How to judge whether the insulation of Rolling Mill Motor is good?

1. Insulation resistance test:
Use a megohmmeter (shaker) to measure the insulation resistance of the motor winding to the ground and between phases. Generally, for motors with a rated voltage below 1000V, the insulation resistance should not be less than 0.5 megohms; for motors with a rated voltage of 1000V and above, the insulation resistance should not be less than 1 megohm per kilovolt.
During the test, connect the two test leads of the megohmmeter to the motor winding and the motor housing (ground) respectively, or connect to different windings, shake the megohmmeter handle at a constant speed, and read the displayed resistance value.
2. Observe the appearance:
Check the appearance of the motor winding to see if there is any discoloration, burning, damage, cracks or discharge marks. If there are these phenomena, it may indicate that the insulation has been damaged.
3. Smell the odor:
If the motor has a pungent burnt smell when running, it may be that the insulation material is overheated and burned, and the insulation is not good.
4. Measure leakage current:
Use a professional leakage current tester to measure the leakage current of the motor when it is running. Excessive leakage current may mean that there is a problem with the insulation.
5. Withstand voltage test:
Perform a withstand voltage test on the motor, apply a certain high voltage between the winding and the casing, and observe whether it can withstand it without breakdown. However, this method usually requires professional equipment and personnel to operate.