BRIDGE METHODS FOR LOCATING RESISTANCE FAULTS 395 



Applying the Rule of Resultant Faults, the apparent location of the 

 faults as determined by the Varley meeisurement will be at a point 

 between the two faults, and at a distance from either fault which is 

 directly proportional to the fault resistances. Let c be the resistance 



End 2 



I 



Fig. 10 — -Location of a resultant fault. 



of the portion of the wire between the distant end of the cable and 

 the apparent location. Then: 



M 

 F 



X + c 

 X — c^ 

 M - F 



C — X 



M + F 

 When the bridge is balanced for the Varley measurement: 



V 



' = -2' 



Equating the two values of c and solving for x: 



_ V M + F 

 ^ ~ 2 M - f' 



(6) 



Comparison of Formula (6) with the more exact Formula (2) for 

 the same case indicates that the Rule of Resultant Faults will give 

 accurate results only if the fault resistances are high compared to the 

 conductor resistances, and if M is of appreciably higher resistance than 

 F. 



If M equals F, the location will be indeterminate: The two faults 

 will have no effect on the balance point of the bridge and V will be 

 zero. 



