SOLUTION

Stator voltage control for the speed control of induction motor is suitable for Fan and Pump Drive.

AC voltage control or the stator voltage control

The torque developed by an induction motor is proportional to the square of the terminal voltage  (T ∝ V²) at a constant value of the supply frequency and the slip. When the applied voltage is varied, a set of speed-torque curves can be obtained.

Stator voltage control for three-phase induction motors of both slip ring as well as squirrel cage type can be implemented by using three-phase ac voltage controllers.

Advantages of Stator voltage control

• The control circuitry is simple, more compact, and weighs less.
• There is a considerable saving in energy and thus, it is an economical method when compared to other methods of speed control.

Disadvantages of Stator voltage control

• Maximum torque available from the motor decreases with a reduction in stator voltage.
• At low speeds, motor currents are excessive and special arrangements should be provided to limit these excessive currents.
• Performance is poor under the running condition at low speeds.
• Operating efficiency is low as resistance losses are high.
• Voltage and current waveforms are highly distorted due to harmonics, to eventually affect the efficiency of the motor.

Application:-

Due to its high loss and low efficiency, this method found application when the load is predictable and where the load torque is relatively low at the reduced speed (fan type load). e.g pumps, fans, blower drive.