Motor protection

Motor protection set

Motor protection is a set of devices and methods to protect a motor from failure and damage.

Type of motor fault

• External motor fault

• Unbalanced supply voltage

• undervoltage

• Reverse phase sequence

• Loss of synchronization

Internal motor fault

• Bearing failure

• superheating

• Winding fault

• Ground fault

Motor protection device

• Fuses: Fuses protect the motor by melting and interrupting the circuit during overload or short circuit.

• Circuit breaker: The circuit breaker can be reset after an interruption failure and provides overload and undervoltage protection.

• Overload relays: These devices interrupt circuits when large currents flow through them due to overload.

• Thermal overload relays:  These devices use bimetal sheets or heating elements to sense the temperature rise of the motor current. When the current exceeds a preset value, the thermal element will bend or melt, causing the contact to open or close.

•  Electronic or digital overload relays: These devices use a current transformer or shunt resistor to measure the motor current and use a microprocessor or solid-state circuit to control the contacts.

•   Differential protective relays: These are devices that compare the current of a motor or its winding input and output terminals. When the current difference exceeds a certain value, it indicates that there is a winding fault, and the relay will trip the circuit.

• Reverse protection relay: A device that detects the direction of rotation of a motor and prevents it from running in reverse.

Select motor protection equipment

Type and size of motor

• Characteristics and ratings of the motor

• Type and severity of the possible fault

• NEC and other standard requirements

• Cost and availability of equipment

Conclusion

Motor protection is an important aspect of electrical engineering, ensuring the safety and efficiency of motors and their circuits. Motor protection equipment is selected based on the type and size of the motor, the type and severity of possible failures, the requirements of NEC and other standards, and the cost and availability of the equipment. Motor protection devices include fuses, circuit breakers, overload relays, differential protection relays and reverse protection relays. Motor protection devices monitor and control parameters such as current, voltage, temperature, speed and torque to prevent or minimize damage to the motor and its circuits in the event of a failure or anomaly.