Co-Gen Wye,Wye Ground connection

[ghostbuster7]

The customer has a 10 MW. generator(4160 volt) wye connected to a wye-wye (27.6 kv.) step-up tx.There is no neutral wiring between generator and tx.The wyes at the tx. are solidly grounded and the wye at the generator is grounded thru a .4 ohm reactor.

There is no power to the high side of the tx.Turning on the generator,the reactor instantly blew and over 300 amps of current was recorded going thru this reactor.

The customer has been told to simply float the grounds either at the geny or tx. end and this will remove this ground current component.

With this proposed new set-up,I am concerned about voltage stability,generator warranties and system phase to ground faults.Any comments?

 

[Skogsgurra]

Better find the problem and fix it. There shouldn't be any current if everything is OK.

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[waross]

I calculate a phase current of around 1400 amps. Your wye-wye connection acts similar to three single phase transformers. Any unbalanced currents must flow in the neutral connection.
If your energization surge is x 10, you will see as or more than 14,000 amps on the neutral connection.
If you float the neutral you may experience switching over voltage transients when energizing the transformer.
I suggest a solid connection from the generator neutral to the transformer neutral. The conductor should have voltage drop and ampacity sufficient for the worst case operating unbalance, and should have a withstand capacity (and voltage drop) suitable for the energization surges.
The grounding issues, (solid ground, impedance ground, and single point or multi point grounding,) will be issues for the protection group.
On the next project consider a wye delta transformer with the delta fed from the generator.

Bill
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"Why not the best?"
Jimmy Carter