Transcript - SIU College of Engineering

Lesson 16: Asynchronous
Generators/Induction Generators
ET 332b
Ac Motors, Generators and Power
Systems
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Learning Objectives
After this presentation you will be able to:




Explain how an induction generator operates
List application for induction generators in the use
renewable resources
Discuss the limitations of induction generators
Compute the power developed from an induction
generator using the per phase circuit model
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Induction Generators
Driving an induction motor faster than synchronous speed
when connected to the grid results in active power
generation
Induction generators (asynchronous generators) designed
with lower rotor R to reduce losses and machine slip.
Applications: Wind Turbines, Hydraulic Turbines (small
scale hydro), Gas engines fueled by
natural gas or biogas
cogeneration
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Induction Generator Starting Sequence
Existing Three Phase System
Breaker
Electric
Power
Out
Induction
Generator
Prime
Mover
1.) Breaker open
2.) Increase prime mover
mechanical power input
until nr >ns.
3.) Close Breaker
4.) Adjust mechanical power
input to match electric
load.
Pmech=Pe+Ploss
nr >ns
Generator
Losses
Mechanical
Power In
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Induction generator can
not vary terminal voltage
or frequency. Set by
system.
4
Induction Generator Speed Power Curves
Induction Machine Speed-Power Curve
Air Gap Power (kW)
100
ns
1.1ns
Generator
Operation
50
0
-50
Pushover
Power
-100
0
500
1000
1500
2000
2500
3000
3500
4000
Rotor Speed (rpm)
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Limitations of Induction Generations
• Require existing power grid for synchronous
operation.
– Can not control frequency or voltage independently
• Can not operate above pushover speed
• Require a source of reactive power to operate
– When connect to grid, system supplies reactive power
to operate generator
• When operating without grid connection
frequency varies with power output.
– Parallel capacitors supply reactive power
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Induction Generator Example
A three-phase, six-pole, 460 V, 60 Hz induction generator operates on
a 480 V system. The generator its rated power output is 20 kW. It
is driven by a turbine at a speed of 1215 rpm. The generator has
the following electrical parameters:
R1 =0.200 W, R2= 0.150 W, Rfe= 320 W,
X1=1.20 W, X2=1.29 W, XM=42.0 W
Find the active power delivered by the generator and the reactive
power it requires from the system to operate.
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Example Solution
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Example Solution
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Example Solution
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Example Solution
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Isolated Operation of Induction Generators
Isolated Three Phase System
Isolated Induction generator
requires residual flux
to build voltage
Electric
Power
Out
Breaker
Reactive
Power from
Capacitors
Induction
Generator
Prime
Mover
nr >ns
Generator
Losses
Capacitors supply reactive
power to load and
generator when voltage
builds.
Voltage falls rapidly when
load is applied.
When nr = ns, no
power delivered
Mechanical
Power In
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Voltage Build-up in Isolated Induction Generators
jX1
R1
-jXc jXm
Vin
External Capacitor provides
Reactive power for operation
R2/s
Rfe
jX2
Operating point set by intersection
between magnetization curve and
Xc
Xc0>Xc1
Voltage
Vop
Xc0
Current
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Xc 
Xc1
Iop
Vop
Iop
Iop  1 
C


Vop  2f 
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Voltage Build-up in Isolated Induction Generators
Lab measurements determine the magnetization curve
Three Phase Induction Motor Magnetization Curve
140
Stator Voltage (V)
120
100
80
60
C
40
Inductance
change
due to rotor
motion
C  2.845 105 F or 28.45F
20
0
0.00
I op  1  1.18  1 




Vop  2f  110  260 
0.25
0.50
0.75
1.00
1.25
1.50
Stator Current (A)
Lab Data
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Linearized Magnetization Curve
Load Line
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Voltage Build-up in Isolated Induction Generators
Single phase motor magnetization curve
Magnetization Curve-Single Phase Motor
140.00
120.00
Voltage (V)
100.00
80.00
60.00
C
40.00
C  1.27  104 F or 127 F
20.00
0.00
0.00
I op  1  5.74  1 




Vop  2f  120  260 
1.00
2.00
3.00
4.00
5.00
6.00
7.00
Current (A)
Lab Measurements
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Linearized Data
Load Line
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ET 332b
Ac Motors, Generators and Power Systems
END LESSON 16: ASYNCHRONOUS
GENERATORS/INDUCTION
GENERATORS
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