What is the thermal relay?

Thermal Relay is an electrical device used for overload protection of motors or other equipment. The following is a detailed introduction to thermal relays:

1. Definition and function

Thermal relay is a device that implements overload protection by detecting current and converting it into heat. It is usually used in conjunction with a contactor. When the motor is overloaded, it can automatically cut off the circuit, thereby protecting the motor from overload damage.

2. Working principle

The working principle of the thermal relay is based on the thermal diffusion effect and the differential principle. Its core component is the thermal element, which is usually composed of a bimetallic strip. When the motor is running, the current passes through the thermal element to generate heat, causing the bimetallic strip to expand due to heat. Since the bimetallic strip is made of two metals with different expansion coefficients, it will bend when heated. When the bending reaches a certain degree, the bimetallic strip will push the contact to disconnect the contact, thereby cutting off the circuit.

3. Main characteristics

Overload protection: The thermal relay can monitor the current and send a signal to cut off the circuit when the current exceeds the rated value when the motor is running.

Short circuit protection: In addition to overload protection, the thermal relay can also monitor whether there is a short circuit fault in the circuit and quickly cut off the circuit when a short circuit occurs.

Phase loss protection: The thermal relay can monitor whether there is a phase loss fault in the circuit and automatically cut off the circuit when one phase loses power.

Selective protection: The thermal relay can achieve multi-level protection and set different protections according to the load characteristics of the motor.

Sensitivity protection: The thermal relay can be adjusted according to actual needs to adapt to the load characteristics of different motors and provide accurate and reliable overload protection.

4. Structure and composition

The thermal relay is usually composed of heating elements, bimetallic strips, connecting rods, contacts and other parts. Among them, the heating element is used to convert current into heat; the bimetallic strip is used to sense heat and bend; the connecting rod is used to convert the bending of the bimetallic strip into the action of the contact; the contact is used to control the on and off of the circuit.

5. Application and precautions

The thermal relay is widely used in overload protection of various motors. When using, you need to pay attention to the following points:

Choose the appropriate model: Choose the appropriate thermal relay model according to the rated current and working environment of the motor.

Correct installation and wiring: Make sure that the installation position of the thermal relay is correct and the wiring is firm and reliable.

Regular inspection and maintenance: Regularly check whether the contacts and thermal elements of the thermal relay are working properly, and clean dust and dirt in time.

Avoid false operation: When adjusting the set current of the thermal relay, it should be accurately set according to the load characteristics of the motor to avoid false operation and unnecessary shutdown.

In summary, the thermal relay is an important motor overload protection device with broad application prospects and important protection functions.