Motor overload issue
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I would like to ask any experienced member who is skilled in motor repair: I have a 5.5KW motor used in a mixing reactor, equipped with a cycloidal pinwheel reducer. The operating current of this motor was found to be 30A. After disassembling the equipment, the no-load current of the motor was measured to be 7–8A (the sound and other aspects of its operation were normal). The resistance between each of the three phases is almost identical, and the insulation resistance is very good. How can this situation be explained? Is it possible that the device being overloaded for long periods or frequently contributes to this situation? Thank you
In the event of a short circuit between coil turns, the resistance between each of the three phases is also almost identical; however, over time this can still cause damage to the motor. Personally, I think it’s due to issues with the load.
The no-load current is too high; if inter-turn short circuits and mechanical problems are ruled out, it is likely a quality issue with the motor (the two most probable causes are 1, large air gap)； 2. Poor quality of silicon steel sheets)
Thanks for the answer from above! I don’t think the issues with the air gap and the silicon sheet are problems, as this motor worked normally right from the start when we first purchased it; any problems arose only after it had been in use for some time (a relatively long period). What could be the causes of inter-turn short circuits in coils? Can long-term overload cause this problem?
Reasons for short circuits between coil turns: 1. Poor quality of the enameled wire itself. 2. Damage to the insulating layer of the enameled wire during the winding process or when it is inserted into the coil slots. Prolonged overloading can cause the coil to overheat; when the motor is turned on, it can be observed that the color of the coil darkens. This occurs in all three-phase windings. If only one-phase winding darkens, it indicates operation with a missing phase. Your motor needs to be replaced.
In the situation you described, there should be no problem with the motor itself; it’s probably the load that’s the issue – the current is too high. Can it still operate?
The no-load current is clearly relatively high; therefore, the current under load is also high. However, the main cause lies in the motor itself. A short circuit between the contacts could be a possibility, as the motor was working fine before. It’s also possible that moisture has entered the motor (which can be resolved by drying it), or that the motor has overheated for some other reason. As for the last possibility, consider whether one of the phase connections is overheating, while the currents in the other two phases are too high
The no-load current is too high; if the three-phase currents are balanced, it is mainly a mechanical issue with the motor.