06 Presentation

7/30/2019 06 Presentation

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Three-Phase AC machines

Three-Phase Wound Rotor Induction Motors

Resource 6


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Three-Phase AC Machines

Resource 6

Aim


To understand the construction, operation and performance of a Three-Phase Wound

Rotor Induction Motor


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Objectives

Three-Phase AC Machines

Resource 6

To be able to describe the construction of a three-phase wound rotor

induction motor

To be able to describe the operation of a three-phase wound rotor

induction motor To be able to describe the performance of a three-phase wound rotor

induction motor



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Motor Construction

1. Terminal Box

2. Outer Casing

6. End Plate

4. Inspection Cover

7. Rotor Shaft

1

2

3

6

7

5. Air Intake Vents

5

3. Mounting Bolts

4

Outside View


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Motor Construction

Terminal Box

1. Rotor Terminals K, L, M

5. Rotor Windings

3. Stator Windings

6. Earth Terminal

1 2

3

6

4. Stator Terminals U2, V2, W2

5

2. Stator Terminals U1, V1, W1

4


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Motor Construction

1. Motor Outer Casing

2. Stator Coils

3. Stator Slots

5. Stator Laminations

6. Slots Insulators

1

2

3

5

6

4. Air Intake Vents

4

The Stator


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Motor Construction

1. Rotor Coils

2. Slip Rings

3. Brushes

4. Rotor Terminals

5. Rotor Laminations

6. Rotor Slots

The Rotor


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Motor Construction

2. Rotor Coils

1. Slip Rings

3. Cooling Fan

4. Rotor Slots

5. Bearing

2

1

3

54

The Rotor


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Motor Construction

2. Carbon Brushes

1. Brass Brush Holders

3. Springs

5. Rotor Terminals

6. External Connecting Wires

1

5

4

6

2

4. Nylon Insulator

3

The Brush Gear


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Motor Operation

1. Motor starts with 3-gang

Rheostat set to highest

resistance giving low starting

current and slow speed.

The Rheostat Method of Starting

2. The Rheostat is adjustedslowly thus reducing rotor

resistance to zero.

3. This increases rotor speed

up to its maximum value

4. Starting torque can beeasily adjusted by initial

resistance setting to suit the

load.


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Motor Operation

1. Motor starts with 3

resistors in each rotor circuit

giving low starting current

and slow speed.

The Contactor Method of Starting

Earth Terminal

Stator Connections

Rotor Connections

Rotor ResistorBank 1

Shorting Relays K1, K2, K3

Rotor Resistor

Bank 2

Rotor Resistor

Bank 3

2. K3 is energised shorting

out resistors R31, R32, R33giving increased speed.

3. K2 is energised shorting

out resistors R21, R22, R23

giving increased speed.

4. K1 is energised shortingout resistors R11, R12, R13

giving full speed.


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Motor Performance

Torque-Speed Curve for a

four pole motor

Increasing Rotor Resistance

6. Decreases Starting Current

3. Increases Starting Torque

4. Decreases Speed in running

region for given load

5. Decreases Speed wheremaximum torque occurs

1. Does not change synchronous

speed

2. Does not change maximum

torque

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