# Insulation resistance testing-won't hold test voltage



## Zog (Apr 15, 2009)

Because you have a wimpy megger:whistling2:

Leakage current is not your problem, it is likely the capacitive charging current and absorbtion currents, both are much higher values than leakage on a good motor. These are prudent to measure to establish a true picture of a motors insulation. By doing a DAR and PI test you can determine which is which.

How long was your test? What readings did you get?

And welcome to the forum.


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## Will_Evo (Apr 6, 2011)

*PI and DAR*

Ha, well if you are referring to the brand, I actually like Megger products, if you referring to the size, we have also tried a 10KV megger for this same test and have got the same results. :thumbsup:

We are running a PI test (so the 10min test) taking readings at the 30 sec and every minute mark to monitor said capacitive and absorption currents. We are noticing the leakage current getting over powered during the test but our PI readings have always been above 1.0. 


According to the manufacturers literature they only require the insulation resistance reading to be 1 M Ohm. When we started using these generators the readings we were getting were in the 25-35 G Ohm range and now after supplying power for 3 months we are down to 5 M Ohm (its a special load that in and of itself is destructive to insulation or at least we think). Anyways recently one of the windings does not hold up at test voltage and I don't know exactly what is causing it to do this. 

-Will


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## Zog (Apr 15, 2009)

That is quite a drop off, are those tempature corrected readings? Is your Megger running off battery power or is it plugged in?


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## Will_Evo (Apr 6, 2011)

Yea, the load issue is something else we are fighting. The temperature here is almost constant so we don't correct the readings, just simply make note there may be small discrepancies. We plug the Megger in during every test.

-Will


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## 76nemo (Aug 13, 2008)

You never took spot after commisioning did you? I've read this three times over again and something is missing. Your wording is good, but something doesn't give.............


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## Will_Evo (Apr 6, 2011)

76nemo said:


> You never took spot after commisioning did you? I've read this three times over again and something is missing. Your wording is good, but something doesn't give.............


I am not sure what you mean? Do you mean take baseline readings when we first got the generators? If so, then yes, we got baseline numbers and have tested every week they have been in service since then, and most recently every day because of the degradation of the insulation. It was on one of these daily tests that we noticed one of the windings not reaching test voltage. Also as an update, today we got a .47 PI on one of the windings with a ending resistance value at 4 M Ohms.:thumbup: haha

I am thinking the same thing, I can't figure out what could be causing this, what am I missing or over looking...which is the exact reason I even brought this discussion to forums in the first place :001_huh:

-Will


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