Out of phase switching on step up transformer

[Bronzeado]

Hi folks,

Anyone has faced problems with transformer out of phase switching?

Is this condition worst than a three-phase short circuit?

Considering a two windings transformer, what about the sense of the winding currents during this condition? Opposite, like in the short circuit condition?

Thank you for any reply.

Best Regards,

Herivelto S. Bronzeado
Brasília, Brazil

http://www.linkedin.com/profile/view?id=46319837&trk=tab_pro

 

[prc]

Yes. It will be same as a dead 3L fault and I have seen GT failures due to such mistake.[pre][/pre]

 

[prc]

Yes.It will be similar to a 3L fault. I have seen GT failures in such scenario from winding damages due to short circuit current forces.

 

[ScottyUK]

If you get it perfectly wrong at the moment of closure then the voltage driving the fault current around the loop will be double that of a three-phase short circuit fault. The currents will be considerably higher, although probably not double because the limiting effect of external impedances.

 

[waross]

A thought for discussion:
At first I thought the currents would be double but then I considered that the impedances would also be doubled. The result for equal transformers would be similar to a bolted fault on each one (neglecting external impedances).
However, in the case of transformers with unequal impedances, the current would be the result of the sum of the voltages of both transformers driving the current through the sum of both transformer impedances. This may result in a greater than expected current through the "less equal" transformer. The magnetic forces may exceed the strength of the bracing in the less equal transformer.


Bill
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