Transformer Secondary conductor and short circuit

[petrovich]

Assuming that i have a 1000kva transformer with 33kV D: 300V floating wye:

In a case of a ground fault on the secondary side, will primary delta side contribute to the total fault current on secondary?

 

[jghrist]

If secondary wye is floating, there is nowhere for ground current to go.

 

[petrovich]

Okay, but, what if on the floating wye side phase conductor touches the enclosure or equipment ground, will that cause primary phase current to flow into the secondary side as a source current? or you are saying zero ground fault on the wye side regardless?

 

[davidbeach]

No ground fault current on the secondary until you ground the neutral.

 

[prc]

The only change, apart from no fault current, is phase to earth voltages in other two phases will increase by root3.

 

[petrovich]

I see, that sounds like a good design (floating wye, delta) if you are concerned about GPR? near zero current through the ground won't affect the GPR or GPR calculations is a different story?

 

[waross]

A better design is to use a high resistance ground or a high impedance ground.
In the case of line to neutral loads, your code may require the neutral to be solidly grounded.

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

 

[7anoter4]

Usually in a high voltage substation the low voltage has not outgoing connection that means the ground fault current-in your case phase-to-phase-to ground -does not flow through ground [even if it circulates through grounding grid].
Line_to_Line short circuit with earth connection on the high voltage side it is more likely to occur.
The GPR is connected with remote sources when the current flows through grounding resistance.
A short-circuit on secondary side will appear in the high-voltage circuit, of course, but no current to ground will circulate here.

 

[petrovich]

helpful comments, what do you guys think about line-to-line-to-ground faults. I read that's the current one needs to consider while doing the GPR calcs for ungrounded systems?