TRANSFORMER OIL

TRANSFORMER OILSIGNIFICANCE SOURCE & SUPPLYMANUFACTURING COMPOSITIONSPECIFICATIONHANDLING METHODSPROCURMENT & ACCEPTANCEMONITORING THE QUALITYCHARACTERISTICS I ) PHYSICAL II ) CHEMICAL III) ELECTRICAL10. DISSOLVE GAS ANALYSIS

1INTRODUCTIONLiquid Dielectrics find extensive application in electrical installations. They are used for filling the inner space in power transformers, reactors, Circuit breakers, Capacitors, Cables & other elements of electrical equipment. Filled under vacuum Liquid Dielectrics serve also as impregnates for winding insulation such as paper, pressboard, improving considerably their dielectric strength. Concurrently, the liquid dielectrics serve as medium for heat removal. Thus in power transformers, transformer oil heats up at winding due to power loss in the coils & the magnetic core & transfers heat to the cool walls of transformer tank. In high voltage oil circuit breakers, liquid serves not only to insulate the conducting parts but also as a suppressive medium that quenches an arc discharge between the disengaging contacts. Now Oil Circuit breakers are obsolete and SF6 and Vacuum breakers are in use. Of all the liquid dielectrics, Petroleum oils are most widely spread. These are obtained by fractional distillation of petroleum which is a complex process consisting of series of operation. The oil so obtained is then refined by Alkalizing & Acidifying with sulphuric acidCLASSIFICACATION OF CRUDESAll the crudes consist mainly of hydrocarbons but they differ in proportion of type of hydrocarbons.NAPTHENIC OIL A term applied to mineral oil derived from special crudes having very low naturally occurring n-paraffin (wax) contents.PARAFFINIC OILA term applied to mineral oil derived from crudes having substantial contents of naturally occurring n-paraffin(wax)MIXED OILA term applied to mineral oil derived from crudes containing both waxes & bitumens.

A mineral insulating oil is characterized by its structural analysis, i.e. the content in

The composition of mineral oil is generally determined by Infrared Spectroscopy. Paraffinic & Naphthenic Hydrocarbons are responsible for physical properties like density, viscosity, & Pour point. Aromatic hydrocarbons have an influence on oxidation resistance, the gassing properties & impulse strength. Table below shows the crude composition of transformer oil feed stock:CRUDE TYPE

.

Paraffinic CarbonCpNapthenic Carbon CnAromatic carbonCaHYDROCARBON TYPE Paraffin Mixed NapthenicParaffin604020Napthenic254065Aromatic(Mixed)152015INSULATING OILWHY WE USE IT ?ACTS AS COOLANTINSULATES ELECTRICALLYARC EXTINGUISHING MEDIUM

SECONDARY USE : - AS A LUBRICANTAS A DAMPER

SIGNIFICANCE OF TRANSFORMER OILThe presence of contaminates like water, minute particles, dirt etc. beyond certain minimum level in mineral insulating used in Transformer affects its insulating properties significantly.Presence of antioxidants considerably influence the oxidative degradation of oil.A third factor which has substantial effect on performance of transformer oil is the depress of refining during manufacturing.Thus, three important factor namely :- Water contentInhibitor content (oxidation inhibiter) DBPC.Degree of refining (SK Value) Are to be determined in Transformer oil before its quality is ascertained.

Oxidation Inhibitor

SK Value- to determine the extent of conc. H2So4 treatment given during manufacture of Transformer oil from the base-stick.DBPC Di tertiary Butyl Para CresolTransformer Oil Present StatusPrior to 1970 - Import of Transformer oil.1970 on wards - Commencement of Indigenous Production Oil process unstable Deterioration of storage Non-attainment of IR value Frequent replacement1976 CPRI Workshop- Processing of improved quality of oil from . indigenous feed stocks. Inclusion of ASTM aging test in IS:3351990 on wards - Import of Transformer Oil Feed StockMANUFACTURING OF TRANSFORMER OILTrans former oil can be obtained by many different process. Acid treatment & clay treatment process is one of the most popular & simplest process generally used by Transformer oil manufacturing companies.ACID TREATING CLAY . TREATING90-98% SULPHURIC ACID Caustic alcohol & water Alcohol water Clay

Acid, Sludge Spent Caustic Steam Spent Clay

MIXER

CENTRIFUGEMIXER SETTLERPERCOLATORSTRIPPER

ACID TREATING : In this process , the oil is treated with concentrated Sulphuric acid. The Oxygen, sulpher & Nitrogen Compounds along with undesirable hydrocarbons are removed in the form of sludge. The amount of acid used & the time of contact depend upon the concentration of impurities in oil. During this treatment the oil is continuously agitated & reacted in large vessels with conical bottoms for sludge drainage. After the sludge has settled down, the oil is drained off, washed with water & treated with 10 to 25% solutions of sodium hydroxide (Alkali wash). This alkali neutralizes the acids completely & Subsequently removed by water washings.2. CLAY TREATING : The neutralized oil is then stripped with steam to remove alcohol & water, then the oil is percolated through a bed of clay percolation step is necessary not only to remove compounds not reacted by acid treating, but also to remove residual traces of sodium sulphonates created by the neutralization of the sulphuric acids. The finished electrical insulating oil is neutral in acidity, non-corrosive & has good electrical properties.SAMPLING OF INSULATION OIL Sampling procedure detailed in IS: 6855-1973 is to be followed strictly.

No of drums in a batchNo of drums from which sample is taken2 to 526 to 20321 to 50451 to 1005101 to 2006201 to 4008401 and more10SEGRAGATION OF CLEAN AND DIRTY OILDIRTY OIL CLEAN OIL

GENERAL PRECAUTIONS WHILE SAMPLING THE OILCare to be taken to avoid contamination of the samples.Hands should not come in contact of the sample.Sample container cap/valves should be tightly secured and test should be carried out on sample until it is at least as warm as surrounding air.Sampling container should preferably be glass or steel with well fitted corks or caps. Cotton waste or fibrous materials should not be used to wipe container.Before a sample is taken the entire sampling apparatus and container should be rinsed with oil thoroughly and then the oil should be discarded.To remove moisture & dirt, about 10L of oil is removed or the oil has to run for about 4 -5 minutes in to the sample container. The container should be rinsed with oil sample and then filled up to its capacity to be sent for test.With the help of a glass tube, sampling can be done by arranging barrel or drum so that oil can be taken from top portion. The upper glass tube is closed with thumb and lower end is dipped in to the liquid for a depth of 300mm. Then remove the thumb and allow the liquid to flow in to the sample container. The container should be tightly capped and sealed with sealing agent and sent to CPRI lab for testing. Normally this is carried out in manufacturer premises. CATEGORIES OF TESTS FOR TRANSFORMER OILPHYSICALDensityViscosityFlash pointPour pointAppearanceInterfacial tension CHEMICALNeutralization numberCopper strip corrosionOxidation stabilityMoisture contentPresence of oxidation inhibitorsELECTRICALDielectric strengthResistivity Dielectric dissipation factor

SIGNIFICANCE OF TESTSDensity(Specific Gravity):Weight Conversion, Heat Transfer property Viscosity :Coolant mediaFlash point :Risk of fireInterfacial tension :Detection of polar contaminatesNeutralization number :Corrosion of Metallic PartsCopper strip corrosion : Traces of free and Combined SulphurOxidation stability : Oil Quality Moisture content : Hazards to dielectric performance of oil . . as well as insulationDielectric strength :Presence of moisture, Dirt, other foreign conducting ParticlesResistivity :Conducting impurities & purity of oilDielectric dissipation factor: Quality control tests presence of moisture, . . Polar Compound-improper refining Techniques

PHYSICALDENSITYDensity of a liquid at temp is the mass of the liquid occupying unit volume at that temperatureTest method : IS:1448(part 16)- 1977Evaluating methods - Hydrometer method - Density bottle method Density range: 0.85-0.89 g/ccFacilitates separation of free oil& oil with dissolved moistureHigh value of density-poor heat dissipation characteristicsMax. limit as per IS:335 0.89 g/cc at 29.5C

KINEMATIC VISCOSITYMeasure of rsistance to gravity flow of a liquid the pressure head being proportional to its density Unit: centistokes( cst or cm2/sec) Limitation :- 27 cst at 270 CTest method-IS:1448 (Part 25) 1976Time reqd. for liquid to flow X viscosity = Kinematic Viscosity through a long capillary Viscosity -Temp. relationshipLow viscosity at high tempEfficient heat removal from windingsPrevents localized over heating

FLASH POINTThe minimum temperature at which oil gives so much vapour that this vapour when mixed with & forms an ignitable mixture and gives a momentary flash on application of small pilot flame.TEST METHOD: IS:1448(P:21)-1970The sample is heated at slow and constant rate(5-6C/min) with constant stirring. A test flame is directed into the cup at regular intervals. At flash point, the vapour above the oil ignites momentarilyLow Value - Risk of fire in transformerMin. limit as per IS:335- 140CMax. reduction for service oils as per -15C IS-1866 POUR POINTThe lowest temperature expressed as a multiple of 3C at which the oil is observed to flow when cooled and examined under prescribed conditions.TEST METHOD- IS: 1448(P:10)-1970The sample oil is cooled and the TEMP at which it does not flow when held horizontally in a tube for 5 sec is noted

FREEZING MIXTURE TEMP.BELOWCrushed ice & water 10CCrushed ice + solid CO2 - 12CCrushed ice + cal. chloride - 26CSolid CO2+ acetone - 57CLimitation :- -60CHigh pour point- increase in viscosity when exposed to weather, hinder convection currents & poor cooling of winding.

APPEARANCEIS:335-1983 SPECIFIES OIL TO BE CLEAR TRANSPARENT & FREE FROM SUSPENDED MATTER AND SEDIMENTSOIL EXAMINED IN 100 ml THICK LAYERLIGHT COLOUR - WELL REFINED OIL CLOUDY APPARANCE - PRESENCE OF MOISTURE GREENISH TINGE- PRESENCE OF COPPER SALTS ACID SMELL - PRESENCE OF VOLATILE ACIDS

NAKED EYE DETECTS PATICLES OF SIZE 22 microns & above INTERFACIAL TENSIONMeasure of molecular attractive force between their unlike molecules at the interface of oil and water UNIT = N/mTEST METHOD- IS:6104-1971 The force required to lift a planar ring of platinum from the oil-water interface into oil is measured

IFT- DETCTION OF POLAR CONTAMINANTS IN OILDROP IN IFT- MEASURE OF OIL DEGRADATION

Limit as per IS: 335-1983- 0.040N/mFor oil in service IS:1866 0.018 N/mCHEMICAL

NEUTRALISATION NUMBERIt is the measure of acidity contents of insulation oil Defined as no of mg of KOH required to neutralize completely the acids presents in 1gm of oilThe presence of acid in oil is highly detrimental It corrodes the various part of transformer Lower the dielectric strengthPolymerize to form insoluble sludge which clog the cooling systemMax permissible limitFor new oil- 0.03 mg of KOH/gFor oil in service- 0.5 mg of KOH/g

COPPER STRIP CORROSIONThis test is carried out to detect any traces of free or combined sulphur that may be presence in an oil.A clean polished strip of pure copper metal of the specified dimension is heated in a fixed quaintly of oil at a fixed Temp for the specified of time.A black, brown or grey tarnish indicates the presence of corrosive sulphur.

OXIDATION STABILITY TESTThis test submits the oil sample to accelerated oxidation in a selectively short time that it is likely to encounter in service.The maximum limits for new oils are acidity-0.4 mg KOH per gram and sludge 0.1% by weight.MOISTURE CONTENTWater will dissolve in insulating oil and its presence contributes a hazard not only to the dielectric performance of oil but also to insulation resistance of the windings.TEST METHOD: KARL FEISCHER METHODMaximum value- 25 ppmPRESENCE OF OXIDATION INHIBITORSThe test is most important to check whether the insulating oil, presumed uninhibited, do not contain anti-oxidation additives.ELECTRICALELECTRICAL STRENGTH( BREAKDOWN VOLTAGE)Measure of resistance in kilovolts required to break down the oil across a specified gap(2.5mm) under specified conditionsMeasure of ability to withstand electrical stressIndicates/detects the presence of free water, dirt, moisture, cellulose fiber or conducting particles(Except dissolved water, acids, sludge)The migration of wet solid matter or contaminants to the stressed area between electrodes leads to formation of strings to bridge the gapLow value of BDV indicates presence of contaminants/moisture/conducting particlesELECTRICAL STRENGTH (BDV):-Min voltage at which oil breaksLimitation after filtration:- 60kV(rms)FACTORS AFFECTING BDV:-Moisture Dirt & other conducting particlesELECTRICAL STRENGTH (BDV):-Min voltage at which oil breaksFACTORS AFFECTING BDV:-Moisture Dirt & other conducting particles

SOLID IMPURITES0.5PPMSOLID IMPURITES 50 PPMSPECIFIC RESISTANCE:- (RESISTIVITY)Measure of volume resistanceResistance per unit volume

dc electric field V-cmResistivity =------------------------------- current density I/cmFACTOR AFFCTING RESISTIVITY:-Conducting Impurities, Ageing products like Acid & SludgeFree ions & ions forming particlesMoisture TESTING:-SPECIFIC RESISTANCE IS TESTED AS PER IS:6103-1971TEST CELL:- 3 TERMINAL CELLSp.Res :- 35X 1012 ohm-cm at 900 C( max) for new oil & 0.2X 1012 ohm-cm for oil in useTESTING EQUIPMENT:-RESISTANCE OR SPECIFIC RESISTANCE MEASURING INSTRUMENT CAN BE USEDCELL CONSTANT, CM=11.3* C, C= CAPACITANCE OF EMPTY CELL,pf

DIELECTRIC DISSIPATION FACTOR( TAN DELTA OR POWER FACTOR)DDF of transformer oil is the tangent of loss angleDDF is the measure of power factor of oil that is cosine of angle between voltage & current I

90 90-

As per IS-335,DDF limits is 0.002(MAX) for new oil & 0.2 for oil in use Tan-0.002, =tan0.002=06 52secFACTORS AFFECTING DDF-Conducting impuritiesPolar substanceAgeing products, like acid & sludgeMoisture

VVDISSOLVED GAS ANALYSIS BY GAS CHROMOTOGRAPHApplication To predict incipient faults in transformers in operationsTo monitor their internal conditionsMethods Analysis and quantification of gases dissolved in the transformer oilUses Helps to eliminate forced outages by preventive actionImportance Reveals the internal condition of the transformer and not the condition of the oilGREATEST ADVANTAGES OF DGA TECHNIQUEAvoidance of unplanned outage as transformer defects are detected at incipient stages it self so that timely remedial measures can be under taken to prevent damages or total loss of equipmentStatus of health check for transformer periodicallyIs a quality test for new transformer/ repaired transformer before dispatch, insulation & commissioningCleaning transformer without internal faults, when they have tripped due to other reasonsSeveral cases where transformers have been saved from total destruction the confidence in DGA technique is so high that the transformer are sent to works for repairs by no other evidence other than that of DGA.Key Gas

Gas Contents

KEY GASCONCENTRATION IN ppmSUSPCETED FAULTC2H2(Acetylene)>30Power dischargeH2 (Hydrogen)>100Partial dischargeC2H4(Ethylene)>150Thermal degradation of oilCO (carbon monoxide)>350Thermal ageing of oilSLNoMAJORMINORNATURE OF FAULT1Ethylene (C2H4)Ethane(C2H6), Methane(CH4)Thermal decomposition of oil2H2 (Hydrogen)Methane(CH4), Ethane(C2H6), Internal Corona3Methane(CH4), H2 (Hydrogen)Hot spots4H2 (Hydrogen)C2H2(Acetylene)Ethylene (C2H4), Ethane(C2H6), Arcing, Electrical discharge of oil5CO,CO2(H2,CH4, C2H2)Cellulose insulation decompositionPermissible concentrations of DG in the oil of a healthy transformerGASUP TO 4 YEARS IN SERVICE (PPM)4-10 YEARS IN SERVICE(PPM)MORE THAN QO YEARS IN SERVICE(PPM)H2100/150200/300200/300CH450/70100/150200/300C2H220/3030/50100/150C2H4100/150150/200200/400C2H630/50100/150800/1000CO200/300400/500600/700CO23000/35004000/50009000/12000INTER NATIONAL STANDARDS It is mandatory for engineers to adhere to the relevant international as well as Indian Standard in determining the quality of oil1. Inter National Electro technical Commission - IEC, pub 296-1969 (for new oil) - IEC, Pub 422-1973 (for oil in service)2. American Society for Testing Materials - ASTMD, 1275-1996 (for corrosive Sulpher)3. British Standards - BS:148:1972 (for new oil) - BS: 5730: 1979 (for oil in service)4. National Standards - IS 335- 1983 (for new oil) - IS 1866-1983 (for oil in service)

SL.NoCharacteristicsRequirementMethod of TestRemarks1AppearanceThe oil shall be clear and transparent and free from suspended matter or sedimentsA representative sample of the oil shall be examined in a 100mm thick layer at 27C-2Density at 29.5C, Max0.89 g/cm

IS 1448 [P : 16] : 1977See note-13Kinematic viscosity max ata) 27Cb) 40C27 cStUnder considerationIS 1448 [P : 25] : 1976-4Interfacial tension at 27C0.04 N/mIS 6104 : 1971-5.Flash point pensky-marten(closed Min0140CIS 1448 [P : 21] : 19706Pour point,Max-6CIS 1448 [P : 10] : 1970SL.NoCharacteristicsRequirementMethod of TestRemarks7Neutralization Valuea) Total Acidity Maxb)Inorganicacidity/ Alkalinity0.03 mg KOH/gmNil

IS 1448 [P : 2] : 1967doAlcoholic potassium hydroxide solution of 0.02 N should be used in place of 0.1 N indicated in test method8Corrosive SulphurNon CorrosiveAnnex B-9Electric Strength (BDV)New unfiltered Oil MinAfter Filtration Min30 kV (rms)

kV (rms)

See note-210Dielectric Dissipation Factor (tan ) at 90C Max0.002IS 6262 : 1971See note-2

11Specific Resistance (resistivity)At 90 C MinAt 27C Min35X 10 12 -cm1500X10 12 -cmIS 6103 : 1971See note-2

SL.NoCharacteristicsRequirementMethod of TestRemarks12Oxidation StabilityNeutralization Value after oxidation MaxTotal Sludge after oxidation Max0.4 mg KOH/gmNil

0.1 % by weightAnnex C-13Ageing characteristics after accelerated ageing ( open beaker method with copper catalyst)a) Specific Resistance (resistivity)i)At 90 C Minii)At 27C Minb) Dielectric Dissipation Factor (tan ) at 90C MaxC) Total acidity, MaxD)Total Sludge, Max2.5XD10 12 -cm0.2X10 12 -cm0.20

0.05 mg KOH/g0.05% by weightIS 12177 : 1987Method A

IS 6103 : 1971

IS 6262 : 1971

IS 1448 [P:2] : 1967Annex A of IS 12177See note-214Presence of Oxidation inhibitorThe oil shall contain anti oxidant additivesIS 13631 : 1992See note-3

15

16Water Content Max

SK Value25ppm

Under Consideration

IS 13567 : 1992

Annex D

-Notes:-1.Density of oil may be measured at ambient Temp. and converted to 29.5C using the following Equation 29.5= t[1+X(t-29.5)]Here t= ambient temp( in C ) t= density measured at Temp. t and X= correction factor ( equal to 65X10-5 Approx)2. As a consequence of the tendency for water absorption to occur due to breathing on storage even when drums are sealed the oil shall be filtered to remove moisture and particulate contaminants present in the original sample before the test as follows. A sufficient quantity of oil is heated to 90 2 C , then filtered hot under vacuum corresponding to an absolute pressure of about 2.5 kPa through a sintered glass filter of porosity grade 4. 3) A portion of the filtrate is cooled in a desiccator & used immediately to measure electric strength, if required specific resistance also at 270 C. The remaining hot filtrate is immediatrely used for measuring dielectric dissipation factor at 900 C & specifc resistance at 900 C4) For both phenol & amine type of indicators,quatitative method as per Annex D shall be adopted. In case of ambiguity (marginal cases) in finding the intensity of colour a quantitative method as given in Annex D shall be adopted. Value of 0.5 (max) shall be treated as absence of DBPC-Phenolic type inhibitor ( Quantitative method for amins is under consideration)) A portion of the filtrate is cooled in a desiccator & used immediately to measure electric strength, if required specific resistance also at 270 C. The remaining hot filtrate is immediatrely used for measuring dielectric dissipation factor at 900 C & specifc resistance at 900 C4) For both phenol & amine type of indicators,quatitative method as per Annex D shall be adopted. In case of ambiguity (marginal cases) in finding the intensity of colour a quantitative method as given in Annex D shall be adopted. Value of 0.5 (max) shall be treated as absence of DBPC-Phenolic type inhibitor ( Quantitative method for amins is under consideration)3) A portion of the filtrate is cooled in a desiccator & used immediately to measure electric strength, if required specific resistance also at 270 C. The remaining hot filtrate is immediatrely used for measuring dielectric dissipation factor at 900 C & specifc resistance at 900 C4) For both phenol & amine type of indicators,quatitative method as per Annex D shall be adopted. In case of ambiguity (marginal cases) in finding the intensity of colour a quantitative method as given in Annex D shall be adopted. Value of 0.5 (max) shall be treated as absence of DBPC-Phenolic type inhibitor ( Quantitative method for amins is under consideration)