300 kW Polarisation Index
300 kW Polarisation Index
(OP)
Hi,
I performed a PI Test on one 300 kW 400 V electric motor and surprisingly got a value of 0.75 which is considered as a worst result. Is there any standard for comparing results,
I performed a PI Test on one 300 kW 400 V electric motor and surprisingly got a value of 0.75 which is considered as a worst result. Is there any standard for comparing results,





RE: 300 kW Polarisation Index
RE: 300 kW Polarisation Index
IEEE std 43-2000 states that with modern insulation system (in random wound and form wound windings) the absorption current becomes zero very fast. So, it recommends in such modern insulation, a 1 min/30 sec value may be taken as PI.
RE: 300 kW Polarisation Index
It specifies a minimum PI of 2.0.
Some exceptions are:
1 - Asphaltic windings. Not present if your machine was built in the 1980's or later.
2 - If the I.R. reading gets too close to the top of your resistance scale it may not be possible to obtain a good pi reading. The standard states PI is not needed if IR exceeds 5,000 megaohms. Depending on your equipment you may have difficulty measuring PI even at lower IR's.
Most often in the field when I see high PI it is an indication the windings are wet. Oh another thing, if you are measuring a long run of cable along with the motor the cable may interfere with your measurement. P.I. is not a standard test for cable.
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RE: 300 kW Polarisation Index
Any comment ?
RE: 300 kW Polarisation Index
Sounds like the winding is very dry and a good steam clean, varnish and bake may do the job. Good Luck
RE: 300 kW Polarisation Index
I am not familiar with older windings, but if these readings are taken directly at the motor (not through long run of cable), in low-humidity conditions, with winding temeprature 40C or below, with no change after 24 hours of drying, I would think the windings are suspect.
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RE: 300 kW Polarisation Index