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Should I fail this transformer?

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    Quote Originally Posted by cjones09 View Post
    So today I re did the test and the problem was not the test leads but the jumper cables I was using to short the windings together. I did the test without the jumpers and the readings went to full scale. Most PI values were well over 4. I've been taught that jumpers help reduce voltage stress on the windings but it clearly has a big effect on the readings.
    Where did you find the information on jumpers reducing stress on the insulation when performing a IR/PI test? I could understand AC when energizing these windings, but not so much on a DC test since there is very little resistance between each phase winding.

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    Kalbi_Rob is offline Seasoned Member Pro Subscriber
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    Quote Originally Posted by Kalbi_Rob View Post
    If a very high initial IR reading >5GΩ is found then further PI tests are not needed.

    Reference:
    https://electrical-testing-safety.co...risation-index

    If the IR1 value (at 40 C) is greater than 5000 MΩ, the P.I. may be ambiguous and can be disregarded (see
    12.2.2).

    Reference: IEEE 43-2013 IEEE Recommended Practice for Practice for Insulation Resistance of Electric Machinery Section 11.2 Suitability for operation or continued testing
    FYI, IEEE 43-2013 states:

    12.2.2 Applicability of polarization index when IR1 is greater than 5000 MΩ
    When the insulation resistance reading obtained after the voltage has been applied for 1 min (IR1) is higher
    than 5000 MΩ, based on the magnitude of applied direct voltage, the total measured current (IT) can be in
    the submicroampere range (see Figure 3). At this level of required test instrument sensitivity, small changes
    in the supply voltage, ambient humidity, test connections, and other non-related components can greatly
    affect the total current measured during the 1 min 10 min interval required for a P.I. Because of these
    phenomena, when the IR1 is higher than 5000 MΩ, the P.I. may or may not be an indication of the
    insulation condition and is therefore not recommended as an assessment tool.
    Last edited by Kalbi_Rob; March 29, 2019 at 11:59 AM. Reason: Misquoted reference name NETA instead of IEEE

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    Questionable Jumpers

    Quote Originally Posted by cjones09 View Post
    So today I re did the test and the problem was not the test leads but the jumper cables I was using to short the windings together. I did the test without the jumpers and the readings went to full scale. Most PI values were well over 4. I've been taught that jumpers help reduce voltage stress on the windings but it clearly has a big effect on the readings.
    I have seen the same effect with using jumpers while IR testing MV cables. The cables failed while trying to test a run of 3 at the same time connected with jumpers. I tried testing each cable individually and bolting the cables together and they all passed with both non-jumper methods. The interesting thing was that the jumpers were suspended in open air with seemingly sufficient clearances from other conductors or ground, all testing was performed indoors in a controlled environment. Now I test with as few jumpers as possible.

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