36 TRANSMISSION LINE FORMULAS 



PROBLEM A. 



Find by the K formulas, the line drop in the following case: 



Length of line ........................ 100 miles. 



Spacing .............................. 8 feet. 



Conductor ........................... No. 3 copper cable. 



Load (at receiver end), 3000 K.V.A., 66,000 volts, 90% P.F., 



three phase, 60 cycles. (Prob. A, Chap. III.) 

 From the tables, r = 1.078, x = 0.840. 



D looo X 3000 X 0.90 

 P = ' - = 40.91. 



66,000 



= looo X 3000 X Q.4359 = gl> 

 66,000 



A = 66,000 66,000 X -- 

 100 



+ 19.81 X 84(1 -f X^) 

 \ 6 100 / 



= 70,580 volts. 



B = 66,000 X^X^ 



0.840 ioo 



* X 



3 ioo 



3150 volts. 



40.9! X 84(1 -X}- 19.81 X 107.8(1- 

 \ 6 ioo/ V 



Supply voltage = 70,580 + * = 70,650. 



Line drop = 4650 volts = 7.05%. 



By the fundamental formulas, using the same line constants, the 

 line drop is 7.08% (Prob. 2, Chap. VI). The discrepancy is 0.03% 



of line voltage. 



PROBLEM B. 



Find by the K formulas the voltage at the supply end of the 

 following line: 



Total length of line ......................... 300 miles. 



Spacing ................................... 12 feet. 



