Fault in Delta source to grounded wye- Delta transformer 1

[NickParker]

What happens when a single line to ground fault happens in the feeder fed from an Ungrounded source (Delta) to Wye grounded - Delta?

Does this behave like a fault on true ungrounded system? (very small fault currents and rise in line to ground voltages by 1.732 on unfaulted phases)
or
The wye grounded - Delta transformer feeds large current to this fault

 

[davidbeach]

The wye-delta will function as a grounding bank and supply considerable fault current.

 

[waross]

The symmetrical fault current will be 1/3 of the available fault current.
Will the asymmetrical fault current also be 1/3 of the conventional fault current or is there another factor making it either more or less than 1/3?

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[mls1]

The magnitude of fault current will be primarily a function of the wye/delta transformer zero-sequence impedance. For example, if the wye/delta is just a small PT bank the fault current will be very low since the kVA base will be very small. In any case, the wye/delta functions very similar to a zig-zag transformer. In fact, this arrangement can be used to derive a neutral and often includes a resister in the wye neutral to high impedance ground the system.