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How to electrical test (PAT test) large transformers?

KC

Hello,

I need to PAT test a range of single-phase and three-phase transformers, from 15kVA up to 90kVA. These include both isolation transformers and step-down transformers.

While I have experience with general PAT testing and various PAT tester devices, I'm unsure of the best procedures when it comes to testing larger items like these.

For example, I understand that performing a leakage test using a traditional PAT tester isn’t feasible in these cases. Any guidance or best practices on how to approach testing of this kind, particularly in terms of safety checks, insulation resistance, earth continuity, and functional testing would be greatly appreciated.

Thanks in advance for your help.

  • 0 in reply to mapj1

    Leakage inductance may be measured by short circuiting one winding of the transformer, and applying a much reduced voltage to the other winding. Adjust this voltage until normal load current passes.

    I have done this, years ago, a few hundred volts was applied to the 11kv side of a distribution transformer, whilst the LV side was short circuited.

  • 0 in reply to broadgage

    This is very true - thinking back I too have seen this sort of thing done, though only as a customer witness, with something like 230 or 110V on the 7/11kV side of things. Rather like running a current transformer with no load one has to know exactly what one is expecting and in my defence I was being a bit quick as I wanted to keep the explanation simple, but just mention it in case the OP had seen both inductance terms somewhere and to point out that there are 2 very different parameters not to be confused, and different tests.

    A fall in magnetising inductance - an increase in no load primary current is a good indicator of trouble cooking.
    M.

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