Transcript PowerPoint presentation

Three-Phase AC machines
Resource 6
Three-Phase Wound Rotor Induction Motors
Three-Phase AC Machines
Resource 6
Three-Phase Wound Rotor Induction Motors
Aim
• To understand the construction, operation and performance of a Three-Phase Wound
Rotor Induction Motor
Three-Phase AC Machines
Resource 6
Three-Phase Wound Rotor Induction Motors
Objectives
•
•
•
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
Motor Construction
1
Outside View
1. Terminal Box
2. Outer Casing
7
3. Mounting Bolts
2
4. Inspection Cover
5. Air Intake Vents
6
6. End Plate
7. Rotor Shaft
5
4
3
Motor Construction
2
1
Terminal Box
1. Rotor Terminals K, L, M
2. Stator Terminals U1, V1, W1
3
3. Stator Windings
4. Stator Terminals U2, V2, W2
5. Rotor Windings
6. Earth Terminal
6
5
4
Motor Construction
1
The Stator
1. Motor Outer Casing
2. Stator Coils
3. Stator Slots
6
2
4. Air Intake Vents
5. Stator Laminations
3
5
6. Slots Insulators
4
Motor Construction
The Rotor
1. Rotor Coils
2. Slip Rings
3. Brushes
4. Rotor Terminals
5. Rotor Laminations
6. Rotor Slots
Motor Construction
The Rotor
1. Slip Rings
2
3
1
2. Rotor Coils
3. Cooling Fan
4. Rotor Slots
5. Bearing
4
5
Motor Construction
The Brush Gear
6
1
1. Brass Brush Holders
2. Carbon Brushes
3. Springs
5
2
4. Nylon Insulator
5. Rotor Terminals
6. External Connecting Wires
3
4
Motor Operation
The Rheostat Method of Starting
1. Motor starts with 3-gang
Rheostat set to highest
resistance giving low starting
current and slow speed.
2. The Rheostat is adjusted
slowly thus reducing rotor
resistance to zero.
3. This increases rotor speed
up to its maximum value
4. Starting torque can be
easily adjusted by initial
resistance setting to suit the
load.
Motor Operation
Stator Connections
The Contactor Method of Starting
1. Motor starts with 3
resistors in each rotor circuit
giving low starting current
and slow speed.
2. K3 is energised shorting
out resistors R31, R32, R33
giving increased speed.
3. K2 is energised shorting
out resistors R21, R22, R23
giving increased speed.
4. K1 is energised shorting
out resistors R11, R12, R13
giving full speed.
Earth Terminal
Shorting Relays K1, K2, K3
Rotor Connections
Rotor Resistor
Bank 1
Rotor Resistor
Bank 2
Rotor Resistor
Bank 3
Motor Performance
Torque-Speed Curve for a
four pole motor
Increasing Rotor Resistance
1. Does not change synchronous
speed
2. Does not change maximum
torque
3. Increases Starting Torque
4. Decreases Speed in running
region for given load
5. Decreases Speed where
maximum torque occurs
6. Decreases Starting Current