Grounding Generators Connected to a Bus at Generator Voltage

These threads may help:

http://cr4.globalspec.com/thread/36055/Neutral-Switch-for-Generators-at-Power-Station

http://cr4.globalspec.com/thread/63974/NGR-of-Parallel-Generators

- MS

Thanks! I should probably search the web and this forum before i post a question. However, one question still remains. What if there is a stator earth fault at one of the generators not connected to the neutral?

Then, the earthed generator would feed into the stator earth fault in the unearthed generator. Now, in the unearthed generator, its REF Relay would trip, as its phase CTs would only sense the fault current and not its neutral Ct. Incidentally, I have recently sent a detailed write-up on tis issue to some other forum members, who were also having similar doubts. Pl. inform me your mail ID thro this forum's mailbox, so that I can send you the same.

But then how the REF Relay would be connected in the un-earthed Genset if its Neutral is not earthed?

Wow, thanks! Would a differential generator protection(87G) work as well as a REF (64R)? If so, under what condition would each be suited for protecting the generator?

Why should you worry about differential protection? Your question revolves around grounding of the neutral and as such your concern should be more on ground fault protection which my paper sent to you would have clearly answered. As regards differential, it does not matter whether the generator neutral is grounded or not. It would operate mainly for phase faults.

The practice of grounding only one generator at a time is good for isolated running plants which are not connected to grid.

But in case of plant connected to grid, then all generators neutrals should be grounded unless and until

1. you have a generating transformer between utility bus and plant bus.

2. gen manufacturer gen damage curve is above the the third harmonic current curve.