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

PREFACE

The significance of the Electrical Machines Lab-II, is renowned in the various fields of engineering applicat applications. ions. For an Electrical Engineer, it is obligatory obligato ry to have 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 practical. The manual prepared very carefully with our level level best. It gives all the Electrical Machines in practical. steps in executing an experiment.

PREFACE

The significance of the Electrical Machines Lab-II, is renowned in the various fields of engineering applicat applications. ions. For an Electrical Engineer, it is obligatory obligato ry to have 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 practical. The manual prepared very carefully with our level level best. It gives all the Electrical Machines in practical. 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 p reparing 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 o n 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 t able, 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 origi nal 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

0

-/3/-

(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 ar e 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 .

C 2

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 X d 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 3 ф Alternators .

(0-2)A MI

DPST Ph

A

115V

2A, 150V, 60W, LPF M

230V

L

V C

1230V 50 Hz AC Supply

Open Circuit

V (0-150)V MI

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

Ph

(0-15)A MI

DPST

15A, 50V, 600W, UPF M

230V

115V

L

A V C

1- Φ 230V 50 Hz AC Supply

N

V

(0-50)V MI

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

Short Circuit

1 Φ -Transformer 3KVA, 230V / 115V

Fig -2

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

Dynamo 3

Wattmeter

2.5A/150V

meter

1 No

(LPF) 4

Auto T/F

230V/0-270V, 8A

1- wire

1 No

wound 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

5

Auto T/F

Fuses

230V/0-270V,

1- wire

8A

wound

5A

-

1 No

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 R o & 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 R 01, 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:

Give connections as per the circuit diagram.

1)

Switch-ON the supply and apply rated voltage to the

2)

primary of the winding by using the auto transformer. Note the readings of Ammeter, Voltmeter & Wattmeter

3) SC Test:

Give connections as per the circuit diagram.

1)

Switch-ON the supply and vary the Dimmerstat till rated

2)

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

I0

W0

volt

ampere

watt

VSC

ISC

WSC

volt

ampere

Watt

Calculations:

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

¾

½

¼

%

% Regulation P.F

PRECAITIONS:

lag

lead

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:

S.NO DESCRIPTION Auto T/F 1

2

2

3

Voltmeter

Ammeter

Wattmeter

RANGE

TYPE

QTY

230V/0-

1- wire

2 Nos

270V, 16A

wound

0-50V

M.I

1 No

0-300V

M.I

1 No

0-500V

M.I

1 No

0-2.5A

M.I

1 No

0-10A

M.I

1 No

2.5A/300V

LPF

1 No

10A/150V

UPF

1 No

5A 4

Fuses

5

SPST switch

10A 20A

2 Nos -

2 Nos 1 No

Precautions:

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..

Theory:

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

5A, 150V, 75W, LPF

(0-5)A MI

DPST Ph

M

A

L

V C


N

V (0-150)V MI

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

(0-15)A MI A

115V 0V 115V

15A, 75V, 750W, UPF M

230V

0V

230V

0V

0V

L

V C

V

(0-75)V MI

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

Circuit Diagram

V

(0-600)V MI

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 Xaxis and O/P power on Y-axis. Observations: O.C Test:

S.C Test:

V0

I0

W0

VSC

ISC

WSC

volt

ampere

Watt

volt

ampere

Watt

Calculations:

Load Cu losses Total losses I/P power O/P power Full ¾ ½ ¼

% Regulation P.F

Result:

lag

lead

%

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

1 KVA

I/P voltage

230V

I/P current

4.34A

O/P

115V

voltage

8.64A

O/P current

50Hz

Frequency Apparatus required:

S.NO

DESCRIPTION

RANGE

TYPE

QTY

Auto T/F

415V/0-

3- wire

1 Nos

470V, 15A

wound

0-2A

M.I

3 No

0-5A

M.I

2 No

0-150V

M.I

2 No

0-250V

M.I

1 No

5A

-

2 Nos

1 2

Ammeter

3

Voltmeters

4

Fuses

230V/05

Load box

10A

1 No Rheostatic

Tp R


115V

100% V 86.6%=Tp

TPST

V

(0-600)V MI

Teaser transformer Primary

100% V Ts Teaser transformer Secondary

V

(0-300)V MI

0% V

Y 3415V 50 Hz AC Supply

0% V

Mp=50% Main transformer Primary

100% V

0% 100% V Main transformerV

V2

B

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.

(0-300)V MI

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, V CD leads VAB by 900 i.e, voltages across primary are 90 0 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 V 1 / 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

N2 /0.866N1 = IR /IX

IR = InK(1.15)

For 2:1 T/F, IR = 0.57xIX Current in Main T/F: N2 /N1 = (IR /2 - IY /2)

For balanced load, since I X & IY are at 900 IR = ⎣1200; IB = ⎣-1200

Like wise, IR, IY & IB are equal in magnitude and are 120 0 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, V T = V21+V22 =

Load applied

Result:

A1

A2

A3

A4

A5

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

5 H.P

Voltage

415V

Current

7.8A

Speed

1500rpm

Frequency

50Hz

Apparatus required: S.NO DESCRIPTION

1

Auto T/F

2

Ammeter

3

Voltmeters

RANGE

TYPE

415V/0-

3- wire

QTY

1 Nos

470V, 15A

wound

0-2A

M.I

1 No

0-10A

M.I

1 No

0-50V

M.I

1 No

0-250V

M.I

1 No

2.5A/300V

LPF

1 No

10A/150V

UPF

1 No

4

Wattmeters

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-

R

M

A


R

R

C

V

V

(0-600)V

W1

Stator

MI Y

B

W2 Y

B

Y

C V


Alternator

L

Rotor L

M

5A, 600V, 600W, LPF

B

Fuse

3-

Auto Transformer

Blocked Rotor Test TPST Switch (0-15)A MI R

15A, 600V, 600W, UPF 3M

A

C


(0-30)A MI

V

W1

V (0-600)V MI

Stator Y

W2 Y

R

R

3-

A

B B

Y

C V

3415V 50 Hz AC Supply B

Fuse

Rotor L

M

15A, 600V, 600W, UPF

3-

Auto Transformer

Alternator

L

S1

S2

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:

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 V L, IO, WO & Cos from the OC test. 2) Obtain the vales of V S.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 I O lag behind V L 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 O 1 and name as O 1X1. 8) Draw a perpendicular bisector to O 1A so that it meets the line O 1X1 at C as center. 9) Draw a semicircle on the line O 1X1 taken O1C as radius and C as center. 10) Draw a perpendicular bisector to O1A so that it meets the line O 1R1 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 = I 1S.C Cos

O

Procedure: No-load test:

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

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 Observations O.C Test:

S.C Test:

V0

I0

W0

VSC

ISC

WSC

volt

ampere

watt

volt

ampere

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

D.C MOTOR

3 -ALTERNATOR

Capacity

5 H.P

3 KVA

Voltage

220V

415V

Current

19A

4.2A

Speed

1500rpm

1500rpm

Excitation

220V, 1.5A

220V, 1.4A


1

Ammeter

RANGE

TYPE

QTY

0-5A

M.I

1 No

0-2A

M.C

1 No

0-300V

M.I

1 No

0-50V

M.I

1 No

2

Voltmeters

3

Rheostat

250 /1.5A

Wire wound

2 Nos

4

Tachometer

0-50000rpm

Digital

1 No

2A 5

Fuses

10A

2 Nos -

2 Nos

OC Test

3 point starter +

DPST Switch

3L

TPST Switch

R

FA

400 / 1.7A

230 V DC Supply

Alternator

FA

V

(0-300)V MI

F A

N

FAA

M AA FF

Y

B Fuse

+

+

400 /

230 V DC Supply

1.7A

A (0-1)A MC

Fuse

SC Test

3 point starter DPST Switch

3-

+

L

TPST Switch

R

FA

400 / 1.7A

230 V DC Supply

Alternator

FA

A

F A

N

FAA

M AA FF

B Fuse

+

+ 230 V DC Supply

400 / 1.7A

Y

A (0-1)A MC

Fuse

(0-10)A MI

Precautions:

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.

Theory:

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 (Z S) = OC voltage / SC current XS = Z2S - R2a From fig.

EO = OB2 + BD2 = (Vcos +IRa)2 + (Vsin +IXS)2

% Regulation = [(E 0-V) / V] 100 Procedure: OC test:

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

1) Give all connections as per the circuit diagram. 2) Switch-ON the supply & by varying the starter, prime mover speed is adjusted to rated. 3) By slowly varying the potential divider, field current is increased & corresponding short Circuit current is noted up to rated value. To find armature resistance (R a): 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 I f and V which is known as OC

curve, by taking I f on X-axis and V on Y-axis. 2) A graph is drawn b/w I f and ISC which is known as SC curve, by Taking I f on X-axis and I SCV on Y-axis.

Observations: OC Test:

SCTest:

Field

OC

Field

SC

current If

voltage

current If

current

Armature resistance:

voltage

current

Resistance R a

MODEL GRAPH Y Isc Eo

% Voltage OCC

1

SCC Leading PF

O

If 2

If 1 If

Result:

X

Lagging PF

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

3 KVA

Voltage

415V

Current

3.5A

Speed

1500rpm

Excitation

220V, 1.4A


1

Ammeter

2

SPST switch

RANGE

TYPE

QTY

0-2A

M.C

1 No

0-5A

M.I

1 No

-

-

1 No

Wire 3

Rheostat

250 /1.5A

4

Starter

-

wound D.O.L

1 No 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 I a 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 I a is gradually decreasing and the angle of lag is gradually reduced. c) At one particular excitation, the magnitude of I a 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 I a again gradually increased and I a,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 I f , Note down the values of armature currents.

5) Switch-Off the supply.

Graph:

A graph is drawn b/w a) Exciting current (I f ) verses armature current (I a) : V curve. b) Exciting current (I f ) verses power factor (cos ) :

curve.

taking I f on X-axis and I a & cos on y-axis.

Without Load (0-5)A MI R

TPST Switch

A


V

(0-500)V MI

5A, 600V, 3KW, LPF M

L

C

3Synchronous Motor

V

FA

FAA

Y


C

V

L

M

5A, 600V, 3KW, LPF

B

+

+ 230 V DC Supply

Fuse

3-

Auto Transformer 415V/(0-470V)

400 / 1.7A

A (0-5)A MC

With Load

(0-10)A R

TPST Switch


V

5A, 600V, 3KW, UPF

MI A

M

(0-500)V MI

C

L

3Synchronous Motor S1

V FA

FAA

Y


C

V L

M

5A, 600V, 3KW, UPF

B +

Fuse

3-

230 V DC Supply

S2

+

400 / 1.7A

A (0-5)A MC

AutoTransformer 415V/(0-470V)

Observations:

Field current I f Armature current I a

cos

Brake Drum

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

1.5 H.P

Voltage

230V

Current

6.5A

Speed

1500rpm

Frequency

50Hz


RANGE

TYPE

QTY

11

2

Auto T/F

Ammeter

3

Voltmeters

4

Wattmeters

5

Fuses

230V/0270V, 8A

wire

1 No

wound

0-5A

M.I

1 No

0-10A

M.I

1 No

0-50V

M.I

1 No

0-250V

M.I

1 No

5A/300V

LPF

1 No

10A/75V

UPF

1 No

10A

-

2 Nos

Digital

1 NO

06

Tachometer

50000rpm

No-Load Test

(0-10)A MI

DPST Ph

A

10A 10A, 300V, 600W, LPF LPF M

L

V C


N

V (0-300)V MI

IM

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

Blocked Rotor Test

DPST

(0-25)A MI

Ph

A

30A, 30A, 150V, 3KW, 3KW, UPF M

L

V

S1

S2

C


N

V (0-150)V MI

IM

Brake Drum

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

Precautions:

1) The Dimmerstat should be kept at minimum O/P position initially. 2) In the t he rotor-blocked rotor-blocked test, the rotor should be blocked firmly. 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 princ iple 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:

No-load test:

4) Give all connections as per the circuit diagram. 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

Observations: O.C Test:

Result:

S.C Test:

V0

I0

W0

VSC

ISC

WSC

volt

ampere

watt

volt

ampere

Watt

8-DETERMINATION OF Xd & Xq OF SYNCHRONOUS MACHINE

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

machine.

Nameplate details:

DESCRPTION

D.C MOTOR

3 -ALTERNATOR

Capacity

5 H.P

3 KVA

Voltage

220V

415V

Current

19A

4.2A

Speed

1500rpm

1500rpm

Excitation

220V, 1.5A

220V, 1.4A


RANGE

TYPE

QTY

1

Ammeter

0-5A

M.I

1 No

2

Rheostat

250 /1.5A

Wire wound

1 Nos

3

Tachometer

0-50000rpm

Digital

1 No

4

Voltmeter

0-300V

M.I

1 No

500V

-

1 No

Auto T/F

415V/0-470V, 15A

Wire wound

1 No 7

Fuses

5A

3 Nos

Phase sequence 5 6

Meter

-

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 X d & 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 X d = (max. armature terminal voltage/ph) / (min. armature current/ph)As the current is small then V t 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 L

(0-5)A MI

FA

R

FA

400 / 1.7A

230 V DC Supply

(0-600)V MI V

F A

R R V

FAA

TPST Switch

A


(0-150)V MI N

N

M

Y

Y B

B

AA

Y 3- 415V 50 Hz AC Supply

FF

B 415 V / 50Hz / 6.4 A / 5 KVA Fuse

3-

AutoTransformer 415V/(0-470V)

Observations:

Vmax

Vmin

Xd = Vmax /I min ;

Xq = Vmin / Imax

Result:

Imix

=

=

Imin

Fuse

9. REGULATION OF 3 Φ ALTERNATOR BY USING ZPF & ASA METHOD.

Circuit Diagram O.C Test:-

3 point

DPST

OC Test 3- Φ Alternator

400Ω 230 V DC

F

R

FA

N

(0-

F

F

B

− Fuse 230 V

400Ω

A

Y

−

(0-

− Fuse

Circuit Diagram for S.C Test:3 point

SC Test

400Ω 230 V DC

3- Φ Alternator

F

R

FAA

N

(0-

F

F

B Fuse 230 V

400Ω

(0-

Y

Circuit Diagram for Z.P.F Test:Diagram with Inductive Load 3 point starter +

ZPF Method

DPST Switch L

3- Φ Alternator

(0-10)A MI A

F A

400Ω /

FA

R

FAA

N

I N D U C T I V E

(0-300)V MI V

1.7A

230 V DC Supply

TPST

F A

M AA FF

B

− Fuse

+ 230 V DC Supply

400Ω / 1.7A

A

L O A D

Y

−

(0-1)A MC

− Fuse

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 1 2 3 4 5 6

Type

Range

Qty

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

1) Give all connections as per the circuit diagram. 2) switch-ON the supply & by varying the starter, prime mover Speed is adjusted to rated. 3) By slowly varying the potential divider, field current is increased & corresponding short Circuit current is noted up to rated value.

To find armature resistance (R a): 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:1) Give all connections as per the circuit diagram. 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 I f and V which is known as OC

curve, by taking I f on X-axis and V on Y-axis. 2) A graph is drawn b/w I f and ISC which is known as SC curve, by Taking I f on X-axis and I SCV 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

Result:-

R in Ω

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:

S.NO DESCRIPTION

1

Starter

2

Ammeter

3 4 5 6

Voltmeter Wattcmeters Fuses Tachometer

RANGE

TYPE

QTY

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 currentdecreasing 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 R

10A, 600V, 3KW, UPF M

A

L

L1 B1

3-

C


V

A1

V

A1 (0-600)V

Starter L2

Y

A2

B2

A2 C1

C1

C2

C V

C2 L

B M

L3

B2

10A, 600V, 3KW, UPF

Procedure:

S

Y / ∆

MI


B1

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).

S2

Volt Ammeter

Net meter

I/P=W1 ±W2

Force

Rea-

Force

Torque

Speed

O/P

%

% Slip

p.f

reading ding O/p W2 V

A

W1

F1

F2

F1~F2

9.8xF e.Re

N

2 NT/

Ns-Na

/i/p

60

/Ns X 100

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, R e = R + t/s

=

IL PF PF IL %η

T % Slip

N %η

T

N % Slip

Output power (W)

Result:

Parallel Operation Of Two Single Phase Transformers

Circuit Diagram:-

(0500 V TA

Ph DPST

LV

(0-10)A MI HV A

V

10A, 300V, 3000W , M

L

(0-20)A 20A, 300V, 6000W, MI M L c3 A C

V

V

C

1- Φ 230V 50 Hz AC Supply

N

L V

(0-300V) MI

(0-300V) MI

O A D

1-Ф ,VARIAC 3KVA

TB LV

(0-10)A MI HV A A2

10A, 300V, 3000W , M

C

2KVA,230/115V Single Phase T/F

L

V

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 2. Voltmeter

3. Ammeters

MI

MI

300V/10A

2NO

300V/20A

1No

(0-500V)

1NO

(0-300V)

1NO

(0-150V)

1NO

(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 V 1 , 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 By Measurement

By calculations

IB By Measurement

VL

SA

By calculations

SB

W Cos фA

Cos фB

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)/(Z A+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{(Z B)/(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 transformers

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

capacities of the respective

WA

WB

PARELLEL OPERATION OF TWO 3- Φ ALTERNATORS Circuit Diagram:-

3- Φ Alternator

A

(0-10)A MI

(0-10)A MI

3- Φ Alternator

A

R

R

F

F

440V ,60w

+

220V DC Supply

N

-

(0-600)A MI

220V DC Supply

V (0-600)A

V

MI

-

FF

FF

400Ω /

Y

+

Y

B

B

400Ω / 1.7A

1.7A

S2

R

A (0-20)A MI

Y B

(0-300)V MI

V

N

3- Φ Resistive Load

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. 2.

Voltmeter MI Ammeter MI

(0-600V)

2NO

(0-300V)

1NO

(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

Electrical Machine lab manual

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