Characteristic Analysis of Motor Phase Loss Fault

Characteristic performance of motor phase loss

The motor phase loss is characterized by increased vibration, abnormal noise, temperature rise, speed drop, and current increase. There is a strong click when starting and it cannot start.
The cause of the motor phase loss is the power supply itself or the connection problem. It may be that the fuse is improperly selected or the press is not good, the fuse is broken; the switch is in poor contact; the connector is loose or disconnected. It is also possible that the motor has a phase winding that is open.
After the motor phase is burnt out, the intuitive fault characteristics of the winding are regular winding burn marks, and the degree of burnout is not too much. In the case of daytime, phase-to-phase or ground faults, the location of the fault point is particularly severe, and the spread of the fault is relatively lighter. This is a feature that the phase loss fault is different from other faults.

Theoretical analysis of motor phase loss operation

● When the electromagnetic and torque motor are running out of phase, the stator rotating magnetic field is seriously unbalanced, so that the stator generates a negative sequence current, and the negative sequence magnetic field and the rotor electromagnetically induce a potential close to 100 Hz, causing the rotor current to increase sharply and the rotor to be severely heated. When the phase is missing, the load capacity of the motor decreases, resulting in a sharp increase in the stator current. The most direct performance is the motor heating. Due to the serious non-uniformity of the motor magnetic field, the motor vibration is severe, resulting in bearing damage. If the motor is running out of phase, the motor will stop rotating, and the direct result is that the motor burns out. In order to prevent this problem from occurring, the general motor has phase loss protection.
●Change of current under different operating conditions
During normal starting or running, the three-phase power is a symmetrical load, and the three-phase currents are equal in magnitude and less than or equal to the rated value. After a phase break occurs, the three-phase current is not balanced or too large.
There is a phase loss at start-up, the motor cannot start, and its winding current is 5 to 7 times the rated current. The calorific value is 15 to 50 times the normal temperature rise, and the motor burns out because it rapidly exceeds the allowable temperature rise.


When there is a phase loss at full load, the motor is in an overcurrent state, that is, the current exceeds the rated current, the motor will change from fatigue to stall, and the line current of the uninterrupted phase increases more, causing the motor to burn quickly.
When the light-loaded motor is out of phase, the winding current of the uninterrupted phase increases rapidly, causing the phase winding to be burnt due to excessive temperature rise.
The lack of phase operation is very harmful to the squirrel-cage motor operating in the long-term working system. About 65% of the accidents in which such motors are burned are caused by the lack of phase operation. Therefore, it is very important to protect the motor from phase loss.

Reprinted from the network