What are the characteristics of winding faults in three-phase motors when there is a phase loss?

Release Time：

2025-03-31

When there is a phase loss problem in the motor winding, it is often accompanied by the fact that the phase to phase insulation and ground insulation are burned out at the same time. However, for relatively large motors, necessary monitoring and protection measures (such as differential protection) are often taken. When the motor voltage or current is unbalanced, the protection device will promptly cut off the power supply, effectively protecting the safety of the motor winding.

What are the characteristics of winding faults in three-phase motors when there is a phase loss?
Under normal circumstances, the power supply and winding of a three-phase motor are symmetrical. When the input voltage of the motor is out of phase due to power phase loss or improper motor connection, it will cause the motor winding to burn out regularly. From the end of the winding, the winding presents a very regular pattern of faults.

The lack of phase in the winding of the delta connection shows the pattern of one phase burning out two phases, while the lack of phase in the winding of the star connection shows the pattern of two phases burning out one phase. The fundamental reason for burning is due to the heating caused by excessive current.

If there is a phase loss during the operation of the motor, the speed of the motor will instantly slow down, and the phase current that is not affected by the phase loss winding will quickly exceed the rated current of the motor, even reaching several times the rated current, causing the phase winding to overheat and burn out severely due to the high current.

The motor in operation has a phase loss. When it is fully loaded, the motor is in an overcurrent state - that is, the current exceeds the rated current. The motor will transition from fatigue to locked rotor, and the current in the unconnected line will increase even more, causing the motor winding to quickly burn out. When a motor running under light load loses phase, the current in the winding of the unconnected phase increases rapidly, causing the winding of this phase to burn out due to excessive temperature rise.

If we analyze the relationship between the load torque and electromagnetic torque of a motor, during normal operation, the load torque and electromagnetic torque of the motor are relatively balanced. When the motor loses phase, the electromagnetic torque of the motor suddenly decreases. In order to meet the requirements of load operation, the current of the motor winding will increase significantly. The increase in current means that the winding will heat up, resulting in the deterioration of the electromagnetic wire insulation layer and other insulation materials of the phase winding, which will be burned out.