Basic Knowledge of Electric Motor Protection Devices

Motor protection is to provide comprehensive protection for the motor, namely to give an alarm or protection when the motor encounters overload, phase loss, locked rotor, short circuit, overvoltage, undervoltage, leakage, unbalanced three-phase, overheat, bearing wear, and eccentricity of the stator and rotor. The device that provides protection for the electric motor is called electric motor protection, including thermal relay, electronic protector, and intelligent protector. Large and important motors generally use intelligent protection devices.

Why is it easier for electric motor protection to burn out now than in the past?

Due to the continuous development of insulation technology, the design of the motor requires both increasing output and reducing volume, which makes the thermal capacity of the new motor getting smaller and the overload capacity weaker. In addition, with the improvement of production automation, the motor is required to operate frequently in various modes such as frequent starting, braking, reversing, and load change, which puts higher requirements on the motor protection device. Moreover, motor protection has a wider application, often working in extremely harsh environments such as damp, high temperature, dust, and corrosion. All of these lead to motors now being more prone to damage, especially for faults such as overload, short circuit, phase loss, and fouling.

Why is the protection effect of traditional electric motor protection devices not ideal?

Traditional motor protection devices mainly use thermal relays, but the sensitivity, accuracy, and stability of thermal relays are low, and the protection is unreliable. In fact, although many devices are equipped with thermal relays, the phenomenon of motor damage that affects normal production is still common.

The current development status of electric motor protection devices

Electric motor protection has developed from mechanical to electronic and intelligent, which can directly display parameters such as motor current, voltage, and temperature, with high sensitivity, reliability, and multiple functions, easy commissioning, fault type clear after protection action, which not only reduces motor damage but also greatly facilitates fault diagnosis on the production site and shortens the restoration time. In addition, the use of motor air gap magnetic field for motor eccentricity detection technology makes online monitoring of motor wear status possible. By displaying the changing trend of the motor eccentricity degree in a curve, early detection of faults such as bearing wear, inner and outer circle walk can be achieved to avoid fouling accidents.

The principles of selecting electric motor protection devices

Rationally selecting electric motor protection devices can fully exert the overload capacity of the motor and avoid damage, thus improving the reliability of power transmission systems and production continuity. The specific function selection should comprehensively consider factors such as the value of the motor itself, load type, use environment, importance of the motor main equipment, whether motor exit operation will cause serious impact on the production system, etc., and strive to achieve economic rationality.

The ideal motor protector is not the one with the most functions or the most advanced, but the one that can meet the actual needs on the site, achieve a unity of economy and reliability, and have a high price-performance ratio. Reasonably selecting the type and function of the electric motor protection devices according to the actual situation on the site, while considering that the protector installation, adjustment, and use should be simple and convenient, it is more important to choose a high-quality protector.