EM-I LAB MANUAL

10 EE 306 ELECTRICAL MACHINES LABORATORY -I

2

HP V I RPM

230 V

DC SUPPLY

CIRCUIT DIAGRAM OF LOAD TEST ON DC SHUNT MOTOR

A1

3 POINT STARTER

-

_ +

M

L F A

D

P

S

T

S

W

I

T

C H

V

A

FUSE

15A

15A

A2

S2 Kg S1 Kg

-

(0-300V)

MC

+

(0-20A) MC

IL

+

220 /1.1 A

F1

F2

NAME PLATE DETAILS

FUSE

BRAKE DRUM


1

Ex. No:

LOAD TEST ON DC SHUNT MOTOR P.Aravindan Date :

AIM

To draw the performance characteristic curves of the given dc shunt motor by

conducting load test.

OBJECTIVES

1. To determine the efficiency of the given dc shunt motor by conducting load test.

2. To find the various parameters such as torque, input power, output power etc.

3. To obtain the electrical and mechanical characteristics for the given dc shunt

motor.

APPARATUS REQUIRED

S.NO APPARATUS

NAME

RANGE TYPE QUANTITY

01. Voltmeter (0300V) MC 1

02. Ammeter (020A) MC 1

03. Rheostat 220 /1.1A Wire wound 1

04. Tachometer Digital 1

FORMULA

1. Torque (T) =(S1 S2) x R x 9.81 Nm

Where

S1, S2 Spring balance readings in kg R Radius of brake drum in m

2. Input power (Pi) = VL x IL watt

Where

VL line voltage in volt IL load current in amp

3. Output power (Po) = 60

2 TNwatt

Where

N Speed of motor in rpm T Torque in Nm

4. % Efficiency ( ) = i

o

P

P

Where

Po Output power in watts Pi Input power in watts


2

TABULAR COLUMN 1.1:LOAD TEST ON DC SHUNT MOTOR

Circumference of brake drum, 2R = m

Radius of brake drum, R = m

S.No

LINE

VOLTAGE

(VL)

Volts

LOAD

CURRENT

(IL)

Amps

SPRING BALANCE

READINGS SPEED

(N)

(rpm)

TORQUE

(T)

(Nm)

INPUT

POWER

(Pi)

(Watts)

OUTPUT

POWER

(Po)

(Watts)

EFFICIENCY

in %

( )

S1

in kg

S2

in kg

S1 S2

in kg

1.

2.

3.

4.

5.

6.

7.


3

PRECAUTIONS

1. Select the fuse such that the current rating is 120% of rated current of the motor.

2. Ensure that the starter handle is in OFF position.

3. The motor field rheostat should be kept at minimum resistance position at the time of starting.

4. Heat produced due to friction between belt and brake drum is reduced by pouring water inside

the brake drum periodically.

PROCEDURE

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

2. The supply voltage of 230 V is applied by closing DPST switch.

3. The motor is started using 3 point starter and hence the flow of high starting current is avoided.

4. The motor field rheostat is adjusted from its minimum resistance position to get the rated speed

of 1500 rpm.

5. The no load readings of the voltmeter, ammeter and spring balances are noted.

6. The load is increased in steps and corresponding voltmeter, ammeter, spring balance readings &

speed for various load currents up to the rated current are noted.

7. Performance characteristic curves are drawn from the tabulated readings & calculated

performance parameters.

MODEL CALCULATION


4

MODEL GRAPH

Figure 1.1 Performance Characteristic Curves Figure 1.2 Mechanical Characteristic Curve

VIVA QUESTIONS

1. What is the role of magnetic field in electromechanical energy conversion?

2. Differentiate a permanent magnet from an electro magnet.

3. Which equation gives the amount of force developed by a current carrying conductor?

4. What is the function of commutator in dc motor?

5. What is the role of back emf in a dc motor?

6. If the terminal voltage is reduced to half and the torque remains constant, what will happen to the

speed and armature current?

7. What will happen to the speed of a dc motor when its flux approaches zero?

8. What is the necessity of a starter for dc motor?

9. What is the function of no volt coil?

10. How the direction of rotation of a dc shunt motor can be reversed?

11. What are the important characteristics of dc shunt motor?

12. What are the applications of dc shunt motor?

13. Which rule gives the direction of rotation of a dc motor?


5

RESULT

MARKS ALLOCATION

Details Marks Allotted Status Marks

Awarded

Preparation 20

Conducting 20

Calculation / Graphs 15

Results 5

Basic understanding (Core

competency learned) 15

Viva 10

Record 15

Total 100

Signature of Faculty

10EE 306 ELECTRICAL MACHINES LABORATORY -I

6

S2

Kg

NAME PLATE DETAILS

F

HP V I RPM

IL

CIRCUIT DIAGRAM OF LOAD TEST ON DC SERIES MOTOR

15A

230 V DC SUPPLY

- +

M

L A

A

D

P

S

T

S

W

I

T

C

H

V

A FUSE

15A

2 POINT STARTER

(0-300)V

MC

+

-

+

- FUSE

(0-20) A

MC

BRAKE DRUM

S1

Kg

A1

A2

E1

E2


7

Ex. No: LOAD TEST ON DC SERIES MOTOR

P.Aravindan Date :

AIM

To conduct the load test on dc series motor and also to draw the performance

characteristics of the given motor.

OBJECTIVES

1. To determine the efficiency of the given dc series motor by conducting load test.

2. To find the various parameters such as torque, input power, output power etc.

3. To obtain the electrical and mechanical characteristics for the given dc series

motor.

APPARATUS REQUIRED

FORMULA

1. Torque (T) = (S1 S2) x 9.81 x R in Nm.

Where,

S1, S2 are spring balance readings in kg

R is the radius of brake drum in m

2. Power output (Po) = 60

2 TN watt

Where,

N is the speed of the motor in rpm.

T is the torque in Nm.

3. Power input (Pi) = VLIL Watt.

Where,

VL is the line voltage in volt.

IL is load current in amp.

4. Percentage efficiency ( ) = Output power (Po) x 100

Input power (Pi)

Where,

Po Output power in watt Pi Input power in watt

S.NO APPARATUS NAME RANGE TYPE QUANTITY

1. Ammeter (020)A MC 1

2. Voltmeter (0300)V MC 1



8

TABULAR COLUMN 2.1: LOAD TEST ON DC SERIES MOTOR

Circumference of brake drum, 2R = m Radius of brake drum, R = m

S.No

LINE

VOLTAGE

( VL )

Volts

LOAD

CURRENT

( IL )

Amps

SPRING BALANCE

READINGS

SPEED

(N)

rpm

TORQUE

(T)

Nm

OUTPUT

POWER

(PO)

Watts

INPUT

POWER

(Pi)

Watts

EFFICIENCY

%

S1 in

kg

S2 in

kg

S1 S2

kg

1.

2.

3.

4.

5.

6.

7.

8.

9.

10.


9

PRECAUTIONS

1. Before the motor is started, the brake drum is to be loaded to avoid high speed

which will damage the winding.

2. Select the fuse, such that its rating is 120% of the rated current.

3. While making any change in the circuit the DPST switch must be kept open.

4. Heat produced due to friction between the belt and brake drum is reduced by

adding water into the brake drum periodically.

PROCEDURE

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

2. After some load is added to the brake drum, the motor is applied with 230 V dc

supply by closing the DPST switch.

3. The motor is started using two-point starter, so that high starting current is

avoided.

4. The voltmeter, ammeter, speed and spring balance readings are noted down.

5. The same procedure is repeated for various loads up to the rated value of current.

6. The motor is switched off after reducing to initial load on brake drum.

7. Performance characteristics are drawn using the tabulated readings & calculated

performance parameters.

MODEL CALCULATION


10

MODEL GRAPH

Figure 2.1: Performance Characteristic Curves Figure2.2:Mechanical Characteristic

Curve

VIVA QUESTIONS

1. Can we use same dc machine as a generator and as a motor?

2. Why series motors are preferred for traction purpose?

3. How can the direction of the dc motor be determined?

4. What is the medium against which the energy conversion takes place in dc

generators and dc motors?

5. What type of dc motor is suitable for variable torque operations?

6. State the precautions to be observed in starting a dc series motor.

7. From the nature of characteristics curves, give the applications of dc series motor.

8. Do maximum output and maximum efficiency occur at the same time? Why?

9. Why does the speed of a dc series motor decrease abruptly when load is

increased?

10. Why does not the line current characteristic start from the origin?

11. Why should the series motor always be started on load?

12. Why dc series motor develops a high starting torque?

13. What will be the effect on the direction of rotation of dc motor if the supply

terminal is reversed?

Torque in Nm

Sp

eed

in

rp

m


11

RESULT

MARKS ALLOCATION


Awarded

Preparation 20

Conducting 20


Results 5



Viva 10

Record 15

Total 100



12

HP V I RPM

C1

C2

(0-20A) MC

-

M

L1 L2 F A

D

P

S

T

S

W

I

T

C H

V

A FUSE

15A

15A

4 POINT STARTER

-

(0-300) V MC

+

-

+ +

220 / 1.1 A

F1

F2

230 V DC SUPPLY

FUSE

BRAKE DRUM

S1

Kg

A1

A2

S2

Kg

CIRCUIT DIAGRAM OF LOAD TEST ON DC COMPOUND MOTOR

NAME PLATE DETAILS


13

Ex. No: LOAD TEST ON DC COMPOUND MOTOR

P.Aravindan Date :

AIM

To draw the performance characteristic curves of the given dc compound motor

by conducting load test.

OBJECTIVES

1. To find the various performance parameters such as torque, input power, output

power.

2. To determine the efficiency of the given dc compound motor by conducting load test.

3. To obtain the electrical and mechanical characteristics for given dc compound motor.

APPARATUS REQUIRED


1. Voltmeter (0300 V) MC 1

2. Ammeter (020 A) MC 1

3. Rheostat 220 /1.1A Wire wound 1


FORMULA

1. Torque (T) = (S1 S2) x R x 9.81 Nm.

Where,

S1, S2 are spring balance readings in kg.

R is Radius of brake drum in m.

2. Input power (Pi) = VL x IL watt

Where,

VL is the line voltage in volt.

IL is load current in amp.

3. Output power (Po) = 60

2 NT watt

Where,

N is Speed of motor in rpm.

T is Torque in Nm.

4. % Efficiency ( ) = i

o

P

P

Where,

Po is Output power in watt.

Pi is input power in watt.


14

TABULAR COLUMN 3.1: LOAD TEST ON DC COMPOUND MOTOR

Circumference of the brake drum, 2R = m Radius of brake drum, R = m

S.No

LINE

VOLTAGE

(VL)

Volts

LOAD

CURRENT

(IL)

Amps

SPRING

BALANCE

READINGS

SPEED (N)

rpm

TORQUE (T)

Nm

INPUT

POWER (Pi)

(Watts)

OUTPUT

POWER (Po)

(Watts)

EFFICIENCY

( )

%

S1 in

kg

S2 in

kg S1 S2

kg


15

PRECAUTIONS

1. Select the fuse such that the current rating is 120% of rated current of the motor.

2. Ensure that the starter handle is in OFF position.

3. The motor field rheostat should be kept at minimum resistance position at the time

of starting.

4. Heat produced due to friction between belt and brake drum is reduced by pouring

water inside the brake drum periodically.

PROCEDURE

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

2. The 230 V dc supply is given by closing DPST switch.

3. The motor is started using 4 point starter so that high starting current is avoided.

4. The motor field rheostat is adjusted from its minimum resistance position to get

the rated speed of 1500 rpm.

5. The ammeter, voltmeter and spring balance reading at no load are noted down.

6. The load is increased in steps and corresponding voltmeter, ammeter, speed and

spring balance readings are noted for various loads up to the rated current.

7. Performance characteristic curves are drawn using the tabulated readings and

calculated performance parameters.

MODEL CALCULATIONS


16

MODEL GRAPH

Figure 3.1: Performance Characteristics Curves Figure 3.2: Mechanical Characteristics

Curves

VIVA QUESTIONS

1. Give an example for singly excited machine.

2. What is the application of dc compound motor? Give reasons in support of your

answer.

3. Compare the performance of differential compounding and cumulative

compounding of DC compound generators.

4. What is the difference between 3 point starter and 4 point starter?

5. Why is differentially compound motor rarely used?

6. Can a 3 point starter be used to start a compound motor?

7. Why does armature torque differ from shaft torque?

8. In which type of compound motor, flux decreases as load increases?

9. Is compound motor suitable for varied torque operations?

10. Why are dc cumulative compound motor used in applications which require

higher starting torque and need definite no load speed?

11. What is the role of residual magnetism?

12. What is the use of dummy coil in DC machines?


17

RESULT

MARKS ALLOCATION


Awarded

Preparation 20

Conducting 20


Results 5



Viva 10

Record 15

Total 100



18

HP V I RPM

CIRCUIT DIAGRAM OF SPEED CONTROL OF DC SHUNT MOTOR

5A

(0-300)V MC

230 V DC SUPPLY

M

D

P

S

T

S

W

I

T

C H

V

A FUSE

5A

F1

F2 A2

V

+

_

+

_

(0-300)V MC

+ _

96/3.2 A

+

_

A1

220 /1.1 A

A

FUSE

(0-5)A

MC

(0-2)A

MC

+

_

NAME PLATE DETAILS


19

Ex. No: SPEED CONTROL OF DC SHUNT MOTOR

P.Aravindan Date :

AIM

To study the speed control characteristics of the given dc shunt motor by field

control method and armature control method.

OBJECTIVES

1. To control the speed of dc shunt motor using armature control method.

2. To control the speed of dc shunt motor using field control method.

3. To obtain the speed characteristics of dc shunt motor by different methods.

APPARATUS REQUIRED

S. NO. APPARATUS NAME RANGE TYPE QUANTITY

1. Voltmeter (0300V) MC 2

2. Ammeter (02 A) MC 1

(05 A) MC 1

3.

Rheostat

220 /1.1A Wire wound 1

96 /3.2A Wire wound 1


FORMULA

Eb = V Ia Ra volt

Eb = K N

N = V Ia Ra /

Where Eb Back emf in volt

V Terminal voltage in volt

Ia Armature current in amp

Ra Armature resistance in ohm

PRECAUTIONS

1. Select fuse in such way that its rating is 120% of the no load current.

2. Keep the spring balance at zero position throughout the experiment.

3. Motor field rheostat should be kept at minimum position and armature rheostat at

maximum position at the time of starting.


20

TABULAR COLUMN 4.1:ARMATURE CONTROL METHOD

S.NO

If = Amp If = Amp If = Amp

Va Volts

N

rpm

Va Volts

N

rpm

Va Volts

N

rpm

TABULAR COLUMN 4.2:FIELD CONTROL METHOD

S.NO

Va = Volt Va = Volt Va = Volt

If

Amps

N

rpm

If

Amps

N

rpm

If

Amps

N

rpm


21

PROCEDURE

ARMATURE CONTROL METHOD

1. Connections are made as per the circuit diagram.

2. A 230 V dc supply is given by closing the DPST switch, and motor starts to run.

3. The field current (If) is maintained at constant value by keeping the field rheostat

in constant position.

4. The armature voltage is varied by varying the armature rheostat and

corresponding variations of speed, N with respect to armature voltage, Va are

noted down.

5. The same procedure is repeated for different set value of field currents (If).

6. The speed control characteristics of Va vs. N are plotted.

FIELD CONTROL METHOD


2. A 230 V dc supply is given by closing the DPST switch, and motor starts to run.

3. The voltmeter connected in parallel to armature should be kept at constant voltage

(Va) by keeping the armature rheostat in constant position.

4. The field current is varied by varying the field rheostat and corresponding

variations of speed, N with respect to field current, If are noted down.

5. The same procedure is repeated for different set value of armature voltages (Va).

6. The speed control characteristics of If vs. N are plotted.


22

MODEL GRAPH

VIVA QUESTIONS

1. What types of dc motors are suitable for varying torque operations?

2. If the terminal voltage is reduced to half and the torque remains constant, what

will happen to the speed and armature current?

3. What will be the effect of change in supply voltage on the speed of a dc shunt

motor?

4. What will happen to the speed of a dc motor when its flux approaches zero?

5. What is the necessity of a starter for dc motor?

6. Why are speeds above rated speed obtained in field control method?

7. Why are speeds below rated speed obtained in armature control method?

8. What parameters control the speed of a dc motor?

9. What would be the most effective method of increasing the speed of a dc shunt

motor rated at less than 5kw?

10. How many speeds can be obtained by paralleling of fields method for a 4pole

series motor?

11. What are the limitations of each method?

12. What type of motor is used in locomotive?

.

Armature voltage, Va in volt Current, If in amp

Sp

eed

in

rp

m

If1

If2

If3

Sp

eed

in

rp

m

Va3 Va2

Va1

Figure 4.1: Armature Control Method Figure 4.2: Field Control Method


23

RESULT

MARKS ALLOCATION


Awarded

Preparation 20

Conducting 20


Results 5



Viva 10

Record 15

Total 100



24

NAME PLATE DETAILS

-

CIRCUIT DIAGRAM OF OCC AND LOAD CHARACTERISTICS OF SEPARATELY EXCITED DC

GENERATOR

-

V (0-300V) MC

+

A1

3 POINT STARTER

M

L F A

D

P

S

T

S

W

I

T

C

H

1

FUSE

15A

A2

+

220 /2.3 A

F1

F2

230 V DC SUPPLY

FUSE

15A

G

A1

A2

A

560 /2.3 A

D

P

S

T

S

W

I

T

C

H

2

A

R

H

E

O

S

T

AT

I

C

L

O

A

D

SPST

(0-20) A

MC

+ -

(0-2) A MC

+

-

F1

F2

230 V / 18 A 230 V / 18 A


25

AIM

To conduct a suitable experiment on the given dc generator and draw the open

circuit and load characteristic curves of the same when its field is separately excited.

OBJECTIVES

1. To find the generated voltage (Eg) of a separately excited dc generator for

different field currents (If) by conducting open circuit test.

2. To determine Internal and External Characteristic curves of given dc generator by


APPARATUS REQUIRED

S.NO. APPARATUS NAME RANGE TYPE QUANTITY

1. Ammeter (020) A MC 1

(02 ) A MC 1

2. Voltmeter (0300) V

(0-50) V

MC 1

1

3. Rheostat 220 / 2.3 A Wire Wound 1

560 / 2.3 A Wire Wound 1


5. DPST switch 1

6. Loading Rheostat 230 V / 18 A 1

FORMULA

Eg = VL + Ia Ra volt

Where Eg Generated emf in volt

VL Load Voltage in volt


Ra Armature resistance in ohm

PRECAUTIONS

1. Select fuse such that its rating is 120 % of rated current.

2. Keep the motor field rheostat at minimum position at the time of starting.

3. Keep the generator field rheostat at maximum position at the time of starting.

4. Keep the DPST switch 2 open during OCC test.

5. Keep the SPST switch open at starting to note the residual voltage.

Ex. No: OCC AND LOAD CHARACTERISTICS OF SEPARATELY

EXCITED DC GENERATOR Dr.M.K.Elango

Date :


26

Figure 5.1: Measurement of Armature Resistance

TABULAR COLUMN 5.1 OPEN CIRCUIT TEST ON SEPARATELY EXCITED

DC GENERATOR

S. No. Field Current

(If)

Amps

Generated Voltage

(Eg)

Volts

TABULAR COLUMN 5.2 LOAD TEST ON SEPARATELY EXCITED DC

GENERATOR

Armature Resistance, Ra =

S. No.

Field

Current

(If)

Amps

Load

Current

(IL)

Amps

Load

Voltage

(VL)

Volts

Armature

Current

(Ia = IL)

Amps

Generated

voltage

Eg =VL + IaRa Volts


27

PROCEDURE

OCC TEST

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

2. By closing the DPST switch 1, the dc motor (prime mover) is supplied with 230 V

dc supply and using 3-point starter the dc motor is started.

3. The motor field rheostat is adjusted from its minimum position and the rated

speed of 1500 rpm is set.

4. The residual voltage (armature voltage at zero excitation) is noted down from the

voltmeter.

5. Close the SPST switch and the generator field rheostat is varied in steps of 0.1 A.

Note down the field current (If) and the corresponding generated voltage (Eg).

6. The same procedure is repeated until the generator reaches its rated voltage of the

generator.

LOAD TEST

1. By adjusting the motor field rheostat, set the rated speed of 1500 rpm.

2. By adjusting the generator field rheostat, set the rated voltage of generator, i.e.

230 V.

3. Note down the no load voltage and field current.

4. Now the DPST switch 2 is closed.

5. Then the load is applied in step using loading rheostat in steps of 2 A up to the

rated current of 12 A and the load current (IL), load voltage (VL) and field current

(If) are noted down for all the loads.

6. For every load, check the speed of the motor which is to be maintained at rated

speed of 1500 rpm.

7. The loading rheostat and generator field rheostat are brought back to initial state.

8. The motor field rheostat is brought back to initial state and the motor is switched

off by opening the DPST switch 1.

MEASUREMENT OF ARMATURE RESISTANCE

1. Connections are made as per the circuit diagram as shown in Fig. 5.1.

2. The dc supply voltage of 230 V is applied by closing the DPST switch.

3. By varying the loading rheostat in steps, the ammeter and voltmeter readings are

noted and tabulated.

4. This procedure is repeated for four steps of readings.

5. Loading rheostat is brought back to initial state and the DPST switch is opened.

6. Calculate the armature resistance and take average of the above values.


28

TABULAR COLUMN 5.3: MEASUREMENT OF ARMATURE RESISTANCE (Ra)

S. No. Armature Voltage

(Va)

Volts

Armature Current

(Ia)

Amps

Armature Resistance

aa

a

VR

I

Ohms

MODEL GRAPH

Figure 5.1: OCC Characteristics Figure 5.2: Load Characteristics

VIVA QUESTIONS

1. What are the basic requirement for the production of emf?

2. In how many ways mmf required to establish the flux in the magnetic circuit of a

dc generator can be had?

3. Which type of winding is selected for low voltage, high current dc machines?

4. Distinguish between separately excited and self excited dc generators.

5. Which generator cant build voltage if there is no residual magnetism?

6. Why should the generator field winding be kept at maximum position at the start

of the experiment?

7. Why should the motor field winding be kept at minimum position at the start of

the experiment?

8. Justify the shape of open circuit characteristics of a dc generator.

9. What is the purpose of the SPST switch in the circuit?

10. What is the voltage drop allowed for all brushes of each polarity?


29

MODEL CALCULATION

RESULT

MARKS ALLOCATION


Awarded

Preparation 20

Conducting 20


Results 5



Viva 10

Record 15

Total 100



30

NAME PLATE DETAILS

230 V DC SUPPLY

- F

CIRCUIT DIAGRAM OF OCC AND LOAD CHARACTERISTICS OF DC SHUNT

GENERATOR

-

V (0-300V) MC

+

A1

3 POINT STARTER

M

L F A

D

P

S

T

S

W

I

T

C

H

1

FUSE

15A

A2

+

220 /2.3 A

F1

F2

FUSE

15A

G

A1

A2

A

560 /2.3 A

D

P

S

T

S

W

I

T

C

H

2

A

R

H

E

O

S

T

A

T

I

C

L

O

A

D

SPST

(0-20) A

MC

+ -

(0-2) A MC

+

-

F1

F2

230 V / 18 A


31

Ex. No: OCC AND LOAD CHARACTERISTICS OF DC SHUNT

GENERATOR Dr.M.K.Elango

Date :

AIM

To conduct the suitable experiment on the given dc shunt generator and to draw

the open circuit and load characteristic curves of the same.

OBJECTIVES

1. To find the generated voltage (Eg) of a self excited dc shunt generator for different

field currents (If) by open circuit test.

2. To determine the Internal and External Characteristic curves of given dc shunt

generator by conducting load test.

APPARATUS REQUIRED


1. Ammeter (020) A MC 1

(02 ) A MC 1

2. Voltmeter (0300) V (0-50)V

MC 1

1

3. Rheostat 220 / 2.3 A Wire Wound 1

560 / 2.3 A Wire Wound 1


5. DPST switch 1


FORMULA

Eg = VL + Ia Ra volt

Ia = IL + If

Where Eg Generated emf in volt

VL Load Voltage in volt


IL Load current in amp

If Field current in amp

Ra Armature resistance in ohm.

PRECAUTIONS


2. Keep the motor field rheostat at minimum position at the time of starting.

3. Keep the generator field rheostat at maximum position at the time of starting.

4. Keep the DPST switch 2 open during OCC test.

5. Keep the SPST switch open at starting to note the residual voltage.


32

Figure 6.1 Measurement of Armature Resistance (Ra)

TABULAR COLUMN 6.1: OPEN CIRCUIT CHARACTERISTICS TEST OF DC

SHUNT GENERATOR

S. No.

Field Current

(If)

Amps

Generated Voltage

(Eg)

Volts

TABULAR COLUMN 6.2: LOAD TEST OF DC SHUNT GENERATOR


S.NO Field

Current

(If)

Amps

Load

Current

(IL)

Amps

Load

Voltage

(VL)

Volts

Armature

Current

Ia = IL+ If Amps

Generated emf

Eg =VL + IaRa Volts


33

PROCEDURE

OCC TEST






4. The residual voltage (armature voltage at zero excitation) is noted down from the

voltmeter.

5. Close the SPST switch and the generator field rheostat is varied in steps of 0.1 A.

Note down the field current (If) and the corresponding generated voltage (Eg).

6. The same procedure is repeated until the generator reaches its rated voltage.

LOAD TEST

1. By adjusting the motor field rheostat, set the rated speed of 1500 rpm.

2. By adjusting the generator field rheostat, set the rated voltage of generator, i.e.

230 V.

3. Note down the no load voltage and field current.

4. Now the DPST switch 2 is closed.

5. Then the load is applied in step using loading rheostat in steps of 2 A up to the

rated current of 12 A and the load current (IL), load voltage (VL) and field current

(If) are noted down for all the loads.

6. For every loading, check the speed of the motor which is to be maintained at rated

speed of 1500 rpm.

7. The loading rheostat and generator field rheostat are brought back to initial state.

8. The motor field rheostat is brought back to initial state and the motor is switched

off by opening the DPST switch 1.










34


S. No Armature Voltage

(Va)

Volts

Armature Current

(Ia)

Amps

Armature Resistance

aa

a

VR

I

Ohms

MODEL GRAPH

Figure 6.2: OCC Characteristics Figure 6.3: Load Characteristics

VIVA QUESTIONS

1. How voltage is build up in a dc shunt generator?

2. What is critical filed resistance of a generator?

3. State the reasons for the drop in terminal voltage of a shunt generator when it

is loaded?

4. List the causes for the failure of self excitation of a DC shunt generator.

5. Why does saturation curve starts from some value higher than zero?

6. What is the use of interpole windings?

7. How does the armature reaction affect the load characteristic?

8. How are the dc shunt generator self protective?

9. Why a dc shunt generator is used for battery charging?

10. What is the net voltage across the armature resistance at the time of plugging?

11. What type of motor is providing zero speed regulation at full load without any

controller?


35

MODEL CALCULATION

RESULT

MARKS ALLOCATION


Awarded

Preparation 20

Conducting 20


Results 5



Viva 10

Record 15

Total 100



36

CIRCUIT DIAGRAM OF LOAD CHARACTERISTICS OF DC SERIES GENERATOR

NAME PLATE DETAILS

HP V I RPM HP V I RPM

_- +

RHEOSTA

T IC LOAD

D

P

S

T

S

W

I

T

C

H

2

C2

A2

A1 (0-300V) MC

220/1.3A

(0-20A)MC

15A

FUSE

-

F1

F2

A1

A2

3 POINT STARTER

+

FUSE

_-

+

230 V

DC SUPPLY

G

L F A

D

P

S

T

S

W

I

T

C

H

1

15A

V

M

A

C1

230 V / 18 A


37

Ex. No: LOAD CHARACTERISTICS OF DC SERIES GENERATOR C.Srinivasan Date :

AIM

To conduct the load test on dc series generator and draw its load characteristic

curves.

OBJECTIVES

1. To determine the Internal (Eg vs. IL) and External Characteristics (VL vs. IL) of

given dc series generator by conducting load test.

APPARATUS REQUIRED


1. Voltmeter (0300)V (0-50) V

MC

MC

1

1


3. Rheostat 220/2.3A 1


5. DPST switch 2

6. Loading rheostat 230 V / 18 A 1

PRECAUTIONS


2. Keep the motor field rheostat should be kept at minimum position at the time of

starting.

PROCEDURE

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





4. The DPST switch 2 is closed and the loading rheostat is varied.

5. The voltmeter and ammeter readings are noted down in the tabular column.

6. The same procedure is repeated up to the rated current.

7. The internal and external characteristic curves are plotted.


38

Fig: (a) Fig :(b)

Figure 7.1 Measurements of (a) Armature Resistance (Ra) and (b) Series Field Resistance (Rse)

TABULAR COLUMN 7.1: LOAD CHARACTERISTICS OF DC SERIES

GENERATOR

S.No. Load Current

(IL)

Amps

Load Voltage

(VL)

Volts

Generated Voltage

Eg = VL + IL (Ra+ Rse)

Volts

TABULAR COLUMN 7.2: MEASUREMENT OF ARMATURE RESISTANCE (RA)

S. No.

Armature Voltage

(Va)

Volts

Armature Current

(Ia)

Amps

Armature Resistance

aa

a

VR

I

Ohms

TABULAR COLUMN 7.3:MEASUREMENT OF SERIES FIELD RESISTANCE (RSE)

S. No.

Series Field

Voltage

(Vse)

Volts

Series Field

Current

(Ise)

Amps

Series Field Resistance

sese

se

VR

I

Ohms


39

MEASUREMENT OF ARMATURE AND SERIES FIELD RESISTANCE

1. Connections are made as per the circuit diagram as shown in Fig. 7.1 (a).


3. By varying the loading rheostat the ammeter and voltmeter readings are noted and

tabulated.



6. The above procedure is repeated for measuring series filed resistance, by replacing

the armature winding terminals by series filed winding terminals as shown in

Fig. 7.1 (b).


MODEL CALCULATION


40

MODEL GRAPH

Fig 7.2: Performance Characteristic Curve

VIVA QUESTIONS

1. Which type of winding is selected for high voltage, low current dc machines?

2. Why is a dc series generator not suitable for general electric supply?

3. What is the function of brushes in a dc machine?

4. Why is carbon preferred for manufacturing brushes?

5. Mention the methods of improving commutation.

6. How is the direction of induced emf found in a dc generator?

7. Why does series field winding have only a few turns?

8. What is the reason for sparking at the brushes?

9. Can a generator produce electricity?

10. What is the critical field resistance of a dc series generator?

11. What is the function of armature in the generator?

12. From the nature of characteristics curves, give the applications of dc series

generator.

Internal Characteristics (Eg vs. IL)

External Characteristics (VL vs. IL)

IL (A)

Eg, V

L (

V)


41

RESULT

MARKS ALLOCATION


Awarded

Preparation 20

Conducting 20


Results 5



Viva 10

Record 15

Total 100



42

CIRCUIT DIAGRAM LOAD CHARACTERISTICS OF DC COMPOUND GENERATOR

NAME PLATE DETAILS


560/ 2.3A

(0-2A)

MC

_-

+

(0-20A)MC

C2

A2

A1

220/ 2.3A

15A

FUSE

-

A1

A2

3 POINT STARTER

+

FUSE

230 V

DC SUPPLY

G

L F A

D

P

S

T

S

W

I

T

C

H

1

15A

F1

F2

M

C1

F1

F2

_- +

RHEOS

TAT IC LO

AD

D

P

S

T

S

W

I

T

C

H

2

(0-300V) MC

_-

+

V

A

A

230 V / 18 A


43

Ex. No: LOAD CHARACTERISTICS OF DC COMPOUND GENERATOR Dr.M.K.Elango Date :

AIM

To conduct the load test on dc compound generator and draw its load characteristic

curves.

OBJECTIVES

1. To study the operation of cumulative and differential compounding.

2. To determine Internal, External Characteristics of given dc compound generator by


APPARATUS REQUIRED


1. Voltmeter (0300)V

(0-50) V

MC

MC

1

1


(020)A MC 1

3. Rheostat 220/2.3A 1

560/2.3A 1


5. DPST switch 1


THEORY

Eg = VL + Ia (Ra+ Rse) volt

Where,

Eg = Generated Voltage in volt

VL = Load Voltage in volt

Ia = Armature Current in amp

Ra = Armature Resistance in ohm

Rse= Resistance of the series field winding in ohm

PRECAUTION

1. Select fuse such that its rating is 120% of the rated current.

2. The field rheostat of the motor should be kept at minimum resistance position and

generator field rheostat should keep at maximum resistance position at the time of

starting.

3. Keep the DPST switch 2 should open during built up of voltage across the armature

of generator


44

Figure 8.1: Measurement of Armature Resistance (Ra)

Figure 8.2: Measurement of Series Field Resistance (Rse)

TABULAR COLUMN 8.1: LOAD TEST OF DC COMPOUND GENERATOR

(CUMULATIVE COMPOUNDING)

Armature and series field resistance (Ra + Rse) =

S.No.

Field

Current

(If)

Amps

Load

Voltage

(VL)

Volts

Load

Current

(IL)

Amps

Armature

Current

Ia = IL + If Amps

Generated emf

Eg =VL + Ia(Ra+ Rse)

Volts


45

PROCEDURE


2. By closing the DPST switch 1, the dc motor (prime mover) is supplied with 230 V dc

supply and using 3-point starter the dc motor is started.

3. The motor field rheostat is adjusted from its minimum position and the rated speed of

1500 rpm is set.

4. The field rheostat of the generator is adjusted to get rated voltage in the voltmeter that

is connected across the generator armature.

5. The DPST switch 2 is closed.

6. Then the rheostatic load is applied in steps and the corresponding values of line

current, field current and load voltage are noted.

7. The same procedure is repeated up to the rated current of the generator.

8. The load and field rheostats are brought back to their initial position and the supply is

switched off.

9. The connections of the terminals C1 and C2 are interchanged which makes the

generator to be differentially compounded.

10. The procedural steps 2 to 8 are followed.

11. The characteristic curves are plotted from the tabulated readings.

MEASUREMENT OF ARMATURE AND SERIES FIELD RESISTANCE







6. The above procedure is repeated for measuring series filed resistance, by replacing

the armature winding by series filed winding as shown in Fig. 8.2..



46

TABULAR COLUMN 8.2: LOAD TEST OF DC COMPOUND GENERATOR

(DIFFERENTIAL COMPOUNDING)

Armature and series field resistance (Ra + Rse) =

S.No.

Field

Current

(If)

Amps

Load

Voltage

(VL)

Volts

Load

Current

(IL)

Amps

Armature

Current

Ia = IL + If Amps

Generated emf

Eg =VL + Ia(Ra+ Rse)

Volts


S. No

Armature Voltage

(Va)

Volts

Armature Current

(Ia)

Amps

Armature Resistance

aa

a

VR

I

Ohms

TABULAR COLUMN 8.4: MEASUREMENT OF SERIES FIELD RESISTANCE (Rse)

S. NO

Series Field

Voltage

(V)

Volts

Series Field

Current

(I)

Amps

Series Field Resistance

seVR

I

Ohms


47

MODEL CALCULATION


48

MODEL GRAPH

Figure 8.3: Differential Compounding Figure 8.4: Cumulative Compounding

VIVA QUESTIONS

1. Mention the reasons for compounding dc generator.

2. When the dc generator is said to be over compounded?

3. Discuss the effect of differential compounding and cumulative compounding on the

performance of DC compound generators.

4. Mention merits and demerits of the types of compounding.

5. Why is only a differentially compounded generator suitable for arc welding?

6. Why are only over compounded dc generators employed for supplying power to

lighting and commercial services?

Eg/Ig

Eg/V

L (

V)

Internal characteristics

External characteristics

IaRa drop

Ig/IL (A)

VL/IL Eg/Ig

Eg/V

L (

V)

Internal characteristics

External characteristics

IaRa drop

Ig/IL (A)

VL/IL


49

RESULT

MARKS ALLOCATION


Awarded

Preparation 20

Conducting 20


Results 5



Viva 10

Record 15

Total 100



50

HP V I RPM

F

NAME PLATE DETAILS

L F A

F1

F2

+

+

VL

+

-

+

A1

(0-2A)MC

A2

-

(0-300V)

MC

220 /1.2 A

3 POINT STARTER

IL

(0-5A)MC

FUSE

-

+

5A

FUSE

_

230 V

DC SUPPLY

M

D

P

S

T

S

W

I

T

C

H

V

A

5A

A

CIRCUIT DIAGRAM OF SWINBURNES TEST ON DC MACHINE


51

Ex. No: SWINBURNES TEST ON DC MACHINE P.Aravindan Date :

AIM

To predetermine the efficiency of the given dc shunt machine while running as a

motor and as a generator by conducting Swinburnes test.

OBJECTIVE

To determine the efficiency at various load current while operating as a motor and

generator and plot a graph output Vs %

APPARATUS REQUIRED


1. Voltmeter (0300)V (0-50) V

MC

MC

1

1

2. Ammeter (05)A & (02)A

MC 2

3. Rheostat 220/1.2A Wire wound 1


FORMULA USED

Input Power = Output power + Total losses (Watts)

At no load output power = 0

Input power = Total losses (Watts)

Total losses = Copper loss + Constant loss (Wc) (W.atts)

Constant loss = Total loss Copper loss

Wc = Input power at no load Copper loss

FOR MOTOR

Armature current, Ia= IL If in A

Constant loss, WC = VLIL (at no load) Ia2 Ra

Copper loss = Ia2 Ra in W

Total loss = Copper loss + Constant loss in W

Input power, Pi = VLIL in W

Output power Po= Input power Total losses in W

Percentage efficiency = i

o

P

P x 100


52


TABULAR COLUMN 9.1: SWINBURNES TEST ON DC MACHINE

S.No No load line voltage

(VL)

Volts

No load line current

(IL)

Amps

No load field current

(If)

Amps


S. No Armature Voltage

(Va)

Volts

Armature Current

(Ia)

Amps

Armature Resistance

(Ra)

Ohms


53

FOR GENERATOR

Armature current, Ia = IL + IF in A

Constant loss, WC = VLIL (at no load) Ia2 Ra

Copper loss = Ia2 Ra in W

Total loss = Copper loss + Constant loss in W

Output Power, Po = VLIL in W

Input power, Pi = Output power + Total losses in W

Percentage efficiency = i

o

P

P x 100

PRECAUTIONS

1. Fuse should be selected such that its current rating is 120% of no load current of the

motor.

2. Motor field rheostat should be kept at minimum resistance position at the time of

starting.

PROCEDURE


2. The DPST switch is closed to apply 230 V dc supply to motor and the motor is started

using threepoint starter.


1500 rpm is set.

4. At rated speed, the values of line voltage, no load current and field current are noted.

5. The efficiency of the machine as a motor and as a generator for each assumed load

current is calculated using the formulas up to the rated current and tabulated in the

respective tabular column.

6. The characteristic curve between the output power and efficiency are plotted for both

the cases.


54

TABULAR COLUMN 9.3: PERFORMANCE OF DC MACHINE AS A MOTOR


Line Voltage, VL =

Constant Loss, Wc =

Field Current If =

S.No

Load

Current

(IL)

Amps

Armature

Current

Ia= IL If Amps

Armature

Copper

Loss

Ia2 Ra

Watts

Total

Losses

WC + WCU Watts

Input

Power

Pi = VLIL

in Watts

Output

Power

P0

Watts

Efficiency

in %

TABULAR COLUMN 9.4: PERFORMANCE OF DC MACHINE AS A GENERATOR

Line Voltage =

Constant Loss =

S.No

Load

Current

(IL)

Amps

Armature

Current

Ia= IL If Amps

Armature

Copper

Loss

Ia2 Ra

Watts

Total

Losses

WC + WCU Watts

Input

Power

Pi Watts

Output

Power

P0 = VLIL Watts

Efficiency

in %


55









MODEL CALCULATION

DC MACHINE AS A MOTOR

DC MACHINE AS A GENERATOR


56

MODEL GRAPH

Figure 9.2: Output Characteristics Curves

VIVA QUESTIONS

1. Can we operate same dc machine as a generator and as a motor?

2. What are the losses taking place in a dc machine?

3. How do the losses vary with load current?

4. How can iron losses be reduced?

5. Differentiate stray losses and constant losses.

6. State the condition for maximum efficiency in a DC motor.

7. Why is power consumed at no load in Swinburnes test?

8. Differentiate determination and predetermination tests.

9. What are the sources of heat generation in rotating electrical machines?

10. What are the limitations of the Swinburnes test?

As a MOTOR

As a GENERATOR

OUTPUT POWER

(Watt)

EF

FIC

IEN

CY

(%)


57

RESULT

MARKS ALLOCATION


Awarded

Preparation 20

Conducting 20


Results 5



Viva 10

Record 15

Total 100



58

CIRCUIT DIAGRAM OF HOPKINSONS TEST ON DC MACHINES SET

NAME PLATE DETAILS

DC MOTOR ALTERNATOR


15A

220 / 2.3 A

(0-20A)MC

I2

(0-300V) MC

-

_- +

(0-2A)

MC

I4

_-

+

F1

F2

570/1.1A

+

(0-20A)MC

I1

A2

A1

(0-300V) MC

F1

F2

A1

A2

3 POINT STARTER

_- +

G

L F A

V

FUSE

-

+

FUSE

230 V

DC SUPPLY

D

P

S

T

S

W

I

T

C

H

15A

M

_- +

(0-2A)MC

I3

A

A

A

SPSTS

A

V

+


59

Ex. No: HOPKINSONS TEST ON DC MACHINES C.Srinivasan Date :

AIM

To conduct full load test on two identical dc shunt machines and draw the

performance characteristic curves.

OBJECTIVE

1. To determine the stray losses of the machines.

2. To obtain efficiency curves for the motor and generator and draw the

performance characteristic curves.

APPARATUS REQUIRED


1. Voltmeter (0300)V

(0-50) V

MC

MC

2

1

2. Ammeter (02)A &

(020)A

MC 2

3. Rheostat 220/2.3A

570/1.1A

Wire wound 1


5. SPST 2 1

FORMULA USED

1. Motor input = V ( I1 + I2 )

Where, V = supply voltage to motor

I1 = current delivered by the generator (generator current)

I2 = current taken from the supply (motor current)

2. Generator output = V I1 Watt

3. Let Ra = Armature resistance of each machine

I3 = Exciting current of the generator

I4 = Exciting current of the motor

Armature cu loss in generator = (I1+ I3)2 Ra watt . (1)

Armature cu loss in motor = (I1+ I2 I4)2 Ra watt . (2)

Shunt cu loss in generator = V I3 watt . (3)

Shunt cu loss in motor = V I4 watt . (4)


60

TABULAR COLUMN 10.1: PERFORMANCE OF THE DC MACHINE AS A DC MOTOR

Stray Loss per Machine = 2

w= Watts

Armature Resistance (Ra) = S. NO. Supply

Voltage

(V)

Volt s

Generator

Current

(I1)

Amps

Motor

Current

(I2)

Amps

Generator

Field

Current

(I3)

Amps

Motor

Field

Current

(I4)

Amps

EFFICIENCY OF DC MOTOR

Input

Power

Pi

Watts

Armature

Copper Loss

in Watts

Shunt

Copper

Loss in

Watts

Total

Loss in

Watts

Output

Power

Po

Watts

Efficiency

%


61

Stray losses of both machine = w (say) . (5)

Power drawn from the supply = V I2 watt . (6)

(1) + (2) + (3) + (4) + (5) = (6)

Total stray loss for the set, w = V I2 [(I1+ I3)2 Ra + (I1 + I2 I4)

2 Ra+ V I3 + V I4]

4. Efficiency for generator

Generator output = VI1 watt

Total losses = (I1 + I3)2Ra + VI3+w/2 = Wg watt

Generator input = VI1+ Wg watt

Efficiency of the generator = VI1 / (VI1+ Wg)

5. Efficiency for Motor

Motor input = V (I1 + I2) watt

Total losses = (I1 + I2 I4)2

Ra + VI4 + w/2 = Wm watt

Motor output = V (I1+ I2) Wm watt

Efficiency of the motor = V (I1 + I2) Wm / V (I1+ I2)

PRECAUTION

1. Keep the field rheostat of the machine marked M at minimum position at the time of

starting.

2. Keep the field rheostat of the Machine marked G at maximum position at the time of

starting.

3. Keep the SPST switch open at the time of starting.

PROCEDURE


2. SPST switch between two machines is still kept opened.

3. DPST switch is closed to apply 230 V dc supply to the machine M and machine M is

started using three-point starter.


1500 rpm is set.

5. Machine M drives machine G as a generator and its voltage is read on voltmeter V1.

6. The generator field rheostat is adjusted. If the voltage is increasing instead of

reducing, interchange the field winding terminals of machine G and adjust the field

rheostat until voltmeter V1 reads zero. It means that now its voltage is the same as

that of the main supply.


62

TABULAR COLUMN 10.2: PERFORMANCE OF THE DC MACHINE AS A DC GENERATOR

Stray Loss per Machine = 2

w= Watts

Armature Resistance (Ra) = S.

NO.

Supply

Voltage

(V)

Volts

Generator

Current

(I1)

Amps

Motor

Current

(I2)

Amps

Generator

Field

Current

(I3)

Amps

Generator

Field

Current

(I4)

Amps

EFFICIENCY OF DC GENERATOR

Input

Power

Pi

Watts

Armature

Copper Loss

in

Watts

Shunt

Copper

Loss in

Watts

Total

Loss in

Watts

Output

Power

Po

Watts

Efficiency

in %


63

7. Now the switch SPST is closed.

8. By adjusting the respective field rheostat, any load can be applied on to the machine.

9. Generator current I1 is adjusted step by step by increasing the excitation of machine G

or by reducing the excitation of machine M.

10. From the tabulated readings, efficiency of the motor (machine M) and efficiency of

the generator (machine G) for different I1 up to rated current can be calculated.

11. Performance characteristic curves can be drawn for both the machines (Output power

vs. Efficiency in %).


64



S.

No

Armature Voltage

(Va)

Volts

Armature Current

(Ia)

Amps

Armature Resistance

(Ra)

Ohms


65


1. Connections are made as per the circuit diagram as shown in Fig. 10.1







MODEL CALCULATION


66

MODEL GRAPH

Figure 1.2 Output Characteristics Curves

VIVAQUESTIONS

1. If the progressive connections of the armature are replaced by retrogressive

connections, how will it affect the operation of the motor?

2. What happens to a dc motor when connected across an AC supply?

3. Why do dc motors sometimes run too fast under load?

4. What causes overheating of the commutator in a DC machine?

5. What are the advantages of Hopkinsons test?

6. What are the conditions for conducting the test?

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

not read zero value what does it indicate?

8. What are the other names of Hopkinsons test?

9. How the interpoles are connected?

10. A DC motor fails to start when switched on. What could be the reasons and

remedies?

11. What are the conditions to be satisfied before connecting two dc generators in

parallel?

12. If the voltmeter across the SPST switch reads zero what does it indicate? If it does not

read zero value what does it indicate?

MOTOR

GENERATOR

OUTPUT POWER (watt)

EF

FIC

IEN

CY

(%)


67

RESULT

MARKS ALLOCATION


Awarded

Preparation 20

Conducting 20


Results 5



Viva 10

Record 15

Total 100



68

CIRCUIT DIAGRAM OF LOAD TEST ON SINGLE PHASE TRANSFORMER

NAME PLATE DETAILS

KVA VP IP VS IS

LAMP

LOAD

W2 300 V/10A/UPF

W1 300 V/10A/UPF

LINK

100%

0%

(0-5)A MI

(0-300)V

MI

0%

100%

5A

FUSE

N

P

D

P

S

T

S

W

I

T

C

H

230 V

50 HZ 1 AC SUPPLY

V

A

Single Phase Transformer 230V/ 230V

P S


69

Ex. No: LOAD TEST ON SINGLE PHASE TRANSFORMER C.Srinivasan Date :

AIM

To draw the load characteristic curves of a given single phase transformer by


OBJECTIVE

To plot the following performance characteristics curves

1. Load current vs. % Efficiency

2. Load current vs. % Regulation

APPARATUS REQUIRED


1. Transformer 1

2. Ammeter (05)A MI 1

3. Voltmeter (0300V) MI 1

4. Wattmeter 300V/5A UPF 2

5. Lamp Load 1

FORMULA USED

1. Percentage of efficiency = 1

2

W

W x 100

2. Percentage of up regulation = fl

flnl

V

VV x 100

3. Percentage of down regulation = nl

flnl

V

VV x 100

Where W1 = Input power in watt

W2 = Output power in watt

Vfl = Full load voltage in volt

Vnl = No load voltage in volt

PRECAUTIONS

1. Fuse should be selected such that its current rating is 120% of rated current of the

transformer.

2. Keep the DPST switch open at the time of starting the experiment while giving

connections.

3. Load should be in the off position while at the start of the experiment.


70

TABULAR COLUMN 11.1: LOAD TEST ON SINGLE PHASE TRANSFORMER

Multiplying Factor for W1 =

Multiplying Factor for W2 =

No Load Voltage, VNL =

S.NO

Secondary

Voltage in

Volts

Secondary

Current in

Amp

Input

Power in

Watts

Output

Power in

Watts

Efficiency in

%

Up

Regulation in

%

Down

Regulation in

%

MODEL GRAPH

Figure 11.1 Load Current Vs Efficiency and Regulation Curves


71

PROCEDURE

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

2. The ac supply of 230 V is applied to the circuit by closing the DPST switch.

3. Before applying the load, the no load readings are noted.

4. By varying the lamp load step by step, corresponding ammeter, voltmeter and

wattmeter readings are noted down.

5. The same procedure is repeated up to the rated current of the transformer.

6. All the readings are tabulated in tabular column and required performance parameters

are calculated to draw their characteristic curves.

MODEL CALCULATION


72

VIVA QUESTIONS

1. Does the efficiency of a transformer depend on kVA rating? Why?

2. Why the efficiency of transformer is very high compared to other machines.

3. How is magnetic leakage reduced to a minimum in commercial transformers?

4. Which is the other method of finding efficiency and regulation?

5. What is the normal nature of output power vs. efficiency curve & why?

6. Give the difference between core type and shell type transformer.

7. Why is the efficiency of a transformer higher than that of motors?

8. What is the condition for maximum efficiency of a transformer? From the graph, find

the load at which it occurs.

9. Why do we perform load test when the efficiency can be determined by O.C. and S.C.

tests?

10. Why the excessive insulation is harmfull to a coil ?

11. What is the function of transformer oil ?

12. What type of load should be connected to the transformer for getting maximum voltage

regulation?

13. By knowing the losses at full load, how can you calculate the efficiency of a

transformer at any other load?


73

RESULT

MARKS ALLOCATION


Awarded

Preparation 20

Conducting 20


Results 5



Viva 10

Record 15

Total 100



74

CIRCUIT DIAGRAM OF OPEN CIRCUIT TEST ON SINGLE PHASE TRANSFORMER

NAME PLATE DETAILS

KVA VP IP VS IS

LINK

1 Auto transformer 230V/(0-270V)

230 V

50 HZ 1 AC SUPPLY

(0-2)A

MI

(0-300)V

MI

W 300 V/5A/LPF

5A

FUSE

N

P

D

P

S

T

S

W

I

T

C

H

V

A

Single Phase Transformer 230V/230V)

100%

0% 0%

100%

OPEN CIRCUIT

P S


75

Ex. No: OPEN CIRCUIT AND SHORT CIRCUIT TEST ON SINGLE

PHASE TRANSFORMER T.R Manikandan

Date :

AIM

To conduct the open circuit and short circuit test on given single phase transformer and

predetermine its efficiency and regulation of the same machine.

OBJECTIVE

1. Predetermine the efficiency at different load at various power factor.

2. Predetermine the full load regulation at different power factor.

3. Draw the following characteristic curves

a. Output vs. %

b. Power factor vs. % Regulation

APPARATUS REQUIRED


1. Single phase Transformer 1kVA/230V 1


2. Voltmeter (0300)V MI 1

3. Wattmeter 300V/5A LPF 1

4. Autotransformer 230V/(0270V) 1

5. Ammeter (05) A MI 1

6. Voltmeter (075) V MI 1

7. Wattmeter 150 V / 5 A UPF 1

FORMULA USED

1. oo

o

IV

WCos 0 2. 0

cos

o

o o

VR

I ohm

3. 0

sin

o

o o

VX

I ohm 4. 201

SC

SC

I

WR ohm

5. SC

SC

I

VZ 01 ohm 6.

2 2

01 01 01X Z R ohm

7. Percentage Efficiency = 2

0

( ) 100

( )

X x KVA rated x pfx

X x KVA rated x pf W X Wsc


76

CIRCUIT DIAGRAM OF SHORT CIRCUIT TEST ON SINGLE PHASE TRANSFORMER

KVA VP IP VS IS

W 75 V/5A/UPF

230 V

50 HZ 1

AC SUPPLY

LINK

(0-5)A

MI

(0-75)V MI

5A

FUSE

N

P

D

P

S

T

S

W

I

T

C

H

V

A

Single Phase Transformer

230V/(230V)

100%

0% 0%

100%

1 Auto transformer 230V/(0-270V)

P S SHORT

CIRCUIT


77

8. Percentage Regulation = 01 01

0 2

X * Isc(R cos sin

V

X x 100

Leading pf

% Regulation = 01 01

0 2

X * Isc( R cos sin )

V

X x 100

Lagging pf

% Regulation = 01 01

0 2

X * Isc(R cos sin )

V

Xx 100

9. Output power = X * VA rated x power factor watt

10. Input power = (X * VA rated x power factor) + Wo + X2

Wsc watt

Where,

cos = Power factor

Wo = Open circuit wattmeter reading or core loss in watt.

Io = Open circuit ammeter reading in amp.

Vo = Open circuit voltmeter reading in volt.

R0 = Primary no load resistance in ohm.

X0 = Primary no load reactance in ohm.

Wsc = Short circuit wattmeter reading in watt.

Isc = Short circuit ammeter reading in amp.

Vsc = Short circuit voltmeter reading in watt

X = Load ratio

R01 = Equivalent Resistance of the transformer as referred to primary in ohm

X01 = Equivalent Reactance of the transformer as referred to primary in ohm

Z01 = Equivalent impedance of the transformer as referred to primary in ohm

oV2 = Voltage across the secondary under open circuit in volt

PRECAUTIONS

1. Fuse should be selected such that its current rating is 120% of rated current of the

transformer.

2. Keep the DPST switch open while making circuit connections.

3. At the time of starting and at the end of the experiment the autotransformer is kept at

minimum position.


78

MODEL GRAPH

Figure 12.1: Performance Characteristic Curves

TABULAR COLUMN 12.1: OPEN CIRCUIT TEST ON SINGLE PHASE

TRANSFORMER

Multiplying Factor =

S. NO.

Open Circuit

Voltmeter Reading

(V0)

Volts

Open Circuit

Ammeter

Reading

(I0)

Amps

Open circuit

Wattmeter

Reading

(W0)

Watts

CORE LOSS ...

TABULAR COLUMN 12.2: SHORT CIRCUIT TEST ON SINGLE PHASE

TRANSFORMER

Multiplying Factor =

S. NO.

Short Circuit

Voltmeter Reading

(Vsc)

Volts

Short Circuit

Ammeter Reading

(Isc)

Amps

Short circuit

Wattmeter

Reading

(Wsc)

Watts

FULL LOAD COPPER LOSS...


79

PROCEDURE

OPEN CIRCUIT TEST


2. The DPST switch is closed and the autotransformer is adjusted to get rated voltage 230 V

in the secondary winding of the transformer.

3. The open circuit readings are taken and tabulated in tabular column.

4. Determine the core loss of the transformer from the obtained no load readings.

SHORT CIRCUIT TEST


2. The DPST switch is closed and the auto transformer is adjusted to get the rated current in

the secondary of the transformer.

3. The short circuit readings are taken and tabulated in tabular column.

4. Determine the full load copper loss of the transformer from the obtained short circuit

readings. From the open and short circuit test readings, percentage regulation and

percentage efficiency of single phase transformer are calculated using the formula and

tabulated in tabular column.


80

TABULAR COLUMN 12.3 PREDETERMINATION OF % REGULATION OF SINGLE

PHASE TRANSFORMER

S. No. Load Ratio

X

Power Factor

cos Percentage Regulation

Leading p.f. Lagging p.f.

1. 0.25

0.2

0.4

0.6

0.8 1.0

2. 0.5

0.2

0.4 0.6

0.8

1.0

3. 0.75

0.2 0.4

0.6

0.8

1.0

4. 1

0.2 0.4

0.6

0.8 1.0

TABULAR COLUMN 12.4 PREDETERMINATION OF % EFFICIENCY OF SINGLE

PHASE TRANSFORMER S. No. Power Factor Load Ratio

X

Output Power

in Watts

Input Power

in Watts

Efficiency in

%

1. 0.25

0.2

0.4

0.6 0.8

1.0

2. 0.5

0.2

0.4

0.6 0.8

1.0

3. 0.75

0.2

0.4

0.6 0.8

1.0

4. 1

0.2

0.4

0.6 0.8

1.0


81

MODEL CALCULATION

% REGULATION OF SINGLE PHASE TRANSFORMER

% EFFICIENCY OF SINGLE PHASE TRANSFORMER


82

VIVA QUESTIONS

1. State the conditions under which OC test is conducted on a transformer.

2. State the conditions under which SC test is conducted on a transformer.

3. What is the significance of OC & SC test?

4. Why h.v. winding is kept open during OC test and 1.v. winding is shorted during SC test

in case of large transformers?

5. In OC test, secondary winding is in open condition, still there is a small current flowing

in the primary winding. Why?

6. Which is the alternate method for finding efficiency and regulation of a transformer other

than OC & SC tests? What are their advantages over each other?

7. What is the importance of equivalent circuit?

8. Why regulation of transformer is negative for leading p.f. load?

9. The wattmeter reading during OC test is considered as core loss while wattmeter

reading during S.C. test is considered as copper loss Justify.

10. State why the open circuit test on a transformer is conducted at rated voltage.

11. Explain why only a low voltage is applied to the transformer during SC test.

12. Which losses are found by using OC test?

13. Which losses are found by using SC test?


83

RESULT

MARKS ALLOCATION


Awarded

Preparation 20

Conducting 20


Results 5



Viva 10

Record 15

Total 100



84

SPSTS

(0-600)V

MI

Auto transformer 230V/(0-270V)

( 0-5)A

MI

(0-75)V

MI

230 V

50 HZ 1 AC SUPPLY

LINK

(0-2)A MI

(0-300)V

MI

N

P

D

P

S

T

S

W

I

T

C

H

5A

FUSE

W1 300 V/5A/LPF

V

A

100%

0% 0%

100%

V

A

100%

0% 0%

100%

V

W2 75 V/5A/UPF

P S S P

CIRCUIT DIAGRAM OF SUMPNERS TEST ON SINGLE PHASE TRANSFORMERS


85

Ex. No: SUMPNERS TEST ON SINGLE PHASE TRANSFORMERS T.R Manikandan Date :

AIM

To conduct Sumpners test on given two identical single phase transformers and to

predetermine the regulation and efficiency of the transformer.

OBJECTIVE

1. To study the paralleling process for two identical transformers.

2. To determine the equivalent circuit parameters of each transformer.

3. To predetermine the efficiency at different loads at 0.8 and 1.0 power factors.

4. To predetermine the full load regulation for different power factors.

5. To draw the following performance characteristic curves

a. Output vs. %

b. Power factor vs. %Regulation

APPARATUS REQUIRED


1. Single phase Transformer

1 kVA

230/230 V

2


(05)A MI 1

3. Voltmeter (0300)V MI 1

(075)V MI 1

(0600)V MI 1

4. Wattmeter 75V/5A UPF 1

300V/5A LPF 1

5. Auto transformer (230V/0270V) 1

FORMULA USED

1. 00

0

0I V

WCos

2. o

RcosI

V

0

0

0 ohm

3. o

XsinI

V

0

0

0 ohm

4. R01= 2SC

SC

I

W ohm

5. Zo1= SC

SC

I

V ohm


86

TABULAR COLUMN 13.1 SUMPNERS TEST ON SINGLE PHASE TRANSFORMER

S. No.

Primary

Voltage

(V0)

volts

Primary

Current

(I0)

Amps

Primary

Power

(W0)

Watts

Secondary

Voltage

(VSC)

Volts

Secondary

Current

(ISC)

Amps

Secondary

Power

(WSC)

Watts

MODEL GRAPH

Figure 13.1: Performance Characteristics Curve


87

6. X01= 2 2

01 01Z R ohm

7. Total loss =Wo+X2

Wsc watt

8. Output power = X x VA rated x cos watt

9. Input power = (X x VA rated x cos ) + Wo+X2 Wsc watt

10. % efficiency = (output power / input power) x 100 watt

11. % Regulation = (X x Isc( R01cos + X01sin )/ 0V2) X 100 for lagging pf

12. % Regulation = (X x Isc( R01cos X01sin )/ 0V2) X 100 for leading pf

Where,

cos = power factor

Wo = open circuit wattmeter reading or core loss in watt.

Io = open circuit ammeter reading in amp.

Vo = open circuit voltmeter reading in volt.

R0 = primary no load resistance in ohm.

X0= primary no load reactance in ohm.

Wsc= short circuit wattmeter reading in watt.

Isc= short circuit ammeter reading in amp.

Vsc= short circuit voltmeter reading in watt

X= load ratio.

R01= Equivalent Resistance of the transformer as referred to primary in ohm

X01=Equivalent Reactance of the transformer as referred to primary in ohm

Z01=Equi

Date post:	12-Oct-2015
Category:	Documents
Upload:	satish-kumar
View:	29 times
Download:	0 times

EM-I LAB MANUAL

Documents