What are the common faults of electric motors?

Due to various reasons during operation, there will be failures. The common faults of motors are mainly divided into mechanical and electrical aspects.

(1) There are mechanical faults such as sweeping bore, vibration, shaft overheating, damage, etc. The air gap between the stator and rotor of the asynchronous motor is very small, which can easily lead to collision between the stator and rotor. Generally, due to the wear of the inner hole of the end cover shaft or the wear and deformation of the end cover stop and the base stop, the different axes of the base, the end cover and the rotor cause the sweeping bore.

The vibration should first distinguish whether it is caused by the motor itself, or caused by poor transmission, or transmitted from the mechanical load end, and then rule it out according to the specific situation. The vibration caused by the motor itself is mostly caused by poor rotor dynamic balance, poor bearing, bent shaft, or different axes of the end cover, base, and rotor, or the motor installation foundation is uneven, the installation is not in place, and the fasteners are loose. Vibration creates noise and additional loads.

(2) Electrical faults include stator winding lack of phase operation, stator winding end to end reverse connection, three-phase current imbalance, winding short circuit and grounding, winding overheating and rotor broken bar, open circuit, etc.

Phase loss operation is one of the common faults. As long as one phase of the three-phase power supply is open, the motor will run out of phase. Phase loss operation may be caused by fuse fusing on the line, poor switch touchpoint or wire connector contact.

After the three-phase motor lacks one-phase power supply, if it is in a stop state, it will stall (cannot start) because the synthetic torque is zero. The stall current of the motor is much larger than the normal working current. Therefore, in this case, if the power is turned on for too long or the power is turned on frequently for many times to start, the motor will burn out. When the running motor is missing one phase, if the load torque is very small, it can still maintain operation, only the speed will drop slightly, and an abnormal sound will be issued; when the load is heavy, the running time will be too long, which will burn the motor winding.

When the three-phase windings are misconnected end to end, after turning on the power supply, there will be a serious imbalance of the three-phase current, the speed will drop, the temperature rise will increase sharply, the vibration will intensify, and the sound will change sharply. If the protection device does not act, it is easy to burn out the motor winding. Therefore, it is necessary to identify the head and tail of the motor outlet end before it can be powered on.

The fault of three-phase current imbalance is often caused by the imbalance of the external power supply voltage of the motor; the internal reason is mainly the short circuit between the windings or the wrong number of coil turns or the wrong wiring when the motor is rewound and repaired.

Both winding grounding and short circuit can cause excessive current. Ground faults can be checked with a megohmmeter. Short-circuit faults can be judged by measuring the current when the power supply voltage of the stator winding is reduced, or by measuring its DC resistance.

The main reason for the overheating of the motor is that the load dragged is too heavy. Too high or too low voltage will also overheat the motor. Severe overheating will cause the motor to emit an insulating burning smell. If it is not dealt with in time or the protection device does not act, it is easy to burn the motor.

When the cast aluminum conductor of the cage motor rotor is broken or the rotor winding of the wound motor is broken, the stator current will be abnormal, the periodic changes will occur at high and low, and the noise and vibration will also appear. The heavier the load, the more pronounced this phenomenon is.