1) Phase loss operation: Any open circuit in one phase of a three-phase power supply will cause the motor to operate in a phase loss state. After a three-phase motor loses one phase of power supply, if it is in a stopped state, it will stall (unable to start) due to zero synthesized torque. The locked rotor current of the motor is much higher than the normal operating current. Therefore, in this situation, turning on the power for too long or repeatedly starting the power will cause the motor to burn out. When a running motor is missing one phase, an elliptical rotating magnetic field with high three-phase harmonic components is generated in the air gap of the motor. If the load torque is small, it can still maintain operation with only a slight decrease in speed and abnormal noise; When the load is heavy and the running time is too long, it will cause the motor winding to burn out.
2) Three phase current imbalance: The fault of three-phase current imbalance is often caused by an imbalance in the external power supply voltage of the motor. Its internal reasons are mainly short circuits between winding turns or incorrect coil turns or wiring during motor rewinding repair.
3). Winding short circuit or grounding: Winding short circuit is divided into turn to turn short circuit and phase to phase short circuit. Phase to phase short circuit can cause the fuse to melt, the circuit breaker to trip, and even affect the upper level switch, leading to system failure; Interturn short circuit is caused by the poor performance of the insulation layer of the winding enameled wire, resulting in damage; As a result, the phase to phase wires directly collide, forming a low impedance current circuit, increasing the inter turn current and causing the wire package to heat up. Over time, this can cause the entire stator winding to overheat, ultimately leading to the destruction of the winding due to a sharp increase in heat. Inter turn short circuit is the biggest cause of abnormal temperature rise in the motor. Short circuit faults can be determined by measuring current or DC resistance while reducing the power supply voltage of the stator winding; Most grounding faults are caused by damage to the winding insulation and water ingress into the motor. Before starting the motor, the insulation of the motor should be tested first, and only after passing the test can it be powered on for operation.