Grounding a transformer

[wbd]

Hello,
First the background, then the question.
My system configuration is a 4160V, 2980 kW generator, impedance grounded that outputs to a 4160 - 44kV transformer in a open wye to delta configuration.
Next to this transformer is a distribution substation that feeds town distribution at 4160 V, grounded wye.
The question has come up is: Can we disconnect the distribution sub from its current source, ground the open wye from the generator and feed the distribution circuits from transformer with the generator still able to generate?
Is there damaging currents from grounding that open wye on a impedance grounded generator?
Thank you

 

[dpc]

If I understand what you're asking: You can do it, but you will have to solidly ground the generator if you have line-neutral loads (2400V).

The main reason for the impedance grounding is to limit generator damage on an internal ground fault and to limit generator short-circuit current in case it isn't braced to handle the full line-to-ground current.

If you have solidly-ground the generator and other transformer wye windings, you will also probably have some third-harmonic circulating current. This will be a function of the generator's harmonic voltage. This will reduce your ratings somewhat, but is not usually a major problem.

The main downside will be increased risk to the generator for ground faults. You will also have to review the generator ground fault protection.

Some of the small islands in Southeast Alaska operate this way - connecting their diesel generators directly to the distribution system.

 

[mc5w]

If your substation transformer is 44 KV delta 2400Y4160 it will act as a grounding transformer for a 4160 volt generator that does not have its neutral connected.

Ohio Power likes to do something similar with 13,200 volt delta tertiary windings of their 80Y138 KV primary 40Y69 Kv secondary transformers to get 7620Y13,200 volts. What they do is to hook up the wye side of wye-delta grounding transformer to the 13,200 volt tertiary winding and that serves as the source of zero sequence current. This saves them the cost of a fully rated 138KV delta primary 7620Y13,200 volt substation transformer and primary circuit breaker. As long as the grounding transformer supplies enough neutral current at a reasonable impedance level it works.

 

[woundtight]

I am trying to get data on the diffrent types of transformers. Which is better and why sort of thing. The 2 are a Stack core and a wound core.I continually get conflicting info. Any help would be appreciated