motor space heater restoration practices
motor space heater restoration practices
(OP)
If a large motor (>500hp) space heater is deenergized during a maintenance period (with motor secured also), should we require a minimum time for space heaters to be energized prior to starting the motor?
In some cases, the maintenance period may have included insulation resistance test, although it may have been very early in the maintenance period. In other cases, there may have been no insulation resistance test (the space heaters may have been unavailable due to maintenance which deenergized the power supply to the space heaters).
Motors in question are in all types of environments: outdoors, enclosed in non-air-conditioned building, and enclosed in air-conditioned building.
The duration of space heater deenergization in question may be 1 day to 1 month.
In some cases, the maintenance period may have included insulation resistance test, although it may have been very early in the maintenance period. In other cases, there may have been no insulation resistance test (the space heaters may have been unavailable due to maintenance which deenergized the power supply to the space heaters).
Motors in question are in all types of environments: outdoors, enclosed in non-air-conditioned building, and enclosed in air-conditioned building.
The duration of space heater deenergization in question may be 1 day to 1 month.
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RE: motor space heater restoration practices
Blacksmith
RE: motor space heater restoration practices
RE: motor space heater restoration practices
I think you most have to take account the age of the motors, and the seasons change because is not the same start the maintenance in winter and finalize in summer or start in summer and finalize in winter, the ambient temperature is different.
I think is a risk if you don“t have the chance to test the insulation, for this is very important you count with all maintenance records including PI, and Insulation test prior the maintenance.I know by experience some large and old motors running with 70 MOhm and stops for maintenance, 1 mounth later with space heaters connected the corrected Insulation is only 5 MOhms.
Is very important to test the Insulation before and after perform the maintenance. The space heaters are used to prevent condensation on windings and other internal parts when the motor is not runing, the idea is to keep the windings warmed 5 or 10 C above the ambient temperature.
The less you can do after maintenance is to keep warm the winding closing the end belts and using some lamps inside the stator.
regards
Petronila
RE: motor space heater restoration practices
I agree with the opinions expressed above.
The space heaters will never dry a winding if it catches moisture. The power they provide is just enough to avoid condensation and will keep the stator only a few degrees above ambient.
After servicing and before energizing a motor, always measure the IR (insulation resistance) and PI (Polarization Index), it does not matter the age or time it has been idle, it could catch moisture in mater of hours.
RE: motor space heater restoration practices
Logic would dictate to do the test at the beginning of a maintenance period so if there is an actual problem (not just moisture) you have time to do something.
If we do it at the front end of the maintenance period to get that good data, it sounds like you guys are saying that we also need to do it at the back end. Lots of work. Particularly in some cases where we have to determ the motor to get any good reading since the cable sometimes is in the neighborhood 50-200 megaohms while the motor is typically 500-5000 megaohms plus for our 4kv and 13.8kv machines. Or do you think 100 megaohms temperature corrected and 2.0 PI is enough to energize it immediately? Regardless If I just turned the heaters on?
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RE: motor space heater restoration practices
In a motor repair shop, it is very difficult to energize space heaters and very easy to do a megger. The logical choice is to never energize space heaters and always do a megger immediately before energizing any motor in a repair shop.
Things are somewhat opposite in a power plant. It's easy fairly easy to get the space heaters back on after maintenance. It may not be quite so easy to do a megger in a power plant as it is in a motor shop. (For example, if my space heater power was down but motor was not being maintained, I now may have to hang a tagout to megger the motor).
I would like to know how many people have ever seen the practice that you guys recommend (always megger if space heaters off) in a power plant or other non-motor-repair industrial facility.
What is the off-time of space heaters before this mandatory megger requirement takes effect? 5 minutes? 1 hour? 24 hours?
Sorry I am not really trying to be argumentative but trying to play devil's advocate. What you guys are suggestign is foreign to me and I think different than what most plants do.
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RE: motor space heater restoration practices
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RE: motor space heater restoration practices