electrical machines-ii laboratory manual - …smec.ac.in/sites/default/files/lab1/em-ii lab...

ELECTRICAL MACHINES-II LABORATORY MANUAL

BY

DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINEERING

DHULLAPALLY, KOMPALLYSECUNDERABAD-500014

ST.MARTIN’S ENGINEERING COLLEGE ELECTRICAL MACHINES-II LAB MANUAL


INDEXList of experiments as per university 3

List of experiments to be conducted for this semester 4

Cycle indicate schedule and the batch size 5

Laboratory Practice Safety Rules Guidelines For Laboratory Notebook

6

S.NO NAME OF THE EXPERIMENT PG.NO1 O.C. &S.C. Tests on single phase transformer. 10-13

2 Sumpner's test on a pair of single phase transformers. 13-17

3 Brake test on three phase squirrel cage induction motor. 18-20

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

21-24

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

25-28

6 V and inverted V curves of a three –phase Synchronous motor. 29-31

7 Equivalent circuit of a single phase induction motor. 32-35

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

36-39

ADDITIONAL EXPERIMENTS9 Parallel Operation of Single Phase Transformers. 40-43

10 Separation of core losses of a single phase transformer. 43-47

11 Scott connection of Transformers. 48-50



JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY

III Year B.Tech EEE I Sem Academic year 2014-2015L 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 three phase alternator.

6. Heat run test on a bank of 3Nosof single phase delta connected transformers.

7. Measurement of sequence Impedance ofa3phase alternator.



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. No-load& Blocked rotor tests on three phase induction motor.

4. Separation of core losses of a single phase transformer.

5. Efficiency of a three phase alternator.

6. Brake test on three phase induction motor.

7. Regulation of a three phase alternator by synchronous impedance & m.m.f methods

8. V and inverted V curves of at here phase synchronous motor.

9. Equivalent circuit of a single phase induction motor.

10. Determination of Xd and Xq of a Salient pole synchronous machine.

Additional Experiments

1. Parallel Operation of Two Single Phase Transformers.

2. Measurement of sequence Impedance ofa3phase alternator.

3. Scott connection of Transformers.



FIRSTCYCLEEXPERIMENTS:

EXP NO EXPERIMENT NAME

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.

SECOND CYCLEEXPERIMENTS:

EXP NO EXPERIMENT NAME

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 Parallel Operation of Single Phase Transformers.

10 Separation of core losses of a single phase transformer.

11 Scott connection of Transformers.



LABORATORY PRACTICE SAFETY RULES

SAFETY is of paramount importance in the Electrical Engineering Laboratories.

1. Electricity NEVEREXECUSES careless persons. So, exercise enough care and attention in

handling electrical equipment and follow safety practices in the laboratory.(Electricity is a

good servant but a bad master).

2.Avoid direct contact with any voltage source and power line voltages.(Otherwise, any such

contact may subject you to electrical shock)

3.Wear rubber-soled shoes. (To insulate you from earth so that even if you accidentally

contact a live point, current will not flow through your body to earth and hence you will be

protected from electrical shock)

4.Wear laboratory-coat and avoid loose clothing.(Loose clothing may get caught on an

equipment/instrument and this may lead to an accident particularly if the equipment

happens to be a rotating machine)

5.Girl students should have their hair tucked under their coat or have it in a knot.

6.Do not wear any metallic rings, bangles, bracelets, wristwatches and neck chains. (When

you move your hand/body, such conducting items may create short circuit or may ouch a

live point and there by subject you to electrical shock)

7.Be certain that your hands are dry and that you are not standing on wet floor. (Wet parts of

the body reduce the contact resistance there by increasing the severity of the shock)

8.Ensure that the power is OFF before you start connecting up the circuit.(Otherwise you will

be touching the live parts in the circuit)

9. Get your circuit diagram approved by the staff member and connect up the circuit strictly

as per the approved circuit diagram.

11. Check power chords for any sign of damage and be certain that the chords use safety

plugs and do not defeat the safety feature of these plugs by using ungrounded plugs.

12. When using connection leads, check for any insulation damage in the leads and avoid

such defective leads.

13.Do not defeat any safety devices such as fuse or circuit breaker by shorting across it.

Safety devices protect YOU and your equipment.

14.Switch on the power to your circuit and equipment only after getting them checked up

and approved by the staff member.

15.Take the measurement with one hand in your pocket. (To avoid shock in case you

accidentally touch two points at different potentials with your two hands)



16.Do not make any change in the connection without the approval of the

staffmember.17.Incaseyou notice any abnormal condition in your circuit (like

insulation heating up,

Resistor heating up etc ), switch off the power to your circuit immediately and inform the

staff member.

18.Keep hot soldering iron in the holder when not in use.

19.After completing the experiment show your readings to the staff member and switch off

the power to your circuit after getting approval from the staff member.

20.While performing load-tests in the Electrical Machines Laboratory using the brake-drums:

Avoid the brake-drum from getting too hot by putting just enough water into the brake-

drum at intervals; use the plastic bottle with a nozzle (available in the laboratory)to pour the

water.(When the drum gets too hot, it will burn out the braking belts)

Do not stand in front of the brake-drum when the supply to the load-test circuit is switched

off.(Otherwise, the hot water in the brake-drum will splash out on you)

After completing the load-test, suck out the water in the brake-drum using the plastic bottle

with nozzle and then dry off the drum with a sponge which is available in the

of data in a concise visual form. Data to be presented in graphical form should be plotted

in the laboratory so that any questionable data points can be checked while the experiment is

still set up. The gridlines in the note book can be used for most graphs. If special graph

paper is required, affix the graph permanently into the notebook. Give all graphs a short

descriptive title. Label and scale the axes. Use units of measure. Label each curve if more

than one on a graph.

21. Determine the correct rating of the fuse/s to be connected in the circuit after

Understanding correctly the type of the experiment to be performed: no-load test or full-

load test, the maximum current expected in the circuit and accordingly use that fuse-

rating.(While an over-rated fuse will damage the equipment and other instruments like

ammeters and watt-meters in case of over load, an under-rated fuse may not allow one even

to start the experiment)

22. At the time of starting a motor, the ammeter connected in the armature circuit over shoots,

as the starting current is around 5 times the full load rating of the motor. Moving coil

ammeters being very delicate, may get damaged due to high starting current. A switch has

been provided on such meters to disconnect the moving coil of the meter during starting.

This switch should be closed after the motor attains full speed. Moving iron ammeters and

current coils of watt meters are not so delicate and hence these can stand short time



overload due to high starting current. No such switch is therefore provided on these meters.

Moving iron meters are cheaper and more rugged compared to moving coil meters. Moving

iron meters can be used for both a.c. and d.c. measurement. Moving coil instruments are

however more sensitive and more accurate as compared to their moving

iron counter parts and these can be used for d.c. measurements only. Good features of

moving coil instruments are not of much consequence for you as other sources of errors in

the experiments are many times more than those caused by these meters.

23. Some students have been found to damage meters by mis handling in the following ways:

Keeping unnecessary material like books, lab records, un used meters etc. causing meters

to fall down the table.

Putting pressure on the meter (specially glass) while making connections or while talking

or listening somebody.

STUDENTS ARE STRICTLY WARNED THAT FULL COST OF THE METER WILL BE

RECOVERED FROM THE INDIVIDUALWHO HAS DAMAGED IT IN SUCH A

MANNER.

Copy these rules in your Lab Record. Observe these yourself and help your friends to observe I

have read and understand these rules and procedures. I agree to abide by these rules and

procedures at all times while using these facilities. I understand that failure to follow these

rules and procedures will result in my immediate dismissal from the laboratory and additional

disciplinary action may be taken.

GUIDELINESFOR LABORATORY NOTEBOOK

The laboratory notebook is a record of all work pertaining to the experiment. This record

should be sufficiently complete so that you or any one else of similar technical back ground

can duplicate the experiment and data by simply following your laboratory note book. Record

everything directly into the notebook during the experiment. Do not use scratch paper for

recording data. Do not trust your memory to fill in the details at a later time. Organization in

your note book is important. Descriptive headings should be used to separate and identify the

various parts of the experiment. Record data in chronological order. A neat, organized and

complete record of an experiment is just as important as the experimental work.

1. Heading:

The experiment identification (number) should beat the top of each page. Your name

and date should beat the top of the first page of each day's experimental work.



2. Object:

A brief but complete statement of what you intend to find out or verify in the

experiment should be at the beginning of each experiment

3. Diagram:

A circuit diagram should be drawn and labeled so that the actual experiment circuitry

could be easily duplicated at any time in the future. Be especially careful to record all circuit

changes made during the experiment.

4.Equipment List:

List those items of equipment which have a direct effect on the accuracy of the data. It

may be necessary later to locate specific items of equipment for rechecks if discrepancies

develop in the results.

5. Procedure:

In general, lengthy explanations of procedures are un necessary. Be brief. Short

commentaries along side the corresponding data may be used. Keep in mind the fact that the

experiment must be reproducible from the information given in your notebook.

6. Data:

Think carefully about what data is required and prepare suitable data tables. Record

instrument readings directly. Do not use calculated results in place of direct data; however,

calculated results may be recorded in the same table with the direct data. Data tables should be

clearly identified and each data column labeled and headed by the proper units of measure.

7. Calculations:Not always necessary but equations and sample calculations are often given to

illustrate the treatment of the experimental data in obtaining the results.8. Graphs:

Graphs are used to present large amounts of results. Theoretical and experimental results should be on the same graph or arrange in the same table in a way for easy correlation of these results.

9.Results:

The results should be presented in a form which makes the interpretation easy. Large

amounts of numerical results are generally presented in graphical form. Tables are generally

used for small amounts laboratory.(The water, if allowed to remain in the brake-drum, will

corrode it)

9. Conclusion:This is your interpretation of the results of the experiment as an engineer. Be brief

and specific. Give reasons for important discrepancies.



1Φ- TRANSFORMER

EXP.NO. 01

1. OC &SCTESTSON 1-Φ TRANSFORMER

AIM:

To conduct OC &SC tests on the given 1- Transformer and to calculate its1) Equivalent circuit parameters

a).Referred to H.V sideb).Referred to L.V side

2) Efficiency at various loads.3) Regulation at various power factors4) Maximum Efficiency.

NAMEPLATE DETAILS:

T/F LV side HV sideRated power

Rated voltage

Rated current

Frequency

APPARATURS REQUIRED:

SL.NO Name of the Apparatus Type Range Quantity

1 Ammeter MI

2 Ammeter MI

3 Voltmeter MI

4 Voltmeter MI

5 Wattmeter EDM(LPF)

6 Wattmeter EDM(UPF)

7 Single phase variac


THEORY:-

Open– Circuit (OC) or No-Load Test:

Thepurposeofthistestistodeterminetheshuntbranchparametersoftheequivalentcircuitofthetransfor

mer.Oneofthewindings is connected to supply at rated voltage, while the other winding is kept

open -circuited. From the point of view of convenience and availability of supply the test is

usually performed from the LV side, while the HV side is kept open circuited.

Voltage =V1; Current =I0and power input=P0

Indeed the no-load current, I0is so small (itisusually2-6% of the rated current)and R01 and

X01are also small, that V1can be regarded as = E1by neglecting the series

impedance.Thismeansthatforallpracticalpurposesthepowerinputonno-

loadequalsthecore(iron)lossi.e.,

P0=V1 I0 cosf0

cosf0 = P0/V1I0

Iw=I0 cosf0, m =I0sinf0

R0=V1/Iw, X0=V1 / Im

Short Circuit (SC) Test:

This test serves the purpose of determining the series parameters of a transformer. For

convenience of supply arrange mentioned voltage and current to be handled, the test is usually

conducted from the HV side of the transformer while the LV side is short-circuited. Since the

transformer resistance and leakage reactance are very small, the voltage Vsc needed to circulate

the full load currentundershortcircuitisaslowas5-8%of the rated voltage. The exciting current

under the second it ions is only about 0.1to0.5%of the full load current. Thus the shunt branch

of the equivalent circuit can be altogether neglected. While conducting the SC test, the supply

voltage is gradually raised from zero till the transformer draws full load current. The meter

readings under these conditions are: Since the transformer is excited at very low voltage, the

iron loss is negligible (that is why shunt branch is left out), the power input corresponds only to

the copper loss, i.e

Vsc=Voltage, Isc=Current, Psc=Power Copper loss)

Z01= VSC/ ISC=√R201 + X2

01


Equivalent resistance, R01=PSC/ (ISC)2

Equivalent reactance, X01= √Z201-R

201

CIRCUIT DIAGRAM: DIAGRAM--1

PROCEDURE:

OC TEST:

(1) All the connections are done as per the circuit diagram of OC test

(2) Byusing1-f variac apply rated voltage to the circuit.

(3) At this rated voltage note down voltmeter, ammeter & wattmeter readings.

(4) From the values we can find R0and X0

SC TEST:

(1) All the connections are done as per the circuit diagram of SC test

(2) By using1-f variac apply rated voltage to the circuit.

(3) At this rated current note down voltmeter, ammeter & wattmeter readings.

(4) From this values we can find out R01&X01


PRECAUTIONS:

(1) Open circuit test is performed on LV side i.e meters are connected LV side and HV side

will be open circuited.

(2) For short circuit test is connect meters on HV side and LV side will be short circuited

(3) Rated voltage and rated current must be maintained in OC test and SC test respectively (4) All the connections must be tight

TABULAR COLUMNSObservations:

OC TEST:

Vo

VoltsIo

AmpsWo

Watts

SC TEST:

Vsc

VoltsIsc

AmpsWsc

Watts

CALCULATIONS:

EFFICIENCY VS LOAD:

LOAD

Power factor lagging

0.2 0.4 0.6 0.8 1

¼

½

¾

1


Regulation:

Power factor lagging UPF Power factor leading

LOAD0.2 0.4 0.6 0.8 1 0.8 0.6 0.4 0.2

1/4

1/2

3/4

1

MODEL GRAPHS:

RESULT:

%Regulation

Pflea Pf lagging

%Regulation


EXP.NO. 02

SUMPNERS TEST ON SINGLE PHASE TRANSEFORMERS

AIM:

To convert three phase system to two phase system with the help of Scott Connection.

NAMEPLATE DETAILS:1Φ- TRANSFORMERS

T/FT/F-1 T/F-2

HV side LV side HV side LV side

Rated power

Rated voltage

Rated current

Frequency



1 Ammeter MI

2 Ammeter MI

3 Voltmeter MI

4 Voltmeter MI



7 Voltmeter MI

THEORY:

Sumpner's test or back to back test on transformer is another method for determining transformer

efficiency, voltage regulation and heating under loaded conditions. Short circuit and open circuit

tests on transformer can give us parameters of equivalent circuit of transformer, but they can not

help us in finding the heating information. Unlike O.C. and S.C. tests, actual loading is

simulated in Sumpner's test. Thus the Sumpner's test give more accurate results of regulation and

efficiency than O.C. and S.C. tests.

http://www.electricaleasy.com/2014/04/transformer-losses-and-efficiency.html

http://www.electricaleasy.com/2014/04/transformer-losses-and-efficiency.html

http://www.electricaleasy.com/2014/04/open-and-short-circuit-test-on-transformer.html

http://www.electricaleasy.com/2014/04/open-and-short-circuit-test-on-transformer.html

http://www.electricaleasy.com/2014/04/equivalent-circuit-of-transformer.html


Both transformers are connected to supply such that one transformer is loaded on another.

Primaries of the two identical transformers are connected in parallel across a supply. Secondaries

are connected in series such that emf's of thm aree opposite to each other. Another low voltage

supply is connected in series with secondaries to get of them are connected in voltage

opposition, i.e. EEF and EGH. Both the emf's cancel each other, as transformers are identical. In

this case, as per superposition theorem, no current flows through secondary. And thus the no

load test is simulated. The current drawn from V1 is 2I0, where I0 is equal to no load current of

each transformer. Thus input power measured by wattmeter W1 is equal to iron losses of both

transformers.

i.e. iron loss per transformer Pi = W1/2.

Now, a small voltage V2 is injected into secondary with the help of a low voltage transformer.

The voltage V2 is adjusted so that, the rated current I2 flows through the secondary. In this case,

both primaries and secondaries carry rated current. Thus short circuit test is simulated and

wattmeter W2 shows total full load copper losses of both transformers.

i.e. copper loss per transformer PCu = W2/2.

From test results, the full load efficiency of each transformer can be given as -



PROCEDURE:

1. The circuit is connected as per circuit diagram.

2. Both the transformers are energized at rated voltage & frequency.

3. With the secondary open, noted down the readings of W1 which gives core loss.

4. Secondary is connected in phase opposition and checked trough voltmeter connected across the secondary.

5. Voltage is induced in secondary with help of booster transformer which is connected to source. Readings of W2 are noted down.

TABULAR COLUMN:

W1 W2

FORMULE:

GRAPH:

RESULT:IL(Amps)

h%


EXP.NO. 03

BRAKE TEST ON 3–Φ SQUIRREL CAGE I NDUCTION MOTOR

AIM:

To draw the performance characteristics of 3-phase squirrel cage induction motor by conducting load test.

NAMEPLATE DETAILS:

Parameters Induction Motor

Rated Power

Rated Voltage

Rated Current

Rated Speed

APPARATUSREQUIRED:

S. No Name of apparatus Type Range Qty.

1. Ammeter MI

2. Voltmeter MI

THEORY:

A 3-phase induction motor consists of stator and rotor with the other associated parts. In the

stator, a3-phase winding is provided. The windings of the three phase are displaced in

spaceby120º. A 3-phasecurrent is fed to the 3-phase winding. These windings produce a

resultant magnetic flux and it rotates in space like a solid magnetic poles being rotated

magnetically.



PROCEDURE:

1. Connections are given as per circuit diagram.

2.3-Ф induction motor is started with DOL starter.

3. If the pointer of one of the wattmeter readings reverses, inter change the current coil

terminals and Take the reading as negative.

4. The no load readings are taken.

5. The motor is loaded step by step till we get the rated current and the readings of the

voltmeter, ammeter, wattmeter’s, spring balance are noted.

PRECAUTIONS:

1.TPST switch is kept open initially.

2.There must be no load when starting the load.

FORMULAE USED:

1) %slip= (Ns-N/Ns)*100

2) Input Power =(W1+W2)watts

3) Output Power=2∏NT/60 watts

4) Torque =9.81*(S1-S2)*R N-m

5) %efficiency=(o/p power/i/p power)* 100


OBSERVATIONS:

S.NO Line Voltage

volts

Input CurrentAmps

Wattmeter Reading Spring Control SpeedW1*4watts

W2*2watts

S1 S2

1

2

3

4

5

6

GRAPHS:

1) Output Power vs Efficiency2) Output Power vs Torque3) Output Power vs Speed4) Output Power vs %s

RESULT:Hence the load test on Squirrel cage Induction motor is performed and performance characteristics are drawn.


EXP.NO. 04NO LOAD AND BLOCKED ROTOR TEST ON 3- PHASE INDUCTION MOTOR

AIM:

To conduct the no load &blocked rotor test on 3- phase induction motor & to draw theequivalent circuit of 3-phase squirrel cage induction motor.

NAMEPLATE DETAILS:

Parameters Induction Motor

Rated Power

Rated Voltage

Rated Current

Rated Speed

APPARATUSREQUIRED:

S. No Name of apparatus Type Range Qty.

1. Ammeter MI

2. Voltmeter MI

3. Wattmeter EDM

4. Tachometer digital

5. Connecting Wires

THEORY :

A 3-phase induction motor consists of stator, rotor & other associated parts. In the stator, a 3-

phase winding (provided) are displaced in spaceby120. A 3- phase current is fed to the

winding so that a resultant rotating magnetic flux is generated. The rotor starts rotating due to

the induction effect produced due the relative velocity between the rotor Winding &the

rotating flux.

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.

CIRCUIT DIAGRAM: DIAGRAM—4


PROCEDURE:

NO LOAD TEST:

(1).Connections are given as pert he circuit diagram.

(2).Precautions are observed and motor is started on the no load.

(3).Autotransformer is varied to have rated voltage applied.

(4).The meter readings are then tabulated.

BLOCKEDROTOR TEST:

(1).Connections are given as per circuit diagram.

(2).Precautions are observed and motor is started on full load or blocked rotor position.

(3).Autotransformer is varied to have rated current flowing in motor.

(4).The meter readings are then tabulated.

PRECAUTIONS:

NO LOAD TEST:

(1).Initially TPST switch is kept open.

(2).Autotransformer must be kept at minimum potential position.

(3).The machine must be started at no load.

BLOCKEDROTOR TEST:

(1).Initially the TPST switch is kept open.

(2).Autotransformer must be kept at minimum potential position.

(3).The machine should be started on full load.

FORMULAUSED:

FOR NO LOAD TEST:

Wsc =√3 Vo Io COSФ watts

Iw = Io cosФ amps

Ro=V0/Iw Ω

Xo=Vo/Iu Ω

FORBLOCKED ROTOR TEST:Wsc =3I2*Ro Watts

Ro1 = Wsc/3(Isc)2 Ω

Zo1 =Vsc/Isc Ω

Xo1 =√Zo1^2-Ro1^2 Ω


TABULAR COLUMNS:

NO LOAD TEST:

Voltage Voc

Volts

CurrentIoc

Amps

Wattmeter readings(W1)


TotalPowerWo(W1-W2)

cosΦo=

Wo/(3 Voc Ioc)Φo=

Voc= open circuit voltageI oc =open circuit current

BLOCKEDROTOR TEST:

Voltage Vsc

Volts

CurrentIsc

Amps



TotalPowerWsc

(W1-W2)

cosΦo=Wsc/(√3VscIsc)

Φsc=

Vsc=short circuit voltage ,Isc =short circuit current

GRAPH:

RESULT:


EXP.NO. 05REGULATION OF3–ΦALTERNATOR BY

SYNCHRONOUS IMPEDANCE AND MMF METHOD

AIM:

To predetermine the regulation of 3-phase alternator by EMF and MMF methods andAlso draw the vector diagrams.

NAMEPLATE DETAILS:

Parameters DC Shunt Motor Alternator

Rated Power

Rated Voltage

Rated Current

Rated Speed

Rated field current



1 Ammeter MC

2 Ammeter MI

4 Voltmeter MI

5 Rheostat Wire wound

6 Potential Divider Wire wound

7 Tachometer Digital

THEORY:

The regulation of a 3-phase alternator may be predetermined by conducting the

Open Circuit (OC) and the Short Circuit (SC) tests. The methods employed for

determination of regulation are EMF or synchronous impedance method, MMF or

Ampere Turns method and the ZPF or Potier triangle method. In this experiment, the

EMF and MMF methods are used. The OC and SC graphs are plotted from the two tests.

The synchronous impedance is found from the OC test. The regulation is then determined


at different power factors by calculations using vector diagrams. The EMF method is also

called pessimistic method as the value of regulation obtained is much more than the actual

value. The MMF method is also called optimistic method as the value of regulation

obtained is much less than the actual value. In the MMF method the armature leakage

reactance is treated as an additional armature reaction. In both methods the OC and SC

test data are utilized.

CIRCUIT DIAGRAM: DIAGRAM---5

PROCEDURE: (FORBOTH EMFAND MMFMETHODS)

1. Note down the name plate details of the motor and alternator.2. Connections are made as per the circuit diagram.3. Switch ON the supply by closing the DPST switch.4. Using the Three point starter, start the motor to run at the synchronous speed

by adjusting the motor field rheostat.5. ConductOpenCircuittestbyvaryingthepotentialdividerforvariousvaluesoffieldcurrent

andtabulate the corresponding Open Circuit Voltage readings.6. ConductShortCircuittestbyclosingtheTPSTswitchandadjustthepotentialdividerto set

the rated armature current and tabulate the corresponding field current.7. TheStatorresistanceperphaseisdeterminedbyconnectinganyonephasestatorwindingof

thealternatorasperthecircuitdiagramusingMCvoltmeterandammeterofsuitableranges.


PROCEDURE TO DRAW GRAPH FOR EMF METHOD:

1. Draw the Open Circuit Characteristic curve (Generated Voltage per phase VS Field current).

2. Draw the Short Circuit Characteristics curve (Short circuit current VS Field current)

3. From the graph find the open circuit voltage per phase(E1(ph)for the rated short circuit current(Isc).

4. By using respective formulae find the Zs, Xs, Eo and percentage regulation.

PROCEDURE TO DRAW GRAPH FOR MMF METHOD:

1. Draw the Open Circuit Characteristic curve (Generated Voltage per phase VS Field current).

2. Draw the Short Circuit Characteristics curve (Short circuit current VS Field current)

3. Draw the line OL to represent

PRECAUTIONS:(i) The motor field rheostat should be kept in the minimum resistance position.(ii) The alternator field potential divider should be kept in the minimum

voltage position.(iii) Initially all switches are in open position.

FORMULAE:1. Armature Resistance Ra= Ω

2. Synchronous Impedance Zs = O.C. voltageS.C. current

3. Synchronous Reactance Xs =√Zs2– Ra2

4. Open circuit voltage for lagging p.f =√(VcosΦ +IaRa)2+ (VsinΦ +IaXs)2

5. Open circuit voltage for leading p.f. =√(VcosΦ+IaRa)2+ (VsinΦ –IaXs)2

6. Open circuit voltage for unity p.f =√(V+IaRa)2+(IaXs)2

7. Percentage regulation=(E0-V)/V


TABULAR COLUMNS:

OPEN CIRCUIT TEST:

S. No.Field Current(If) Open Circuit Line

Voltage (VoL)Open circuit Phase

Voltage (Voph)Amps Volts Volts

1234567891011

SHORT CIRCUITTEST:

S. No. Field Current(If)Short Circuit

Current(120%to 150%of rated current)(ISC)

MODELGRAPH:

RESULT:

Thus the regulation of 3-phase alternator has been predetermined by the EMF and MMF methods.


EXP.NO. 6

V AND INVERTED VCURVES OF 3–Φ SYNCHRONOUS MOTOR

AIM:

To draw the V and inverted V curves ofa3 phase Synchronous Motor.

NAMEPLATE DETAILS:

Parameters Synchronous Motor DC Generator

Rated Power

Rated Voltage

Rated Current

Rated Speed

APPARATUSREQUIRED:

S. no Name of Apparatus Type Range Quantity

1 Ammeter MI

2 Voltmeter MI

3 Wattmeter EDM

4 Rheostat Wire Wound


6 Connecting Wires

THEORY:

The variation of field current effects the power factor at which the synchronous motor

operates. For a synchronous 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) Note down the name plate details of the motor.

(2) Connections are made as per the circuit diagram..

(3) Close the TPST switch.

(4) By adjusting the auto transformer from the minimum position to the

maximum position the rated supply is given to motor. The motor starts as

an induction motor.

(5) In order to give the excitation to the field for making it to run as the

synchronous motor, close the DPST switch.

(6) By varying the field rheostat note down the excitation current, armature

current and the power factor for various values of excitation.

(7) The same process has to be repeated for loaded condition.

(8) Later the motor is switched off and the graph is drawn.


PRECAUTION:

(1) The Potential barrier should be in maximum position.

(2) The motor should be started without load.

(3) Initially TPST switch is in open position.

OBSERVATION TABLE:

S.NO IF

Amps

V

Volts

IaAm

ps

W1

Watts

W2

Watts

WW1+W2

Watts

COSΦ=W/(VLIL)

1

2

3

4

5

6

7

MODELGRAPHS:

The graph is drawn for-(1) Armature current Vs Excitation current.(2)Power factor Vs Excitation current.

RESULT: The determination of V and inverted V curves of three phase synchronous motor wasobtained.


EXP.NO.07

EQUIVALENT CIURCUIT AND PRE-DETERMINATION OF PERFORMANCE

CHARACTERISTICS OF1Ф INDUCTION MOTOR

AIM:

To draw performance characteristics of 1- Ф Induction motor by performing no load blocked rotor test.

NAMEPLATE DETAILS:

Parameter 1Ф-Induction Motor

Rated Power

Rated Voltage

Rated Current

Rated Speed

APPARATUSREQUIRED:

S. No Name of Apparatus

Range Type Qty.

1 Voltmeter MI2 Ammeter MI3 Wattmeter UPFEDM4 Connecting wires

THEORY:

A 1-Ф induction motor consists of stator, rotor and other associated parts. In the rotor of a

single phase winding is provided. The windings ofa1-Ф winding(provided)are displaced in

space by120º.A single phase current is fed to the windings so that a resultant rotating

magnetic flux is generated. The rotor starts rotating due to the induction effect produced due

to the relative velocity between the rotor winding and the rotating flux.


CIRCUIT DIAGRAM: DIAGRAM—7

PROCEDURE:

NO LOAD TEST:

1. Connections are given as per the circuit diagram.2. Precautions are observed and the motor is started at no load.3. Autotransformer is varied to have a rated voltage applied.


BLOCKEDROTOR TEST:1. Connections are given as per the circuit diagram.2. Precautions are observed and motor is started on full load or blocked rotor position.3. Autotransformer is varied to have rated current flowing in motor.4. Meter readings are the noted.

PRECAUTIONS:

NO LOAD TEST:

∑ Initially TPST Switch is kept open.∑ Autotransformer is kept at minimum potential position.∑ The machines must be started on no load.

BLOCKEDROTOR TEST:∑ Initially the TPST Switch is kept open.∑ Autotransformer is kept at minimum potential position.∑ The machine must be started at full load (blocked rotor).

Reff=1.5*Rdc

FORMULAE:

NO LOAD TEST:

∑ cos Ф = Wo/VoIo∑ Iw=IocosФ∑ Im =Io sin Ф∑ Ro = Vo/Iw∑ Xo =Vo/Im

BLOCKEDROTOR TEST:

Zsc= Vsc/Isc ΩRsc= Wsc/Isc2 ΩXsc= √(Zsc2– Rsc2) Ω

TABULAR COLUMNS:

NO LOAD TEST:

S.No. Vo(volts) Io(amps) Wo (watts)

1


BLOCKEDROTOR TEST:

S.No. Vsc (volts) Isc (amps) Wsc(watts)

1

EQUALENT CIRCUIT:

RESULT: Thus the pre-determination of Equivalent circuit parameters and efficiency of 1-phase induction motor was obtained as follows


EXP.NO. 08

DETERMINATRION OF Xd AND Xq OF SALIENT POLE SYNCHRONOUS MACHINE

AIM:

To measure Direct Axis (Xd) and Quadreture Axis (Xq) synchronous reactance of Synchronous

machine by performing SLIP Test.

NAMEPLATE DETAILS:

PARAMETERS DC Shunt Motor Alternator

Rated Power

Rated Voltage

Rated Current

Rated Speed

Rated field current



1 Ammeter MI

2 Voltmeter MI

3 Variac

4 Rheostat Wire Wound


6 Connecting Wires MI

7 Ammeter

THEORY:

In a salient pole alternator, the reactance of magnetic circuit along is along its quad stator

axis. The alternator is driven by auxiliary prime mover at a speed slightly less than the

synchronous speed under these conditions. The armature current is when the armature

current mmf is in line with the field poles. The reactance by the magnetic field current is

minimum. The ratio of maximum voltage to minimum current gives the direct axis


impedance and the ratio of minimum voltage to maximum current gives the armature axis

impedance.

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 alongq-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. Note down the name plate details of motor and alternator.2. Connections are made as per the circuit diagram.3. Give the supply by closing the DPST switch.4. Using the three point starter, start the motor to run at the synchronous speed by

varying the motor field rheostat at the same time check whether the alternator field has been opened or not.

5. Apply20%to 30% of the rated voltage to the armature of the alternator by adjusting the autotransformer.

6. To obtain the slip and the maximum oscillation of pointers the speed is reduced slightly lesser than the synchronous speed.

7. Maximum current, minimum current, maximum voltage and minimum voltage are noted.

8. Find out the direct and quadrature axis impedances.

PRECAUTIONS:

1. The motor field rheostat should be kept in minimum.

2. The direction of the rotation due to prime mover and the alternator on the motor

should be the same.

3. Initially all the switches are kept open.

TABULAR COLUMNS:

To find the Direct Axis and Quadrature axis impedances:

S.NO Vmax Vmin Imax Imin

1

OPEN CIRCUIT TEST:

S.No.Field Current(If) Open Circuit Line

Voltage (VoL)Open circuit Phase

Voltage (Voph)Amps Volts Volts

1


SHORT CIRCUITTEST:

S.No. Field Current(If)Short CircuitCurrent(120%to150% of rated

current)(ISC)Amps Amps

1

FORMULAE USED:

1. Rac=1.6RacΩ

2. Zd =Vmax/Imin Ω

3. Zq =Vmin/ImaxΩ

4. Xd =√Zd2– Rd2 Ω

5. Xq =√Zq2– Rd2 Ω

6. Id=IasinФamps

7. Iq=Iacos Ф amps

8. %Reg = (Eo-V/V)*100Where,

Zd =direct axis impedance in ΩZq =quadrate axis impedance in ΩXd =direct axis reactance in ΩXq =quadrate axis reactance in ΩId= direct axis current in ampsIa= quadrate axis current in amps

RESULT: Hence by performing slip test we find the values of Xd= And Xq=


EXP.NO. 09Parallel Operation of Two Single Phase Transformers

AIM:

To operate the given two2KVA, 230/110V singles phase Transformers in parallel and study the load sharing between them when supplying resisters load.

NAMEPLATE DETAILS:1Φ- TRANSFORMERS



1 Ammeter MI

2 Ammeter MI

3 Voltmeter MI

4 Resistive Load


6 Single Phase Transformer

THEORY:

It is economical to install numbers of smaller rated transformers in parallel than installing bigger

rated electrical power transformers. This has mainly the following advantages, to maximize

electrical power system efficiency: Generally electrical power transformer gives the maximum

efficiency at full load. If we run numbers of transformers in parallel, we can switch on only

those transformers which will give the total demand by running nearer to its full load rating for

T/FT/F-1 T/F-2

HV side LV side HV side LV side

Rated power

Rated voltage

Rated current

Frequency


that time. When load increases, we can switch none by one other transformer connected in

parallel to fulfill the total demand. In this way we can run the system with maximum efficiency.

To maximize electrical power system availability: If numbers of transformers run in parallel, we

can shutdown any one of them for maintenance purpose. Other parallel transformers in system

will serve the load without total interruption of power.

To maximize power system reliability: if any one of the transformers run in parallel, is tripped

due to fault of other parallel transformers is the system will share the load, hence power supply

may not be interrupted if the shared loads do not make other transformers over loaded.

To maximize electrical power system flexibility: There is always a chance of increasing or

decreasing future demand of power system. If it is predicted that power demand will be

increased in future, there must be a provision of connecting transformers in system in parallel to

fulfill the extra demand because, it is not economical from business point of view to install a

bigger rated single transformer by forecasting the increased future demand as it is unnecessary

investment of money. Again if future demand is decreased, transformers running in parallel can

be removed from system to balance the capital investment and its return.

Conditions for Parallel Operation of Transformers

When two or more transformers run in parallel, they must satisfy the following conditions for

satisfactory performance. These are the conditions for parallel operation of transformers.

1. Same voltage ratio of transformer.

2. Same percentage impedance.

3. Same polarity.

4. Same phase sequence.



PROCEDURE:

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

b) Switch on the mains, seethe volt meter reading of V1 , if this

readingis460V(double the secondary voltage of both the machines) then

switch of and interchange 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 0 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.


CAULATIONS:

For a given load current ILat 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 share disproportional to the KVA capacities of the respective transformers

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


EXP.NO. 10

SEPERATION OF CORE LOSSES 1-f TRANSFORMER

AIM: To separate hysteresis and eddy current losses ofagiven1-f transformer.

NAMEPLATE DETAILS:

DC Motor Alternator Transformer

Rated Power

Rated voltage

Rated current

Rated speed

Rated field current

APPARATUSREQUIRED:


1 Ammeter MC

2 Voltmeter MI

3 Wattmeter EDM

4 Rheostat Wire wound

5 Potential Divider Wire wound




THEORY:

Hysteresis and eddy current losses are called iron loss and take place in core of the transformer. Hysteresis loss is given by = Wh = KBmox1.6 f = Af

Eddy current loss also depends on the frequency f and is given by

We = KB2mox f2 t2 =Bf2

B max = Maximum flux density weber / m2

F = frequency cycles/ seconds

t = thickness of stamping

The iron loss will be expressed by

W i = Af +B f2 , W i/ f = A + B f ,

y = m x + c

This is equation of straight line y = m x + c, when y = w i / f , c = A , and m = B and x = f. Eddy current and Hysteresis loss can be separated when A and B are found.

The variable frequency supply is obtained from an alternator when frequency can be varied.

CIRCUITDIAGRAM: DIAGRAM--10



PROCEDURE :(1) Connections are done as per the circuit diagram.

(2) Initially rheostat in the armature circuit of motor is kept at maximum position, the rheostat

in the field circuit of motor is kept at minimum position and the rheostats in the field

circuit (potential divider)of the alternator are kept so that minimum voltage is applied to

the field circuit of the alternator.

(3) Start the motor with the help of 3-point starter

(4) Bring the speed of the motor to the rated speed by using the rheostats of the motor.

(5) By increasing the excitation of alternator using the potential divider bring the voltage of

the alternator to the rated voltage.

(6) Apply the rated voltage to the high voltage side of the transformer by closing the DPDT

switch.

(7) Note down all the meter readings and speed.

(8) Alternator is made to run at different speeds below the rated speed and adjust the voltage

of the alternator, so that v / f ratio is constant.

(9) At each and every speed, note down the readings of voltmeter, ammeter, wattmeter and

the speed of the motor.

(10) Perform the experiment up to 80% of the rated speed and graphs are drawn between

PRECAUTIONS :

(1) Care must be taken about the v / f value constant so that the flux density is maintained

constant.

(2) The rheostat in the field circuit of motor should be minimum position, the rheostat in the

armature circuit of motor should be maximum position and potential divider of alternator

should give voltage to the alternator at the time of starting.



TABULAR FORM:

S. noVoltage

(V)Wattmeter

reading(W)Speed(rpm)

f =PN / 120 V/f Wi / f

123456789101112

MODELGRAPH:

W/ f

f

RESULT:

Separate hysteresis and eddy current losses ofagiven1-f transformer are obtained as follows:Eddy current losses = Hysteresis losses

Total Core losses=

A



EXP.NO. 11

SCOTT CONNECTION OF TRANSFORMER

AIM:

To convert three phase system to two phase system with the help of Scott Connection.

NAMEPLATE DETAILS:



1 Ammeter MI

2 Ammeter MI

3 Voltmeter MI

4 Voltmeter MI




THEORY:

The Scott Connection is also called T-T connection. This scheme of connection is widely used

for 3-f to2-f and vice versa. In this arrangement two transformers are required, one of the two

transformers must have at least two primary and two secondary coils so that a centre tap may be

brought out from each side. The other transformer, known as teaser transformer must have primary

and secondary winding, the number of turns of which are 0.866 times of the respective turns the main

transformer.

Main Transformer Teaser Transformer



CIRCUIT DIAGRAM: DIAGRAM –11

PROCEDURE:

(1) Connections are done as per the circuit diagram.

(2) Loads are connected at secondary’s of 2 T/F’s.

(3) Byusing3-f autotransformer apply different voltages to the circuit.

(4) Note down the all the meter readings.

(5) Observe different meter readings.

CALUCULATIONS:

I1T = 2/√3 * K * I2T

Where K=

I1M = K*I2M

Ib = Ic = √( I1M)2+( I1T/2)2



There fore ,IA = I1T

1) I1T= 1.15*K* I2T2) I1M= (K*I2M)2 + (0.5*K* I2T)2

3) If V2T=V2M then[V2T

2] + [V2M2] = 2 V2T+ 2 V2M; K=N2/N1

For Balanced Load:

S. No Load condition Teaser transformer Main transformerI1T I2T V1T I1M I2M V1M V2M

1 No load2 1 KW load on

both transformers

For Unbalanced Load:

S.No Load condition Teaser transformer Main transformerI1T I2T V1T I1M I2M V1M V2M

1 No load2 1 KW load on

both transformers

RESULT: Therefore the Scott connection has been studied.

electrical machines-ii laboratory manual - …smec.ac.in/sites/default/files/lab1/em-ii lab...

Documents