THE LOCALISATION OF BREAKS AND FAULTS. 493 



to that of the cable (176) the absolute resistance of the con- 

 denser had to be reduced to 



— -=1-78 megohms. ^ 



Toe condenser was accordingly shunted with a resistance of 

 — - — - — -=2*16 megohms. The result was a perfect balance 



on the slides, the apparent capacity being equal to the true 

 capacity, without any correction, within 0-03 per cent. (Note 

 by F.W., The Electrician, February 5, 1892.) 



In another case the insulation resistance per microfarad of 

 the cable was higher than the condenser ; and, notwithstanding 

 that the insulation was reduced by an artificial leak at the 

 home end, the test showed the apparent capacity equal to the 

 true within as close a limit as 0*4 per cent. The figures in this 

 were 



Cable (331-8 nauts) 2-5 megohms and 97 microfarads, 

 Condenser 0-41 „ 59-448 „ 



The condenser was therefore 



0'41 X 59-448=24-25 megohms per microfarad. 



The cable resistance was reduced by the artificial leak to 

 24-25 



97 



= 0-25 megohm 



to have the same insulation per microfarad as the condenser. 



But artificial equalisation is not always practicable, as a 

 shunt of several megohms may be necessary, and high resis- 

 tances of this order are not, as ^a rule, available, and, even if 

 so, lack means of adjustment. In such cases the leakage cor- 

 rection must be calculated and applied. 



In a series of capacity tests on condensers alone, Messrs. 

 Harold W. Ansell and Julian E. Young have shown that there 

 is a very considerable error to be accounted for if only a 

 moderate leakage exists on one of the condensers {The Elec- 

 trician, December 12, 1890, p. 168). The dielectrics being 

 similar, there was no question of any absorption error, and the 

 experiments showed that the leakage error under not unusual 

 conditions might easily put the apparent capacity out to a 

 much greater extent than that due to absorption. 



