With a neat sketch, explain the working of Thermal relay.
Working of Thermal Relay:
1) When the system is in normal operating condition, the heating element carries normal current from CT, this current produces heat = I2Rt. This heat is not sufficient to bent bimetallic strip hence relay contact remain open. 2) The insulated liver arm is connected to the trip coil along with the spring and the bimetallic strips. The tension of the spring is varied by the help of the sector-shaped plate 3) When the fault occurs on the system, the heating element carries abnormal current supplied by the CT, hence developing more heat which bents bimetallic strip, the tension of the spring releases which operates relay contacts resulting into providing trip signal to trip circuit.