Polarization index in MV motors and genrators
Polarization index in MV motors and genrators
(OP)
As IEEE 43-2000(Cl no 12.2.2) says , If 1 min IR is greater than 5000Mega-Ohm then Polarization index may or may not be indication of insulation condition.
Can any one elaborate what is phenomena behind this.
regards
Zafar
Can any one elaborate what is phenomena behind this.
regards
Zafar





RE: Polarization index in MV motors and genrators
But it raises in my mind a question why we wouldn't apply a P.I. limit at higher insulation resistance levels IF we know our test equipment is operating within its reliable indicating range. Maybe they are trying to provide allowance for very small degree of resistive tracking in vicinity of test leads (small enough to be insignificant at lower insulation resistance levels but dominate at this level)? Or is there some characteristic of the insulation itself that suggests PI should not be relevant when IR very high (haven't heard of that). Beats me.
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(2B)+(2B)' ?
RE: Polarization index in MV motors and genrators
RE: Polarization index in MV motors and genrators
An interesting one I heard about from our repair shop recently was dc step voltage test of 13.2kv stator to around 30kvdc… they had very non-linear results during initial test with unlugged extra-long motor T-leads tied to each other with bare wire at some distance far away from any ground (I think it was 3 feet from ground). Clamping the T-lead ends removed the non-linearity. From what I can gather, there must have been some corona originating at some of the strands where they feathered apart at the ends (corona is enhanced by small effective conductor diameter and by the end/tip of the conductor), even though the leads were very far from ground. Also again the resistance of the newly rewound stator was very high so as you point out it didn't take much current (from corona) to affect the reading.
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(2B)+(2B)' ?
RE: Polarization index in MV motors and genrators
RE: Polarization index in MV motors and genrators