Thermal relay working principle

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Introduction: This article mainly introduces the working principle of thermal relays . Those interested in basins are coming to browse it. The content is rich and should not be missed~~~~

1. Thermal relay working principle - introduction

Thermal relays are protective devices used for overload protection of electric motors or other electrical equipment and electrical circuits. The thermal relay is a protection device that uses the principle of the thermal effect of the current to cut off the motor circuit in the event of an overload that the motor cannot withstand, providing overload protection for the motor. The thermal relay is mainly used for overload protection of the asynchronous motor. As an overload protection component of the motor, it is widely used in production due to its small size, simple structure and low cost.

2. Thermal relay working principle - structure

A thermal relay is an electrical protection component that is a protective device that uses the thermal effect of current to push the action mechanism to close or open the contact. It is mainly used for overload protection, phase failure protection, current imbalance protection, and other electrical equipment of the motor. Control in the hot state. Thermal relays usually consist of the following five parts, the structure of which is shown in the figure.

Temperature sensing element: It consists of two resistance wires on a bimetal with different expansion coefficients. There are main bimetals and compensation metal pieces.

Contact system: consists of normally closed contacts, normally open contacts and leaf springs.

Action mechanism: It consists of a guide plate, a link system, and the like.

Reset device: It consists of a manual reset button and a reset adjustment screw.

Current setting mechanism: It consists of a current adjustment cam and a compression spring.

3. Thermal relay working principle

Thermal relays work with the thermal effects of current. The bimetal is its main measuring component. It is a metal material that is formed by mechanically rolling two metal sheets with different linear expansion coefficients. The large linear expansion coefficient is called the active layer, and the linear expansion coefficient is small. It is called the passive layer.

When the temperature rises, since the linear expansion coefficients of the two are different, the elongation of the two is different when the temperature is raised, and it is inevitably bent toward the side of the passive layer. If the protected circuit is overloaded, the temperature of the bimetal rises rapidly, and the degree of bending changes rapidly, so that the guide plate connected to the metal piece pushes the temperature compensation piece to cause the action of the link mechanism to drive the normally closed contact to open, so that the relay contacts The control part of the circuit loses power, and the power of the device is cut off to protect the device.

When using a thermal relay, the bimetal heater should be connected in series with the protected equipment. The normally closed auxiliary contact should be in series with the control circuit of the device being protected. The bimetal is heated in three ways: direct, indirect and composite. The difference in the linear expansion coefficient of the bimetal determines the sensitivity of the thermal relay. The temperature compensation sheet will make the action more accurate. Adjusting the reset screw allows the thermal relay to be reset automatically or manually. Adjusting the current adjustment cam adjusts the protection current of the thermal relay. In addition, the thermal relay can also be set with differential single-phase operation protection.

Expand reading:

1. The working principle of thermal relay

2. The working principle of the relay

3. Relay principle

Single phase asynchronous motor