10 MVA generator and vacuum breaker - best practice?

[Skogsgurra]

I was dragged into a discussion about a 10 MVA 6 kV generator that had an insulation failure after five years of operation. It turned out that the company that had delivered the electrical gear (one of the Top Ten - one could say Top Three - suppliers in Europe) had chosen vacuum breakers for the turn-key delivery and also chosen not to include any overvoltage protection. So, after around 750 operations, there was enough damage to the stator winding to create a flash-over during operation.

Problems with vacuum breakers are well known (I had my first experience with that in 1974) and that makes me wonder: If you choose to use vacuum breakers for a 6 kV 10 MVA generator, wouldn't you also choose to install surge arresters? I, personally, regard that as best practice. What is your opinion?

Gunnar Englund

http://www.gke.org

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

 

[edison123]

If it is connected to a grid (direct or through a trafo, doesn't matter), surge arresters should have been a part of the system.

What sort of winding failures did they face ?

*Why make the same mistake twice when there so many new ones available*

 

[dpc]

For a 10 MVA unit, we would always specify surge arrester and surge capacitor at the generator terminals. We also typically require surge arrester at the switchgear.

Surge protection at the generator is standard practice for medium-voltage, and part of IEEE recommendations for generator protection, I believe.