Post on 16-Oct-2021
EE-362 ELECTROMECHANICAL ENERGYCONVERSION-II
Starting Methods and Operating Modes ofInduction Machines
Ozan Keysan
keysan.me
Office: C-113 • Tel: 210 7586
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Induction Motors
20 MW Induction Motor for HMS Queen Elizabeth3 / 26
Induction Motors
Single Line Diagram of HMS Queen Elizabeth Power System4 / 26
Typical Torque Curve of an Induction Motor
Torque Graphs
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What is wrong with directly connecting motor to aconstant voltage supply (i.e. grid)?
High Start-up Current
Low(or high) Torque at Start-up
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Starting Methods (Source Side):
1- Use Auto-transformer (Variac)
Apply a smaller voltage during start-up, and increase it gradually.
Remember: Torque ∝ V2
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Starting Methods (Source Side):
2- Use ( ) switchY − Δ
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Starting Methods (Source Side):
3- Soft Starters
Soft Starters, Soft starter vs Motor Drive
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Starting Methods (Source Side):
4- Induction Motor Drives
Variable Voltage-Frequency Source (or Variable Frequency Drives)
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Starting Methods (Source Side):
4- Induction Motor Drives
Variable Voltage-Frequency Source (or Variable Frequency Drives)
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Starting Methods Comparison:
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Starting Methods (Machine Side):
How to increase the starting torque, but reduce thestarting current at the same time?
=smaxT
r′
2
+ ( +R2
1X1 X ′
2)2‾ ‾‾‾‾‾‾‾‾‾‾‾‾‾‾√
= 3Tmax0.5V 2
ωs
1
( +R1 + ( +R2
1X1 X ′
2)2‾ ‾‾‾‾‾‾‾‾‾‾‾‾‾‾√
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Starting Methods (Machine Side):
Increase rotor resistance ( )
Torque Graphs
r′
2
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Starting Methods (Machine Side):
Increase rotor resistance ( )r′
2
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How to modify ( )?
1 - Add External Resistor: Easy for wound rotorinduction motors by using external resistance
r′
2
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How to modify ( ) for squirrel cage
motors?
2 - Use Deep Rotor Bars: Utilize rotor resistancechange with skin e�ect
r′
2
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How to modify ( ) for squirrel cage
motors?
2 - Use Deep Rotor Bars: Utilize rotor resistancechange with skin e�ect
r′
2
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Rotor Bar Shapes
For curious students: Rotor design, Motor design classes
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Complete Torque Characteristics
Can slip be larger than 1, or can it be less than 0?
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Operation Modes of Induction Motors
1- Motoring
2- Generating
3- Braking
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Motoring
Power Flow: Electrical to Mechanical
Slip: 0 < s < 1
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Generating
Power Flow: Mechanical to Electrical
Slip: s < 0
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Braking (Plugging)
Power Flow: Mechanical+Electrical to Heat
Slip: s > 1
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Machine Dynamics
Torque Balance Equation
− − = JTelec Tload Tf riction
dω
dt
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Four-Quadrant Operation
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