This document discusses the operation and applications of induction generators, particularly in utilizing renewable resources like wind and hydropower. It outlines the starting sequence, limitations, and technical parameters of induction generators, as well as examples of their use and operational requirements in both grid-connected and isolated systems. Key concepts include active and reactive power calculations, magnetization curves, and the importance of existing power grids for their functionality.

1. et332bInd.ppt
Lesson 16: Asynchronous
Generators/Induction Generators
ET 332b
Ac Motors, Generators and Power
Systems
1

2. et332bInd.ppt
Learning Objectives
2
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

3. et332bInd.ppt 3
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

4. et332bInd.ppt 4
Induction Generator Starting Sequence
Induction
Generator
Breaker
Prime
Mover
Mechanical
Power In
Generator
Losses
Electric
Power
Out
nr >ns
Existing Three Phase System
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
Induction generator can
not vary terminal voltage
or frequency. Set by
system.

5. et332bInd.ppt 5
Induction Generator Speed Power Curves
0 500 1000 1500 2000 2500 3000 3500 4000
-100
-50
0
50
100
Induction Machine Speed-Power Curve
Rotor Speed (rpm)
Air
Gap
Power
(kW)
ns
1.1ns
Generator
Operation
Pushover
Power

6. et332bInd.ppt 6
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

7. et332bInd.ppt 7
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.

8. et332bInd.ppt 8
Example Solution

9. et332bInd.ppt 9
Example Solution

10. et332bInd.ppt 10
Example Solution

11. et332bInd.ppt 11
Example Solution

12. et332bInd.ppt 12
Isolated Operation of Induction Generators
Induction
Generator
Breaker
Prime
Mover
Mechanical
Power In
Generator
Losses
Electric
Power
Out
nr >ns
Isolated Three Phase System
Reactive
Power from
Capacitors
When nr = ns, no
power delivered
Isolated Induction generator
requires residual flux
to build voltage
Capacitors supply reactive
power to load and
generator when voltage
builds.
Voltage falls rapidly when
load is applied.

13. et332bInd.ppt 13
Voltage Build-up in Isolated Induction Generators
R1
-jXc
R2/s
jX2
jX1
jXm Rfe
Vin
Current
Voltage
Iop
Vop
Xc0
Xc1
Xc0>Xc1










f
V
I
C
I
V
X
op
op
op
op
c
2
1
External Capacitor provides
Reactive power for operation
Operating point set by intersection
between magnetization curve and
Xc

14. et332bInd.ppt 14
Voltage Build-up in Isolated Induction Generators
Lab measurements determine the magnetization curve
Three Phase Induction Motor Magnetization Curve
0
20
40
60
80
100
120
140
0.00 0.25 0.50 0.75 1.00 1.25 1.50
Stator Current (A)
Stator
Voltage
(V)
Lab Data Linearized Magnetization Curve Load Line
F
28.45
or
F
10
845
.
2
C
60
2
1
110
1.18
f
2
1
V
I
C
5
op
op





















Inductance
change
due to rotor
motion

15. et332bInd.ppt 15
Voltage Build-up in Isolated Induction Generators
Single phase motor magnetization curve
Magnetization Curve-Single Phase Motor
0.00
20.00
40.00
60.00
80.00
100.00
120.00
140.00
0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00
Current (A)
Voltage
(V)
Lab Measurements Linearized Data Load Line
F
127
or
F
10
27
.
1
C
60
2
1
120
5.74
f
2
1
V
I
C
4
op
op





















16. et332bInd.ppt
END LESSON 16: ASYNCHRONOUS
GENERATORS/INDUCTION
GENERATORS
ET 332b
Ac Motors, Generators and Power Systems
16