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Why is LL bigger than 3ph fault

Why is LL bigger than 3ph fault

Why is LL bigger than 3ph fault

(OP)
Hi,

I have just obtained some fault currents result from using SKM, it shows that both the SLG and LL(phase to phase) is much higher than the 3ph fault.

With SLG fault I can figure out that it is possible (due to low sequence impedance) but why is the phase to phase fault bigger than the 3ph fault?

Thanks

RE: Why is LL bigger than 3ph fault

(OP)
Correction...

it should be LLG (double phase to ground fault) not LL....

Why is LLG bigger than 3ph fault? Because of low zero sequence impedance from generators and transformers?

Thanks

RE: Why is LL bigger than 3ph fault

Not necessarily LLG is greater than 3 phase fault. This is a function of the system sequence impedance at the fault location. See the enclose figure that may be used as a guide to determine maximum fault level.

http://cuky2000.250free.com/SC_Highest_Sort_Circuit.jpg

RE: Why is LL bigger than 3ph fault

Delta/wye transformers ahead of the fault location short circuit the upstream zero impedance network regardless of fault type. Any fault involving the zero sequence network will see a low zero sequence value.

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