Motor Protection Relay Operation

Type of motor protection?

1. Overload protection

Protects motor from running at high currents for too long (due to mechanical overload, jam, etc.).

Example: Thermal overload relay.

2. Short-circuit protection

Protects motor winding from very high fault currents.

Example: Circuit breakers (MCB, MCCB, fuse).

3. Ground fault (earth fault) protection

Protects against leakage currents to earth, preventing electric shock and fire.

Example: Earth fault relay.

4. Phase failure (single phasing) protection

Protects against loss of one phase in 3-phase motors.

Example: Phase failure relay. 

5. Phase sequence protection

Ensures correct rotation direction and protects against wrong phase sequence.

Example: Phase sequence relay. 

6. Under-voltage protection

Trips the motor if voltage drops below safe limits, preventing overheating or staling. 

Example: Under-voltage relay.

7. Over-voltage protection

Protects against high voltage which can damage insulation.

Example: Over-voltage relay.

8. Locked rotor protection

Protects when the rotor cannot turn while current is high (e.g., mechanical blockage).