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BELL SYSTEM TECHNICAL JOURNAL 



cable, the capacitances and hence the fault current may be fairly large, 

 particularly if the voltage is high. Of course, in an actual system 

 the capacitances to ground are distributed throughout the system so 

 that the amount of residual current in the lines will vary from location 

 to location, being a maximum at the fault and tapering to zero at the 

 end of each branch of the system. 



STEP-UP 

 TRANSFORMER 



TRANSMISSION LINE 



(A) 



LOAD 



STEP-UP 

 TRANSFORMER 



TRANSMISSION LINE 



LOAD 

 TRANSFORMER 



Fig. 8 — Types of power systems. {A) Isolated neutral system under normal 

 conditions. (B) Grounded neutral system under normal conditions. (C) Isolated 

 neutral system with single fault. {D) Grounded neutral system under fault 

 conditions. 



If, in a power system, a second fault-to-ground occurs on another 

 phase while the first persists, a large residual fault current will exist in 

 the line between the faults even if the neutrals are isolated. Simul- 

 taneous faults on two phases at different points may occur on any 

 type of system, but are more likely to occur on an isolated neutral 

 system than on one in which the neutral is solidly grounded. This is 



