PRV Question

You should follow your local codes or whomever is the Authority Having Jurisdiction (AHJ). CR4 has no authority or jurisdiction over anyone, anywhere. If you desire us to translate into English the reasoning of the AHJ, that we might be able to help.

If I were the AHJ and I knew more about the type of transformer in question I might say just purge and pressurize with inert Nitrogen and put the transformer back in storage. Then again I might declare the transformer as now scrap metal, buy a replacement. There are also a myriad of other intermediate options involving hi-pot testing, oil replacements, among other things.

You have to determine why the PRV operated before you re-energize the transformer.

Did something bump into the tank, was there any switching/lightning in the area, was the PRV defective, did any other protective relaying operate, do you have any prefault DGA to compare with, is there a TDR that caught the misoperation, have you compared the insulation resistance readings with the previous tests, have you done an oil BDV test, any particulate matter/water in the oil, etc., etc.

Contact a trained professional, especially if the transformer is a critical asset.

Once we had PRV operation on a transformer in our plant. It was because the conservator was isolated.

When the transformer was returned to service after maintenance, the personnel forgot to open the isolation valve in the pipe connecting the transformer tank to the conservator.

As we know when the transformer is loaded, the rise in temperature causes oil to expand and there was no way to go as the conservator is isolated.

You may like to check.

Still you should seek your AHJ. We are not your AHJ.

If you are hoping to put this transformer into operation at the very least you must verify that the PRV is the only thing that vented when it was over pressured. If coolant or liquid insulation (oil) is allowed to drip out you may produce a bigger disaster than just an oily floor.

The pressure relief is only there to tell you that some event took place that produced excessive pressure. You have to determine what that is. Certainly your oil tests, if they were done correctly, should help you know whether that "event" that took place was an arc or other fault in the oil. But the only way to be sure your transformer is in acceptable condition to put back in service is to do a complete battery of tests to verify that all the major systems (windings, insulation, bracing, etc.) are good.

I would recommend that you find a good, independent high voltage testing company that can do this, preferably one that is a member of the InterNational Electrical Testing Association (NETA - see www.netaworld.org). They should conduct tests per the "Standard for Maintenance Testing Specifications for Electrical Power Equipment and Systems" published by NETA, which will include such tests as:

• DC Insulation resistance
• DC winding resistance
• Turns ratio test
• Doble Insulation Power Factor or dissipation factor test

These can tell you whether the transformer has experienced a fault that compromises its ability to be put back in service. Don't gamble on something that is probably the largest single cost in your substation.