Should I fail this transformer?

[Lukedl83]

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.

[Kalbi_Rob]

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.

[Jgilsen]

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.