,800 volts. Ans. 



(e) The line n-gnlntinn is dcfim-d as the rise in voltage when full load is 

 thrqym off the line, divided by the load voltage. 



. . 37,800 - 33,000 



Regulation = - or 14.4 per cent. . 1 us. 



oo,uuu 



164. Three-phase Line Calculations. The advantage of 



working t r;in>mii<>ii line problems to neutral is much nuuv 

 obvious in tlnvc-pliMM' lines th;m in single-phase lines. I 

 354(f/ i 1 1m < --phase system, each romlm-tor >! \\lnVh 



/.' "(mis and a n-:ii-t:mr^ of .V olmi-. The 

 to neutral at the load is E R and t h< voltage to neutral at the send- 



