laboratory manual electrical machines and application s

LABORATORY MANUAL Electrical Machines and Applications

Laboratory

Department of Instrumentation Engineering

JORHAT ENGINEERING COLLEGE

Assam-785007

Do’s

➢ Be punctual, maintain discipline & silence.

➢ Keep the Laboratory clean and tidy.

➢ Leave your shoes in the rack outside.

➢ Handle the equipments carefully.

➢ Save all your files properly.

➢ Come prepared with programs/algorithms/related manuals.

➢ Follow the procedure that has been instructed.

➢ Get the signature on experiment result sheet daily.

➢ For any clarification contact faculty/staff in charge only.

➢ Log off the system properly before switching off .

Don’ts

➢ Avoid unnecessary chat or walk.

➢ Disfiguring of furniture is prohibited.

➢ Avoid using cell phones unless absolutely necessary.

➢ Do not use personal pen drives without permission.

➢ Do not displace monitor, keyboard, mouse etc.

➢ Avoid late submission of laboratory reports.

IN408 EMA LABORATORY Semester IV L-T-P

0-0-2

1 CREDIT

Experi

ment

No.

Title of the Experiment Objective of the Experiment

1 Open circuit characteristics

of a DC generator To draw the open CIRCUIT CHARACTRISTICS (OCC)

or magnetization characteristic and to determine the critical

field resistance and the critical speed of a DC shunt

generator.

2 Load test on a shunt

generator

To determine the external and internal characteristic of a

DC shunt generator.

3 Characteristic of a dc shunt

generator

To determine the external and internal characteristic of a

DC series generator.

4 Speed control of a dc shunt

motor

I.

To control the speed of a DC shunt motor by the method of

a. Armature control and

b. Flux control or field control

c.

5 Open circuit test and short

circuir test on a single phase

transformer

To perform open circuit test and short circuit test on a

single phase transformer and to calculate the parameters of

the equivalent circuit. Also to estimate the efficiency and

regulation of the transformer for the full range of loading.

6 Polarity test and load test on

a single phase transformer

To perform polarity test on a single phase transformer also

to estimate the efficiency and regulation of the transformer

for the full range of loading.

7 Regulation of an alternator To perform the open-circuit and short-circuit tests on a three

phase alternator and to determine the regulation by

synchronous impedance method

8 Measurement of power in

three phase circuit by two

wattmeter method

To measure the power and power factor in a three phase

balanced circuit by two wattmeter.

Text book

➢ Electrical Machines, D P Kothari and R J Nagrath

Student Profile

Name

Roll Number

Department

Year

Student Performance Sl. No. Title of the Experiment Remarks

1 Open circuit charactristics of a DC generator

2 Load test on a shunt generator

3 Characteristic of a dc shunt generator

4 Speed control of a dc shunt motor

5 Open circuit test and short circuir test on a

single phase transformer

6 Polarity test and load test on a single phase transformer

7 Regulation of an alternator

8 Measurement of power in three phase circuit

by two wattmeter method

Office Use

Checked and found

…………………………………………………

Grade/ Marks

………………………………………………… Signature

……………………………………………………

ExperimentNo:1

TITLE:OPENCIRCUITCHARACTRISTICSOFADCGENERATOR

OBJECT: To draw the open CIRCUIT CHARACTRISTICS (OCC) ormagnetizationcharacteristicandtodeterminethecriticalfieldresistanceandthecriticalspeedofaDCshuntgenerator.

CIRCUITDIAGRAM:

LISTOFAPPARATUS:

SLNo Item Range Maker MakersNo

MACHINESPECIFICATIONS:

THEORY: The open circuit characteristic or themagnetization characteristic oftheDCgeneratorgivestherelationshipbetweenfluxperpoleandexcitingcurrentorthefieldm.m.f.perpole. If themachine isrunatconstantspeedonno load,the induced e.m.f. is proportional to the flux per pole (and hence the fieldcurrent);ife.m.f.isplottedagainsttheexcitingcurrentthegraphisnearlycalledtheopen-circuit characteristic. In aDCgenerator, the inducede.m.f. is givenasEg=

!"#$%&'

volt.HenceifspeedNisconstant,Eg=kΦ.Itisobviousthatwhenthefieldcurrent, If is increased from its initial value, the flux and hence the generatede.m.f. Eg increasesdirectlyas Ifwhile thepolesareunsaturated.Butas the fluxdensity increases, the poles become saturated, so a greater increase in If isrequiredtoproduceagivenincreaseinEgthanonthelowerpartofthecurve,asshown.Alsoduetoresidualmagnetisminthepolessomee.m.f.isgeneratedevenwhenIf iszero.Hencecurvestartsalittlewayupasshown.Ifthemachineisonopen circuit, the shunt circuit of theDC generator canbe regarded as in serieswith the armature. A straight line is drawn through origin so as to cut thecharacteristicatP1;thenifE1istheinducede.m.f.andIshshuntcurrent,P1M1=E1,O1M1=Ish

Therefore,tan 𝛼1=,-.-/-.-

= 1-234

=Rsh,thetotalresistanceoftheshuntcircuit.Henceif we draw any straight line thro. The origin, such as OP2 whose inclination,α2representstheshuntresistancethenitsordinateP2M2willgivetheinducede.m.fcorresponding to that resistance and its abscissaOM2 the shunt current. If thestraight line OP3 doesn’t intersect the characteristic, the shunt resistance itrepresentsistoogreatforthemachinetobeabletobuildupitsfieldandfunctionasgenerator.Theslopeα3ofthetangentOTthereforerepresentsthemaximumallowablevalueoftheshuntresistance,calledthecriticalfieldresistance,Rc.Thecorrespondingspeed,calledthecriticalspeed,Ncisfoundbydrawingthestraightline OP1 with a slope equal to the shunt field resistance Rc andmeasuring thelengthsACandBCgiving56

'6= 89

:;<<=>??@,orNc=

56'6×𝐹𝑢𝑙𝑙𝑠𝑝𝑒𝑒𝑑(𝑅𝑎𝑡𝑒𝑑𝑠𝑝𝑒𝑒𝑑)

PROCEDURE:

1. Connectthecircuitasshowninthediagram.2. WiththegeneratorG fieldcircuitOFFstart themotorMwith thehelpof

thestarter.Notethevoltmeterreadingandthespeedofthemachine.Themachinemayberunatratedspeedbyadjustingthefieldregulatorofthemotor.Thevoltmeterwillindicatethevoltageduetoresidualmagnetisminthefieldofthegenerator(atIf=0).

3. Adjusttheoutputvoltagepotentialdivideratzeroandthenptthesupplyon.(notethatinsteadofusingtwoDCsupplythesamesupplyinthemotor

circuitmaybeused.Butcareshouldbetakentokeeptheoutputvoltageofthepotentialdivideratzero)

4. Increase the field current in regular steps, nothing at least ten sets ofreadingsofvoltageandfieldcurrent,toabout125%oftheratedvoltageofthegenerator.(Note:whileincreasingthefieldcurrentdon’tdecreaseittoobtainareadingofparticularvalue).

5. TakereadingsfordecreasingfieldcurrentinthesimilarmannertillIfiszero.6. Put themotor and generator supplyOFF (P.S.: the speedof themachine

shouldremainconstantthroughouttheexperiment.7. Drawasmoothcurveasshown.

OBSERVATION:

IncreasingfieldcurrentDecreasingfieldcurrent

SL.No. If(Amps)

InducedVoltage(V)

SpeedN(RPM)

SL.No. If(Amps)

InducedVoltage(V)

SpeedN(RPM)

• PlotOCC forboth If increasinganddecreasing.DetermineRc andNc fromOCCforincreasingIfonly.

• Report:1. PlottheOCCcurveandDetermineRcandNcforratedspeed.2. Thecurvefordecreasingvalueoffieldcurrentliesslightlyabove

oftheincreasingvalueofIf.Explainwhy?3. Whatdoyoumeanbytheterm“Residualmagnetism”?4. Howwill you determine he OCC at another speed N2 from the

OCCofashuntgeneratorrunningatspeedN1andhasshuntfieldresistance,Rsh?

5. Whydoesn’ttheOCCstartsfromtheorigin?6. Define“criticalspeed”ofashuntgenerator.

Signatureoftheteacher Date

ExperimentNo:2

TITLE:LOADTESTONASHUNTGENERATOR

OBJECT: To determine the external and internal characteristic of a DC shuntgenerator.

CIRCUITDIAGRAM:

LISTOFAPPARATUS:



MOTOR:

GENERATOR:

THEORY:InaDCshuntgenerator,onno-loadtheterminalp.d.isequaltothenoload induced e.m.f. E.When the armature delivers current, i.e. the generato isloaded:

a) The induced e.m.f. decreases because the armature reaction reduces thefluxperpole.

b) V becomes less than E because of the voltage drop IaRa,where Ra is thetotalresistanceofthearmaturecircuit.

Thegraphofinducede.m.f.againstarmaturecurrentistheinternalcharacteristic, and the graph of terminal voltage against load current is the externalcharacteristic,orvoltagecharacteristic.Weseeboththecharacteristicdropfromnoloadpoint,N,thesecondmorethanthefirst,asshown.WhentheloadcurrentIlprogressivelyincreased(byreducingtheloadresistance),atfirstthetendencyofdecreasedresistanceto increasethecurrent isgreaterthanthetendencyofthearmaturereactionandthevoltagedroptoreducedterminalpotentialDifferenceandtherefore,thecurrent.Eventuallyapointwillbereachedatwhichthesetwoeffectsneutralizeeachother.Beyondthatsecondtendencywillbepredominateandthecharacteristicwillturnbackasshown.

ThepointAatwhichtheexternalcharacteristiccutsthecurrentaxiscorrespondstoshortcircuit-agradualshortcircuit.TheinternalcharacteristicstopsshortatBdirectlyaboveA,andthedistanceABgivestheinternale.m.f.requiredtoproducetheshortcircuitcurrent,OA.IfatangentOPisdrawntotheinternalcharacteristictheresistancerepresentedbyitsslopegivestheminimumexternalresistanceforwhichthegeneratorwillexcite if ithas tobuildup its fieldwiththe loadcircuitclosed.IftheexternalresistanceislessthanrepresentedbytheslopeofOP,itwillfail to excite. Thus the shunt generatorhas two critical resistances, one for thefieldcircuitandotherfortheexternalcircuit.

Inashuntgenerator, Ia=Il+If ,where, Ia isarmaturecurrent, Il isthe loadcurrentand If shunt fiend current and E0=VT+ IaRa, E0=induced e.m.f. in armature,VT=Terminal voltage, Ra=armature winding resistance. Thus , once the externalcharacteristicoftheshuntgeneratorisknown,andafterdrawingtheIaRaline,theinternal characteristic can be determined. The value of Ra can be found outconventionallybythevoltagedropmethod,asshown

PROCEDURE:

1. Connectthecircuitasshowninthediagram.2. Startthemotorwiththehelpofthestarterandobtaintheratedspeed.3. Intheexperiment,itisnecessarytoobtainthenoloade.m.f.oftheshunt

generator which will give the rated voltage at rated load (see thespecification on the name plate of the generator). This is achieved by

adjusting the field regulator so that the generator induced e.m.f. is wellabovetheratedvoltageandthenactuallyloadingistoitsratedvoltageatratedloadcurrent.

4. Once the step3. Is obtainedat rated speedof the generator, notedownthemeterreadingsandthespeedofthegenerator

5. Reducetheloadonthegeneratorsoastoobtainatleastabout10setsofreadings

6. Switch off all the loads, reduce field current of the generator and thenswitchoffthemotor

7. Measure armature resistance Ra of the generator, or its value may besupplied.

8.

NOTE: The loading on the generator may be as high as 120% of its full loadcapacity.ThearmatureshaftmustnotrotatewhilemeasuringRa.

OBSERVATIONS:

SLNo LoadcurrentIl(amps)

TerminalvoltageVT(volts)

FieldcurrentIf(amps)

Speed in(rpm)

Remarks

PrepareanotherexperimentallistofobservationsincludingE0,Ia,IaRaintheabovelistfordetermininginternalcharacteristic.

REPORTS:

1. Plottheexternalcharacteristic.2. Deduce the internal characteristic from 1. And estimate the full load

voltagedropduetoarmaturereaction.3. Isispossibletoshortcircuitashuntgenerator?Explain.4. Statesomeapplicationsofashuntgenerator.

*While measuring Ra, at least three sets of readings should be taken and theaverageofRabconsidered.


ExperimentNo:3

TITLE:CHARACTERISTICOFADCSHUNTGENERATOR

OBJECT:To determine the external and internal characteristic of a DC seriesgenerator.

CIRCUITDIAGRAM:

LISTOFAPPARATUS:



MOTOR:

GENERATOR:

THEORY:ADCseriesgeneratorisaself-excitingtypeofmachineanditcandosoonlyiftheloadcircuitisclosed.Inthegeneratortheinducedorgeneratede.m.f.E=kΦN=k/Ia,ifNisconstant.Terminalvoltage,V=E-Ia(Ra+Rse),whereRaisarmatureresistanceandRse=seriesfieldresistance.

ThereforeV~K/Ia,providedRaandRsearesmall.ThustherelationshipbetweenVandIawillexhibitanearlylinearrelationatsmallerloadtilltheonsetofarmaturereaction.TheplotVvs IagivesexternalcharacteristicandthatbetweenEand Iagivesthe internalcharacteristicoftheseriesgenerator. Itwillbenotedthatthegeneratorhasrisingvoltagecharacteristic,i.e.withincreaseinloads,voltagealsoincreases. But at high loads, the voltage starts decreasing due to excessivedemagnetizing effects of armature reaction. In fact external voltage startsdecreasing as the load current is increased. The internal characteristic can bedeterminedaddingIa(Ra+Rse)withtheexternalcharacteristic.

PROCEDURES:

1. Connectthecircuitasshown.2. With generator load off start themotorwith the help of the starter and

bringittoratedspeedbyadjustingitsfieldregulator(themotorgivenisacompoundmotor).

3. Put the generator load on and increase it gradually. Note down all themeterreadings.Takeatleast10setsofreadings.

4. Graduallyputofftheloadonthegeneratorandnotedownabout10setsofreadingfordecreasingcurrent.

5. Switchofthemotorsupply.6. Measure the combined resistance of the armature, series pole and

interpoles (if any) by voltage drop method. (Refer load test on shuntgenerator),orthevaluemaybesupplied.

OBSERVATIONS:

Ratedspeed,N=

Ra+Rsc=

IncreasingloadDecreasingload

SL.No TerminalvoltageV,(volts)

Loadcurrent(amps)

SL.No TerminalvoltageV,(volts)

Loadcurrent(amps)

Prepare another chart showing E,V,Ia etc. to draw the external and internalcharacteristicsofthegenerator.ConsiderIa=Ilfordecreasingvalues

REPORT:

1. Explainhowwill youobtain theexternal characteristic curve from theopencircuitcharacteristicifthemachineis

a) Adequatelycompensatedb) Uncompensated

2. StatesomeapplicationsofDCshuntgeneratorandmotor


ExperimentNo:4

TITLE:SPEEDCONTROLOFADCSHUNTMOTOR

OBJECT:TocontrolthespeedofaDCshuntmotorbythemethodof

I. ArmaturecontrolandII. Fluxcontrolorfieldcontrol

CIRCUITDIAGRAM:

LISTOFAPPARATUS:



THEORY:

1. Let anadjustable resistanceRa/beplaced in serieswith thearmatureof

theshuntmotor,makingthetotal resistance in thearmaturecircuit (Ra+Ra

/), where Ra is the resistance of the armature winding; then the backe.m.f. foranyarmaturecurrent Ia isgivenbyEb=V-(Ra+R/

a)Ia. atno load,and no series resistance, Ra

/,in circuit, the back e.m.f. is approximatelyequal to the applied voltage. Since, for constant excitation, the speed isproportional to the back e.m.f., we have denoting no load speed byN0, NOP =

QR(STUS/T)WTQ therefore

NowputtingRa+Ra/=Rt;thenN=N0(1-

XY2Z[)

For a given resistance Rt, the speed N, is thus a linear function of thearmaturecurrentIa,thegraphofNvs.Iabeingadroppingstraightline,asshown.Theamountofdrop isobviouslydependsuponRt,andthereforeupon R/

a graph of family of speed/current curves can be drawn. In thegraph,Im=V/Rt

*Thismethodisusedwhenspeedsbelowtheno-loadspeedorratedspeedarerequired

2. ForaDCmotorthebacke.m.f.Eb=(ΦZN/60)P/A,where,Φ=fluxperpole;Z=noofarmatureconductors;N=speed;P=noofpolesandA=noofparallelpathinthearmaturewinding.IfV=Supplyvoltage,thenresultinge.m.f.actinginthearmaturecircuitisV-Eb=V-(ΦZN/60)P/A; Armature current, Ia=(V- Eb)/Ra or Ia=

[\(]^8/%&),/_XZ

and the speed is N=[\2ZXZ(%&_/,)"

N=speed in r.p.m. since IaRa is smallcomparedtoVandΦ,Z,AandPareallconstantsforagivenmotor.N∞1/ΦsolongasVconstant.ThusthespeedofaDCmotorisinverselyproportionaltotheflux/pole,i.e.the field current If. The field current may be varied by means of aresistance(Rf)putthefieldcurrentinseries.

**This method of speed control of the shunt motor gives speed greater thannormalspeed,i.e.abovetheratedspeed.

PROCEDURES:

a) Armaturecontrolmethod:1. Connectthecircuitasshown.2. WithswitchSclosed,R/

aandRf intheirminimumposition ,switchonthesupplyandstartthemotorbymeansofthethreepointstarter.

3. AsthemotorspeedsupopentheswitchSandnotedownthevariousmeterreadings.TheresistanceRfmaybeadjustedpartiallysothatthemotorrunsatratedspeed.

4. Increase R/a insteps and note down the various instrument readings

andthespeed5. Repeatstep4.Tonotedownabout10setsofreading.6. AdjustR/

asuchthatthemotorjuststalls.7. Switchoffthesupply.

b) Fluxorfieldcontrolmethod1. Closedtheswitchoff.2. MakeR/

a andRf in theirminimumposition , switch on the supplyandstartthemotorasbefore

3. CutoutthefieldregulatorRf instepsandnotedownspeedNandthe field current (If). The other meters will indicate more or lesssamereadings.

4. Repeatstep3.Tonotedownabout10setsofreadings,tillspeedis10-15%morethantheratedvalue.

5. BringRftoitsminimumposition,switchoffthesupply.

OBSERVATIONS:

Armaturecontrol,If(constant)= Field control, Supply voltage(constant)=

SLNO Armaturevoltage(volts)

Armaturecurrent(amps)

Speed(RPM)

SLNO Armaturevoltage(volts)

Armaturecurrent(amps)

Speed(RPM)

REPORT:

1. PlotthegraphsNvs.Va(armaturevoltage)andNvs.If(fieldcurrent)fromresultobtained.Compareonyourresults.

2. Statesthemeritsanddemeritsofthesemethods.3. Writeindetailsaboutthevoltagecontrolmethod(Ward-Leonardmethod)

forcontrollingthespeedofashuntmotor.


ExperimentNo:5

TITLE: OPEN CIRCUIT TEST AND SHORT CIRCUIR TEST ON A SINGLE PHASETRANSFORMER

OBJECT:Toperformopen circuit test and short circuir testona singlephasetransformer and to calculate theparameters of the equivalent circuit.Also toestimate theefficiencyand regulationof the transformer for the full rangeofloading.

CIRCUITDIAGRAM:

OPENCIRCUITTEST:-

SHORTCIRCUITTEST:-

LISTOFAPPARATUS:


TRANSFORMERSPECIFICATIONS:

THEORY:Thepurposeoftheopencircuitortheno-loadtestonatransformeristo determine the no load losses or the core loss (or iron loss comprising thehysteresisandtheeddycurrentlosses)andthenoloadprimarycurrent(I0)whichishelpful infindingthecomponentsrepresentingthecorelossconductanceG0(orresistanceR0)andmagnetizingsuceptanceB0(orreactanceX0).Onewindingof the transformer leftopenand theother is connected to its supplyofnormalvoltageandfrequency.TheprimarycurrentIohastwocomponents,firstoneisamagnetizing component Iμ lagging behind V1 by 900 and the second one is aworking component Iω,producing the iron lossof the transformerand inphasewith V1. The no load vector diagram is shown. IfW0 is the wattmeter reading(referdiagramforOCtest),then,

W0=V1I0cos𝛷0,cos𝛷0=W0/V1I0

Iμ=I0sinΦ0,IW=I0cosΦ0,X0=V1/Iμ,R0=V1/Iw

The purpose of the short circuit test or impedance test on a transformer is todetermine-

I. Eqvt. Impedance (Z01 or Z02), leakage reactance, (X01 orX02) and totalresistance ( R01 or R02) of the transformer as referred to the winding inwhichthemetersareplaced

II. Fullloadcopperloss(orlossatanyotherload)tobeusedforcalculatingefficiencyofthetransformer

III. Having known Z01 or Z02, the total voltage drop in the transformer asreferred to theprimaryor secondary side,which isused to calculate theregulationofthetransformer.Inthistest,areducedvoltageisappliedonthe primary so as to calculate full load current in the secondary. As thecorelossisverysmall(fluxbeingsmall).Thetransformer(referdiagramforSC test) represents the full load copper loss of the transformer , Vsc thevoltagerequiredtocalculateratedloadcurrent,I1primarycurrentandW=wattmeterreadingduringshortcircuit,thenZ01=Vsc/I1,AlsoW=I12R01orR01=W/I12andX01= (Z012-R01

2)

Theequivalentcircuit:

Efficiencyof a transformer,η=Output/(Output+Cu loss+ Iron loss(constant)) X100%,Alsoη=(V1I1cosΦ1- I12R01-W1)/V1I1cosΦ1) X100%,sothatηatany loadandpowerfactorcanbecalculated.

Forηmax,variablecopperloss=Ironloss(constant)

Regulationofatransformer

%Regulation=((V02–V2)/V02)X100%

V02=Secondaryvoltageatnoload

V2=Secondaryvoltageatfullload

Itcanbeshownas

%Regulation= ((I1R01cosΦ +- I1R01sinΦ)/V1)X100%, in termsofprimaryvalues“+”forlaggingpowerfactorand“-“forleadingpowerfactor.

Thus regulation of the transformer at any load and power factor can becalculated.

PROCEDURE:-(O.C.TEST):

i. Connectthecircuitassown.ii. Putonthesupplywith0appliedvoltagetotheprimaryofthetransformeriii. Increasethevoltagebymeansofautotransformerptotheratedvoltageof

thevoltageiv. Notedowntheinstrumentreadings.v. Decreasevoltageandswitchoffthesupply.

OBSERVATION:

Multiplyingfactororwattmeterconstant,

K=((Ratedvoltage)X(Ratedcurrent))/(Noofscaledivisions),Watts/div

=

SLNo PrimaryVoltageV1(volts)

Primary(no-load)current,I0(amps)

W-meterReadings(divisions)

W-meterReadings(watts)

SecondaryVoltageV2(volts)

PROCEDURE:(S.C.TEST):

i. Connectthecircuitasshown.ii. Putonthesupplywith0appliedvoltagetotheprimaryofthetransformeriii. Increase theprimaryvoltage slowlyandcarefully soas toobtain full load

currentintheshortedsecondarywinding(throughtheammeter)iv. Notedowntheinstrumentreadings.v. Decreasevoltageandswitchoffthesupply.

OBSERVATION:

K=

SLNo PrimaryVoltageV1(volts)

Primary(no-load)current,I0(amps)

W-meterReadings(divisions)

W-meterReadings(watts)

SecondarycurrentI2(amps)

REPORT:

i. Draw the equivalent circuit and calculate all the parameters of thetransformerfromthistwotests

ii. Determine the efficiency and regulations of the transformer at1/4th,1/2th,3/4th and full load at .8 (lagging) , .8 (leading) and unity powerfactoroftheload.

iii. Determinethemaximumefficiencyofthetransformer


ExperimentNo:6

TITLE:POLARITYTESTANDLOADTESTONASINGLEPHASETRANSFORMER

OBJECT: To perform polarity test on a single phase transformer .Also toestimate theefficiencyand regulationof the transformer for the full rangeofloading.

CIRCUITDIAGRAM:

POLARITYTEST:

Theroy:Whenatransformer(singlephaseorthreephase)isconnectedwithanac voltage, its terminals develop instantaneous polarities either positive ornegative.Forparalleloperationsoftransformersitisamustthatterminalsofthesecondary side with identical polarities can only be grouped together. If thesecondary terminals with opposite polarities are joined together then a localcircuit among secondary windings will be formed causing a condition of shortcircuits.Thus,beforeparallelingabankoftransformers,hepolaritytestmustbecarriedout.

The efficiency and the regulation of the transformer can be determined byactuallyloadingittofullcapacity.

%Efficiency=(Output/Input)X100%

The output of the transformer can be read by means of a voltmeter and aammeter (V X 1), if the load is resistive. For inductive and capacitive load, awattmetermaybeused

%Regulation=((V02–V2)/V02)X100%

V02=Secondaryvoltageatnoload

V2=Secondaryvoltageatfullload

Thusregulationofatransformeristhepercentagedifferencebetweennoloadafull load secondary voltagesat a givenpower factorof the load. ThesecondaryterminalvoltageVfallsduetoincreaseinloadthatcausesanincreaseindropinthesecondarywindingimpedance.

PROCEDURE:POLARITYTEST:

Insteadofusingseveralvoltmetersforthepurposeasinglevoltmetercanbeusedandthevoltageacrosstheterminals(P,Q,RandS)canbetapped.

i. Switchonthesupplyandmeasurethesupplyvoltage,thesecondaryvoltageandthevoltageacrossPandQ(Figa).

ii. SimilarlymeasurethevoltageacrossPandS(Figb)afterjoiningtheappropriateterminals.

OBSERVATIONS:POLARITYTEST:

Typeofconnection Voltmeterreading(volts) InferenceFig(a) Fig(b)

PROCEDURE:LOADTEST:

i. Connectthecircuitasshownii. Switchonthesupplyandnotethemeterreadingsiii. Increase the load gradually in steps and note down the

correspondingmeterreadingsiv. Repeattheprocedureforaroundfivedifferentsetsaroundnoload,

halfloadandfullloadv. Switchofftheloadandsupply.

SlNo

PrimaryVoltage,V(volts)

PrimaryCurrent,I(amps)

W-meterReading(Divisions)

W-meterReading(watt)

Syvoltage,(volts)

Sycurrent(amps)

%Effecy

%Regn

Multiplyingfactororwattmeterconstant,

K=((Ratedvoltage)X(Ratedcurrent))/(Noofscaledivisions),watts/div

cos𝛷=


ExperimentNo:7

TITLE:REGULATIONOFANALTERNATOR

OBJECT:Toperform theopen-circuit and short-circuit testsona threephasealternatorandtodeterminetheregulationbysynchronousimpedancemethod

CIRCUITDIAGRAM:

LISTOFAPPARATUS:



THEORY:

Theregulationofanalternator is thepercentagedifferencefromno loadtofullloadvoltagewhentheloadissuddenlythrownoff,themachinebeingdeliveringtheloadatagiverpowerfactorandratedspeed,i.e.

%Regulation=((ІE0І)-ІVІ)/(ІVІ))X100%

The synchronous impedancemethodofdetermining the regulation involves thefollowingsteps;

i. Theopencircuitcharacteristicistobeplottedformthetest.ii. The short circuit characteristic is to be plotted from the test. This

characteristic is a straight line passing through the origin. Thecharacteristicsareshownbelow.

PROCEDURE:(O.C.TEST):

i. Connectthecircuitasshown.ii. Keeptheoutputvoltageforsupplyingtherotord.c.fieldatzero.Startthe

motor (M)with thehelpof thestarterkeeping the field regulatorof themotoratitsminimumposition.

iii. Adjustthefieldregulatorsoastoobtaintheratedspeedofthealternatorandmeasurethespeedbyatachometer.

iv. Increase the rotor field current gradually and note down the alternatorinduced e.m.f. and the rotor field current. Take about ten sets ofreadings….

v. Decreasethefieldcurrenttozeroandswitchoffthesuppliestothemotorandrotor

(N.B.:D.C.supplyusedforrunningthemotor(M)maybeusedtosupplytherotorfield also.But caremustbe taken so that theoutputof thepotential divider isinitialatzeroposition)

PROCEDURE:(S.C.TEST):

i. ConnectthecircuitasshownfortheS.C.testii. Keeptheoutputvoltageof thepotentialdividerso that thesupplyat the

rotord.c.fieldisatzeroiii. Withthefieldregulatorofthemotor(M)atitsminimumpositionstartthe

motorasbeforeandadjustthespeedofthealternatorattheratedvalue

iv. Very carefully adjust the rotor field current gradually in steps of 4-5numbers and circulate full load current in the static winding. Slightoverloadingisallowable.Notethesetsofreadinginalltheinstruments

v. Graduallydecreasetheexcitation intherotor fieldandswitchoff thed.c.supplies.

MeasurementofRa:Refertheconnectiondiagramshownbelow:

i. Withthecaseresistance(orlampload)off,switchond.c.supply.ii. Putonloadandnote3-4setsofreadingin“A”and“V”preferablytowards

highersideofcurrentsinstatorphasewinding(AN)andwithinratedvalue.iii. Switchofftheloadandsupply

OBSERVATIONS:

Let E1 be theO.C. voltage corresponding to a field current, If.When the statorwindingisshortedtheterminalvoltageiszero,meaningthatE1isbeingutilizedtocirculateS.C.currentI1againstthesynchronousimpedance,Zs.

Zs=(E1(opencircuitvoltage))/(I1(shortcircuitcurrent))

The effective or the a.c. resistance, Ra of the stator winding/ phase can bedetermined,asshownbelow.

The a.c. resistancemay be taken as 1.6 times the d.c. valuemeasured. HavingknownRa,

Xs= (Zs2-Ra2),ohms

Having known Ra, Xs, a phasor diagram can be drawn for any load and powerfactorasshown,where,

Sothattheregulatorofthealternatorcanbedetermined.

i. O.C.TESTSLNo Fieldcurrent,

If(amps)O.C voltage E0(volts)

RatedNR.P.M.

ii. S.C.TestSLNo Fieldcurrent,

If(amps)O.C voltage E0(volts)

RatedNR.P.M.

iii. MeasurementofRaSLNo V

(volts)I(amps)

Ra(ohms)

MeanRa(ohms)

Ra(a.c.)(ohms)

REPORT:

1. Determine the regulationof the alternator at¼th,½th, 3/4th and

thefull loadat .8(lagging)andunitypowerfactorofthe loadfromtheexperimental data. Plot thenecessary for regulationvs load atthepowerfactorgiven.

2. Derive the condition for maximum regulation of an alternator.Determinethevalueforthisalternator.

N.B. For O.C. first regulate the regulator to make speed 1500. Then take thereadings of If & V. Keep the variable point at maximum resistance. Increasecurrentbyrheostatslowly&takereadings.

NextforS.C.adjustspeedto1500,takereadingsofIfbyadjustingrheostato18.9AcurrentintheS.C.ammeter.


laboratory manual electrical machines and application s

Documents