Dear Sirs, I am a technical persons.In one of our Electrical Sub- Station, We

Dear Sirs,
I am a technical persons.In one of our Electrical Sub-
Station, We have installed three numbers of
1250KVA ,11KV/0.415KV Transformer to feed the Factory load.
We have found some abnormality. In one of our Transformers
the leakeage current from transformer body to earth through
earth continuity wire is almost 86 Amp but in other
transformer it is (5-10)Amp. where the load current on
three phase and neutral are respectively
1360Amp,1400Amp,1370 Amp & 176Amp. So please any technical
person help me about the reasons of this situation and how
I can rectify the fault. Moreover,I have measured the earth
resistance of the Earth continuity wire which is less than
1 Ohm.

Thanks

Tapas Barua

Question Posted / tapas barua

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Dear Sirs, I am a technical persons.In one of our Electrical Sub- Station, We have installed three..

Answer / anadi biswas

Hi dear,
First of all tell me the condition
Are all these running parallel?If yes,then check the
individual winding to body insulation resistance with a
Multimeter.
Also you may check the transformer oil properties i.e.
dielectric strength as well in order ensure the minimum
leakages.

If individually connected , then check all the above+ the
nature of loads connected with the earthing system.
Also in all the above case check the body earthing of each
tranformer with Earth pits connected and individual earth
pits and measure the value. You will get the conclusion.

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Dear Sirs, I am a technical persons.In one of our Electrical Sub- Station, We have installed three..

Answer / sreenu

Hi dear,

Pls check the differential relay is not working properly, if its work this problem not faced. Pls check the primary current is equal to secondary current more than 30 times to the secondary winding.

Ex; if u have 2500kva transformer gives secondary current as per designing it vl gv 3477Amps is equal to primary current. Both r matches their is no problems transformer.

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Dear Sirs, I am a technical persons.In one of our Electrical Sub- Station, We have installed three..

Answer / k.prakashchandra

Check the insulation resistance of No. 1.Connect a voltmeter
between body and the earth and measure the leakage voltage
which is expected to be more 86V.Unbalanced currents are
also due to contact resistance .

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