What Is the Basic Principle of the Electric Motor Protection Device?

Overview of electric motor protection devices

As a driving mechanical device, the electric motor has become the foundation of all power machinery in modern industry. With the continuous progress of science and technology and the continuous improvement of process control, especially the requirements of automated production, it is urgently needed to develop and improve the control and protection equipment of electric motors, so as to realize remote control, remote measurement, remote adjustment, fault diagnosis and centralized control of production processes and large machinery.

At the same time, the characteristics of the petrochemical industry itself are high-flow and full-load continuous operation, so the reliability and stability of electric motor safety devices are extremely high. Once an accident occurs, the cause of the fault must be found immediately and eliminated in time to ensure timely resumption of production. In the past, thermal relays were used as overload protection and control components for electric motors, but due to limited component quality and technology, they can no longer meet the requirements of increasingly developed process automation.

Basic working principle of electric motor protection devices

Electric motor safety device is a new type of electronic multifunctional motor comprehensive protection device developed in the past decade. It integrates low-voltage protection such as over (under) load protection, phase loss, over (under) voltage, blockage, leakage, grounding, and three-phase unbalance protection, and has high setting accuracy, power saving, sensitive action, and reliable operation. It is an ideal substitute product for traditional thermal relays. It is usually composed of several parts such as a current sensor, a comparison circuit, a single-chip microcomputer, or an output relay.

The sensor linearly reflects the current change of electric motor safety device to the sampling port of the protector. After rectification, filtering, and other linkages, it is converted into a DC voltage signal proportional to the motor current, and sent to the corresponding part for comparison and processing with the given protection parameters. Then, the single-chip microcomputer circuit is processed, and the power circuit is pushed to make the relay act. When the motor current increases due to overload of the driving part, the voltage signal obtained from the current sensor will increase. When this voltage value is greater than the setting value of the protector, the overload circuit will work. After a certain (adjustable) delay, the delay circuit drives the output relay to act, and the contactor cuts off the main circuit. The working principle of undervoltage and phase loss protection functions is basically the same.