Generator Protection systems 1

[ruggedscot]

Have one to ask....

Setting up for a generator panel I take it requires some specialist theory, Im looking at a situation that happened and want to try and work out if this would have been an expected result or if there was an issue with protection grading.

Scenario multiple generators set up to a paralleling board. This linked as a neutral seperated system. ie the first generator to start and connect to bus the neutral breaker closes. All other sets the neutral breaker remains open - reduces circulating currents.

The generator board feeds out to other boards that have utility / generator automatic selection fitted. No utility availiable then the source changes to generator. A signal is sent to start the genertators. If already running supply will connect when the generator breaker closes at panel. Anyway fault happens at remote board. This causes shut down on the generators as an overcurrent fault.

I think that this indicates a problem with the set up - should I have not seen the breaker on the generator board feeding the faulted board open and the generators keep running ? Lost all supplied boards as the breaker did not clear the fault allowing the fault to affect multiple users.

Generic thinking of this leads me to think that these must be some differentiation on setting up of ACB's as generators can not supply what would be typically supplied from a utility source under a faulted condition. Is there a specific routine that is followed up for setting acbs up that are supplied from generator and not utility sources?

All advice and thoughts would be greatly appreciated.

 

[ScottyUK]

Rugged,

Implementing zone protection - not a trivial task, especially as a retrofit - would remove some of the need for coordination between breakers. Zone protection is designed to operate very quickly for a fault within the zone and to remain stable for a fault outside the zone. You might want to read up on the classic Merz-Price circulating current relay as an introduction. The old names 'Translay' and 'Solkor' were competing products from GEC Relays (happy days before the French got involved) and Reyrolle respectively and there is a lot of information out there. Areva's MBCI relay is a good modern(ish) example of a Translay relay which is designed for feeder protection. For differential protection of the generator and possibly the switchgear Areva's MFAC series of realys is worth a look as an example.

The following link is absolutely worth downloading, better still if you can spend some of your employer's budget on a hard copy:

http://www.areva-td.com/static/html...typid=1107432285131&productline=1079943326752

Chapters 10, 15, 17, and 18 would make particularly good reading given what has happened, but better to read the whole thing if you have time.


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