Electrical Machine lab manual

ELECTRICAL MACHNIES LAB -II

DEPARTMENT OF

ELECTRICAL AND ELECTRONICS ENGINEERING

ACADEMIC YEAR 2012-2013

III B.Tech EEE I-SEMESTER

PADMASRI DR B.V.RAJU INSTITUTE OF TECHNOLOGY

VISHNUPUR, NARSAPUR, MEDAK (DIST.) – 502313

Phone No: 08458 – 222031, www.bvrit.ac.in

http://www.bvrit.ac.in/

PREFACE

The significance of the Electrical Machines Lab-II, is renowned in the various fields of

engineering applications. For an Electrical Engineer, it is obligatory to have the practical ideas

about the Electrical Machines . By this perspective we have introduced a Laboratory manual cum

Observation for Electrical Machines Lab-II.

The manual uses the plan, cogent and simple language to explain the fundamental aspects of

Electrical Machines in practical. The manual prepared very carefully with our level best. It gives all the

steps in executing an experiment.

EleACKNOWLEDGEMENT

It is one of life’s simple pleasures to say thank you for all the help that one has extended their

support. I wish to acknowledge and appreciate Assoc Prof K.V.B.Reddy, Foreman. P Prabhu Dass, and

G.Suresh for their sincere efforts made towards developing the Electrical Machines Lab-II. I wish to thank

students for their suggestions which are considered while preparing the lab manual.

I am extremely indebted to Sri.Col Dr. T. S. Surendra, Principal and Professor, Department of

Electrical and Electronics Engineering, BVRIT for his valuable inputs and sincere support to complete the

work.

Specifically, I am grateful to the Management for their constant advocacy and incitement.

Finally, I would again like to thank the entire faculty in the Department and those people who

directly or indirectly helped in successful completion of this work.

(Prof. N. BHOOPAL)

HOD – EEE

GUIDELINES TO WRITE YOUR OBSERVATION BOOK

1. Experiment Title, Aim, Apparatus, Procedure should be on right side.

2. Circuit diagrams, Model graphs, Observations table, Calculations table should be

left side.

3. Theoretical and model calculations can be any side as per your convenience.

4. Result should always be in the ending.

5. You all are advised to leave sufficient no of pages between experiments

for theoretical or model calculations purpose.

DO’S AND DON’TS IN THE LAB

DO’S:-

1. Proper dress has to be maintained while entering in the Lab. (Boys Tuck in and

shoes, girls with apron)

2. All students should come to the Lab with necessary tools. (Cutting Pliers 6”,

Insulation remover and phase tester)

3. Students should carry observation notes and record completed in all aspects.

4. Correct specifications of the equipment have to be mentioned in the circuit

diagram.

5. Student should be aware of operating equipment.

6. Students should be at their concerned experiment table, unnecessary moment is

restricted.

7. Student should follow the indent procedure to receive and deposit the equipment

from the Lab Store Room.

8. After completing the connections Students should verify the circuits by the Lab

Instructor.

9. The reading must be shown to the Lecturer In-Charge for verification.

10. Students must ensure that all switches are in the OFF position, all the

connections are removed.

11. All patch cords and stools should be placed at their original positions.

DON’Ts:-

1. Don’t come late to the Lab.

2. Don’t enter into the Lab with Golden rings, bracelets and bangles.

3. Don’t make or remove the connections with power ON.

4. Don’t switch ON the supply without verifying by the Staff Member.

5. Don’t switch OFF the machine with load.

6. Don’t leave the lab without the permission of the Lecturer In-Charge.

JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY

III Year B.Tech EEE ISem Academic year 2012-2013

L T/P/D C

0 -/3/- 2

(55602) ELECTRICAL MACHINES LAB –II

The following experiments are required to be conducted as compulsory experiments.

1. O.C. & S.C. Tests on single phase transformer .

2. Sumpner's test on a pair of single phase transformers .

3. Brake test on three phase squirrel cage induction motor.

4. No-load & blocked rotor tests on three phase Slip ring Induction motor.

5. Regulation of a three phase alternator by synchronous impedance (EMF & MMF) method.

6. V and inverted V curves of a three - phase Synchronous motor .

7. Equivalent circuit of a single phase induction motor .

8. Determination of Xd and Xq of a salient pole synchronous machine .

In addition to the above experiments, at least any two of the experiments from the following list are

required to be conducted.

1. Parallel Operation of Single Phase Transformers. 2. Separation of core losses of a single phase transformer.

3. Scott connection of Transformers .

4. Regulation of a three phase alternator by ZPF & ASA method.

5. Efficiency of a tree phase alternator.

6. Heat run test on a bank of 3 No s of single phase delta connected transformers.

7. Measurement of sequence Impedance of a 3phase alternator .

Academic year 2012-2013

Experiments Conducted by the Department:-

1. O.C. & S.C. Tests on single phase transformer .

2. Sumpner's test on a pair of single phase transformers .

3. Scott connection of Transformers .

4. No-load & blocked rotor tests on three phase Slip ring Induction motor.

5. Regulation of a three phase alternator by synchronous impedance (EMF & MMF)

method.

6. V and inverted V curves of a three - phase Synchronous motor .

7. Equivalent circuit of a single phase induction motor .

8. Determination of Xd and Xq of a salient pole synchronous machine .

9. Regulation of a three phase alternator by ZPF & ASA method.

10. Brake test on three phase squirrel cage induction motor.

Additional Experments

1. Parallel Operation of Two Single Phase Transformers.

2. Parallel Operation of Two 3ф Alternators .

230V

V

115V

V

(0-15)A

MI

(0-50)V

MI

1- Φ

230V

50 Hz

AC

Supply

Ph

N 1 Φ -Transformer

3KVA, 230V/ 115V

Short

Circuit

DPST

Variac

3KVA, 230V/ (0-270)V

15A, 50V, 600W, UPF

L M

C

V

Fig -2

V

A

DPST

(0-2)A MI

2A, 150V, 60W, LPF 115V 230V

Ph

1- 230V

50 Hz AC

Supply

A

V (0-150)V MI

M C

L V

Open Circuit

N

Variac 3KVA, 230V/ (0-270)V

1 -Transformer 3KVA, 230V/ 115V

1. OC & SC TESTS ON 1- TRANSFORMER

Aim: To conduct OC & SC tests on the given 1- Transformer and to calculate its

equivalent

circuit parameters, efficiency & regulation.

Name plate details:

1- TRANSFORMER

Capacity 3 KVA

I/P voltage 230V

I/P current 13.04A

O/P voltage 115V

O/P current 26.08A

Frequency 50Hz

Apparatus required:

S.NO DESCRIPTION RANGE TYPE QTY

OC TEST

1 Voltmeter 0-150V M.I 1 No

2 Ammeter 0-2.5A M.I 1 No

3 Wattmeter 2.5A/150V

Dynamo

meter

(LPF)

1 No

4 Auto T/F 230V/0-270V, 8A 1- wire

wound

1 No

5 Fuses 5A - 2 Nos

SC TEST

1 Voltmeter 0-50V M.I 1 No 2

Ammeter 0-5A M.I 1 No

Dynamo

3 Wattmeter 5A/50V meter 1 No

(UPF)

4 Auto T/F 230V/0-270V, 1- wire 1 No

8A wound

5 Fuses 5A - 2

Nos

Theory: Transformer is a static device which transfers electrical power from

one circuit to another circuit either by step up or step down the voltage with

corresponding decrease increase in the current, with out changing the

frequency.

OC Test

The main aim of this test is to determine the Iron losses & No- load

current of the T/F which are helpful in finding Ro & Xo.In this test generally

supply will be given to primary and secondary kept open. Since secondary is

opened a small current(magnetizing current will flow and it will be 5 to 10%

of full load current. The wattmeter connected in primary will give directly the

Iron losses (core losses).

SC Test:

The main aim of this test is to determine the full load copper losses which

is helpful in finding the R01, X01, Z01, efficiency and regulation of the T/F.

Generally low voltage side will be short circuited and supply will be given to

high voltage side & it will be of 5-10% of the rated voltage. The wattmeter

connected in primary will give directly the full load copper losses of the T/F.

Procedure

OC Test:

1)

2)

3)

SC Test:

1)

2)

:

Give connections as per the circuit diagram.

Switch-ON the supply and apply rated voltage to the

primary of the winding by using the auto transformer.

Note the readings of Ammeter, Voltmeter & Wattmeter

Give connections as per the circuit diagram.

Switch-ON the supply and vary the Dimmerstat till rated

full load current flows through transformer.

3) Note the readings of Ammeter, Voltmeter & Wattmeter

Graph: A graph is drawn between P.F and % regulation by taking P.F

on X- axis and % regulation on Y-axis.

Observations:

O.C Test: S.C Test:

V0

volt

I0

ampere

W0

watt

VSC volt

ISC

ampere

WSC Watt

Calculations:

Load Cu losses Total losses I/P power O/P power

Full

¾

½

¼

%

% Regulation P.F

lag lead

PRECAITIONS:

1) The Dimmer stat should be kept at minimum O/P

position initially.

2) In OC test, rated voltage should be applied to the

Primary of the Transformer.

3) In SC test, the Dimmer stat should be varied up to the

rated load current only.

4) The Dimmer stat should be varied slowly & uniformly.

Result:

2-SUMPNER'S TEST

Aim: To predetermine the equivalent circuit parameters, efficiency & regulation

of a given pair of 1-phase Transformers by conducting Sumpner's test.

Name plate details:

1- TRANSFORMERS

1- TRANSFORMER

Capacity 3 KVA

I/P voltage 230V

I/P current 13.04A

O/P voltage 115V

O/P current 26.08A

Frequency 50Hz

Apparatus required:


Auto T/F 230V/0- 1- wire 2 Nos 1

270V, 16A wound

0-50V M.I 1 No


0-500V M.I 1 No

2 Ammeter 0-2.5A M.I 1 No

0-10A M.I 1 No

2.5A/300V LPF 1 No 3 Wattmeter

10A/150V UPF 1 No

5A 2 Nos 4 Fuses -

10A 2 Nos

5 SPST switch 20A - 1 No

Precautions: Theory:

1) The Dimmerstat should be kept at minimum O/P

position initially.

2) In OC test, rated voltage should be applied to the primary

of the Transformer.

3) In SC test, the Dimmerstat should be varied upto the

rated load current only.

4) For sc test, close the polarity switch only when both

secondaries are at same potential

4) If the polarity voltmeter indicates some voltage, change

secondary winding connections..

Sumpner's test is also known as back-to-back test. This test requires two identical

transformers and is connected as shown in circuit diagram. By this test ,the

equivalent Circuit parameters, efficiency, regulation & heating of both the T/F can

be determined. Each T/F is loaded on the other and both are connected to same

supply. The primaries of Two T/Fs are connected in parallel across same supply

and the Wattmeter connected in Primaries reads the core losses (Iron losses) of

both transformers. The secondaries are so connected such that their potentials are

in opposite to each other.By connecting so there would be no secondary current

flowing around the loop formed by the two secondaries.

Procedure:

OC Test:

1) Give connections as per the circuit diagram.

2) Switch-ON the supply keeping the polarity switch open and

apply rated voltage to the primary of the winding by using the

auto transformer.

3) Note the readings of Ammeter, Voltmeter & Wattmeter

DPST

(0-5)A MI

5A, 150V, 75W, LPF

Ph

1- 230V 50 Hz AC

Supply

A

V (0-150)V MI

M

C

L

V

N

Variac 230V/ (0-270) V, 1- , 50 H

115V

0V 115V

0V

(0-15)A MI

15A, 75V, 750W, UPF

230V

0V

230V

0V

V

A

(0-75)V MI

M

C

L

V

V

(0-600)V MI

Variac 230V/ (0-270) V, 1- , 50 Hz

Circuit Diagram

SC Test:

1) Keeping the primary supply as it, Switch-ON the supply and

close the polarity switch.

2) Vary the Dimmerstat till rated full load current flows through

transformers.

3) Note the readings of Ammeter, Voltmeter & Wattmeter.

Graph:

1) A graph is drawn between P.F and % regulation by taking P.F on X-axis and

% reg on Y-axis

2) A graph is drawn between efficiency & O/P power by taking efficiency on X-

axis and O/P power on Y-axis.

Observations:

O.C Test:

V0

volt

I0

ampere

W0

Watt

S.C Test:

VSC

volt

ISC

ampere

WSC

Watt

Calculations:

Load Cu losses Total losses I/P power O/P power

Full ¾

½ ¼

% Regulation P.F

%

lag lead

Result:

3-SCOTT CONNECTION OF TRANSFORMERS

Aim: To observe that:

1) The voltage across Teaser secondary and that across main transformers

are in quadrature to each other.

2) If Teaser transformer and Main transformer are equally loaded primary

will also be at balanced.

Name plate details:

SCOTT TRANSFORMERS

Capacity

I/P voltage

I/P current

O/P

voltage

O/P current

Frequency

1 KVA

230V

4.34A

115V

8.64A

50Hz

Apparatus required:


Auto T/F 415V/0- 3- wire 1 Nos 1

470V, 15A wound

2 Ammeter 0-2A M.I 3 No

0-5A M.I 2 No

0-150V M.I 2 No 3 Voltmeters

0-250V M.I 1 No

4 Fuses 5A - 2 Nos

230V/0- 1 No 5 Load box Rheostatic

10A

R

TPST

Tp

100% V 86.6%=Tp

115V

100% V

Ts

3- 415V 50 Hz AC

Supply

Y

V

(0-600)V

MI

Teaser transformer Primary

Teaser transformer Secondary

0% V

V

(0-300)V MI

0% Mp=50% 100% 0% 100%

3- 415V 50 Hz AC

Supply

B

V Main transformer Primary

V V Main transformerV V2

(0-300)V

MI

PRECAITIONS: 1) The Dimmerstat should be kept at minimum O/P position

initially.

2) The Dimmerstat should be varied slowly & uniformly.

3) Rated voltage should be applied to the primary of the

Transformer.

Theory: In some cases, we may require 2 power instead of 3 or 1 power. For

that it is necessary to convert 3 to2 power (since 3 power is available at every

nook corner).

Scott connection is one by which 3-phase to 2-phase

transformation is accomplished with the help of two identical 1 T/Fs having same

current rating. One T/F has a center tap on primary side and it is known as Main

transformer. It forms the horizontal member of the connection. Another T/F has

0.866tap on primary side and known as Teaser transformer. The 50% tap point on

primary side of the main T/F is joined to 86.6% tap on primary of the teaser T/F.

Obviously full rating of the T/Fs is not at all used. Refer to the fig. The main T/F

primary winding center tap point D is connected to one end of the primary of the

teaser T/F on secondary side, both the main & teaser T/F turns are used (not only

86.6%).Hence the voltage per turn will be equal for both T/Fs.

Since point D is located midway on AB, VCD leads VAB by 900 i.e, voltages across

primary are 900 apart also.

Position of Neutral point N on primary side:

Remember point D is not the neutral on primary , since its

voltages w.r.t R, Y, B are not equal to V1/ 3 i.e, the neutral point is that one

which gives equal voltage with R, Y, B. The neutral point is one third the

waydown the teaser T/F winding from C to D Or point N divides the teaser

primary winding in the ratio of 1:2. Hence the neutral must be

At 86.6/3=28.8% from D

Current in Teaser T/F:

w.r.t

For 2:1 T/F,

Current in Main T/F:

N2 /0.866N1 = IR/IX

IR = InK(1.15) IR = 0.57xIX

N2/N1 = (IR/2 - IY/2)

For balanced load, since IX & IY are at 900

IR = ⎣1200; IB = ⎣-1200

Like wise, IR, IY & IB are equal in magnitude and are 1200 apart

from each other.

Procedure:

1) Give all connections as per the circuit diagram.

2) Switch-ON the supply and apply rated voltage to the primaries.

3) Note the voltmeters readings of both sec. Sides of both T/Fs. 4)

Now join the sec. in series aiding as shown in fig.and note he

resultant voltage.

5) Load both the T/Fs equally with out exceeding the rating And

note the ammeter readings on primary side.

Observations:

V4 (across sec. of teaser T/F) =

V5 (across sec. of main T/F) =

Resultant voltage, VT = V21+V22 =

Load applied A1 A2 A3 A4 A5

Result:

4-NO LOAD & BLOCKED ROTOR TESTS ON SLIP RING

INDUCTION MOTOR

Aim: To conduct No-load & rotor blocked tests on the given 3 Slip ring

induction motor and to draw its circle diagram.

Nameplate details:

3 -INDUCTION MOTOR

Capacity

Voltage

Current

Speed

Frequency

5 H.P

415V

7.8A

1500rpm

50Hz

Apparatus required:


415V/0- 3- wire 1 Auto T/F 1 Nos

470V, 15A wound

0-2A M.I 1 No 2 Ammeter

0-10A M.I 1 No


0-250V M.I 1 No

2.5A/300V LPF 1 No 4 Wattmeters

10A/150V UPF 1 No

5 Fuses 10A - 3 Nos 6

Tachometer 0-50000rpm Digital 1 NO

No Load Test TPST Switch

(0-5)A 5A, 600V, 600W, LPF MI 3- Alternator

R A M L

R R

3- 415V

50 Hz AC

Supply

V

C

(0-600)V MI

W1

V

Y

Stator

B

Y

3- 415V

50 Hz AC

C M

W2

V

L

B

Rotor

Y

Supply 5A, 600V, 600W, LPF

B

3- Auto Transformer

Fuse

Blocked Rotor Test TPST Switch

(0-15)A 15A, 600V, 600W, UPF MI 3- Alternator

R

3-

A M C

L

V

R R (0-30)A

MI

415V 50 Hz

AC Supply

V (0-600)V MI

W1 Y

Stator B

A

Y

3- 415V

50 Hz AC

C

M

W2

V

L

B

Rotor

Y

S1

S2

Supply 15A, 600V, 600W, UPF

B

3- Auto Transformer

Fuse

Precautions:

Theory:

1)The Dimmerstat should be kept at minimum O/P position

initially.

2) In the rotor-blocked test, the rotor should be blocked firmly.

3) In SC test, the Dimmerstat should be varied slowly such that

current should not exceed the rated value.

4) If the wattmeter shows negative deflection, then reverse either

pressure coil or current coil & take that reading as negative.

With the help of circle diagram, the behavior of the Induction motor

under various load conditions i.e, the characteristics can be studied. Apart from

that the max torque and max O/P that can be developed by the motor can be

predetermined. Efficiency, slip, p.f, rotor cu losses, stator cu losses, no-load

losses, full load O/P, stable region of operation etc. can also be predetermined. To

draw a circle diagram, it is necessary to conduct two tests on the motor.

a) No-load test and b) blocked rotor test.

Construction of circle diagram:

1) Obtain the values of VL, IO, WO & Cos from the OC test.

2) Obtain the vales of VS.C, IS.C, WS.C & Cos S.C from the SC test.

3) Represent the voltage vector on Y-axis to to some convenient scale.

4) Take a suitable current scale.

5) Represent the vector IO lag behind VL by O as per the current scale.

6) Name the vector as OA.

7) Join O1A & Draw a le line to the X-axis through O1 and name as O1X1.

8) Draw a perpendicular bisector to O1A so that it meets the line O1X1 at C as

center.

9) Draw a semicircle on the line O1X1 taken O1C as radius and C as center.

10) Draw a perpendicular bisector to O1A so that it meets the line O1R1 at C.

11) Draw a perpendicular from A to X-axis so that it meets X-axis at C.

O1Z = IO Cos O similarly: AB = I1S.C Cos O

Procedure:

No-load test:


2) Switch-ON the supply & apply the rated voltage to motor with

out any load.

3) Note the readings of voltmeter, ammeter & wattmeter.

Blocked rotor test:


2) Apply a low voltage to motor with auto transformer so that

rated load current flows through the stator.

3) Note the readings of voltmeter, ammeter & wattmeter

Observations

O.C Test: S.C Test:

V0

volt

I0

ampere

W0

watt

VSC

volt

ISC

ampere

WSC

watt

Model Graph

Result:

5. REGULATION OF ALTERNATOR BY SYNCHRONOUS IMPEDANCE

METHOD

Aim: To conduct OC test & SC test n the given 3 -Alternator and to

determine its regulation by synchronous impedance method.

Nameplate details:

DESCRPTION

Capacity

Voltage

Current

Speed

Excitation

D.C MOTOR

5 H.P

220V

19A

1500rpm

220V, 1.5A

3 -ALTERNATOR

3 KVA

415V

4.2A

1500rpm

220V, 1.4A

Apparatus required:



0-2A M.C 1 No


0-50V M.I 1 No

3 Rheostat 250 /1.5A Wire wound 2 Nos

4 Tachometer 0-50000rpm Digital 1 No

2A 2 Nos 5 Fuses -

10A 2 Nos

3 point starter OC Test DPST Switch 3- Alternator TPST Switch

+

230 V

DC Supply

F

FF

L FA 400 / 1.7A

A

AA

M

FA

FAA

B

R

N

Y

V

(0-300)V

MI

Fuse +

230 V

400 /

+ A

DC Supply

1.7A (0-1)A MC

Fuse

3 point starter SC Test DPST Switch 3- Alternator TPST Switch

+

230 V

DC Supply

F

FF

L FA

400 / 1.7A

A

AA

M

FA

FAA

B

R

N

Y

A

(0-10)A

MI

Fuse + 400 /

+ A

230 V DC

Supply

1.7A (0-1)A MC

Fuse

Precautions:

Theory:

1) Operate the 3-point starter slowly & uniformely.

2) Keep the speed of the prime mover to its rated value through

out the experiment.

3) In OC test, there should not be any load on Alternator.

4) In SC test, the SC current should not exceed its rated value.

Alternator is a machine, which converts mechanical energy to

electrical energy. Regulation of an Alternator can be calculated by synchronous

impedance method. In OC test the terminals of the alternator are kept opened and a

voltmeter is connected. Keeping speed constant, a relation b/w field current & open

circuit voltage are obtained. In SC test, the terminals are short circuited with a

suitable ammeter & a relation b/w field current & short circuit Current are

obtained.

Voltage regulation:

It is defined as the rise in terminal voltage of an isolated

Machine when full load is thrown off w.r.t voltage on the full load,

when speed & excitation remaining constant.

Now, Syn.Impedance (ZS) = OC voltage / SC current

XS = Z2S - R2a

From fig. EO = OB2 + BD2

= (Vcos +IRa)2 + (Vsin +IXS)2

% Regulation = [(E0-V) / V] 100

Procedure: OC test:


2) Switch-ON the supply & by varying the starter, prime mover

speed is adjusted to rated.

3) Now keeping the field current at zero, note the induced emf in

armature duo to residual Magnetism.

4) By slowly varying the potential divider, field current is increased

& corresponding emf Induced is noted up to above 20% of rated

voltage.

SC test:


2) Switch-ON the supply & by varying the starter, prime mover

speed is adjusted to rated.


& corresponding short Circuit current is noted up to rated value.

To find armature resistance (Ra):

Give the connections as per diagram and by slowly varying the

rheostat, note the values of ammeter & voltmeter up to some

value and average them.

Graph: 1) A graph is drawn b/w If and V which is known as OC

curve, by taking If on X-axis and V on Y-axis.

2) A graph is drawn b/w If and ISC which is known as SC

curve, by Taking If on X-axis and ISCV on Y-axis.

Observations:

OC Test: SCTest:

Field OC Field SC

current If voltage current If current

Armature resistance:

voltage current Resistance Ra

MODEL GRAPH

Result:

If 2

1

Isc

SCC

X O

Eo

Y

If

OCC

% Voltage

Regulation

Leading PF Lagging PF

If1

6 - V & CURVES OF SYNCHRONOUS MOTOR

Aim: To conduct a no-load test on the given Synchronous motor and to draw its

V & curves.

Nameplate details:

3 -SYNCHRONOUS MOTOR

Capacity

Voltage

Current

Speed

Excitation

3 KVA

415V

3.5A

1500rpm

220V, 1.4A

Apparatus required:


0-2A M.C 1 No 1 Ammeter

0-5A M.I 1 No

2 SPST switch - - 1 No

Wire 3 Rheostat 250 /1.5A 1 No

wound

4 Starter - D.O.L 1 No

3 5 Fuses 5A -

Nos

Precautions:

1) There should not be any load on the motor.

2) Initially the field current should be adjusted to rated value.

3) The direction of the rotation of the rotor should be in proper direction only.

4) If Ia value is increased more than rated value, then it should be brought to rated value by adjusting the field current.

5) The I/P voltage should be kept constant through out the experiment.

6)After completion of the experiment only 3-phase supply should be disconnected

first and then DC supply.

Theory :The variation of field current effects the power factor at which the

synchronous motor operates. For a syn motor, the armature current phasor is

given by Ia=V-E where V is the applied voltage .From the above equation it is

clear that the magnitude and phase angle of phasor Ia depends upon the value of

DC excitation. When the syn. Motor is operated at constant load with variable

field excitation , it is observed that:

a) When the excitation is low, the armature current is lag in

nature & the magnitude is comparatively high.

b) If the excitation is gradually increased, the magnitude of Ia is

gradually decreasing and the angle of lag is gradually

reduced.

c) At one particular excitation, the magnitude of Ia

corresponding to that load in minimum and vector will be in

phase with V vector.

d) If the excitation is further increased, the magnitude of Ia

again gradually increased and Ia,vector goes to leading state

and the angle of load is also gradually increased.

Procedure: 1) Give all connections as per the circuit diagram.

2) Switch-ON the supply and apply the rated voltage by using

D.O.L starter keeping SPST switch open.

3) Now field supply is given to the field by closing SPST

switch. At this position, the rotor will be pulled into

synchronism.

4) By varying the field current If , Note down the values of

armature currents.

5) Switch-Off the supply.

Graph:

A graph is drawn b/w

a) Exciting current (If) verses armature current (Ia) : V curve.

b) Exciting current (If) verses power factor (cos ) : curve.

taking If on X-axis and Ia & cos on y-axis.

(0-5)A MI

5A, 600V, 3KW, LPF

Without Load

3- Synchronous

3-

R TPST Switch A

(0-500)V

M

C

L

V

Motor

415V 50 Hz AC

Supply

Y

3- 415V

V MI V

C

FA

FAA

50 Hz AC

Supply

L

M

5A, 600V, 3KW, LPF

B

Fuse

+

230 V DC

Supply

400 / 1.7A

+

A

(0-5)A MC

3- Auto Transformer 415V/(0-470V)

(0-10)A

5A, 600V, 3KW, UPF

With Load

3- Synchronous

R TPST Switch MI A

M L Motor S1

S2

3- 415V

50 Hz AC

Supply

Y

3- 415V

50 Hz AC

V

(0-500)V

MI

C

V L

V C

M

FA

FAA

Brake

Drum

Supply

B

5A, 600V, 3KW, UPF

+

Fuse

+ 230 V

400 / A

3- Auto Transformer

415V/(0-470V)

DC Supply

1.7A (0-5)A MC

Observations:

Field current If Armature current Ia cos

Model Graph:-

Result :-

7-EQUIVALENT CIRCUIT OF 1 -INDUCTION MOTOR

Aim: To conduct OC & SC tests on the given 1 -Induction motor and to

Determine its equivalent circuit parameters.

Nameplate details:

1 -INDUCTION MOTOR

Capacity

Voltage

Current

Speed

Frequency

1.5 H.P

230V

6.5A

1500rpm

50Hz

Apparatus required:


1- 230V/0-

1 Auto T/F wire 1 No 270V, 8A

wound


0-10A M.I 1 No


0-250V M.I 1 No

5A/300V LPF 1 No 4 Wattmeters

10A/75V UPF 1 No

5 Fuses 10A - 2 Nos

0- 6 Tachometer Digital 1 NO

50000rpm

DPST

(0-10)A MI

No-Load Test

10A, 300V, 600W, LPF

Ph

1- 230V

50 Hz AC

Supply

A

V (0-300)V MI

M C

L V

IM

N

Variac 230V/ (0-270V)/28A

Blocked Rotor Test

DPST

(0-25)A

MI

30A, 150V, 3KW, UPF

Ph

1- 230V

50 Hz AC

Supply

A

V (0-150)V MI

M C

L V

IM

S1

S2

Brake Drum

N

Variac 230V/ (0-270V)/28A

Precautions: 1) The Dimmerstat should be kept at minimum O/P position

initially.

2) In the rotor-blocked test, the rotor should be blocked firmly.

3) In SC test, the Dimmerstat should be varied slowly such that

current should not exceed the rated value.

4) If the wattmeter shows negative deflection, then reverse either

pressure coil or current coil & take that reading as negative.

Theory: Single phase induction motor also woks on the principle of

'Faraday's laws of electromagnetic induction. The equivalent Circuit of such motor is

based on double field revolving theory i.e, an alternating uniaxial quantity can be

represented by two oppositely rotating vectors of half magnitude. So here the

single phase motor has been imagined to be made up of one stator winding and two

imaginary rotors. Each rotor will be assigned half the actual value of resistance. In

order to find the equivalent circuit parameters, it is need to conduct OC & SC tests

on it. In OC test, rated voltage will be given to motor with out any load on it. In SC

test, the rotor is blocked and a reduced voltage will be given upto the rated load

current.

Procedure:

Observations:

O.C Test:

No-load test:


5) Switch-ON the supply & apply the rated voltage to motor with

out any load.

6) Note the readings of voltmeter, ammeter & wattmeter.

Blocked rotor test:

1. Give all connections as per the circuit diagram.

2. Apply a low voltage to motor with auto transformer so

that rated load current flows

through the stator.

3. Note the readings of voltmeter, ammeter & wattmeter

S.C Test:

V0

volt

I0

ampere

W0

watt

VSC

volt

ISC

ampere

WSC

Watt

Result:

8-DETERMINATION OF Xd & Xq OF SYNCHRONOUS MACHINE

Aim: To determine the values of Xd & Xq of the given salient pole synchronous

machine.

Nameplate details:

DESCRPTION

Capacity

Voltage

Current

Speed

Excitation

D.C MOTOR

5 H.P

220V

19A

1500rpm

220V, 1.5A

3 -ALTERNATOR

3 KVA

415V

4.2A

1500rpm

220V, 1.4A

Apparatus required:


1 Ammeter 0-5A M.I 1 No

2 Rheostat 250 /1.5A Wire wound 1 Nos

3 Tachometer 0-50000rpm Digital 1 No


Phase sequence 5 500V - 1 No

Meter

6 Auto T/F 415V/0-470V, 15A Wire wound 1 No 7

Fuses 5A - 3 Nos

Precautions:

1) Check the phase sequence of the machine with that of external supply before

closing the switches.

2) Disconnect the excitation supply of the alternator while giving external supply.

3) Slip should be made as small as possible.

Theory: The values of Xd & Xq are determined by conducting the slip-test. The

syn. machine is driven by a separate prime mover at a speed slightly different

from synchronous speed. The field winding is left open and positive sequence

balanced voltages of reduced magnitude (around 25% of the rated value) and of

rated frequency and impressed across the armature terminals. Here, the relative

velocity b/w the field poles and the rotating armature mmf wave is equal to the

difference b/w syn. speed and the rotor speed i.e, the slip speed . When the rotor is

along the d-axis, then it has a position of min reluctance, min flux linkage and

max flux produced links with the winding.then Xd = (max. armature terminal

voltage/ph) / (min. armature current/ph)As the current is small then Vt will be high

as drop will be small.When the rotor is along q-axis, then it is max, then the flux

linkage would be max.Then The min flux produced links with winding. So max

emf. Xq = (min. armature terminal voltage/ph) / (max. armature current/ph)

Procedure: 1) Give all connections as per the circuit diagram.

2) Run the machine at syn speed and give a small excitation so that

to generate a small voltage.

3) Check the phase sequence of the machine with the incoming

external supply.

4) Now, remove the supply for field winding and run the machine

slightly above or below the rated speed.

5) Apply the external supply slowly and observe the oscillations in

ammeter & voltmeter.

6) Note the max & min voltage and current.

3 point starter DPST Switch (0-5)A

+ L FA

FA

R

A

MI

R

TPST Switch R

230 V

DC Supply

F

400 / 1.7A

A

(0-600)V

MI

V

FAA

N

V

(0-150)V MI

N

3- 415V

50 Hz AC

Supply

FF

AA

M

B

Y

B

Y

Y

3- 415V

50 Hz AC Supply B

Fuse

Observations:

415 V/50Hz/6.4 A/ 5 KVA 3- Auto Transformer

415V/(0-470V)

Fuse

Vmax Vmin Imix Imin

Xd = Vmax /I min ; =

Xq = Vmin / Imax =

Result:

9. REGULATION OF 3 Φ ALTERNATOR BY USING ZPF & ASA METHOD. Circuit Diagram O.C Test:-

Y

3- Φ Alternator

F

A

FA

A

−

230

V

DC

Supp

ly

400Ω

/ 1.7A

V

A

OC Test

(0-1)A

MC

+ − +

400Ω

/

1.7A

−

A

A

F

M

F

F

230

V

DC

Supp

ly

+ DPST

Switch

Fuse

3 point

starter F L A

A

N

R

B

TPST Switch

Fuse

(0-

300)V

MI

Circuit Diagram for S.C Test:-

Y

3- Φ Alternator

F

A

FAA

−

230

V DC

Supply

400Ω

/

1.7A

A

A

SC Test

(0-1)A

MC

+ − +

400Ω

/

1.7A

−

A

A

F

M

F

F

230

V

DC

Supp

ly

+ DPST

Switch

Fuse

3 point

starter F L A

A

N

R

B

TPST Switch

Fuse

(0-

10)A

MI

−

(0-10)A

MI

(0-300)V

MI

Y

3- Φ Alternator

FA

FAA

−

230 V DC

Supply

400Ω/

1.7A

A

ZPF Method

(0-1)A

MC

+ +

400Ω/

1.7A

−

AA

F

M

FF

230 V

DC

Supply

+ DPST Switch

Fuse

3 point starter

F L A

A

N

R

B

TPST

Fuse

A

I

N

D

U

C

T

I

V

E

L O

A

D

V

Circuit Diagram for Z.P.F Test:-

Diagram with Inductive Load

9. REGULATION OF 3 Φ ALTERNATOR BY USING ZPF & ASA METHOD. Aim:- To find the regulation of 3Φ Alternator by ZPF & ASA Method, comparing the values obtained by two methods Name plate details:- D.C Shunt Motor Alternator Power Speed Current Voltage Field Excitation Apparatus:-

S.No Name of the Item Type Range Qty

1

2

3

4

5

6

Procedure:-

O.C Test:-


2) switch-ON the supply & by varying the starter, prime mover

Speed is adjusted to rated.

3) Now keeping the field current at zero, note the induced emf in

Armature duo to residual Magnetism.


& corresponding emf Induced is noted up to above 20% of rated

voltage.

SC test:


2) switch-ON the supply & by varying the starter, prime mover

Speed is adjusted to rated.


& corresponding short Circuit current is noted up to rated value.

To find armature resistance (Ra):

Give the connections as per diagram and by slowly varying the

Rheostat, note the values of ammeter & voltmeter up to some

value and average them.

Z.P.F Test:-


2) Verify the connections by the instructor.

2) switch-ON the supply & Start the motor with the 3-pont

starter, Adjust the rated speed of prime mover by varying the

field rheostat.

3) Gradually increasing the field excitation bring the alternator voltage to rated value 4) Switch on the inductive load and adjust, so that the full load current will flow through the ammeter. In mean time rated voltage must be maintained.

Graph: 1) A graph is drawn b/w If and V which is known as OC

curve, by taking If on X-axis and V on Y-axis.

2) A graph is drawn b/w If and ISC which is known as SC

curve, by Taking If on X-axis and ISCV on Y-axis.

Observations:-

O.C Test:- If(A) E0(v)

S.C Test:- If(A) Ise(A) Z.P.F Test:- If(A) I Load V

Circuit Diagram for Ra:-

Ia V R in Ω

Result:-

10 - BRAKE TEST ON 3 -SQUERREL CAGE INDUCTION MOTOR

Aim: To conduct a brake test on the given 3 -Slip ring Induction motor and to

draw its performance Characteristics.

Nameplate details:

3 -INDUCTION MOTOR

Capacity

Voltag

Current

Speed

Frequency

Apparatus required:


1 Starter

2 Ammeter

3 Voltmeter 4 Wattcmeters 5 Fuses 6 Tachometer

Precautions:

1) There should not be any load on the motor initially.

2) The brake drum should be filled with water to cool it.

3) If the wattmeter shows negative deflection, reverse either

pressure coil or current coil and take that reading as

negative.

4) The rotor external resistance should be kept at max

resistance position initially.

Theory: As a general rule, conversion of electrical energy to mechanical energy

takes place in to the rotating part on electrical motor. In DC motors, electrical

power is conduct directly to the armature, i.e, rotating part through brushes and

commutator. Hence, in this sense, a DC motor can be called as 'conduction motor'.

However, in AC motors, rotor does not receive power by conduction but by

induction in exactly the same way as secondary of a two winding T/F receives

its power from the primary. So, these motors are

known as Induction motors. In fact an induction motor can be taken as rotating

T/F, i.e, one in which primary winding is stationary and but the secondary is free.

The starting torque of the Induction motor can be increase by improving its p.f

by adding external resistance in the rotor circuit from the stator connected rheostat,

the rheostat resistance being progressively cut out as the motor gathers speed.

Addition of external resistance increases the rotor impedance and so reduces the

rotor current. At first, the effect of improved p.f predominates the current-

decreasing effect of impedance. So, starting torque is increased. At time of starting,

external resistance is kept at maximum resistance position and after a certain time,

the effect of increased impedance predominates the effect of improved p.f and so

the torque starts decreasing. By this during running period the rotor resistance

being progressively cut-out as the motor attains its speed. In this way, it is possible

to get good starting torque as well as good running torque.

(0-15)A MI

10A, 600V, 3KW, UPF

R

3-

A M

C

L

V

L1

B1

A1

415V 50 Hz AC

Supply

V (0-600)V

Y/∆

A1 B1 S S2

Y

3- 415V

MI Starter

L2

A2

C1

A2

C1

C2

B2

50 Hz AC Supply

B

C

M

V

L

L3

C2 B2

Procedure:

10A, 600V, 3KW, UPF

1) Give all the connections as per the circuit diagram.

2) Switch -ON the supply and press the ON button of the

starter.

3) Now put the rotor external resistance switch to run

position in steps & slowly.

4) Note the no-load readings of ammeter, voltmeter,

wattmeter, speed & loads.

5) Gradually increase the load on the motor by tightening the

hand-swivels and note the corresponding meter's

readings.

6) Remove the load completely & Switch-Off the power.

Graph: A graph is drawn b/w O/P power in watts (on X-axis) verses speed,

torque, current, slip, efficiency & p.f (on Y-axis).

Volt

meter

Rea-

ding

Am-

meter

reading

I/P=W1 ±W2 Force

Net

Force

Torq-

ue Speed O/P % % Slip p.f

V A W1

W2

F1 F2 F1~F2

9.8xF

e.Re N

2 NT/

60

O/p

/i/p

X 100

Ns-Na

/Ns

Volt ampere watt Watt kg kg kg FxRe rpm watt - - -

Thickness of the belt, t=

Circumference of the drum, 2 R =

Radius, R = C/2 =

Effective radius, Re = R + t/s =

Result:

PF

IL

% η

T

% Slip

N

PF

IL

N

% η

T

% Slip

Output power (W)

L

C

V

(0-10)A

MI

A

1

C

M

10A, 300V, 3000W,

UPF

M

V

(0-10)A

MI

10A, 300V, 3000W,

UPF L

A

(0-500)V

MI V

3 M

V

(0-20)A MI

20A, 300V, 6000W,

UPF L

L

O

A

D

c A3

V

1

(0-300V) MI

A2

2KVA,230/115V

Single Phase T/F

LV HV

LV HV

C

V

1

(0-300V)

MI

1-Ф ,VARIAC

3KVA

TA

TB

1- Φ

230V

50 Hz

AC

Supply

Ph

N

DPST

Parallel Operation Of Two Single Phase Transformers

Circuit Diagram:-

ADDITIONAL EXPERIMENT NO:-1

Parallel Operation Of Two Single Phase Transformers

Aim:-

To operate the given two 2KVA, 230/110V single phase Transformers in parallel and study the

load sharing between them when supplying resistive load .

APPRATERS:-

1. Watt meters UPF 300V/10A 2NO

300V/20A 1No

2. Voltmeter MI (0-500V) 1NO

(0-300V) 1NO

(0-150V) 1NO

3. Ammeters MI (0-10A) 2NO

(0-20A) 1NO

NAME PLATE DITEALS:-

PROCEDURE :-

a) Make connections as for circuit diagram, keep the load switch and switch S open .

b) Switch on the mains , see the volt meter reading of V1 , if this reading is 460V(double

the secondary voltage of both the machines) then switch of and inter change the

connections of secondary of any transformer . if reads zero then the switch S can be

closed , this way the polarities can be checked since wrong polarity will short circuit

the transformers if operated in parallel .

c) Close switch S and then close the load switch.

d) For various values of load current , record terminal voltage ,current in two secondary’s

,power supply by the two transformers and the total power,(do not exceed 10 A for

total current)

e) Switch of load and switch of main.

f) Determine the equivalent reactance’s and resistance’s of both transformers referred

to HV winding by SC test

Observation Table:-

S. NO

I

IA IB VL SA SB W Cos фA

Cos фB

WA WB

By Measurement By calculations By Measurement By calculations

CAULATIONS :-

For a given load current IL at an angle ф the current and power supply by each

transformer can be found out by the following formula

IA = (IL)X(ZB)/(ZA+ZB)

IB = (IL)X(ZA)/(ZA+ZB)

If S is the load KVA, then the KVA shared by the transformers can be found out by

SA = (S)X(ZB)/(ZA+ZB)

SB = (S)X(ZA)/(ZA+ZB)

Check the result obtained with the Theoretical calculations .

RESULTS:-

a) With the help of phasor diagram verify if IA = IB= I.

b) Check if the load shared is proportional to the KVA capacities of the respective

transformers

c) From the results state if RA /XA =RB /XB

3- Φ Alternator

N

A

1

V

A

1

V

A

1

V

(0-20)A MI

(0-300)V MI

(0-600)A MI

(0-600)A MI

R R

Y B B Y

FF

F

400Ω / 1.7A

400Ω / 1.7A

FF

F

3- Φ Alternator

440V ,60w

S 2

3- Φ

Resistive

Load

R

Y

B

N

+

-

220V DC Supply

220V DC Supply

+

-

(0-10)A

MI

(0-10)A

MI

PARELLEL OPERATION OF TWO 3- Φ ALTERNATORS

Circuit Diagram:-

EXPERMENT NO -12

PARELLEL OPERATION OF TWO THREE PHASE ALTERNATORS

Aim:-

To run two 3φ Alternators in parallel and to study the load sharing .

Operators:

1. Voltmeter MI (0-600V) 2NO

(0-300V) 1NO

2. Ammeter MI (0-10A) 2NO

(0-20A) 1NO

3. Switch Board for parallel operation 1NO

4. 3φ Resistive load 5KW 1NO

5. Rheostat 400Ω/1.7A 2NO

Name Plate Details:-

Procedure:-

1. Make connections as for circuit diagrams, and verify the connections by the lab

Instructor.

2. Ensure that the paralleling switch S1 is open and the change our switch S2 is in OFF

position

3. Then start the alternator no 1 and adjust the field excitation so that it generates the

rated voltage

4. Put switch S2 in position 1 gradually increase the load current in steps.

5. Not down the current and voltage of 1 alternator at ever step , repeat the step up to full

load of the alternator

6. Bring the load 0 stop the alternator .

7. Put the change our switch S2 in OFF position. Now start the alternator number 2 and

adjust excitation to its rated value and repeat the steps done for alternator 1.

8. Stop the machine and put change our switch in OFF position .

9. Now run both alternators keeping parallel switch S1 open adjust the voltage both

alternators to its rated value, for Dark lame method if phase sequence and voltage of

both alternators is same then the lamp will glows OFF . then switch on the parallel in

switch , put the change our switch to either position 1 OR 2 load the alternators and

note down the individual alternator load current and the total load current and the bus

bar voltage

Observation Table :-

S.NO ALTERNATOR -1 ALTERNATOR -2 ALTERNATOR 1&2 PARELLEL TOTAL CURRENT

BUSBAR VOLTAGE

VOLTAGE CURENT VOLTAGE

CURRENT LOAD CURRENT OF ALT-1

LOAD CURRENT OF ALT-2

GRAPH :

Bus bar voltage Vs Total Current

Electrical Machine lab manual

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