Part 2 : Employer’s Requirements 235

1. P
ower Transformers

1 SCOPE

1.1 Thisspecificationis
providedforinformationfordesign,engineering,manufacture,assembly,stagei
nspection,finalinspectionandtestingbeforedispatch,packinganddeliveryatde
stinationstoresbyroadtransport,transitinsurance
of3.15/5/6.3/8/10/12.5MVA,33/11KVPowerTransformer(s),completewitha
llfittings,accessories,associatedequipment’s,spares,10%extraTransformerO
il,requiredforitssatisfactoryoperationinanyofthesub-stationsof
thepurchaser.

1.2 The core shall be constructed either from high grade, non-aging Cold
Rolled Grain Oriented (CRGO) silicon steel laminations conforming to
HIB grade of BIS certified with lamination thickness not more than
0.23mm to 0.27mm or better (Quoted grade and type shall be used). The
maximum flux density in any part of the cores and yoke at normal voltage
and frequency shall be such that it should under 10% overvoltage
condition should not be more than 1.9 Tesla. The supplier shall provide
saturation curve of the core material, proposed to be used. Laminations of
different grade(s) and different thickness (s) are not allowed to be used in
any manner or under any circumstances.

1.3 Thescopeofsupplyincludestheprovisionoftypetest.Theequipmentofferedsho
uldhavebeensuccessfullytypetestedwithinfiveyearsfromdateoftenderandthe
designsshouldhavebeeninsatisfactoryoperationforaperiodnot
lessthanthreeyearsasonthedateoforder.Complianceshallbedemonstratedbys
ubmitting,(i)authenticatedcopiesofthetypetestreportsand(ii)performancecer
tificatesfromtheusers,specificallyfromCentralGovt./StateGovt.
ortheirundertakings.

1.4 ThePowerTransformershallconforminallrespectstohigheststandardsofengin
eering,design,workmanship, thisspecification andthe latestrevisions
ofrelevant standardsatthetime
ofofferandtheemployershallhavethepowertorejectanyworkormaterial,which
,inhisjudgment,isnotinfullaccordancetherewith.TheTransformer(s)offered,s
hallbecompletewithallcomponents,necessaryfortheireffectiveandtrouble-
freeoperation.Suchcomponentsshallbedeemedtobewithinthescopeofsupply
,irrespectiveofwhetherthosearespecificallybroughtout
inthisspecificationand /orthecommercialorder ornot.

TheEmployerreservestherighttorejectthetransformersifontestingthelossese
xceedthedeclaredlossesbeyondtolerancelimitasperISorthetemperaturerisei
Part 2 : Employer’s Requirements 236
noiland/orwindingexceedsthevalue,specifiedintechnicalparticularorimped
ancevaluedifferfromtheguaranteedvalue includingtoleranceas perthis
specificationandifanyofthetest resultsdo
notmatchwiththevalues,givenintheguaranteedtechnicalparticularsandasper
technicalspecification.

2 SPECIFICTECHNICALREQUIREMENTS

1 RatedMVA (ONANrating) 3.15/5/6.3/8/10/12.5MVA

2 No.ofphases 3

3 Typeofinstallation Outdoor
4 Frequency 50 Hz (± 5%)
5 Coolingmedium InsulatingOil(ONAN)

6 Typeofmounting On Wheels,Mountedonrails.
7 Ratedvoltage
a) High voltagewinding 33KV
b) Lowvoltagewinding 11KV
8 Highestcontinuoussystemvoltage
a)Maximum system voltageratio (HV / LV)
36KV / 12 KV
b) Ratedvoltage ratio (HV /LV) 33KV /11 KV
9 No.ofwindings TwowindingTransformers
10 Typeofcooling ONAN (Oil natural / Airnatural)
11 MVARating corresponding 100%
toONANCoolingsystem
Method of connection:

12 HV : Delta
LV : Star
13 Connectionsymbol Dyn11
14 Systemearthing NeutralofLVside tobesolidly
earthed.

15 Intendedregularcyclicoverloadingofwindings As perIEC–76-1,Clause4.2

16 a) Anticipatedunbalancedloading Around10%

b) Anticipated continuousloadingofwindings 110 % ofratedcurrent

(HV / LV)
Part 2 : Employer’s Requirements 237
17 a) Typeoftapchanger (For3.15,5,6.3,8,10 &12.5 MVA
only)
On or Off load tapchanger as per
BOQ
b) Rangeoftaping + 5% to–15%in9 equalstepsof
2.5%each for Off-load tap and in
17 equal steps of 1.25% each for
On-load tap changer on HV
winding

18 Neutralterminals tobe broughtout On LVsideonly

19 OverVoltageoperatingcapabilityandduration 112.5 % ofratedvoltage (Cont.)

20 Maximum Flux Density in any part of the 1.9 Tesla

core and yoke at rated MVA with +12.5%
combined voltage and frequency variation
from rated voltage and frequency.
21 Insulation levels for windings:- 33kV 11kV

a) 1.2 / 50 170 75
microsecondwaveshapeImpulsewithstand
(KVP)
b) Powerfrequencyvoltagewithstand(KVrms) 70 28

22 Type ofwinding insulation

a) HVwinding
Uniform
b) LVwinding Uniform

23 Withstand time for threephaseshort circuit 2 Seconds

24 Noise levelatratedvoltageandfrequency AsperNEMAPublicationNo. TR-

1.
Permissible Temperature rise over ambient temperature shall be as per IS-2026*
* Amendment issued vide letter No. REC/DDUGJY/SBD/TS/2017-
18D. No.3091 Dated 25.08.2017.

25 Minimum clearancesinair (mm) :- Phaseto Phase Phase to

ground
a) HV 400 320
b) LV 280 140
26 Terminals
a. HV windinglineend36 KV oil filledcommunicatingtypeporcelainbushings
(Anti-fog type)
Part 2 : Employer’s Requirements 238
b. LVwinding12 KV porcelaintypeofbushing(Anti-fogtype) – for outdoor 11 KV
breakers
(11KVPowercablesshallbeusedforextendingsupplyto11KVbreakersincaseofindo
orcircuitbreakers.Theterminationof11KVcablesonLVbushingshallbethroughex
tendedcopperbusbarssuitabletoholdpowercablestermination.Ametalliccableter
minationbox,completelysealed,shallbeinstalledonLVsideofthetransformerinwhi
chcablesshallenterfrombottomglandplates.)
27 Insulation levelofbushing
LV HV
a)LightningImpulsewithstand(KVP) 170 75
b)1 MinutePower Frequencywithstand 70 28
voltage (KV–rms)
c)Creepagedistance(mm)(minimum) 900 300
28 Material ofHV &LVConductor ElectrolyticCopp
er
29 Maximum currentdensityforHV andLV
As perbestpractice
windingfor ratedcurrent
30 Polarization index
(HV to LV,HV toEarth&LVto earth)
IRTest=1minutevalue/15secs.valuewillnotbelessthan1.5
IRTest=10minutesvalue/1minutevaluewillnotbemorethan5 andlessthan1.5
31 CoreAssembly Boltlesstype

32 TemperatureIndicator
a. Oil One number
b. Winding One number

35. Losses: - The lossesshallnot exceed thevaluegivenbelow

MVARatin No-loadlosses Loadlossesat Percentage
g (Fixedloss)KW 75°C impedancevoltageonnormalt
KW apandMVAbaseat75oC
3.15 3 16 7.15
5 4 23 7.15
6.3 4.6 36 7.15
8 5.5 40 8.35
10 7 50 8.35
12.5 7.5 65 10
2.1 MARSHALLINGBOX
Ametalenclosed,weather,verminanddustproofmarshallingboxfittedwithrequi
redglands,locks,glassdoor,terminalBoard,heaterwithswitch,illuminationlam
pwithswitchetc.shallbeprovidedwitheachtransformertoaccommodatetemper
atureindicators,terminalblocksetc.Itshall havedegree ofprotectionofIP55 or
betteras perIS:2147 (ReferClause3.12 of IS).
2.2 CAPITALIZATIONOF LOSSESANDLIQUIDATEDDAMAGES
Part 2 : Employer’s Requirements 239

Capitalization of losses will be as per Annexure B which is attached herewith.

No (+) ve tolerance shall be allowed at any point of time, on the quoted losses
after the award. In case, the losses during type testing, routine testing etc. are
found above the quoted losses, the award shall stand cancelled. In such a case,
the CPG money shall also be forfeited.
2.3 PERFORMANCE

a. Transformershallbecapableofwithstandingfortwosecondswithoutdamagetoanye
xternalshort circuit,with theshort circuitMVAavailableatthe terminals.
b. ThemaximumfluxdensityinanypartofthecoreandyokeatratedVoltageandfrequen
cyshallbesuchthatthefluxdensitywith+12.5%combinedvoltageandfrequencyva
riationfromratedvoltageandfrequencyshall notexceed1.9 Tesla.
c. Transformershallunderexceptionalcircumstancesduetosuddendisconnectionofth
eload,becapableofoperatingatthevoltageapproximately25%abovenormalrated
voltageforaperiod ofnotexceedingoneminuteand40%above normalfor a period
of 5 seconds.
d. Thetransformermaybeoperatedcontinuouslywithoutdangeronanyparticulartappi
ngatthe ratedMVA± 1.25%ofthevoltagecorresponding to thetapping.
e. Thethermal ability to withstandshortcircuitshall be demonstrated by
calculation.
f. Transformershallbecapableofwithstandingthermalandmechanicalstresscausedb
yanysymmetricalandasymmetrical faultsonanywinding.

2.4 DRAWINGS/DOCUMENTSINCORPORATINGTHE
FOLLOWINGPARTICULARSSHALLBESUBMITTEDWITHTHEBID

a. Generaloutlinedrawingshowingshippingdimensionsandoveralldimensio
ns,netweightsandshippingweights,qualityofinsulatingoil,spacingofwhe
elsineitherdirectionofmotion,location of coolers, marshalling
boxandtap changersetc.
b. Assembly drawings of core,windingsetc.and weightsof maincomponents/
parts.
c. Heightof centerline onHVandLV connectorsoftransformersfrom the
railtoplevel.
d. Dimensions ofthelargestpart tobetransported.
e. GAdrawings / detailsofvarious types of bushing
f. Tap changingandNamePlatediagram
g. Typetestcertificatesofsimilartransformers.
h. Illustrative & descriptive literature of theTransformer.
i. MaintenanceandOperatingInstructions.

2.5 MISCELLANEOUS

i) Padlocksalongwithduplicatekeysasaskedforvariousvalves,marshallingboxe
tc.shallbesupplied by thecontractor,wherever locking
Part 2 : Employer’s Requirements 240
arrangementisprovided.
ii) Foundation boltsforwheellocking devices of Transformershallbe supplied by
theContractor.

2.6 DELIVERY

The full quantity of the equipments shall be delivered as per the delivery
schedule appended to this specification.

2.7 SCHEDULES

All Schedules annexed tothespecificationshall be dulyfilled

bythebidderseparately.

2.8 ALTITUDEFACTOR

Iftheequipmentistobeinstalledinthehillyarea,necessarycorrectionfactorsasgi
venintheIndianStandardforoiltemperaturerise,insulationleveletc.shallbeapp
liedtotheStandardTechnicalParametersgivenabove.

2.9 NAMEPLATE

Transformerratingplateshallcontaintheinformationasgiveninclause15ofIS-
2026(part-
I).Thedetailsonratingplateshallbefinalizedduringthedetailedengineering.Further,e
achtransformershallhaveinscriptionofEmployer’sname.Thenameplateshallalsoin
clude(i)Theshortcircuitrating,(ii)Measurednoloadcurrentandnoloadlossesatratedv
oltageandratedfrequency,(iii)measuredloadlossesat75°C(normaltaponly),(iv)D.C
resistanceofeachwindingat75°C.

3. SERVICECONDITIONS

The service conditionsshall be asfollows: (Tobe confirmed by PIAas per locality

ofproject)
Plainarea Hillyarea
Maximumaltitudeabovesea level 1000m 5000m
Maximum ambientair temperature 50° C 50° C
Maximum daily average ambient air 35° C 40° C
temperature
Minimum ambientair temperature -5°C -30° C
Maximumtemperatureattainablebyanobjec 60 ° C 60 ° C
t exposed to thesun
Maximumyearly weighted average 32° C 32° C
ambient t emperature
maximumrelativehumidity 100% 100%
Part 2 : Employer’s Requirements 241
averagen u m b e r ofthunderstormdays 70 70
perannum(isokeraunic level)
average numberofrainydays perannum 120 120
average annualrainfall 1500 mm 1500 mm
maximumwind pressure 260Kg/m² 260Kg/m²
* HP, J&K, Uttrakhand, Sikkim, Assam, Meghalaya, Manipur, Nagaland,
Tripura and Mizoram will be considered as Hilly Area.
Environmentally,theregionwheretheequipmentwillbeinstalledincludescoastalareas
,subjecttohighrelativehumidity,whichcangiverisetocondensation.Onshorewindswil
lfrequentlybesaltladen.Onoccasions,thecombinationofsaltandcondensationmaycre
atepollutionconditionsforoutdoorinsulators.Therefore,outdoormaterialandequipme
ntshallbedesignedandprotectedforuseinexposed,heavilypolluted,salty,corrosive,tro
picalandhumidcoastalatmosphere.
SYSTEMCONDITIONS

Theequipmentshallbesuitableforinstallationinsupplysystemsofthefollowing
characteristics.
Frequency 50Hz± 5%

Nominalsystemvoltages 33 KV
11 KV

Maximumsystemvoltages 33KVSystem 36.3 KV

11KV System 12 KV

33KVSystem 31.5KA
Nominalshortcircuitlevel 11KV System 13.1KA
(Basingonapparentpower)

Insulationlevels: 1.2/50 μ 33KVSystem 170KV (peak)

secimpulsewithstandvoltage

11KV System 75 KV (peak)

Powerfrequencyone 33KVSystem 70KV(rms)

minutewithstand(wet
anddry)voltage
Part 2 : Employer’s Requirements 242
11KV System 28KV (rms)

Neutralearthing 11 KV System Solidlyearthed

arrangements

CODES&STANDARDS

4.1 Thedesign,material,fabrication,manufacture,inspection,testingbeforedispatchandp
erformanceofpowertransformersatsiteshallcomplywithallcurrentlyapplicablestatut
oryregulationsandsafetycodesinthelocalitywheretheequipmentwillbeinstalled.Thee
quipmentshallalsoconformtothelatestapplicablestandardsandcodesofpractice.Nothi
nginthisspecificationshallbeconstruedtorelievethecontractorofthisresponsibility.

4.2 Theequipmentandmaterialscoveredbythisspecificationshallconformto
thelatestapplicableprovisionofthe followingstandards.

IS:5 Colourforready mixed paints

IS:325 Three PhaseInductionMotors
IS:335 Newinsulating oilfortransformers, switch
gears
IS:1271
Classificationofinsulatingmateri
alsforelectricalmachineryandappar
atusinrelationtotheirstabilityinserv
ices
IS:2026(Part Ito IV) PowerTransformer
IS:2071 Method of highvoltagetesting
IS:2099 Highvoltage porcelain bushings
IS:2147 Degreeofprotection
IS:2705 CurrentTransformers
IS:3202
Codeofpracticeforclimateproofing
ofelectricalequipment
IS:3347 DimensionsforporcelainTransformerBushings
IS:3637 Gasoperated relays
IS:3639 FittingsandaccessoriesforpowerTransformers
IS:5561 ElectricPowerConnectors
IS:6600/BS: CP‟10:0 GuideforloadingofoilimmersedTransformers
IS:10028
Codeofpracticeforselection,install
ationandmaintenance
oftransformers,PartI. IIandIII
C.B.I.P.Publication ManualonTransformers
Part 2 : Employer’s Requirements 243
Ifthestandardisnotquotedforanyitem,itshallbepresumedthatthelatestversionofIndia
nStandardshall be applicable to thatitem.
The equipment c o m p l y i n g otherinternationallyacceptedstandards,mayalso
beconsidered if they ensureperformance superiorto the Indian Standards.
4.3 DRAWINGS

a) Thecontractorshallfurnish,withinfifteendaysafterissuingofLetterofAward.Sixcop
ieseachoft h e following drawings/documents incorporating the transformer
rating forapproval.

i) Detailedoverallgeneralarrangementdrawingshowingfrontandsideelevationsandpl
anofthetransformerandallaccessoriesincludingradiatorsandexternalfeatureswithd
etailsofdimensions,spacingofwheelsineitherdirectionofmotion,netweightsandshi
ppingweights,craneliftforun-
tanking,sizeoflugsandeyes,bushingliftingdimensions,clearancesbetweenHV and
L.Vterminalsandground,quantityofinsulatingoil etc.

ii) Assembly drawings of core and wingingandweightsofmain components /parts

iii) Foundationplanshowingloadingoneachwheellandjackingpointswithrespecttocent
re lineoftransformer.

iv) GAdrawingsdetailsof bushing andterminalconnectors.

v) Nameplatedrawingwithterminal markingandconnectiondiagrams.

vi) Wheel lockingarrangement drawing.

vii) Transportationdimensionsdrawings.

viii) Magnetization characteristiccurvesof PS classneutralandphase side current

transformers,ifapplicable.

ix) Interconnectiondiagrams.

x) Overfluxing withstandtime characteristicof transformer.

xi) GAdrawing of marshalling box.

xii) Controlscheme/wiringdiagramofmarshallingbox.

xiii) Technicalleafletsof majorcomponentsand fittings.

xiv) Asbuilt drawings of schematics,wiring diagrametc.

xv) Setting ofoil temperature indicator,windingtemperature indicator.

Part 2 : Employer’s Requirements 244
xvi) Completedtechnicaldatasheets.

xvii) Detailsincludingwrite-up oftap changinggear.

xviii) HV& LV bushing.

xix) BushingAssembly.

xx) Bi-metallicconnector suitablefor connection to 100 mm2up to232 mm2 AAAC

Conductor.

xxi) GAof LVcable Box.

xxii) Radiatortype assembly.

b) Alldrawings,documents,technicaldatasheetsandtestcertificates,resultscalculations
shallbefurnished.

4.4 AnyapprovalgiventothedetaileddrawingsbytheEmployer’sshallnotrelievethecont
ractoroftheresponsibilityforcorrectnessofthedrawingandinthemanufactureoftheeq
uipment.Theapprovalgiven by theemployer shallbe generalwith
overallresponsibility with contractor.

GENERALCONSTRUCTIONALFEATURES

6.1 Allmaterialusedshallbeofbestqualityandoftheclassmostsuitableforworkingu
ndertheconditionsspecifiedandshallwithstandthevariationsoftemperaturean
datmosphericconditionswithoutdistortionordeteriorationorthesettingupofun
duestresseswhichmayimpairsuitability of
thevariouspartsfortheworkwhichtheyhave toperform.

6.2 Similarparts particularly removableones shallbe interchangeable.

6.3 Pipesandpipefittings,screws,studs,nutsandboltsusedforexternalconnections
shallbeasper therelevant standards.Steel boltsand nuts exposed
toatmosphereshallbe galvanized.

6.4 Nuts,boltsandpinsusedinsidethetransformersandtapchangercompartmentss
hallbeprovided with lock washer or locknuts.

6.5 Exposed partsshallnothave pocketswherewatercan collect.

6.6 Internaldesignoftransformershall ensurethat air is nottrappedinanylocation.

Part 2 : Employer’s Requirements 245
6.7 Materialincontactwithoilshallbesuchasnottocontributetotheformationofacid
inoil.Surfaceincontactwithoil shall not be galvanizedor cadmium plated

6.8 Labels,indeliblymarked,shallbeprovidedforallidentifiableaccessorieslikeRe
lays,switchescurrent transformersetc.Alllabel plates shallbe ofin
corrodiblematerial.

6.9 Allinternalconnectionsandfasteningsshallbecapableofoperatingunderoverlo
adsandover-excitation,allowedas perspecifiedstands withoutinjury.

6.10 Transformerandaccessoriesshallbe designedto

facilitateproperoperation,inspection,maintenanceandrepairs.

6.11 Nopatching,plugging,shimmingorothersuchmeansofovercomingdefects,dis
crepanciesorerrorswillbe accepted.

6.12 SchematicDrawingofthewiring,includingexternalcablesshallbeputunderthe
pros panesheeton the inside doorof thetransformermarshalling box.

6.13 Painting

6.13.1 Allpaintsshallbe appliedinaccordancewith the

paintmanufacturer’srecommendations.
Particularattentionshall be paid to the following:
a. Proper storage to avoid exposureaswellas extremesoftemperature.
b. Surface preparationpriorto painting.
c. Mixingandthinning
d. Application ofpaints and therecommendedlimit ontimeintervals between
coats.
e. Shelflifeforstorage.

6.13.1.1 Allpaints,whenappliedinnormalfullcoat,shallbefreefromruns,sags,wrinkles,pa
tchiness,brushmarksorother defects.

6.13.1.2 Allprimersshallbewellmarkedintothesurface,particularlyinareaswherepainting
isevident,andthefirstprimingcoatshallbeappliedassoonaspossibleaftercleaning.The
paintshallbeappliedbyairlesssprayaccordingtothemanufacturer’srecommendations.
However,whereverairlessspray isnot possible, conventional spray be used with
priorapproval of Employer.

6.13.1.3 Thesuppliershall,priortopaintingprotectnameplates,letteringgauges,sightglass
es,lightfittingsandsimilar such items.

6.13.2 CleaningandSurfacePreparation

6.13.2.1Afterallmachining,formingandweldinghasbeencompleted,allsteelworksurf
Part 2 : Employer’s Requirements 246
acesshallbethoroughlycleanedofrust,scale,weldingslagorspatterandotherco
ntaminationpriortoanypainting.

6.13.2.2
SteelsurfacesshallbepreparedbySand/ShotblastcleaningorChemicalcleanin
gbySeventankprocessincludingPhosphate tothe appropriatequality.

6.13.2.3
ThepressureandVolumeofthecompressedairsupplyfortheblastcleaningshall
meettheworkrequirementsandshallbesufficientlyfreefromallwatercontamin
ationpriortoanypainting.6.13.2.4Chipping,scrapingandsteelwirebrushingusi
ngmanualorpowerdriventoolscannotremovefirmlyadherentmill-
scaleandshallonlybeusedwhereblastcleaningisimpractical.

6.13.3ProtectiveCoatingAssoonasallitemshavebeencleanedandwithinfourhoursofth
esubsequentdrying,they shallbe given suitable anticorrosion protection.
6.13.4 PaintMaterial

Followingsarethetypeofpaintsthatmaybesuitablyusedfortheitemstobepaintedatshopa
ndsupply ofmatchingpaintto site:
a. Heat resistant paint (Hot oilproof)forinside surface.
b. ForexternalsurfacesonecoatofThermoSettingPaintor2coatsofZincchr
omatefollowedby2coatsofPOLYURETHANE.
Thecolorofthefinishingcoatsshallbedarkadmiralgreyconforming toNo.632or
IS 5:1961.

6.13.5 PaintingProcedure

6.13.5.1 Allpaintingshallbecarriedoutinconformitywithbothspecificationsandw
iththepaintmanufacture’srecommendations.Allpaintsinanyoneparticularsys
tem.Whethershoporsiteapplied, shalloriginate fromone paint manufacturer.

6.13.5.2 Particular attention shall be paid to the manufacture’s instructions

on storage, mixing,
thinning and pot life. The paint shall only be applied in the manner
detailed by the manufacturer e.g. brush, roller, conventional or airless
spray and shall be applied under the manufacturer’s recommended
conditions. Minimum and maximum time intervals between coats shall be
closely followed.
6.13.5.3 Allpreparedsteelsurfacesshouldbeprimedbeforevisiblere-
rustingoccursorwithin4hourswhicheverissooner.Chemical treated steel
surfacesshall be primed as soon as thesurfaceis dry andwhilethesurfaceis
warm.

6.13.5.4 Wherethequalityoffilmisimpairedbyexcessfilmthickness,
(wrinkling,mudcrackingorgeneralsoftness)thesuppliershallremovetheunsati
sfactorypaintcoatingsand
Part 2 : Employer’s Requirements 247
applyanother.Asageneralrule,dryfilmthicknessshouldnotexceedthespecifie
dminimumdryfilmthicknessbymorethan25%.Inallinstances,wheretwoormo
recoatsofthesamepaintsarespecifies, such coatingsmay ormay not be
ofcontrasting colors.

6.13.5.5 Paintappliedtoitemsthatarenotbepainted,shallberemovedatsupplier's
expense,leavingthesurfaceclean,un-stainedandundamaged.

6.13.6 DamagestoPaintsWork

6.13.6.1 Anydamageoccurringtoanypartofthepaintingschemeshallbemadego
odtothesame standard of corrosion protection and appearanceasthat
originally employed.

6.13.6.2 Any damaged paintwork shall be made as follows:

a) The damagedarea,togetherwithan area extending25mmaroundits

boundary, shallbecleaneddown to bare metal.
b) Aprimingcoatshallimmediatelyapplied,followedbyafullpaintfinishequal
tothatoriginally appliedand extending50mmaroundtheperimeterofthe
originallydamaged.

6.13.6.3 Therepaintedsurfaceshallpresentasmoothsurface.Thisshallbeobtain
edbycarefullychamferingthepaintedgesbefore &afterpriming.

6.13.7 DryFilmThickness

6.13.7.1 Tothemaximumextentpracticable,thecoatsshallbeappliedasacontinu
ousfilmofuniformthicknessandfreeofpores.Over-
spray,skips,runs,sagsanddripsshouldbeavoided.The different coats may
ormaynot be samecolor.

6.13.7.2 Eachcoatofpaintshallallowedtohardenedbeforethenextisappliedaspe
rmanufacture‟srecommendations.

6.13.7.3 Particular attentionmust be paid to full film thickness atedges.

6.13.7.4 Therequirementforthedryfilmthickness(DFT)ofpaintandthematerial
tobeusedshallbe asgiven below:

Sl.No PaintType Areatobe Noof TotalDryfilm

painted Coats thickness(Min)
Part 2 : Employer’s Requirements 248
1 Liquidpaint
a) Zinc OutsideO 02 45micron
Chromate(Primer) utside 02 35micron
b) POLYURET
HANEPaint(Finish inside 01 35micron
Coat)
c) HotOilpaint

7.1 DETAILEDDESCRIPTION

7.2 Tank

7.2.1 TheTransformertankandcovershallbefabricatedfromhighgradelowcarbonpl
atesteeloftestedquality.Thetankandtheshall be ofweldedconstruction.

7.2.2 Tankshallbedesignedtopermitliftingbycraneorjacksofthecompletetransform
erassemblyfiled with oil.Suitable lugsand bossedshallbe providedforthis
purpose.

7.2.3 Allbreams,flanges,liftinglugs,bracesandpermanentpartsattachedtothetanksh
allbeweldedandwherepracticable,they shall bedoublewelded.

7.2.4 Themaintankbodyofthetransformer,excludingtapchangingcompartmentsan
dradiators,shallbe capableof withstandingpressureof760mmofHg.

7.2.5 Inspectionhole(s)withweldedflange(s)andboltedcover(s)shallbeprovidedon
thetankcover.Theinspectionhole(s)shallbeofsufficientsizetoaffordeasyacces
stothelowerendsofthebushings, terminalsetc.

7.2.6 Gasketsofnitrilerubberorequivalentshallbeusedtoensureperfectoiltightness.
Allgasketsshallbecloseddesign(withoutopenends)andshallbeofonepieceonl
y.Rubbergasketsusedforflange typeconnectionsof thevariousoil
compartments, shallbe laid ingroovesoringroove-
equivalentsectionsonboltsidesofthegasket,throughouttheirtotallength.Cares
hallbetakentosecureuniformlydistributedmechanicalstrengthoverthegaskets
andretainsthroughoutthetotallength.Gasketsofneopreneand/oranykindofim
pregnated/bondedcoreorcorkonlywhichcaneasilybedamagedbyover-
pressingarenotacceptable.Useofhempasgasketmaterialis also
notacceptable.

7.2.7 Suitable guides shallbe provided for positioning thevariousparts during

assembleordismantling.Adequate spaceshall be
providedbetweenthecoresandwindings andthebottom ofthetank
forcollectionof any sediment.

7.3 TankCover
Part 2 : Employer’s Requirements 249

The transformer top shall be provided with a detachable tank cover with
bolted flanged gasket joint. Lifting lugs shall be provided for removing the
cover. The surface of the cover shall be suitable sloped so that it does not
retain rain water.

7.4 UNDERCARRIAGE

7.4.1 The transformer tank filled with oil shall be supported on steel structure
with detachable plain rollers. Suitable channels for movement of roller
with transformer shall be space accordingly, rollers wheels shall be
provided with suitable rollers bearings, which will resist rust and
corrosion and shall be equipped with fittings for lubrication.

7.5 CORE

7.5.1 Eachlaminationshallbeinsulatedsuchthatitwillnotdeteriorateduetomechanic
alpressureand theactionof hottransformeroil.

7.5.2 Thecoreshallbeconstructedeitherfromhighgrade,non-
agingColdRolledGrainOriented(CRGO)siliconsteellaminationsconforming
toHIBgradewithlaminationthicknessnotmore
than0.23mmto0.27mmorbetter(Quotedgradeandtypeshallbeused).Themaxi
mumfluxdensityinany part ofthe cores and yoke
atnormalvoltageandfrequency shallnot be more than
1.69Tesla.TheBiddershallprovidesaturationcurveofthecorematerial,propos
edtobeused.Laminationsofdifferentgrade(s)_anddifferentthickness(s)arenot
allowedtobeusedinanymanneror underanycircumstances.

CRGO steel for core shall be purchased only from the approved vendors,
list of which is available at
http://apps.powergridindia.com/ims/ComponentList/Power-
former%20upto%20420%20kV-CM%20List.pdf

7.5.3 Thebiddershouldofferthecoreforinspectionstartingfromthedestinationportto
enableEmployerfordeputinginspectingofficersfordetailverificationasgivenb
elowandapprovalbytheEmployerduringthemanufacturingstage.Bidder‟scall
noticeforthepurposeshouldbeaccompaniedwiththefollowingdocumentsasap
plicableasaprooftowardsuseofprimecorematerial:Thecorecoils,iffoundsuita
ble,aretobesealedwithpropersealswhichshallbeopenedinpresenceoftheinspe
ctingofficersduringcore-cuttingatthemanufacturer’sorit’ssub-vendor’s
premisesas per approveddesigndrawing.
a) PurchaseOrderNo. &Date.
b) Invoice ofthesupplier
c) Millstestcertificate
d) Packinglist
Part 2 : Employer’s Requirements 250
e) Billoflading
f) Billof entrycertificate tocustoms

Corematerialshall be directly
procuredeitherfromthemanufacturerorthroughtheiraccredited
marketingorganizationofrepute,but notthroughanyagent.
Please refer to “Check-list for Inspection of Prime quality CRGO for
Transformers” attached at Annexure-A. It is mandatory to follow the
procedure given in this Annexure.

7.5.4 Thelaminationsshallbefreeofallburrsandsharpprojections.Eachsheetshallha
veaninsulting coatingresistant to the actionofhotoil.

7.5.5 Theinsulationstructureforthecoretoboltsandcoretoclampplates,shallbesucha
stowithstand2000 V DCvoltagefor oneminute.

7.5.6 Thecompletedcoreandcoilshallbesoassembledthattheaxisandtheplaneoftheo
utersurfaceofthecore assembleshall notdeviatefrom thevertical plane by
more than25mm.

7.5.7 Allsteelsectionsusedforsupportingthecoreshallbethoroughlyshotorsandblast
ed,aftercutting,drillingandwelding.

7.5.8 Thefinallyassembledcorewithalltheclampingstructuresshallbefreefromdefo
rmationandshallnotvibrateduring operation.

7.5.9 The core clampingstructureshall be designed tominimizeeddycurrent loss.

7.5.10 The framework andclampingarrangements shall be securelyearthed.

7.5.11 Thecoreshallbecarefullyassembledandrigidlyclampedtoensureadequatemec
hanicalstrength.

7.5.12 Oilductsshallbeprovided,wherenecessary,toensureadequatecoolinginsideth
ecore.Thewelding structureand major insulation shallnot obstructthe free
flowofoil through suchducts.

7.5.13 Thedesignofmagneticcircuitshallbesuchastoavoidstaticdischarges,develop
mentofshortcircuit paths withinitselfor to
theearthclampingstructureandproductionof flux
componentatrightangletotheplaneofthelamination,whichmaycauselocalheat
ing.Thesupportingframeworkofthecoresshallbesodesignedastoavoidthepres
enceofpockets,whichwouldpreventcompleteemptyingofthetankthroughthed
rainvalveorcausetrappingofairduringfilling.

7.5.14 Theconstructionistobeofboltlesscoretype.Thecoreshallbeprovidedwithlugss
Part 2 : Employer’s Requirements 251
uitableforliftingthecompletecoreandcoilassembly.Thecoreandcoilassemble
shallbesofixedinthetank thatshifting will notoccurduringtransport or
shortcircuits.

7.5.15 Thetemperaturegradientbetweencore&surroundingoilshallbemaintainedles
sthan20deg.Centigrade.Themanufacturershalldemonstratethiseitherthrough
test(procurementtobemutually agreed)or bycalculation.

7.6 INTERNALEARTHING

7.6.1 Allinternal metal partsofthetransformer,with theexceptionof individual

laminations and theirindividual clampingplates shall be earthed.

7.6.2 Thetopclampingstructureshallbeconnectedtothetankbyacopperstrap.Thebot
tomclamping structureshallbe earthed by oneormore thefollowingmethods:
a) By connection through vertical tie-rodstothetop structure.
b) Bydirect metal to metal contactwiththetankbase.
c) Byaconnectiontothestructureonthesamesideofthecoreasthemainearthco
nnection to thetank.

7.6.3 The magnetic circuitshall be connected to theclampingstructure

atonepointonlyandthis
shallbebroughtoutofthetopcoverofthetransformertankthroughasuitablyrated
insulator.Adisconnectinglinkshallbeprovidedontransformertanktofacilitate
disconnectionsfromgroundforIR measurement purpose.

7.6.4 Coilclampingringsofmetalatearthpotentialshallbeconnectedtotheadjacentco
reclampingstructureonthesamesideasthemainearthconnections.

7.7 WINDING

7.7.1 Windingshallbesubjectedtoashrinkingandseasoningprocess,sothatnofurther
shrinkageoccursduringservice.Adjustabledevicesshallbeprovidedfortaking
uppossibleshrinkageinservice.7.6.2Alllowvoltagewindingsforuseinthecircu
larcoilconcentricwindingshallbewoundonaperformedinsulatingcylinderfor
mechanicalprotectionofthewindinginhandlingand placingaroundthecore.

7.7.2 Windingshallnotcontainsharpbendswhichmightdamagetheinsulationorprod
ucehighdielectricstresses.Nostripconductorwoundonedgeshallhavewidthex
ceedingsixtimesthethickness.
Theconductorsshallbeofelectrolyticgradecopperfreefromscalesandburrs.Th
econductorinsulationshallbemadefromhigh-
density(atleast0.75gm/cc)paperhavinghighmechanicalstrength.Thebarrierin
sulationincludingspacersshallbemadefromhigh-densitypre-
compressedpressboard(1.1gm/ccminimumforloadbearingand1to1.3gm/ccm
inimumfornon-load bearing) tominimizedimensional changes.
Part 2 : Employer’s Requirements 252

7.7.3 Materials usedintheinsulationandassemblyofthewindings shall

beinsoluble,non catalytic
andchemicallyinactiveinthehottransformeroilandshallnotsoftenortheotherw
iseaffectedunder the operating conditions.

7.7.4 Winding andconnections shallbe bracedto withstandshocks

duringtransportorshortcircuit.

7.7.5 Permanentcurrentcarryingjointsinthewindingsandleadsshallbeweldedorbra
zed.Clampingboltsforcurrentcarryingpartsinsideoilshallbemadeofoilresista
ntmaterialwhichshallnotbe affectedby acidityintheoil steel
bolts,ifused,shall besuitably treated.

7.7.6 Terminalsofallwindingsshallbebroughtoutofthetankthroughbushingsforext
ernalconnections.

7.6.6.1 Thecompletedcoreandcoilassembleshallbedriedinvacuumatnotmorethan0.
5mmofmercuryabsolutepressureandshallbeimmediatelyimpregnatedwitho
ilafterthedryingprocesstoensuretheeliminationofairandmoisturewithinthei
nsulation.Vacuummaybeapplied ineithervacuum overor
inthetransformertank.

7.6.6.2 Thewindingshallbesodesignedthatallcoilassemblesofidenticalvoltageratin
gsshallbeinterchangeableandfieldrepairstothewindingcanbemadereadilyw
ithoutspecialequipment.The coilsshall have highdielectricstrength.

7.6.6.3 Coilsshallbemadeofcontinuoussmoothhighgradeelectrolyticcopperconduc
tor,shapedandbraced to providefor expansion andcontractiondue
totemperaturechanges.

7.6.6.4 Adequatebarriersshallbeprovidedbetweencoilsandcoreandbetweenhighan
dlowvoltagecoil. End turnshallhaveadditionalprotectionagainst abnormal
line disturbances.

7.6.6.5 Theinsulationofwindingshallbedesignedtowithstandvoltagestressarisingfr
omsurgeintransmission lines due to atmospheric or transientconditions
caused by switchingetc.

7.6.6.6 Tappingshallnotbebroughtoutfrominsidethecoilorfromintermediateturnsan
dshallbesoarranged asto preserve asfar aspossible magnetic balanceof
transformeratallvoltage ratios.

7.6.6.7 MagnitudeofimpulsesurgestransferredfromHVtoLVwindingsbyelectroma
gneticinductionandcapacitancecoupling shallbe limited to
BILLofLVwinding.
Part 2 : Employer’s Requirements 253

7.7 INSULATING OIL

7.7.1 TheinsulatingoilforthetransformershallbeofEHVgrade,generallyconformi
ngtoIS:335.Noinhibitorsshallbe usedintheoil.

7.7.2 Thequantityofoilrequiredforthefirstfillingofthetransformeranditsfullspecif
icationshallbestatedinthebid.transformershallsuppliedcompletewithallfitti
ngs,accessoriesandnewtransformeroilrequiredforfirstfillingplus10%extrao
il.Theextraquantityofoilshallbesuppliedinnon-
returnabledrumsalongwiththeoil requiredfor theradiator banks.

7.7.3 Thedesignandmaterialsusedintheconstructionofthetransformershallbesuch
astoreducethe riskofthedevelopmentofacidityin theoil.

7.7.4 The oil parameters shall be asper Table-1 ofIS335.

7.8 VALVES

i) Valvesshallbeofforgedcarbonsteelupto50mmsizeandofgunmentalorofcasti
ronbodieswithgunmetalfittingsforsizesabove50mm.Theyshallbeoffullwayt
ypewithscrewedendsandshallbeopenedbyturningcounterclockwisewhenfa
cingthehandwheel.Thereshallbenooilleakagewhenthevalves are
inclosedposition.

Eachvalveshallbeprovidedwithanindicatortoshowtheopenandclosedpositio
ns andshallbeprovided with facilityforpadlocking ineither openor closed
position.Allscrewedvalvesshall be
furnishedwithpipeplugsforprotection.Padlockswithduplicatekeysshallbesu
ppliedalongwiththevalves.
ii) Allvalvesexceptscrewedvalvesshallbeprovidedwithflangeshavingmachine
dfaceddrilledtosuittheapplicablerequirements,Oiltightblankingplatesshallb
eprovidedforeachconnectionforusewhenanyradiatorisdetachedandforallval
vesopeningtoatmosphere.Ifanyspecialradiatorvalve toolsarerequired
thecontractorshallsupply the same.

iii) Eachtransformer shallbe provided withfollowing valves on the tank:

a) Drainvalvesolocatedastocompletelydrainthetank&tobeprovidedwithl
ockingarrangement.

b) Twofiltervalvesondiagonallyoppositecornersof50mmsize&tobeprovi
dedwithlockingarrangement.

c) Oilsamplingvalvesnotlessthan8mmattopandbottomofmaintank&tobe
providedwith locking arrangement.
Part 2 : Employer’s Requirements 254

d) One15mm air release plug.

e) Valvesbetweenradiatorsandtank.Drainandfiltervalvesshallbesuitablef
orapplyingvacuumas specifiedinthespecifications.

7.9 ACCESSORIES

7.9.1 Bushing

i) Allporcelainusedinbushingsshallbehomogeneous,non-
porous,uniformlyglazedtobrowncolourand free fromblisters,burnsand
otherdefects.

ii) Stressdue to expansionandcontractioninanypartofthebushingshallnotlead to

deterioration.

iii) Bushing shall be designedandtested to comply withtheapplicablestandards.

iv) Bushing rated for400A and above shall have non-ferrousflanges and hardware.

v) Fittingsmade ofsteelor malleable ironshallbe galvanized

vi) Bushingshallbesolocatedonthetransformersthatfullflashoverstrengthwillbe
utilized.MinimumclearancesasrequiredfortheBILshallberealizedbetweenli
vepartsandlivepartstoearthedstructures.

vii) Allapplicableroutineand typetests certificatesofthebushings shallbe

furnishedforapproval.

viii) Bushingshallbesuppliedwithbi-
metallicterminalconnector/clamp/washerssuitableforfixingto
bushingterminalandtheEmployersspecifiedconductors.Theconnector/clam
pshallberatedtocarrythebushingratedcurrentwithoutexceedingatemperatur
eriseof550Co veranambientof500C.Theconnector/clampshallbedesignedt
obecoronafreeatthemaximumrated line to groundvoltage.

ix) Bushing ofidentical voltageratingshall be interchangeable.

x) Theinsulationclassofhighvoltageneutralbushingshallbeproperlycoordinate
dwiththeinsulation class oftheneutralofthelowvoltage winding.

xi) Eachbushingshallbesocoordinatedwiththetransformerinsulationthatallflas
hoverwilloccuroutside thetank.

xii) Theextendedbushingbusbarsshallbeusedforterminationof11KVcables.LV
Part 2 : Employer’s Requirements 255
busingshallbehoused incompletelysealedmetallic enclosure.

xiii) Sheetsteel,weather,verminanddustproofcableboxfittedwithrequiredglands,
locks,glassdoor,terminalBoard,heaterwithswitch,illuminationlampwithswi
tch,water-
tighthingedandpadlockeddoorofasuitableconstructionshallbeprovidedwith
eachtransformertoaccommodate11KVcablesetc.Theboxshallhaveslopping
roofandtheinteriorandexteriorpaintingshallbeinaccordancewiththespecific
ation.Padlockalongwithduplicatekeysshallbesuppliedformarshalingbox.T
hedegreeofprotectionshallbeIP-
55orbetter.Topreventinternalcondensation,ametalcladheaterwiththermosta
tshallbeprovided.TheheatershallbecontrolledbyaMCBofsuitableratingmou
ntedinthebox.Theventilationlouvers,suitablypaddedwithfelt,shallalsobepr
ovided.Thelouversshallbeprovidedwithsuitablefeltpadstopreventingressof
dust.Allincomingcablesshallenterthekioskfromthebottomandtheminimum
4mmthick,non-
magnetic,glandplateshallnotbelessthan600mmfromthebaseofthebox.Thegl
andplateandassociatedcompartmentshallbesealedinsuitablemannertopreve
nttheingressofmoisturefromthecabletrench–
forthosetransformerswhichareusedinpartlyindoorsubstation,If
required as per BOQ, a cable box for LV bushings shall be provided.

7.9.2 Protection &MeasuringDevices

i) OilConservatorTank

a) TheConservatortankshallhaveadequatecapacitybetweenhighestandlow
estvisiblelevelstomeettherequirementofexpansionofthe
totalcoldoilvolumeinthetransformerandcooling equipment.

b) Theconservatortankshallbeboltedintopositionsothatitcanberemoveforc
leaningpurposes.

c) Theconservatorshallbefittedwithmagneticoillevelgaugewithlowlevelel
ectricallyinsulated alarm contact.

d) Plainconservatorfitted withsilicagel breather.

PressureReliefDevice.

Thepressurereliefdeviceprovidedshallbeofsufficientsizeforrapidreleaseofa
nypressurethatmay
begeneratedinthetankandwhichmayresultindamageoftheequipment.
Thedeviceshalloperateatastaticpressureoflessthanthehydraulictestpressure
oftransformertank.Itshallbemounteddirectonthetank.Apairofelectricallyins
Part 2 : Employer’s Requirements 256
ulatedcontractshallbeprovidedforalarmand tripping.

BuchholzRelay

AdoublefloattypeBuchholzrelayshallbeprovided.Anygasevolvedinthetrans
formershallcollectinthisrelay.Therelayshallbeprovidedwithatestcocksuitab
leforaflexiblepipeconnectionfor checkingits operation.A coppertubeshall
beconnectedfrom thegas collector
toavalvelocatedabout1200mmabovegroundleveltofacilitatesamplingwitht
hetransformerinservice.Thedeviceshallbeprovidedwithtwoelectricallyinde
pendentpotentialfreecontracts,one foralarm on gasaccumulationand the
otherfortripping onsuddenrise ofpressure.

TemperatureIndicator

a) OilTemperatureIndicator(OTI)

Thetransformersshallbeprovidedwithamicroswitchcontacttypethermomete
rwith150mmdialfortopoiltemperatureindication.Thethermometershallhave
adjustable,electricallyindependentpotentialfreealarmandtripcontacts.Maxi
mumreadingpointerandresettingdeviceshallbemountedinthelocalcontrolpa
nel.Atemperaturesensingelementsuitablylocatedinapocketontopoilshallbef
urnished.ThisshallbeconnectedtotheOTIbymeansofcapillarytubing.Accura
cyclassofOTIshallbe±1%orbetter.OneNoelectricalcontactcapableofoperati
ngat 5A ac at230voltsupply.

WindingTemperatureindicator(WTI)

Adeviceformeasuringthehotspottemperatureofthewindingshallbeprovided.
Itshallcomprisethefollowing.

i) Temperature sensingelement.

ii) ImageCoil.

iii) Microswitchcontacts.

iv) AuxiliaryCTS,Ifrequiredtomatchtheimagecoil,shallbefurnishedandmount
edinthelocalcontrolpanel.

v) 150mmdiallocalindicatinginstrumentwithmaximumreadingpointermounte
dinlocalpanelandwithadjustableelectricallyindependentungroundedcontac
ts,besidesthatrequiredforcontrolof cooling equipment,one forhighwinding
temperature alarm and on for trip.
Part 2 : Employer’s Requirements 257
vi) Two numberelectrical contacteach capableofoperatingat5A ac at230 Voltsupply.

7.9.3 OilPreservationEquipment

7.9.3.1O i l Sealing

Theoilpreservationshallbediaphragmtypeoilsealinginconservatortoprevent
oxidationandcontamination of oildue tocontact with atmosphericmoisture.

The conservator shallbe fittedwith a dehydratingfilterbreather.Itshallbe

sodesignedthat.

i) Passage ofair is through a dustfilter &Silicagel.

ii) Silicagelis isolatefromatmosphere by anoilseal.

iii) Moistureabsorptionindicatedbyachangeincolourofthecrystalsofthesilicagel
canbeeasilyobserved fromadistance.

iv) Breatheris mountednotmore than1400 mm aboverail toplevel.

7.10 MARSHALLINGBOX

i) Sheetsteel,weather,verminanddustproofmarshalingboxfittedwithrequiredg
lands,locks,glassdoor,terminalBoard,heaterwithswitch,illuminationlampw
ithswitch,water-
tighthingedandpadlockeddoorofasuitableconstructionshallbeprovidedwith
eachtransformertoaccommodatetemperatureindicators,terminalblocksetc.
Theboxshallhavesloppingroofandtheinteriorandexteriorpaintingshallbeina
ccordancewiththespecification.Padlockalongwithduplicatekeysshall
besuppliedformarshalingbox.ThedegreeofprotectionshallbeIP-55orbetter.

ii) Theschematicdiagramofthecircuitryinsidethemarshalingboxbepreparedan
dfixedinsidethe doorunder aproponesheet.

iii) The marshaling box shallaccommodate the following equipment:

a) Temperatureindicators.

b) SpaceforaccommodatingControl&Protectionequipmentinfutureforthe
coolingfan(forONAFtype cooling, maybe provided in future).

c) Terminalblocks andglandplates forincomingandoutgoingcables.

Alltheaboveequipmentexceptc)shallbemountedonpanelsandbackofpanelw
iringshallbeusedforinter-
Part 2 : Employer’s Requirements 258
connection.Thetemperatureindicatorsshallbesomountedthatthedialsarenot
morethan1600mmfromthegroundlevelandthedoor(s)ofthecompartment(s)s
hallbeprovidedwithglazedwindowofadequatesize.Thetransformershallbeer
ectedonaplinthwhichshall be 2.5 feetaboveground level.

iv) Topreventinternalcondensation,ametalcladheaterwiththermostatshallbepr
ovided.TheheatershallbecontrolledbyaMCBofsuitableratingmountedinthe
box.Theventilationlouvers,suitablypaddedwithfelt,shallalsobeprovided.Th
elouversshallbeprovidedwithsuitable feltpadsto prevent ingress ofdust.

v) Allincomingcablesshallenterthekioskfromthebottomandtheglandplateshall
notbelessthan450mmfromthebaseofthebox.Theglandplateandassociatedco
mpartmentshallbesealed insuitablemanner to preventtheingress
ofmoisturefromthecabletrench.

7.11 TAPCHANGER

7.11.1 ON-LOADTAP-CHANGERS

i) The3.15/5/6.3/8/10/12.5MVAtransformersshallbeprovidedwithOn-
loadTaps.Specificationof OLTCis attached herewithasAnnexure.

ii) TheTransformerwithoff-
loadtapchanginggearshallhavetapsrangingfrom+5%to-15%in9 equalsteps
of 2.5%each for Off Load Tap.

iii) Thetapchangingswitchshallbelocatedinaconvenientpositionsothatitcanbeo
peratedfromgroundlevel.Theswitchhandleshallbeprovidedwithlockingarra
ngementalongwithtapposition indication,thus enablingtheswitch tobe
lockedinposition

7.12 FITTINGSANDACCESSORIES

Thefollowing fittingsandaccessoriesshallbeprovided on thetransformers:

i) Conservatorwithisolatingvalves,oilfillingholewithcapanddrainvalve.Thec
onservator vesselshallbe filled withconstant oil pressure diaphragm
oilsealing system.

ii) Magnetic typeoil levelgauge(150 mm dia)withlowoil levelalarm contacts.

iii) Prismatic/toughened glassoillevel gauge.

iv) Silicagelbreatherwithoilsealandconnectingpipecompletewithfirstfillofacti
vatedsilicagelorAlumina mountedat a levelof1300 mm abovegroundlevel.
Part 2 : Employer’s Requirements 259
v) A doublefloattypeBuchholzrelaywithisolatingvalve.Bleedingpipeand a
testing
cock,thetestcockshallbesuitableforaflexible(pipeconnectionforcheckingits
operation).A5mmdia.Copperpipeshallbeconnectedfromtherelaytestcockto
avalvelocatedatasuitableheightabovegroundleveltofacilitatesamplingofgas
withthetransformerinservice.Interconnectionbetweengascollectionboxand
relayshallalsobeprovided.Thedeviceshallbeprovidedwith
twoelectricallyindependentungroundedcontacts,oneforalarmongasaccumu
lationandtheotherfortrippingonsuddenoilsurge.Thesecontactsshallbewired
uptotransformermarshalingbox.Therelayshallbeprovidedwithshutoffvalve
ontheconservatorsideaswellas onthetankside.

vi) Pressurereliefdevices(includingpressurereliefvalve)andnecessaryairequali
zerconnectionbetweenthisandthe conservator with necessary alarmandtrip
contacts.

vii) Airrelease plugs in thetopcover.

viii) Inspection cover,access holeswith boltedcoversfor accesstoinner endsofbushing

etc.

ix) Windingtemperature(hotspot)indicatingdeviceforlocalmountingcompletei
nallrespects.Winding temperatureindicatorshall havetwo setofcontactsto
operateat differentsettings :

a) Toprovide windingtemperature high alarm

b) Toprovide temperature toohigh trip

x) Dialthermometerwithpocketforoiltemperatureindicatorwithonesetofalarm
andonesetoftrip contacts andmaximum readingpointer.

xi) Lifting eyesorlugs forthe topcover,coreand coilsand forthecomplete transformer.

xii) Jackingpads

xiii) Haulage lugs.

xiv) Protected typemercury / alcohol inglass thermometer and a pocketto

housethesame.

xv) Topandbottomfiltervalvesondiagonallyoppositeendswithpadlockingarran
gementonbothvalves.

xvi) Top and bottomsamplingvalves.

xvii) Drainvalvewithpadlockingarrangement
Part 2 : Employer’s Requirements 260

xviii) Ratingandconnectiondiagram plate.

xix) Two numbers tank earthing terminals with associated nuts and bolts for
connections to Employer’s grounding strip.

xx) MarshalingBox (MB)

xxi) Shutoffvalveonbothsidesofflexiblepipeconnectionsbetweenradiatorbanka
ndtransformertank.

xxii) CoolingAccessories:

a) Requisite numberof radiatorsprovidedwith :-

- Oneshut offvalve ontop

- Oneshut offvalve atbottom

- Airreleasedeviceon top

- Drainandsamplingdeviceatbottom

- Liftinglugs.

b) Airreleasedevice andoildrain plug on oil pipe connectors:

xxiii) Terminalmarking platesforCurrent Transformer and Main Transformer

xxiv) On/Off Load Tap changer as per BOQ

xxv) OilPreservationEquipment

xxvi) OilTemperature indicator

xxvii) Transformershallbesuppliedwithallcontrolcable,WTI&OTI,sensingcable,
glands,lugsetc(completecontrol).

Note:

1. Thefittingslistedaboveareindicativeandanyotherfittingswhicharegenerallyr
equiredforsatisfactoryoperationofthetransformeraredeemedtobeincludedin
thequotedpriceofthetransformer.
2. Thecontactsofvariousdevicesrequiredforalarmandtripshallbepotentialfreea
ndshallbeadequatelyratedfor continuous,makingandbreakingcurrentduties
as specified.
Part 2 : Employer’s Requirements 261

7.13 CONTROLCONNECTIONSANDINSTRUMENT
ANDWIRINGTERMINALBOARDANDFUSES

i) NormallynofusesshallbeusedanywhereinsteadoffusesMCB‟s(bothinAC&
DCcircuits)shallbeused.OnlyincaseswhereaMCBcannotreplaceafusedueto
systemrequirements,aHRCfusecanbe accepted.

ii) Allwiringconnections,terminalboards,fusesMCB‟sandlinksshallbesuitabl
efortropicalatmosphere.Anywiringliabletobeincontactwithoilshallhaveoilr
esistinginsulationandthebareends of strandedwire shall be sweated
together topreventseepageof oil along thewire.

iii) Panelconnectionsshallbeneatlyandsquarelyfixedtothepanel.Allinstruments
andpanelwiringshallberuninPVCornon-
rustingmetalcleatsofthecompressiontype.Allwiringtoapanel shall be
takenfromsuitableterminalboards.

iv) Whereconduitsareused,therunsshallbelaidwithsuitablefalls,andthelowestp
artsoftherunshallbeexternaltotheboxes.Allconduitrunsshallbeadequatelydr
ainedandventilated.Conduitsshall not be runator belowgroundlevel.

v) When400voltconnectionsaretakenthroughjunctionboxesormarshalingboxe
s,theyshallbeadequatelyscreenedand400voltsDangerNoticemustbeaffixedt
otheoutsideofthejunctionboxesormarshaling box.Proper
colourcodeforRed, Yellow, Bluewiresshallbe followed.

vi) AllboxwiringshallbeinaccordancewithrelevantISS.Allwiringshallbeofstra
ndedcopper(48strands ) of1100 Voltgradeandsizenotless than2.5 sq.mm

vii) Allwiresonpanelsandallmulti-
corecablesshallhaveferrules,foreasyidentifications,whichbear
thesamenumberatbothends,asindicatedinthe relevant drawing.

viii) Atthosepointsofinterconnectionbetweenthewiringcarriedoutbyseparatecon
tractors,whereachangeofnumbercannotbeavoideddoubleferrulesshallbepro
videdoneachwire.The changeofnumberingshall be
shownontheappropriatediagram oftheequipment.

ix) The sameferrulenumbershall not be usedonwires indifferentcircuits on

thesamepanels.

x) Ferrulesshallbeofwhiteinsulatingmaterialandshallbeprovidedwithglossyfi
nishtopreventtheadhesionofdirt.Theyshallbeclearlyanddurablymarkedinbl
ackandshallnotbeaffectedby dampnessor oil.
Part 2 : Employer’s Requirements 262
xi) StrandedwiresshallbeterminatedwithtinnedRossCourtneyterminals,claww
ashersorcrimpedtubularlugs.Separatewashersshallbesuitedtothesizeofthew
ireterminated.Wiringshall,ingeneral,beaccommodatedonthesidesofthebox
andthewiresforeachcircuitshallbeseparatelygrouped.Backofpanelwiringsh
allbearrangedsothataccesstotheconnectingitemsofrelays
andotherapparatus is notimpeded.

xii) Allcircuitsinwhichthevoltageexceeds125volts,shallbekeptphysicallysepar
atedfromtheremainingwiring.Thefunctionofeachcircuitshallbemarkedonth
eassociatedterminalboards.

xiii) Whereapparatusismountedonpanels,allmetalcasesshallbeseparatelyearthe
dbymeansofstranded(48No.)copperwireofstriphavingacrosssectionofnotle
ssthan2sq.mmwherestripisused,thejointsshallbesweated.Thecopperwiresh
allhavegreencolouredinsulationforearth connections.

xiv) Allwiringdiagramforcontrolandrelaypanelshallpreferablybedrawnasviewe
dfromthebackand shall showtheterminalboards arrangedas inservices.

xv) Terminalblockrowsshouldbespacedadequatelynotlessthan100mmaparttop
ermitconvenient access to external cables andterminations.

xvi) Terminalblocksshallbeplacedwithrespecttothecablegland(ataminimumdist
anceof200mm) as topermitsatisfactoryarrangement ofmulticorecabletails.

xvii) Terminalblocksshallhavepairsofterminalsforincomingandoutgoingwires.I
nsulatingbarriersshallbeprovidedbetweenadjacentconnections.Theheighto
fthebarriersandthespacingbetweenterminalsshallbesuchastogiveadequatep
rotectionwhileallowingeasyaccesstoterminals.Theterminalsshallbeadequat
elyprotectedwithinsulatingdustproofcovers.Nolivemetalshallbeexposedatt
hebackoftheterminalboards.CTterminalsshallhaveshortingfacilities.Theter
minalsforCTsshouldhaveprovisiontoinsertbananaplugsandwithisolatinglin
ks.

xviii) Allinterconnectingwiring,asperthefinalapprovedschemebetweenaccessori
esoftransformerandmarshalingboxisincludedinthescopeofthisspecification
andshallbedonebytheTransformersupplier.

xix) The schematic diagramshallbe drawnandfixedunder a

transparentprospanesheetontheinnersideof the marshaling boxcover.

xx) ToavoidcondensationintheMarshalingBox,aspaceheatershallbeprovidedwi
thanMCBandthermostat.

xxi) Suitable MV, CFL light shall beprovided intheMarshaling Box

forlightningpurpose.
Part 2 : Employer’s Requirements 263

7.14 RADIOINTERFERENCEANDNOISELEVEL

Transformersshallbedesignedwithparticularcaretosuppressatleastthethirda
ndfifthharmonicvoltagesso astominimizeinterferencewith
communicationcircuits. Transformer noiselevelwhen energizedatnormal
voltageandfrequencyshall be as perNEMA stipulations.

8 INSPECTIONANDTESTING

(i) TheContractorshallcarryoutacomprehensiveinspectionandtestingprogram
meduringmanufactureofthetransformer.Thisis,however,notintended to
formacomprehensiveprogrammeasitiscontractor’sresponsibilitytodrawupa
ndcarryoutsuchaprogrammedulyapprovedby theEmployer.

(ii) Transformer ofeach ratingwill be as per pre-typetesteddesign.

(iii) The pre-shipment checks shallalso be carriedout by thecontractor.

(iv) The requirements onsitetests are as listedinthespecifications.

(v) CertifiedtestreportandoscillogramsshallbefurnishedtotheEmployerConsul
tantsforevaluationasperthescheduleofdistributionofdocuments.TheContra
ctorshallalsoevaluatethetestresultsandrectifythedefectsintheequipmentbas
edonhisandtheEmployersevaluationsofthetestswithoutanyextrachargestot
heEmployer.Manufacturer’sTestCertificatesinrespect
ofallassociatedauxiliaryandancillaryequipmentshallbe furnished.

(vi) Thebiddershallstateinhisproposalthetestingfacilitiesavailableathisworks.I
ncasefulltestingfacilitiesarenotavailable,thebiddershallstatethemethodpro
posedtobeadoptedsoastoascertain the
transformercharacteristicscorresponding tofullcapacity.

8.1 INSPECTION

Transformersnot manufactured asper Type-Testeddesignshall be rejected.

i) TankandConservator

a) Inspection of majorweld.

b) Crackdetectionofmajor strengthweldseams by dyepenetrationtest.

c) Checkcorrectdimensionsbetweenwheels,demonstrateturningofwheels,thr
ough900
Part 2 : Employer’s Requirements 264
andfurtherdimensional check.
d) Leakagetestofthe conservator.
ii) Core
a) Sampletestingofcorematerialsforcheckingspecificloss,properties,magneti
zationcharacteristicsandthickness.
b) Checkonthequalityofvarnishifusedonthestampings.
c) Check on theamount ofburrs.
d) Visualanddimensional checkduringassemblystage.
e) Checkoncompletedcoreformeasurementofironloss,determinationofmaxim
umfluxdensity,
f) Visualanddimensionalchecksforstraightnessandroundnessofcore,thicknes
soflimbsand suitabilityofclamps.
g) HighvoltageDCtest(2KV foroneminute)between core andclamps.

Please refer to “Check-list for Inspection of Prime quality

CRGO for Transformers” attached at Annexure-A. It is
mandatory to follow the procedure given in this Annexure.

iii) InsulatingMaterial

a) Sample checkforphysical propertiesofmaterials.

b) Check fordielectric strength
c) Check for thereactionofhotoil oninsulatingmaterials.

iv) Winding

a) Sample checkonwindingconductorfor mechanical andelectrical

conductivity.
b) Visualanddimensional checks onconductorfor scratches,dentmarketc.
c) Sample checkoninsulatingpaperfor PHvalue,electric strength.
d) Checkfor thebondingoftheinsulatingpaperwithconductor.
e) Checkandensurethatphysicalconditionofall
materialstakenforwindingsissatisfactoryand freeofdust.
f) Check forabsenceof shortcircuit betweenparallelstrands.

v) ChecksBeforeDrying Process

a) Check conditionofinsulationontheconductor andbetweenthewindings.

b) Checkinsulationdistancebetweenhighvoltageconnections,between
highvoltageconnectioncablesandearth and otherliveparts.
c) Checkinsulatingdistances between lowvoltage
Part 2 : Employer’s Requirements 265
connectionsandearthandotherparts.
d) Insulating testfor coreearthing.

vi) Check DuringDryingProcess

a) Measurement andrecordingof temperatureanddrying timeduringvacuum

treatment.
b) Checkforcompletenessof drying

vii) AssembledTransformer

a) Checkcompletedtransformeragainstapprovedoutlinedrawing,provi
sionforallfittings, finishleveletc.

b) Jacking test ontheassembled Transformer.

viii) OilAllstandardtestsinaccordancewithIS:335shallbecarriedoutonTransform
eroilsamplebeforefilling in thetransformer.

ix) TestReportforboughtout
itemsThecontractorshallsubmitthetestreportsforallboughtout/subcontracte
d itemsforapproval.

a) Buchholzrelay
b) Sudden pressurerise relayonMain Tank
c) Winding temperatureindicators(for TXcapacity 5 MVA )
d) Oiltemperature indicators
e) Bushings
f) Bushingcurrent transformersinneutral(IfProvided)
g) Marshalingbox
h) On/Off Load Tap changer as per BOQ
i) Any otheritem required to completetheworks.
j) Porcelain,bushings,bushingcurrenttransformers,whereverprovided
,windingcoolers,controldevices,insulatingoilandotherassociatedeq
uipmentshallbetestedbythe
contractorinaccordancewithrelevantIS.Ifsuchrequirementispurchas
edbythecontractoronasub-
contract,heshallhavethemtestedtocomplywiththeserequirements.

8.2 FACTORYTESTS

i) Allstandards routinetestsinaccordanceIS:2026 withdielectric

testscorresponding asper latestamendments to IS:2026 shall be
carriedout.
ii) All auxiliary equipmentshallbe tested as perthe relevant
IS.Testcertificates shall be submittedforbought outitems.
Part 2 : Employer’s Requirements 266
iii) Highvoltagewithstandtestshallbeperformedonauxiliaryequipmentandwirin
gaftercompleteassembly.
iv) Following additionalroutine testsshallalsobe carried out on each transformer:

a) Magnetic CircuitTestEach core shall be tested for 1 minuteat2000

VoltAC
b) Oilleakage test ontransformer

8.2.1 TypeTest

8.2.1.1 Themeasurementsandtestsshouldbecarriedoutinaccordancewiththe
standardspecifiedineachcaseasindicatedinthefollowingtableifthesa
metestswerenotconductedearlieratCPRIoranyNABLaccreditedLa
boratoryonthetransformersoftheoffered designwithoutany
costimplicationonemployer.
Table6:Transformertypetests

TypeTest Standard

Temperature Rise Test IEC76/IS2026/I

ImpulseVolt ageWithstandTest,includingFull S6600
IEC76/IS2026
Wavesand ChoppedWavesas listed below
NoiseLevel Measurement IEC551

InaccordancewithIEC76-
3thefollowingsequenceofimpulsesshouldhavebeen/should be
applied;
• Onefullwaveat50%BIL;
• Onefullwaveat100%BIL;
• Onechopped waveat 50%BIL
• Two choppedwavesat100%BILand
• Two fullwaves at100%BIL.

8.2.1.2 Ifthetypetestreport(s)submittedbythebidderdonotfulfillthecriteria,a
sstipulatedinthistechnicalspecification/Bidder’soffer,therelevantty
petest(s)has/havetobeconductedbytheBidderathisowncostinCPRI/
NABLaccreditedlaboratoryinthepresenceofemployersrepresentati
ve(s)withoutanyfinancialliabilitytoemployerinthe eventof
orderplacedonhim.

8.2.1.3 Theofferedtransformermustbemanufacturedaspertypetesteddesign.
AcopyoftypetestcertificatemustbesubmittedbymanufacturertoEngi
neer/Employer.Transformersofferedwithouttypetestedhoweverdes
ignshall notbe
accepted.Incasemanufactureragreesfortypetestingoftransformers,t
estingshallbeconductedonmanufacturer’scost.Noclaimshallbeacce
Part 2 : Employer’s Requirements 267
ptabletowardstypetesting.Thetransformersshallbe acceptedonly
onacceptanceoftypetesting results by employer.

8.2.1.4 ThesuppliershallfurnishcalculationsinaccordancewithIS:2026tode
monstratetheThermalability of the transformerstowithstandShort
Circuit forces.

8.2.1(A)SpecialTest

Theshortcircuittestshall beamandatorytestforeachdesignshall
besuppliedbythemanufacturerandnoexceptionshall be allowed.
Thetestshall beconductedas perlatest standardtabledbelow:
ShortCircuitTest IEC76 / IS2026

8.2.2 STAGEINSPECTION

Thesuppliershallofferthecore,windingsandtankofeachtransformerf
orinspectionbytheEmployersrepresentative(s).DuringstageInspecti
on,allthemeasurementslikediameter,windowheight,legCentre,stac
kwidth,stackthickness,thicknessoflaminationsetc.forcoreassembly
,conductorsize,Insulationthickness,I.D.,O.D,windingheight,major
andminorinsulationsforbothH.VandL.Vwindings,length,breadth,h
eightandthicknessofplatesofTransformertank,thequalityoffittingsa
ndaccessorieswillbetaken/determined.Thesuppliercanofferforfinal
inspectionofthe transformerssubject to clearance of the stage
Inspection report bythe Employer.

8.2.3 RoutineTests

TransformerroutinetestsshallincludetestsstatedinlatestissueofIS:20
26(Part–1).These tests shall also includebutshall not be limitedto
thefollowing :
(i) Measurement ofwindingDCresistance.

(ii) Voltage ratio oneach tappingandcheck ofvoltagevector relationship.

(iii) Impedance voltageatall tappings.

(iv) Magneticcircuittestas per relevant ISSor CBIP manual or

lateststandardbeing followed.

(v) Measurement ofLoad losses at normal tapand extremetaps.

(vi) Noloadlossesandnoloadcurrentatratedvoltageandratedfrequ
ency,alsoat25%to120 % ofratedvoltageinsteps.
Part 2 : Employer’s Requirements 268

(vii) Absorptionindexi.einsulationresistancefor15secondsand60s
econds(R60/R15)andpolarizationindexi.eInsulationResista
ncefor10minutesandoneminute(R10mt /R1 mt).

(viii) Inducedovervoltagewithstandtest.

(ix) Separate sourcevoltagewithstandtest.

(x) Tandeltameasurementandcapacitanceofeachwindingtoearth(withall
otherwindingsearthed)&betweenall windings connectedtogether
toearth.

(xi) Measurement of zerosequence impedance

(xii) Tests on On/Off Load Tap changer as per BOQ (fully assembled on
transformer) as per IS 2026

(xiii) Auxiliarycircuittests

(xiv) OilBDV tests

(xv) Measurementofneutralunbalancecurrentwhichshallnotexceed2%oft
hefullratedcurrentofthetransformer.

(xvi) Magnetic balancetest

(xvii) Leakage test.

Six(6)setofcertifiedtestreportsandoscillographsshallbesubmittedforevaluationpriort
odispatchoftheequipment.Thecontractorshallalsoevaluatethetestresultsandshallcorr
ectanydefectindicatedbyhisandEmployersevaluationofthetestswithoutchargeto
theEmployer.

8.4 TANKTESTS

a) OilleakageTest:

The tankandoilfilledcompartments shallbe testedfor oiltightnesscompletelyfilled

with air
oroilofviscositynotgreaterthanthatofinsulatingoilconformingtoIS:335attheambientt
emperatureandapplyingapressureequaltothenormalpressureplus35KN/m2measured
atthebaseofthetank.Thepressureshallbemaintainedforaperiodofnotlessthan12hours
ofoil andonehour for airandduringthattimeno leak shall occur.

b) PressureTest
Part 2 : Employer’s Requirements 269

WhererequiredbytheEmployer,onetransformertankofeachsizetogetherwithitsradiat
or,conservatorvesselandotherfittingsshallbesubjectedtoapressurecorrespondingtot
wicethenormalheadofoilortothenormalpressureplus35KN/m2whicheverislower,me
asuredatthebaseofthetankand maintainedfor onehour.

c) VacuumTest

Onetransformertankofeachsizeshallbesubjectedtothevacuumpressureof60mmofme
rcury.Thetanksdesignedforfullvacuumshallbetestedataninternalpressureof3.33KN/
m2(25mmofmercury)foronehour.Thepermanentdeflectionofflatplatesafterthevacuu
mhasbeenreleasedshallnotexceedthevaluespecifiedinC.B.I.P.ManualonTransforme
rs(Revised 1999) withoutaffectingthe performance ofthe transformer.

8.5 PRE-SHIPMENTCHECKATMANUFACTURERSWORKS

i) Checkforproperpackingandpreservationofaccessorieslikeradiators,bushing
s,explosionsvent,dehydratingbreather,rollers,buchholzrelay,controlcubicle
connectingpipesandconservatoretc.

ii) Checkforproperprovisionofbracingtoarrestthemovementofcoreandwindin
gassemblyinsidethetank.

iii) Gastightnesstest toconformtightness.

8.6 INSPECTIONANDTESTINGATSITE

Onreceiptoftransformeratsite,shallbeperformeddetailedinspectioncovering
areasrightfromthereceiptofmaterialuptocommissioningstage.Anindicative
programofinspectionasenvisaged by theEngineeris givenbelow.

8.6.1 ReceiptandStorageChecks

i) Checkandrecordconditionsofeachpackagevisiblepartsofthetransformersetc
foranydamage.

ii) Check andrecordthegas pressurein thetransformertank as well as in thegas

cylinder.

iii) Visualcheckofcoreandcoilsbeforefillingupwithoilandalsocheckconditiono
fcoreandwindingingeneral.

8.6.2 InstallationChecks

i) Inspection and performancetesting ofaccessorieslike tapchangersetc.

Part 2 : Employer’s Requirements 270

ii) Check chokingofthetubes ofradiators

iii) Testonoilsamplestakenfrommaintanktopandbottomandcoolingsystem.Sa
mplesshouldbetaken onlyaftertheoil has beenallowed to settlefor 24
hours.

iv) Check thewholeassemblyfor tightness,general appearanceetc.

v) Oilleakagetests.

8.6.3 Pre-CommissioningTests

After thetransformerisinstalled, thefollowing pre-commissioning tests and

checksshall be donebeforeputtingthetransformer inservice.
i) MeggerTest

ii) Phaserelationshiptest ( Vector grouptest)

iii) Buchholz relayalarm &surgeoperationtest (Physical)

iv) Ratio test on all taps

v) Lowoillevel ( inconservator) alarm

vi) TemperatureIndicators (Physical)

vii) Marshalingkiosk (Physical)

8.6.4 Thefollowingadditionalchecksshallbemade:

i) Alloilvalves areincorrect positionclosed or opened asrequired

ii) Allair pocketare cleared.

iii) Thermometer pocketsare filled withoil

iv) Oilis atcorrect levelin thebushing,conservator, diverterswitch& tanketc.

v) Earthing connections are made.

vi) Bushing arcing horn issetcorrectlyand
gapdistanceisrecorded.
vii) CTpolarityand ratio iscorrect.

8.7 PERFORMANCE
Part 2 : Employer’s Requirements 271

The performance of thetransformer shallbe measured on the following aspects.

i) Thetransformershallbecapableofbeingoperatedwithoutdangeronanytappin
gattheratedKVAwithvoltagevariationsand ± 10% corresponding to
thevoltageofthetapping

ii) Radiointerference andNoise Level

iii) Thetransformershallbedesignedwithparticularattentiontothesuppressionoft
hirdandfifthharmonicssoastominimize interferencewith communication
circuits.

8.8 FAULTCONDITIONS

a) Thetransformershallbecapableofwithstandingfortwo(2)secondswithoutda
magesanyexternalshortcircuit to earth

b) Transformershallbecapableofwithstandingthermalandmechanicalstressesc
onveyedbysymmetricalorasymmetricalfaultsonanywinding.Thisshallbede
monstratedthroughcalculationas perIS :2026.

c) Transformershallaccept,withoutinjuriousheating,combinedvoltageandfreq
uencyfluctuationwhichproducethe125%overfluxing conditionfor
oneminuteand 140%for 5 seconds.

8.9 WITNESSINGOFTESTSANDEXCESSIVELOSSES

i) TheEmployerreservestheright
torejecttheTransformeriflossesexceedthemaximumspecifiedasperClauseN
o2.SPECIFICTECHNICALREQUIREMENTS(STANDARDCONDITIO
NS),item-
35ofthisspecificationoriftemperatureriseofoilandwindingexceedthevaluess
pecifiedatitem -26 ofthe aboveclause.

9 LIQUIDATEDDAMAGESFOREXCESSIVELOSSES

Thereisnopositivetoleranceontheguaranteedlossesofferedbythebidder.Ho
wever,thetransformer(s)shallberejectedoutrightly,ifanyofthelossesi.e.nolo
adlossorloadlossorbothexceed(s)theguaranteedmaximumpermissiblelossfi
guresquotedbythebidderintheTechnical Data Schedule with thebid.

10 SPAREPARTS

Incasethemanufacturergoesoutofproductionofspareparts,thenheshallmakea
vailablethedrawingsofsparepartsandspecificationofmaterialsatnoextracostt
Part 2 : Employer’s Requirements 272
otheEmployertofabricate orprocure sparepartsfromother sources.

MandatorySpareParts

Thesuppliersshallprovide the following mandatoryspares

foreachofTransformersupplied
1. H.V.&L.V.Bushing&Studs–Each 2 Nos
2. Bimetallicconnector for H.V &L.V. Bushings–Each 2 sets

10.1 INSTRUCTIONMANUAL

Eightsetsoftheinstructionmanualsshallbesuppliedatleastfour(4)weeksbefor
etheactualdispatchofequipment.Themanualsshallbeinboundvolumesandsh
allcontainallthedrawings
andinformationrequiredforerection,operationandmaintenanceofthetransfor
mer.Themanualsshallinclude amongstother,thefollowingparticular:

a) Markederectionprintsidentifyingthecomponents,partsofthetransformerasdi
spatchedwithassembly drawings.

b) Detailed dimensions, assemblyand descriptionof all auxiliaries.

c) Detailedviewsofthecoreandwindingassembly,windingconnectionsandtapi
ngstapchangerconstruction etc.Thesedrawingsare
requiredforcarryingoutoverhauling operationatsite.

d) Salient technicalparticularsof thetransformer.

e) Copiesofallfinal approved drawings.

f) Detailed O&M instructions withperiodical checklists andPerforma etc.

10.2 COMPLETENESSOFEQUIPMENT

Allfittingsandaccessories,whichmaynotbespecificallymentionedinthespeci
ficationbutwhicharenecessaryforthesatisfactoryoperationofthetransformer,
shallbedeemedtobeincludedinthespecificationandshallbefurnishedbythesu
pplierwithoutextracharges.Theequipmentshallbecompleteinalldetailswhet
hersuchdetailsarementionedinthespecification or not,withoutanyfinancial
liability to theEmployer underanycircumstances.

11.0 COMMISSIONING
The utility will give a 10 days’ notice to the supplier of transformer
before commissioning. The manufacturer will depute his representative
to supervise the commissioning. In case, the manufacturer fails to depute
his representative, the utility will go ahead with the commissioning and
Part 2 : Employer’s Requirements 273
under these circumstances, it would be deemed that commissioning is
done as per recommendations of manufacturer.

12.0 GUARANTEE

The manufacturers of the transformer shall provide a guarantee of 60

months from the date of commissioning. In case the transformer fails
within the guarantee period, the supplier will depute his representative
within 15 days from date of intimation by the utility for joint inspection.
In case, the failure is due to the reasons attributed to supplier, the
transformer will be replaced/repaired by the supplier within 2 months
from the date of joint inspection.
 Part 2 : Employer’s Requirements 274

Annexure-B
) Methodologyforcomputingtotalowningcost for
Power Transformer

TOC=IC+(AxWi) +(BxWc) ; Losses in KW

Where,
TOC = TotalOwningCost
IC = Initialcost ta o transfor a quo b the
including xe f mer s ted y
s
manufacturer
Afactor = Cost of no load lossesinRs/KW (A = 334447)
Bfactor = Cost of load lossesin Rs/KW (B = 151616)
Wi = Noloadlosses quoted by themanufacturerin KW
Wc = Load losses quotedby the manufacturer in KW
Part 2 : Employer’s Requirements 275

ONLOAD TAPCHANGERFOR33/11KV POWERTRANSFORMER

ThetappingrangeofOnLoadTapChangershallbe+5%to-
15%instepsof1.25%each.Thenooftapsshallbe17.TheOnLoadTapChangershall
besuppliedwithRTCC panelandAVR(AutomaticVoltage Regulating Relay)

TheContinuouscurrentratingofthetapchangershallbebasedonconnectedwindin
grating and shallhaveliberalandamplemargin.
Lowerratedtapchangersconnected inparallelare not acceptable.

Theon-
loadtapchangingequipmentshallhavetheprovisionformechanicalandelectricalc
ontrolfromalocalpositionandelectricalcontrol
fromaremoteposition.Forlocalmechanicaloperation,theoperatinghandleshallb
ebroughtoutsidethetankforoperationfromfloorlevelwithprovisiontolockthehan
dleineachtapposition.RemoteelectricaloperationshallhaveanAUTO-
MANUALselectionattheremotelocation.WhenselectedAUTO,thetapchanging
gearshallmaintainsteadyvoltagewithinpracticallimitonthetransformersseconda
rybusfromwhichthereferenceshallnotrespondtotransientvariationofvoltagedue
togriddisturbance andsystemfault.

Therequiredvoltagerelayshallnotbesensitivetofrequencyvariationandshallbesu
itableforsensingvoltagefromthesecondaryofpotentialtransformersmountedon
the 66KV,33KV,or11KVbus.

Thetapchangershallbeprovidedwithover-
currentprotectioninordertopreventthetap-changeoperationduring
ashortcircuit,whichwould
togreatlystressthecontactsofthediverterswitch.Thefunctionofprotectionshallbe
arrangedasfollows;

(i) Wheneverovercurrentoccurs,thecontrolcircuitforcommandingOLTCmotorope
rationshallbeblockedbythenormallyclosecontractsoftheovercurrentrelays.

(ii) Ifduring
tapchangeovercurrentoccurs,theOLTCmotorcircuitshallbeblockedthroughthe
mechanicalcamswitch,whichisclosefromtheverybeginningtotheveryendofever
ytapchangeoperationandtothenormallyopencontactsoftheovercurrentrelays.Th
estopactionofthemotorshallbemade throughthe motorbrakecontactor.

Thedesignofthetapchangingequipmentshallbesuchthatthemechanismwillnotst
opinanyintermediateposition;however,ifthemechanismthroughfaultyoperatio
ndoesstopinanintermediateposition,thefullloadmustbecarriedbythetransforme
rwithoutinjurytotheequipment.Themechanical position
indicatorshallbeequippedin themotor
drivecubicle.Themotorshallbedesignedtobeofstepcontrol.Inanycasetheoperati
onshallbeofstepbystep.

Thevoltageregulatingrelayshallbesuppliedtogetherwiththetimerandundervo
Part 2 : Employer’s Requirements 276
ltagerelay.Thesignalorderfromthevoltageregulatingrelaytoexecutethetapchan
geroperation,whentheregulatingvoltageisoutofthevoltageregulatinglevelshall
bedesignedtobedelayedbytheadjustabletimer.Ifthecontrolvoltageabnormally
falls,
themovementofthetapchangershallbelockedbythecontactoftheundervoltagere
lay,evenifthecontactsofthevoltageregulatingrelayare working.

Thecontrolcircuitofthetransformershallbecompletelydesignedandprovisionss
hallbemadeforparalleloperationwithanothertransformer.

Thefollowingaccessories,controlandselectorswitchesandothernecessaryacces
soriesshallbefurnished.

Remotetapchangercontrolboard
(Placedinthecontrolroom)
 Voltmeter
 “AUTO-MANUAL” controlswitch
 “RAISE-LOWER”controlswitch
 Tappositionindicator
 Tapchangeroperationprogramindicator.

TransformerTapChangerdrivingmechanismcontrolcubicle
 “REMOTE-LOCAL-TEST”selector switch
 “AUTOMATIC-MANUAL” controlswitch
 “RAISE-LOWER” controlswitch
 Tappositionindicator
 Tapchangeroperationprogramindicator
 Voltmeter
 Tapchangeoperationcounter
 Meansformanualoperationwhenpowersupplyislost
Part 2 : Employer’s Requirements 277

Check-list for Inspection of Prime quality CRGO for Transformers

During inspection of PRIME CRGO, the following points needs to be checked by the
Transformer manufacturer. Utilitity’s inspector shall verify all these points during
inspection:-
i) In case PRIME CRGO cutting is at works of Transformer Manufacturer:

Review of documents:

Purchase Order (unpriced) to PRIME CRGO supplier/Authorised Agency

Manufacturer’s test certificate

Invoice of the Supplier

Packing List

Bill of Lading

Bill of Entry Certificate by Customs Deptt.

Reconciliation Statement as per format below

Certificate of Origin
BIS Certification

Format for Reconciliation/Traceability records

Packing List No./date /Quantity of PRIME CRGO received
Name of Manufacturer
Manufacturer test certificate No./date

Serial Deatails of Drawing Quantity Commulative Balance

No. Package/Job Reference Invoved Quantity Stock
Consumed

(i) .1 Inspection of PRIME CRGO Coils:

PRIME CRGO-Manufacturer’s Identification Slip on PRIME CRGO

Coils
Visual Inspection of PRIME CRGO Coils offered as per packing list ( for
verification of coil details as per Test certificate & healthiness of packaging).
Unique numbering inside of each sample of PRIME CRGO coil and
verification of records to be maintained in the register for consumption of
CRGO coil.
ISI logo sticker on packed mother coil and ISI logo in Material TC.
Part 2 : Employer’s Requirements 278
2.2. During inspection of PRIME CRGO, surveillance testing of sample shall be
carried out for Stacking Factor, Permeability, Specific watt loss at 1.5 Tesla
and/or 1.7 Tesla depending on the grade of PRIME CRGO and aging test etc.
applicable as per relevant IS/ IEC standard, Tech. Spec., MQP and Transformer
manufacturer plant standard.
Inspection Clearance Report would be issued after this inspection

3 Inspection of PRIME CRGO laminations: Transformer manufacturer will

maintain records for traceability of laminations to prime CRGO coils and
burr/bow on laminations shall be measured. Utility can review these records on
surveillance basis.

4. Inspection at the time of core building:

Visual Inspection of PRIME CRGO laminations. In case of suspected mix-up/
rusting/decoloration, samples may be taken for testing on surveillance basis for
tests mentioned in A.2.2 above.
Above tests shall be witnessed by Utility. In case testing facilities are not
available at Manufacturer’s work, the sample(s) sealed by Utility to be sent to
approved labs for testing.
Inspection Clearance Report would be issued after this inspection
(i) In case PRIME CRGO cutting is at Sub-vendor of Transformer
Manufacturer:

Review of documents:

Purchase Order (unpriced) to PRIME CRGO supplier/ Authorised Agency

Purchase Order (unpriced) to Core Cutter

Manufacturer test certificate

Invoice of the Supplier

Packing List

Bill of Lading

Bill of Entry Certificate by Customs Deptt.

Reconciliation Statement as per format below

Certificate of origin
BIS Certification

Format for Traceability records as below:-

Packing List No./date /Quantity of PRIME CRGO received
Name of Manufacturer
Manufacturer test certificate No./date
Part 2 : Employer’s Requirements 279
Serial Name of Deatails of Drawing Quantity Commulative Balance Dispatch
No. Customer Package/Job Reference Invoved Quantity Stock details
Consumed

(ii) 1 Inspection of PRIME CRGO Coils:

PRIME CRGO-Manufacturer’s Identification Slip on PRIME CRGO Coils

Visual Inspection of PRIME CRGO Coils offered as per packing list ( for
verification of coil details as per Test certificate & healthiness of packaging).
Unique numbering inside of each sample of PRIME CRGO coil and
verification of records to be maintained in the register for consumption of
CRGO coil.
ISI logo sticker on packed mother coil and ISI logo in Material TC.

2.2. During inspection of PRIME CRGO, surveillance testing of sample shall be

carried out for Stacking Factor, Permeability, Specific watt loss at 1.5 Tesla
and/or 1.7 Tesla, thickness depending on the grade of PRIME CRGO and
aging test etc. applicable as per relevant IS/ IEC standard, Tech. Spec., MQP
and Transformer manufacturer plant standard.

Inspection Clearance Report would be issued after this inspection

3 Inspection of PRIME CRGO laminations:
Transformer manufacturer representative will inspect laminations and issue
their internal Inspection Clearance Report. Inspection will comprise of review
of traceability to prime CRGO coils, visual Inspection of PRIME CRGO
laminations and record of burr/bow. After clearance given by transformer
manufacturer, Utility will issue an Inspection Clearance Report after record
review. If so desired by Utility, their representative may also join transformer
manufacturer representative during this inspection.

Inspection Clearance Report would be issued after this inspection

vi) Inspection at the time of core building:

Visual Inspection of PRIME CRGO laminations. In case of suspected mix-

up/rusting/decoloration, samples may be taken for testing on surveillance basis
for tests mentioned in B.2.2.

Inspection Clearance Report would be issued after this inspection

NOTE :-
a) Transformer Manufacturer to ensure that PRIME CRGO is procured from
POWERGRID approved vendors and CRGO manufacturer should have valid
BIS Certificate for respective offered Grade.
14.1 Transformer Manufacturer should also involve themselves for ensuring the
Part 2 : Employer’s Requirements 280
quality of CRGO laminations at their Core Cutter’s works. They should visit the
works of their Core cutter and carry out necessary checks.

a) General

If a surveillance sample is drawn and sent to TPL (if testing facility not available
with the manufacturer), the Transformer manufacturer can continue manufacturing
at their own risk and cost pending TPL test report on PRIME CRGO sample
drawn. Decision for acceptance of PRIME CRGO shall be based upon report of
the sample drawn.
These checks shall be read in-conjunction with approved Quality Plan,
specification as a whole and conditions of contract.
Sampling Plan (PRIME CRGO)
st
33 / 11 kV -1 transformer and subsequently at random 10%
ofTransformers (min. 1) offered for inspection.
DTs and other ratings -1st transformer and subsequently at random 2%
ofTransformers (min. 1) offered for inspection.
NOTE: - One sample for each lot of CRGO shall be drawn on surveillance basis.
CRGO has to be procured only from Discom/POWERGRID approved vendors. List of
such vendors is available at the following website. Since the list is dynamic in nature,
the site may be checked from time to time to see the list of approved vendors.
http://apps.powergridindia.com/ims/ComponentList/Power-
former%20upto%20420%20kV-CM%20List.pdf
Part 2 : Employer’s Requirements 281

SCHEDULE OF GUARANTEED TECHNICAL PARTICULARS : ( To be

furnished and signed by the tenderer for each category of Transformer ).

GUARANTEED TECHNICAL PARTICULARS

Sl.
N Particulars
o.
1. Name and address of the manufacturer :
2. Country of origin :
3. Applicable standard :
4. Maximum continuous rating (in MVA) :
5. No load voltage ratio at :
Principal (Nominal) tap (in
KV/KV)
6. Rated frequency (in Hz) :
7. Number of phases :
8. Type of Cooling :
9. Connections :
(i) H.V. Winding :
(ii) L.V. Windi ng :
10. Vector Symbol :
11. Tappings :
( a ) Range :
(b) Number of steps
(c ) Variation of voltage in each step
(in KV)
(d) No load voltage ratio in each tap (in :
KV/KV) for 6.3 & 10 MVA 33/11KV
TR.

GUARANTEED TECHNICAL
PARTICULARS

Tap Number Voltage ratio in Tap Number Voltage ratio in KV/KV

KV/KV
1. 10.
2. 11.
3. 12.
4. 13.
5. 14.
6. 15.
7. 16.
8. 17.
9.
Part 2 : Employer’s Requirements 282
12. (i) Temperature rise under normal operating :
condition above ambient temperature
(a) Top oil (in Degree C) :
(b) Windings (in Degree C) :
(ii) Maximum hot spot temperature of :
Copper windings (in Degree C)
13. Magnetising current referred to H.V. at rated :
frequency
(a) at 90% rated voltage : (in Amps) :
(b) at 100% rated voltage : (in Amps) :
(c ) at 110% rated voltage (in Amps) :
14. Power factor of magnetizing current at 100% rated :
voltage & frequency
15. No load current at rated voltage and Rated :
frequency (in Arms)
16. No load loss in KW at rated frequency and voltage :
(a ) at Low est tap :
(b) at principal tap :
(c ) at highest tap :
17. Load loss in KW at 75 Deg. C. at Rated output :
and frequency

GUARANTEED TECHNICAL
PARTICULARS

(a ) at Low est tap :

(b) at principal tap :
(c ) at highest tap :
18. Percentage Regulation at full load at 75 Deg.C :
(a) at unity power factor :
(b) at 0.8 power factor lagging :
19. Efficiencies at 75 Deg.C (in percentage) :
a) at full load (i) at unity power factor :
(ii) at 0.8 power factor lagging :
(b) at 3/4 full load (i) at unity power factor :
(ii) at 0.8 power factor lagging :
(c) at 1/2 full load (i) at unity power factor :
(ii) at 0.8 power factor lagging :
20. Impedance voltage on rated MVA base at rated :
current and frequency for the Principal tapping 75
Deg.C. (in percentage)
Part 2 : Employer’s Requirements 283
21. a) Reactance voltage at rated current and :
frequency for the principal tapping at 75 Deg.C. (in :
percentage)

b) Resistance voltage at rated current and

frequency for the principal tapping at 75 Deg.C. (in
percentage)
22. Resistance at H.V. base at 75 Deg.C.
(a ) at Low est tap :
(b) at principal tap :
(c ) at highest tap :
23. Reactance at H.V. base at 75 Deg.C.
(a) at Lowest tap :
(b) at principal tap :
© at highest tap :
24. Withstand time without injury for three phase dead :
short circuit at terminal (in seconds)
25. Short time current rating for short circuit with:
duration
a) H.V. winding (in K. Amps) :
b) L.V. winding (in K Amps) :
c) Duration (in seconds) :
26. Permissible overloading with time :
27. Core :
i) Type :
ii) Flux density of Core and yoke at principal tap :
a) at 100% rated voltage at 50 Hz (in lines/sq.cm :
b) at 110% rated voltage at 50 Hz (in lines/sq.cm.) :
iii) Thickness of Stamping (in mm) :
iv) Type of insulation between core laminations :
v) Core bolt withstand Insulation (in KV rms for 1 :
min)
vi) Approximate area of Cross Section of Core and :
yoke (in sq.mm.)
vii) Material of Core clamping plate :
viii) Thickness of Core clamping plate (in mm) :
ix) Insulation of Core clamping plate :
x) Describe location/Method of Core grounding :
28 Terminal Arrangement :
i) High Voltage :
ii) Low Voltage :
29 Positive Sequence Impedance between HV & L.V. :
winding on rated MVA base at rated Current and
frequency at 75 Deg.C. winding temperature
Part 2 : Employer’s Requirements 284
i) At principal tapping (in percent) :
ii) At lowest tapping (in percent) :
iii) At highest tapping (in percent) :
30 Zero Sequence Impedance at reference temperature :
of 75 Deg.C at principal tap (in percent)
31 Details of windings :
i) Type of Winding :
(a) High Voltage :
(b) Low Voltage :
32 Winding conductor :
i) Material of the winding conductor
(a) High Voltage :
(b) Low Voltage :
ii) Conductor Area :
(a) High Voltage (in sq.cm) :
(b) Low Voltage (in sq.cm) :
iii) Current density of windings at rated At principal At lowest At highest
MVA tapping tapping tapping
1 2 3
(a) High voltage (Amp.per sq.cm)
(b) Low voltage (Amp.per sq.mm)
iv) Insulating material used for
(a) High volt age winding :
(b) Low volt age winding :
v) Insulting material used between :
(a) High voltage and low voltage :
winding
(b) Low voltage winding and core :
vi) Whether adjustable coil clamps are
38. Bushing : High voltage Low voltage

i) Make
ii) Type
iii) Applicable standard
iv) Insulation withstand test Voltage
a) Lightning Impulse withstand test
voltage (1.2 x 50 micro seconds in
KV peak)
b) Power frequency withstand test
voltage (in KV rms for 1 min)
1)Dry
2)Wet
v) Creepage distance
a) Tot al ( in mm)
b) Protected (in mm)
vi) Minimum height of the bushing
Part 2 : Employer’s Requirements 285
39. Minimum clearance (in mm)
In Oil In Air

Betwee Phase to Between Phase to

n Ground Phases Ground
Phases
i) H.V.
ii) L.V.
40. Particulars of Bushing & Neutral
C.T.
i) Type
ii) Rat io
iii) Accuracy Class
iv) Knee Point Volt age
v) RCT at 75 Deg.C
vi) Magnetising Current at
Knee Point Voltage
vii) Additional winding particulars :
of testing on the C.T.
viii) Short Time Rat ing
ix) Reference St andard
41 Approximat e weight of
Transformer (in Kgs)
i) Core wit h clamping
ii) Coil wit h insulat ion
iii) Core and winding
42. Tank and fitt ing wit h
accessories
v) Unt anking weight
vi) Oil required for first filling
vii) Tot al weight wit h
Core, Winding, Oil
Fitt ings
43. Det ails of Tank
i) Type of t ank
ii) Approximat e t hickness of Sheet
(in mm)
a ) Sides
b ) Bottom
c ) Cover
d ) Radiat ors
iii) Vacuum recommended for hot
oil circulat ion (in torr.)
Part 2 : Employer’s Requirements 286
iv) Vacuum to which t he t ank can
be subject ed wit hout distorsion
(in torr.)
v) Under carriage dimensions
a)No. of bidirect ional wheels
provided
b) Track gauge required for t he Axis
wheels

Transverse Longitudinal
Dimension of base channel (in
mm x mm)
vi) Type of Pressure relie f
device / Explosion Vent and
pressure at which it operat es
44. Conservator

i) Tot al volume (in Lit res)

ii) Volume bet ween t he
highest and Lowest visible
oil level (in lit res)
45. Oil Qualit y

i) Applicable st andard
ii) Tot al quant it y of oil (in
Lit res)
46. Radiat or
i) Number of Radiator Bank
ii) Number of t ubes/fins in each
radiator Bank
iii) Thickness of tubes/fins (in
mm)
iv) Overall dimensions (in mm)
a ) Lengt h

b ) Breadt h

c ) Height
v) Type of mount ing
viii) Vacuum wit hst and
capabilit y
47 Gas And Oil Act uat ed Relay
i) Make
ii) Type
iii) Number of float cont act s
Part 2 : Employer’s Requirements 287
48 Temperature Indicators Oil Temprature Winding Temprature
Indicator Indicator
i) Make
ii) Type
iii) Permissible setting ranges for alarm
and trip
iv) Number of contacts
v) Current rating of each contact
49. Approximate overall Dimensions (in
mm)
a) Length
b) Breadth
c) Height
d) Minimum height of bottom
most protion of bushing from
bottom of base channel
50. Minimum clearance height for lifting
tank cover (in mm)
51. Make of OLTC
52. Whether OLTC is Type tested
53. whether OLTC is in line with the
specification
54. Make of RTCC
whether RTCC is in line with the
specification
55. Whether agreeable to carry out Type
Tests, in line with specification at
your Cost ?
56. Whether all particulars as specified
above are furnished?