TESTING 



675 



or 



y = 



L- 



L - 



-Ri 



(L - 



ifr-a 



iRi (L - Ri) 



~ \B^~grx 



(2) 

 (3) 



Practical details concerning the application of this test to long 

 submarine cables are given in the Journal of the Institution of 

 Electrical Engineers, 1885, vol. 16, page 581. 



The Volt-ammeter Test. In this method it is necessary 

 to have between the testing stations, a second and unfaulted 

 conductor which can be used as a potential lead to the far end 

 of*. 



FIG. 417. Volt-ammeter method for fault location. 



In Fig. 417 the faulted wire is shown by ab, the unfaulted one 

 by dc] V is a voltmeter and A is an ammeter. With these con- 

 nections a regular fall of potential measurement of x may be 

 made. 



The P.D., V x , between the terminals of x, will be given by 



where Fi is the reading of the voltmeter and R v is the voltmeter 

 resistance. If /i is the reading of the ammeter, the current 

 through x will be 



If r is an appreciable fraction of R v , it may be eliminated; to 

 do this transfer the ammeter connection to d and make a second 

 measurement. Call the reading of the voltmeter, V*, and that of 

 the ammeter. 7 2 . Then the voltage accross the ends 



V r = 



