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Speed Control of Three Phase Induction Motor

on 24/2/2012 & Updated on Tuesday 10th of July 2018 at 11:00:48 PM
A three phase induction motor is basically a constant speed motor so it’s somewhat difficult to control its speed. The speed control of induction motor is done at the cost of decrease in efficiency and low electrical power factor. Before discussing the methods to control the speed of three phase induction motor one should know the basic formulas of speed and torque of three phase induction motor as the methods of speed control depends upon these formulas.

Synchronous Speed

Where, f = frequency and P is the number of poles

The speed of induction motor is given by, Where, N is the speed of the rotor of an induction motor, Ns is the synchronous speed, S is the slip. The torque produced by three phase induction motor is given by,

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Speed Control of Three Phase Induction Motor

When the rotor is at standstill slip, s is one. So the equation of torque is, Where, E2 is the rotor emf Ns is the synchronous speed R2 is the rotor resistance X2 is the rotor inductive reactance

The Speed of Induction Motor is changed from Both Stator and Rotor Side. The speed control of three phase induction motor from stator side are further classified as :

The speed controls of three phase induction motor from rotor side are further classified as:

Speed Control from Stator Side

Speed Control from Rotor Side

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