INDUCTION MACHINESMODULE 1

Prepared by:

Aswathy Mohandas P

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INTRODUCTION

Three-phase induction motors are the most common and frequently encountered machines in industry simple design, rugged, low-price, easy maintenance run essentially as constant speed from no-load to

full load called as asynchronous motors described as ―transformer type a.c machine in

which electrical energy is converted into mechanical energy.

Its speed depends on the frequency of the power source not easy to have variable speed control requires a variable-frequency power-electronic drive for

optimal speed control

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Advantages

It has simple and rugged construction.

It is relatively cheap.

It requires little maintenance.

It has high efficiency, good speed regulation and reasonably good power factor.

It has self starting torque.

Disadvantages

It is essentially a constant speed motor and its speed cannot be changed easily.

Its starting torque is inferior to d.c motors.

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PARTS OF INDUCTION MOTOR

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CONSTRUCTION Frame:

It is the outer body of the motor. Its function are to support the stator core and winding, to protect the inner parts of the machine and serve as a ventilating housing or means of guiding the coolant into effective channels.

Stator:

It consists of a steel frame which encloses a hollow, cylindrical core made up of thin laminations of silicon steel . A number of evenly spaced slots are provided on the inner periphery of the laminations.

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Rotor:The rotor consists of a laminated core, with slots cut on its outer periphery where windings are placed. The windings may be either of squirrel cage type or wound rotor type. The core is mounted on a steel shaft, provided with bearings on both sides and is supported on end covers attached to the main frame of the motor

Shaft and bearings:The rotor shaft is supported by bearings housed in the end shield.

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TYPES OF ROTOR

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Squirrel cage rotor Wound rotor

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ROTATING MAGNETIC FIELD DUE TO 3-PHASE CURRENTS

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At instant 1, ωt = 0°. Therefore, the three fluxes are given by,

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At instant 2, ωt = 30°. Therefore, the three fluxes are given by,

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At instant 3, ωt = 60°. Therefore, the three fluxes are given by,

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At instant 4, ωt = 90°. Therefore, the three fluxes are given by,

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SLIP

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ROTOR CURRENT FREQUENCY

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EQUATION FOR STATOR AND ROTOR EMFS

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ROTOR CURRENT

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ROTOR TORQUE

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STARTING TORQUE

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CONDITION FOR MAXIMUM STARTING TORQUE

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TORQUE UNDER RUNNING CONDITION

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MAXIMUM TORQUE UNDER RUNNING CONDITION

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FULL LOAD, STARTING AND MAXIMUM TORQUES

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TORQUE- SLIP CHARACTERISTICS

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TORQUE – SPEED CHARACTERISTICS

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EFFECT OF ROTOR RESISTANCE UPON TORQUE - SLIP OR TORQUE - SPEED CHARACTERISTIC

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EFFECT OF CHANGE IN SUPPLY VOLTAGE ON TORQUE – SPEED CHARACTERISTIC

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POWER STAGES IN AN INDUCTION MOTOR

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INDUCTION MOTOR TORQUE

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ROTOR OUTPUT

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INDUCTION MOTOR TORQUE EQUATION

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PHASOR DIAGRAM

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CIRCLE DIAGRAM

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