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Onsite high voltage test for 420MVA

Onsite high voltage test for 420MVA

Hello Everyone,
We had just finalized onsite repair for 420MVA/18/220kV.The high voltage exit leads had been replaced due to poor crimping.
Part of the repair scope is to conduct high voltage test by the repair company.
What is the best practice in this case, should we hire third party to witness the test and judge/interpret the test results.should the repair company provide test procedure and acceptance criteria.
Appreciate your advice.

RE: Onsite high voltage test for 420MVA

If HV test is part of the scope by the repair company, which is the usual norm, then why would you need a 3rd party to certify the testing? Normal standard is for the repair company to provide the valid calibration certificates for their test equipments and then accept their test results.


RE: Onsite high voltage test for 420MVA


I guess you need third-party verification if you don't have sufficient expertise in-house to be certain that the tests are being performed correctly, or if you have a suspicion that the repair company is trying to take short-cuts.

On a transformer of that size - a generator transformer by any chance? - the companies with the required skills to undertake the repair are fairly limited in number and all have a reputation to protect, at least in this patch of the world.

RE: Onsite high voltage test for 420MVA

Hi Scotty

"the companies with the required skills to undertake the repair are fairly limited in number and all have a reputation to protect".

That's why I don't see them cutting corners, especially if they carry the warranty.


RE: Onsite high voltage test for 420MVA

powerzizo, I am referring to your posting nearly one year back on the subject. First of all, the poor crimping was on HV neutral end leads to tap changer. In service these leads are not at 220 kV potential but at earth potential. The defect was in crimping of copper lead and nothing to do with lead insulation. One unit has been already repaired and in service with out HV testing. Then why do you want to do HV testing on this unit? It is not an easy task to do any overvoltage test on transformers at site and it is done very rarely using special test equipment. The points to check in this repair- are they using proper terminals and crimping tool and dies so that similar defects will not be repeated. Are they employing skilled technicians? In factory we generally employ only certified technicians. Measure and confirm the winding resistance of lead (that was repaired) before oil filling. I don't think any HV test other than normal LV tests are required in this case.

RE: Onsite high voltage test for 420MVA

Site testing of 420kV transformer HV test, I have not heard about such capabilities of any contractor!

RE: Onsite high voltage test for 420MVA

Those that don't have the capability in-house will sub-contract it out to the likes of IPH in Berlin or CESI in MIlan. From the client's perspective the repair contractor is delivering the required tests.

RE: Onsite high voltage test for 420MVA

The high voltage test may determine that no debris was inadvertently left behind in the transformer.
A spot of dirty grease left behind from a tool can cause a flash-over in the transformer oil.

"Why not the best?"
Jimmy Carter

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