LV Motor insulation resistance
LV Motor insulation resistance
(OP)
Motor Insulation resistance yes in general when measured comes in the order of hundreds of meg-ohms.
But there can be a condition that due to mositure or motor not being in use for few days the insulation resistance goes down.
As per IEC 60364-6 for low voltage motors , @ 500/1000 V if the insulation resistance comes out to be 1 Mega Ohms, then the motor is safe to be operated.
Further when the motor will run , it will end up gaining more insulation mega ohms due to heat kicking out moisture.
Opinion needed.
But there can be a condition that due to mositure or motor not being in use for few days the insulation resistance goes down.
As per IEC 60364-6 for low voltage motors , @ 500/1000 V if the insulation resistance comes out to be 1 Mega Ohms, then the motor is safe to be operated.
Further when the motor will run , it will end up gaining more insulation mega ohms due to heat kicking out moisture.
Opinion needed.





RE: LV Motor insulation resistance
Keith Cress
kcress - http://www.flaminsystems.com
RE: LV Motor insulation resistance
"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington
RE: LV Motor insulation resistance
Though, it's a good idea to keep these motors, LV/MV doesn't matter, warm via inbuilt space heaters/external external heaters to keep the IR values high. All it takes is a few watts.
Muthu
www.edison.co.in
RE: LV Motor insulation resistance
If you measured insulation resistance at ambient temperature, then it should recalculated with correction factor and minimum insulation resistance of the windings for 400 V motor should be over 20 mega Ohm.
Good luck
RE: LV Motor insulation resistance
IEEE 43-2000 (r2006) is a little different. Reference temperature for instulation resistance temperature correction is 40C (104F). Minimum corrected resistance for machines rated below 1kv is given as 5 mega-ohms although there is an allowance for windings made below 1970 and for field windings the minimum given is 1 megaohms.
The scenario of potential insulation damage due to rapid vaporization of moisture would not apply to random wound windings to my thinking since the insulating materials are primarily varnish and phase separator paper and groundwall paper (in contrast a form wound machine can have many layers of tape and the scenario seems more plausible). But out of an abundance of caution I sometimes have concern for starting these motors in this condition. For one thing the moisture in conjunction with conductive contaminants make it more likely to bridge between inevitable magnet wire film insulation imperfections (by NEMA magnet wire specs these imperfections are expected/allowed, just not so many of them that they would likely end up next to each other) resulting in turn to turn short. (If you get through the first few minutes you're fine, but will the motor make it that far... plenty fail soon after start for various reasons) For another thing although we assume it's moisture based on most experience and circumstances, there's always the possibility that it's telling us about something else we should be attending to (drying the machine first allows us to confirm it was moisture and not something else).
imo it's not an exact science and there's plenty of room for situational judgement (what is normal, how critical is the application etc).
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(2B)+(2B)' ?
RE: LV Motor insulation resistance
Better to follow IEEE 43-2000 then
Thanks