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What to expect on primary of delta-star (grounded) transformer with an L-G fault on secondary?

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Power0020

Electrical
Jun 11, 2014
303
I am a bit confused with the behavior of a delta-star (grounded) transformer with a line-to-ground fault on secondary.

Basically as I understand, fault current affecting faulty wye phase will induce a similar current on corresponding delta limb to sustain magnetic balance of the yoke. The confusion is about the line current in the delta side, would it be affected by the fault? or the induced current will tend to circulate inside the delta since its basically a zero sequence current that has no path outside the delta?

Any clue?
 
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Well if it is three transformers in a bank, a line to ground fault will be a line to line load or fault on the primary.
If it is a three phase transformer with a three legged core the phantom delta may add some unexpected results.

Bill
--------------------
"Why not the best?"
Jimmy Carter
 
If the fault current on the wye side is in only phase winding the it will also only be in one winding of the delta. No current in windings of the delta that don't also have corresponding current in the wye. Thus, a low-side line-ground fault on the wye shows up as a line-line fault on the delta side.
 
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