Two Transformer in Parallel-LV Bus Fault Current.

       Consider a S/S having two transformers of 132/33kV operating in parallel. one transformer of 25 MVA having leakage reactance of  ??.? %  . and other transformer of 50 MVA having leakage reactance of  ??.? %  . Let the S/S source impedance be negligible as compared to transformer leakage reactance. Find out the 3-phase fault current for 33kV Bus fault.

(Note: Consider Base MVA as 100).

Impedance of 50 MVA transformer to base of 100 MVA (XT1)    %

Impedance of 25 MVA transformer to base of 100 MVA (XT2)    %

Equivalent impedance between source and fault point will be XT1||XT2     %

Using the formula for 3-Ph short circuit MVA = BaseMVA*100/X1, 3-Ph short circuit MVA at 33kV bus will be     MVA

Converting 3-Ph fault MVA to equivalent current at 33kV we get 3-Ph fault current as     Amp.

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