Tag: thermal overload relay

Thermal overload relays are protective appliances used for overload protection of motors or other electrical equipment and electrical lines. In the actual operation of the motor, for example, in the process of dragging the production machinery to work, if the machinery is abnormal or the circuit is abnormal and the motor is overloaded, the motor speed will drop and the current in the winding will increase, which will make the winding temperature of the motor. If the overload current is not large and the overload time is short, and the motor winding does not exceed the allowable temperature rise, this overload is allowed.

Thermal overload relays are overload relays that apply the principle of current thermal effect and use electrical thermal bimetallic sheets as sensitive components. The electrical thermal bimetal sheet is made by heating and rolling two alloys with large difference in linear expansion coefficient. When heated, the bimetallic sheet bends from the high expansion layer to the low expansion layer. When the current is too large, the element acts due to "heat", so that its linked moving contact cuts off the power supply of the controlled circuit and the protected equipment.

Modern industrial automated machinery is powered mostly by motors. The torque generated from a rotating motor provides the driving force for moving conveyor belts, gears, chains and other mechanical components, so a motor naturally becomes such an integral part that is key to the driving system. When it comes to the protection of the core power part, you can't pay too much attention to it. Thermal overload relays are used to provide overload protection, open-phase protection and protection against the unbalanced current for motors and they can also avoid heating in electrical equipment. The thermal overload relay works by the thermal effect of electric current to push the action mechanism to make or break contacts for the protection of electrical appliances.