APAR Industries Ltd , India Emerging trends and challenges in Quality and Performance standards of Transformer Oil – Critical Properties & Issues By D.V.Jagannathan Contents 1 ) Emerging Trends & Challenges 2 ) Copper Sulphide Corrosion in Transformers 3 ) Changing Demands in Oil 4 ) New Standards for Corrosive Sulphur 5 ) New Standards for Oxidation Stability 6 ) Sulphur Vs Oxidation – The Balancing Act 7 ) Requirements of Transformer Oil 8 ) Critical Oil Properties and Significance 9 ) Sulphur in Transformer Oil 10 ) National Vs International Standards 11 ) Special Requirements and High Grade Options 12 ) Conclusions Emerging Trends and Challenges Transformer Industry has seen three dimensional effects of Demand - Increased Power demands. Higher Loads & Extra High Voltage requirements. Design - Compactness driven by Material Cost considerations leading to more severe Operating conditions. Disasters - Major Transformer failures largely attributed to Copper Sulphide formation. - Predominant in Power Transformers & Sealed Systems. Transformer Failures The Issues: • Large Power Transformer and Reactor failures starting in 2000. • Doble has recorded about 25 + units that have failed worldwide. • Many of these are units only 5 to 7 years old. • Sudden failures with no / hardly any advance warnings. COPPER SULPHIDE CORRSION IN TRANSFORMERS • Transformer failures due to Copper Sulphide Corrosion problem being reported since the turn of the century world wide - ( U S.A, Brazil, Sweden and also recently in India • PROBABLE CAUSES 1. Higher Corrosive & Mercaptan Sulphur levels in oils 2. Increased severity of working conditions - Higher Temperatures & Electrical Stress 3. Influence of Transformer Materials -Type & condition of paper insulation 4. Time Temperature Dependence 5. Change of Service Conditions 6. Impact of Transformer Design - Changing towards more compactness • Proper assessment based on Oil Properties & Performance, Operational Conditions, Materials & Design Aspects of Transformer is essential • In most cases of such failures, sulphur content of oils were in the range of 0.3 to 0.5 % . • Modern Transformers demand non corrosive oils with lower sulphur contents made from very low sulphur crudes and by deep hydro de sulphurization methods. Changing Demands in Transformer Oil • Compact Designs of higher operating temperatures require better Cooling. • Longer trouble free Service Life requiring higher Oxidation Stability. • Non Corrosive Oils to avoid Copper Sulphide Corrosion. • Lower Gas evolution requirements in Transformers. • Compliance to environmental / safety factors – PCB free / Low PCA. • Revised standards with increased severity of Test conditions and new Tests for : - Oxidation Stability – IEC 61125 Method C and - Corrosive Sulphur – ASTM D 1275 B & Cigre TF A2.32.01- CCD. • For EHV Power / HVDC Transformers it is imperative to select the right quality oil of upgraded specification for trouble free higher performance. New Standards for Corrosive Sulphur 150 ASTM D 3487 – 2000 ( Reapproved 2006 ) Doble TOPS – 2006 (ASTM D 1275 B – Modified) CIGRE TF.A2.32.01 * Copper Copper + Kraft Paper 140 ASTM D 3487 – 1988 / 2000 Temp 0 C. Copper (ASTM D 1275 A) Copper IEC 62535 Ed.1 (proposed) 100 IEC 296 - 1982 / BS 148 -1984 Paper rating by SEM - EDX (ISO 5662 / BS 5680) Copper 0 19 Hours 48 72 Other sensitive Test: DIN 51353 – IEC 60296 (2003) – Silver Strip, 100 0 C, 18 hrs. * CIGRE TF.A2.32.01 (CCD) Test -- Produces results close to real case. Oils that previously passed the less severe Tests are NOT able to handle the higher Temperature & Duration of the new Tests NTS New Standards for Oxidation Stability 120 IEC 60296 – 2003 IEC 61125 C (U) (T) (I) Air Air Air 110 ASTM D 3487 – 00 ( 2006 ) - Type I & II Doble TOPS – 2006 Uninhibited ,Type I & Type II - Inhibited Temp 0 C. ASTM D 2440 Oxygen 100 IEC 296 -1982 IEC 74 Oxygen 0 72 Hours 164 332 500 NTS Other Tests: PFVO & SFL in Doble TOPS – 2006 for all Types of Oils ( U , T (Type I) & I ( Type II) ASTM D 2112 – RBOT in ASTM D 3487 – 00 ( 2006 ) for Type II Inhibited Oil & in Doble TOPS – 2006 for Type I & Type II Inhibited oils Also stringent Oxidation Stability limits for Special Applications in IEC 60296 – 2003 Sulphur Vs Oxidation – Balancing Act for Refiner Requirement Oxidation Sulphur Oxidation Sulphur Corrosive High Stablility Non Corrosive Low Stablility Sulphur • Increased Oxidation Stability and Non Corrosive requirements in oils are contradictory challenges for refiner. • Sulphur removal also causes depletion of aromatics lowering oxidation stability. • Thiophenes & Mono aromatics / lower size PCAs are natural inhibitors – preferred in oil for control of oxidation stability and sulphur corrosion. • Low aromatic oils have low corrosive sulphur but better BHT response. • Optimized selective refining requires the right balancing act of - Not just total sulphur removal but selective removal of the corrosive sulphurs - Retaining the required aromatics for maintaining increased oxidation stability Oxidation Non Corrosive High Stablility Requirements of Transformer Oil 1. Good Electrical Properties - For effective Insulation - High BDV & Resistivity and Low Tan Delta ( Power Factor ). 2. High Oxidation Stability - For longer life and trouble free operation. 3. Low Viscosity - For good circulation and cooling – better heat transfer. 4. Low Gassing Tendency - For better Gas absorption and effective diagnostics by DGA & Safe operation 5. Low Sulphur and Non corrosive 6. High Solubility - To avoid copper sulphide corrosion on conductors and damage to winding under stressful conditions - For less sludge and less oil deterioration Consistent behavior with respect to time - Performance Durability Constant availability of same quality base oils - Consistency Transformer Oil Properties - Classification FUNCTIONAL - HAVE IMPACT ON ITS FUNCTION AS INSULATING AND COOLING LIQUID Viscosity, Density , Pour Point , Water Content ,Volume Resistivity , Breakdown voltage , Dielectric Dissipation Factor ( Tan Delta ) REFINING & STABILITY - INFLUENCED BY QUALITY, TYPE AND DEGREE OF REFINING & ADDITIVES Appearance , Interfacial Tension ( IFT) , Acidity, Carbon Type Composition ( PNA ) , Aromatic Content , SK Value , Corrosive Sulphur, Total Sulphur & Mercaptan Sulphur Content, Oxidation Inhibitor Content PERFORMANCE - RELATED TO LONG TERM BEHAVIOR OF OIL IN SERVICE AND ITS REACTION TO HIGH ELECTRIC STRESS AND TEMPERATURE Oxidation Stability , Gassing Tendency , Gas Content (DGA) , Impulse Breakdown Voltage, Electrostatic Charging Tendency, Furan Content , Corrosivity HEALTH,SAFET - RELATED TO SAFE HANDLING & ENVIRONMENT PROTECTION & ENVIRONMENT Flash Point , Density , PCA ( Polycyclic Aromatics ) , PCB / PCT ( Polychloro Biphenyls / Polychloro Terphenyls ) Oil Properties - Significance / Preference Sr.No PROPERTY SIGNIFICANCE PREFERENCE 1. Density at 20 o C / Specific Gravity Mass Volume Calculations Values Indicate Type of Oil < 0.895 Values range from 0.81 to 0.895 Paraffinic Oils – 0.81 to 0.84 Naphthenic Oils – 0.85 to 0.895 2. Kinematic Viscosity In Heat transfer / Cooling Lower Value < 12 cSt at 40o C 3. Flash Point Safety & Fire Hazard Higher Value > 135 o C 4. Pour Point Minimum Operating Temp Lower Value < - 40 o C 5. Interfacial Tension Refining Quality Higher Value > 40 x 10 -3 n / M 6. Acidity / Neutralization No Corrosion / Sludge build up / affects electrical properties Lower Value < 0.01 mg KOH / g 7. Water Content Affects electrical properties Sludge / Paper deterioration Lower Value < 30 ppm 8. Sulphur Content Decides corrosion chances Lower Value < 0.15 % 9. Corrosive Sulphur Copper conductor corrosion copper sulphide formation To pass more severe test ASTM D1275 B 10. Oxidation Stabilitry Service life / Deterioration of electrical properties / Sludge To pass more severe / stringent tests IEC 61125 C Oil Properties - Significance / Preference Sr.No PROPERTY SIGNIFICANCE PREFERENCE 11. Ageing Characteristics Service life / Deterioration of electrical properties / Sludge To pass specified test limits to ensure ageing stability 12. Breakdown Voltage Electrical Strength – Lower values indicate impurities like moisture / dirt / particles Higher Values > 50 delivered & > 70 after filtration treatment 13. Specific Resistance / Resistivity, ohm - cm Lower values indicate conducting impurities Higher Values > 2000 x 1012 at 27 o C & > 150 x 1012 at 90 o C 14. Dielectric Dissipation Factor , Tan Higher values - presence of polars / Decides refining quality Lower Values < 0.005 15. Power Factor , % Percentage power loss - DDF x 100 Lower Values < 0.5 16. Gassing Tendency Decides extent of Gas evolution /absorption,Important for DGA Lower Values < + 5 In HVDC Transformers < 0 17. Impulse Breakdown Voltage Decides Insulation Life Higher Values > 145 18. PCA - Poly Cyclic Aromatics Decides Gassing Tendency / Health hazards while handling Lower Values < 3 % but not < 0.75 % due to higher gassing 19. PCB / PCT Highly Hazardous / Banned Must be non detectable < 2 ppm 20. 2 FAL / Furans Quality of refining / Higher values due to used / rerefined oils Very low level In new oil < 0.1 ppm VISCOSITY & VISCOSITY INDEX • Viscosity - • Viscosity Index - Influences Heat Transfer - Temperature rise Lower the Viscosity better the circulation & cooling Rate of change of Viscosity with respect to Temperature Lower the VI better the circulation & cooling Hydrocracked Parrafinic Oil ( Higher VI ) • Viscosity @ 70oC,mm2/Sec 4.2 Hydrotreated Naphthenic Oil ( Lower VI ) 3.2 ( 25 % Reduction ) WATER CONTENT & DIELECTRIC DISSIPATION FACTOR • Lower the Water Content higher the electric strength & lower the dissipation losses • Water solubility in oil depends on temperature & amount of polar / aromatic molecules Higher aromatic content gives higher water saturation • Water ingress takes place due to breathing of drums when stored in areas of high humidity and temperature . G - 4 filtration reduces water content to achieve higher breakdown voltage but care to be taken to avoid over heating while filtration as water solubility increases with temperature -------------------------------------------------------------------------------------------------------------------------• DDF is measure of dielectric losses caused by the oil , depends on ionisable and polar molecules in the oil • DDF increases with contamination by moisture , particles , soluble polar contaminants and poor refining quality. • Very sensitive to contaminants like Engine Oils, Lubricants , Used Oils that can enter from the filter machines due to their earlier use if proper care is not taken while filling Transformers CARBON TYPE COMPOSITION PARAFFINIC - SATURATED NORMAL (Straight Chain ) & ISOPARAFFINS ( Branched Chain) Higher Pour Points, Higher Viscosities, Low Solubility for water and oxidation products forming precipitated sludge, Lower Thermal stability NAPHTHENIC - CYCLIC SATURATED HYDROCARBONS CYCLOHEXANE TYPE & SIMILAR HIGHER RING COMPOUNDS Excellent Low Temperature Properties, Better Solvency power than Paraffins, Excellent Chemical & Oxidation Stability, Lower VIs help in better Circulation and Cooling AROMATIC - CYCLIC UNSATURATED HYDROCARBONS BENZENE TYPE & SIMILAR HIGHER RING COMPOUNDS Different from Paraffinics & Naphthenics both chemically and physically, Unstable and polar in nature GENERAL GUIDE LINE FOR CLASSIFICATION OF OILS BY CP % CP Below 50 % CP 50 To 56 % CP Above 56 % - Naphthenic Oils Intermediate Oils Paraffinic Oils AROMATICS & PCA CONTENT • Aromatic Content in oil depends on Degree of Refining Higher the degree of refining lower the aromatic content and vice versa • Mono aromatics & lower ring Poly Cyclic Aromatics up to certain levels act as good natural radical destroying oxidation inhibitors - hence selectively retained in the oil for better Oxidation Stability and better Gas Absorption with optimum Electrical Properties • PCA content increases with increase in boiling range and aromatic content • Higher molecular size Poly Cyclic Aromatics are not preferred in the oil as they have negative effect on the electrical properties like impulse breakdown voltage and streaming charges • PCAs are also classified as carcinogens – need to be controlled up to acceptable levels in the oil - Maximum limit of 3 % is specified in BS : 148 & IEC : 60296 standards and also as allowed by the severe environmental standard for labeling in confirmation with the EU Regulation as per IP- 346 OXIDATION STABILITY • Improves with Degree of Refining thus with decrease in Aromatic Content Oxidation Stability drops appreciably below 4 % CA and also above 12 % CA • Over refining causes depletion of preferable natural inhibitors like mono aromatics and lower size poly cyclic aromatics • Oxidation stability is controlled by mono aromatics, poly cyclic aromatics and the Nitrogen, Oxygen & Sulphur hetero cyclic polar compounds • IS 335 - 1993 Specifies Oxidation Stability at less severe conditions of 100 o C • To be measured in accordance with the more stringent, IEC 61125 - Method C - Low air flow of 0.15 ltr / hr in oil with 90 cm copper coil at 120 0 c for test duration of 164 hrs for Uninhibited oil , 332 hrs for Trace Inhibited oil & 500 hrs for Inhibited oil • Inhibition of oil with DBPC helps to increase oxidation stability but requires careful monitoring of inhibitor content and proper replenishment when it drops below the minimum required level ( half of original level ), otherwise the inhibited oil deterioration will be much faster. Sulphur in Transformer Oil Sulfur exists in varying Forms and Concentrations in transformer Oil after all Processes. Some sulfur types are non Corrosive to Transformer Metals, where as certain types become very Corrosive at higher operating temperatures. Very corrosive in transformers: ELEMENTAL SULFUR ( S ) - Most likely to be found residual after Solvent Extraction - Not likely to survive Hydrotreating or Hydrocracking HYDROGEN SULFIDE ( H2S ) - Exists as a stable Molecule and very Corrosive acid Gas but rarely found in Purge Dried / Vacuum Dehydrated Oil MERCAPTAN SULFUR ( RSH ) - Possibly found in the Oil after all Refining Processes - Concentration will depend on the severity of process Sulphur in Transformer Oil THIOPHENES - Non Corrosive • Found in the oil after all refining processes. • Cyclic compounds with Sulfur embedded in the Ring are very Stable. • They also Aid in the natural Inhibiting Process of Totally Uninhibited Oil. Dibenzo Thiophene Most simple Polyaromatic Thiophene S SULFIDES-THIO ETHERS ( RSR ) - Moderately Corrosive • These compounds can be found after all refining processes. • Concentrations found in the oil will be relative to the process severity. Sulphur in Transformer Oil DISULFIDES ( RSSR ) - Can exist after all Refining Processes. • Normally non Corrosive Stable compounds when ( R ) is straight chain paraffinic. • When ( R ) is a ring structure - becomes susceptible to heat breakdown and forms Mercaptan ( RSH ) & Hydrogen Sulfide (H2S) - very Corrosive to Transformer Metals. • Some past studies rated Disulfides as Stable until this chemistry was better understood. S S S S Dibutyl Disulfide ( R ) is Paraffinic Dibenzyl Disulfide ( R ) is Aromatic or Ring DBDS & Selective Refining Problems due to DBDS • Transformer failures were attributed to presence of DBDS in Oils. • Earlier Sulphur Tests could not detect but the new Tests could detect. • Should not remain in Hydrotreated Oil unless added to enhance Oxidation Stability. • DBDS breaks up at higher Hot Spot Temperatures ( > 140 o C ) forming Corrosive Elemental / Mercaptan Sulphurs. • Essential that Oils are free of any DBDS. Selective Refining • Total Sulphur alone is not a sure indicator of whether an Oil is Corrosive. • Corrosive character of Oil is the result of Sulphur type. • Can be controlled by increasing Severity of treating Process to selectively remove the unwanted Sulphurs. Mitigation Methods • Copper Sulphide formation is not reversible. • Further Corrosion can be controlled by Mitigation methods. • Commonly sugested Mitigation method is use of a Passivator. • Depletion of Passivator while in service has been observed in some cases. • Replenishment of Passivator on line - difficult to Monitor and Administer. • Side effects of Passivator on Long Term usage – still not clear. Solution does not lie in Mitigation by Passivation, but in Replacement with Oils FREE of any Corrosive Sulphur CORROSIVE AND MERCAPTAN SULPHUR • Type and levels of Sulphur compounds depend on origin of crude & degree and type of refining. • Have both characteristics - Negative - copper sulphide corrosion Positive - as peroxide destroying inhibitors during oxidation process . • Most of the standards specify only qualitative Corrosive Sulphur tests and not quantitative Corrosive & Mercaptan Sulphur content tests. • Type test provided in IS 335 and other standards are not adequate enough to assess the exact levels of detrimental sulphur in oils as they are qualitative tests and at less severe test conditions . • Only IEC 60296 specifies Total Sulphur Content limit as 0.15 %, max , by ISO 14596 ( WDXRF- Wave length X - Ray Fluorescence Spectrometry ) / IP 373 ( Microcoulometry Oxidative) Methods & Corrosive Sulphur by DIN 51353 ( Silver Strip , Temp 100 o C , Heating Time 18 Hrs ). • Need to specify more stringent tests like : A ) Modified ASTM D 1275 Method B for Corrosive Sulphur ( Temp 150 0c, Heating Time 48 hrs , N2 bubbling for15 mints. pre and 30 mints post start of test and keeping oxygen free subsequently ) B ) CIGRE TF. A2. 32. 01- CCD – Covered Conductor Deposition ( OIL + KRAFT PAPER,Temp 150 0 c, Heating Time 72 hrs ) & IEC 62535 – CCD + SEM – EDX for detection of Copper Sulphide on Paper. C ) Mercaptan Sulphur content by ASTM D 3227- 04 A / IP 342( Potentiometric Titration ) with very low acceptance limits. GASSING TENDENCY • Gassing Tendency / Gas Absorption under electrical stress is an important performance property for safe functioning of High Voltage Transformers • It is a measure of rate of absorption or evolution of hydrogen in to oil in prescribed laboratory conditions by method A of IEC 60628 or ASTM D 2300 • Gassing Tendency limits are specified in BS 148 ( maximum + 5 ) and ASTM D 3487 ( maximum + 30 ) standards for uninhibited oils. IEC 60296 standard allows limits to be decided between oil manufacturer / user. Doble TOPS specifies negative gassing. Not included in BIS - IS 335 standard • Mainly controlled by amount and type of Aromatics and PCA s in oil. Gassing Tendency decreases with increase in Aromatic & PCA content • Also seen that it decreases with increase in Naphthenic content and increases with increase in Paraffinic content even though these types of hydrocarbons have no direct bearing on the Gassing Tendency BREAKDOWN VOLTAGE UNDER IMPULSE CONDITION • Not commonly included in specifications except ASTM D 3487 / Doble TOPS ( minimum 145 k V ) of negative impulse breakdown voltage. • Breakdown behavior with DC impulse and heterogeneous gap is very different from the AC breakdown strength. It is sensitive to both polarity and electrode geometry. • Measured by simulating lightning impulse striking a transformer during thunder strom by the IEC 60897 or ASTM D 3300 Method. • It is the capacity of the oil for reducing short electric shocks such as arcing of wires or the load on transformer while being connected and disconnected during switchovers. • Critical in electrical equipments as it indicates ability of the oil to resist electric breakdown under transient voltage stresses ( lightning and switching surges ). • Impulse Breakdown Voltage decreases with increase in PCA content and vice versa. Possible to achieve > 200 kV value in optimum refined oils with up to maximum 3 % PCA. 2- FAL , FURANS & PCB / PCT CONTENT 2- FAL - Caused from improper distillation in solvent extracted oils during refining leaving residual furfural or from contamination with used oil. - Preferable to have low level of 2 - FAL and related compounds in oils. - IEC 60296 standard specifies maximum acceptable limit of 2- FAL in new oil as 0.1 mg / kg as measured by IEC 61198 Method. FURANS - - PCB / PCT - Furanic compounds ( Furfuraldehyde ) are generated as byproducts during degradation of cellulose materials such as paper, pressboard,wood , etc. Serves as indicator of solid insulation degradation as they give more precise and early warning of paper insulation deterioration in oil filled transformers. Limit of Total Furans is specified in BS -148 Standard as1.0 mg / kg,max. as measured by HPLC Method. Doble TOPS specifies Furanic Compounds as optional test with limit of 25 µg / Litre,max. by ASTM D 5837 method. Polychlorinated Biphenyls / Terphenyls - Not present in new insulation oils produced from crude oils. Present only in synthetic / re-refined / used oils. - To be measured in any mixture of old and new oils. - Have negative environmental impact and hence banned by many countries. Classified as hazardous waste and require special method of disposal. - Unused mineral insulating oil should be free from PCB / PCT as tested by IEC 61619 / BS EN 61619 / ASTM D 4059 Method. Transformer Oil Standards - National Versus International Sr. No CHARACTERISTICS IS 335 / IS12463 ASTM D 3487 TYPE I / II DIN 57370 VDE 0370 AS 1767.1 CL I / II IEC 60296 U/T/I BS 148 CL I / II Doble TOPS Uninhibited / Type I / Type II 1. Aniline point , o C -- 63 Min -- -- -- -- 63 Min 2. Colour , Max. -- 0.5 -- -- -- -- 0.5 3. Flash point ( PMCC ), o C , Min 140 145 ( COC ) 130 140 / 130 135 140 / 130 145 ( COC ) 4. I.F.T. @ 25 o C N/m, Min 0.04 0.04 -- 0 .04 -- -- 0.04 5. Pour Point o C Max -6 - 40 -- - 30 / - 45 - 40 - 30 / - 45 - 40 6 Specific gravity @ 20 o C Max 0.89 @ 29.5 o C @ 15 o C 0.91 0.895 0.895 0.895 0,895 0.91 @ 15 o C 7. Kinematic Viscosity, cSt ( SUS ) @100 o C Max @40 o C , Max @ 27 o C , Max @ 0 o C , Max @ -15 o C , Max @ -30 o C , Max --27 ---- 3 (36) 12 (66) -76 (350) --- --25(20O c) -1800 - -16.5 / 11 --800 / --- / 1800 -12 ---1800 -16.5 / 11 --800 / --- / 1800 3 11 -76 --- Clear,Tpt, free of suspend matter & Sediment Clear & bright Clear & bright Clear & bright Clear bright Clear & bright -- 8. Visual examination Transformer Oil Standards - National Versus International S.No CHARACTERISTICS IS 335 / IS12463 ASTM D 3487 TYPE I / II DIN 57370 VDE 0370 AS 1767.1 CL I / II IEC 60296 U/T/I BS 148 CL I / II Doble TOPS Uninhibited / Type I / Type II 9. Dielectric breakdown voltage, KV Min. Delivered / After treatment 30 / 60 30 / 50 30 / 50 30 / 50 30 / 70 30 30 10. Dielectric breakdown voltage Impulse conditions, 25o C, KV Min. Needle negative to sphere grounded 1-in ( 25.4 mm ) gap , Min. -- 145 -- -- -- -- 145 11. Dissipation Factor @ 60Hz, % , Max @ 25 o C @ 90 o C 0.002 0.05 @ 100oC 0.30 -0.005 -0.005 -0.005 -0.005 0.05 0.3 @ 100 o C 12. Water Content, ppm , Max 50 35 -- 30 (B) 40 (D) 30 (B) 40 (D) 20 (B) 30 (D) 30 13. Gassing Tendency F/G µL / min , Max. ASTM D 2300 Method B -- + 30 -- -- -- +5 Negative Transformer Oil Standards - National Versus International S. No CHARACTERISTICS IS 335 / IS12463 ASTM D 3487 TYPE I / II DIN 57370 VDE 0370 AS 1767.1 CL I / II IEC 60296 hrs. U / T / I 164 / 332 / 500 BS 148 CL I / II Doble TOPS Uninhibited / Type I / Type II 14. Oxidation stability (Acid Sludge Test),Max . 72 hrs. Sludge % mass TAN mg KOH/mg 100 o C O2 --- 110 o C O2 0.15 0.50 100 o C O2 --- 120 o C Air --- 120 o C Air 110 o C O2 0.15 / 0.15 / 0.1 0.5 / 0.5 / 0.3 164 hrs. Sludge % mass TAN mg KOH/gm] DDF at 90 o C 0.1 0.4 -- 0.30 0.60 -- 0.06 0.30 -- 0.80 1.20 0.500 -Genl. Special 0.80 0.05 1. 20 0.30 0.500 0.05 120 oC Air, --0.80 1. 20 -- 0.3 / 0.3 / 0.2 0.6 / 0.6 / 0.4 -- ---- ---- 0.60 0.05 0.18 ---- ---- ---- ---- Oxidation Stability - RBOT minutes, Min -- / 195 195 -- -- -- -- NA / 195 / 220 Oxidation inhibitor content % mass , MaxUninhibited Trace inhibited ( Type I ) Inhibited oil (Type II ) 0.05 -0.3 Nil 0.08 0.3 Nil --- Nil -0.15 - 0.4 NIL 0.08 0.08 - 0.4 Nil --- NIL 0.08 0.3 15. 16. 17. Ageing Resistance according to Baader (140 hrs / 110 o C) Saponification No., mg KOH/gm Sludge content, wt%, max Dielectric Dissipation Factor @90 o C, Max Transformer Oil Standards - National Versus International Sr. No CHARACTERISTICS IS 335 / IS12463 ASTM D 3487 Type I / II DIN 57370 VDE 0370 AS 1767.1 CL I / II IEC 60296 U/T/I BS 148 CL I / II Doble TOPS Uninhibited / Type I / Type II 18. Corrosive Sulphur Non corrosive Non corrosive Non corrosive Non corrosive Non corrosive Non corrosive Non corrosive Test Method IS 335 Annex - B ASTM D 1275 A / B DIN 51353 ASTM D 1275 A DIN 51353 BS 5680 ASTM D 1275 B Cu , 140 , 19 Cu , 140 , 19 / Cu , 150 , 48 Ag, 100 ,18 Cu , 140 , 19 Ag, 100 ,18 Cu,100 ,19 Cu , 150 , 48 (Strip , Temp o C , Hrs ) 19. Total Sulphur content, % Max. -- -- -- -- 0.15 Spl.Appln -- -- 20. TAN, mg KOH/gm, Max 0.03 0.03 0.03 0.01 0.01 0.03 0.015 21. PCB Content, ppm -- ND ND ND ND ND ND 22. PCA Content , %, -- -- -- < 3.0 < 3.0 < 3.0 -- 23. Total Furans , mg / kg, Max -- -- -- -- -- 1 25 µg / L 24. 2 - Furfural Content mg / kg , Max -- -- -- -- 0.1 -- -- 25. Power FactorValued Oxidation ( PFVO ) -- -- -- -- -- -- To pass Doble Limit Curve 26. Sludge Free Life – ( SFL ) @ ± 8 Hrs -- -- -- -- -- -- 40 / 64 / 80 Hrs Min Changes in new IEC 60296 : 2003 from the earlier IEC 296 : 1982 Standard Three Classes are replaced by only two namely Transformer Oil and Low Temperature Switchgear oil. New concept of Lowest Cold Start Energizing Temperature ( LCSET ) for different ambient temperature conditions have been included and new property like Electrostatic Charging Tendency ( ECT ) has been added and values for the other properties have been revised. Class I , Class II , Class III for Uninhibited Oils & Class I A , Class II A & Class IIIA for Inhibited Oils of IEC 296 are replaced with only three Types - (U) Uninhibited , (T) Trace Inhibited & (I) Inhibited in IEC 60296. Merging differences in the physical properties between the Classes and making it as one general specification with lower Viscosity (< 12 cSt at 40 o C) & Pour point ( - 40 o C max) Increasing severity of Oxidation Stability Test conditions in IEC 61125 C (to 120 o C ) and with Air instead of Oxygen to make it represent the real life Transformer operating condition. Differentiating the duration of Oxidation Stability test to 164 Hrs for ( U ), 332 Hrs for (T) and 500 Hrs for ( I ) grades instead of only 164 Hrs as common for all types of grades. Including Special Application Requirements of higher oxidation stability for High Grade Oils with more stringent limits for Total Acidity , Sludge, DDF @ 90 o C.and Sulphur Content. Special Application Requirements • Sealed Transformers / High Voltage applications including HVDC need non corrosive oils with considerably higher oxidation stability. • These special requirements are achieved with very low Sulphur and low Aromatic Oils that have excellent BHT( Anti oxidant ) response. • High Grade Oxidation Stability of special application requirements of IEC 60296 Standard are generally met with Trace or fully Inhibited Oils. • To meet this High Grade requirements very severely treated inhibited Naphthenic or inhibited Iso Dewaxed Iso Paraffinic Oils are available. • High performance Hydrotreated & Hydrocracked Oils can be designed for effective Cooling, Low Gassing and essentially Sludge Free Life. Conclusions • Transformer Operating conditions have thrown new challenges for refiners to produce high quality oils meeting latest standards and tests. • Refiner needs to take a tight rope walk to satisfy the contradictory requirements of both high oxidation stability and non corrosive oils. • Fingerprinting of oil by signature analysis and optimization of oil properties by selective refining methods is essential to achieve this. • Standard high oxidation stability and non corrosive requirements can be met in Uninhibited Naphthenic oils by optimizing aromatics & sulphurs. • For still higher special application oxidation stability and non corrosive requirements new options of Inhibited Naphthenic and Isoparaffinc oils are emerging. Conclusions Characterization of a good Transformer Oil is based on its : Electro insulating properties Cooling characteristics Chemical and Oxidation stability Behavior under severe electrical stresses Compatibility with Transformer materials Compliance to environmental factors Satisfactory long service life Transformer Oil constitutes only 5 to 7 % of the cost of Transformer. Easy to compare the high cost incurred in Transformer failures to the relatively negligible differential cost of High Grade Oils. TRANSFORMER IS HEART OF POWER SYSTEM AND INSULATING OIL ITS BLOODLINE Thank You