EE 2192 Laboratory Practice IV

INDUCTION GENERATOR

Name

Index No.

Field

Group

Date of Performance

Date of Submission

: W.M.C.N.S.Kirinde

: 100255K

: Electrical Engineering

: G6

: 2012/11/15

: 2012/11/29

Instructed by : K.L.J..Jayaranga

OBSERVATION SHEET

PRACTICAL

NAME

INDEX NO.

FIELD

GROUP

DATE OF PERFORMANCE

DATE OF SUBMISSION

INSTRUCTED BY

: Induction Generator

: W.M.C.N.S.Kirinde

: 100255K

: Electrical Engineering

: G6

: 2012/11/15

: 2012/11/29

: K.L.J. Jayaranga

(1) Self – Excited Induction Generator

Part (a): No - load characteristics for varying capacitance and constant prime mover speed

Speed: 2500 rpm

Residual Voltage: 2.912 V

Capacitance (µF) Voltage (V) Current (A) Frequency (Hz)

50 0 0 41

55 0 0 42

60 0 0 42

62 240 2.2 41

65 250 2.4 41

70 274 2.8 41

Part (b): No load characteristics for varying prime mover speed and constant capacitance

Capacitance: 62 µF

Voltage (V) Speed (rpm) Current (A) Frequency (Hz)

200 2380 1.75 39.50

220 2432 1.95 40.35

240 2500 2.20 41.30

260 2560 2.50 42.60

270 2600 2.60 43.20

Part (c): Performance of load generator with constant speed

Speed: 2500 rpm

Capacitance: 70 µF

Voltage (V) Gen. Current (A) Load Current (A) Frequency (Hz) Torque (Nm)

270 2.80 0.0 41.40 1.7

265 2.75 0.4 41.00 2.1

262 2.70 0.8 41.10 2.6

258 2.70 1.2 41.22 2.8

245 2.60 1.5 40.90 3.2

Part (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 270 2.80 0.00 41.40 1.6

2426 266 2.50 0.38 40.05 2.0

2373 224 2.25 0.70 39.10 2.2

2339 205 2.10 0.96 38.40 2.3

2320 190 1.90 1.18 37.90 2.4

(2) Grid Connected Induction Generation

Current (A) Voltage (V) Power (W) Speed (rpm) Frequency (Hz) Torque (Nm)

1.6 230 0 3014 50.10 1.4

1.6 230 40 3025 50.20 1.6

1.7 230 240 3050 50.20 2.3

1.9 230 420 3073 50.10 2.9

2.1 230 480 3086 50.25 3.1

CALCULATIONS

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(1) Self – Excited Induction Generator

Part (a): No - load characteristics for varying capacitance and constant prime mover speed

From the graph Line Voltage vs. Magnetizing Current,

Magnetizing Current at the voltage 240V, Im = 2.2A

Frequency at the voltage 240V, f = 41.30 Hz

From the graph Line Voltage vs. Magnetizing Current,

Magnetizing Current at the voltage 240V, Im = 2.2A

⁄

⁄

√

√

(2) Grid Connected Induction Generator

Efficiency

Specimen Calculation

Wattmeter Reading = 24W

Multiplication Factor = 20

Hence,

output power =

Torque = 3.1 Nm

Angular Speed = 3086 rpm

Power Factor

Specimen Calculation

GRAPHS

1) (a) No-Load characteristics for varying capacitance and constant prime mover speed

Line Voltage vs. Magnetizing Current

Line Voltage vs. Capacitance

(b) No-Load characteristics for varying prime mover speed and constant capacitance

Voltage vs. Speed

Frequency vs. Speed

Magnetizing Current vs. Speed

(c) Performance of the loaded generator with constant speed

Voltage vs. Load Current

Frequency vs. Load Current

Generator Current vs. Load Current

(d) Performance of the load generator without speed regulation

Voltage vs. Load Current

Frequency vs. Current

Torque vs. Speed of the prime mover

2) Grid Connected Induction Generator

Power Output vs. Speed

Line Current vs. Speed

Efficiency vs. Speed

Power Factor vs. Speed

DISCUSSION

Comment why the no-load test was designed to result in a lower frequency than the

rated frequency of 50 Hz.

In this no-load test we need to obtain parameters for a wide range of line voltage like

from 200V to 280V for better results. In order to do that, we need to keep the operating point

of the induction generator to be in the non-linear region. If the operating point lies on the

linear region, then the range of the voltage won’t be considerably large enough to do the

practical over a wide range. When the frequency increases and reaches a value like 50Hz,

the gradient increases and operating point lies on the linear region then. Thus, the no-load

test is designed to result in a lower frequency than the rated frequency of 50Hz.

Discuss the importance of induction generators both self-excited and grid connected in

power generation of Sri Lanka.

Induction generators have the ability to produce useful power at varying rotor speeds.

Hence, they are really important for the usage in wind turbines and mini and micro hydro

installations. In Sri Lanka, we can find a lot of small waterfalls, especially in the central

parts. Induction generators can play a vital role in the mini and micro hydro power stations

because of their simplicity in electrical and mechanical aspects. Induction generators are not

appropriate for high power applications. Because of the coastal areas all around Sri Lanka,

wind power stations can be installed. These induction generators are more rugged than other

types and require no brushes or commutators. Thus, inductions generators are really

important for windmills too. They usually require no regulation process and the power factor

correction also can be easily provided by capacitor banks. Induction generators are

comparatively cheap and compact in size making them ideal for small scale generation in Sri

Lanka.

Self-Excited Induction Generators are really useful in isolated power generation in Sri

Lanka. They do not need an external power supply to produce the magnetic field. It makes

them the ideal choice for the wind power generation in remote areas. The magnetic field

does not deteriorate with the time which causes a drop in generated voltage in these

generators unlike the other generators with permanent magnets. The synchronous alternator s

in standalone power generation is being replaced gradually by these generators due to their

advantages over the alternators.

In grid connected systems, the frequency and the voltage at the machine are governed

by the electric grid. Grid connected systems are usually between 10 kW and 100 kW. The

power should be normally conditioned using an inverter before fed to the grid. Self-

commutated inverters need a reference from the utility grid to hold synchronization. This

can be easily done with induction generators.

Discuss about each graph plotted.

1. Self-excited Induction Generator

Part (a):- No Load characteristics for varying capacitance and constant prime mover speed

Line Voltage vs. Magnetizing Current

When the magnetizing current increases, the line voltage also increases. But after some time,

the line voltage tends to saturate with the further increment of magnetizing current. The

relation between the two parameters as follows where E, Im, ω, Lm indicates Line voltage,

magnetizing current, angular frequency and inductance of the equivalent magnetic circuit of

the machine respectively.

| | | |

Line Voltage vs. Magnetizing Current

With the increment of capacitance, the line voltage increases drastically. Further, line

voltage tends to saturate in lower capacitance conditions when the prime mover speed is at a

constant.

Part (b):- No Load characteristics for varying prime mover speed and constant capacitance

Voltage vs. Speed

With the speed of the prime mover, voltage increases linearly.

Frequency vs. Speed

With the speed of the prime mover, frequency increases linearly.

Magnetizing Current vs. Speed

With the speed of the prime mover, magnetizing current increases linearly.

Part (c):- Performance of the loaded generator with constant speed

Voltage vs. Load Current

Voltage decreases when the load current increases. At lower load currents the decrement of

the voltage is very low. However with the load current, voltage decreases drastically.

Frequency vs. Load Current

According to the results obtained, it is significant that frequency remains constant while load

current is being increased. Hence, it is found that at constant speeds, the frequency of the

loaded generator does not depend on load current.

Generator Current vs. Load Current

Generator current is being decreased with the load current.

Part (d):- Performance of the load generator without speed regulation

Voltage vs. Load Current

The voltage decreases with the load current in this case too. But in numbers, the decrement

of voltage is dramatically large when there’s no speed regulation.

Frequency vs. Load Current

Frequency decreases with the load current in the absence of speed regulation unlike in the

earlier case, the speed regulated scenario. It is tend to remain constant for very low load

currents for a moment; but drastically decreases then.

Torque vs. Speed of the prime mover

Torque, speed relationship here is somewhat linear and torque decreases uniformly with the

speed of the prime mover.

2. Grid Connected Induction Generator

Power Output vs. Speed

The increment of power output with respect to the speed of the grid connected induction

generator is somewhat linear.

Line Current vs. Speed

Line current increases with the speed in a linear manner.

Efficieny vs. Speed

Efficiency increases with the speed. However it is tend to reach a maximum at more speeds

because the gradient is decreasing. Then after reaching its maximum, the efficiency will

decrease again at very high speeds.

Power factor vs. Speed

Power factor shows a non-linear relationship with the increment of speed. At lower speeds

close to 3000rpm the increment is very low and when it reaches a values like 3030, 3040

rpm it tends to show a linear relationship. Then again at higher speeds close to like 3100rpm

the power factor tends to reach a maximum point and then decreases with further increment.

REFERENCES

http://en.wikipedia.org/wiki/Induction_generator

http://autonopedia.org/renewable_energy/Generators/motors_as_generators.html

http://www.ijcee.org/papers/278-E747.pdf