SWITCHBOARDS AND SWITCHBOARD APPLIANCES. 339 



the essential features of the compensating device are as follows : 

 The voltmeter V is connected to the mains through a potential 

 transformer PT and in series with an adjustable resistance r 

 and an adjustable reactance x through which a current i pro- 

 portional to the line current / is sent from a current trans- 

 former CT, as shown in Fig. 290. The relationship between 



main 



Fig. 290. 



the voltage E Q at the generating station, the voltage E l at the 

 receiving station, the line current /, the line resistance R and 

 the line reactance X is shown in Fig. 291. Let e , Fig. 292, 



Fig. 291. 



Fig. 292. 



represent the secondary voltage of the potential transformer, and 

 let ri and xi be the voltage drops across the resistance r and 

 the reactance x, of Fig. 290, respectively, so that e l is the 

 voltage which acts on the voltmeter. Then, since i bears a 

 fixed ratio to 7 (the ratio of transformation of the current trans- 



