Motor protection should involve the detection of the following hazards:
1. Faults in the windings or associated feeder circuits, including both phase and ground fault detection.
2. Excessive overloads. Overloads result in thermal damage to the insulation and can be caused by continuous or intermittent overload, or a locked rotor condition (failure to start or a jam condition).
3. Reduction or loss of supply voltage. Any reduction of supply voltage directly affects the applied torque to the connected mechanical load.
4. Phase reversal. Starting a motor in reverse can be hazardous to the load.
5. Phase unbalance. A small amount of unbalance can result in a significant increase in the motor temperature.
6. Out-of-step operation for synchronous motors.
7. Loss of excitation for synchronous motors.
Size : 80 mb
Size : 80 mb