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3-PHASE INDUCTION

MOTORS

Engr. Hassan Mohy-ud-DinInstructor, Electric Machines 3rdSemester

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Induction Motor Action

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Induction Motor: Rotating Field

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Induction Motor Operation

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Rotating Field Sweeping a Rotor Bar

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Induction Motor Construction

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Induction Motor Components

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Induction Motor Components

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Squirrel Cage Rotor

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Squirrel-Cage RotorCast Aluminum Conductors

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Squirrel-Cage RotorBrazed Conductors and End Rings

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Wound Rotor

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Wound-Rotor Induction MotorWhat if Rheostat is reduced to Zero?

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Induction Motor: Stator Winding

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Pole Pitch

Pole Pitch = Stator Circumference / PEquivalently expressed asStator SlotsorStator Arc

Full Pitch WindingCoil Pitch or Coil Span = Pole Pitch

Fractional Pitch Winding

Coil Pitch or Coil Span < Pole Pitch

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Synchronous Speed

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Synchronous Speed

Frequency of Supply Voltage

Frequency of Current inStator Coils

Flux rotates atIncreases Speed

Synchronous Speed

Pole ChangeFrequencyConverter

CONTROL

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Definitions

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Slip-Effect on Rotor Frequency and

Voltage

Assuming ConstantSupply Voltage and Frequency

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Reluctance Synchronous Motor

At no Shaft Load, relative motion b/w rotor androtating flux will be less

Rotor will be magnetized along a path ofMinimum Reluctance

Rotor locked in synchronismwith the RotatingFlux

Slip = 0, Motor Torque = 0

How to pull out of this state?

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Effect of Slip on Rotor Frequency

At blocked rotor, slip = 1, and fBR= fStator

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Effect of Slip on Rotor Voltage

Er= 4.44 N fr max

Er = 4.44 N s fBR max

Er = s EBR