PREVENTIVE MAINTAINANCE AND PREVENTIVE MAINTAINANCE AND CONDITION MONITORING FOR CONDITION MONITORING FOR

POWER TRANSFORMERSPOWER TRANSFORMERS

PRESENTED BY -PRESENTED BY -M/s VISHVAS POWERM/s VISHVAS POWER

ENGINEERING SERVICES PVT. ENGINEERING SERVICES PVT. LTD. NAGPURLTD. NAGPUR

SEMINAR ON

INFORMATION ABOUT INFORMATION ABOUT COMPANYCOMPANY

NAMES OF DIRECTORS :Mr. R. M. Bhave NAMES OF DIRECTORS :Mr. R. M. Bhave : : Mr.S.V.D’melloMr.S.V.D’mello :Mr.Kiran Joharapurkar :Mr.Kiran Joharapurkar

PRODUCT SKILLS OF DIRECTORSPRODUCT SKILLS OF DIRECTORS :HT switchgrars :HT switchgrars : : TransformersTransformers (all make) (all make) :On load tap changers (all :On load tap changers (all type)type)

No. of engineers/site managers:10No. of engineers/site managers:10 Office staff:04Office staff:04 Other staff/skilled workers:80Other staff/skilled workers:80

INFORMATION ABOUT COMPANYINFORMATION ABOUT COMPANY

AREAS OF BUSINESS INTERESTAREAS OF BUSINESS INTEREST Capital overhaul/servicing of power transformersCapital overhaul/servicing of power transformers Servicing of SF6 breakers Servicing of SF6 breakers Servicing of on load tap changers.Servicing of on load tap changers. Annual maintenance contracts for substation and control Annual maintenance contracts for substation and control

room maintenance.room maintenance. Testing of oil and bushings.Testing of oil and bushings. RLA studies on power transformers.RLA studies on power transformers. Testing of oil and bushings.Testing of oil and bushings. Installation services for power transformers, HT switchgears Installation services for power transformers, HT switchgears

and substation equipments and substation equipments Retrofitting of LT air circuit breakersRetrofitting of LT air circuit breakers Installion of rubber balloons in conservator of power Installion of rubber balloons in conservator of power

transformers to retard oxidation of oiltransformers to retard oxidation of oil Testing and commising of substations Testing and commising of substations Testing of transformersTesting of transformers

Doubts raised by usersDoubts raised by users

Whether oil filteration or dry out Whether oil filteration or dry out Criterions of stopping dryout/filterationCriterions of stopping dryout/filteration Whether overhauling/reinsulationWhether overhauling/reinsulation Frequency of condition monitoringFrequency of condition monitoring Oil mixing ---------- preconditionsOil mixing ---------- preconditions Dissolved Gas AnalyisDissolved Gas Analyis

PLEASE LET ME KNOWPLEASE LET ME KNOW

WHAT YOU EXPECT FROM THIS WHAT YOU EXPECT FROM THIS SESSION?SESSION?

Areas of concernAreas of concern OILOIL PAPERPAPER Wood (treated / Wood (treated /

parmali parmali WINDINGWINDING TANKTANK LEADSLEADS OLTCOLTC

BUSHINGBUSHING COOLING BANKS/ COOLING BANKS/

HEAT EXCHANGERHEAT EXCHANGER AUXILIARIESAUXILIARIES

IMPORTANT STANDARDS IMPORTANT STANDARDS TRANSFORMER USER SHOULD TRANSFORMER USER SHOULD

KNOWKNOW

IS 335IS 335 IS 12463IS 12463 IS 1866IS 1866 IS 2099IS 2099 IS 2026IS 2026

TRANSFORMER FOR OVERHAULING

PROCESS OF OVERHAULINGPROCESS OF OVERHAULING

TESTING

POST SHUT DOWN OBSERVATIONS

P.t.o

POST SHUT DOWN POST SHUT DOWN OBSERVATIONS(CONT..)OBSERVATIONS(CONT..)

OIL DRAINING

DISMANTLING

125 MVA TOP COVER LIFTING

GASKET REPLACEMENT

INTERNAL INSPECTION

PREPARING TRS FOR EVACUATION

N2 PRESSURE TEST

VIEW OF LEAD TAKE OFF

IEEE GUIDELINES INTERNAL IEEE GUIDELINES INTERNAL InspectionInspection

Winding - Lead clampingWinding - Lead clamping Winding support system Winding support system Clamping Clamping Insulation discoloration Insulation discoloration Lead distortion Lead distortion Lead movement Lead movement Indications of hot spots Indications of hot spots

IEEE GUIDELINES INTERNAL IEEE GUIDELINES INTERNAL InspectionInspection

Loose connections - Loose connections - Tap leadsTap leads Bushings Bushings Terminal Boards Terminal Boards Spacers Spacers Core Core

bolt nuts.bolt nuts. Physical status- ContactsPhysical status- Contacts Operating Operating

mechanismmechanism Coupling shafts Coupling shafts ShieldingShielding

IEEE guidelines forIEEE guidelines for Internal Inspection Internal Inspection

– Oil- Oil- Odour Odour Color Color Moisture Moisture Free Water Free Water

Discoloration-Discoloration- Tank walls Tank walls Bushing Bushing TerminalsTerminals Corona shields Corona shields Copper Copper connectorsconnectors Bus bars Bus bars

VacuumVacuum dryingdrying

Vacuum drying is based on the principle of Vacuum drying is based on the principle of TThermodynamics hermodynamics

Boiling point of moisture in insulation isBoiling point of moisture in insulation is reduced by reduced by way of way of PressurePressure ReductionReduction PrinciplePrinciple

Thermal energy needs to be impartedThermal energy needs to be imparted externally for externally for achieving faster and better moisture extractionachieving faster and better moisture extraction

DRY OUT PROCESS INVOLVING CYCLES

Vacuum drying( continued)Vacuum drying( continued)

Under vacuum (pressure reduction)boiling Under vacuum (pressure reduction)boiling point of water reduces to 50point of water reduces to 500c0c

medium of heating can be medium of heating can be Old oilOld oil

NitrogenNitrogen Hot airHot air

other methods of heating are also under use.other methods of heating are also under use.

Prepare TRS for evacuation

Fill N2 over air to get pressure 0.2KG/CM2

Attend leakages

Process of dryout

NITROGEN PRESSURE

PRESSURE TEST

Continue to heat tillCore_< 70 cMed _< 75cWdg _<70c

COMPARISON OF HEATING COMPARISON OF HEATING METHODSMETHODS

OI LOI L

REQUIRES OLD OIL FOR REQUIRES OLD OIL FOR HEATINGHEATING

REQUIRES FILTER PLANT REQUIRES FILTER PLANT OIL RESERVIORSOIL RESERVIORS

REQUIRES LESS REQUIRES LESS MONITORINGMONITORING

NITROGENNITROGEN

REQUIRES NITROGEN REQUIRES NITROGEN GASGAS

REQUIRES EXTRNAL REQUIRES EXTRNAL HEATING ELEMENTS HEATING ELEMENTS SUCH AS HEATERSSUCH AS HEATERS

REQUIRES MORE REQUIRES MORE

VIGILLANT MONITORINGVIGILLANT MONITORING

OIL SOAKED INSULATION OIL SOAKED INSULATION DOES NOT RELEASE DOES NOT RELEASE MOISTURE VERY FASTMOISTURE VERY FAST

IF OIL IS ACIDIC THEN IT IF OIL IS ACIDIC THEN IT

CAN AFFECT INSULATION CAN AFFECT INSULATION PAPERPAPER

THIS METHOD IS NOT THIS METHOD IS NOT CONSIDERED PRESENTLY AS CONSIDERED PRESENTLY AS USER FRIENDLY METHOD USER FRIENDLY METHOD

DRY AND NON SOAKED DRY AND NON SOAKED INSULATION RELEASES INSULATION RELEASES MORE MOISTURE AND MORE MOISTURE AND IN FASTER WAYIN FASTER WAY

IF NITROGEN IS PURE IT IF NITROGEN IS PURE IT CANNOT AFFECT CANNOT AFFECT INSULATION PAPER & INSULATION PAPER & COPPERCOPPER

OILOIL

MONITORING MONITORING PARAMETERS ARE OIL PARAMETERS ARE OIL BDV & MOISTURE BDV & MOISTURE CONTENT OF OIL USED CONTENT OF OIL USED FOR HEATING PURPOSEFOR HEATING PURPOSE

OIL WILL LOSE/REDUCE OIL WILL LOSE/REDUCE ITS PARAMETERS SUCH ITS PARAMETERS SUCH AS RESISTIVITY, AS RESISTIVITY, TANDELTA WHEN HEATED TANDELTA WHEN HEATED ABOVE 60ABOVE 600C0C

NITROGENNITROGEN

THIS METHOD IS THIS METHOD IS PRESENTLY CONSIDERED PRESENTLY CONSIDERED AS USER FRIENDLY AND AS USER FRIENDLY AND TECHNICALLY BETTER .TECHNICALLY BETTER .

MONITORING MONITORING PARAMETERES ARE PARAMETERES ARE CONPARISON OF IR VALUE CONPARISON OF IR VALUE AND DRYNESS OF AND DRYNESS OF NITROGEN GAS USED FOR NITROGEN GAS USED FOR HEATING PURPOSEHEATING PURPOSE

NITROGEN HEATINGNITROGEN HEATING DOES DOES NOT INVOLVE OIL NOT INVOLVE OIL HEATING ABOVE 60HEATING ABOVE 600C0C

Details of nitrogen heatingDetails of nitrogen heating

Nitrogen gasNitrogen gas:: 99.6% pure99.6% pure Dew point-40c &Dew point-40c & betterbetter

Pressure gauge:Pressure gauge: 0.1 To 1.0KG 0.1 To 1.0KG//SQ.CMSQ.CM Vacuum gauge:Vacuum gauge: MM scale: BourdenMM scale: Bourden

torr scale: Macleoidtorr scale: Macleoid M-bar scaleM-bar scale

HEATING ARRANGEMENT

HALOGEN HEATING OF TANK

VIEW OF HEATING ARRANGEMENT

VIEW OF SHED FOR HEATING

DRY OUT IN PROGRESS

PT 100 SENSOR FOR TEMPERATURE MONITORING

Heating cycle duration will depend upon size of Heating cycle duration will depend upon size of trstrs

72 hrs

48 hrs

24hrs

100-250 MVA

50 MVA

25 MVA

Vacuum cycles 1 for 60/72 hrs

Heating cycles 2 :36/48 hours

Vacuum cycle 2 : 48/60 hrs

Heating cycle 3 :24/36 hrs

Vacuum cycle 3 :36 hrs

Heating cycle 4 :36 hrs

Vacuum cycle iv

N2 filling Ir. value measurement dew pt

measurement

Take vacuum and fill up oil

While filling oil fill under vacuum and fill from top filler valve

Break vacuum over oil

by N2/ dry air

Oil toppling up oil circulation

Oil testing at site for

BDV >_ 60 kV

moisture content

<- 10 ppm

Stop filtration if oil parameters are satisfactory as per voltage

class of trs.

VIEW OF FILTERPLANT OIL TANK AND DG SET

TRANSFORMER AFTER OVERHAULING

TRENDS IN OILTRENDS IN OILNapthene based oilNapthene based oil

1. Low pour point enabling the use in low 1. Low pour point enabling the use in low ambient temp.areasambient temp.areas

2. Oxidation products are soluble in oil.2. Oxidation products are soluble in oil.3. High resistivity.3. High resistivity.4. High Viscosity.4. High Viscosity. Paraffin based oilParaffin based oil1. High pour point but no problem in country like 1. High pour point but no problem in country like

INDIA.INDIA.

ALKYL BENZENE BASED OILALKYL BENZENE BASED OIL

1. Low Tan Delta1. Low Tan Delta 2. High resistivity.2. High resistivity. 3. No sludge.3. No sludge. 4. Low viscosity.4. Low viscosity. 5. Very low pour point.5. Very low pour point. 6. Non hygroscopic and does not form 6. Non hygroscopic and does not form

gum and sludge. gum and sludge.

OIL COMPARISIONOIL COMPARISION

PARAFFIN NAPTHA ABTO TAN DELTA 0.09 0.03 0.0009

RESISTIVITY 2*10 10*10 50*10 IFT 18 21 42

VISCOCITY 23 21 15.1 SLUDGE

CONTENT 0.1 0.05 NIL

SYNTHETIC OILSYNTHETIC OIL1.1. Used due to fire resistance propertyUsed due to fire resistance property

22. Contain polychlorinated biphenyl.. Contain polychlorinated biphenyl.

33. Hazardous for dumping in earth or . Hazardous for dumping in earth or otherwise.otherwise.

EFFECT OF MOISTURE CONTENT IN OIL ON EFFECT OF MOISTURE CONTENT IN OIL ON IMPULSE STRENGTHIMPULSE STRENGTH

MOISTURE CONTENT

30 ppm

100%

70%IMPULSESTRENGTH

Oil color Interpretation Oil color Interpretation ASTM- color ASTM- color

ASTM - D1500-91ASTM - D1500-91

Clear Clear New conditionNew condition Pale yellow Pale yellow Good conditionGood condition Yellow Yellow Service condition Service condition Bright yellow Bright yellow Marginal conditionMarginal condition Amber Amber Bad condition Bad condition BrownBrown Severe bad Severe bad

conditioncondition

OIL COLOUR INTERPRITATIONOIL COLOUR INTERPRITATION

Dark brown - Extremely bad conditionDark brown - Extremely bad condition

Sludge - To detect presence of pentane Sludge - To detect presence of pentane insoluble sludge in serviced insoluble sludge in serviced

oiloilTHE TEST IS not Performed unlessTHE TEST IS not Performed unless IFT <26 dynes/cmIFT <26 dynes/cm

ACIDITY> 0.15 mg of KOH gm of oilACIDITY> 0.15 mg of KOH gm of oil

IS 335IS 335

Density Density o.89 gm/cmo.89 gm/cm33 at 29.5º C at 29.5º CViscosity Viscosity 27 MAX at 27º C 27 MAX at 27º CIFT IFT 0.04 N/M0.04 N/MFlash point Flash point 14014000ccPour point Pour point -6-600ccBDV BDV 30 KV unfiltered 30 KV unfiltered 60 KV 60 KV

filteredfilteredTAN TAN DELTA DELTA 0.002 0.002RESISTIVITY RESISTIVITY 35*10 35*101212 ohm-cm AT 90º c ohm-cm AT 90º c

1500*101500*1012 12 ohm-cm AT 27º cohm-cm AT 27º c

IS 335IS 335

Acidity Acidity 0.4(max) 0.4(max) Sludge Sludge 0.1% (max)0.1% (max) Corrosive sulphur Corrosive sulphur No traces No traces oxidation inhibitor oxidation inhibitor 0.05% (max)0.05% (max) Water content Water content 50 PPM max 50 PPM max (unfiltered)(unfiltered)

15 PPM max 15 PPM max (filtered)(filtered)

DISSOLVED GAS ANALYSISDISSOLVED GAS ANALYSIS

Most widely used and effective technique.Most widely used and effective technique.Requires skill to draw inference.Requires skill to draw inference.

FAULTSFAULTS

Thermal aging - overhead metallic partsThermal aging - overhead metallic parts Partial dischargePartial discharge ArcingArcing

FACTORS INFLUENCING GAS FACTORS INFLUENCING GAS PRODUCTIONPRODUCTION

Meaningful assessment of a Transformer on Meaningful assessment of a Transformer on basis of DGA is possible if information and basis of DGA is possible if information and data is considered on following factors data is considered on following factors which influence gassing rate & gassing which influence gassing rate & gassing comparisoncomparison

Oxygen content of oil Oxygen content of oil Oil temperatureOil temperature Ambient temperatureAmbient temperature

Dissolved Gas AnalysisDissolved Gas AnalysisMethodologyMethodology

Gas tight syringe with a 3 way stop cock Gas tight syringe with a 3 way stop cock Stainless steel tubular bottleStainless steel tubular bottle Bottle capable of being air/gas tight with Bottle capable of being air/gas tight with

screwed capscrewed cap

LabelingLabeling

Details of transformersDetails of transformers Date of sampling Date of sampling History of transformersHistory of transformers Temp of transformerTemp of transformer Charged/service conditionCharged/service condition Ambient Temp.Ambient Temp.

STAGESSTAGES

Collection of oil sample.Collection of oil sample. Extraction of gases in dissolved oil.Extraction of gases in dissolved oil. Separation identification and Separation identification and

quantitative determination of gasquantitative determination of gas Interpretation.Interpretation.

Key gas and fault patternKey gas and fault pattern

CC22HH2 2 (Acetylene) :Arcing(Acetylene) :Arcing HH2 2 (Hydrogen) :Partial discharge (Hydrogen) :Partial discharge CC22HH4 4 (Ethylene) :Oil overheating.(Ethylene) :Oil overheating. Co/CoCo/Co2 2 (Carbon monoxide & Carbon (Carbon monoxide & Carbon

Dioxide)Dioxide) :Conductor :Conductor overheatingoverheating

Various Various h h22 ch ch22 c c22hh66 c c22hh44 c c22hh22 co co co co2 2

sourcessources IEEE IEEE 140 160 115 190 11 580 -- 140 160 115 190 11 580 -- GTR GTR 100 120 65 50 35 350 2500100 120 65 50 35 350 2500CIGRE CIGRE 28.6 42.2 85.6 74.6 -- 289 28.6 42.2 85.6 74.6 -- 289

37713771DOBLE DOBLE 100 100 60 100 5 250 -- 100 100 60 100 5 250 --New TrsNew Trs 200 100 100 150 15 500 ---- 200 100 100 150 15 500 ----Old trs Old trs 250 200 200 300 35 1000 -- 250 200 200 300 35 1000 --Oil overheating Oil overheating cc22hh44 c c22hh6 6 ch ch44

Cellulose overheating Cellulose overheating cocoPartial discharge in oil Partial discharge in oil h h22 ch ch44

Arcing in oilArcing in oil cc22hh2 2 hh22

KEY GASKEY GAS : Hydrogen : Hydrogen

ARCINGARCING : Between leads. Leads to coil. : Between leads. Leads to coil.

KEY GASKEY GAS :Acetylene , Hydrogen :Acetylene , Hydrogen

IEEEIEEEArcingArcing :Acetylene C :Acetylene C22HH22

:Hydrogen H:Hydrogen H22

Carona : HCarona : H22

Overheated oil :Ethylene COverheated oil :Ethylene C22HH2 2

:Methane CH:Methane CH44

Thermal degradation of insulation material Thermal degradation of insulation material =Co, Co=Co, Co22, H, H22oo

Healthy ratio of Co/CoHealthy ratio of Co/Co22 = 5 = 5

If ratio is below 3, it indicates severe If ratio is below 3, it indicates severe overheating of paper.overheating of paper.

Oil degradationOil degradation : Methane(CH : Methane(CH44), ), Ethane(CEthane(C22HH66) ) Ethylene(C Ethylene(C22HH55))

Partial DischargePartial Discharge : Occurs due to ionization in : Occurs due to ionization in high stressed areas where gas/vapour filled high stressed areas where gas/vapour filled voids.voids.

STRATEGIC END OF LIFE STRATEGIC END OF LIFE ECONOMIC END OF LIFE ECONOMIC END OF LIFE TECHNICAL END OF LIFETECHNICAL END OF LIFE

DEGREE OF POLYMERIZATIONDEGREE OF POLYMERIZATIONINITIAL : 1200INITIAL : 1200POOR : 300POOR : 300

AFFECTING PARAMETERSAFFECTING PARAMETERS TEMPERATURETEMPERATURE

MOISTUREMOISTUREACIDITYACIDITY

Comparison of Furful content in Comparison of Furful content in various generator transformersvarious generator transformers

Sr. Of GTR

Nameplate age

Calculated Furful mg/lit

Actually Found Furful Content

Elapsed Age

1 15.60 0.216 3.170 29.30

2 14.66 0.180 0.150 13.65

3 6.0 0.030 0.035 6.30

4 5.0 0.027 0.032 6.00

Site DP Estimated age

Furful value

Estimated age

A 392 25.0 0.60 20.6

B 710 12.0 0.20 15.6

C 978 1.0 0.01 02.0

D 458 22.0 0.4 18.8

Interpretations of impedance testInterpretations of impedance test

Variation in short circuit impedance of a transformer Variation in short circuit impedance of a transformer winding indicates possible movement of winding indicates possible movement of winding/deformation within the transformerwinding/deformation within the transformer

Variations upto 2% --NegligibleVariations upto 2% --Negligible

Variations upto 3% --SignificantVariations upto 3% --Significant

CASE IIICASE III

16 MVA TRANS 110/22KV

2U-N 2V-N 2W-N

232 175 52

54 232 175

18 215 232 EXCITATION CURRENT IN MILI AMPS

350 95 101.9

AGEINGAGEING OF INSULATING PAPEROF INSULATING PAPER

With advanced instruments available With advanced instruments available forfor technical analysis of aged insulation it is technical analysis of aged insulation it is possible to determine /measure following possible to determine /measure following properties of insulation paper properties of insulation paper

1. Thickness1. Thickness2. Water content 2. Water content 3. Tensile strength3. Tensile strength4. Degree of polymerization4. Degree of polymerization

TENSILE STRENGTHTENSILE STRENGTH1. 1. Determined as per IS 1924Determined as per IS 1924 determined in determined in

both machine direction and cross machine both machine direction and cross machine directions.directions.

2. Deterioration of tensile strength is further 2. Deterioration of tensile strength is further dependendependent on t on temp. factor.temp. factor.

3. 3. The rate of tensile strength deterioration is The rate of tensile strength deterioration is exponential with time.exponential with time.

Tensile strength

Ageing (days)

Degree of polymerizationDegree of polymerization

This proves to be the most informative This proves to be the most informative parameter for assessing the ageing or the parameter for assessing the ageing or the process of ageing of cellulose . The process of ageing of cellulose . The connection between deterioration in material connection between deterioration in material properties and formation of aging products properties and formation of aging products is degree of polymerization.is degree of polymerization.

This is also direct decomposition of cellulose.This is also direct decomposition of cellulose.

DETERIORATION OF PAPERDETERIORATION OF PAPER

1501200c

1050c

900 c

Days

Degree of polymerization

Source documents / forumsSource documents / forums

IEEEIEEE ANSIANSI I.S.I.S. C.B.I.P.’s INT. ConferenceC.B.I.P.’s INT. Conference CIGRE’s working groupCIGRE’s working group Our own field experienceOur own field experience

Abnormalities observed during internal Abnormalities observed during internal inspection/ capital overhaulinginspection/ capital overhauling

EXTERNALEXTERNAL1 Pumps running in Pumps running in

reverse directionreverse direction2 Thermosyphon Thermosyphon

blankedblanked3 Thimble-terminal cap Thimble-terminal cap

fusion due to fusion due to heating.heat heating.heat generated due to generated due to faulty term.connector. faulty term.connector.

INTERNALINTERNAL1 Cotton tape used for 1 Cotton tape used for

gasket locating not gasket locating not removed causing removed causing leakageleakage

2 Core bolt insulation Core bolt insulation zerozero

3 Selector switch Selector switch contact arm assy not contact arm assy not making adequate making adequate contactcontact

Abnormalities(Abnormalities(continuedcontinued))

4 Bucholz pipeline slope Bucholz pipeline slope not propernot proper

5 Lens screw of OLTC Lens screw of OLTC shaft not properly fittedshaft not properly fitted

6 Oil leakges in box type Oil leakges in box type stiffner, between main stiffner, between main tank and stiffnertank and stiffner

4 Core earthing melted.Core earthing melted. Part of laminations Part of laminations

fused.fused.

BUSHINGBUSHINGTYPETYPE SRBP/OIP/RIPSRBP/OIP/RIPTEST TAPTEST TAP FOR MEASUREMENTFOR MEASUREMENT MUST BE EARTHED MUST BE EARTHED PROPER EARTHINGPROPER EARTHING CORROSION OF THREADS ON CORROSION OF THREADS ON

CONNECTION CAUSES HIGH CONNECTION CAUSES HIGH RESISTANCE AND SPARKINGRESISTANCE AND SPARKING

33 Measurement of mounted bushing done Measurement of mounted bushing done

in UST mode , using test tap connectionin UST mode , using test tap connection

4 4 Measurement of winding is done in GST Measurement of winding is done in GST

mode using connections between mode using connections between bushing top terminal and grounded.bushing top terminal and grounded.

11

GST UST

SPECIMEN INSULATION SPCIMEN IS GROUNDED

UNGROUNDED

MEASURING CIRCUIT/ EQUIPMENT

UNGROUNDED GROUNDED/g IS PROVIDED THROUGH EQUIPMENT

22 10 kV is a referred as a preferred reference 10 kV is a referred as a preferred reference

voltage although usually measurements of voltage although usually measurements of tan delta and capacitance should not vary tan delta and capacitance should not vary with applied voltage.with applied voltage.

Usually measurements at 2 KV,5KV and Usually measurements at 2 KV,5KV and 10KV are taken at site.10KV are taken at site.

Capacitance value measurement is equally Capacitance value measurement is equally important.important.

Tan delta value measurement may get Tan delta value measurement may get affected by conditions such as oil. affected by conditions such as oil. temperature, humidity, surface cleanliness temperature, humidity, surface cleanliness and inductions in the switchyard. and inductions in the switchyard.

DGA OF OIL FOR BUSHING DGA OF OIL FOR BUSHING [IEC-36A][IEC-36A]

Type of key gas Permissible limit H2 100 ppm

CH4 30 ppm C2H6 50 ppm C2H4 300 ppm C2H2 02 ppm CO 1000 ppm CO2 3000 ppm

Predictive maintenance for OLTCPredictive maintenance for OLTC

Contact resistance measurement .Contact resistance measurement . Measurement of divertor motor acoustic Measurement of divertor motor acoustic

signals.signals. Temp difference between oil in main tank Temp difference between oil in main tank

and oil in divertor switch.and oil in divertor switch. Dissolved gas analysis.Dissolved gas analysis. Deposition of solid carbon. Deposition of solid carbon.

Predictive maintenance(cont...)Predictive maintenance(cont...)

Changes in switching time weak springs, Changes in switching time weak springs, OverhaulingOverhauling Contact wear Contact wear

Precautionary steps for ensuring Precautionary steps for ensuring correct installationscorrect installations

Paper MoisturePaper Moisture420 KV420 KV 0.5 or less0.5 or less245 KV245 KV less than1.0less than1.0145 KV145 KV less than 2less than 2Oil MoistureOil Moisture420 KV420 KV less than 10less than 10245 KV245 KV less than 15less than 15145 KV145 KV less than 20less than 20

SETTLING TIMESETTLING TIME

KVKV TimeTime 420 KV 420 KV 72 hours72 hours 245 KV 245 KV 48 hours48 hours 145 KV145 KV 36 hours36 hours

Magnetic balance test is like a Magnetic balance test is like a signature testsignature testDiagnostic tool with focus on current Diagnostic tool with focus on current is more importantis more importantQualityQuality of core is not assessedof core is not assessedif voltage distribution is in order but if voltage distribution is in order but current are not then further analysis current are not then further analysis is requiredis required

Partial DischargePartial Discharge

1 Effective for comparing at factory/ at site Effective for comparing at factory/ at site after repairs. after repairs.

2 Advanced diagnostic system used for off Advanced diagnostic system used for off line PD detection.line PD detection.

3 Background noise suppression, using a 3 Background noise suppression, using a Spectrum analyzer to do selective Spectrum analyzer to do selective filtration. filtration.

FREQUENCY RESPONSE FREQUENCY RESPONSE ANALYSISANALYSIS

Short circuit high fault currents can lead to Short circuit high fault currents can lead to displacement of windings.displacement of windings.

An already weak coil or an insulation system An already weak coil or an insulation system can fail, during over voltage stress. can fail, during over voltage stress.

Background.Background.Electrical measurements are not sufficient to Electrical measurements are not sufficient to

indicate this type of displacement of coil or indicate this type of displacement of coil or insulation.insulation.

Principle Principle Deformation results in minor changes of Deformation results in minor changes of

internal inductance and capacitance of internal inductance and capacitance of winding.winding.

These deformations can be noted by These deformations can be noted by noting a difference in response of noting a difference in response of particular winding on network analyzer particular winding on network analyzer when 1 signal (sinusoidal) having when 1 signal (sinusoidal) having frequency band 50 Hz to 500 Hz is frequency band 50 Hz to 500 Hz is connected to bushing and response is connected to bushing and response is measured through neutral bus.measured through neutral bus.

Procedure for FRAProcedure for FRA Identify two ends of winding.Identify two ends of winding. Connect two cables from measuringConnect two cables from measuring Unit giving sinusoidal output of two Unit giving sinusoidal output of two

V rms and one measuring input V rms and one measuring input Other end of winding is connected to Other end of winding is connected to

measuring input.measuring input. Other windings are grounded.Other windings are grounded. Voltage transfer function is measured Voltage transfer function is measured

for each winding for four frequency for each winding for four frequency scans between 5 Hz to 2 MHz.scans between 5 Hz to 2 MHz.

BENEFITSBENEFITS

Immune to Electro-magnetic interference.Immune to Electro-magnetic interference.

Easy to perform on site. Easy to perform on site.

Identical results for similar transformers.Identical results for similar transformers.

DRAW BACKS DRAW BACKS

Above data required effectively used more as signatureAbove data required effectively used more as signature

FREQUENCY RESPONSE ANALYSIS

INDICATIONS INDICATIONS Shift in response of windingShift in response of winding

Differences in response between Differences in response between phases of same transformer.phases of same transformer.

Difference between responses of Difference between responses of transformer of same design.transformer of same design.

CONTROL OF LEAKAGE FLUX IN CONTROL OF LEAKAGE FLUX IN POWER TRANSFORMERPOWER TRANSFORMER

NETT FLUX WHICH IS NOT LINKED BY BOTH NETT FLUX WHICH IS NOT LINKED BY BOTH COILSCOILS

Magnetic flux which energizes core abd induces Magnetic flux which energizes core abd induces required flux density.required flux density.

Load flux which is balanced by load flux of Load flux which is balanced by load flux of secondary winding.secondary winding.

Leakage flux which links the winding conductors Leakage flux which links the winding conductors and returns through a path outside the core.and returns through a path outside the core.

EFFECT OF LEAKAGE FLUXEFFECT OF LEAKAGE FLUX

Leakage flux will follow a path of low resistanceLeakage flux will follow a path of low resistance Will be attracted to magnetic steel.Will be attracted to magnetic steel. This induces Eddy Currents and hence generate This induces Eddy Currents and hence generate

heat.heat. REMEDYREMEDY

Increase the distance of tank wall from source of Increase the distance of tank wall from source of leakage flux.leakage flux.

Continuously transposed conductor (CTC).Continuously transposed conductor (CTC). To provide shunt plates to carry leakage flux.To provide shunt plates to carry leakage flux.

CASE STUDYCASE STUDY New 390 MVA generator transformerNew 390 MVA generator transformerPROBLEM PROBLEM Core overheating Core overheating Yoke overheating Yoke overheating

Tank & top cover overheating Tank & top cover overheating

VISIBLE EFFECTSVISIBLE EFFECTS Due To overheating caused by eddy currents flowing in Due To overheating caused by eddy currents flowing in

top cover or bell cover visible deterioration of gasket top cover or bell cover visible deterioration of gasket was observedwas observed

DESIGN REMEDY:DESIGN REMEDY: To subdivide the plate width of outermost pocketsTo subdivide the plate width of outermost pockets Use of nonmagnetic material for frames.Use of nonmagnetic material for frames. Use of flux shunt plates at LV side of the tankUse of flux shunt plates at LV side of the tank

CONCEPT OF AIR CELLCONCEPT OF AIR CELL

1. 1. Oil Deteriorates majorly because of Oxidation.Oil Deteriorates majorly because of Oxidation.2. Atmospheric breathing is a continuous process.2. Atmospheric breathing is a continuous process.3. To avoid atmospheric breathing, rubber 3. To avoid atmospheric breathing, rubber

cell/balloon/separator is inserted in conservator.cell/balloon/separator is inserted in conservator.4. The balloon / air cell is INFLATED INITIALLY. The 4. The balloon / air cell is INFLATED INITIALLY. The

breathing of transformer is then through this cell.breathing of transformer is then through this cell.5. When air expands, air cell contracts.5. When air expands, air cell contracts.6. When oil contracts , air cell expands6. When oil contracts , air cell expands7. There can be a substantial reduction in oil deterioration, 7. There can be a substantial reduction in oil deterioration,

preserving or at least retarding its increase parameters preserving or at least retarding its increase parameters like acidity moisture content and dielectric dissipation like acidity moisture content and dielectric dissipation factor.factor.

THERMOSYPHON FILTER THERMOSYPHON FILTER CHAMBERSCHAMBERS

On line acidity ReductionOn line acidity Reduction1 Acidity of oil is bad for insulation. Acidity of oil is bad for insulation. 2 Aluminum granules can reduce acidity and Fuller’s Aluminum granules can reduce acidity and Fuller’s

earth can reduce acidity.earth can reduce acidity.3 Above materials are contained in cylinder Above materials are contained in cylinder

chamber/chambers in wire mesh.chamber/chambers in wire mesh.4 Cylinder/ cylinders are fitted to transformer tank Cylinder/ cylinders are fitted to transformer tank

and connected through valvesand connected through valves..5 Oil passing through the column of Alumina or Oil passing through the column of Alumina or

fuller’s earth reduces the acidityfuller’s earth reduces the acidity6 Continuous use of facility can help in maintaining Continuous use of facility can help in maintaining

acidity low since commissioning.acidity low since commissioning.

Hydran 2011 systemHydran 2011 system Continuos monitoring of key gases Continuos monitoring of key gases

Alarm facilityAlarm facility

Hourly and daily changes in levelHourly and daily changes in level

Adjustable alarm levelsAdjustable alarm levels

Self test system Self test system

Possibility of connection to SCADA systemsPossibility of connection to SCADA systems

SF6SF6 INSULATED INSULATED TRANSFORMERSTRANSFORMERS

MANUFACTURING RANGE: MANUFACTURING RANGE: 275KV300MVA275KV300MVA

COMPACT SIZE COMPACT SIZE REDUCED SIZEREDUCED SIZE

EXTRA LIFEEXTRA LIFEHIGHER COST ALMOST DOUBLEHIGHER COST ALMOST DOUBLE

RATE OF LOWERING DP VALUE IS RELATIVELY RATE OF LOWERING DP VALUE IS RELATIVELY MUCH SLOWER IN SF6 THAN NITROGEN AND MUCH SLOWER IN SF6 THAN NITROGEN AND

OILOIL

THANK YOUTHANK YOU

FILTER PLANT HIGH VACUUM WITH DOUBLE DEGASSING CHAMBER

TRANSFORMER ASSEMBLY IN PROGRESS