Ground fault on Wye side of Delta-Wye Transformer with grounded Wye Secondary 2

[Ollie94]

When a ground fault occurs on the secondary side of a Delta/Wye Transformer which has it’s Wye secondary grounded, how does the Primary see it as a phase to phase fault?

 

[davidbeach]

Draw out the transformer windings and the current flows. Amp*turn balance must be maintained for each winding; if there's current on one side, there has to be current on the other side, likewise if there's no current on one side then there's no current on the other side.

 

[Ollie94]

Ah right thanks, that makes more sense. What would happen if phase A had an SLG fault on the grounded Wye secondary? Would it appear to be a phase to phase fault between phase A and phase B? And for an SLG fault on phase B it would appear to be a phase to phase fault between phase B and phase C on the Delta primary?

 

[RRaghunath]

It depends on the transformer vector group.
If vector group is Dyn1, SLG fault in r-phase on secondary will have currents in R&B phases on Primary. If Dyn11, it will be in R&Y phases.
If you had done vector group test on transformer, it would be easy to appreciate.

 

[Ollie94]

That’s cleared things up. Thanks for the explanation.