Induction Generator (2)

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LABORATORY PRACTICE IV

INDUCTION GENERATOR

NAME : R.M.R.A.RATHNAYAKA

INDEX NO : 090433K

FIELD : EE

GROUP : G 11

DATE OF PER : 22-08-2011

DATE OF SUB : 01-09-2011

CONDUCTED BY : Mr. H.A.I .De Silva


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Objectives:

To study the characteristics of operation of

1. A self-exited induction generator.2. A grid connected induction generator.

Introduction:

The induction machine as a motor is very popular due to its many advantages. Though not popular

as such, it is also capable of working as a generator, either isolated or connected to the grid supply.

Irrespective of the form of operation, lagging reactive power has to be supplied to the induction

machine by an external source.

When operated as an isolated generator, asset of capacitors used to supply the reactive power

required. The residual magnetism present in the machine causes a voltage to build up across the

terminals. Thus the residual flux in the machine is of utmost importance when operated as anisolated induction generator.

When induction generator is connected to the grid supply, lagging reactive power requirement is

drawn from the grid supply and by driving the machine at the super synchronous speed in the

correct direction; real power can be fed in to the grid.

Apparatus:

1. Induction machine2. DC dynamometer3. Stroboscope4. 3-phase wattmeter5. AC voltmeter (300V)6. 2 AC ammeters (5A)7. Frequency meter(5-10Hz)8. Oscilloscope9. Isolating voltage transformer10.

2 banks of variable resistive loads

11.Capacitor bank (0-120F)PROCEDURE

1) Isolated induction generator

Part (a) No load characteristic for varying capacitance and constant prime mover speed

Connect the circuit as shown below


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DC Dynamometer

Induction Machine Capacitor bank

A

V

Drive the dynamometer (prime mover of the induction generation) at 2500 rpm using field current

controller of the DC motor. With the terminal of the induction machine open, measure the terminal

voltage.(this voltage connect the residual magnetism in the machine).Connect the variable capacitor

bank at the machine terminal and increase the capacitor from zero for each value of the capacitance

measure the voltage frequency of the generator and magnetizing line current on no-load-at 2500rpm

without exceeding 280V.

Part b) No load characteristic for varying prime mover speed and constant capacitance

Connect the circuit as in part (a) .Connect the capacitance required to obtain the rated voltage under

no-load at 2500rpm. Drive the prime mover at different speeds such that the no-load line voltagewithin the range 200V-280V. Get the reading of Speed, voltage, frequency and the magnetizing current

for five different voltages.

Part c) Performance of the loaded generator with constant speed

Connect circuit as below

Drive the prime mover at 2500rpm. Select the capacitance such that the no-load generator voltage is280V. While keeping the speed constant, vary the load resistance. (Without exceeding 5A in load

circuit. ) Measure voltage, current under different loading conditions.

Part (d). Performance of the loaded generator without speed regulation

Repeat the same procedure as in (C) above, the prime mover at 2500rpm under no-load and without

adjusting the speed at each loading step.

DC Dynamometer

Induction MachineCapacitor bank

A

V

A

Resistor Bank


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2. Grid connected Induction Generator

Connect the circuit as below

Drive the dynamo meter and observe the rotating direction, also drive the induction machine as a

motor and observe the rotational direction and how those terminal was connected, it can useful to drive

the both in to same direction. Drive the prime mover at 300rpm. Connect 240V, 50Hz supply to the

induction machine.

Increase the speed slightly to get the zero wattmeter reading. Under this condition no real power is

delivered to the grid. The current read from the ammeter is the excitation current drawn by the

induction generator. Note down the line current, voltage, frequency, speed and torque. Increase the

speed in steps of 25rpm and until the rated power is delivered to the grid and note down all quantities

at each step.

DC Dynamometer

Induction Machine

A

V

3-Ph

Wattmeter

Grid


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1. Self exited Induction Generator

Part (a)-Line voltage vs Magnetising current

220

230

240

250

260

270

280

1.5 2 2.5 3 3.5

Line

voltage(V)

Magnetizing Current (A)


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Part (a)-Line voltages vs Capacitance

Capacitance required;

At 240V C=I/ (2fV) At 240V & 50 Hz C=I/ (2fV)= 2.3/ (2*41*240) = 2.3/ (2*50*240)

= 37.2F (Theoretical) = 30.50F

Practical67F

220

230

240

250

260

270

280

290

50 55 60 65 70 75 80

LineVoltage(V)

Capacitance (uF)


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Part (b)-Voltage vs Speed

180

200

220

240

260

280

300

2350 2400 2450 2500 2550 2600 2650 2700

Voltage(V)

Speed (rpm)


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Part (b)-Frequency vs Speed

39.5

40

40.5

41

41.5

42

42.5

43

43.5

44

44.5

2350 2400 2450 2500 2550 2600 2650 2700

Frequncy(Hz)

Speed (rpm)


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Part (b)-Magnetising Current vs Speed

0

0.5

1

1.5

2

2.5

3

2350 2400 2450 2500 2550 2600 2650 2700

Magnetizingcurrent(A)

Speed (rpm)


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Part (c) / Part (d)-Voltage vs Load Current

180

190

200

210

220

230

240

250

260

270

280

0 0.5 1 1.5 2

Voltage(V)

Load Current (A)

with constant speed(2500rpm)

without speed regulation

Poly. (with constantspeed(2500rpm))

Poly. ( without speed

regulation)


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Part (c)/ Part (d)-Frequency vs Load Current

38.5

39

39.5

40

40.5

41

41.5

42

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8

Frequency(Hz)

Load Current (A)

with constant

speed

(2500rpm)

without speed

regulation

Log. (with

constant speed

(2500rpm))

Poly. (without

speed

regulation)


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Part (c) Generator Current vs Load Current

0

0.5

1

1.5

2

2.5

3

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8

G

en.

Current(A)

Load Current (A)


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Part (d)-Torque vs Speed of prime mover

1.5

1.7

1.9

2.1

2.3

2.5

2.7

2.9

3.1

3.3

3.5

2400 2420 2440 2460 2480 2500 2520

Torque(Nm)

Speed(rms)


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2. Grid connected Induction generatorPower output vs Speed

0

10

20

30

40

50

60

70

2980 3000 3020 3040 3060 3080 3100 3120

Pow

erOutput(W)

Speed (rpm)


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Line Current vs Speed

0

0.5

1

1.5

2

2.5

3

3.5

4

3000 3020 3040 3060 3080 3100 3120

LineCurrent(A)

Speed (rpm)


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Calculating Efficiency at each conditions

%

For a sample calculation

2.866%

II. Calculating power factor:

Wattmeter reading =real power

Apparent power = V

Sample calculation

p.f =10/(1.5220)

=0.03

Current(A) Voltage(V) Power(w) Speed(rpm) Torque(Nm) Efficiency % Power factor

1.5 220 0 3003 1.0 00

1.5 220 10 3028 1.1 2.8660.03

1.7 220 30 3048 2.0 4.6990.08

2 224 40 3076 2.7 4.5590.09

3.35 22460 3100

3.25.77

0.08


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Efficiency Vs speed

0

1

2

3

4

5

6

7

2980 3000 3020 3040 3060 3080 3100 3120

Efficiency(%)

Speed(rpm)


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Power factor Vs speed

0

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09

0.1

2980 3000 3020 3040 3060 3080 3100 3120

Powerfactor

Speed (rpm)


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DISCUSION:

1. Why the no-load test done under lower frequency than the rated 50HzAt no load condition output power is zero. This can be achieved by keeping synchronous speed

(Ns) greater than rotor speed (Nr)

(NS ) = 60 fs/p

(Nr ) = 60 fr/p NS > Nr

60 fs/p>60 fr/p

fs > fr

50Hz> fr

To achieve that objective the no-load test was designed to result in a lower frequency

than rated frequency of 50 Hz.

2. Cause of variation of the voltage and current wawe forms of the generator when loading In the two cases where we load the generator with load and without loading we can

obtain different values of voltage and current wave forms. If we do not change the

speed when we increase the load, frequency of the generator decreases. There for the

voltage waveform will expand in the time axis as the rotor speed reduces.

When we apply more load the generator will have to gives more power. There forwhen load of the generator is increasing the amplitude of the current wave form will

grow higher. And also when frequency drops the current will automatically will

expand in the time axis.

3. Importance of induction generator in Sri Lanka Induction generators are often used in wind turbines and some micro hydro installations

due to their ability to produce useful power at varying rotor speeds. Sri Lanka is rich in

waterfalls which can be used to produce electricity using micro hydro power plants or

mini hydro power plants.

Also our country have sufficient wind pattern in coastal areas for power generation.This induction generators can be used for generate power using wind. Induction

generators are particularly suitable and usually used for wind generating stations as in

this case speed is always a variable factor, and the generator is easy on the gearbox. By considering the prices of these generators this induction generators are much more

suitable for a developing country like Sri Lanka for power generate to supply to the

national grid or use in their own premises.

Induction generators are mechanically and electrically simpler than other generatortypes. So with little technical knowledge this generator can be installed or repaired even

without a help of an engineer.

They are also more rugged, requiring no brushes or commutators . repair is easy andthis machine can last long than other moters.

There are two methods that we can use this machine. With grid connect or without gridconnection. So we can supply power to the rural areas as well as urban areas.


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Advantages of induction generator

Induction generators are much suitable for mini & micro small scale power plants andgrid wind power plants

Cheap compare to Synchronous Generator Size is considerable small No need of supporting structure Robust and Reliable in operation. Simple in construction easy to maintain.

4. Discuss about each graph plotted1) Self-excited Induction Generator

Part (a)

Line Voltage (V) Vs Magnetizing Current (I)According to this graph we can see the line voltage is increasing while increasing the

magnetizing current. And even close to a linear relationship.

Line Voltage Vs CapacitanceAccording to this graph we can see the line voltage is increasing while increasing the

Capacitance. Its close to a linear relationship.

Part (b)

Voltage Vs SpeedAccording to this graph we can see the line voltage is increasing while increasing the Speed.

Its very close to a linear relationship. Frequency Vs Speed

According to this graph we can see the frequency is increasing while increasing the speed. Its

very close to a linear relationship.

Magnetizing Current Vs SpeedAccording to this graph we can see the Magnetizing Current is increasing while increasing the

speed. Its close to a linear relationship.

Part (c)

Voltage Vs Load CurrentAccording to this graph we can see the Voltage is decreasing while increasing the Load

Current. Its so close to a curve relationship.

Load Current Vs Frequency


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According to this graph we can see the Frequency is decreasing while increasing the load

current. Its close to a linear relationship.

Load Current Vs Generator CurrentWhen load current increases the generator current decreases.This has a linear relationship.

Part (d)

Voltage Vs Load CurrentWhen load current is increasing voltage decreases. It decrease some kind of exponentially way.

The voltage in the constant speed case is much larger than without speed regulation one

Frequency Vs Load CurrentWhen load current increases frequency decrease. It decrease in a linear way. Frequency in the

constant speed motor is higher than frequency in motor which has not got speed control in same

load current.

Torque Vs SpeedAccording to this graph we can see the Torque is decreasing while increasing the speed, this is

a linear graph.

2) Grid connected Induction Generator Power Output vs. Speed

According to this graph we can see the power output is increasing while increasing the speed.

And also its close to a linearrelationship with speed of the generator.

Line Current vs. SpeedLine current also increases while increasing the speed. This graphs also not a linear one. So line

current has no linear relationship with speed. Its kind of polynomial one.

Efficiency vs. SpeedWhile the speed is increasing the efficiency of this graph is increase non linearly.

Power Factor vs. SpeedAccording to this graph the power factor is increasing with speed up to some limit. And this

graph has non linear behavior.

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Induction Generator (2)