EM-1 LAB MANUALS(1)

8/10/2019 EM-1 LAB MANUALS(1)

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SWINBURNES TEST

AND

SPEED CONTROL OF

D.C. SHUNT MACHINE


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Experiment no: 1

SWINBURNES TEST AND SPEED CONTROL OF DC SHUNT

MACHINE

AIM : To Pre-determine the efficiency and performance characteristics of a DC Shunt machine.

(both as a generator & motor). Determination of the speed characteristics of DC shunt machine

by a) Field control b) Armature control

NAME PLATE DETAILS:

S.No Type DC Shunt Motor

01 Ratings 3.0HP

02 Volts 220 V DC

03 Current 12 A

04 Exc. Volts 220 V DC

05 Exc. Current 0.6 A

06 Duty S 1

07 Ins. Class B

08 Speed 1500 rpm

APPARATUS:

S.No Apparatus Required Rating Type Qty

01 Voltmeter (0-300) M.C 1

02 Ammeter (0-10) M.C 1

03 Ammeter (0-5) M.C 2

04 Rheostat 360 Ohm / 1.2 A M.C 1

05 Tachometer Digital 1

06 Fuse 20 2


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THEORY:

SWINBURNES TEST: - It is a simple method in which losses are measured separately and from their knowledge,

efficiency at any load can be pre-determined in advance. The onlyrunning test needed is

a no load test.

Swinburne s test is applicable to those machines in which flux is practically constant i.e.

Shunt wound and Compound wound machines.

The machine is running as a motor on no-load at its rated voltage and its speed be

adjusted to its rated value using Shunt regulator.

The no-load armature current Iao is measured using an ammeter, where as shunt field

current Ish is given by another ammeter. The no-load input current is given by

Io = Iao + Ish Let the supply voltage be V volts

No-load input = V Io watts

Power input to armature = V Iao watts

Power input to shunt = V Ish watts

No-load input supplies Copper losses (Armature & Field), Iron losses (Hysteresis &Eddy current) & Mechanical losses ( Friction losses & Windage).

Constant losses = No load input power - Armature copper losses

Wc = V Io Iao Ra watts. Predetermination of efficiency of a motor at any load

Input = V I L watts. Rated value I L = 12A

Armature Cu losses = I a 2 Ra

Constant losses = Wc

Total losses = Wc + ( I L - Ish) Ra

Efficiency = (Input - Total losses) / (Input)


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(Efficiency) x = (x Input - Wc + ( x I L - Ish) Ra) / x input

X may be , , , full load(1)

Predetermination of efficiency of a generator at any load

Output = V I L watts.

Armature Cu losses = Ia 2 Ra

Constant losses = Wc

Total losses = Wc + ( I L + Ish) Ra

Efficiency = (Output) / (Output + Total losses)

(Efficiency) x = (x Output) / (x output+ Wc + ( x I L + Ish) Ra)

X may be , , , full load (1)

Maximum Efficiency condition : Variable losses (Ia Ra) = Constant losses ( Wc)

SPEED CONTROL: Speed control of DC shunt motor can be done in the following two ways Field control

method Armature control method

F ield Control M ethod:-

This method of speed control also called as Field weakening method gives speeds only

above the rated speed.

The field flux and the speed of the shunt motor can be controlled easily by varying the

field regulating resistance.

By increasing the field circuit resistance under steady conditions, the field current (If) and

field flux () are reduced since the rotor speed cannot change suddenly due to inertia.

This decrease in flux also causes a reduction in the counter EMF. As a result more

current flows through the armature.

The percentage increase in the armature current is much more than the percentage

decrease in the field flux and hence electromagnetic torque increases. This being more

than the load torque, the motor gets accelerated. As field flux is inversely proportional to

speed, as it decreases, the speed of the motor increases at constant armature voltage.

N = ((V-Ia Ra) 60A) / (ZP)

N proportional to 1/


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Ar mature contr ol method:-

This method is used when speeds below the no load speed are required.

As the supply voltage is normally constant, the voltage across the armature

is varied by inserting a variable rheostat in series with the armature. The

Potential difference across the armature is decreased, thereby decreasing the

Armature speed.

Eb = (ZNP) / (60A)

Therefore at constant flux (field current), as the voltage across the armature increases, the speedof the motor also increases and vice versa.

SWINBURNES TEST 1. Connect the circuit as per the Circuit diagram.

2. Initially the starter must be in off position.

3. Switch on the D.C. Motor to 220V D.C. Supply by closing the DPST Switch.

4. Start the D.C. motor using the three point starter and thereby adjust the speed to its rated speed

using field rheostat.230

5. Note down the readings of Voltmeter & Ammeters in Table

6. Switch off the D.C. Motor from 220V D.C. Supply by opening the DPST Switch.

SPEED CONTROL

1. Connect the circuit as shown in the circuit diagram.

2. Keep the armature rheostat resistance at maximum position and the field rheostat at minimum

position before starting the experiment.

3. The DC supply is switched ON and motor is started with the help of a three point starter.

4. Keep the field current constant and vary the rheostat in series with the armature.

5. Note down the corresponding readings of the voltmeter across the armature and speed of theDC shunt motor.

6. Now the rheostat of the armature is kept as it is and now the field rheostat is varied and note

down the corresponding readings of field current and the speed of the DC shunt motor.


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OBSERVATION TABLES:

SWINBURNES TEST

At Constant speed of 1500r.p.m.

S.No. Input Voltage V Armature Current Field Current

1

230 0.6 0.6

Wc = V Io Iao Ra Watts = _275.28_______ Watts

FIELD CONTROL METHOD

At Va =

Speed, N (rpm)

0.6

0.5

0.4

0.3

0.2

1500

1565

1610

1660

1710

ARMATURE CONTROL METHOD

At

Voltage Speed, N (rpm)

228

223

218

214

209

1480

1450

1420

1400

1352


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CALCULATION TABLE:

SWINBURNES TEST:

I) For Motor

S.No Input

Voltage

(V)

Input

Current

(I)

Field

Current

(Ish)

Armature

Copper

Losses

Total

Losses

Input

Power

228

228

228

228

228

228

5

6

8

10

12

14

0.6 38.72

58.32

109.52

176.72

259.92

359.12

314

333.6

384.8

455

535.2

634.2

1140

1368

1824

2280

2736

3192

72.45

75.61

78.2

80

80.12

80.11


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For Generator

S.No Output

Voltage

(V)

Output

Current

(I)

Field

Current

(Ish)

Armature

Copper

Losses

Total

Losses

Input

Power

228

228

228

228

228

2

4

6

8

10

0.6 13.52

42.32

87.12

147.92

224.72

288.8

318.12

362.4

423.2

500

456

912

1368

1824

2280

61

71

79

81

82


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MODEL GRAPHS:

SWINBURNES TEST

FIELD CONTROL METHOD AT CONSTANT ARMATURE VOLTAGE


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Ar matur e control method at constant f ield curr ent

PRECAUTIONS:-

1. The field rheostat of the motor must be kept in minimum before switching on the 220V D.C

supply.

2. Ensure that the starter arm is at extreme left position.

3. Avoid loose connections

4. Note down the readings from the meters without any parallax error


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RESULTS: Constant losses = ____275.28_____ Watts Current at which Max. occurs for motor = _____14____ A Current at which Max. occurs for generator = ___10______ A Maximum Efficiency for motor = __79.6________ %. Maximum Efficiency for generator = _81.2_________ %.

CONCLUSIONS:

VIVA VOCE QUESTIONS:1 What is the significance of Swinburne s test?

2 What are the advantages & disadvantages of this test?

3 Why this test is not suitable for D.C series motor?

4 What is the purpose of 3 point starter?

5 What happens if field is open in D.C motor?

6 Why we have to keep the field rheostat in minimum position?

7 In how many ways, we can control the sped?

8 Compare the speed control methods?

9 What are the different losses in D.C machines?

10 What is the purpose of starter?

11 How do you reduce the iron losses?


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LOAD

CHARACTERISTICS

OF A DC

SHUNT GENERATOR


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Experiment no: 2

LOAD CHARACTERISTICS OF A DC SHUNT GENERATOR

AIM : To determine the internal and external characteristics of dc shunt generator by performing

a load test.

NAME PLATE DETAILS:

Type DC Shunt Motor DC Shunt Generator

Ratings 3.0HP 2 KW

Volts 220 V DC 220 V DC

Current 12 A 12 A

Exc. Volts 220 V DC 220 V DC

Exc. Current 0.6 A 0.7 A

Duty S 1 S 1

Ins. Class B B

Speed 1500 rpm 1500 rpm

APPARATUS:


01 Voltmeter (0-300)V M.C 1

02 Ammeter (0-20)A M.C 2


04 Rheostat 360 ohm/ 1.2A - 2

05 Tachometer - Digital 106 Fuse 20A - 2


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THEORY: Generator is run at rated speed and the field current is adjusted to give rated voltage at no

load.

DPST is closed and the load is gradually increased in steps and the readings are recorded

at each step. A plot of terminal voltage Vt and load current IL with respect to the

particular value of field current If and speed gives the external characteristic curves.

The drop in voltage is due to Ra drop, reduction of main field flux due to armature

reaction and further reduction in If.

This test is applicable for two similar shunt machines. The two machines are coupled

mechanically. One machine runs normally as a motor and drives generator.

PROCEDURE:

1. Connect the circuit as per the circuit diagram.2. Close the DPST1 switch and start the motor with the help of starter.

3. Adjust the field regulator of the motor till the generator reaches it s rated speed.

4. By adjusting the field regulator of the generator rated voltage can be applied to the generator

at it s terminals.

5. Apply the load gradually in steps by closing the switch DPST2 and note down the readings of

the load current, terminal voltage and field current of the generator for every change in load.

6. Continue the above said procedure until the ammeter shows a reading of near to full load

current.

7. Then bring the rheostats to initial positions and switch off the supply

OBSERVATION TABLE:

Field

Current,

Terminal

Voltage, Load

Current,

Armature

Current, Generated

emf, 0.6 221

218

212

208

203

199

0

0.8

2.0

3.1

4.2

5.2

0.6

1.4

2.6

3.7

4.8

5.8

221.3

22.8

217.2

215.4

211.6

210.6


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194

190

6.3

7.8

6.9

7.8

207.8

205.6

CALCULATIONS:

Armature current = load current + field current

Ia = + If

Generated emf = terminal voltage + armature resistance drop

Eg = Vt +IaRaMODEL GRAPHS:

PRECAUTIONS:

Field regulator of the motor must be in minimum position while starting the motor. While loading the generator, at each step, the speed of the generator is maintained at its

rated value.


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Generator should not be overloaded. Ensure that the starter arm is at extreme left position. Avoid loose connections Note down the readings from the meters without any parallax error Tachometer should be kept horizontal to the shaft while measuring the speed. Before switch OFF the motor make sure that there is no load connected to motor

RESULTS:

VIVA VOCE QUESTIONS:

1) what is the difference between internal & external Characteristics?

2) What are the applications of D.C shunt Generator?

3) Why the field rheostat of the Generator should be kept in maximum position?

4) What is voltage regulation ?

5) What is residual voltage?

6) What are the losses in D.C Shunt Generator?Where losses occur?

7.) What is the condition for maximum efficiency?

8.) Define stray losses, from which test stray loss are found.


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BRAKE TEST ON A

D.C. SHUNT MOTOR


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Experiment no: 3

BRAKE TEST ON A D.C. SHUNT MOTOR

AIM : To obtain the Performance characteristics curves of a D.C. shunt motor by conducting

brake test on it.

NAME PLATE DETAILS:


01 Ratings 3.0HP

02 Volts 220 V DC

03 Current 12 A



06 Duty S 1

07 Ins. Class B

08 Speed 1500 rpm

APPARATUS:





04 Rheostat 360 ohm/1.2A - 1

05 Tachometer - Digital 1

06 Fuse 20A - 2


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THEORY: It is a simple method of testing low rating DC machines and consists of applying a brake

to a water-cooled drum mounted on the motor shaft.

The four important characteristics curves of a D.C. Shunt Motor, namely, Torque, Speed,

Armature Current & efficiency, each plotted against the useful Power, as shown in the

model graph are known as Performance characteristics

A belt is wound round the brake drum and its two ends are attached to two spring

balances S1 & S2. The tension of the belt can be adjusted with the help of swivels.

The force acting tangentially on the drum is equal to the difference between the readings

of the two spring balances.

0the readings of Spring balances 1& 2 in Kg.f.

Shaft torque, T developed by the motor is 9.81 (S1 S2) R Nm where, R is the radius ofthe pulley in meters & N is the speed in rpm

Useful Output Power = Watts Input Power = V Watts, where = (Ia + Ish) % Efficiency , = (Output power / Input power) x 100.

Speed Regulation = [ (No Load speed ) - ( Full load speed )] / Full Load. Speed =

The size of the motor that can be tested by this method is limited from the consideration

of the heat that can be dissipated at the brake drum Where the output power exceeds about 2 H.P., or where the test is of long duration, it s

necessary to use a water cooled brake drum.

PROCEDURE:

1. Connect the circuit as per the Circuit diagram.

2. Initially the starter must be in off position.


4. Start the D.C. motor using the three point starter and thereby adjust the speed to its rated speedusing field rheostat.

5. Note down the readings of Voltmeter & Ammeters in Table under No Load condition.

6. Apply the Load on the drum gradually in steps by tightening the belt around it. At each step,

note down the readings of the Ammeters, Voltmeter, two Spring balances and the Tachometer.

7. Pour water in the pulley and cool it often when the motor is loaded.


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8. When the full load is reached, slowly reduce the load and switch off the Motor from 220V

D.C. Supply by opening the DPST Switch

OBSERVATION TABLE:

S.No Input

Voltage (V)

Armature

Current

Field

Current

Spring Balances Speed

(N)

225

220

215

210

205

200

195

190

185

180

1

2.4

3.4

4.4

5.4

6.4

7.4

9.4

10.4

11.9

0.6 0

2.5

4

5.2

7

8.1

9.5

11.6

12.8

14

0

1.1

1.8

2.6

3

3.5

4

4.6

5.1

5.6

1520

1510

1500

1486

1472

1465

1458

1452

1436

1426


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CALCULATION TABLE:

Radius of the Brake Drum, R = ______ mts.

S.No Input

Voltage

(V)

Input

Current

Torque,

N-m

(T)

Output

Power

Input

Power %

1.5

3

4

5

6

7

8

10

11

12.6

0

2.06

3.23

3.8

5.8

6.7

8.09

10.59

11.46

12.93

0

325.75

507.33

592.44

898.88

1031.33

1236.6

1607.2

1729.5

1894.21

360

660

860

1050

1230

1400

1560

1900

2035

2256

0

49.35

58.99

59.46

73.65

73.62

79.2

84.6

84.12

84.13

PRECAUTIONS:

1. The field rheostat of the motor must be kept in minimum before switching ON the motor.



4. Note down the readings from the meters without any parallax error

5. Tachometer should be kept horizontal to the shaft while measuring the speed.6. Before switch OFF the motor make sure that there is nos load connected to motor.


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MODEL GRAPHS:

RESULTS:

At full load:

i) Torque = __________ Nm.

ii) Speed = __________ rpm

iii) Armature Current = __________ A

iv) Efficiency = __________ %.

v) Speed Regulation = _________

CONCLUSIONS:


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1) What is Speed regulation?

2) What are the different types of motor?

3) What are the characteristics of D.C shunt motor?

4) What is the condition for maximum efficiency?

5) What are the different methods to reduce the iron losses?

6) What are the application of D.C Shunt Motor?

7.)Define armature reaction?

8.) Difference between interpole and compensating winding.

9. ) Define breake horse power (B.H.P).


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MAGNETIZATION

CHARACTERISTICS OF A

D.C. SHUNT GENERATOR


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Experiment no: 4

MAGNETIZATION CHARACTERISTICS OF

A D.C. SHUNT GENERATOR

AIM : To obtain the Magnetization Characteristics of a D.C. Shunt Generator and to determineits Critical field resistance & Critical speed.

NAME PLATE DETAILS:


Ratings 3.0HP 2 KW


Current 12 A 12 A



Duty S 1 S 1

Ins. Class B B


APPARATUS:

S.No Apparatus Required Rating Type Qty01 Voltmeter (0-300)V M.C 1



04 Rheostat 360 ohm/1.2A -



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THEORY:

I) Magnetization Characteristics

The magnetization characteristics shows the relation between the no load generated emf

in armature, E0 and the field (or) exciting current, If at a given fixed speed as shown in

model graph.

These characteristics are also known as the No load saturation characteristics or Open

circuit characteristics. The shape of these characteristics is practically same for all

generators whether separately excited or self excited

Due to the residual magnetism in the poles, some emf is generated even when If = 0

represented by OD**. Hence, the curve starts a little way up.

The slight curvature, DE** at the lower end is due to magnetic inertia. It is seen that the

first part of the curve, EC** is practically straight. This is due to the fact that at low fluxdensities, reluctance of iron path being negligible (due to high permeability), total

reluctance is given by the air gap reluctance, which is constant. Hence, the flux and

consequentially the generated emf are directly proportional to the exciting current.

How ever at high flux densities, where m is small, iron path reluctance becomes

appreciable and straight relation, CF** between Eo and If no longer holds good, i.e.,

saturation of poles start.

(** refers to the model graph)

II) Critical resistance

It is that maximum value of the field resistance, above which the machine fails to excite

i.e. there will be no build up of the voltage.

This resistance corresponds to the straight-line position of the magnetization

characteristic because the magnetic circuit does not offer any appreciable reluctance to

the magnetic flux.

III) Critical speed

It is that speed for which the given shunt field resistance will represent critical field

resistance

(OR) It is that minimum value of the speed of the machine below which the machine fails

to excite .


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PROCEDURE:

1. Connect the circuit as per the circuit diagram.

2. Initially the starter must be in OFF & SPST Switch in open positions.


4. Start the D.C. motor using the three point starter and thereby adjust the speed of it to the rated

speed of the D.C.generator using field method of speed control.

5. Note down the voltage of the voltmeter which represents the residual voltage of the generator

when SPST switch is in open condition.

6. Excite the field winding D.C.generator in steps by decreasing its external resistance gradually

and note down various corresponding readings of ammeter and voltmeter till 1.1 to 1.25 times

the rated voltage of the generator is reached, maintaining constant speed .

7. Gradually reduce the field current of generator and make it to zero finally by opening SPSTswitch. and disconnect the D.C. Motor from the 220V D.C. Supply

.

OBSERVATION TABLE:

At constant speed of 1500r.p.m.

S.No Field Current A Armature Voltage V

0.10.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

3390

146

173

201

224

238

254

266

275


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MODEL GRAPHS:

CALCULATIONS:

TO FIND CRITICAL FIELD RESISTANCE :

1. Plot the magnetization curve.

2. Draw the tangent such that it touches most of the linear part of the curve. This line is the

Critical field resistance line.

3. The slope of the above line gives the Critical field resistance.

TO FIND CRITICAL SPEED:

1. Draw the constant field resistance line Rf .

2. From point draw a line on to the Critical field resistance line.

Now the Critical speed, Nc = (AB /AC) N, where N is the rated speed of

D.C. generator i.e., 1500 r.p.m.


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PRECAUTIONS:-

1. The field rheostat of the motor must be kept in minimum & for the generator in

maximum positions before switching on the D.C. supply.



4. Note down the readings form the meters without any parallax error

RESULT: Critical field resistance = ________ ohms. Critical speed = ________ r.p.m.

CONCLUSIONS:


1. What are Magnetization Characteristics?

2. What do you mean by Critical field resistance?

3. What do you mean by Critical speed?

4. How do you obtain the O.C.C at any other speed other than rated speed?

5. What are the different types of Generators?

6. What are the applications of D.C Shunt Generators?


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LOAD TEST ON DC

SERIES GENERATOR


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Experiment no: 5

LOAD TEST ON DC SERIES GENERATOR

Aim : To perform load test on a DC series generator and to draw the initial and external

characteristics.Name Plate Details:

Type DC Shunt Motor DC Series Generator

Ratings 3.0HP 2 KW


Current 12 A 12 A



Duty S 1 S 1

Ins. Class B B


Apparatus:

S.No Apparatus Required Rating Type Qty01 Voltmeter (0-300)V M.C 1



04 Rheostat -



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NO-LOAD CHARACTERISTIC :

In a DC series generator the armature winding and field winding and load resistance are

connected in series, therefore the field current is equal to the armature or load current. In view of

this, even though the series field current is zero the generator will build some voltage which is

due to residual flux and is known as residual voltage and it is very low when the load is opened.

However if the generator terminals are closed, through the load rheostat the armature current will

flow. This improves the residual flux and then residual voltage. The magnetization curve at one

speed for a series generator is illustrated by curve 1.

EXTERNAL CHARACTERISTICS (EgVs Ia):

This is known as total characteristics which give the relation between EMF actually induced in

armature and armature current. When the load side switch is open, the small voltage due toresidual flux will be indicated by the voltmeter. When that switch is closed field current equal to

load current starts flowing. If the current in series field produces a flux aiding the residual flux,

the generator will build up voltage till point C is reached. At point C the field resistance line OC

meets the saturation curve. The field resistance line OC depends on the total resistance in series

circuit i.e., it implies the slope of the line OC is determined by the sum of the armature circuit

resistance, series field resistance and load resistance. If the total resistance is more than the

critical field resistance, just like a self-excited shunt generator, the build up process will not

begin. Increase the load on dc series generator in steps and at each step, record load voltage and

load current. A curve passing through these plotted points gives external characteristic of curve

2. In the figure shown AB is load voltage or armature terminal voltage for a load current of OA.

INTERNAL CHARACTERISTICS (V Vs ):

This is known as Performance characteristics which give the relation between terminal voltage

and load current.

If total resistance drop IaR is added to the ordinates of curve2, the internal characteristic shown

by curve 3 is obtained. R is the sum of series field resistance and armature circuit resistance

(including brushes).Thus voltage drop BD is equal to the total armature resistance drop IaR and

the voltage drop CD is due to armature reaction. A horizontal line through D meets the

magnetization curve at F and DF gives demagnetizing effect caused by the armature reaction for

a load current equal to OA.


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MODEL GRAPH:-

PROCEDURE:


2. Start the DC shunt motor using 3-point starter and adjust its speed with the help of its field

Rheostat to the rated speed of generator.

3. Note down the reading of voltage generated across the armature of generator at the

corresponding load current.4. Now switch on the load in steps and note down the corresponding readings of load current and

terminal voltage maintaining at rated speed.

5. The procedure is repeated until the rated current is reached.

6. Reduce the load to zero and switch off the load.

7. Make all the Rheostats to its initial positions and then switch off the DC Supply.


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OBSERVATIONS:

S.No Terminal Voltage, Volts Load Current, (Amp) (Volts)

17

18

19

21

23

26

29

36

50

84

0.1

0.4

0.6

0.8

1.1

1.4

1.9

2.6

4.1

7.3

17.28

19.12

20.68

23.21

26.08

29.92

34.32

43.28

61.43

104.4

MODEL CALCULATIONS:

= Load current

= Armature current

V = Terminal Voltage

Eg = Generated EMF

= V+ (Ra+Rse)

PRECAUTIONS:-


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1. The connections should be tight and clear.

2. Before starting the DC machine, the armature and field rheostats should be kept at maximum

and minimum positions

.

RESULT:

CONCLUSION:

VIVA QUESTIONS:

1. What is a DC series generator?

2. What are the factors on which the generated emf in a DC series generator depends?

3. Why is value of the series field resistance low?

4. Comment on the shapes of the load characteristics of DC series generator.

5. How does armature reaction affect the terminal voltage of a DC series generator at high load

current?


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HOPKINSONS TEST

ON

D.C. SHUNT MACHINES


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Experiment no:6HOPKINSONS TEST ON DC SHUNT MACHINES

Aim : To perform Hopkinson s test on a given motor generator set and determine the efficiency

of both motor and generator.

Name Plate Details:


Ratings 3.0HP 2 KW

Volts 220 V DC 220 V DCCurrent 12 A 12 A



Duty S 1 S 1

Ins. Class B B


Apparatus:







06 Fuse 20A - 2


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Theory: Hopkinson s test is also known as back to back test. This test is regenerative test. By this method full-load test can be carried out on two shunt machines, preferably

identical machines without wasting their output.

The two machines are mechanically coupled and their fields are so adjusted that one of

them acts as motor and the other acts as generator.

The power taken from the supply is that required to overcome the losses only. Two identical machines of any size can be tested under full load condition and therefore

this method is very useful for determining efficiency and also a heat run test for

determining the temperature rise.

The electrical output of the generator plus the small power taken from the supply is taken

in by the motor and given out as mechanical power after supplying the motor losses.PROCEDURE:

1. Connect the circuit as per the circuit diagram

2. Keep the field rheostats of motor, generator at minimum, and maximum positions

respectively.

3. Close the DPST switch and open the switch .

4. Start the motor using the 3-point starter and adjust the speed to the rated value.

5. Build up the voltage across the generator by adjusting the field current till the voltmeter across

switch S2 is zero then close the switch S2.

6. Note down the readings of all the ammeters and voltmeters.

7. Switch off the DC supply

OBSERVATIONS:

S.No (V) (A) (A) (A) (A) (V)

225

225

225

1.8

1.9

2.0

0.6

0.6

0.6

0.2

1

2.8

0.58

0.58

0.58

225

225

225


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MODEL CALCULATIONS:

Supply voltage = V

Motor armature resistance = Ram

Generator armature resistance = Rag

Motor armature current = Iam

Generator armature current = Iag

Motor field current = Ifm

Generator field current = Ifg

Current taken from supply = IL

Motor armature copper losses = Ram

Motor field copper losses = V Ifm

Generator armature copper losses = Rag

Generator field copper losses = V Ifg

Power drawn from the supply = V IL

Total Stray losses (Wc) =

Stray losses per machine = Wc / 2

Motor :Motor Input

Motor losses = Armature copper losses + Shunt copper losses + Stray losses

=

Motor efficiency =

x=percentage of load

( )


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Generator:

Generator Output

Generator losses = Armature copper losses + Shunt copper losses + Stray losses

=

Generator efficiency =

GRAPHS :

1.Output VS Efficiency (of generator)

2. Output VS Efficiency (of motor)


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PRECAUTIONS:

1. The switch S is closed only when the voltmeter across the switch reads zero.

2. Loose connections are to be avoided.

3. The rheostats are to be kept at proper positions while starting the motor.

4. The readings of all the metres are to be noted down without any error.

RESULT:

CONCLUSIONS:


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VIVA QUESTIONS:

1. What is the purpose of Hopkinson s test?

2. What are the advantages of Hopkinson s test?

3. What are the conditions for conducting the test?

4. Why the adjustments are done in the field rheostat of generator and motor?

5. If the voltmeter across the SPST switch reads zero what does it indicate?

6. If the field got opened in the running condition in DC shunt generator what happens?


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BRAKE TEST ON

D.C.

COMPOUND MOTOR


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Experiment no:7

BRAKE TEST ON A DC COMPOUND MOTOR

Aim : To perform Brake test on a given D.C. Compound motor and obtain the performance

characteristics of the motor from the test observation.Name Plate Details:

S.No Type DC Compound Motor

01 Ratings 3.0HP

02 Volts 220 V DC

03 Current 12 A



06 Duty S 1

07 Ins. Class B

08 Speed 1500 rpm

Apparatus:



02 Ammeter (0-20A) M.C 1




06 Fuse 20A - 2


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THEORY:

It is a direct method and consists of applying brake to a water cooled pulley mounted on the

motor shaft. The simple brake test can be used for small motors only. Because, in case of large

motors, it is difficult to dissipate the large amount of heat generated at the brake. The simple

method of measuring motor output is by the use of pulley brake method. A rope is wound round

the pulley and its two ends are attached to two spring balances S1 & S2. The tension of the rope

can be adjusted with the help of swivels. The force acting tangentially on the pulley is equal to

the difference between the two spring balances. If is the pulley radius, the torque at the pulley

is Tsh=(S1~S2)r. If =2 N is the angular velocity of the pulley, then

Motor output =

=

Efficiency may, as usual, be formed by using the relation:

PROCEDURE:


2. Decrease the field regulating variable resistor of motor to a minimum value.

3. Put ON the DPST switch.

4. Using a 3-point starter start the motor and bring it to a rated speed.

5. Note all the readings at no load i.e., the terminal voltage, load current and speed of the motor.

6. Now tighten the belt of the pulley so that the load increases gradually. While doing this, note

again all the above readings mentioned and also the spring balance readings.

7. Pour water into the pulley and cool it whenever the motor is loaded heavily and see that the

drum of the pulley doesn t get much heated.

8. Run the motor till the full load is reached and now release the load slowly and stop the motor

by switching OFF the DPST switch.


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OBSEVATIONS:

S.No (Kg)

(Kg)

LineCurrent

(A)

TerminalVoltage

V (volts)

SpeedN

(rpm)

Torque

(N-m)

InputPower

(Watts)

OutputPower

(Watts)

Efficiency

0

1

1.8

2.6

3.5

4.2

5

0

2.1

4.5

7

9.4

11.8

14

1.5

3

5

7

9

11

13

230

231

230

234

230

231

230

1506

1501

1500

1496

1512

1496

1516

0

1.618

3.97

6.47

8.68

11.18

13.2

345

690

1150

1610

2070

2536

2990

0

254.6

623.8

1016.3

1354.2

1770.1

2095.5

0

36.9

54.2

63.12

65.42

69.9

70.8

MODEL CALCULATIONS :

Terminal Voltage , V= Volts

Radius of the pulley, r=0.15m

Input Power Watts

Torque Speed N= rpm

Output Power, Watts


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%Efficiency

=

MODEL GRAPHS :


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PRECAUTIONS :

1. Loose connections must be avoided to prevent from short-circuits.

2. Starter should be operated gently and the brake should be slowly applied in steps to avoid over

loading.3. See that the drum of the pulley doesn t get much heated by pouring water.

RESULT:

CONCLUSION:


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VIVA QUESTIONS:

1) Where are dc compound motors used?

2) Where are differentially compounded shunt motors used?

3) What may be the causes of sparking in a motor?

4) How can be the direction of rotation of motor be reversed in DC compound motor?

5) What is the purpose of using 3-point starter to start compound motor?


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LOAD TEST ON

D.C.

COMPOUND GENERATOR


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Experiment no:8

LOAD TEST ON DC COMPOUND GENERATOR

AIM: To determine the load characteristics of a DC compound generator.

NAME PLATE DETAILS: Type DC Shunt Motor DC Compound

Generator

Ratings 3.0HP 2 KW


Current 12 A 12 A



Duty S 1 S 1

Ins. Class B B


APPARATUS:


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THEORY:

The external characteristics of a compound generator are shown in graph. In a cumulatively

compound generator with increase in load current the series field flux aids the shunt field flux.

Depending upon the number of series field turns, the cumulative compound generator may be

under compounded, over compounded and flat compounded. Cumulative compound generators

are more common because they can furnish almost constant voltage from no load to full load.

In differentially compound generator, with the increase of load, series field flux opposes shunt

field flux and consequently the terminal voltage falls more rapidly, these are not damaged by

short circuit. In view of this, these types of generators may be used for welding purposes, where

sudden short circuit occurs every time the electric touches the working part. The degree of

compound can be controlled by connecting a suitable low resistance called diverter in parallel

with series field windingPROCEDURE:

1) Connect the circuit as shown in the circuit diagram.

2) Keep the field and armature rheostats of motor and the field rheostat of the generator in

minimum, maximum and maximum positions respectively.

3) Start the motor using a 3-point starter and there by the generator. Run the motor to its rated

speed by varying the armature and field rheostats of the motor and keep it constant

4) Adjust the shunt field rheostat of the generator to obtain rated voltage at no load.

5) Note down the no load terminal of the generator.

6) Apply the load in steps on the generator and for each load note down the corresponding field

current, line current and terminal voltage. Then remove the load and switch off the supply


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MODEL CALCULATIONS:

Vt = Ish =

Ia = + Ish

Ra = Rse =

Eg = Vt + IaRa + Rse

PRECAUTIONS:

1) Ensure that the armature rheostat is kept at the maximum position and the field rheostat is kept

at minimum position before switching on the supply .

2) Speed must be maintained constant throughout the experiment.

3) The tachometer should be kept in line with the shaft while measuring the speed.

4) Ensure that the starter arm is at the extreme left position before switching on the

supply.

RESULT:

CONCLUSION:

VIVA QUESTIONS:

1.How the compound generator operates?

2.What is the application of cumulative compound wound generator?

3.When the compound wound generator will be called as over compound?

4.Explain the characteristics of all types of compound wound generators?


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SEPARATION OF LOSSES

IN D.C. SHUNT

MACHINE


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Experiment no:9SEPARATION OF LOSSES IN D.C. MACHINE

Aim : To determine suitable tests on the given D.C. shunt machine and determine from the

experiment, the stray losses and separate these into friction, hysteric and eddy current losses.

Name Plate Details:


01 Ratings 3.0HP

02 Volts 220 V DC03 Current 12 A



06 Duty S 1

07 Ins. Class B

08 Speed 1500 rpm

Apparatus:






05 Fuse 20A - 2


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Theory:

D.C. machine consist the following losses.

1. copper loss

2. Rotational losses

Copper loss consist of armature copper loss and field copper loss. Rotational losses consist of

iron losses mechanical losses and stray load losses. Iron loss again subdivided into hysteresis

loss and eddy current loss. By performing no load test on D.C. Shunt machine at different fixed

field currents all the above losses can be separated.

Procedure:

1. The connections are made as per the circuit diagram.

2. The motor is started slowly using the starter keeping the field and armature rheostats in

minimum and maximum positions respectively.3. The field current is adjusted to the rated value at no-lead.

4. The armature ckt resistance is reduced in steps while increasing the speed.

5. The readings of the voltmeter, ammeter and tachometer are taken at constant field current.

6. The experiment is continued till the maximum speed is obtained by cutting out the complete

resistance in armature circuit.

7. The armature rheostat is brought back to its initial maximum position.

8. The motor is stopped.

9. The armature resistance is measured using a multimetre.

10. The readings are tabulated.


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Observation Table:

S.No V(Volts) N (rpm)

0.83

227

221

218

210

205

195

0.5

0.4

0.4

0.3

0.3

0.3

1511

1471

1452

1396

1365

1300

113

88.08

65.33

62.82

61.32

58.32

0.0747

0.0597

0.0446

0.0444

0.0445

0.0447

0.64

227

223

215

210

205190

0.5

0.4

0.4

0.4

0.40.4

1700

1650

1590

1560

15201378

113

88.89

85.68

83.68

81.6537.98

0.0665

0.054

0.0538

0.0561

0.05370.0275


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Model Graph:

The plot of Ws/N versus N is to plotted to find out the intercept and slopes.

Precautions:1. The rheostats are to be kept in proper positions while starting the motor.


3. The field current is to be maintained constant for a particular excitation though the speeds are

varied, by using the armature rhestat.

Results :

Conclusions:


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VIVA QUESTIONS:

1. What are the losses in a DC machine?

2. Why is the field copper loss negligible at no load?

3. Why does the armature resistance increase when the motor is running?

4. How can the mechanical losses be reduced?

5. How can the core losses be minimized?

6.What will happen to the losses in a dc motor when its supply voltage is: a) doubled b) halved?


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FIELDS TEST ON D.C.

SERIES MACHINES


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Experiment no:10

FIELDS TEST ON D.C. SERIES MACHINES

Aim : To perform FIELD test on a given D.C series motor generator set and determine the

efficiency of both motor and generator

Name Plate Details:

Type DC Series Motor DC Series Generator

Ratings 3.0HP 2 KW


Current 12 A 12 A



Duty S 1 S 1

Ins. Class B B


Apparatus:




03 Rheostat 360Oohm/1.2A - 1


05 Fuse 20A - 1


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Theory:

Small series machines can be tested by brake test similar to shunt machines, but the large series

machines cannot be tested by Swinburne s test in the same way as shunt machines, because

series motors cannot be run on no load due to dangerous high speed. In view of this field test is

quite suitable for D.C. series machines

In this test two similar D.C. machines are required. These two machines are mechanically

coupled together and their fields are connected in series in order to make iron losses of both

machines equal. One of the machines operates as a motor and drives the other machine operating

as a separately excited generator.

PROCEDURE:


2. Start the DC series motor using 2-point starter and adjust its speed with the help of Rheostat tothe rated speed of generator.

3. Note down the reading of voltage generated across the armature of generator at the

corresponding load current.

4. Now switch on the load in steps and note down the corresponding readings of load current and

terminal voltage maintaining at rated speed.

5. The procedure is repeated until the rated current is reached.

6. Reduce the load to zero and switch off the load.

7. Make all the Rheostats to its initial positions and then switch off the DC Supply.

OBSERVATIONS:

S.No Terminal Voltage, (Volts) Load current, (Amp) (Volts)

200

200

200

200

200

8.1

9.4

10.6

11.8

12.9

160

156

146

142

139


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MODEL CALCULATIONS:

Let Supply Voltage = V volts

Motor input current =

Terminal voltage of generator =

Load current of generator =

Armature resistance of each machine =

Series field resistance of each machine=

Input to the total set =

Output power =

Total losses of the set,

Series field and armature copper losses of motor =

Ser Series field and armature copper losses of generator =

Total copper losses of the set,

Stray Power losses for the set =

Stray Power losses for the set, Stray

MOTOR EFFICIENCY :

Motor input =

Motor losses=

Motor output=

Motor efficiency=


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GENERATOR EFFICIENCY

Generator input =

Generator losses=

Generator output=

Generator efficiency=

GRAPHS :

1.Output VS Efficiency (of generator)

2. Output VS Efficiency (of motor)

PRECAUTIONS:

2. The switch S is closed only when the voltmeter across the switch reads zero.


3. The rheostats are to be kept at proper positions while starting the motor.

4. The readings of all the metres are to be noted down without any error.

RESULT:

CONCLUSIONS:


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VIVA QUESTIONS:

1. What is the advantage of fields test?

2. How the direction of rotation of DC series motor can be reversed?

3. If a DC motor is connected across AC supply what happens?

4. What type of motor will be used for traction purpose and why?

5. Why the stator is not laminated in D.C. machines?

6. Difference between two point starter and three point starter?

7. What is relationship between torque Vs speed in Series, Shunt, Compound motors.

8. What are the applications of series and shunt, cumulative compound motors.

Documents

EM-1 LAB MANUALS(1)