Thermal relays are protective appliances used for overload protection of motors or other electrical equipment and electrical circuits. In the actual operation of the motor, if the production machinery is driven to work, if the machine is abnormal or the circuit is abnormal, the motor encounters an overload, the motor speed decreases, the current in the winding will increase, and the temperature of the motor winding high. If the overload current is not large and the overload time is short, the motor winding does not exceed the allowable temperature rise, this overload is allowed. However, if the overload time is long and the overload current is large, the temperature rise of the motor winding will exceed the allowable value, aging the motor winding, shortening the service life of the motor, and even burning the motor winding in severe cases. Therefore, this type of overload cannot be sustained by the motor. Thermal relay is the use of the thermal effect principle of current to cut off the motor circuit when there is an overload that the motor cannot withstand, and provide a protective appliance for the motor to protect it from overload.
The working principle of the thermal relay is to generate heat from the current flowing into the thermal element, so that the bimetallic plates with different expansion coefficients are deformed. When the deformation reaches a certain distance, the connecting rod is pushed to move, the control circuit is disconnected, so that the contactor When the power is lost, the main circuit is disconnected to realize the overload protection of the motor. As an overload protection element of the motor, the relay has been widely used in production due to its small size, simple structure and low cost.
Technical Parameters:
Rated voltage: the highest voltage value that the thermal relay can work normally, generally AC 220V, 380V, 600V.
Rated current: The rated current of the thermal relay mainly refers to the current through the thermal relay
Rated frequency: Generally speaking, its rated frequency is designed according to 45 ~ 62HZ.
Setting current range: The setting current range is determined by its own characteristics. It describes that the operating time of the thermal relay is inversely proportional to the square of the current under certain current conditions. It is mainly used for overload protection of asynchronous motors. His working principle is that after the overload current passes through the thermal element, the bimetallic sheet is heated and bent to push the action mechanism to drive the contact action, thereby disconnecting the motor control circuit to realize the motor power-off and shutdown , Play the role of overload protection. In view of the fact that during the bending process of the bimetal, the heat transfer takes a long time. Therefore, the thermal relay cannot be used for short-circuit protection, but can only be used as overload protection for the overload protection thermal relay.
