PI test show (OL) the tester reached the limits of reading 40G

Electrical Testing Talk
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Testing 11kva transformer LV to HV - 1000v PI test 10min/1min

at 10 sec IR read 7.39G ,at 60 secs IR tester read 22.8G but after 3 mins the tester reached the limits of reading 40G for 1000v and show OL.on the screen.

How can the PI test be continued in this way? Are there other options to complete the test?

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So you reached 40G after 3 minutes? Full scale is good, keep running for the remaining 7 minutes and document your readings as 40G. Assuming the insulation you are testing is 1000V rated, 40G is well above acceptable.

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Thanks for reply
I am confused how to complete the PI test If I don’t get 10 minutes reading؟ resistance is too high.
Should I try lowering the voltage 500v? but i know that 20G is the limits reading for 500v option.

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Reducing the voltage to 500V is not a good method. Prepare the device manual indicating that the measurement device displays ‘OL’ when it exceeds ‘40G’, and take a photo showing ‘OL’. In the report, note it as 40G< and then calculate the PI as 40G.

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Sounds like a pass. Document it. I’ve had to include pictures when my MEGGER maxes out because just putting a 3TOhm~ as a result for minutes 5 and up with a flat line graph doesn’t really relate to non testers.

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PI test is technically only viable if the 1 minute reading is below 5 gigohms and if required another form of insulation resistance is required:

IEEE 43 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.

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