Thermal relay overload protection circuit

Due to frequent operation of production machinery and excessive load, a large current flows through the stator winding of the motor for a long time, and this large current cannot blow the fuse, causing the stator winding of the motor to overheat, and in severe cases, the stator may be burned. winding. The above fault can be avoided by using a thermal relay overload protection circuit, as shown in the figure. FT is a thermal relay connected in series to the main circuit. When the motor M is overloaded, the internal thermal element of the FT generates heat, bending the bimetallic sheet, pushing the normally closed contact of the FT to open, causing the AC contactor KM coil to cut off power, and the main contact KM is disconnected and motor M stops, thus eliminating the failure of overload burning the winding. After the overload fault is eliminated, press the "reset" button of the thermal relay and then press the start button ST, and the motor can start again.