Delta Wye Transfomrer Grounding 3

[HamidEle]

We have a Generator Delta Wye step-up transformer ( 4160V/27600V) to be connected to the Utility. The 27,600V Utility Side is normally solid grounded system, but not in the rural areas. So it is likely that the 27600V line around the Delta winding side of the transformer see the transient overvoltages during the ground faults. One solution is to add a Zig-zag transformer to mitigate this overvoltage. But it would be very expensive to do that. How successful it would be, i don't know. Are there other solutions?

Thanks in advance.

 

[HamidEle]

One disvantage of adding Zig-zag transformer to delta side of the transformer is, two grounding sources will make the grounding system less sensitive and the utility side may have to adjust their ground fault setting..

 

[xxjohnh]

Use surge arestors on the high side, nothing to worry about.

 

[waross]

If the utility side wye is connected to ground couldn't there be an issue with overheating the wye point for unbalancd loads on the secondary delta when operating from the utiltiy source?

If the primary wye point of a wye/delta transformer bank is connected to neutral (which is probably grounded) unbalanced primary voltages may cause circulating currents in the delta.

Couldn't there also be an issue with false ground current returing on this wye grounded connection for unbalanced delta secondary? I always thought it was best to leave this wye primary floating for such reasons?

You don't get "false ground current", you get true neutral current returning on the neutral.

Leaving this floating however would then create an ungrounded situation when operating with the generator as the source.

Yes. if unbalanced high voltages may be an issue it is better to go with a wye/wye transformer. The conditions most likely to cause issues are a generator that is small relative to the utility system and a connection to a distribution circuit with a lot of single phase loads that may cause neutral currents and neutral phase shifts.

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

 

[QBplanner]

Hi HamidEle:

To answer your question, if the O/V is the power frequency positive sequence one, we can solve the O/V by adding high voltage reactors or high energy arrestors.

If in your cases, the O/V has zero sequence components due to the unblanaced fault and system grounding conditions, you already got answers from the others.