Trx Oil Test Properties

7/23/2019 Trx Oil Test Properties

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BSc.EE.

January2014.

PROPERTIES OF TRANSFORMER OIL

THAT AFFECT EFFICIENCY.

DERICKNJOMBOGTANTEH.

SHAFIQYOUSEFALLIDDAWI.

DANIELSSEKASIKO.

School of Engineering,Department of Electrical Engineering,

Blekinge Institute of Technology, S-371 79 KarlskronaPhone: +46 - 455 - 38 50 00

Fax: +46 - 455 - 38 50 57


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ii

ThisthesisissubmittedtotheSchoolofEngineeringatBlekingeInstituteofTechnologyin

partialfulfillmentoftherequirementsforthedegreeofBachelorofScienceinElectrical

Engineering.Thethesisisequivalentto15ECTSpoints.

Contact:

DerickNjombogTanteh:

Email: [email protected]

ShafiqYousefAlLiddawi:

Email:[email protected]

DanielSsekasiko:

Email: [email protected]

Supervisor:

Dr.MattiasEriksson.

SeniorLecturer,

SchoolofEngineering,

BlekingeInstituteofTechnology,

Email:[email protected]

ToourParents:

DominicandBeatriceTanteh,

YousefandTamamAlLiddawi,

LivingstoneandRuthKiwanuka.


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TABLEOFCONTENTS

Chapter1:Introduction1

1.1ProblemStatement1

1.2Scope1

1.3Outline.2

Chapter2:Background.3

2.1Corona..3

2.2Pyrolysis(Overheating)3

2.3Arcing4

2.4Transformers..4

2.5TransformerOils6

2.5.1Mineraloil7

2.5.2Vegetableoil.9

2.6OilTestingandanalysis..9

Chapter3:TransformerOilInsulatingProperties11

3.1Totalacidity.11

3.2Breakdownvoltage..12

3.3Viscosity...12

3.4Dielectricdissipationfactor(tandelta).13

3.5Specificresistance14

3.6Flashpoint..15

3.7Moisturecontent15

3.8Dielectricconstant(relativepermittivityr)..16


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3.9InterfacialTension..17

3.10DielectricStrength17

3.11Transformerinsulation(Paperinsulation)..18

Chapter4:TransformerOilAnalysis.19

4.1Partialdischarge(PD).19

4.2DissolvedgasAnalysis(DGA)...20

4.2.1DissolvedMoistureinTransformerOil..20

Chapter5:ExperimentalSetup...22

5.1Requirementsforexperiment..22

5.2ConditionsoftheoilSamples.25

5.3Breakdownvoltagemeasurementinoil.25

Chapter6:ExperimentalResultsanddiscussions....26

6.1VegetableOilexperiment..26

6.2MineralOilexperiments..31

6.3ComparisonbetweenVegetableandMineralOilCharacteristics..36

6.4Discussion.37

Chapter7:Conclusionandrecommendations...39

References..41


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Abstract.

Transformerexplosionscausedbydielectricfailureaccountforover50%ofthedisasters.Theaimof

thisthesisistoexamine,compareandoutlinethedifferences,infunction,asdielectricinsulators,

vegetablesoilhas,withrespecttothemineraloilusedinhighpowertransformers.Wewillfirst

considerthevegetableoilwhichhaslessdielectriccapabilitiesthanthemineraloilusedinpower

transformers.Laterintheexperiments,wewillfocusmainlytoexaminethebreakdownvoltage

property,aswetrytoaltersomepropertiesoftherespectiveoilsused.

Consideringthefactthatvegetableoilhaslowviscosity,withitschemicalcompoundsconstituting

lessmolecularmassescomparedtomineraloil,weendorse,fromourexperimentalfindings,that

mineraloilisindeedworthyandreasonabletobeusedasadielectricinhighpowertransformers.

Inthiswriteup,wehaveconsideredeleventransformeroilproperties.Intheexperimentproper,we

consideredonlytheacidity,whoseconcentrationinthetransformeroilincreaseswithagingifthe

transformer,moisture,andasuitableimpuritylikeNaOH(aq).Atfirstglance,onewouldbetempted

tothink,aswewere,thatsincetheincreaseinacidcontentoftheoildeterioratesitsdielectric

performance,anincreaseinalkalinecontentofthetransformeroil,wouldincreaseitsdielectric

ability;reversingtheacideffect.Butasweseeintheresultsfromourexperiments,thisisfalse.Wethinkthatthevisibledegradationoftheinsulatingpropertyoftheoil,withtheintroductionof

NaOH(aq),isbecauseitactsasanimpuritytosuitabledielectricfunction.

Fromtheexperiments,theheatingproceduresresultedintheproductionoftoxicgases.This

indicatedtheactuallossofchemicalstructureandsignificantbreakageofchemicalbonds.The

resultingchemicalcompositionoftheoildoesnotproducethesamedielectricpropertiesasthe

initialoilsample.

Also,herehasbeenconsiderableinconsistencyintheadditionofNaOH(aq)orHCl(aq)tobothoils.We

onlyaddedHCl(aq),beforeeverymeasurement,intwooftheexperiments.Theotherexperiments

wereeitherwithmoisture,orasingleadditionofsmallamountsofeitherHCl(aq)orNaOH(aq)before

heating;afterwhichseveralmeasurementsweretaken,atspecificintervals, asthemixturecools.

Wedidso,inthelatter,inwhichwehadonlyoneadditionofeitherchemical;becauseinreallife,

giventheshorttimeframeoftheexperiment,thetotalamountofacidintheoilhasanegligible

change.So,inafunctioningheatedtransformer,withinashorttimeframe,thereisactuallyavisible

tinydeteriorationinoilinsulationproperties.


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Chapter1:Introduction.

1.1

Problemstatement.

Electricalfaultsthatoccurinpowertransformersaccountforoverfiftypercentoftransformer

failuresexpendituresintheUnitedStates,withinafiveyearperiod[1].Thenumbersare

probablymoreinthedevelopingworldduetolowtechnicalabilitiestomaintainandrecyclethe

oil.

Fig1.1.1. Numberoftransformerfa ilures ,causesoffa ilure ,and

expenditure.

FromFig1.1.1,weseethatfiftypercentoftransformerfailuresexpendituresarecausedby

insulation,dielectric,andoilrelatedfaults.Theneedforbetterdielectricsandtransformeroils

forinsulationisunequivocal.

1.2 Scope.

Thereareseveralpropertiesoftransformeroils.Wehaveconsideredtheelevenmostcommon

ones.Agoodnumberofthesepropertiesareexperimenteduponbyusingthebreakdownvoltagetodeterminethevalueoftheparameterintheconsideredproperty.Acidity,moisture


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content,aswellasgeneralimpuritycontentaresomeofthepropertiesthatincreasewithageof

theoil,whileviscosity,flashpoint,specificresistance,transformerinsulation,interfacialtension

decreasewithage.Therespectiveincreaseordecreasearedetrimentaltothetransformer

functioning.Intheexperiments,theonlyparameterformeasurementweusedwasbreakdown

voltage(BDV);afteralteringacidcontent,impuritycontent,andmoisturecontent,whichareall

processingintheartificialagingprocess.

1.3 Outline.

Chapteroneintroducesthemaincauseforconcernfortransformerfailuresspecificallyinthe

UnitedStatesdielectricbreakdown.Themaincauseisasurgeinvoltage,followedbyalargecurrentsflowthroughadielectricgap.

TheSecondchapterexplainsstandardfindingsonphenomenaandprocessesrelatedtothe

studyoftransformeroilproperties.Theseincludethechemicalandcausesofthespecific

physicalpropertiesofthetestoils.

Inchapterthreeandfour,anextendeddiscussiononthetransformeroilpropertiesismade,

takingintoconsiderationtheelevenmostimportantones.Afurtherexaminationofthephysical

phenomenaofpartialdischargeandcorona,arcing,andpyrolysisisdoneinchapterfour.For

thecaseofpyrolysis,therespectivegasesfromthedecomposition,byoverheatingtheoil,are

reexamined.

Theexperimentalsetup,results,anddiscussionisdoneinchaptersfiveandsixrespectively.

Here,applyingahighvoltageacrosstheelectrodes,inatreatedoilsampleisourmaintoolto

examinethepropertiestested.Thepropertiesincludeacidity(HCl(aq)),moisture(water)andan

impurity(NaOH(aq)).

Thelastchaptercontainstheconclusionandrecommendationsfromsomeworldleading

companiesinthisarealikeABBinSweden.


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Chapter2:Background.

Inapowertransformer,thelightemittedbyasparkoccursbecauseofthematerialmedium

fluorescesasaresultofcollisionsfromtheelectrons.Ascollisionsoccurbetweenelectronsand

moleculesinthegap,electronontheatomshellsareexcitedtohigherenergylevels.Whenthe

electronsnolongergetmoreexcitation,thefallbacktothepreviousenergylevel,releasingthe

extraenergyintheformofheat,lightandsometimessound.[2]Thisiscalledthephotoelectric

effect.Thesparkscannotforminavacuumbecausetherewouldbenoairparticlesforcollision.

Withoutinterruptingelectromagnetictransitions,onecanseethespark.However,inoil,itis

possibleforthesparkstooccurbutnotasreadilyasinair.ItisalsoworthmentioningthatOil

helpsextinguisharcs.Mostpowertransformersthatuseoilhavethreedielectricmaterials;oil,

paper(onthewallsandwindings),and/orpaintonthewindings.Thesethreelinesofdefense

istomakesurethatsparks,arcsorpartialdischargeofanykindshouldnotoccurinthe

transformer.

2.1Corona.

Therearesomevitaldevelopmentalstepsforapositivecoronadischargetooccur.[3]

First:apositiveandnegativeelectrodecharacteristicconfigurationmustbemet.

Second:Ahighvoltageshouldbesupplied.

Third:Aroundthegapbetweentheelectrodes,freeelectronsshouldbeafloat.

Fourth:Accumulationofelectronsshouldbuildupinthegap,readytocauseanavalanche

breakdown.

Fifth:theupanddownchangeofelectronsfromhigherenergytolowerenergylevelsproduce

photons;asenergyisgainedandlost,whichinturnenergizenewchargecarriersaroundthegap

Sixth:The

initial

avalanche

breakdown

causes

acascade

effect

tocharges

closer

tothe

cathode

(negativeelectrode).

2.2Pyrolysis(Overheating)

Pyrolysisbeginwhentheoilheattoabout2000C.Atthistemperature,onlyhydrogenismost

likelytobethegaseousproductofthemilddecomposition.Astemperatureissteadilyincreased

toabout7000C,thereisalmostatotaldecompositionoftheoil,givingamixtureofmethane,

ethane,ethylene,acetylene,andhydrogengasasproductsofseveredecomposition.[4]

analytically,weconcludethatheatingincreasesoildecomposition.


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2.3Arcing.

Anarcisaluminouscurrentdischargeformedwhenalargecurrentforcesadielectricgapto

conductthelargecurrentbetweentwoelectrodes.[5]

Themaindifferencebetweenarcingandcoronaisthat;incorona,theaccumulationofcharges

issustained,resultinginabreakdown.Inarcing,asurgeincurrentcausesanimmediate

breakdownofthedielectric,releasinghugeenergy.Consequently,arcsaremoredangerous,

releasemoreenergy,andmoredifficulttohandle.

Arcsoccurusuallyduringvoltagetesting,shutdownandstartupofasystem,accidentalcontact

withenergizedcomponents,miscalculationsofratingparameters,rusting,decayand

degradationoftheequipmentthatcancausepotentiallyharmfulshortcircuitpaths.

Technologyhashowevermadearcsusefulinwelding.ThiscameasresultofthedesignofArc

weldingtransformers.[6]

2.4Transformers.

Wewill

begin

with

asimple

transformer

like

the

one

pictured

below[7a].

Fig1.1.1. Asimple stepup transformer.


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Transformersweredevelopedfromtheknowledgeofthelawofelectromagneticinduction.

Transformerscanbeeitherstepuptransformer;wherethenumberofprimaryturnsislessthan

thenumberofsecondaryturns,seeFig1.1.1,orstepdowntransformer;wherethenumberof

secondaryturnsislessthanthenumberofprimaryturns.

Aseverepartialdischarge(PD)betweenanynumberofturnsinanypartofthetransformer,

resultsintheaffectednumberofturnstobehaveasone reducingthetotalnumberofturns.

Evidently,fromtheformulabelow,thenumberofturnsaffectsvoltageeitherway,hence,

efficiency.

N2/N2=V1/V2=I2/I1..(1)

Wherepower=P,current=I,voltage=V,Numberofturns=N.

Inanidealtransformerthepowerinputvalueissameasthepoweroutputvalue.

Power=P=V1xI1=V2xI2.............(2).

Inarealworld,equation(2)becomesinvalidsincethereareusuallylossesinafunctioning

transformer.[7b]

Efficiency=Poweroutput/Inputpower.

Efficiency=1

.

Wherelosses=cupperlosses+ironlosses.

Thetransformerwindingsmust,therefore,beinsulated.Theoperationofthetransformer

producesheat.Thesearethemainfocusofthisthesis:heatandinsulation.

Transformeroilsperformatleastfourbasicfunctionsinanoilimmersedtransformer.Oil

providesinsulation,cooling(heatdistribution),andhelpsextinguisharcs(voltaicdischarge).Oil

alsodissolvesgasesgeneratedbyoildegradation,deterioration,andgasesandmoisturefrom

whateveratmospheretheoilisexposedto.Closeobservationofdissolvedgasesintheoil,and

otheroilproperties,providesthemostvaluableinformationabouttransformerhealth.

DissolvedGasAnalysis(DGA)isthemostimportanttransformerdiagnostictool.

Themineraloil,withthemainrolesofinsulatingandcoolinginpowertransformers,issimilarto

thebloodinhumanbody.Consideringtheworldwideneedforhighefficiencyofpower

transformersandtherisingpriceoftheoil,wehavetocontrolandmonitorthetransformeroil

characteristicsconsistently.Thereareseveralcharacteristicswhichcanbemeasuredtoassess

thepresentconditionoftheoil.Usingacombinationofthesediagnostictestsallowstheoilto

beexaminedforitsbehaviorwithrespecttovariouscharacteristicsasageincreases,whether

thechangesareduetothermal,dielectricorchemicaleffects.Thebenefitofexamininghow

quicklytheoilisagingisthatitpermitstheoiltobeusedaslongaspossible.Ifthisisdone

properly,areplacementorpurificationcanbedonebeforeitcancausedamagetothecontainer

orothermaterialsinsidethetransformer,ortotheenvironment.Wedonotwantthe

transformerstoundergoleakages,explosions,sparks,firesoranykindofdestructiontoitselfor

theenvironment.Thetransformermineraloilisoneofthemostexpensiveextractsproducedby

itsrefinementofcrudeoil.Refiningisthecollectivetermfortheprocessesinvolvedinchanging


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thecrudeoilintooilwiththerequiredpropertiesforaparticularapplication.Onlyaboutthree

percentofthecrudeoilisappropriateforproductionoftransformeroil.Becauseofthe

importanceofthepowertransformersinelectricalnetworks,permanentlytakingcareoftheoil

qualityisvital.

Insulatingoilinatransformerduringoperationissubjectedtoheat,oxygenandelectrical

discharge,whichmayleadtoitsdegradationespeciallythroughtheprocessofoxidation.[8]This

severelycausestheoiltocarryoutitsprimaryfunctionsofinsulationandheattransferasaging

productsreduceelectricalpropertiesandcoolingefficiency.Oxidationproducts,suchasacids

andconsequentlytheformationofsludge,arealsovitalinagingacceleration.Therefore,

monitoringandmaintainingoilqualityisessentialinensuringthereliableoperationofoilfilled

electricalequipment.Eveninidealconditions,oilagesanddegradesovertime,asitsuseful

servicelifeisfinite.

Therateofagingisnormallyafunctionoftemperatureandmoisture,aswewilldiscusslaterinDissolvedgasAnalysis(PDA).Oilwillagerapidlyathightemperaturesandmoistureactsasa

catalystforitsagingTherefore,oilaginginoilfilledtransformersisinevitable.Therearesome

catalystspresentinatransformerthatcouldaccountforoildegradation.Theseincludecopper,

paint,varnishandoxygen[9].Themainprocessofoildeteriorationisoxidation,whichcauses

somepolarcompoundstobeformed.Theseoxidationproductswillhaveadeleteriouseffect

endresult,givingrisetothevariationweseektogetourconclusion.Theprincipaloilproperties

areclassifiedintothephysical,chemicalandelectricalcharacteristics.Someofthemore

importantpropertiesoftheoilareviscosity,specificgravity,flashpoint,oxidationstability,total

acidnumber,dissipationfactor,volumeresistively,breakdownvoltage,anddielectricconstant.

2.5Transformeroils.

GenerallytransformerOilexistsintwotypes[10]:

ParaffinbasedTransformerOil

NaphthabasedTransformerOil

Oncomparisonofbothtransformeroils,paraffinoilislessoxidizedthanNaphthaoil,though

oxidationproductforinstancesludgeinthenaphthaoilisextremelysolublecomparedto

paraffinoil.Hencethesludgecontentinnaphthabasedoilisneverprecipitatedatthe

transformerbottom.Thereforeitallowsoilcirculation,hencethetransformercoolingsystem

runningnormally.ForparaffinoilwhoseoxidationrateislowercomparedtothatofNaphthaoil

issludgeandinsoluble,itisprecipitatedatbottomofthetankthereforehindering

thetransformercoolingsystem.

Goodtransformeroilactsasaliquidinsulationinanelectricalpowertransformeranddissipates

heat from thetransformer (coolant).Also,because ithelpspreservethecoreandwindingsof

thetransformerfortheyaredipped in it.Duetooxidationsusceptibilityofthecellulosepaper


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insulationmade for theprimaryand secondarywindings, the transformeroilpreventsdirect

contactofatmosphericoxygen.

2.5.1Mineral

oil

Petroleumoilhasbeenusedfortransformeroilsince1891.Anoverviewofthesourceand

purificationprocessofpetroleumisasfollows:[11]

a).Crudepetroleum

Crudeoilcomesfromtheextractionsourceknownascrudepetroleum.Itcontainslongchains

ofcarboncompoundsandalsosmalleramountsofsulphurandnitrogen,depositedovermillions

ofyearswithhighpressureundertheearthscrust.Basically,hydrocarbonmoleculescanbe

classified

into

three

main

groups

as

described

below:

-Paraffin:

Thisthemaincontentofpetroleum,intermsofpercentage.

-Cycloalkanes:

Characteristicallycontainaringstructurewithsixcarbonatoms(withinsixmemberedrings)or

fourteencarbonatoms(withinthreememberedrings).

-Aromatics:

Ithassixmemberedringstructures,fallintotwogroups:monoaromatics(singlerings)and

polyaromatics(twoormorerings).

b).

Refining

petroleum

Crudepetroleumhastoberefinedtosomeoftheseclassifiedpetroleumproductslikegasoline,

kerosene,liquidpetroleumgas(LPG),lubricatingoils,etc.Fractionaldistillationisthenameof

theprocessofrefiningofcrudeoil.Itcomprisesavacuumdistillationcalledafractionating

towerwhereseveralcatalystsanddifferenttemperaturesareusedtogetthedifferent

products.[12]Youcanworkouttheformulaofanyofthemusing:CnH2n+2.[13]

Cycloalkaneshaveaclosedring.Theyareoneofthreemainconstituentsofcrudeoil,theother

twobeingalkanesandaromaticcompounds.

Cycloalkanesareclassifiedintovarioussizescycloalkanes,wherecyclopropaneandcyclo

butanearethesmallestsizedcycloalkanes. cyclopentane,cyclohexane,cycloheptanearethe

commonones,cyclooctanethroughcyclotridecanearethemediumones,andtherestare

largerones.

Cycloalkanesaresimilartoalkanesintheirgeneralphysicalproperties,buttheirringstructures

allowthemtohavehigherphysicalpropertieslikeboilingpoints,meltingpoints,anddensities,

thanalkanes.Theirmeltingandboilingpointsare10Kto20Khigherthantheircorresponding

straightchainalkanes.[13]


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Theclassificationofalkanesisderivedfromtheirsizesandshapesfromthechemicalstructure.

Methane,beingthesimplestofall,hasjustonecarbonatom.Thenethanehastwocarbon

atoms,propanewiththree,butanewithfour,andsoon.

Boilingpoints,meltingpoints,anddensitiesincreaseasthenumberofcarbonatomsincrease.

Thelongerthecarbonchain,thehigherthetotalmolecularmassofthemolecule;thus,increase

indensity,boilingpoints,meltingpoints,etc.

Fig2.5 .1 Structure ofbenzene.

Benzene,whosestructureisdepictedinFig2.5.1isapetroleumcomponent.[14]Chemical

processeslikeselectivesolventextraction,sulphuricacidextraction,fractionaldistillation,earth

filtration,Oxidation,halogenation,Hydrogenation,cracking,redistillation,filtration,and

dehydrationareusedintheformationandmodificationoftheseorganiccompounds.

Mineraloilrefinedfromcrudeoilisawellknown,goodinsulatingmaterialhasgoodelectrical

properties,agingbehavior,andlowviscosity.Othercharacteristicslikethelowrelative

permittivitygiveanadvantageregardingtheirbehaviorforinsulationintransformeroperation.

NB:Mineraloilisproducedbyseveralcountriesandisrelativelyinexpensive.But,themain

drawbackoccurswhenthereisatransformerleakageandthemineraloilwillcontributeto

environmentalhazardsbecauseofitspoorbiodegradability.

2.5.2Vegetableoil.

Thereexistbothsyntheticandnaturalvegetableoils.Esteroilshaveafunctionalgrouplikethe

onebelow.[15]


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Fig2.5.2. GeneralStructure ofan estermolecule.

RandR1representalkylgroups.Thetwooxygenatomsbondedtothecarbonatomconstitute

thefunctionalgroup.Theremainingcarbonatomscouldbelongchainsofcarbonmolecules

(complex)orassimpleastheseintheFig2.5.2.Thegeneralformulaandtheesterification

process(ProductionofEsters,RCOOH)istheequilibriumreactionbetweenacarboxylicacidand

alcohol(R1OH).Water(H2O)istheby product.

RCOOH+R1OHRCOOR1+H2O.

Esterscanbeextractedfrompalmnuts,soybeans,groundnutsetc.

Syntheticestersalsoexist.Theyaremadefrompetroleum.

2.6OilTestingandanalysis.

Statisticsproofthatmostdestroyedtransformerssufferedfromseveralconditionssuchas

overloadcondition,which,moreoftenthannot,isthemaincauseoftransformerfailures,as

discussedandshowninthefirstchapter.Othercomponentssuchasthematerialofthecore

andtypeoflaminationarealsovital,buttheinsulationsystemplaysoneofthemostimportant

rolesinthetransformerslife,courtesyofthestatisticsofmosttransformerfailures.

Acoupleoftestsareviewedinourstudy;knownasDissolvedGasAnalysis(DGA)andPartial

DischargeMeasurement(PD).Thedissolvedgasanalysis(DGA)iscarriedoutontheaged

samplestopredicttheincipientfaults.Thoughthereisnodirectmethodtodetectthese

incipientfaults,itisknownthatthesefaults,especiallyintheformofoverheating,

arcingorpartialdischarge,developcertaingaseoushydrocarbons,whichareretainedbythe

insulatingoilasdissolvedgases.Thustheevaluationofthesegascompositionsandtheir

interpretationknownasDissolvedGasAnalysis(DGA)seemstobeoneofthelifesaving

diagnostictestsonconditionmonitoringoftransformers.

Theearlydetectionofpartialdischargepresentinatransformerisveryimportantto

avoid/reducethelossestothecatastrophicfailureoftransformer.Also,oncethePDisdetected,

thelocationofthesameisveryimportantsothatthedefectscanbepinpointedandsolved

effectively.


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Chapter3:TransformerOilInsulatingProperties

Transformer/Insulatingoilisahighlyrefinedmineraloilthatisstableathightemperaturesand

excellentinsulatingproperties.Itisobtainedfromfractionaldistillationprocesswithsubsequent

processingofcrudepetroleum.Ithastwomainfunctionstoinclude:

Actingasaliquidinsulationinanelectricalpowertransformerandsecondlydissipatingheatof

thetransformer(coolant).Also,becauseithelpspreservethecoreandwindingsofthe

transformerfortheyaredippedinit.

Duetooxidationsusceptibilityofthecellulose(paperinsulation)madeforthewindings,the

transformeroilpreventsdirectcontactofatmosphericoxygen.[16][17]

TheTransformerOilparametersarecategorizedas:

Electrical Parameters Dielectric Strength, Specific Resistance, Dielectric Dissipation

Factor,ChemicalParametersWaterContent,Acidity.

PhysicalParametersInterFacialTension,Viscosity,FlashPointandothersasexplained

indetailbelow.

3.1Totalacidity

Totalacidityalsocalledtotalacidnumber(TAN)referstothemeasurementofaciditythatis

gottenbytheamountofpotassiumhydroxide(expressedinmilligrams)whichisrequiredto

neutralizethehydrogenions(H+(aq))inonegramofoil.Thetotalacidnumbervalueshowstothe

crudeoilrefinery,thepossibilityofcorrosionproblems.Tofindthetotalacidity,different

methodscanbeusedtoinclude:

Potentiometrictitration;wheretolueneandpropanolaredissolvedwithasampleandalittle

waterthentitratedwithalcoholicNaOH(aq).Areferenceelectrodeandaglasselectrodeis

immersedinthesampleandconnectedtoavoltmeter/potentiometer.Themeterreading(inmillivolts)isplottedagainstthevolumeofthetitrantthentheendpointtakenatthedistinct

inflectionoftheresultingtitrationcurvecorrespondingtothebasicbuffersolution.

Colorindicatingtitration:ArightpHcolorindicatorforinstance,phenolphthalein,isused.

Titrantisaddedtothesamplebymeansofaburetteandthevolumeoftitrantusedtocausea

permanentcolorchangeinthesampleisrecordedandusedtocalculatetheTANvalue.

Transformeroilacidityisnevergoodfortheperformanceofthetransformer,ifatanymoment,

oilgetsacidifiedthenthemoisturecontentintheoilshallgethighsolubilitylevels.Thisshall

lateraffectthepaperinsulationofthewinding.Acidityincreasestheoxidationprocessinthe

transformer

oil.

Acid

presence

also

accelerates

rusting

of

iron

in

combination

with

moisture.

The


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KOHinmgisusedtocombatacidityofoilbyneutralizingitineverygramofoil.Thisisreferred

toasneutralizationnumber.[18]

3.2Breakdownvoltage

Thebreakdownvoltageofaninsulatorreferstotheminimumvoltagewhichresultsinpartofan

insulatortobecomeanelectricconductor.Itisusuallyauniquepropertyofaninsulatorthat

definesthemaximumvoltagedifferencethatcanbeputacrossthematerialbeforeitsinsulator

conducts.Insolidinsulatingmaterials,thisoftencreatesaweakenedpathwithinthematerialby

creatingpermanentmolecularorphysicalchangesbythesuddenhighcurrent.

Thebreakdownvoltageofamaterialisnotadefinitevalue.Breakdownvoltageisalsoreferred

toas withstandvoltagewheretheprobabilityoffailureatagivenvoltageissolowthatitis

consideredatthemomentofdesigninginsulation,withassurancethatthematerialwillnotfail

atthisvoltage.

Thereexiststwowaysformeasurementofbreakdownvoltageofamaterialwhichincludethe

impulsebreakdownandtheACbreakdownvoltages.ACvoltagesarethelinefrequenciesofthe

mains,whilewiththeimpulsebreakdownvoltages,theyaresimulatinglightningstrikes.[19]

3.3Viscosity

Herewemainlyfocusofliquids/fluidsandtheviscosityofafluidreferstoameasureof

itsresistancewithreferencetoitsgradualdeformationbyshearstressortensilestress.

Itcorrespondstotheinformalnotionof"thickness";ifwefocusonliquids.Forexample,water

hasalowerviscositycomparedtohoney.Viscosityisbroughtaboutbyhighfrictionbetween

neighboringmoleculesofthefluidthataremovingatdifferentspeeds.Onforcingafluidintoa

tube,itwillmovefasterslowestnearthewallsofacontainerwhenpouredout.Thereforea

littlestressisneededtoovercomethefrictionbetweenlayersandkeepthefluidmoving.Sogenerally,viscosityofafluidishighlydependentontheshapeandsizeofitsparticlesplus

attractionsacrosstheparticles.[20]

Atverylowtemperatures,whenviscositycanbeobservedinsuperfluids.Afluidwithno

resistancetoshearstressiscalledanidealfluid.Otherwiseallfluidshavepositiveviscosity.For

instanceiftheviscosityisveryhighatpitch,thefluidismostlikelyto appearasasolidinshort

while,Aliquidwithaviscositygreaterthanwaterisreferredtoasaviscousliquidandtheother

liquidwhoseviscosityislowerthanthatofwateriscalledamobileliquid.


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WithemphasisonViscosityoftransformeroil,viscosityreferstooppositiontoflowatallfactors

constant(normalcondition).Withreferencetotransformeroil,resistancetoflowsimply

describesoppositiontoconvectioncirculationofoilinthetransformer.

Oilusedintransformerswithlowviscosityisessentialandsimultaneouslyimportantinthat,

transformeroilviscosityshouldnotchangemuchiftemperatureisdecreased.Itshouldbe

notedthatallliquidsgetmoreviscouswithdecreaseintemperature.Lowviscosityisonethat's

betterrecommendedinordertoprovideenvironmentforlowresistancetoconventionalflowof

oilhencepropertransformercooling.

Itisworthmentioningthatviscosityofaliquid,moreoftenthannot,isusedtodeterminingitas

acoolingagent.Thustransformeroil,whichisthickandscarcelyfacilitatesconvection,inhibits

thespreadofheatbyconvectioninatransformer.However,sinceeveryliquidbecomesless

viscoswithtemperatureincrease,convectiontakesplacetofacilitatecoolingaswell.[21]

3.4Dielectricdissipationfactor(tandelta).

Dissipationfactorreferstoameasureoflossrateofenergyofamodeofoscillationina

dissipativesystem.Itisaswellreferredtoaslossfactor.Thedielectricdissipationfactorofan

insulatingmaterialisthetangentofthedielectriclossangle.Thisisanangleinwhichthephase

differencebetweentheappliedvoltageandconsequentialcurrentdivergesfrom/2rad,atthe

pointwherethecapacitor'sdielectricencompassesonlyofinsulatingmaterial.

Thedielectricdissipationfactorinrelationtotransformeroilisbrokendownasinthissimple

description:Thelossangleisavitalpropertyofdielectricoil.Withanidealdielectricmaterial,

voltageandcurrenthasaphaseangleas90betweenthem.Butbecauseofimpurities,certain

leakagecurrentflowsthroughthedielectricandactualphaseangleisslightlylessthan90.A

risingdissipationfactorisanindicationofoilcontaminationoroilageing.Polarcomponents

stronglyinfluencethedissipationfactorandarethereforeaverysensitiveparameter.Thetan

deltaoftransformeroilhappenswhenaninsulatingmaterialisplacedbetweenthelivepartand

groundedpartofanelectricalcircuit;resultinginleakagecurrentflow.Theinsulationideally

leadsthevoltageby90o

becauseoftheinsulatingmaterialbeingdielectricnaturally,therebycreatinginstantaneousvoltagebetweenlivepartandgroundoftheequipment.Inapractical

world,noinsulatingmaterialsareperfectdielectricinnature.ThisissimplycalledDielectric

DissipationFactororsimplytandeltaoftransformeroilcourtesyoftangentofanangleslightly

shortof90oduetoimperfectionsininsulatingmaterialsandtheirdielectricproperties.[22]

Wearegoingtoillustratetheaforesaidwithagraphthatillustratesthatasthetransformer

ages,impuritiesincrease,thereforedecreasingdielectricresistance.Impuritieswillincrease

currentflowthroughthedielectric.[23]Theangledeltaislessthan900whentheimpuritiesare

more.


18/48

13

NB:TheTanDeltatestworksontheprinciplethatanyinsulationinitspurestateactsasa

capacitor.ThetestinvolvesapplyingaverylowfrequencyACvoltage.Thevoltageisgenerally

doublethe

rated

voltage

of

the

cable

or

winding.

Alowfrequencycausesahighervalueofcapacitivereactancewhichleadstolesserpower

requirementduringthetest.Besides,thecurrentswillbelimitedenablingeasiermeasurement.

Inapurecapacitor,thecurrentisaheadofthevoltageby90degrees.Theinsulation,inapure

condition,willbehavesimilarly.However,iftheinsulationhasdeterioratedduetotheentryof

dirtandmoisture,thecurrentwhichflowsthroughtheinsulationwillalsohavearesistive

component.

Thiswillcausetheangleofthecurrenttobelessthan90degrees.Thisdifferenceintheangleis

knownasthelossangle.ThetangentoftheanglewhichisIr/Ic(opposite/adjacent)givesusan

indicationoftheconditionoftheinsulation.Ahighervalueforthelossangleindicatesahigh

degreeofcontaminationoftheinsulation.

ReresistancewillreduceasFig3.4.1belowillustrates.[17]

Fig3.4.1. Tandeltaillustration.

3.5Specificresistance.

Specificresistancewithreferencetoelectricalresistanceofanelectricalconductorreferstothe

oppositioninthepassageofanelectriccurrentthroughaconductor.TheSIunitofelectrical

resistanceistheohm(),andthatofelectricalconductanceisSiemens(S).[19]

Anyconductorwithspecifiedcrosssectionhasaresistancerelativelyproportionalto

itsresistivity,

length

and

isinversely

proportional

toits

cross

sectional

area.

Apart

from

superconductors,whichhavearesistanceofzero,therestofthematerialsshowsome


19/48

14

resistanceatanygivenpointintime.Aconductor'smaterialandtemperaturegreatly

determinesitsspecificresistance.

Resistance(R)

of

an

object

is

defined

as

the

ratio

of

voltage

across

it

(V)

to

current

through

it

(I).

Andconductance(G)istheinverse:

Wherevoltage(V)andcurrent(I)aredirectlyproportionalforawiderangeofmaterials.This

automaticallysetsRandGasconstantsbutcanaswelldependonotherfactorslike

temperatureasearlierexplained.

SpecificResistanceoftransformeroilfocusesonmeasureofresistancebetweentwoopposite

sidesof

one

cm3

block

of

oil,

the

standard

unit

is

taken

as

ohm

cm

at

aspecific

temperature.

The

resistivityofoilreducesdrasticallywhentemperatureincreases.Whenatransformerhasbeen

shutoffforalongtime,itsoiltemperatureshallbethesameasthatatambient.Withafullload,

thetemperaturecanriseupto90oCespeciallyatanoverloadedcondition.Thereforeinsulating

oilresistanceshouldbeabletoaccommodatetheneedsofboththehighandlowtemperatures;

thatisatambientlevel.

Itishighlyrecommendedtomeasurespecificresistivityoftransformeroilbothat27oCaswell

as90oChencecoveringtheexpectedhightemperaturesandminimum.

Thestandardsareasfollows:

Theactual

minimum

standard

for

specific

resistance

of

transformer

oil

at

90oC

is

35X

1012

ohm

cm(maximum)andatthelowerboundaryisestimatedat27oCis1500X10

12ohmcm

(minimum).[25]

3.6Flashpoint.

Theflashpointofachemicaloranyvolatilematerialisthelowesttemperatureatwhichitcan

evaporatetoformanignitablemixtureinairorcombustibleconcentrationofgas.Thispoint

indicateshow

hard

or

easy

this

volatile

material

may

burn.

Materials

with

higher

flash

points

are

lessflammableorhazardousthanchemicalswithlowerflashpoints.Determiningaflashpoint

requiresanignitionsource.Theflashisnotdependentonthetemperatureoftheignition

source.

Mineraloilisaderivedproductofcrudepetroleum.Athighertemperatures,itwillvaporize.

Afteracertaintemperature,themixtureofthisoilvaporandatmosphericairproducesahighly

combustibleproductwhichiseasilyignitablebyanykindofspark.Anyburningfireoropen

flamewillnotnecessarilyignitethegasbutahotsurfacelikeaheaterwilldoforchemicalswith

morethanhighhazard.


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15

Theflashpointhascommonlybeenusedtoexplainanddistinguishliquidfuel,andaswellhelp

uniquelyidentifythefirehazardsofliquids.

SobasicallyFlashpointmeansbothflammableliquidsandcombustibleliquids.Various

standardsfordefiningeachtermexist.

Thiscanbeevidencedmoreasfollows;Liquidswithaflashpointlessthan 37.8Care

consideredflammableandthosewithaflashpointabovethepreviouslymentioned

temperaturesareconsideredcombustible.

Thistemperatureistheflashpointoftransformeroil.Generally,140Cistheminimum

thresholdflashingpointforstandardpowertransformers.

Flashpointwithreferencetotransformeroilappliesinthesamewayashasbeenexpressed

abovefortheotherliquids.Itisthetemperatureatwhichoilevaporatestoproducea

flammablemixturewithair.Themainimportanceofthemixtureistobrieflygiveaflashon

applicationofflameunderstandardcondition.

Thisprocessisveryvitalforitsignifiesthechancesoffirehazardinthetransformerforthat

reasonahigherlevelsoftemperaturepointsoftransformeroilflashpointaredesired. [25]

3.7Moisturecontent.

Moisturecontentisdescribedastheamountofwatercontainedinamaterial,suchassoil soil

moisture,apple,foodandothers.Moisturecontentisusedinbothtechnicalandscientificareas

plusdaytodaylifeactivities.Itisoftenusedinrationswhichvaryfrom0tomeanwhenthe

materialiscompletelymoisturefree(dry)uptothevalueofthematerials'beingporousat

saturationpoint.Themoisturecontentisalwaysmeasuredinvolumeormassascontainedin

thematerialinfocus.

Waterisaveryundesirablepollutanttotransformeroilandotherinsulatorsinatransformer.

Firstly,consideringmoistureinoil,moisturemakestheoillessthickwithalowerboilingpoint

thanoil.Moisturecontentisadirectproportionalitytotransformeroilaging.

Secondly,thepaperwinding,whichisalsoaninsulatorandadielectricintheoiltransformer,is

alsoadverselyaffectedbymoisture.Themoistureslowlysoaksthepaperasthetransformeroil

ages.Asoakedpaper,ontransformerwindings,decreasesinsulation,andthusthetransformers

functioningandefficiency.Whenthetemperaturehasincreasedinthetransformer

environment,thisverysoakedpaperagainreleaseswaterintothetransformeroil.Thisleadsto

oxidation,hence,increasestheamountofacidandwater.Thiscausesoilqualityreductiondue

tooildecomposition.[19]

Fortheabovereasons,itishighlyrecommendedtoavoidwaterintransformeroilforincreased

performance.


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16

3.8Dielectric

constant

(relative

permittivity

r)

Relativepermittivity,inthiscontext,isthemeasureoftheresistanceencounteredinthe

formationofelectricfieldsbetweentheelectrodesintheoilinsulationmedium.

Adielectricmaterialisanelectricalinsulatorthatgetspolarizedwhenanelectricfieldisapplied

toit.Whenadielectricisplacedinanelectricfield,electricalchargesneverflowthroughthe

materialascomparedtothewaytheyflowinaconductor;theyjustslightlyshiftfromtheir

meanequilibriumpositionscausingdielectricpolarization.Theeffectofdielectricpolarizationis

that:positivechargesaredisplacedtowardsthefieldandnegativechargesshiftintheopposite

direction.

Dielectricconstantisanelementofanelectricalinsulatingmaterialwhichisequaltotheratioof

thecapacitanceofacapacitorfilledwiththegivenmaterialtothecapacitanceofanidentical

capacitorinavacuumwithoutthedielectricmaterial.Asaresult,aninternalelectricfieldis

createdthatreducestheoverallfieldwithinthedielectricitself.Moleculesofadielectric

materialthatareweaklybondedshallbepolarizedandtheiraxisofsymmetrywillgetre

organizedtothefield.[26]

Studiesfocusedondielectricpropertiesemphasizestorage,dissipationofelectricandmagnetic

energyinmaterials.

Amaterialwitharelativepermittivityequalingtoafrequencyofzero isreferredtoas itsstatic

relativepermittivity. [27]

3.9InterfacialTension.

Thisisdescribedassurfacetensionatthesurfaceseparatingtwononmiscibleliquids.Itisa

tensionwithacontractivetendencyofthesurfaceofaliquidthatgivesitthepotentialtoresist

anexternalforce.Whatactuallyhappensis;allmoleculesatthesurfaceoftheliquidforma

weakbondwitheachothercreatingasurfaceblankettotheothermoleculesoftheliquid

beneath.Agoodexampleisfloatingobjectsonthesurfaceofwater,eventhoughtheyaremore

densecomparedtowater.[19]

Interfacialtensionhasdimensionofenergyperunitarea,thiskindofenergyisusedcommonly

insurfacetensionorsurfacefreeenergy.

Cohesiveforcesbetweenliquidmoleculescreateinterfacial/surfacetension.Whenreferringtoa

heavyorbulkoftheliquid,everymoleculeisseparatedequallyineverydirectionbyneighboringliquidmoleculeshenceanetforceequalingtozero.Themoleculesatthetopoftheliquidhave


22/48

17

noneighboringmoleculesontopofthemsotheyareonlypulledinwardsorneighboring

moleculesunderthem.Asaresult,internalpressurewillbecreatedcausingtheliquidsurfaces

tocontracttotheminimalarea.

Surfacetensionisresponsiblefortheshapeofliquiddrops;dropletsofwatertendtobepulled

intoasphericalshapebythecohesiveforcesofthesurfacelayereveniftheyareeasilyde

shaped.Withoutforcesforinstancegravity,dropsofalmostallliquidswouldnormallybe

sphericalwhichshapereducesthenecessary"walltension".

Alsowithemphasistoenergy,moleculesincontactwiththeirneighborsareinalowerstateof

energythaniftheywerenotincontactwithadjacentneighbors.Insidemoleculeshavemany

neighborsasmuchastheycouldbutthemoleculesontheboundarymissneighborsandso

automaticallyhavehigherenergy.Therefore,ifaliquidistoreduceitsenergystate,thenumber

ofmoleculesofhigherenergyontheboundaryshouldbereduced.Thiswilldefinitelyreducesurfacearea.

Withminimizingthesurface,itwillhaveasmoothshapehencehighenergywillbegained,and

gravitationalpotentialenergyshallaswellbereduced.

Withsurfacetensionisresponsibleforseparationofoilandwaterduetotensioninthesurface

betweendissimilarliquids.Newlyacquiredtransformeroilshowshighinterfacialtensionwhile

contaminants,duetooxidation,lowertheInterfacialtension.Thisphenomenonisusefulin

determiningthepresenceofpolarcontaminantsandtransformeroildecayproducts.[28]

3.10DielectricStrength.

Thetermdielectricstrength(canaswellmeanvoltagebreakdown)hasdifferentmeanings

dependingontheprimaryfocus,withreferencetoaninsulatingmaterialitreferstothe

maximumelectricfieldstrengththatthematerialcanwithstandcontinuouslywithoutbreaking

down;tobespecific,withoutexperiencingfailureofitsinsulatingproperties.[19]

Withmajorfocusontransformers,dielectricstrengthappliestotransformeroil.Thedielectric

strengthisdeterminedtakingnoteofatwhatvoltage,sparksbetweentwoelectrodesimmersed

inoilandaspecificgapbetweenthem.Lowvalueofdielectricstrengthshowspresenceof

moistureandmaybeotherconductingsubstancesintheoil.Thisisdonewithabreakdown

voltagemeasuringkitinwhichonepairofelectrodesisfixedandhasagapmeasuringabout

2,5mmapart.Thenvoltageshallbeappliedtothepairofelectrodes.

Withcarefulincreasingofvoltageonbothelectrodes,criticalobservationshouldthenbetaken

onwhenthesparksbetweenelectrodeshappen;exactlywhenthedielectricstrengthof

transformeroilbetweenelectrodeshasbeenbrokendown.[29]


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18

3.11Transformerinsulation(Paperinsulation)

Paperinsulationisusedforseveralinsulationpurposesintheelectricalfield;severalelectrical

insulationpapertypesexistandareusedinmanyapplications,thisisbecausepurecellulosehas

unbelievablygreatelectricalproperties.Celluloseisanoutstandinginsulatoraswellasapolar

substance.Thisisbecauseofitshavingadielectricconstantsignificantlygreaterthanone.

Classificationofelectricalpaperdependsonthicknessfromlessthan1.5mmtoover20mils

(0.508mm)thickness.[19]

Moisturecontentintransformeroilisneveragoodcombinationforitinterferesgreatlytheoil

dielectricproperties.Thewatercontent inoilalsoaffectsthepaper insulationofthecoreand

windingof transformer. Paper isextremelyhygroscopic so it absorbs a lotofwater fromoil

whichaffectspaperinsulationpropertyplusloweringitslifespan.Withaloadedtransformer,oil

temperature increases, resulting in the solubility of water in oil increase. Hence the paper

releasesmoisture,resultingtoanincreaseinthewatercontentinthetransformeroil.[30]


24/48

19

Chapter4:TransformerOilAnalysis.

4.1Partialdischarge(PD)

SignsofpartialdischargewerefirstobservedinanoscilloscopeintheSixties.Laterinthe

Eighties,computerizeddataacquisitionbecamecommonlyavailable.Thisgreatlyenhanced

storageanddigitalprocessingofdischargepatterns.[31]

PD,moreoftenthannot,startsinsidetinybubbles,voids,cracks,orinclusionswithinasolid

insulator(dielectric),atconductordielectricinterfaceswithinsolidorliquiddielectrics,orin

voidsthatoccurinliquidinsulatorsusedasdielectrics.SincePDsonlyoccurataparticular

portionintheelectrode,thefaultscreatedbythedischargesonlypartiallyconnecttheseparationoftheelectrodes.

PDintransformersdegradesthepropertiesoftheinsulatingmaterialsandcanleadto

eventualfailures.PDscanbeidentifiedbyusinganalysisfromacousticmeasurementsorby

measurementsoftheelectricalsignals.Anotherpreferredmethodisbydoingchemicalteststo

analyzethegasesproducedfromthepartialdischarges.

PDscauseconsiderabledeteriorationtotheinsulation(dielectric)itoccursin.Itisworth

mentioningagainthatwhenthegasesarecollectedbyupwarddeliveryordownward

displacementofair,andtheresultoftheanalysisofthegasescanbeusedtodeterminethetypeoffaultthatoccurred.Forthecaseofpartialdischarge,hydrogengasisproduced.

Generally,andforalloiltypes,thepartialdischargeexperimentsshowthattherateofpartial

dischargeisdirectlyproportionaltoageoftheoil.

Thisisreasonablebecauseduringpartialdischarge,manychemicalbondsarebrokentoform

severalgasesandthiseffectivelyshortensthenhydrocarbonchainsoftheoil.PD,therefore,

wouldbeworthwhiletobedetectedearlyfortechnicalintervention;else,itcanruinthe

transformer.

Someofthegasesdissolveintheoil.ThisbringsustoDissolvesGasAnalysis.

4.2DissolvedgasAnalysis(DGA)

Dissolvedgasanalysisisthestudyofdissolvedgassesintransformeroil.Thegassescomefrom

thedeteriorationofthematerialsthatformthecontainerofthetransformeroil.These

materialsincludeboththeelectricalequipment,theinsulatingmaterialsforthecoils,andthe

ore.

Whenthegasesareanalyzed,thestatisticscanbeusedtodeducetherealelectricalfaultofthe

transformer,ortheequipmentatfault.


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20

Sincetheoilisincontactwiththeinternalequipment,thegasesformedbyoxidation,

vaporization,decomposition,insulation,oilbreakdownandelectrolyticaction,aredissolvedin

thetransformeroil.Atthatinstance,theoilishot.Theheatenhancesthedissolutionofthe

gasses.

Duringnormaltransformeroperation,gassesareproduced.Butwhenthereisafault,thegasses

areproducedinlargerquantities.Thegassesproducedareproportionaltothefault.Below,are

themostcommonfaultsandgassesproduced;inincreasingseverity.[32]

Partialdischargeorcorona:Produceshydrogengas(H2(g)).

Localizedhotspots(Pyrolysisorthermalheating):Atlowertemperatures,itproducesCH4,C2H6

andathightemperatures,itproducesamixtureismethane,C2H4(ethylene),ethaneand

hydrogengas.

Arcing:producesamixtureofethaneacetylene(C2H2),ethylene,methane,andhydrogen

gas.[33]

4.2.1DissolvedMoistureinTransformerOil.

Free water causes few problems with the dielectric strength of oils in transformers;

however,itshouldbedrainedassoonasitisnoticed.

Moisture isgiven in thedissolvedgasanalysis inppm,and some laboratoriesalsogive

percent saturation.Percent saturationmeanspercent saturationofwater in theoil.This isa

percentageofhowmuchwaterisintheoilcomparedwiththemaximumpossiblesaturationof

waterinoil.Thesaturationofwaterinoilgreatlydependsontemperature.

Thecurves,inFig4.,belowshowsomepercentsaturationcurves.Ontheleftline,findthe

ppmofwaterfromyourDGA.Fromthispoint,drawahorizontallineandextrapolatetoreadthe

corresponding temperature and corresponding levelofpercentage saturationonorbetween

thecurves.[34]


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21

Fig4.: TransformerOilPercentSaturation Curves.

Forexample,iftheoil is50ppmandthetemperatureis40C,youcanseeonthecurves

that thispointof intersection fallsabouthalfwaybetween the20%curveand the30%curve.

Thismeansthattheoilisapproximately35%saturated.

However,expertsdisagreeonhowtotellhowmuchmoistureintheinsulationbasedon

howmuchmoistureisintheoil(ppm).Atbest,methodstodeterminemoistureintheinsulation

basedsolelyonDGAarenotveryaccurateinaccurate.


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22

Chapter5:ExperimentalSetup.

Thischapterwilldiscusstheexperimentalsetupsusedinthisthesisproject,includingtheaging

processonbothtypesofoil,themeasurementprocedureofBreakdownvoltage.

Fig(5.1.1.)

Diagram

of

the

experimental

setup.

Asitshowninthediagramoftheexperimentalsetup,ithas,installed,twopoles(electrodes)in

themiddleofthecontainer,immersedintestoil,oneofthemconnectedtothehighvoltage

sideandothertoground.

5.1Requirementsforexperiment.

Ac voltage control (7K Volts Power supply):

Usedtocontrolthevalueofvoltagethatappliedtotheoil,andincludedofoursmadea

protectionsystemthatwillbeoperatedwhenthebreakdownvoltageappearintheinsulation.

Resistors:

Theresistorshaveconnectedinserieswithsetvalueto500(ohms).

Syringe:

Ithasusedasaunitofmeasurementtoaddthesolutiontothemineralandvegetableoil.

Multimeter (VoltOhm meter):

Itusedtomeasurethevoltage,current,resistantintheexperiment.

Heat source (Extreme temperature):

Itusedtoheattheoilandincreaseitsagingtime.A6000Cheatsourcewasused.


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23

Additionalrequirementsusedintheexperiment:

1.HydrochloricAcid(HCL).

2.SodiumHydroxideNaOH(aq).

Theoldsamplesarepreconditioned.Then,theacceleratedthermalagingprocessisstarted.

First,thesamplecontaineriscleanedbeforeitisfilledwithnewoilsample.

Fig(5.1.2): Shows theexperimentequipment.

Thesetupwasasshowninthepictureabovethattheywereusedintheexperimental

measurements.Afteraddtheoilsampleinthecontainer,theoilsampleissubjectedtoa

steadilyincreasingalternatingvoltageuntilbreakdownoccursinthedielectricintheBDVtest

kit.Thebreakdownvoltageisthevoltagereachedatthetimeofthefirstsparkappearsbetween

theelectrodes.Thesparkvoltage,whichindicatesthehighsurgeofcurrent,isrecorded.The

test

is

carried

out

nine

times

on

each

sample.

The

electrodes

are

mounted

on

a

horizontal

axis

withatestspacingofabout0.1mm.

Fig(5.1.1)showsthelogicallayoutofthephysicalexperimentallayoutweconductedasshown

inFig(5.1.2).Thenextpagecontainsthepicturesduringtheartificialagingprocess.InFig

(5.1.3),theoilwasheatedwithaheatsourceof6000C,aswellastheoilsphysicalstateduring

thethermaldisintegration.


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24

Fig(5.1.3): The operationofheatingthemineraloilabout60minutewitha

600 degrees heatsource. Figures ofartificialaginginthelab.


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25

5.2Conditionsoftheoilsamples

Beforestartingtheacceleratedthermalagingprocess,theoldsamplewasreplacedbeforethe

acceleratedthermalagingprocessisstarted.Afterthat,thecompletesetupwasconnectedasin

thelayoutaboveandthentheresultsweretaken.Thisoiltreatmentprocedureelevatesthe

humidityoftheoilduringandaftertheheating.

Also,treatmentoftherespectiveoilsampleswithHClandNaOH,includetheintroductionof

calculatedamountsofthechemicals;aslatershowninchaptersix.Themoisturecontentofthe

oilaffectsitsdielectricproperties,suchasbreakdownvoltageanddielectriclossangle(tan

delta).

5.3Breakdownvoltagemeasurementinoil

TheBreakdownvoltage,knownastheminimumvoltagethatthesparksoccurbetweenthe

electrodes,causesaportionofaninsulatortobecomeelectricallyconductive.

Inourmeasurementstheelectrodeswereinstalledinhorizontalposition.

Theelectrodeswerepolarized,andtheaxisoftheelectrodesystemshallbehorizontalandat

least20mmbelowthesurfaceofthetestoil.Thegapbetweentheelectrodesissetto0.1mm,

andthecontainershouldbealmostfilledwithoilsample.Themeasurementsarecarriedout

untilninebreakdownsoneachsample,andthentheoilsampleissubjectedtoasteadily

increasingalternatingvoltageuntilbreakdownoccursinthedielectricintheBDVtestkit.


31/48

26

Chapter6:ExperimentalresultsandDiscussion.

Allpresenteddatafromthedielectricpropertymeasurementswhichincludethebreakdown

voltage,relativepermittivity,andhumiditycontentaremeasuredandthedataarepresentedin

trendplotstobeusedforcomparingthedielectriccharacteristicsbetweenmineraloiland

(vegetable)esteroil.

6.1VegetableOilexperiment

HCLwasaddedwithdifferentpercentage.Weuseda4MHCLsolutionappliedvoltagetotheoil

andincreasedthevoltagecarefullybyanACvoltagecontroluntilbreakdownoccurs.

Firstreading:3.1KVrms.

Secondreading:3.1KVrms.

Thirdreading:3.1KVrms.

Average:3.1KVrms.

Theresultsofbreakdownvoltage(BDV)measurementsforthevegetableoilscoolingarelisted

intables.

Coolingtimeforvegetableoil Breakdownvoltage

0 2.51

2 2.50

4 2.00

6 2.18

8 1.99

10 2.02

12

2.01

14 2.01

20 2.02

Table (6.1.1): Shows minutesofcooling afterheatedfor60 minuteswith

10mlofwateragainstbreakdown voltage.


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27

Fig(6.1.1): Agraphicrepresentation ofthebreakdown voltage ofvegetable

oilalongthetime.

Theoilisartificiallymoisturizedbyheatingtheoilforsixtyminuteswith10mlofwater.Atthe

beginningoftheplottingonFig(6.1.1),theBreakdownVoltageofvegetableoilhasnotchanged

between02minutes.Thenthebreakdownvoltagedecreasedslightlytowardsthefourth

minute.Whenapproachingthe6thminute,theBDVslightlywentupagain,beforegoingdown

againateighthminute.Approachingthetenthminute,theBDVincreasedslightlytovaluewhich

wasstilllowerthantheBDVatthebeginningoftest,anditbecomesmorestabletotheendofagingtime.Inspiteofinconsistencies,thegeneraltrendisaslightnegativegradient.The

generalslopedetectedbythecomputerisaslightdecrease;indicatedbytheblackline.The

irregularityofthegraphcanbeaccountedforbytheunstabledielectricgapandtinydust

particlesfromtheenvironmentthatenteredtheoil.Whenheatingstopped,thereisa

continuousdecompositionoftheoilschemicalcomponents.Thisgraduallydecreasesastheoil

cools,givingrisetothenegativegradientofthegraph.

CoolingtimeofVegetableoilwithHCl. Breakdownvoltage

0 2.21

2 2.22

4 2.106 2.14

8 1.92

10 2.04

12 1.91

14 1.81

20 1.82

Table (6.1.2): Shows minutesofcoolingafterheatedfo r60 minwith

addition of2mlof4mol/dm3HCLsolution againstBreakdown voltage.

0

0,5

1

1,5

2

2,5

3

0 5 10 15 20 25

BDV

coolingtimeofVegetableoilwithexposuretomoisture

Figer(611)cooling

timeVsBDV

Linear(Figer(611)

coolingtimeVsBDV)


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28

Fig(6.1.2): Agraphicrepresentation ofthebreakdown voltage comparison

vegetableoilalongthe timewith HCL.

AftertheadditionofHCLsolutiontovegetableoil,asimilartrendtoFig6.1.1wasplotted.When

wemonitortheBDVandminutesofcoolingafterheatingfor20minweseetheinitial

breakdownvaluefornewvegetableoilwithHCLwaslowerthanvegetableoilintheprevious

measurement.Inthebeginningitjumpedupinthe2ndminute.Later,theBDVdecreasedslightly

ascoolingapproachedto4thminute,andthenthegraphshowedatendencyofdeclininguntil

20thminuteofartificialaging.Thegeneralslopedetectedbythecomputerisaslightdecrease;indicatedbytheblackline.Theirregularityofthegraphcanbeaccountedforbytheunstable

dielectricgapandtinydustparticlesfromtheenvironmentthatenteredtheoil.Whenheating

stops,thereisacontinuousdecompositionoftheoilschemicalcomponents.Thisgradually

decreasesastheoilcools,givingrisetothenegativegradientofthegraphinFig6.1.2.

VegetableoilwithNaOH(aq)testing:

Weweregiven4mol/dm3NaOH(aq)butwithoutthepercentagemass.Tocalculatethemass,we

needthenumberofmoles.Sincemolarmass,MofNaOHis34wecancalculatethenumberof

grams(ofNaOH)usedintheexperimentbyusingmolarityasfollows:

TotalMass,mtot=434=136g.

1361000100%=13.6%.

Foreachexperiment,weused2cm3ofNaOH.

MassofNaOHineachdrop,mexp=2%X136=0.27g.

Volumeofoilis250cm3.Therefore,0.27252100=0.11g

0.11gistheamountofsoluteNaOH(aq)weuseintheexperimentbelow.

0

0,5

1

1,5

2

2,5

0 5 10 15 20 25

BDV

coolingtimeofVegetableoilwithHCL

Figure(612)cooling

timeofvegetableoil

withHCL

Linear(Figure(61

2)coolingtimeof

vegetableoilwithHCL)


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29

Timeofcoolingafteradding2cm3ofNaOH

andheatingfor60mins.

Breakdownvoltage

0 2.54

2 2.30

4 2.00

6 2.88

8 2.92

10 2.42

12 2.11

14 1.21

20 2.22Table (6.1.3): Shows minutesofcoolingafterheatedfo r60 minwithadded

NaOH(aq) solution VsBreakdown voltage.

Fig(6.1.3): Agraphicrepresentation ofthebreakdown voltage comparison

vegetableoil

along

the

time

with

NaOH(aq).

AsshowninthismeasurementsandtheresultinggraphonFig6.1.3,theminutesofcoolingafter

theoilisheatedfor60minuteswithaddedNaOH(aq)solutionagainstbreakdownvoltage;the

initialbreakdownvalueforanewsamplewithNaOH(aq)solutionshowedconsistentresultsfor

thefirst4minutes.Itthenjumpeduphigherthanthefirstvaluebetween68minbeforegoing

downagainat14minutes.Between1420minutes,BDVvalueincreasedtothehighestvalue

whichwasstilllowerthantheBreakdownvalueatthebeginningoftest.Whencoolingstarted,

therewasacontinuousdecompositionoftheoilschemicalcomponents.Thisgradually

decreasesastheoilcools,givingrisetothenegativegradientofthegraph. Thegeneralslope

detectedbythecomputerisaslightdecrease;indicatedbytheblackline.Theirregularityofthe

0

0,5

1

1,5

2

2,5

3

3,5

0 5 10 15 20 25

BDV

coolingtimeofvegetableoilwithNaOH

vegetableoilwith

NaOH

Vs

BDV

Linear(vegetableoil

withNaOHVsBDV)


35/48

30

graphcanbeaccountedforbytheunstabledielectricgapandtinydustparticlesfromthe

environmentthatenteredtheoil.

Intable(6.1.4),wegotthesolutepercentagecontentofHCLinthevegetableoilbythis

equation,

12%ofHCL=>120g/dm3ofsolutionbecause12gexistin100g(givenacidsolutionmass).

Therefore0.24gexistsin2gofsolution.

TogetthepercentagemassofHCLin250gofoilintheexperiment,

Sowesaythat(0.24)(250+2)

Volumeofoilis250cm3.Therefore,thegeneralequationwillbe[(N0.24)(250+M)]X100.

N:istheexperimentnumber.

M:numberofmillilitersof12%ofHCL.

VariationofHCLMolarityinpercentage Breakdownvoltage(BDV)

0.09 3.15

0.18 3.04

0.28 2.830.37 2.62

0.46 2.22

0.54 2.01

Agraphicpresentationofthe breakdown voltage comparison vegetableoil

alongthetime isdescribedin Figure (6.1.4.)


36/48

31

Fig(6.1.4): Relation betweenBDVVersus HCLin vegetableoil.

Afteraddingthesolutionandatapplyingthevoltage,thebreakdownvoltagedecreasedslightly

between3.15to3.04andtheBDVslightlywentdownto2.83KVandthencontinuouslygoes

downtill2.01KV. TheBDVvalueofvegetableoilwasreducedfrom3.15kV(newoil)to2.01kV

(endofaging).Fig(6.1.4)isaconcisecharacteristicgraphofartificiallyagedvegetableoils

breakdownvoltagecharacteristic.

6.2Mineraloilexperiment.

Theoilsampleissubjectedtoasteadilyincreasingalternatingvoltageuntilbreakdownoccursin

aBDVtestkit.Thebreakdownvoltageisthevoltagereachedatthetimeofthefirstspark

appearsbetweentheelectrodes.Thetestiscarriedoutninetimesoneachsample.The

electrodesaremountedonahorizontalaxiswithatestspacingofabout0,1mm.Wereplace

theoldoilbyanewsample,andthenweaddedHCLwithdifferentquantities.

Weuseda4MHCLsolution,appliedvoltagetotheoil,andincreasedthevoltagecarefullybyan

Acvoltagecontroluntilbreakdownoccurs.

Firstreading:4.50KVrms.

Secondreading:4.45KVrms.

Thirdreading:4.44KVrms.

Average:4.46KVrms

0

0,5

1

1,5

2

2,5

3

3,5

0 0,2 0,4 0,6

BDV

percentageHCL

Figure(614)

VariationofHCL

Molarityin

percentageVsBDV

Linear(Figure(614)

VariationofHCL

Molarityin

percentageVsBDV)


37/48

32

Coolingtimeofheatedmineraloil Breakdownvoltage

0 4.24

2 4.21

4 4.22

6 4.12

8 4.19

10 4.20

12 4.15

14 4.09

20 4.10

Table (6.2.1): Minutesofcooling afterheated60 minuteswith10mlof

wateragainstrecordings fo rbreakdown voltage .

Fig(6.2.1): Minutes ofcooling afterheatedfo rabout60 minutes.

Theoilisfirstartificiallymoisturizedbyheatingwith10mlofwaterfor60minutes.Atthe

beginningoftherecordingtime,thecurveonFig(6.2.1)showsthattheBreakdownvoltageof

mineraloildecreasedslightlybetween02minutes.ThentheBDVslightlyjumpedupastime

approaches4minutesbeforegoingdownagainduringthe6thminute.Betweenthe6th 10th

minutes,theBDVvalueincreasedtoaveryhighvalue,whichwasstilllowerthanthebreakdown

voltageatthebeginningoftest.Itthendecreasestothelowestvaluebetween1014minutesof

cooling,beforeslightlyincreasingslightlytill20min. Inspiteofinconsistencies,thegeneral

trendisaslightnegativegradient.Thegeneralslopedetectedbythecomputerisaslight

decrease;indicatedbytheblackline.Theirregularityofthegraphcanbeaccountedforbythe

unstabledielectricgapandtinydustparticlesfromtheenvironmentthatenteredtheoil.

4,08

4,1

4,12

4,14

4,16

4,18

4,2

4,22

4,24

4,26

0 5 10 15 20 25

BDV

coolingtimeofMineraloilwithexposuretomoisture

Fig(621)coolingtime

VsBDV

Linear(Fig(621)coolingtimeVsBDV)


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33

Coolingtimeofmineraloilafterheatedwith

HCl.Breakdownvoltage

0 4.20

4 4.23

8 4.25

12 4.29

16 4.27

20 4.28

24 4.15

28 4.05

32 3.77

Table(6.2.2):

Minutes

of

cooling

after

heated

60

minutes

with

add

HCL

solution

to

the

mineraloilagainstbreakdown voltage.

Fig(6.2.2): Agraphicrepresentation ofthebreakdown voltage ofMineral

oilversus cooling timewithHCLin mineraloil.

Fig(6.2.2)showsanotherfigureofbreakdownvoltagesasapropertyofmineraloilaffectedby

heatingwithHCl(aq).TheBreakdownvoltageofmineraloilincreasesslightlybetween012

minutes.ThentheBDVslightlydecreasedbetween1216minutesbeforeitincreasedagainto

20minutes,afterwhich,thedecreasebecomesmoreandmoreevidenttillthe32ndminute.In

spiteofinconsistencies,especiallyinthebeginning,thegeneraltrendisaslightnegative

gradient.Thegeneralslopedetectedbythecomputerisaslightdecrease;indicatedbytheblack

line.Whencoolingstarts,atthebeginningofthegraph,thereisacontinuousdecompositionof

theoilschemicalcomponents.Thisgraduallydecreasesastheoilcools,givingrisetothe

negativegradientofthegraph.Theirregularityofthegraphcanbeaccountedforbythe


3,7

3,8

3,9

4

4,1

4,2

4,3

4,4

0 10 20 30 40

BDV

coolingtimeofMineraloilwithHCL

Figure(622)cooling

timeofvegetableoil

withHCLVSBDV

Linear

(Figure(6

2

2)

coolingtimeof

vegetableoilwithHCL

VSBDV)


39/48

34

Weweregiven4mol/dm3NaOH(aq)butwithoutthepercentagemass.Tocalculatethemass,we

needthenumberofmoles.Sincemolarmass,MofNaOHis34wecancalculatethenumberof

grams(ofNaOH)usedintheexperimentbyusingmolarityasfollows:

TotalMass,mtot=434=136g.

1361000100%=13.6%.

Foreachexperiment,weusedat2.0cm3ofNaOH.

MassofNaOHineachdrop,mexp=2%X136%=0.27g.

Volumeofoilis250cm3.Therefore,0.27252100=0.11g

0.11gistheamountofsoluteNaOH(aq)weuseintheexperimentbelow.

Mineraloil(NaOH) Breakdownvoltage

0 4.45

2 4.42

4 4.34

6 4.28

8 4.02

10 4.42

12 4.01

14 4.91

20 4.02

Table(6.2.3): Minutesofcooling afterheatedfo rabout60 minuteswith

NaOH.

Fig(6.2.3):Minutes ofcooling afterheatedfo rabout60minutes with NaOH

againstBDV.

0

1

2

3

4

5

6

0 10 20 30

BDV

coolingtimeofMineraloilwithNaOH

Figur(623)cooling

timeofmineraloil

withNaOH

Linear(Figur(62

3)coolingtimeof

mineraloilwith

NaOH)


40/48

35

Intheaboveexperiment,afterheatingtheoilwithNaOHsolutionfor60mins,andcoolingfor

20minutes,thebehaviorofthedielectricpropertyslightlydeteriorates,almostuniformlytillthe

8thminuteasseenonthefirstpartofFig(6.2.3).Later,werecordedirregularresultstillthe20th

minute.Inspiteofinconsistencies,especiallyinthebeginning,thegeneraltrendisaslight

negativegradient.Thegeneralslopedetectedbythecomputerisaslightdecrease;indicatedby

theblackline.Fromthebeginningofthisexperiment,thereisacontinuousdecompositionof

theoilschemicalcomponents.Thisgraduallydecreasesastheoilcools,givingrisetothe

negativegradientofthegraph. Theirregularityofthegraphcanbeaccountedforbythe


Inthefollowingexperiment,wegotthesolutepercentagecontentofHCl(aq)inthemineraloilby

thisequation:

(N0.24)(250+M)X100.where:

N:istheexperimentnumber.

M:numberofmillilitersof12%ofHCL.

VariationofHCLMolarity Breakdownvoltage

0.09 4.55

0.18 4.44

0.28 4.30

0.37 4.12

0.46 3.99

0.54 3.86

Table (6.2.4): Thesolute pe rcentage contentofHClin themineraloilby

multiplying the12%4MHClwe had, bythequantityofmineraloilwe used

(250cm3).

Fig(6.2.4): Relation betweenBDVVersus HCLin mineraloil.

3,8

3,9

4

4,14,2

4,3

4,4

4,5

4,6

4,7

0 0,2 0,4 0,6

BDV

precentageofHCL

Figure(624)Variation

ofHCLMolarityin

percentageVsBDV

Linear(Figure(624)

VariationofHCL

Molarityinpercentage

VsBDV)


41/48

36

Afteraddingthesolutionandatapplyingthevoltage,thebreakdownvoltagedecreasedslightly

between4.55to4.44andtheBDVslightlywentdownto4.30andthencontinuouslygoesdown

till3.86. TheBDVvalueofmineraloilwasreducedfrom4.55kV(newoil)to3.86kV(endof

aging).Fig(6.2.4)isaconcisecharacteristicgraphofartificiallyagedmineraloilsbreakdown

voltagecharacteristic.

6.3ComparisonbetweenVegetableandMineralOilCharacteristics

Asearliermentioned,Mineraloilcanbeobtainedfrompetroleumanditisagoodinsulating

materialbecauseofitsgoodelectricalproperties.OthercharacteristicssuchashighBDValso

enhancetransformeroperation.Themostimportantthingisthatmineraloilisalreadyproduced

worldwideandofferedatalowcost.Butthebiggestproblemwilloccurwhenthereisa

transformerleakageandthemineraloilwillendangertheenvironmentbecauseofitspoorbiodegradability.

Thevegetableoilhasnearlythesamedielectricconstantasthatfoundinmineraloil.The

mineraloilmainlyconsistsofrefinedpetroleumwhichcontainsnonpolaralkanemolecule.So

wecancomparethetwotypesofdifferentoilsbylookingattheirexperimentresults.

Vegetableoilcanbeobtainedfromfishoil,animalfats,palmfruitsorseedswithdifferent

processes.Severaltypicaloilseedswhichareobtainedandprocessedbeforetheyarereadyto

beusedasthetransformerinsulationarerepresented.

Whenwementioncomparisonbetweenmineraloilandvegetableoilcharacteristic,wehavetomentionseveralCriteriabetweenbothofthosetypes:

Forexample; Keypropertiesformineraloilcharacteristic:producedfrompetroleumcrudeand

nonrenewablepowerandscarcesources.

Keypropertiesforvegetableoilcharacteristic:Producedfromdomesticallygrownandfrom

renewablesources,suchassoybeansandcorn.

EnvironmentalPropertiesforthemineraloil:Containscompoundsthatdonotreadily

biodegrade.Itmayalsocontaintracesofaconfirmedcarcinogen.

Environmental

Properties

for

the

vegetable

oil:

Highly

biodegradable;

non

toxic;

does

not

containpetroleum,silicone,orhalogens.

LeaksandSpillsforthemineraloil:Thelatestfindingsofthescientistsofgeneticengineeringto

eliminatethisproblem.Somebacteriahavetheabilitytoabsorbthesesubstancestoxicoilsand

syntheticallyconvertitintoafooditems.Itcouldbeformedbyhybridizationformorethanone

typeofbacteriafoundinnature.Thiscouldpossiblycausealargenumberofexchanges

betweendifferentgenestoreachthedesiredqualitiestoproduceanewtypeofbacteriathatdo

notexistinnature.


42/48

37

LeaksandSpillsforvegetableoil:Relativelyrapidbiodegradationmayeliminatetheneedfor

environmentalawarenessrelatedtofindnewcomplicateddynamicprocessestocurbeco

concernsduringspills.

FireRiskforthemineraloilcharacteristic:Catchesfiremoreeasily,leadingtohigherprobability

oftransformerfires

FireRiskforthevegetableoilcharacteristic:reducesthefrequencyandimpactoftransformer

fires; virtuallyeliminatessustainedfires.

TransformerPerformanceforthemineraloil:Doesnotslowdownthestandardinsulationaging

rate,requiresspecialandexpensiveprocessingtodryoutthepaperinsulation.

Transformerperformanceforthevegetableoil:ithasproventoslowdowntheagingrateofthe

insulationsystem,resultinginanincreaseintheexpectedlifeofatransformerbydecades,alsopromotesautomaticdryoutofpaperinsulation.

UtilityCostforthemineraloil:Itleadstoshortenedlifeofthetransformeranddiminished

economicreturns;increasesliability

UtilityCostforthevegetableoil:Itprolongstransformerlifeandleadstolongertermeconomic

benefits.

6.4Discussion.

Theacceleratedthermalagingprocessshowedadifferenteffecttothecolorofthevariousoil

samples.Thecoloroftheagedmineraloilchangedmorethanagedvegetableoiltodarker

probablybecauseoftheirspecificchemicalproperties.Therewasalsoindicatedsludgecontent

inagedmineraloil,whileinthevegetableoil,itwashardlyobserved.TheBDVofbothtypesof

oilshowedadynamicbehavioralongtheacceleratedthermalagingprocess.Therewasa

tendencyofalloilsamplestogetlowerBDVattheendofaging.Wenotethatpuretransformer

oilreachbreakdownvoltageatvaluearound4.46KVrms.Whencontaminationispresentin

theoilthenthebreakdownvoltageanddielectricstrengthoftheoilwilldecrease.

Alltheheatingproceduresresultsintheproductionofsomegases.Thisindicatedtheactualloss

ofchemicalstructureandsignificantbreakageofchemicalbonds.Theresultingchemicalcompositionoftheoildoesnotproducethesameeffectastheinitialoilsample.

WhenweaddHCLtothevegetableoilwithpercentageof4Mandheatedfor20minutes,then

appliedvoltagetotheoil,withdistanceofabout0.1mmbetweentheelectrodes,thebreak

downvoltagedecreasedto3.1KV.

WecanconcludethattheadditionofHCLandheatedmoisturebadlydecreasestheBDVofthe

oilaswhenwecompareFigures(6.1.1)with(6.1.2).


43/48

38

WhenweaddNaOH(aq)tothevegetableoilwithpercentage4MFig(6.1.3)andheatedfor20

minutes,thenappliedvoltagetotheoil,thebreakdownvoltagedecreasedthenincreaseandat

thedecreased. SowecanconcludethatwhenweheattheoilandaddapercentageofNaOH(aq)

isbadlydecreasingtheBDVoftheoil.

WegotthesolutepercentagecontentofHCLinthevegetableoilbymultiplyingthe12%

4mol/dm3ofHCLwehad,bythequantityofvegetableoilweused,whichwas0.25dm.Fig

(6.1.4)wasthenobtainedwiththeotherspecificationskeptsame.WhenweaddHCl(aq)tothe

vegetableoilwithpercentageof4mol/dm3andheatedfor20minutes,thenappliedvoltageto

theoil,withdistance0.1mmbetweentheelectrodes,thebreakdownvoltagedecreasedfrom

3.15KVto2.01KV.

Whenweheatthemineraloilforabout60minuteswithexposuretomoisture,wegetFig

(6.2.2).Thesamedistanceof0.1mmbetweentheelectrodeswasused

WhenweaddHCl(aq)tothemineraloilwithpercentageof4Mandheatedfor60minutes,thenappliedvoltagetotheoil,withdistance0.1mmbetweentheelectrodes,thebreakdownvoltage

decreasedto3.77KV .

WhenweaddNaOH(aq)tothemineraloilwithpercentageof4Mandheatedfor60minutes,

thenappliedvoltagetotheoil,withdistanceofabout0.15mmbetweentheelectrodes,the

breakdownvoltagedecreasedfrom4.45KVto4.02KV.

WegotthesolutepercentagecontentofHCl(aq)inthemineraloilbymultiplyingthe12%4M

HCl(aq)wehad,bythequantityofmineraloilweused(0.25dm3).SotheBDVdecreasedto

3.86KV .

Wecanconcludethattheadditionofmoisture,HCl(aq)andNaOH(aq)tothemineraloiland

vegetableoils,aswellastheheating,forsomereasonableamountoftime,badlydecreasesthe

BDVoftheoil.


44/48

39

Chapter7:Conclusionandrecommendations.

Followingthefactthatalltheheatingproceduresresultsintheproductionofatoxicgas,we

concludethattherewastheactuallossofchemicalstructureandsignificantbreakageof

chemicalbonds.Theresultingchemicalcompositionoftheoildoesnotproducethesameeffect

astheinitialoilsample.Thereis,ineffect,areasonablepointtoconcludethat;viewingthe

interestingtrendswegotfromourgraphs,andconsideringthealreadyprovenscientific

statementsontransformeroilproperties,wecameoutwiththefollowingconclusions:

1. Aged(acidified)transformeroilhasalowerbreakdownvoltage.Itcanruinthe

transformerssmoothfunctioning.Thisourconclusionisanalogoustothefollowing

publicationbyPowerSubstationServices:[35]

Acid

content

in

Oil.

(N)

Oil

status

0.010.03 Excellent

0.050.10 Good

0.110.15 Marginal

0.160.40 Bad

0.410.65 VeryBad

0.661.50 Extremelybad

0ver1.50 HighRisk(Transformerfailureimminent)

N=Normality.

2. Moisturizedtransformeroilhasalowerbreakdownvoltage.Heatincreasesmoisturesolubilityandsoakingofthepaperonthetransformerwindings.

3. Contaminatedtransformeroilcanalsoreducebreakdownvoltagebydecreasingits

dielectricinsulationproperties.Weseethatinthedecreasingtrendintheexperiments

withNaOH(aq).

4. Alsowewouldnotleaveoutcommentingonthebeautifultrendygraphwegotfromthe

experimentwithmoisturizedandoverheatedtransformerandvegetableoil.Therewas

aremarkabledecreaseinthetransformeroilinsulationproperties.Thiswasdefinitely

becauseofthebreakingofbondsandformationofsmallermolarmasscompounds

whichdonothavegoodinsulationanddielectricproperties.Aswecanseefrom

Fig(6.2.1),weobservedtheformationofmanybubbleswhenwereachedhigh

temperatures.Bubbles,whichconsiderablydecreasesurfacetension,areaveracious

indicationofthepresenceofimpurities;inthiscase,moisture.

5. Arcinghorngapscanbeusedtopreventovervoltagesandotherimpulsevoltage

surges.[36]

6. Coronaringscouldalsobeusedtodistributetheelectricalfields,preventingthe

protectedhardwareandthecoronaringitselffromcorona.Thiscanbeusedon138Kv

voltagelinesorhigher.

7. Mostimportantly,acknowledgingthefactthattransformeroil,despiteitsfantastic

insulationandcoolingproperties,ithasamajordisadvantageofbeinghighlytoxicto


45/48

40

theenvironment,andverylowbiodegradability.Wewouldlovetoborrow,wordfor

word,SwedensABBsidealsontransformeroilpurificationandrecyclingwiththemain

goalofsustainability:[37]

ReclaimingoilwithareactivatedFullersearthsystemistheonlyeconomicalmethodto

restorethepropertiesofthetransformeroiltoclosetothevaluesofnewoilwitha

lastingeffect.Alsoreclaimingoilprovidesanenvironmentaladvantageinsteadof

replacinganonrenewableresource,theoilisprocessed.


46/48

41

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