Polarization Index
Polarization Index
(OP)
For PI results for newly installed dry type transformers less than 2 (I have results @ 1.9) what are strategies and/or remedies aside from having the manufacturer replace the transformer to get a beter result? Or do we just have a monitoring program implemented to watch insulation?
Thanks.
b
Thanks.
b






RE: Polarization Index
RE: Polarization Index
1 minute is 169,000 megohms. The values look good to me but the ratio doesn't indiacte that.
I am begining to belive the PI is not accurate indication of IR conditions.
Thanks.
b
RE: Polarization Index
Have you made absolutely certain that everything is clean? Terminations and bushings obviously should be clean. How about your test leads? It is well worth running a cloth dampened with a mild solvent - isopropyl alcohol for example - down the length of the test leads before doing any measurements. You will be amazed how much crap adheres to silicone leads, even ones which look clean. Dirty leads can give all sorts of screwy readings - I have been lead a merry dance with this in the past, especially when chasing readings in the GΩ range.
RE: Polarization Index
But 169,000 megaohms @ 1 minute seems pretty darned high to me. Certainly it is for motors.
And in the motor world, IEEE43 for motors does not require PI is the 1-minute reading is above 5,000 mega-ohm because the reading tends to get inaccurate at very high resistances since this equates to low measurement currents.
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(2B)+(2B)' ?
RE: Polarization Index
What are the primary and secondary voltages of the transformer, and is the PI result you quote the LV winding to earth?
RE: Polarization Index
RE: Polarization Index
secondary voltage: 480v
The PI results are from the LV winding.
RE: Polarization Index
RE: Polarization Index
I agree that the measured values alone are an indication of good insulation. But when you apply the PI ratio, that would point to a "fair" condition. I am starting to see that PI ration cannot be relied upon.
Thanks.
b
RE: Polarization Index
If the eye test comes back OK I am going to book myself in for a brain test, see if they can find one...
Apologies for my earlier post - disregard everything I said.
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