EM Lab Manual - Cycle - I 1

1

EASWARI ENGINEERING COLLEGE

RAMAPURAM, CHENNAI – 89

DEPARTMENT OF ELECTRICAL AND ELECTRONICS

ENGINEERING

EI2208- ELECTRICAL MACHINES LABORATORY - MANUAL

REGISTER NUMBER :

ROLL NUMBER :

NAME :

DEPARTMENT/SEM/SEC :

AC YEAR :

2

LIST OF EXPERIMENTS

1. OPEN CIRCUIT CHARACTERISTICS OF DC SHUNT

GENERATOR.

2. LOAD TEST ON DC SHUNT GENERATOR

3. SPEED CONTROL OF DC SHUNT MOTOR.

4. BRAKE TEST ON DC SHUNT MOTOR.

5. BRAKE TEST ON DC SERIES MOTOR.

6. REGULATION OF AN ALTERNATOR.

7. OC AND SC TEST ON SINGLE PHASE TRANSFORMER.

8. LOAD TEST ON SINGLE PHASE TRANSFORMER.

9. LOAD TEST ON THREE PHASE SQUIRREL CAGE

INDUCTION MOTOR.

10. BRAKE TEST ON SINGLE PHASE INDUCTION MOTOR.

11. V CURVES OF A SYNCHRONOUS MOTOR.

12. POWER MEASUREMENT IN THREE PHASE CIRCUIT

USING TWO WATTMETER METHOD

3

CYCLE - 1

Sl.

NO

DATE NAME OF THE EXPERIMENT PG.

NO REMARK

S

SIGN

OPEN CIRCUIT CHARACTERISTICS OF

DC SHUNT GENERATOR.

LOAD TEST ON DC SHUNT GENERATOR

SPEED CONTROL OF DC SHUNT MOTOR.

BRAKE TEST ON DC SHUNT MOTOR.

BRAKE TEST ON DC SERIES MOTOR

POWER MEASUREMENT IN THREE

PHASE CIRCUIT USING TWO

WATTMETER METHOD

CYCLE - 2

REGULATION OF AN ALTERNATOR.

OC AND SC TEST ON SINGLE PHASE

TRANSFORMER.

LOAD TEST ON SINGLE PHASE

TRANSFORMER.

LOAD TEST ON THREE PHASE

SQUIRREL CAGE INDUCTION MOTOR.

BRAKE TEST ON SINGLE PHASE

INDUCTION MOTOR.

V CURVES OF A SYNCHRONOUS MOTOR

4

Ex. No: OPEN CIRCUIT AND LOAD CHARACTERISTICS OF

Date : SEPARATELY EXCITIED DC GENERATOR

Aim:

To draw open circuit characteristics of the given separately excited

DC generator at rated speed and determine the critical resistance.

To determine load characteristics (Internal & External) of the given

DC separately excited generator.

Apparatus required:

Sl.No. Name Range Type Quantity

1 Voltmeter (0-300V) MC 1

2

Ammeter

(0-10A)

(0-2A)

MC

MC

1

1

3 Rheostat 300Ω/1.4 A Wire wound 2

4 Tachometer (0-1500) rpm Analog/Digital 1

5 Connecting wires Required

Formula:

Where, Rc – Critical resistance

∆Eg – Incremental generated EMF (measured from the linear portion

on the OCC)

∆If – Incremental field current (measured from the linear portion on the

OCC).

5

Circuit Diagram:

+

-

DPST

Switch

Fuse

220

Volts

D.C

Supply

+

-

220

Volts

D.C

Supply

LF

A

DPST

Switch

Fuse

F1

F2

A1

A2

3-Point Starter

Motor Name Plate Details

KW________

RPM________

Volts________

Amps________

Fuse

Fuse

Variable

Resistive

Load

(0-10 A) MC

(0-300 V)

MC

DPST

Switch

10 A

10 A

A

A

V

(0-2 A)

MC

F1

F2

Fuse

Fuse

300 Ω/

1.4 A

15 A

15 A

M G

15 A

15 A

300 Ω/

1.4 A

Fuse Rating Calculation

125% of Rated Current

Motor =

Generator = O.C & Load Characteristics of DC Separately Excited Generator

Generator Name Plate Details

KVA________

RPM________

Volts________

Amps________

6

Precaution:

1. The field rheostat on the motor side must be kept at minimum

resistance position at the time of starting.

2. The field potentiometer on the generator side must be kept at

minimum potential position at the time of starting.

3. DPST switches must be kept open at the time of power on.

Procedure:

1. Connections are given as per the circuit diagram.

2. Observing the precautions the motor side DPST switch is closed.

3. The motor is started with the help of three- point DC starter slowly.

4. The speed is measured with the help of a hand tachometer.

5. If the speed is below the rated value, then it is brought to the rated

value by adjusting the field rheostat.

6. With DPST switch on the generator field side open, the voltmeter

reading is noted down. (This is the residual voltage at the rated speed

at which the motor-generator set is running now.)

7. The DPST switch on the generator field side is closed.

8. By adjusting the potentiometer on the generator field side suitably for

various increasing field currents, note down the terminal voltages till

around 125% of the rated voltage. The speed is maintained constant

throughout this process.

9. The generator terminal voltage is minimized to zero.

10. The speed is brought down to minimum value and the motor is

switched off with the help of DPST switch. (Note the starter holding

coil releasing the handle else bring it back to start position)

7

Tabulation:

Speed = _________rpm

Residual voltage = ________ Volts

S. No. If (amps) Eg (volts)

Model graph:

Eg ∆E

g

∆If

If

8

Load Characteristics:

Precaution:



2. The field potentiometer on the generator side must be kept at

minimum potential position at the time of starting.


4. There should be no load at the time of starting.

Procedure:






value by adjusting the field rheostat.

6. By adjusting the potentiometer on the generator side the generator

terminal voltage is brought to the rated value.

7. Load side DPST switch is closed.

8. The load is applied gradually. For various load currents voltmeter and

ammeter readings are noted down till full current of the generator.

(Avoid sustained overload.)

9. The load is brought back to initial no load position.

10. DPST switch on the load side is opened.

11. Generator field circuit potentiometer is brought to minimum potential

position.

12. DPST switch on the generator field side is opened.


switched off with the help of DPST switch. (Note the starter holding

coil releasing the handle else bring it back to start position)

14. Disconnect and return the apparatus.

9

Tabular column:

Ra = _________ Ohms

Load

current

IL(amps)

Shunt

Field

current

I sh

(amps)

Load

voltage

VL

(volts)

Armature

current

Ia = IL + I sh

(amps)

Generated voltage

Eg = V + Ia Ra

Model graph:

I a & IL

Eg Vs Ia

V Vs IL

V

&

Eg

10

Ia = IL + I sh Amps

Eg = V + Ia Ra Volts

Ra – Armaure resistance ohms

Eg – generated voltage volts

V – Terminal voltage volts

I sh – Shunt field current Amps

Result:

The Open Circuit Characteristics of the given separately excited DC

generator was obtained and the Critical resistance at rated speed is found to

be ______ohms.

The Load Characteristics (Internal & External) of the given separately

excited DC generator was obtained.

11

Ex. No: LOAD CHARACTERISTICS OF SELF EXCITIED

Date : DC SHUNTGENERATOR

Aim:

To determine load characteristics (Internal & External) of the given DC self

excited generator.

Apparatus required:

Sl. No Name Range Type Quantity

1 Voltmeter (0-300) V MC 1

2 Ammeter (0-10) A MC 1

3 Ammeter (0-2) A MC 1

4 Rheostat 300 Ω / 1.4 A

100 Ω / 4 A Wire wound Each 1

5 Tachometer Analog / Digital


Formulae:

Eg = V + Ia Ra

Ia = IL + I sh

Where,

Ra – Armature resistance

Eg – Generated voltage

V – Terminal Voltage

I sh – Shunt field current

IL – Load Current

12

Circuit Diagram:

+

-220 Volts

D.C

Supply

LF

A

DPST

Switch

F1

F2

A1

A2

3-Point Starter

M

FuseFuse

A

v

Fuse

Variable

Resistive

Load

(0-10 A)

MC

(0-300 V)

MC

(0-2 A)

MC

f1

f2

100 Ω/4A

DPST

SwitchFuse

300 Ω/

1.4 A

15 A

15 A 10 A

10 A

G

A1

A2


KW________

RPM________

Volts________

Amps________

Generator Name Plate Details

KVA________

RPM________

Volts________

Amps________



Motor =

Generator =

O.C & Load Characteristics of DC Shunt Generator

A

13

Precaution:



2. The field rheostat on the generator side must be kept at maximum




Procedure:






value by adjusting the motor field rheostat.

6. By adjusting the field rheostat on the generator side the generator

terminal voltage is brought to the rated value.

7. Load side DPST switch is closed.

8. The load is applied gradually. For various load currents voltmeter and

ammeter readings are noted down till full current of the generator.

(Avoid sustained overload.)

9. The load is brought back to initial no load position.

10. DPST switch on the load side is opened.

11. Generator field circuit rheostat is brought to maximum resistance

position.

12. DPST switch on the generator field side is opened.


switched off (Note the starter holding coil releasing the handle else

bring it back to start position)

14

Tabular column:

Ra = ________ Ohms

S.

No. IL(amps)

I sh

(amps) V(volts) Ia = IL + I sh

(amps)

Eg = V + Ia Ra

Model graph:

Result:

Thus the Load Characteristics (Internal & External) of the given self-

excited DC shunt generator was obtained.

I a & IL

Eg Vs Ia

VL Vs IL

VL

&

Eg

15

Ex. No: LOAD TEST ON DC SHUNT MOTOR

Date :

Aim:

To perform load test on the given D.C shunt motor and to obtain the

performance characteristics.

Apparatus Required:

Sl.No

Name of the apparatus

Range

Type

Quantity

1. Ammeter (0-2) A

(0-20) A MC Each 1

2. Voltmeter (0-300) V MC 1

3. Tachometer (0-1500) rpm Analog/Digital 1

4. Rheostat 300Ω/1.4 A Wire wound 1

5. Connecting wires Required

Formulae:

IL = Ia + I sh

Input power = V x IL (Watts)

Torque (T) = (S 1 ~ S 2) x 9.81 x R (Nm) S 1, S 2 – spring balance

readings (Kg)

Output power = 2 N T (Watts) N – speed of the motor in rpm

60

Efficiency = Output power x 100

Input power

Ia - Armature current (Amps) I sh – Shunt field current (Amps)

IL - Load Current (Amps) V – Supply voltage (Volts)

R – Radius of the brake drum = Circumference / 2 (m).

16

Circuit Diagram:

+

-220 Volts

D.C

Supply

DPST

Switch

A1

A2

Fuse

Fuse

15 A

15 A

M

LF

A

F1

F2

3-Point Starter

300 Ω/

1.4 A

A

A

V

(0-20 A) MC

(0-300 V)

MC

(0-2 A)

MC

Spring

Balance

Brake

Drum

S1 S2


KW________

RPM________

Volts________

Amps________



Motor =

Load Test on DC Shunt Motor

17

Tabular column:

Sl.

No

Input

voltage

(Volts)

(V)

Load

Current

(Amps)

(IL)

Field

Current

(Amps)

(Ish)

Armature

Current

(Amps)

(Ia = IL - Ish )

Speed

(N)

(rpm)

Spring Balance

Readings

Torque

(T)

(Nm)

Input

Power

(Watts)

Output

Power

(Watts)

Efficiency

(%) S1

kg

S2

kg

(S1~ S2)

kg

18

Model Graph:

ELECTRICAL CHARACTERISTICS MECHANICAL CHARACTERISTICS PERFORMANCE CHARS

Torque

(T)

(Nm)

1

2 3

4

1 – Output Vs Speed

2 – Output Vs % Efficiency

3 - Output Vs Torque

4 – Output Vs Armature

Current

Speed (N)

% Efficiency (η)

Torque (T)

Arm. Current (Ia)

Output power in

watts

Torque

(Nm)

Arm. Current (Ia) in

Amps

Speed (N)

(rpm)

19

Precautions:

1. The motor field rheostat must be kept at minimum resistance position at

the time of starting.


Procedure:

1. Make the connections as per the circuit diagram

2. Switch on the supply and move the starter handle slowly and

gradually to start the motor

3. Now observe the speed. If the speed is less than the rated speed adjust

the field rheostat and bring the speed to rated value.

4. Readings are taken for no load.

5. Load on the motor is varied with the help of pony brake arrangement.

6. Spring balance, ammeter, voltmeter and speed-readings are noted

down for various line currents as the load is increased (till the rated

current is reached).

7. Pour water in the brake drum to avoid over heating.

8. Unload the machine and bring back the rheostat to minimum position.

9. Switch off the supply

Result:

Thus the load test on the given DC Shunt motor was conducted and its

performance characteristics were drawn.

20

Ex. No: LOAD TEST ON DC SERIES MOTOR

Date :

Aim:

To perform load test on the given D.C shunt motor and to obtain the

performance characteristics.

Apparatus Required:

Sl.No


Range

Type

Quantity

1. Ammeter (0-20) A MC 1

2. Volt meter (0-300) V MC 1



Formulae:

IL = Ia = ISe

Input power = V x IL (Watts)

Torque (T) = ( S 1 ~ S 2 ) x 9.81 x R (Nm) S 1 , S 2 – spring balance

readings(Kg)

Output power = 2 N T (Watts) N – speed of the motor in

rpm

60

Efficiency = Output power x 100

Input power

Ia - Armature current (Amps) I se – Series field current (Amps)

IL - Load Current (Amps) V – Supply voltage (Volts)

R – Radius of the brake drum = Circumference / 2 (m)

21

Circuit Diagram:

+

-220 Volts

D.C

Supply

DPST

Switch

A1

A2

Fuse

Fuse

15 A

15 A

M

2-Point Starter

A

V

(0-20 A) MC

(0-300 V)

MC

Spring

Balance

Brake

Drum

S1 S2


KW________

RPM________

Volts________

Amps________



Motor =

L A

S1 S2

Load Test On DC Series Motor

22

Tabular column:

Sl.

No

Input

voltage

(Volts)

(V)

Load

Current

(Amps)

(IL = Ia)

speed

(N)

(rpm)

Spring Balance

Readings

Torque

(T)

(Nm)

Input

Power

(Watts)

Output

Power

(Watts)

Efficiency

(%) S1

kg

S2

kg

(S1~ S2)

kg

23

Model Graph:

ELECTRICAL CHARACTERISTI MECHANICAL CHARACTERISTICS PERFORMANCE CHARS

% Efficiency

Speed Speed

(N) Torque

Torque (T) rpm Arm. Current

(Nm)

Arm. Current (Ia) in Amps Torque (Nm)

Output power in watts

1

2

3

4

1 – Output Vs Armature

Current

2 – Output Vs Torque

3 – Output Vs % Efficiency

4 – Output Vs Speed

24

Precautions:

1. The motor should be started with some load.

2. Brake drum should be cooled throughout the experiment.

Procedure:

1. Connections are given as per the circuit diagram

2. Observing the precautions the DPST switch is closed.

3. The motor is started with the help of two-point dc starter slowly.

4. Load on the motor is varied with the help of pony brake arrangement.

5. Spring balance, ammeter, voltmeter and speed readings are noted

down for various line currents as the load is applied. Care must be

taken to avoid the speed reaching dangerously high values while

reducing the load.

6. Pour water in the brake drum to avoid overheating.

7. At a minimum safe load the DPST switch is opened.

8. Disconnect and return the apparatus.

Result:

Thus the load test on the given DC Series motor was conducted and

its performance characteristics were drawn.

25

Ex. No: SPEED CONTROL OF DC SHUNT MOTOR

Date :

Aim:

To vary the speed of the given dc shunt motor by the following

methods.

(i). Armature control method (below rated speed)

(ii). Field control method (above rated speed)

Apparatus Required:

Sl. No Name of the apparatus Range Type Quantity

1. Ammeter (0-2) A M.C 1

2. Volt meter (0-300) V M.C 1


4. Rheostat 300 Ω / 1.4 A

100 Ω / 4 A Wire wound Each 1


Precautions:

1. The field rheostat must be kept at minimum resistance position at the

time of starting.

2. The armature rheostat must be kept at maximum resistance position at

the time of starting.

26

Circuit Diagram:


KW________

RPM________

Volts________

Amps________

+

-220

Volts

D.C

Supply

DPST

Switch

A1

A2

Fuse

Fuse

2 A

2 A

V

(0-300 V)

MC



Motor =

F1

F2

300 Ω/

1.4 A

(0-2.5 A)

MC

M V

100 Ω / 4 A

Speed Control of DC

Shunt Motor

A

Model Graph:

(i) Armature Control method (ii) Field control method

Speed

(Rpm) Speed

(Rpm)

Armature voltage (volts) Fieldcurrent (amps)

27

Tabulations:

(i). Armature control method:

Field current (If) = ______ Amps kept constant

SL.

No

Armature voltage

(Volts)

Speed

(rpm)

(ii) Field control method

Armature voltage (Va) = ______ Volts kept constant

SL.

No

Field current

(Amps)

Speed

(rpm)

28

Procedure:

(i). Armature control method:


2. Switch on the supply

3. Keep the field current constant and for different armature voltage (by

varying armature rheostat) note down the corresponding speed.

4. Bring back the rheostat to initial position and switch off the supply

(ii). Field control method

1. Switch on the supply

2. Start the motor by closing the DPST switch

3. Keep the armature voltage constant and for various field current (by

varying field rheostat) note down the corresponding speed.

4. Bring back the rheostat to initial position and switch off the supply

Result:

Thus the speed of the given DC shunt motor is varied by both armature

control and field control method and the graphs are plotted. The speed is

directly proportional to the armature voltage by graph (i) and inversely

proportional to the field current by graph (ii).

29

Ex. No: OC AND SC TEST OF SINGLE PHASE

Date : TRANSFORMER

Aim:

To perform open circuit and short circuit test on a single phase

transformer and predetermine the efficiency at various loads and also draw the

equivalent circuit.

Apparatus Required:

Sl.No


Range

Type

Quantity

1. Ammeter (0-2) A

(0-5) A MI Each 1

2. Volt meter (0-150) V

(0-30) V MI Each 1

3. Watt meter 150V, 2A, LPF

30V, 5A, UPF Dynamo meter Each 1

4. 1- Autotransformer (0-270) V 1


Formulae:

Transformer Ratings: 1 KVA, 220 V/ 110V, 50HZ

V1 = 220 V & V2 = 110 V

I 1 = 1000/220 = 4.55 A & I2 = 1000/110 = 9.09 A

K = V2 / V1 = 110/220 = 0.5

From open circuit test:

In the open circuit test the primary is open circuited and the meters are

connected on L.V side, which is secondary of the transformer. Thus O.C test

will give us no load current, I01. (i.e referred to secondary)

Since K = V2/V1, the corresponding no load primary current, I0 = I01 * K

W0 = V1 I0 Cos 0 ( watts)

Where,

W0 = No load input power = core (or Iron) loss = Wi

I0 - No load input current

V1 - No load rated input voltage

30

Cos - Power factor

Cos 0 = W0 / V1 I0

I w = I0 Cos 0 A ( Iron loss component)

I = I0 Sin 0 A ( Magnetizing component)

R0 = V1 / I w (Resistance to represent core loss)

X0 = V1 / I (Reactance to represent magnetizing component)

From short circuit test:

In the Short circuit test the secondary is short circuited and the meters

are on H.V side, which is primary of the transformer. Hence it gives

parameters referred to primary.

R01 = Wsc / Isc 2

Z01 = Vsc / Isc

X01 = Z012 - R01

2

I21 = I2 * K & I1 = I0 + I2

1

Where,

R01 - Equivalent resistance of transformer referred to primary side

X01 - Equivalent reactance of transformer referred to primary side

Z01 - Equivalent impedance of transformer referred to primary side

Wsc – Full load copper loss

Isc – Short Circuit Current

Vsc – Short circuit voltage corresponding to Isc

Equivalent Circuit Parameters referred to secondary side:

R01 = R0 * K

2 I0

1 = No load current from O.C Test

X01

= X0 * K 2 I w

1 = V1

1 / R0

1

R02 = R01 x K 2

I1 = V1

1 / X0

1

X02 = X01 x K 2

Where, V11 = V1 * K

Z02 = Z01 x K 2

I11 = I0

1 + I2

Regulation = [ I2 R02 Cos + I2 X02 Sin / V2 ] X 100

+ Ve for lagging Power factor

- Ve for leading power factor

(X * KVA * P.f)

% Efficiency at various loads = x 100

[(X * KVA * P.f ) + (Wi + X 2 Wsc)

]

X-Load ratio

31

Circuit Diagram:

DPST

Switch

Fuse

230 V

1-φ 50 HZ

AC Supply V

A

C

M L

V

Fuse

5 A

5 A

(0-270 V) 1φ

Auto

Trnsformer

(0-150 V)

MI

(0-2 A) MI

150 V, 2A, LPF

Wattmeter

110 V 220 V

Open Circuit

Name Plate Details

Single Phase Transformer

Auto TransformerFuse Rating Calculation

KVA________

Voltage Ratio________

20 % of Rated Current

(Max. Load of A.T )

Maximum Load =

Maximum KVA =

Input =

0 V 0 V

Open Circuit Test on Single Phase Transformer

P

N

32

Circuit Diagram:

DPST

Switch

Fuse

230 V

1-φ 50 HZ

AC Supply V

A

C

M L

V

Fuse

5 A

5 A

(0-270 V) 1φ

Auto

Trnsformer

(0-30 V)

MI

(0-5 A) MI

30 V, 5A, UPF

Wattmeter

220 V 110 V


Short Circuit

0 V 0 V

Isc = KVA / V

= Short Circuit Test on Single Phase Tranformer

P

N

33

Equivalent circuit referred to primary side:

V1

I21

I0

I1

IW Iµ

X0R0

R01 X01

ZL1

V21

Equivalent circuit referred to secondary side:

V11

I11

I01

I2

IW1 Iµ

1

X01R0

1

R02 X02

ZL

V2

34

Model Graph:

UPF

%Reg.

% 0.8

Leading P.F Lagging P.F

O/P Power (Watts) %Reg.

Tabulations:

Open circuit test:

Short circuit test:

Sl.

No

Vo

(Volts)

Io

(Amps)

Wo

(Div)

Wo x M.F

(Watts)

Sl.

No

Vsc

(Volts)

Isc

(Amps)

Wsc

(Div)

Wsc x M.F

(Watts)

35

Tabulation to determine the Efficiency:

Sl.

No

Load

ratio

(X)

Output power

(Watts)

Wi

(Watts)

Wcu

(Watts)

Input Power

(Watts) % Efficiency

UPF 0.8 UPF 0.8 UPF 0.8

1 ¼

2

½

3

¾

4

1

Tabulation to determine the Regulation:

Sl.No Power Factor (Cos )

% Regulation

Leading Lagging

1 0

2 0.2

3 0.4

4 0.6

5 0.8

6 1.0

36

Precautions:

Autotransformer must be kept at minimum potential point during starting

condition.

Procedure:

Open circuit test:


2. Switch on the supply and vary the autotransformer to get rated voltage

3. Note down ammeter, voltmeter and wattmeter readings.

4. Bring back the autotransformer to original position.


Short circuit test:


2. Switch on the supply and vary the autotransformer to get rated short

circuit current.

3. Note down ammeter, voltmeter and wattmeter readings.

4. Bring back the autotransformer to original position.


Result:

Thus the open circuit and short circuit tests were performed on a

single-phase transformer and the efficiency was predetermined at various

loads.

37

Ex. No: LOAD TEST ON SINGLE PHASE TRANSFORMER

Date :

Aim:

To perform load test on a single phase transformer and determine its

performance characteristics

Apparatus Required:

Sl.no


Range

Type

Quantity

1. Ammeter (0-5) A

(0-10) A MI Each 1

2. Volt meter (0-150) V

(0-300) V MI Each 1

3. Watt meter 150V, 5A, UPF

300V, 10 A, UPF Dynamo meter Each 1

4. 1- Autotransformer (0-270) V 1


Formulae:

Input power = W1 x M.F1 watts

Output power = W2 x M.F2 watts

% Efficiency = Output power / Input power X 100

% Regulation = (E02 – V2) / E02 x 100

E 02 - No load secondary voltage

V 2 - Secondary voltage at various loads

M.F – Multiplication factor

W1, W2 - Wattmeter readings

V I cos

Multiplication factor (M.F) =

No of divisions in the watt meter

38

Precautions:

1. Autotransformer must be kept at minimum potential point during

starting condition.

2. There should be no load at the time of starting the experiment

Procedure:

1. Make the connections as per the circuit diagram.

2. Switch on the supply and vary the autotransformer to get rated

primary voltage.

3. Note down the no load readings.

4. Add the load in steps and note down all the meter readings till the

rated secondary current is reached.

5. Remove the load and bring back the autotransformer to original

position.

6. Switch off the supply.

39

Circuit Diagram:

DPST

Switch

Fuse

230 V

1-φ 50

HZ AC

Supply

A

C

M L

V

Fuse

15 A

15 A

(0-270 V)

1φ Auto

Trnsform

er

(0-150 V)

MI

(0-5 A) MI

150 V, 5A, UPF

Wattmeter

110 V 220 V


0 V 0 V

Load Test on Single Phase Tranformer

C

M L

V

A

DPST

Switch

Fuse

Fuse

10 A

10 A

(0-10 A) MI

300 V, 10A, UPF

V V(0-300 V)

MI

Wattmeter

Load

Name Plate Details

Primary Side Secondary Side

Power =

Voltage =

Current =

Power =

Voltage =

Current =

Primary Side: 125 % of Rated Current

=

Secondary Side: 125 % of Rated Current

=

P

N

40

Tabulation:

Sl.

No

Primary

Voltage

Primary

Current

Input Power Secondary

Voltage

Secondary

Current

Output Power Efficiency Regulation

W1 W1 X M.F W2 W2 X M.F

(Volts) (Amps) (Div) (Watts) (Volts) (Amps) (Div) (Watts) % %

42

Model Graph:

% Vs Output Power

% Efficiency

&

% Regulation % Reg. Vs Output Power


Result:

Thus the load test on a single-phase transformer was performed and

its performance characteristics were determined and plotted.

43

Ex. No: REGULATION OF ALTERNATOR BY EMF & MMF

METHOD

Date :

Aim:

To pre-determine the regulation of alternator by EMF & MMF methods.

Apparatus required:

Sl.No. Name Range Type Quantity

1 Voltmeter (0-300) V MI 1

2 Ammeter ( 0-2 ) A MC 1

3 Ammeter ( 0-10 ) MI 1

4 Rheostat 300 /1.4 A

100 /1 A Wire wound

1

1


Formula:

(i) EMF Method:

Open circuit voltage, V0 (From graph)

Zs = at constant field current

Short circuit current, ISC (From graph)

Re = 1.6 x Ra

XS = √ ZS2 –

Re2

ZS → Synchronous impedance (Ω)

XS → Synchronous Reactance (Ω)

Re → Effective Resistance (Ω)

44

E0 = √ (Vcosφ + IaRe)2 + (Vsinφ ± IaXS)

2

+Ve → lagging p.f

-Ve → leading p.f

V → Rated voltage (volts)

Ia → Rated armature current (Amps)

Cosφ→ power factor

E0 – V

% Regulation = ---------- x 100

V

(ii) MMF Method:

Ifr = √ If12 + If2

2 + 2 If1 If2 Cos (90±φ)

+ → lagging p.f

- → leading P.f

If1 → Field current required to generate rated terminal voltage

If2 → Field current required circulating rated short circuit current

Ifr → Resultant field current

E0 → The generated emf corresponding to Ifr (from graph)

E0 – V

% Regulation = ---------- x 100

V

45

Precautions:

TPST switch must be kept open.

Motor side rheostat must be kept in minimum position and

alternator side rheostat in maximum position.

Procedure:

Open circuit test:

Make the connections as per the circuit diagram.

Switch on the supply.

Start the motor – alternator set by using starter.

Adjust the field rheostat of the motor to get the rated speed.

Increase the alternator field current in convenient steps and note down

all the meter readings up to 125% of the rated voltage.

Bring back the rheostat to the original position.

Short circuit test:

Close the TPST switch and adjust the potential divider such that the

maximum full load current flows through the armature winding.

Note down all the meter readings.

Bring back the rheostats to original position and switch off the supply.

46

Circuit Diagram:

+

-

DPST

Switch

Fuse

220 Volts

D.C Supply

FF1

R

YB

TPST

Switch

Fuse

+

-

220 Volts

D.C Supply

LF

A

DPST

Switch

Fuse

F1

F2

A1

A2

3-Point Starter


KW________

RPM________

Volts________

Amps________

Alternator Name Plate Details

KVA________

RPM________

Volts________

Amps________

A

Regulation of Alternator By EMF and MMF Method

FF2

(0-300 V)

MI

(0-2 A)

MC

(0-10 A)

MI

300 Ω/

1.4 A

Fuse

Fuse

V

100 Ω/

4 A

M

10 A15 A

10 A

10 A

10 A15 A

A

47

Tabulation:

Open circuit test:

S. No If

(Amps)

Open circuit voltage

E0 (Volts)

Short circuit test:

S. No If (Amps) Isc (Amps)

To find Regulation (for EMF Method):

S. No Cosφ

% Regulation

Leading Lagging

E0 (V) % R E0

(V) % R

1 0

2 0.2

3 0.6

4 0.8

5 1

To find the Regulation (for MMF Method):

S. No Cosφ Lagging pf Leading pf

Ifr E0 %R Ifr E0 %R

1 0

2 0.2

3 0.6

4 0.8

5 1

48

MODEL GRAPH (for EMF Method):

V0

E0

Isc

ISC

If

Fig.1 O.C & S.C Characteristics

%Reg.


%Reg.

Fig.2 Regulation Graph

49

Model Graph (for MMF Method):

E0

E0

Isc

If

Fig.1 O.C & S.C Characteristics

%Reg.


%Reg.

Fig.2 Regulation Graph

If1 If2

Ifr

50

Result:

Thus the regulation of the alternator was predetermined by EMF &

MMF method and the graphs were plotted.

51

Ex. No: LOAD TEST ON 3φ SQUIRREL CAGE INDUCTION

MOTOR

Date :

Aim:

To determine the performance characteristics of the given 3φ squirrel cage

induction motor by conducting load test.

Apparatus required:

Sl.No. Apparatus Range Type Quantity

1 Voltmeter (0-600V) MI 1

2 Ammeter (0-10A) MI 1

3 Wattmeter 600V,10A,UPF Dynamometer 2



Formula:

Input power = W1 x MF1+ W2 x MF2 (watts)

Torque (T) = (S1 ~ S2) x 9.81 x r (N-m)

Output power = 2 Π NT / 60 watts

Efficiency = output power / input power x 100%

% Slip = [(NS – N) / NS] x 100

Power Factor = Input Power / √3VL IL

52

VI cosφ

Multiplication factor =

No. of divisions in the wattmeter

S1, S2= Spring balance readings in Kg.

r = Radius of the brake drum in m (circumference / 2Π)

N = Actual speed of the rotor in rpm

T = Torque in N-m

NS = Synchronous speed in rpm

Precautions:

There should be no load at the time of starting.

Auto transformer must be kept at minimum position

Procedure:


Switch on the supply and adjust the autotransformer to get the

rated voltage and note down the no load readings.

Adjust the loads and for various loads note down the

corresponding meters reading till the rated current is reached.

Unload the motor, bring back the autotransformer to minimum

position and switch off the supply.

53

CircuitDiagram:

VC

M L

C

M L

V

Spring

Balance

Brake

Drum

S1 S2

415 Volts

Three Phase 50Hz

AC Supply

TPST

Switch

R

Y

B

V

A

(0-600 V)

MI

(0-10 A) MI

10 A

10 A

10 A M1

L1

M3

M2

L3

L2

(0-470) Volts

Three Phase Auto

Transformer

600 V, 10 A, UPF

600 V, 10 A, UPF

Dynamometer

DynamometerMotor Name Plate Details

KW________

RPM________

Volts________

Amps________

Frequency________



=

Load Test on Three phase Squirrel cage Induction Motor

Fuse

Fuse

Fuse

54

Tabulation:

S.

No

V

(volts)

IL

(Amps)

W1

(div)

W2

(div)

W1x

Mf1

(Watts)

W2xMf2

(Watts)

Input

Power

(Watts)

Spring balance

readings

Speed

N

(rpm)

Torque

(N-m)

T

Output

power

(Watts)

η

%

Power

Facto

r

Slip

%

S1

Kg

S2

Kg

(S1 ~ S2)

kg

55

Model Graph:

Result:

Thus the performance characteristics of the given Three – Phase

squirrel cage induction motor were determined by conducting load test.

Torque in N-m

Speed in

rpm

PF Vs O/P

IL Vs O/P

Efficiency Vs

O/P

N Vs O/P

T Vs O/P

Slip Vs O/P


Efficiency

Slip

Speed

Power

factor

Load

current

Torque

56

Ex. No: LOAD TEST ON SINGLE PHASE SPLIT PHASE

Date : CAPACITIVE START INDUCTION MOTOR

Aim:

To determine the performance characteristics of the given single phase

split phase capacitive start induction motor by direct loading.

Apparatus required:

Sl.No Apparatus Required Range Type Quantity

1 Voltmeter

(0-300) V MI 1

2 Wattmeter 300V, 20A, UPF Dynamometer 1

3 Ammeter (0-20) A MI 1

4 1- Autotransformer (0-270) V 1



Formulae:

Cos = W/VI

%S = (NS - N) / N *100%

NS Synchronous Speed = 1500 rpm

Torque T = (S1 S2) 9.81 * r N-m

r Radius of the brake drum in m.

Output power P0 = 2 NT/60 watts

% Efficiency = [O/P Power / I/P power] *100.

57

Circuit Diagram:

C

M L

V

230 Volts

Single Phase 50Hz

AC SupplyDPST

Switch

P

N

A

(0-300 V)

MI

(0-20 A) MI

10 A

10 A

(0-270) Volts

Single Phase Auto

Transformer

300 V, 20 A, UPF

Dynamometer


KW________

RPM________

Volts________

Amps________

Frequency________



=

Load Test on Single phase Induction Motor

V

Spring

Balance

Brake

Drum

S1 S2M1 S1

M2 S2

Main

WindingStarting

Winding

Rotor

C

CS

Fuse

Fuse

58

Tabulation:

S. No

Current

(Amps)

I

Voltage

(Volts)

V

Input Power (Watts) Speed

(rpm)

N

Spring Balance

(Kg) COS

Slip

(%)

Torque

(Nm)

T

Output

Power

(Watts)

Efficiency

(%)

η W WxM.F S1 S2

59

Model Graph:

PF Vs O/P

IL Vs O/P

Efficiency Vs

O/P

N Vs O/P

T Vs O/P

Slip Vs O/P

Efficiency

Slip

Speed

Power

factor

Load

current

Torque

60

O/p Power

Precautions:

1. Auto – transformer should be kept at the minimum position during starting.

2. Load should be kept free during the starting condition.

Procedure:


Switch on the supply and adjust the autotransformer to get the rated voltage and note down the no load

readings.

Adjust the loads and for various loads note down the corresponding meters reading till the rated current is

reached.

Unload the motor, bring back the autotransformer to minimum position and switch off the supply.

Result: Thus the performance characteristics were determined for the given single phase split phase capacitive

start induction motor by direct loading.

61

Exp. No : MEASUREMENT OF 3 PHASE POWER USING TWO

Date: WATTMETER METHOD

Aim:

To measure the three phase power p.f using two-wattmeter method.

Apparatus required:

S.No APPARATUS TYPE RANGE QUANTITY

1. Three phase variac - (0-415) V 01

2. 3 phase Inductive load 01

3. Wattmeter Dynamometer 600V/15A 02

4. Ammeter MI (0-15A) 01

5. Voltmeter MI (0-600V) 01

Theory:

Three-phase circuits may be balanced or unbalanced. In case of the balanced circuits, if three-watt meters are

connected (one in each phase), equal readings will be obtained. Therefore, only one wattmeter may be connected in any one

phase, and the total power will be obtained by multiplying the power per phase by three.

In case of an unbalanced circuit, three-watt meters may be connected, one in each phase. The total power will then be

obtained by adding the three-wattmeter readings. However, there are some practical difficulties in doing so. For example,

62

the load neutral may not be available in case of Y-connected load (and then the supply neutral must be connected) or in a

delta connected system; it may not be possible to cut through the delta to connect the meters. (In the later case of the delta-

connected load, one has to connect using the supply neutral).

r

r r

r

r

V

A

(0-600V)MI

600V/10A

UPF

600V/10A

UPF

(0-10A)10A

10A

10A

3

415V

50 Hz

AC

SUPPLY

R

Y

B

N

T

P

S

T

S

CIRCUIT DIAGRAM FOR POWER AND p.f MEASUREMENT BY TWO WATTMETER METHOD

3 LOAD

MIM

M

L

L

C

CV

V

63

TABULAR COLUMN:

Sl.No. VRY

(Volts)

IR

(Amp)

W1

(Watts)

W2

(Watts) P=W1+W2

cos =(P1/P)* 3

Where P1= W1-W2

1.

2.

3.

4.

5.

Observation and calculation of power & p.f in 3 balanced ckt with 2-watt meters.

A more convenient and a popular method of measuring three-phase power are to use two-watt meters in a particular

way. The method is known as

“TWO WATTMETER METHOD”, since two watt meters are required.

They are connected as shown in the circuit diagram. It does not require the neutral point. It also does not need

opening or cutting through in case of the delta connected system.

Another important point is that this method is valid for both the balanced as well as the unbalanced conditions.

Further, the method of connecting is same irrespective of the delta or Y- connections of the supply or the load.

64

The circuit diagram using method needs the connections of the two current coils in series with the load in series with

the load in two phases, and the two pressure coils are connected between these two phases and the third phase respectively.

For example, as in circuit diagram the current coils carry iR and iY and the pressure coils are VRB and VYB.

In terms of the instantaneous currents iR, iY, iB and the instantaneous phase voltage vR, vY and vB, the instantaneous

total power (=p) is given by

p = vR iR + vY iY + vB iB -------------- eqn. (1)

The sum of the three phase currents must be zero, in case of three wire systems (i.e., without the neutral wire).

Hence, at all instants,

iR + iY + iB = 0 -------------- eqn. (2)

(or) iB = (iR + iY) – This equation is true for delta or Y-connected, balanced or unbalanced, 3 wire 3 phase systems.

Since, iB is not being passed through the meters, it should be eliminated from eqn. (1)

p = vR iR + vYiY + vB (-iR – iY)

= (v0 – vB) iR + (vY – vB) iY

= VRB iR = VYBiy ------------- eqn. (3)

The average power is obviously obtained by taking the r.m.s values and the power factor.

Note: The wattmeters read only the average power.

The eqn. (3) suggests that two-watt meters can obtain the power in 3 phase circuits as follows:

Wattmeter No.1 (i.e., W1) current coil carrying iR

65

Pressure coil across VRB

Wattmeter No.2 (i.e., W2) current coil carrying iY

Pressure coil across VYB

This is exactly what has been shown in fig. 6.1 in terms of average power, r.m.s voltage and currents, and the power

factors, eqn. (3) can be rewritten as follows:

P = VRB IR cos 1 + VYB IY cos 2 -------- eqn. (4)

= (Reading of wattmeter No.1) + (Reading of wattmeter No.2)

Thus, the total (time averaged) power for a 3 circuit is obtained by adding the two-wattmeter readings.

In eqn. (4), the power factors, cos 1 and cos 2 have the phase angle 1 between VRB and IR. The above method is

valid for both balanced as well as for unbalanced conditions.

For balanced loads: There are certain simplifications for the balanced loads. The three-phase quantities are equal and

have a mutual phase difference of 120 .

Fig.6.2 shows the phasor diagram for the balanced conditions. The voltage, current and the phase angles between

them are given below for the two-watt meters.

Using eqn. (4), with values substituted for the 3 Ph. Balanced load having a p.f of cos (lagging), we have

P = VRB IR cos (30+ ) + VYB IB cos (30- ) -------eqn. (5)

= ( 3 Vph) Iph (cos 30 * cos - sin 30 * sin )

+ ( 3 Vph) Iph (cos 30 * cos + Sin 30 * Sin )

66

= 3 Vph Iph (2* cos 30 * cos )

= 3 Vph Iph (2* ( 3/2)* cos

= 3 Vph Iph cos = 3 VL IL cos -------- eqn. (6)

The eqn. (6) is valid for delta as well as Y – connected systems.

Thus, P = W1 + W2 = Total power in the circuit.

Precautions:

1. Check the mains before connection wires.

2. The three phase variac should be in zero position.

3. The ammeters are connected using thick wires.

4. The voltmeters are connected using thin wires.

Procedure:

1. Connections are made as per the circuit the circuit diagram

2. Set the variac to zero output and switch on the main.

3. Adjust the variac output to obtain about 200 volts as the line voltage.

4. Note down the readings of the ammeters, voltmeters and the two-watt meters.

5. Calculate the total power consumed from these readings to verify the method. Note that for purely resistive

loads, the p.f is unity.

67

6. Repeat steps (3) to (6) above for different readings.

Result:

Thus we find the three-phase power & p.f using two-wattmeter method

EM Lab Manual - Cycle - I 1

Documents

Transcript of EM Lab Manual - Cycle - I 1