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.