84 ELEMENTS OF ELECTRICAL ENGINEERING. 



39. Voltage drop in transmission lines. A transmission line is 

 of course in series with the circuit to which it delivers current, 

 and the complete solution of the problem of the loss of voltage 

 in a transmission line depends upon the complete solution of the 

 problem of coils in series. This general problem is discussed in 

 detail in Chapter V. 



(a) Voltage drop in a transmission line which delivers current 

 to a non-inductive receiving circuit. Let Of, Fig. 77, represent 



JE t 



Fig. 77. 



the current flowing through the transmission line and the receiv- 

 ing circuit. The voltage E l at the terminals of the receiving 

 circuit is in phase with /, and the generator voltage E Q is the 

 vector sum of E v r/, and xl ; where ;-/ is the electromotive 

 force used to overcome the line resistance, and xl is the electro- 

 motive force used to overcome the line reactance. An examina- 



tion of the figure shows that when 

 the receiving circuit is non-induct- 

 ive the line resistance produces a 

 difference in value between E Q and 

 E v whereas the line reactance pro- 

 duces a difference in phase between 

 E Q and E r * 



(b) Voltage drop in a transmission 

 line which delivers current to a highly 

 ___ , inductive receiving circuit of small re- 

 sistance. Let 01, Fig. 78, represent 

 the current flowing through the trans- 



mission line and the receiving circuit. The voltage E l at the ter- 

 minals of the receiving circuit is nearly 90 ahead of / in phase 

 as shown, and the generator voltage E Q is the vector sum of E lt 



* This statement is made on the assumption that xl is small as compared with JS r 



