Working principle of thermal overload relay

Working principle of thermal overload relay

1. The main control component of the overheat relay is the bimetallic strip. The working principle is that after the overload current passes through the thermal element, the bimetallic strip is heated and bent in one direction, which drives the action mechanism to separate the contacts, thereby disconnecting the motor control circuit and realizing the power-off stop of the motor, playing the role of overload protection. 2. The AC contactor is driven by three sets of moving contact strips simultaneously operated by the moving iron core. When the coil is energized, the static iron core generates electromagnetic attraction to attract the moving iron core. As the contact system is linked with the moving iron core, the contacts close, thereby connecting the power supply. When the coil loses power, the suction force disappears, and the linkage part of the moving iron core separates by the reaction force of the spring, causing the main contact to disconnect and cutting off the power supply.

Wiring diagram of thermal overload relay

The main control component of the overheat relay is the bimetallic strip. The working principle is that after the overload current passes through the thermal element, the bimetallic strip is heated and bent in one direction, driving the action mechanism to separate the contacts, thereby disconnecting the motor control circuit, achieving power-off and stopping of the motor, and playing the role of overload protection. The action time of a thermal relay varies in inverse time relationship with the magnitude of the overload current. As a thermal relay for motor overload protection, it must ensure that the normal starting and operation of the motor are not affected, and can maximize the carrying capacity of the motor. Therefore, the action characteristic curve of the thermal relay should be located below and close to the allowable heating characteristic curve of the motor.