Question

Describe the effect of change in speed, rotor current and torque as load is applied to an induction motor

How does the motor adjust to its stator current with changes in mechanical load?

When the motor is running light i.e. unloaded, the torque is only that required to overcome friction and wind age losses.

The stator draws little current from the supply.

As the motor is loaded i.e. the load torque increased there is a dip in speed or speed falls slightly.

As the speed falls, it allows for more cutting of the stator flux by the rotor conductors, hence the emf and the current increases.

This in turn would lead to increase in torque Developed by the motor and the speed is determined when the power developed equals the power required and a state of balance is reached.

The fall in speed from no load to full load is 4-5% for small motor and

The stating current of an induction motor is quite high.

But when running on no load motor [stator] draws a little current from the supply.

The net current required = no load current + current varied as per mechanical loading.

As the motor is loaded, stator draws more current to meet the balance condition i.e. power developed by motor and the power required by the load.