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We are having a problem in one unit auxiliary transformer which is having rating of 1600 KVA, 15.75/6.6 KV, oil cooled that one day after normalisation of unit by putting the transformer into service BUSGROUND annunciation has come while racking in its line PT. So after racking out the line PT that annunciation has reset, but since the problem couldn't be eliminated it was not able to be put into service. The 6.6 KV system is ungrounded system here. On meggering the transformer its IR value is found to be about 4 Megaohms while the IR value of the line PT is found to be 20 Gigaohms. So could anybody please help us with what may be the reason behind it and what may be the possible remedy?

Waiting for your sincere reply.

Raj, this query is a repeat of your 24-Sep-08 post. In response, several questions were asked regarding measurements that could be used evaluate the problem.

Your reply to those questions will be helpful.

Regards, Phil Corso (cepsicon@aol.com)