EE303
INDUCTION GENERATOR
Instructed By: Ms. P.M.A.U. Karunapala Name : G.R. Raban
Index Number : 070384P
Field : EE
Group : 8
Date of Performance : 17/11/2009
Date of Submission : 08/12/2009
OBSERVATIONS
NAME : G. R. Raban
INDEX NO. : 070384P
GROUP : 8
FIELD : EE
PRACTICAL : Induction Generator
DATE OF PERFORMANCE : 17 – 11 – 2009
INSTRUCTED BY : Ms. P. M. A. U. Karunapala
1) Self-excited induction generator
a) No load characteristics for varying capacitances and constant prime mover speed
Speed = 2500 rpm
Residual voltage = 3.064 V
Capacitance (µF) Voltage (V) Mag. Current (A) Frequency (Hz)
71.2 276.4 2.95 40
69.7 273.6 2.90 40
67.7 268.4 2.70 40
65.7 263.6 2.60 40
60.7 246.1 2.30 40
50.7 174.8 1.30 40
b) No load characteristics for varying prime mover speed and constant capacitance
Capacitance = 60.7 µF
Voltage (V) Speed (rpm) Current (A) Frequency (Hz)
243 2496 2.25 40
229 2448 2.05 40
212 2402 1.90 39
188 2348 1.65 38
164 2302 1.70 37
c) Performance of loaded generator with constant speed
Speed = 2500 rpm
Capacitance = 71.2 µF
Voltage (V) Gen. Current
(A)
Load Current
(A)
Frequency (Hz) Torque (Nm)
280 3.00 0 40 2.2
269 2.90 0.50 40 3.0
262 2.90 1.00 40 3.8
251 3.00 1.40 40 4.5
238 3.05 1.75 40 4.9
d) Performance of the loaded generator without speed regulation
No load speed = 2500 rpm
Speed (rpm) Voltage (V) Gen. Current
(A)
Load Current
(A)
Frequency
(Hz)
Torque (Nm)
2500 278 3.00 0 40 2.3
2472 264 2.80 0.5 40 3.0
2458 249 2.75 0.9 40 3.6
2448 234 2.70 1.3 39 4.1
2438 217 2.70 1.6 38 4.4
2) Grid connected induction generator
Current (A) Voltage (V) Power (W) Speed (rpm) Frequency (Hz) Torque (Nm)
1.60 222.0 0 3037 49 2.4
1.75 222.3 40 3052 49 2.8
1.85 222.1 80 3063 49 2.8
2.10 222.3 160 3078 49 3.3
2.35 222.2 220 3098 49 3.7
Calculations
1. Self Excited Induction Generator
Part (a)
No load characteristics for varying capacitances and constant prime mover speed
(i) Plot of Line Voltage Vs Magnetizing Current
100
120
140
160
180
200
220
240
260
280
300
1 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9
Lin
e V
olt
ag
e (V
)
Magnetizing Current (A)
Line Voltage Vs Magnetizing Current
(ii) Plot of Line Voltage Vs Capacitance
100
120
140
160
180
200
220
240
260
280
300
50.5 52.5 54.5 56.5 58.5 60.5 62.5 64.5 66.5 68.5 70.5
Lin
e V
olt
ag
e (V
)
Capacitance (μF)
Line Voltage Vs Capacitance
Using the above graphs, following values can be calculated.
(i) Capacitance required to obtain the rated voltage of 240 V at 2500 rpm is;
68 µF
(ii) Capacitance required to obtain the rated voltage of 240 V at the rated frequency of 50
Hz. Take this capacitance as C0.
Ic = VCω
Im = E
ωLm
Take, Ic = Im
Im = VC0ω
By the graph, Im = 2.175 A
∴ C0 = Im
Vω =
2.175
240×2π×50 F
C0 = 28.85 µF
Part (b)
No load characteristics for varying prime mover speed and constant capacitance
(i) Plot of Voltage Vs Speed
100
120
140
160
180
200
220
240
260
2300 2320 2340 2360 2380 2400 2420 2440 2460 2480 2500
Vo
lta
ge
(V)
Speed (rpm)
Voltage Vs Speed
(ii) Plot of Frequency Vs Speed
35
36
37
38
39
40
41
2300 2320 2340 2360 2380 2400 2420 2440 2460 2480 2500
Fre
qu
ency
(H
z)
Speed (rpm)
Frequency Vs Speed
(iii) Plot of Magnetizing Current Vs Speed
1
1.2
1.4
1.6
1.8
2
2.2
2.4
2300 2320 2340 2360 2380 2400 2420 2440 2460 2480 2500
Ma
gn
etiz
ing C
urr
ent
(A)
Speed (rpm)
Magnetizing Current Vs Speed
Part (c)
Performance of loaded generator with constant speed
(i) Plot of Voltage Vs Load Current
210
220
230
240
250
260
270
280
290
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8
Vo
lta
ge
(V)
Load Current (A)
Voltage Vs Load Current
(ii) Plot of Frequency Vs Load Current
0
5
10
15
20
25
30
35
40
45
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8
Fre
qu
ency
(H
z)
Load Current (A)
Frequency Vs Load Current
(iii) Plot of Generator Current Vs Load Current
2.8
2.85
2.9
2.95
3
3.05
3.1
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8
Gen
era
tor
Cu
rren
t (A
)
Load Current (A)
Generator Current Vs Load Current
Part (d)
Performance of the loaded generator without speed regulation
(i) Plot of Voltage Vs Load Current
100
120
140
160
180
200
220
240
260
280
300
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2
Volt
ag
e (
V)
Load Current (A)
Voltage Vs Load Current
(ii) Plot of Frequency Vs Load Current
33
34
35
36
37
38
39
40
41
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2
Fre
qu
ency
(H
z)
Load Current (A)
Frequency Vs Load Current
(c)
(d)
Plot of Torque Vs Speed of Prime Mover
0
1
2
3
4
5
6
2430 2436 2442 2448 2454 2460 2466 2472 2478 2484 2490 2496 2502
To
rqu
e (N
m)
Speed (rpm)
Torque Vs Speed
2. Grid Connected Induction Generator
(i) Plot of Power Output Vs Speed
0
50
100
150
200
250
3035 3045 3055 3065 3075 3085 3095
Po
wer
Ou
tpu
t (W
)
Speed (rpm)
Power Output Vs Speed
(ii) Plot of Line Current Vs Speed
1
1.2
1.4
1.6
1.8
2
2.2
2.4
2.6
3035 3045 3055 3065 3075 3085 3095
Lin
e C
urr
ent
(A)
Speed (rpm)
Line Current Vs Speed
Calculation of Efficiency and Power Factor
Efficiency = Output Power
Input Power
Input Power = τ × ω
Output Power = Wattmeter Reading
E.g. By the data obtained from the observations;
τ = 2.8 Nm ω = 3052 rpm W = 40 W
Input Power = 2.8 × 3052 × 2π
60 W = 894.89 W
∴ Efficiency = 40
894.89 × 100% = 4.47%
Power Factor = Real Power
Apparent Power
Real Power = Wattmeter Reading
Apparent Power = VI
E.g. By the data obtained from the observations;
V = 222.3 V I = 1.75 A W = 40 W
∴ Power Factor = 40
222.3 × 1.75 = 0.10
Speed (rpm) Efficiency (%) Power Factor
3037 0 0
3052 4.47 0.10
3063 8.91 0.19
3078 15.04 0.34
3098 18.33 0.42
(iii) Plot of Efficiency Vs Speed
0
5
10
15
20
25
3035 3045 3055 3065 3075 3085 3095
Eff
icie
ncy
%
Speed (rpm)
Efficiency Vs Speed
(iv) Plot of Power Factor Vs Speed
0
0.1
0.2
0.3
0.4
0.5
0.6
3035 3045 3055 3065 3075 3085 3095
Pow
er F
act
or
Speed (rpm)
Power Factor Vs Speed
Discussion
Reasons for the no-load test to be designed to result in a lower frequency than the rated
frequency of 50 Hz;
The Induction generator normally runs on negative slip. This is because its rotor runs
faster than the synchronous speed of the equivalent induction motor.
During the no-load test, there will be no active power output. The slip of the generator
will be zero or a positive value under this condition. Therefore, in order to achieve a positive
slip, the no-load test is designed to result in a lower frequency than 50 Hz.
The cause for variations of the voltage and current waveforms of the generator when
loading;
In the case of an induction motor, the motor speed is decreased when the load is
increased. But in an induction generator, the power output increases as the load increases, which
in turn increases the speed. Therefore, as the load on an induction generator changes, the speed
of the generator changes with it. This causes the current and voltage output to change.
The importance of induction generators in power generation in Sri Lanka
Induction generators can be used in wind turbines and micro hydro installations due to
their ability to produce useful power at varying rotor speeds. It is especially useful in wind
power generating stations where the speed is always a variable factor. Induction generators are
not suitable for high power applications.
Induction generators are mechanically and electrically simpler than other generator
types. They are also more rugged, requiring no brushes or commutations. Other advantages of
the induction generator are; it is cheaper, reliable in service, light weight, does not require
routine maintenance. Therefore, induction generators are ideal for use in remotely located mini
hydro plants and wind power generation stations.
Self Excited Induction Generators (SEIG) are very useful in isolated power generation
because it can easily handle dynamic loads.
Discussion about the above plotted graphs;
1. Self Excited Induction Generator
a) No Load characteristics for varying capacitance and constant prime mover speed.
i. Line Voltage Vs Magnetizing Current
Increase in Line Voltage decreases with increasing Magnetizing Current at constant
speed according to equation; Im = E
ωLm
ii. Line Voltage Vs Capacitance
Line Voltage increases with the Capacitance. But the curve tends to saturate at higher
values of capacitance.
b) No Load characteristic for varying prime mover speed and constant capacitance.
i. Voltage Vs Speed
Voltage increases with the Speed in a nearly linear manner.
ii. Frequency Vs Speed
Frequency increases with the Speed in a nearly linear manner.
iii. Magnetizing Current Vs Speed
Magnetizing Current also increases with the Speed.
c) Performance of loaded generator with constant speed.
i. Voltage Vs Load Current
The Voltage decreases as the Load Current increases. The curve is nearly linear.
ii. Frequency Vs Load Current
Frequency remains constant as load current increases. Therefore, it can be concluded that
the frequency does not depend on load current at constant speed.
iii. Generator Current Vs Load Current
Graph does not indicate a clear relationship between these two parameters.
d) Performance of the loaded generator without speed regulation.
i. Voltage Vs Load Current
Voltage decreases with increasing Load Current. The curve is nearly linear.
ii. Frequency Vs Load Current
Frequency is almost constant for low values of load current, but decreases rapidly for
higher values of load current. These characteristics are shown when there is no speed regulation.
Torque Vs Speed
Torque decreases with increasing speed in a nearly linear manner.
2. Grid connected Induction Generator
i. Power Output Vs Speed
Power Output increases with increasing Speed in a linear manner.
ii. Line Current Vs Speed
Line Current increases with Speed in a nearly linear manner.
iii. Efficiency Vs Speed
Efficiency increases with Speed.
iv. Power Factor Vs Speed
Power factor increases with increasing Speed in a nearly linear manner.