Question

List the factors that determine the maximum developed torque of the induction motor

Condition for maximum torque under running condition

From above, it is found :

(1) that the maximum torque is independent of rotor resistance as such

(2) However, the speed or slip at which maximum torque occurs is determined by the rotor resistance.

As seen above, torque becomes maximum when rotor reactance equals its resistance.

Hence, by varying rotor resistance (possible only with slip-ring motors) maximum torque can be made to occur at any desired slip (or motor speed).

(3) Maximum torque varies inversely as standstill reactance.

Hence, it should be kept as small as possible.

(4) Maximum torque varies directly as the applied voltage.

(5) For obtaining maximum torque at starting (s = l), rotor resistance must be equal to rotor reactance.