Classifications

• • C—CHEMISTRY; METALLURGY
  • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
  • C10M—LUBRICATING COMPOSITIONS; USE OF CHEMICAL SUBSTANCES EITHER ALONE OR AS LUBRICATING INGREDIENTS IN A LUBRICATING COMPOSITION
  • C10M127/00—Lubricating compositions characterised by the additive being a non- macromolecular hydrocarbon
  • C10M127/04—Lubricating compositions characterised by the additive being a non- macromolecular hydrocarbon well-defined aromatic
• • C—CHEMISTRY; METALLURGY
  • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
  • C10M—LUBRICATING COMPOSITIONS; USE OF CHEMICAL SUBSTANCES EITHER ALONE OR AS LUBRICATING INGREDIENTS IN A LUBRICATING COMPOSITION
  • C10M127/00—Lubricating compositions characterised by the additive being a non- macromolecular hydrocarbon
  • C10M127/06—Alkylated aromatic hydrocarbons
• • C—CHEMISTRY; METALLURGY
  • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
  • C10M—LUBRICATING COMPOSITIONS; USE OF CHEMICAL SUBSTANCES EITHER ALONE OR AS LUBRICATING INGREDIENTS IN A LUBRICATING COMPOSITION
  • C10M129/00—Lubricating compositions characterised by the additive being an organic non-macromolecular compound containing oxygen
  • C10M129/02—Lubricating compositions characterised by the additive being an organic non-macromolecular compound containing oxygen having a carbon chain of less than 30 atoms
  • C10M129/16—Ethers
• • C—CHEMISTRY; METALLURGY
  • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
  • C10M—LUBRICATING COMPOSITIONS; USE OF CHEMICAL SUBSTANCES EITHER ALONE OR AS LUBRICATING INGREDIENTS IN A LUBRICATING COMPOSITION
  • C10M169/00—Lubricating compositions characterised by containing as components a mixture of at least two types of ingredient selected from base-materials, thickeners or additives, covered by the preceding groups, each of these compounds being essential
  • C10M169/04—Mixtures of base-materials and additives
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
  • H01B3/00—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties
  • H01B3/18—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances
  • H01B3/20—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances liquids, e.g. oils
• • C—CHEMISTRY; METALLURGY
  • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
  • C10G—CRACKING HYDROCARBON OILS; PRODUCTION OF LIQUID HYDROCARBON MIXTURES, e.g. BY DESTRUCTIVE HYDROGENATION, OLIGOMERISATION, POLYMERISATION; RECOVERY OF HYDROCARBON OILS FROM OIL-SHALE, OIL-SAND, OR GASES; REFINING MIXTURES MAINLY CONSISTING OF HYDROCARBONS; REFORMING OF NAPHTHA; MINERAL WAXES
  • C10G2300/00—Aspects relating to hydrocarbon processing covered by groups C10G1/00 - C10G99/00
  • C10G2300/20—Characteristics of the feedstock or the products
  • C10G2300/30—Physical properties of feedstocks or products
  • C10G2300/302—Viscosity
• • C—CHEMISTRY; METALLURGY
  • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
  • C10G—CRACKING HYDROCARBON OILS; PRODUCTION OF LIQUID HYDROCARBON MIXTURES, e.g. BY DESTRUCTIVE HYDROGENATION, OLIGOMERISATION, POLYMERISATION; RECOVERY OF HYDROCARBON OILS FROM OIL-SHALE, OIL-SAND, OR GASES; REFINING MIXTURES MAINLY CONSISTING OF HYDROCARBONS; REFORMING OF NAPHTHA; MINERAL WAXES
  • C10G2300/00—Aspects relating to hydrocarbon processing covered by groups C10G1/00 - C10G99/00
  • C10G2300/20—Characteristics of the feedstock or the products
  • C10G2300/30—Physical properties of feedstocks or products
  • C10G2300/304—Pour point, cloud point, cold flow properties
• • C—CHEMISTRY; METALLURGY
  • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
  • C10M—LUBRICATING COMPOSITIONS; USE OF CHEMICAL SUBSTANCES EITHER ALONE OR AS LUBRICATING INGREDIENTS IN A LUBRICATING COMPOSITION
  • C10M2203/00—Organic non-macromolecular hydrocarbon compounds and hydrocarbon fractions as ingredients in lubricant compositions
  • C10M2203/06—Well-defined aromatic compounds
• • C—CHEMISTRY; METALLURGY
  • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
  • C10M—LUBRICATING COMPOSITIONS; USE OF CHEMICAL SUBSTANCES EITHER ALONE OR AS LUBRICATING INGREDIENTS IN A LUBRICATING COMPOSITION
  • C10M2203/00—Organic non-macromolecular hydrocarbon compounds and hydrocarbon fractions as ingredients in lubricant compositions
  • C10M2203/10—Petroleum or coal fractions, e.g. tars, solvents, bitumen
  • C10M2203/1006—Petroleum or coal fractions, e.g. tars, solvents, bitumen used as base material
• • C—CHEMISTRY; METALLURGY
  • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
  • C10M—LUBRICATING COMPOSITIONS; USE OF CHEMICAL SUBSTANCES EITHER ALONE OR AS LUBRICATING INGREDIENTS IN A LUBRICATING COMPOSITION
  • C10M2203/00—Organic non-macromolecular hydrocarbon compounds and hydrocarbon fractions as ingredients in lubricant compositions
  • C10M2203/10—Petroleum or coal fractions, e.g. tars, solvents, bitumen
  • C10M2203/102—Aliphatic fractions
  • C10M2203/1025—Aliphatic fractions used as base material
• • C—CHEMISTRY; METALLURGY
  • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
  • C10M—LUBRICATING COMPOSITIONS; USE OF CHEMICAL SUBSTANCES EITHER ALONE OR AS LUBRICATING INGREDIENTS IN A LUBRICATING COMPOSITION
  • C10M2203/00—Organic non-macromolecular hydrocarbon compounds and hydrocarbon fractions as ingredients in lubricant compositions
  • C10M2203/10—Petroleum or coal fractions, e.g. tars, solvents, bitumen
  • C10M2203/106—Naphthenic fractions
  • C10M2203/1065—Naphthenic fractions used as base material
• • C—CHEMISTRY; METALLURGY
  • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
  • C10M—LUBRICATING COMPOSITIONS; USE OF CHEMICAL SUBSTANCES EITHER ALONE OR AS LUBRICATING INGREDIENTS IN A LUBRICATING COMPOSITION
  • C10M2205/00—Organic macromolecular hydrocarbon compounds or fractions, whether or not modified by oxidation as ingredients in lubricant compositions
  • C10M2205/02—Organic macromolecular hydrocarbon compounds or fractions, whether or not modified by oxidation as ingredients in lubricant compositions containing acyclic monomers
  • C10M2205/028—Organic macromolecular hydrocarbon compounds or fractions, whether or not modified by oxidation as ingredients in lubricant compositions containing acyclic monomers containing aliphatic monomers having more than four carbon atoms
• • C—CHEMISTRY; METALLURGY
  • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
  • C10M—LUBRICATING COMPOSITIONS; USE OF CHEMICAL SUBSTANCES EITHER ALONE OR AS LUBRICATING INGREDIENTS IN A LUBRICATING COMPOSITION
  • C10M2207/00—Organic non-macromolecular hydrocarbon compounds containing hydrogen, carbon and oxygen as ingredients in lubricant compositions
  • C10M2207/04—Ethers; Acetals; Ortho-esters; Ortho-carbonates
• • C—CHEMISTRY; METALLURGY
  • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
  • C10M—LUBRICATING COMPOSITIONS; USE OF CHEMICAL SUBSTANCES EITHER ALONE OR AS LUBRICATING INGREDIENTS IN A LUBRICATING COMPOSITION
  • C10M2207/00—Organic non-macromolecular hydrocarbon compounds containing hydrogen, carbon and oxygen as ingredients in lubricant compositions
  • C10M2207/28—Esters
  • C10M2207/2805—Esters used as base material
• • C—CHEMISTRY; METALLURGY
  • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
  • C10M—LUBRICATING COMPOSITIONS; USE OF CHEMICAL SUBSTANCES EITHER ALONE OR AS LUBRICATING INGREDIENTS IN A LUBRICATING COMPOSITION
  • C10M2229/00—Organic macromolecular compounds containing atoms of elements not provided for in groups C10M2205/00, C10M2209/00, C10M2213/00, C10M2217/00, C10M2221/00 or C10M2225/00 as ingredients in lubricant compositions
  • C10M2229/02—Unspecified siloxanes; Silicones
  • C10M2229/025—Unspecified siloxanes; Silicones used as base material
• • C—CHEMISTRY; METALLURGY
  • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
  • C10N—INDEXING SCHEME ASSOCIATED WITH SUBCLASS C10M RELATING TO LUBRICATING COMPOSITIONS
  • C10N2020/00—Specified physical or chemical properties or characteristics, i.e. function, of component of lubricating compositions
  • C10N2020/01—Physico-chemical properties
  • C10N2020/02—Viscosity; Viscosity index
• • C—CHEMISTRY; METALLURGY
  • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
  • C10N—INDEXING SCHEME ASSOCIATED WITH SUBCLASS C10M RELATING TO LUBRICATING COMPOSITIONS
  • C10N2030/00—Specified physical or chemical properties which is improved by the additive characterising the lubricating composition, e.g. multifunctional additives
  • C10N2030/02—Pour-point; Viscosity index
• • C—CHEMISTRY; METALLURGY
  • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
  • C10N—INDEXING SCHEME ASSOCIATED WITH SUBCLASS C10M RELATING TO LUBRICATING COMPOSITIONS
  • C10N2030/00—Specified physical or chemical properties which is improved by the additive characterising the lubricating composition, e.g. multifunctional additives
  • C10N2030/08—Resistance to extreme temperature
• • C—CHEMISTRY; METALLURGY
  • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
  • C10N—INDEXING SCHEME ASSOCIATED WITH SUBCLASS C10M RELATING TO LUBRICATING COMPOSITIONS
  • C10N2030/00—Specified physical or chemical properties which is improved by the additive characterising the lubricating composition, e.g. multifunctional additives
  • C10N2030/22—Degreasing properties
• • C—CHEMISTRY; METALLURGY
  • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
  • C10N—INDEXING SCHEME ASSOCIATED WITH SUBCLASS C10M RELATING TO LUBRICATING COMPOSITIONS
  • C10N2040/00—Specified use or application for which the lubricating composition is intended
  • C10N2040/14—Electric or magnetic purposes
• • C—CHEMISTRY; METALLURGY
  • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
  • C10N—INDEXING SCHEME ASSOCIATED WITH SUBCLASS C10M RELATING TO LUBRICATING COMPOSITIONS
  • C10N2040/00—Specified use or application for which the lubricating composition is intended
  • C10N2040/14—Electric or magnetic purposes
  • C10N2040/16—Dielectric; Insulating oil or insulators

Definitions

• the present invention generally relates to dielectric fluids for transformers, and more particularly to the use of certain aromatic compounds as additives to a transformer liquid in order to reduce the viscosity, and especially the low-temperature viscosity thereof.
• the invention also relates to the use of such dielectric liquid having reduced viscosity in a transformer.
• the energy of these losses is converted in the steel sheet core, the copper windings and other conductors and parts to so-called "loss heat" that leads to an increase of temperature in a transformer.
• the heat losses are different for different transformers.
• the high temperature in a transformer also stresses construction materials which are sensitive to high temperatures, particularly materials based on cellulose. According to IEC 60076 the design peak temperature is 98°C at the spots with highest temperature in the transformer in the case of a transformer with normal paper that is meant to last at least 40 years of service.
• Transformer cooling systems are engineered and designed to keep the temperature of the transformer below the design peek temperature under normal conditions. Normally transformer cooling systems are designed with a flowing dielectric liquid, commonly mineral oil.
• the effectiveness of the cooling depends on the transformer design, including i.a. oil volume, diameter of oil ducts and dimensions of the coolers and pumps. Beside design factors, the specific heat capacity, designated C p , the viscosity of the oil at operating temperatures, and the flow properties (laminar/turbulent flow) also influence the cooling. Assuming that most mineral transformer oils have similar specific heat capacity, it is the viscosity that plays the most important role in the heat transfer and dissipation calculations, and hence low viscosity oils have an advantage.
• the oil can, in some cases, be exposed to partial discharges due to poor impregnation of the solid insulation, or if the insulation is wet. Design or assembly error may be other factors causing partial discharges. With partial discharges, some oil molecules will break and the fragments may combine to form hydrogen and methane, which dissolve in the oil. Some reactions in the oil can absorb dissolved hydrogen, this is tested with the industry standard gassing tendency IEC 60626 or ASTM D3300. In the gassing tendency standard the oil is saturated with hydrogen or nitrogen gas in a sealed container and exposed to discharges. The hy- drogen absorbing reactions occur mainly when aromatic structures are present, and, to some degree, are dependent on the amount of aromatic structures.
• Insulating oils with high natural aromatic content absorb more hydrogen gas in the gassing tendency tests but this property can also be altered by certain additives.
• the trend for power transformers is that they are built for higher voltages and run at higher average loads closer to their maximum capacity. All parts of the transformer need to be optimized and so must also the dielectric liquid.
• the dielectric liquid must also have excellent oxidation stability to last in the transformer for many years at high temperature.
• the dielectric liquid must also have good solubility properties to keep any impurities formed in solution where they will make no harm.
• When choosing an insulating liquid for electrical equipment there are many material properties that need to be considered.
• the common requirements for mineral insulting oil are found in the specifications I EC60296 and ASTM D3487. To fulfil all demands of modern high voltage transformers naphthenic super grade oil is most often chosen as the insulating liquid.
• the transformer design must take the oil properties into consideration and with high quality oil the design can be optimised better.
• US 2010/0059725 teaches that addition up to 10 wt% of reformer distillate, containing 1- and 2-ring aromatic compounds, to a transformer oil improves the gassing tendency of the trans- former oil.
• Suitable 1- and 2-ring aromatics are e.g. alkylated benzene, naphthalene, alkylated naphthalenes, indanes, biphenyls and diphenyls.
• US 4 493 943 teaches the use of a combination of at least one diarylalkane, and at least one of mono- and and/or diolefin having two condensed or noncondensed a romatic nuclei, for obtain- ing an electrical insulating oil having i.a. good hydrogen absorbing capacity.
• Preferred diaryla l- kanes are diarylmethane, 1,1-diarylethane, 1,2-diarylethane, and among these especially com- pounds having a benzene ring, which is not substituted with an alkyl group, e.g. ar- ylphenylethane.
• US 5 601 755 teaches a dielectric composition comprising benzyltoluene, benzylxylene, (methylbenzyl)toluene and (methylbenzyl)xylene.
• the composition can be mixed with mineral oils typically used in transformers. Summary of invention
• the present inventor has surprisingly found that diphenylmethane, diphenylethane and similar compounds when added in a small amount to mineral oil will markedly reduce the viscosity of the oil.
• the extent of reduction of viscosity is unexpected. For example, at -40°C the viscosity of the fluid is almost reduced by 50% when 5% diphenylmethane is added thereto.
• the present invention relates to the use of a Ci 2 -Ci 6 aromatic compound consisting of a naphthalene, biphenyl, biphenyl ether, or diphenylalkane structure, optionally substituted with one, two, three, or four Ci-C 4 alkyl groups, as an additive to a dielectric liquid for a transformer in an amount of 1-10 % by weight, for reducing the viscosity of the dielectric liquid.
• the cold start-up specification of a given dielectric liquid will be improved, and the compound can thus be used as an additive for improving the cold start-up specification of a given dielectric liquid.
• the invention will thus enable a given dielectric liquid comprising the inventive additive to be used as having a cold start-up classification corresponding to a lower temperature as compared to the cold start-up specification of the oil without the additive.
• the invention relates to the use of a dielectric liquid containing the inventive additive for improving the cold start-up performance and characteristics of a transformer.
• the invention consequently relates to the use of a dielectric liquid containing the inventive additive as having a cold start-up specification corresponding to a lower tempera- ture than that of the cold start-up specification of the dielectric liquid without the additive.
• the present invention relates to the use, e.g. including start-up, of the inventive transformer at an ambient temperature or temperature of the transformer of below -20°C.
• the viscosity dependent heat transfer coefficient of the system will also be improved, and hence also the overall heat transfer coefficient of the system.
• the invention allows for cooling of the transformer to a lower temperature.
• a lower temperature of the transformer will in turn extend the service life of the transformer.
• the improved heat transfer coefficient of the system will further enhance the cooling performance of the inventive dielectric liquid.
• the lower the temperature can be kept in a transformer the lower the power losses will be.
• the lower power losses at lower temperatures are due to i.a. a lower resistance in the metal conductors, and a lower dielectric dissipation factor in the oil at such lower temperatures.
• a number of the compounds of the invention are known from the prior art to decrease the gassing tendency of an insulating oil.
• the compounds of the invention can thus be used as a multi- purpose additive to dielectric fluids to decrease both gassing tendency and viscosity thereof. ln cold climate areas there is a need to have insulating oils with low viscosity at low temperatures in order to ensure safe start-ups.
• the additives of the present invention enables achievement of a combination of a low viscosity at a vide temperature range, e.g. from -40°C to +100°C, and a negative gassing tendency, without affecting flash point negatively or having health and safety issues.
• the present invention is especially intended for use in the power industry, particularly in power transformers.
• the cooling system of the inventive transformer can e.g. be of ONAN, ONAF, OFAN, OFAF, OFWF, ODAN, ODAF, or ODWF type.
• oil oil
• dielectric oil dielectric liquid
• dielectric fluid dielectric fluid
• LCSET Lowest Cold Start Energizing Temperature
• Ci 2 -Ci 6 aromatic compounds of a naphthalene, biphenyl, biphenyl ether, or diphenylalkane structure, optionally substituted with one, two, three, or four Ci-C 4 alkyl groups have been found to both decrease the viscosity and the gassing tendency of a dielectric liquid. The extent of the reduction of the viscosity is however unexpected.
• addition of 5% by weight of the additive to a dielectric fluid will typically produce a decrease in viscosity about twice the expected decrease, e.g. as estimated using Ref- utas equation.
• the decrease in viscosity according to the invention will generally be even greater at lower temperatures.
• the addition of 5% of the additive may even result in a reduction of the viscosity of the dielectric fluid by about 50%.
• the inventive additive is generally more efficient at lower temperatures, such as at 0°C, and below.
• a reduced viscosity of a given dielectric liquid will correspond to an improved cold start-up specification of the dielectric liquid.
• the inventive dielectric liquid containing the additive can thus be used in new applications, requiring a cold start-up specification corresponding to a lower temperature than that of previous specifications of the dielectric liquid, to which applications the dielectric liquid previously has not been qualified.
• the function of an oil in a transformer is cooling and insulation.
• the oil flows through the transformer and removes heat and therefore it is not only viscosity but also the viscosity dependent heat transfer coefficient that is interesting to look at.
• Heat transfer works in different ways depending on the design of the system to be cooled (e.g. ONAN, ONAF, OFAN, OFAF, OFWF, ODAN, ODAF, or ODWF).
• addition of 5% by weight of the additive to a dielectric fluid can e.g. improve the heat transfer coefficient of the system at 40°C with about 14%.
• suitable compounds for use as an additive according to the invention are diphe- nylether, diphenylmethane, biphenyl, both isomers of diphenylethane, all isomers of methylbi- phenyl, dimethylbiphenyl, ethylbiphenyl, dimethylnapthalene, trimethylnapthalene, ethylme- thylnapthalene, propylnaphthalene, isopropylnapthalene, methylpropylnapthalene, isopropyl- methylnaphthalene and diethylnapthalene, or a mixture of any of the previous compounds.
• An especially preferred compound is diphenylmethane.
• Another preferred compound is diphe- nylether.
• the viscosity decreasing effect is been found to be greater when compounds in the range of 12-C14 are being used.
• the C12-C16 compounds of a diphenylalkane structure are preferably diphenyl C1-C3 alkane compounds, and more preferably diphenyl Ci-C 2 alkane compounds, i.e. diphenylmethane and di- phenylethane structure compounds.
• inventive compounds preferably exhibit 0, 1, or 2 C1-C4 substituents, and more preferably no substituents.
• any C1-C4 substituents present are C1-C3 substituents.
• the compounds used as additives according to the invention are preferably non-halogenated.
• the flash point is another important property of transformer oils, especially when fire hazard is a critical factor.
• diphenylmethane has a flash point around 130°C, as compared to 77°C for tetralin.
• the additive is mixed into an insulating fluid for the purpose of decreasing the viscosity, especially the low temperature viscosity, and to decrease the gassing tendency of the fluid.
• the insulating fluid could be e.g. of the following kinds, naphthenic mineral oil, paraffinic mineral oil, natural ester, synthetic ester, poly-alpha olefin, silicon oil, syn- thetic iso-paraffin or a mixture of any of said insulating fluids.
• a generally preferred group of dielectric fluids according to the invention is the group comprising naphthenic mineral oil, paraffinic mineral oil, natural ester, synthetic ester, and mixtures thereof. At low temperatures, e.g. at below 0°C, natural esters may be less suitable as the dielectric liquid, due the relatively low pour point.
• Preferred insulating fluids for use at low temperatures are naphthenic mineral oil, paraffinic mineral oil, synthetic ester, and mixtures thereof.
• the means of addition of the additive to the dielectric fluid and the mixing thereof is not critical as long as an adequate mixing of the components can be accomplished.
• the mixture should be heated to a temperature above the melting point of the additive, in order to enable adequate mixing.
• a suitable temperature of addition of the additive to the dielectric fluid is a temperature at which both additive and dielectric fluid are in a liquid state.
• the additive should be added in an amount low enough in order that crystallization of the addi- tive in the dielectric fluid is avoided also at the low temperature end of the intended service temperature range. If crystallization of the additive occurs, the dielectric solution may freeze, or become unduly high in viscosity.
• diphenylmethane may crystallize at -40°C when used in an amount greater than 5% in naphthenic insulating oil.
• solubility of the additive may also vary for different oils.
• a naphthenic oil will probably be able to dissolve more additive than a paraffinic oil.
• specific compounds for use in the invention are diphenylether, diphenylmethane, 1,2-diphenylethane, 1,1-diphenylethane, and benzyltoluene.
• IEC61125C thenic oil) - no imthenic oil) - no imthenic oil) - no impact on ox. stab. pact on ox. stab. pact on ox. stab.
• Hazard statements - H351 Suspected of - H400: Verv toxic to - H319: Causes sericausing cancer aquatic life. ous eye irritation.
• diphenylmethane which has a melting point of about 25°C
• naphthenic mineral oil i.e. Oil A above
• the oil was heated to 40°C, and mixed using a magnetic stirrer.
• the resulting viscosity of the mixture at 40°C was estimated to be 7.02 mm 2 /s.
• the actual viscosity of the resulting mixture was measured to be 6.53 mm 2 /s using ASTM method D7042. In other words, the resulting decrease in viscosity was a factor of about two larger than expected.
• the heat transfer coefficient for the pipe was calculated based on the the Nusselt-number, a friction factor/ 0.34, a dimensionless number describing turbulence in a system that in itself relies on viscosity, density, thermal conductivity and heat capacity. Adding 5% of diphenylmethane to Oil A will increase the heat transfer coefficient at 40°C with about 14% in the previously described pipe-system.
• diphenylmethane as an additive was mixed with different dielectric fluids to demonstrate the effect on the viscosity of the fluids.
• the gassing tendency of the resulting mixtures was established according to ASTM D2300.
• Six different dielectric fluids (A-F, as defined above) were used.
• Example 5 bibenzyl (also referred to as 1,2-diphenylethane or dibenzyl)

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• General Chemical & Material Sciences (AREA)
• Organic Chemistry (AREA)
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• Physics & Mathematics (AREA)
• Spectroscopy & Molecular Physics (AREA)
• Organic Insulating Materials (AREA)
• Lubricants (AREA)
• Compositions Of Macromolecular Compounds (AREA)

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