Earth Fault Current of a Generator

If it isn't in your text book, then this may help: Fault (power engineering) - Wikipedia, the free encyclopedia

Wasn't what you needed? My point is that as with your previous questions, this can be found by performing a simple search.

assuming the sequence impedances of the generator are all equal zero .

X1 = 0 & X2 = 0 & X0 = 3*63.5 = 190.5

for (L-G) fault the fault current will be 100 as you said .

for (L-L-G) fault the fault current will be (6350)/(x1+x2//x0) = infinity

for 3-phase fault the fault current will be (6350)/x1 which equals infinity or the maximum capacity of the generator

so for proper calculations you should know the sequence impedance of that generator

For 1 phase to ground, that is simple and Ok for 100A

For 2 phases to ground, there will be inter-phase current that does not go thru the NGR, but directly via ground resistance (which could be very small resistance compared to the NGR of 63.5Ω!) and high, limited by earth resistance at site...

For 3 phases, the fault is similar to 2 phase fault in the sense that it will be via ground and not thru the neutral dround resistance! This will be almost a short circuit condition on the generator terminals, limited only by earth resistance between the phases: Site conditions and type of ground location where it occurs. This will not be ZERO!!! even though you thing that the vectors eliminate at the neutral, that is only for Neutral returning currents but not the phase current flowing within the generator!!

Up to you to figure out the equations! I give only a tip of what is the problem...

If more than one phase is grounded at once, expect the conductor overcurrent protection device to operate on at least one of the phases. The imbalance device will pull out the final phase if its overcurrent device didn't operate at the point of grounding one or both of the other two phases. If none of these devices operates then expect the generator to be on fire/scrap metal/exploding.

Please makse sure all other CR4 readers are standing well back before carrying out this particular madness.