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520) Basil Cleves 5.1. Introduction AC motors are becoming widespread in industrial drives in the recent past. Broadly a.¢ nto synchronous motors and asynchronous motors. Synchronoys motors can be classified i r20f ih n at synchronous speed given by Ns = p> where f is the frequency of the he number of poles. Asynchronous motors run at speeds lower d. They are basically induction motors and commutator motors, motors ru supply voltage and P ist than the synchronous spee Various constructions are possible in these motors. Of all the motors, the three phase induction motor is extensively used. It offers Many advantages such as, e Simple and rugged construction e Low cost e Reliable e Reasonably good power factor and efficiency e Does not need additional starting motor e Minimum maintenance. The main disadvantages are e Speed cannot be varied widely e Speed decreases with increase in load e Starting torque is lower than d.c. shunt motor. In the following sections we study the three phase induction motor in detail. 5.2. Construction The three phase induction motor essentially consists of (a) rotor (b) stator. The stator is made up of a number of stampings, slotted to house the windings. The Stator has a three phase winding fed from a three phase supply. It is wound for a definite number of poles. The rotors are of two types: squirrel cage and wound rotor. 5.2.1, Squirrel - Cage rotor aoe has the simplest construction and is the most rugged. The construction is shown Scanned by CamScanner