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pc1981
Active Contributor

Join Date: Oct 2012
Posts: 16

Just Lost a GT

03/23/2013 12:05 AM

One of the station GT's tripped with 87 relay. The IR of the HV winding to earth was measured and found to be very low - 5 MOhms with a 5KV insulation tester. While performing the Tan Delta test (Chg) the tan delta test set tripped at 7.3KV and smoke came out from the Neutral Bushing of the GT. The BDV of the insulating oil is good 50KV, moisture content is low 40 ppm. Transformer was in service for the last 40 odd years. We will be carrying out further tests today to make an assessment of the condition of the transformer.
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Anonymous Poster #1
#1

Re: Just Lost a GT

03/23/2013 10:54 AM

Keep the boss informed. Nothing for us to go on yet! :-)
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pnaban
Guru

Join Date: Jun 2010
Location: srilanka
Posts: 2725
Good Answers: 5
#2

Re: Just Lost a GT

03/24/2013 5:44 AM

give more details of GT

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 pnaban
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67model
Guru

Join Date: Dec 2010
Posts: 1686
Good Answers: 116
#3

Re: Just Lost a GT

03/27/2013 5:56 AM

It is not clear if you are testing the GT generator or the step-up transformer or both.

Often, generator cabled or busbar-ed direct to transfo at LV in normal use - with overall 87 relay.

You need to split them (un-boltable busbar sections in generator line cubicle??) to isolate fault.

67model
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pc1981
Active Contributor

Join Date: Oct 2012
Posts: 16
#4
In reply to #3

Re: Just Lost a GT

03/27/2013 8:03 AM

Thanks guys for your inputs...we have managed to recover the transformer...it was a strange case of failure of neutral bushing...after replacement of the bushing the transformer is alright now
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67model (1); Anonymous Poster (1); pc1981 (1); pnaban (1)

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