Motor insulation resistance
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I have a 250KW 380V motor that was accidentally exposed to water during maintenance; it has been shut down for over 20 days now. When tested with a megohmmeter, the resistance is only 0.1 M ohms. Using a 100W light bulb to dry it doesn’t seem to have much effect. Can I restart it? How confident are you?
For a 250kW motor, the resistance measured with a megohmmeter is only 0.1 MΩ; it definitely cannot be used – the resistance should be at least 0.5 MΩ. Furthermore, using a 100W ordinary light bulb to heat an electric motor of this size is definitely not sufficient; it would be better to consider using several infrared heating plates for heating.
0.1 megohms is absolutely unacceptable; a 100-watt bulb heating a 250-kilowatt motor has no effect on it, and other methods must be used to heat it until the resistance reaches over 0.5 megohms before power can be applied.
I tried using charcoal fire to heat the shell, but the temperature was too high, so it didn’t work. The bulb has been baked for two days, and its value has risen to 0.2 – is it safe to take a risk now? Actually, I used to have a 95KW motor that only had 0.1 of its capacity when in use.
It started with a forceful launch of 0.2, and it succeeded on the first attempt; now everything is working properly. I think the standard of 0.5 set is sufficient.
Generally, a value of 0.1 is sufficient for small motors, while for large motors, 0.3 is necessary
It is best to let it dry naturally; a resistance of 0.1 ohms is not acceptable – it should be at least 0.5 ohms.
It is best to remove the stator of the motor, dry it out, and then apply some insulating paint, which will extend its lifespan. If it is simply treated by baking with a light bulb, the ground insulation clearly reaches 0. It can be used after 22, but its service life is not long.
0.5 is the standard value in industry, but many devices can also operate at around 0.2, such as submersible pumps; however, 0.1 seems a bit too low to me.
Insulation goes without saying. Motor heating for drying is achieved by applying direct current, which is fast and safe. Connect the windings of the three-phase motor in series and supply it with direct current. Note: If the power of the DC supply is sufficient, a configuration with three phase windings in parallel can also be used. A DC welding machine will do; just change gears gradually. Monitor the motor temperature.
Bro: “Started at 0.2, it worked on the first try; now everything is working properly.” Congratulations, the electric motor is fine; but if there is a problem and the insulation of the 250kW motor fails, the losses will be **significant**.