Why prolonged overloading protection is required for Induction motor?

Prolonged overloading on induction motor can cause excessive temperature rise in the stator and rotor windings of induction motor and also it damages the insulation resulting in the winding fault. Hence overloading protection is provided irrespective size and rating of the motor. Overload protection for the motor should not operate during starting of the motor

Thermal overload relays or inverse over current relays are provided for protecting motors against prolonged overloading conditions.