Three-phase Induction Motors

INTRODUCTION

Three phase induction motor is the most popular type of a.c motor.It is very commonly used for industrial drives since it is cheap,robust,efficient and reliable.It has good speed regulation and high starting torque.it requires little maintenance.It has a reasonable overload capacity.

CONSTRUCTION
A three-phase induction motor essential consists of two parts:the stator and the rotor.The stator is the stationary part and the rotor is the rotating part.The stator is build up of high-grade alloy steel lamination to produced to reduce eddy-current losses.The laminations are slotted on the inner periphery and are insulated from each other.These laminations are supported in a stator frame of cast iron or fabricated steel plate.The insulated stator conductors are placed in these slots.The stator conductors are connected to form a three-phase winding.The phase winding  may be either star or delta-connected.
The rotor is also built up of thin laminations of the same material as stator. The laminated cylindrical core is mounted directly on the shaft or a spider carried by the shaft.These laminations are slotted on their outer periphery to receive the rotor conductors.There are two types of  induction motor rotors:
(a)Squirrel-cage rotor or simply cage rotor.
(b)Phase wound or wound rotor.Motor using this type of rotor are also called slip-ring motors. 

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