WO2014078156A1 - Compositions d'huile mélangée utiles comme compositions de fluide diélectrique et procédés de préparation de ces dernières - Google Patents

Compositions d'huile mélangée utiles comme compositions de fluide diélectrique et procédés de préparation de ces dernières Download PDF

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WO2014078156A1
WO2014078156A1 PCT/US2013/068837 US2013068837W WO2014078156A1 WO 2014078156 A1 WO2014078156 A1 WO 2014078156A1 US 2013068837 W US2013068837 W US 2013068837W WO 2014078156 A1 WO2014078156 A1 WO 2014078156A1
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composition
astm
determined
polyol ester
synthetic
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PCT/US2013/068837
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English (en)
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Hari Babu Sunkara
Weiming Qiu
Sam COTTERILL
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E. I. Du Pont De Nemours And Company
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Priority to JP2015542696A priority Critical patent/JP2015536548A/ja
Priority to EP13792834.7A priority patent/EP2920794A1/fr
Priority to CN201380059273.7A priority patent/CN104798143A/zh
Publication of WO2014078156A1 publication Critical patent/WO2014078156A1/fr

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    • 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

Definitions

  • This invention relates to dielectric fluid compositions suitable for use as electrical transformer insulation and cooling fluids.
  • dielectric fluids for cooling electrical equipment such as transformers, power cables, breakers, and capacitors.
  • these dielectric fluids are used in combination with solid insulation in liquid-filled transformers.
  • examples include mineral oil, high molecular weight hydrocarbons (HMWH), silicone fluid, and synthetic hydrocarbon oils (polyalpha-olefins).
  • HMWH high molecular weight hydrocarbons
  • silicone fluid silicone fluid
  • synthetic hydrocarbon oils polyalpha-olefins
  • Electrotechnical Commission Standard IEC 61099 sets specification limits for synthetic ester fluids and IEC 60296 Edition 4 sets specification limits for uninhibited mineral oils.
  • Additives are added often to the dielectric fluids to enhance the performance of the fluids and thereby increase the life of electrical distribution and power transformers.
  • One common practice is the addition of oxidation inhibiting additives to the uninhibited oils.
  • Another common practice is the addition of anti-gassing additives to fluids that have a positive gassing tendency.
  • Dielectric fluids used in transformers for example, can produce gas during the course of use, which can create pressure issues if used inside of a closed container. Also, the
  • A1 describes an electrical insulating oil comprising a heavy reformate as an anti-gassing agent.
  • a biodegradable dielectric fluid would be desirable for electrical apparatus such as transformers used in populated or ecologically sensitive areas.
  • Natural and synthetic esters can be used as dielectric fluids to replace mineral oils for safety and environmental reasons.
  • Published Canadian Patent Application CA 2,492,565 discloses a dielectric coolant having at least a pour point of about -40°C and comprising a mixture of more than one polyol ester of specified chemical structures, wherein the alkyl groups have chain lengths of C 5 to C 22 .
  • U.S. Pat. 8,187,508 B2 describes a base agent for electrical insulating oils mainly containing an esterified product of glycerin and a linear or branched fatty acid having 6- 14 carbon atoms.
  • the present invention is a composition useful as a dielectric fluid, the composition comprising or alternatively, consisting essentially of, a renewably sourced synthetic saturated polyol ester having less than about 3000 ppm of unreacted or partially reacted polyol, wherein the polyol ester is the completely esterified reaction product obtained from a reaction mixture comprising (i) a polyhydroxyl component having at least 3 hydroxyl groups and (ii) a mixture of saturated carboxyl derivatives, wherein at least about 95 mol% of the carboxyl derivatives comprise from 6 to 12 carbon atoms, wherein: the composition has a fire point as determined by ASTM D-92 of at least 300°C, and a viscosity as
  • the present invention is a composition useful as a dielectric fluid, the composition comprising a renewably sourced synthetic polyol ester having less than about 3000 ppm of unreacted polyol and further comprising a synthetic antioxidant, wherein the polyol ester is the completely esterified reaction product obtained from a reaction mixture consisting essentially of: (i) a glycerol oligomer component having at least 4 hydroxyl groups; (ii) a mixture of saturated linear carboxyl derivatives, wherein at least about 95 mol% of the carboxyl derivatives comprise from 6 to 12 carbon atoms; and (iii) optionally an esterification catalyst; wherein: the composition has a dielectric constant (Dk) of about 4.5 as determined by ASTM D924, fire point as determined by ASTM D-92 of at least 300°C, and a viscosity as determined by ASTM 445 of less than about 30 centiStokes at 40°C.
  • Dk dielectric constant
  • the present invention is composition useful as a dielectric fluid, the composition being a blend comprising: (1 ) from about 1 to about 99 wt% of a renewably sourced synthetic saturated polyol ester, wherein the polyol ester is the completely esterified reaction product obtained from a reaction mixture comprising (i) a polyhydroxyl component having at least 3 hydroxyl groups and (ii) a mixture of saturated linear carboxyl derivatives, wherein at least about 95 mol% of the carboxyl derivatives comprise from 6 to 12 carbon atoms; and (2) from about 1 to about 99 wt% of a triacylglycerol natural oil obtained from a natural source, consisting essentially of long chain fatty acid esters; wherein the blend has a reduced gassing tendency -- without the addition of aromatic anti-gassing additives -- compared to the gassing tendency of component (1 ) of the blend.
  • the present invention is a composition useful as a dielectric fluid, the composition being a blend consisting essentially of: (1 ) from about 1 to about 99 wt% of a renewably sourced synthetic polyol ester, wherein the polyol ester is the completely esterified reaction product obtained from a reaction mixture comprising (i) a polyhydroxyl component having at least 3 hydroxyl groups and (ii) a mixture of saturated linear carboxyl derivatives, wherein at least about 95 mol% of the carboxyl derivatives comprise from 6 to 12 carbon atoms; (2) from about 1 to about 99 wt% of a triacylglycerol natural oil obtained from a natural source, consisting essentially of long chain fatty acid esters comprising greater than about 75 mol% oleyl esters; and (3) optional additives selected from the group consisting of: pour point depressants, metal passivators, anti- foaming agents, and electrostatic charging tendency depressants, wherein: (a) the blend is uninhibited; (b)
  • Figure 1 is a graph of Oil Stability Index (OSI) versus Percentage of high oleic soybean oil in the blended composition.
  • OSI Oil Stability Index
  • the present invention is a composition that is useful as a dielectric fluid comprising a synthetic, renewably sourced polyol ester.
  • the synthetic ester can either be used alone or as a blend with other natural oils, such as triacylglycerol oils and/or mineral oil.
  • Renewably sourced synthetic polyol ester fluids of the present invention are synthetic inasmuch as they are obtained by an
  • esterification/transesterification ((trans)esterification) reaction or process under controlled process conditions.
  • the (trans)esterification reaction may be conducted by any known conventional or nonconventional means, including the use of catalysts that can be acidic, basic, or enzymatic. In one embodiment, no added catalyst is required because the reaction can be self-catalytic under certain conditions.
  • esterification of an alcohol can be accomplished by contacting the alcohol with a carboxylic acid, or a derivative thereof, under suitable conditions to form a carboxyic ester.
  • a carboxylic acid when starting with a carboxylic acid the process can be catalyzed using an acid catalyst - for example a strong mineral acid such as hydrochloric acid, phosphoric acid, sulfuric acid, or other such strong protic acids that are well-known and conventional in the chemical art such as p-toluenesulfonic acid.
  • Lewis acids can be suitable for the esterification process that can provide the synthetic oils of the present invention.
  • Lewis acids such as, aluminium, titanium and tin compounds (such as tin(ll) chloride dihydrate and dibutyl tin oxide) are known and conventional for such processes.
  • the esterification of an alcohol can be accomplished using excess of carboxylic acid to ensure complete esterification, and no added catalyst. The excess fatty acid can be stripped off completely after the reaction under reduced pressure. If not, the residual acids present in the product can impact the properties such as oxidative stability, hydrolytic stability, power factor and other
  • Refining the oil can be effective to improve the oil quality. This is particularly important when the reacting carboxylic acid is short or medium chain fatty acid.
  • esters of the present invention can be obtained using carboxylic acid derivatives such as carboxylic acid halides, for example carboxylic acid chlorides and bromides.
  • carboxylic acid halides for example carboxylic acid chlorides and bromides.
  • Carboxylic acid anhydrides or esters can also be useful derivatives of carbloxylic acids to produce the synthetic esters of the present invention.
  • natural oils and/or esters can be suitable sources for the carboxyl group (also referred to herein as the "acyl” group) of the synthetic esters of the present invention, and can be used in a conventional process known as transesterification, wherein the acyl group of an the starting ester is transferred to a different hydroxyl-containing compound to form a different ester, and wherein the transesterification reaction is catalyzed by typical esterification catalysts.
  • carboxylic acids or derivatives used in the practice of the present invention to prepare the synthetic esters of the present invention comprise from 6 to 12 carbon atoms.
  • Carboxylic acids or derivatives having from 6 to 12 carbon atoms are referred to herein as medium chain acids or derivatives.
  • carboxylic acids and derivatives having carbon chain lengths of 14 or more are considered long-chain acyl compounds.
  • the synthetic medium chain polyacyl esters of the present invention comprise or consist essentially of saturated fatty acid carbon chains. That is, there are essentially no carbon to carbon multiple bonds.
  • hexanoic acid, octanoic acid, decanoic acid, dodecanoic acid, derivatives thereof as set forth herienabove, and mixtures of any of these can be suitable for use in the practice of the present invention.
  • hexanoic acid is also known as caproic acid
  • octanoic acid is known as caprylic acid
  • decanoic acid is known as capric acid
  • dodecanoic acid is also known as lauric acid.
  • Caproic acid (C6) for the purposes of the present invention, shall be considered a medium chain fatty acid, together with caprylic (C8), capric (C10) and lauric (C12) acids.
  • the synthetic esters of the present invention are prepared from renewably sourced materials.
  • renewably sourced medium chain carboxylic acids can be obtained from a natural source such as palm kernel oil or coconut oil, which naturally comprises a large proportion of the medium chain fatty acids suitable for use herein.
  • the oil obtained from palm kernels and coconut can be hydrolyzed by conventional methods known to those of ordinary skill in the edible oil industry, and the medium chain carboxylic acids fractionated - that is, separated from higher chain acids - by known methods such as distillation or separation based on molecular weight or polarity differences, and used to prepare the synthetic esters of this invention from suitable polyols.
  • the synthetic esters of the present invention are prepared by reacting a polyol with a mixture of medium chain fatty acids.
  • the percentage of each meduim chain fatty acid in the mixture can be tailored to provide an ester with properties that are desirable, but any one of the individual medium chain fatty acids can comprise from about 5 to about 90 % of the mixture used to prepare the synthetic ester, with the caveat that at least about 95% of the total ester linkages of the synthetic ester comprise medium chain esters, the residual esters being short and/or long chain esters.
  • at least about 90% of the ester linkages of the synthetic ester comprise a mixture of caprylyl, capryl and/or lauryl esters. It has been discovered herein that compositions derived from carboxylic acids and derivatives thereof that conform to these parameters can provide a balanced set of desirable properties that enhance the performance of the synthetic esters and blends thereof, particularly when used as dielectric cooling fluids.
  • the synthetic esters of the present invention comprise less than 5 mol% of unsaturated esters, preferably less than 3 mol% and more preferably less than 1 mol%.
  • the synthetic esters of the present invention are obtained from reaction of the medium chain carboxyl components with a polyhydroxyl component, which can include polyhydroxy alcohols having at least three hydroxyl functional groups per molecule.
  • polyhydroxyl alcohols may be alternatively referred to herein as "polyols".
  • Polyols of the present invention can be monomeric polyfunctional alcohols such as glycerol or pentaerythritol (PE) or trimethylolpropane (TMP) or trimethylolethane (TME), or oligomeric alcohols -- such as diglycerol, triglycerol, ditrimethylol propane,
  • Polyols of the present invention can include naturally ocurring compounds such as sugars or sugar alcohols - including mono- and disaccharides and/or derivatives thereof - as a minor component.
  • sugars or sugar alcohols - including mono- and disaccharides and/or derivatives thereof - as a minor component.
  • sucrose, glucose, fructose, mannose, sorbitol, or starches and other cellulosic materials can be considered polyols suitable for use in the practice of the present invention.
  • polyhydroxyl alcohol and polyol
  • the terms may be used interchangeably with no effect on the scope of the present invention intended.
  • the polyol is
  • the polyol is diglycerol, triglycerol, tetraglycerol or mixture thereof.
  • the synthetic ester compositions of the present invention can be blended with natural oils.
  • a blend of the present invention can comprise a suitable triacyl glycerol oil in a relative amount of from about 5 to about to about 90 wt% of the blend, with the renewably sourced synthetic ester providing from about 10 to about 95 wt% of the blend.
  • the blend can comprise the triacyl glycerol in an amount of from about 10 to about 80 wt%, or from about 10 to about 70 wt%, or from about 20 to about 50 wt%, or from about 30 to about 40 wt%.
  • composition of the blend is tailored to provide a blend that can be classified as a K-class fluid, and in those applications where the relative amount of the triacyl glycerol component should be blended with the goal of providing a K-class dielectric fluid, the actual percentage of triacyl glycerol can be tailored to achieve a balance of desirable properties to meet that standard.
  • the blends of the present invention can comprise a triacyglycerol oil comprising esters of carboxylic acids that comprise or consist essentially of long chain acids.
  • Long chain acid esters of glycerol can be obtained from natural or biologic sources, such as oil-producing crops including soy bean, canola, sunflower, palm, palm kernel, coconut, and other known sources of natural oils.
  • the triacyl glycerol oil component of the presently claimed composition can be a mixture of oils.
  • suitable triacyl glycerol oil for use in the present invention have high, that is 60 mol% or more, monounsaturated ester content.
  • oil high in monounsaturated content can be obtained from natural sources that provide high oleic acyl (oleyl) composition, such as the soy bean oil described in U.S. Pat. No. 5,981 ,781 , which is incorporated herein by reference as if completely set out.
  • high oleic soybean (HOS) oil has a high oleyl (C18:1 ) content of 75 mol% or more of the acyl component, with a combined polyunsaturated ester (C18:2 and C18:3) content of less than 10 mol%.
  • Other natural oils having high oleic acid content are: sunflower oil, safflower oil, olive oil, and canola oil for example.
  • natural esters having low to medium monounsaturated acid content can be suitable for use herein.
  • oils include soybean oil, sunflower oil, safflower oil, and canola oil, for example.
  • any renewably sourced saturated polyol ester having desirable low and high temperature properties can be blended with natural esters so that the total unsaturation in the blend does not exceed an iodine value of 100.
  • the preferred renewably sourced synthetic polyol esters are selected from glycerol based esters, trimethylolpropane based esters, glycerol oligomer based esters and mixtures thereof.
  • the blends of the present invention can provide surprising synergistic effects that are not readily predictable based on the properties of the individual components alone.
  • renewably sourced saturated synthetic polyol esters as described herein are prepared using fatty acid
  • feedstocks obtained from natural or biologic feedstocks, wherein the feedstocks can be regenerated via conventional farming techniques.
  • cooling fluid compositions wherein the cooling fluids have properties that are customized or tailored to meet the specific needs of the application.
  • dielectric cooling fluids used in transformers should have high dielectric strength, high volume resistivity (at least about 10 1 1 Ohm cm at 25 C as determined by ASTM D -1 169), high impulse strength, low dissipation factor, low viscosity, high specific heat, high thermal
  • the cooling fluid can have a dielectric constant (Dk) that is similar to solid insulation used in the electrical equipment.
  • Dk dielectric constant
  • a single basestock fluid with all of the desired properties is difficult to provide.
  • the fluid compositions of the present invention provide an overall balance of desirable properties in blended compositions that comprise renewably sourced polyol esters.
  • Dielectric cooling fluids described herein may be generically referred to using various alternate terms.
  • transformer oils may be used generically to refer to dielectric cooling fluids, or other terms referring to the specific compositions of the presently claimed invention may be used interchangeably in the body of this specification.
  • the contextual use of such terms herein should readily convey to one of ordinary skill such instances where a term is intended to be generic or where it is specific for a given use or composition.
  • the physical properties of the synthetic esters and blends of the present invention make them particularly suited for use as dielectric fluids.
  • the ester compositions of the present invention can be formulated to embody a range of properties that balance desirable low temperature properties (for example, viscosity and pour point), high temperature properties (for example, flash and fire points), chemical stability (that is, thermal and oxidative stability) and electrical properties (for example, dissipation factor, dielectric constant), which are believed by the applicants to be critical to the performance of the synthetic ester compositions of the present invention.
  • the gassing tendency of a dielectric fluid is a critical property of any dielectric fluid, because it is useful as a performance metric for suitable fluids to indicate whether they will be suitable under the conditions of use.
  • Dielectric cooling fluids of the present invention have a pour point of lower than about -20°C, alternatively lower than about -30°C, or lower than about -40°C as determined by ASTM D- 97.
  • the fluid in order for cooling fluids to be efficient in their capacity as heat transfer fluids, it is desirable that the fluid have low viscosity, high thermal conductivity, high specific heat, and high expansion coefficient - particularly at transformer operating temperatures, which can range from temperatures below 0°C to temperatures above 100°C.
  • the viscosity is considered to be the more influential property for the heat transfer by either natural convection in smaller self-cooled transformers or forced convection in larger units with pumps.
  • the generally accepted trend is: the lower the kinematic viscosity the higher the heat dissipation.
  • Kinematic viscosity is the ratio of the dynamic viscosity of a liquid to its density.
  • Insulating cooling fluids of the present invention have kinematic viscosity not greater than 40 cSt at 40°C as determined by ASTM D-445, yet can meet the criteria of being K-class fluids.
  • Viscosity index (VI) is an empirical, unitless number indicating the effect of temperature change on the kinematic viscosity of the oil The higher the VI of an oil, the lower its tendency to change viscosity with temperature.
  • Dielectric cooling fluids with lower VI such as, for example, napthenic mineral oil, tend to be thinner at transformer operating temperatures and thus dissipate the generated heat very effectively whereas the fluids with high VI such as, for example, natural ester oils comprising saturated esters, tend to have lower viscosity at low
  • Natural vegetable oils in general have high viscosity index value (>200) compared to synthetic esters and mineral oils.
  • High temperature properties such as flash point and fire point are critical properties of a dielectric fluid.
  • the flash point represents the temperature of the fluid that will result in an ignition of a fluids' vapors and the fire point represents the temperature of the fluid at which combustion occurs when exposed to air and an ignition source.
  • Dielectric cooling fluids of the present invention meet specifications for less flammable liquids that qualify them as K-class materials, which is the highest fire performance standard for dielectric fluids. Cooling fluids of the present invention have a fire point of at least 300°C as determined by ASTM D-92, which is the standard for K-class materials.
  • One other important desirable feature for a dielectric fluid is good aging stability, which is primarily associated with oxidative stability over time. Oxidation is a critical factor in the aging of a dielectric fluid and it is particularly important for a fluid used in a free breathing transformer, versus one used in a sealed transformer. Good oxidative stability minimizes the formation of sludge and acid which can improve electrical conduction, ensure acceptable heat transfer, and preserve system life.
  • Fluids comprising natural esters typically have a higher rate of oxidation than do mineral oils, and will typically polymerize when exposed to the atmosphere and heat. Therefore, conventional practice is that natural ester fluids are not recommended for free breathing transformers.
  • dielectric cooling fluids that are oxidatively stable compared to conventional fluids comprising natural esters are obtained by blending natural oils having some degree of unsaturation with the renewably sourced synthetic polyol esters having no unsaturation as described herein.
  • improved dielectric fluid compositions comprising unsaturated natural oils and renewably sourced synthetic polyol esters are obtained by blending the components in a manner to control the iodine number of the blended composition, wherein the blended composition has an iodine number of 100 or less.
  • An iodine number of less than 100 can be indicative of a cooling fluid that is oxidatively stable under the conditions of use.
  • the iodine number is an indication of the degree of unsaturation present in the compositions described herein.
  • Natural oils include naturally occuring antioxidants such as tocopherols. However, the natural antioxidants that are present in natural oils are typically not as effective in stabilizing the oils relative to synthetic antioxidants. As a result, it can be conventional to add one or more synthetic antioxidants such as, for example: 2,6-di-f-butyl-p-cresol
  • DBPC butylated hydroxytoluene
  • BHT butylated hydroxytoluene
  • BHA butylated hydroxyanisole
  • TBHQ f-butylhydroquinone
  • the fluids of the present invention have excellent oxidative stability, as indicated by the Oil Stability Index (OSI), even in the substantial absence of synthetic antioxidants, that is, where no synthetic antioxidants are added to the fluid composition.
  • Uninhibited cooling fluids obtained according to the present invention can be used alone or can be added to another uninhibited dielectric fluids for use in both sealed and free breathing electrical equipment.
  • excellent oxidative stability is indicated by an OSI induction time of at least 20 hours, measured at 130°C according to the methods of the American Oil Chemists Society (AOCS method 12b-92).
  • Uninhibited dielectric fluid blends as described herein comprise renewably sourced saturated polyol esters and high monounsaturated acid based natural esters, and these dielectric cooling fluids provide good chemical stability even when essentially free from synthetic antioxidants.
  • a dielectric fluid is "uninhibited” if it comprises less than 0.08 wt% of a synthetic antioxidant, based on the weight of the fluid.
  • synthetic additives including aromatic anti-gassing additives, metal passivators, anti-foaming agents, electrostatic charging tendency depressants, and pour point depressants - - can be added to the uninhibited fluids to enhance the stability further.
  • a fluid of the present invention is said to be “inhibited” if it comprises greater than 0.08 wt% antioxidant but does not comprise more than 0.4 wt% total of synthetic antioxidant. Inhibited fluids can comprise any effective amount of other synthetic additives.
  • uninhibited blends of synthetic esters of the present invention with at least one natural oil having about 75 mol% or greater monounsaturated ester content demonstrate a surprising stability, as indicated by an induction time as determined from the OSI of the blend that is longer than that of either of the uninhibited individual components.
  • blends of synthetic esters and natural oils can demonstrate improved oxidative stability wherein the synthetic ester is refined to an acid number of less than about 0.07 mg KOH/g ester prior to blending with the natural oil.
  • Refining, or purifying, the synthetic esters of the present invention prior to blending can improve properties of the blended composition, such as reducing the power factor, for example, and enhance the performance of the blends when used as dielectric fluids such as, for example, the volume resistivity.
  • Treatment of the synthetic ester to remove impurities such as unreacted hydroxyl compounds, unreacted acids, particularly unsaturated acids or esters can improve the performance of the synthetic esters and of blends comprising the esters.
  • a synthetic ester suitable for use in the practice of the present invention has an acid number according to ASTM D-974 of less than about 0.05 mg KOH/gram, preferably the acid number is less than about 0.03, and most preferably the acid number is about 0.01 mg KOH/gram or less.
  • a commercially available synthetic ester having a higher than desired acid number can be treated to reduce the acid number to a level that provides a fluid that is useful as a dielectric fluid.
  • a treated fluid of the present invention comprises a synthetic ester having less than 3000 ppm of unreacted or partially reacted polyol, preferably less than 1500 ppm unreacted polyol and more preferably less than 500 ppm of unreacted polyol.
  • a synthetic ester useful in the practice of the present invention comprises less than from about 50 to about 0 ppm of unreacted or partially reacted polyol.
  • Purified dielectric fluids of the present invention have a power factor, as determined by ASTM D-924, of less than about 0.5% at
  • the purified dielectric fluids of the present invention have a volume resistivity, as determined by ASTM D-1 169, of greater than 10 11 ohm cm at 25°C.
  • the gassing tendency of a dielectric fluid i.e. its tendency to absorb or evolve gasses under electrical stress, can affect the performance of liquid-filled transformers, cables and capacitors. Gassing tendency can be measured by ASTM D2300, wherein a decrease or increase in pressure indicates the fluid behavior under this electrical stress. Low gassing performance is highly desirable because a liquid having a low gassing tendency tends to generate less gasses and/or absorb any evolved gasses better, which can be desirable, particularly in a closed system.
  • ASTM D-1 169 volume resistivity
  • Standard D3487-00 which sets a limit for gassing tendency - as measured by ASTM D2300-8 - of +30 L/min for transformer cooling fluids.
  • the International Electro-technical Commission (IEC) does not set a standard for gassing tendency of an insulating fluid, but suggests a maximum of +5 L/min, as measured by IEC60628, for special
  • dielectric fluids of the present invention are formulated to control the gassing tendency of the fluids so that it is within the range of from +30 to -30 L/min, as measured by ASTM D2300-8, by a process of blending at least one dielectric fluid having a positive gassing tendency with a natural ester having a negative gassing tendency.
  • the gassing tendency of the blended dielectric fluids described herein are controlled without the use of aromatic anti-gassing additives, which are used in conventional practice to control the gassing behavior of dielectric fluids.
  • the dissipation factor is a measure of the dielectric losses in fluid which in turn indicates the amount of energy dissipated as heat.
  • the dissipation factor value must be as low as possible.
  • Natural esters and synthetic ester insulating fluids usually have higher dissipation factors than non-polar mineral insulating oils especially at elevated temperatures.
  • the typical values for the fluids of the present invention are less than about 0.5% at 25 °C and less than about 5.0% at 100 °C. If the unaged fluids exceed these values indicating the presence of soluble polar contamination, the fluids can be be refined to eliminate or reduce the levels of contaminants.
  • Dielectric constant (Dk) is defined as the amount of electrostatic energy which can be stored per unit volume per unit potential gradient and it can be measured for dielectric fluid by ASTM D924.
  • the conventional mineral oil has dielectric constant about 2.2 and the solid cellulose insulation has about 4.5.
  • the dielectric constants of natural ester and polyol esters are higher than mineral oil and are in the range of about 2.5 to 4.5 at 25 °C. Increasing the dielectric constant, Dk, of liquid insulation in transformers and matching them to that of the solid insulation, balances the insulation system and improves the utilization of the mixed dielectric without increasing the stress in the oil channels.
  • the ratio (Dk r ) of the dielectric contstants of the cooling fluid to the insulating solid material is engineered to be greater than 0.5, or can be in the range of from 0.5 to about 1 .0. Liquid insulation with a high Dk yield savings in design and operation of transformers. It is an aspect of the present invention that the dielectric fluids of the present invention can be formulated so that their dielectric constant values are closer to solid insulation materials such as cellulose, Nomex® or cellulose-Nomex® blend.
  • the synthetic polyol ester comprises a glycerol oligomer ester, wherein the ester is the product obtained after esterification of a glycerol oligomer or an oligomeric mixture thereof.
  • Glycerol oligomers for the purposes of the present invention, include diglycerol up to hexaglycerol oligomers, and mixtures thereof.
  • One of the advantages of using di-, tri-, or higher glycerol oligomer esters (GOE) in the practice of the present invention is that glycerol oligomer esters have higher dielectric constant (about 4.5) than natural oils, which typically have a dielectric constant of about 3.1 .
  • glycerol oligomers include from 2 to 6 glycerol repeat units, preferably 2 or three glycerol repeat units, or mixtures thereof, and have from 4 to 8 hydroxyls. Preferably at least about 90% of the oligomer is diglycerol.
  • blends of renewably sourced synthetic esters with mineral oil can be effective as dielectric cooling fluids.
  • the mineral oil is severely hydro-treated
  • Blends of the present invention with mineral oils do not, however, require a aromatic gassing additive to provide a dielectric fluid having a low or a negative gassing tendency, that is a gassing tendency of less than about +30 to about -30 ⁇ _/ ⁇ .
  • Blends can comprise from at least about 25 wt%, or alternatively from about 50 wt % to about 99 wt%, or from about 75 to about 95 wt% mineral oil and from about 1 to about 75 wt% of a renewably sourced composition of the present invention, including blends thereof with natural oils having high monounsaturated ester content.
  • Mineral oil can be blended with either (1 ) a natural oil or blend thereof, particularly one having significant monounsaturated ester content (2) a synthetic polyol ester or blend thereof, or (3) a blend comprising both a natural oil as in (1 ) and a synthetic ester as in (2).
  • Mineral oil blends as described herein can be formulated according to the methods of the present invention to provide a blended insulating fluid having a balance of desirable properties such as: improved oxidative stability, low pour point, low viscosity, low viscosity index and improved gassing tendency, while potentially improving cost effectiveness with fluids other than mineral oil.
  • the blends of the present invention are formulated to meet standards set to provide fluids that are stable and effective in use as dielectric fluids but do not require a gassing additive to meet the gassing tendency standards.
  • Additives can be optional to improve the performance of the cooling fluids described herein. In some embodiments, the improvements observed are surprising in view of the absence of additives. For example, oxidative stability can be improved to a surprising degree without the use of antioxidants by blending synthetic esters and natural oils. Additives can be used, however, if desired.
  • the blended compositions of the present invention may or may not require added synthetic additives such as antioxidants, pour point depressants, anti-gassing aromatic agents, metal passivators, anti-foaming agents, and electrostatic charging tendency depressants.
  • synthetic additives such as antioxidants, pour point depressants, anti-gassing aromatic agents, metal passivators, anti-foaming agents, and electrostatic charging tendency depressants.
  • the blended compositions of the present invention comprise a renewably sourced saturated synthetic polyol ester as the major component, from about 51 to about 99 wt% of the blend, and a natural ester as the minor component for use in open breathing transformers, from about 1 wt% of the blend to about 49 wt% of the blend, with additives optionally added.
  • the blended compositions of the present invention comprise the renewably sourced synthetic polyol ester as minor component, from about 1 wt% of the blend to about 49 wt% of the blend, and natural based ester as major component, from about 51 to about 99 wt% of the blend for use in sealed transformers, with additives optionally added.
  • the blended composition of the present invention comprises either naphthenic or isoparaffinic mineral oil as major component, from about 51 to about 99 wt% of the blend, and the minor component, from about 1 wt% of the blend to about 49 wt% of the blend, comprises a blend of the renewably sourced synthetic saturated polyol ester and high oleic acid based triglyceride for use in power transformers, with additives optionally added.
  • antioxidants are included, a high molecular weight phenolic antioxidant such as IRGANOX® 259 can be included, or TBHQ can be added or BHT can be added for blends comprising mineral oil. It can be advantageous to match a specific antioxidant with a particular major component of the fluid blend for optimal results. For example, blends comprising a synthetic ester as the major component of the blend are substantially better stabilized by antioxidants such as IRGANOX® 259 than by TBHQ. Blends comprising a natural ester as the major component are substantially better stabilized by TBHQ. It is surprising that blends of the synthetic antioxidants were not as effective in improving the stability of the blended fluid compositions as when an individual antioxidant is matched with the appropriate major component of the fluid blend.
  • the United State Department of Agriculture has established a minimum standard of 66% renewable carbon or bio-based carbon content for a synthetic polyol ester and 95% renewable carbon or bio-based carbon content for a natural ester.
  • the compositions of the present invention have greater than 66% renewable carbon or bio-based carbon content.
  • the blend compositions of the present invention are useful in liquid-filled transformers comprising insulation paper selected from normal Kraft paper, thermally upgraded cellulose paper, Nomex® paper and cellulose/Nomex® blend paper.
  • Refined, bleached, and deodorized high oleic soybean oil (RBD HOS oil) containing triglycerides of the following fatty acids: palmitic acid (6.5 wt%), stearic acid (4.15 wt%), oleic acid (73.9 wt%), linoleic acid (8.77 wt%), and linolenic acid (2.94 wt%) was obtained according to United States Patent No. 5,981 ,781 .
  • Commodity soybean oil was obtained from Homestead Farms, Des Moines, IA.
  • Glycerol and trimethylolpropane were obtained from Aldrich Company (Milwaukee, Wl).
  • Glyceryl tricaprylate-caprate is sold under the tradename Grindsted® MCT 60 X by DuPont.
  • Trimethylolpropane tricaprylate-caprate (WAGLINOL 3/13480)
  • PTCC pentaerythritol tetracaprylate-caprate
  • Silica gel was obtained from EMD Chemicals.
  • Activated carbon was obtained from Calgon.
  • Iodine values of natural esters were determined by quantifying the unsaturation using proton NMR.
  • Turbidity measurements on the compositions were carried out using a nephelometric turbidimeter (MicroTPW, Model 20000, Scientific Inc.
  • NTU Nephelometric Turbidity Unit
  • the commercially available synthetic saturated polyol esters (GTCC, TTCC and PTCC) were evaluated to determine their suitability as basestock for use in transformers. These esters include the same mixture of (C8/C10) fatty acids but differ only in the identity of the polyol used to prepare the esters. The measured properties of these polyol esters are reported in Table 1 . Table 1 Properties Of Commercial Polyol Ester Fluids
  • the Dean-Stark trap was replaced with a condenser fitted with a collection flask and the nitrogen inlet to the headspace was replaced with a nitrogen purge.
  • the reaction was heated to 225°C at 5mmHg pressure with a fast nitrogen purge and stirring at 400 rpm and the distillate was collected over 7h yielding trimethylolpropane tricaprylate-caprate (523.5g, 98.3%).
  • the pressure was reduced to 75 mmHg in steps of approximately 100 mmHg over 5 hours and held for a further 6 hours during which time distillate collected in the trap.
  • the Dean-Stark trap was replaced with a condenser fitted with a collection flask and the nitrogen inlet to the headspace was replaced with a nitrogen purge.
  • the reaction was heated to 225°C at 5mmHg pressure with a fast nitrogen purge and stirring at 400 rpm and the distillate was collected over 7h yielding trimethylolpropane triester (429.9g, 97.9%).
  • thmethylolpropane tricaprylate/caprate (3005.9g, Waglinol 3/13480), activated carbon (30.0g, Calgon, PWA powdered,) and basic alumina (30.0g, BASF, G250).
  • activated carbon 30.0g, Calgon, PWA powdered,
  • basic alumina 30.0g, BASF, G250
  • the fluid was allowed to cool and passed through a coarse frittered funnel layered with 1/2" Celite 545 (approximately 30g, EMD) atop 1/2" silica gel 60 (approximately 30g, Alfa Aesar) using reduced pressure and a nitrogen blanket yielding purified trimethylolpropane triester (2793. Og, 92.9%).
  • the properties of the purified triester in comparison with as received commercial ester are reported in Table 3.
  • the purification of the commercial product as received improved the quality of the product and its electrical properties. Significant reduction in power factor and increase in volume resistivity were observed for the purified product. The oxidative stability of the fluid was improved by the purification procedure.
  • reaction mixture was cooled to room temperature, the distillation column was removed and a distillation head was directly connected to the flask.
  • the reaction mixture was distilled at a pressure of 1 torr until the pot temperature reached 217 °C, at which termperature the unreacted acids (694 g) were recovered.
  • the reaction mixture was diluted with hexanes (7 L) and transferred to a 30 L bottom valved resin kettle. The material was then washed with a mixture of saturated NaCI (1 L), NaOH solution (10%, 2L) and Dl water (3L), NaOH (10%, 3 X 2 L), and with Dl water (5 X 3L).
  • the hexane solvent was removed on a rotary evaporator to form a crude product.
  • the crude product was passed through a thin (3 ⁇ 4") of silica gel and the filtrate was dried on vacuum at 1 10°C for 1 hour to give oil (1 1 .8 Kg).
  • the oil sample was treated with activated carbon (2%) at 1 10°C under 1 torr vacuum for 1 hour. After being cooled to room temperature, the carbon was removed by filtration through a silica gel bed to give almost colorless oil. About 3.2 L of the filtrate was passed through a 10" silica gel column and about 3L of eluent was collected.
  • the FAME analysis indicated the following contents:
  • Oil for analysis 30mg/ml in toluene.
  • the internal standard is a triglyceride which will react along with the oil sample to form methyl esters there by minimizing the effect of less than 100% conversion of all the oil into methyl esters because the internal standard's reaction rate should be close to that of the oil's reaction rate.
  • the standard was purchased form Nu-Chek Prep, Inc. catalog code T-145, which is tripentadecanoin (C15:0). Sample run
  • methyl ester relative weight percent for methyl ester from the oil is calculated. Three repeats of each of the in process samples are made using the same stock oil solution. From each of these samples, the FAME profile is established and an average for three repeats is calculated for each methyl ester present along with the standard deviation. Table 4: Properties of glycerol oligomer ester
  • Connparative Examples 5-8 The oxidative stability of the two neat synthetic polyol ester fluids (Comparative examples 5 & 6) and two natural ester fluids such as high oleic soybean oil (HOS) and commodity soybean oil (Soy) (Comparative Examples 7 & 8) in the absence of added antioxidants were evaluated by oil stability index (OSI). The OSI determinations were made at 130°C using the Oxidative Stability
  • Blends were prepared by mixing the purified TTCC fluid of Example 2 with high oleic soybean oil at weight ratio ranging from 10 to 50%.
  • Example 8 Separately, another blend was prepared by mixing 90 wt% of GOE of Example 3 with 10 wt% high oleic soybean oil .
  • Example 9 A blend was prepared by mixing 90 wt% of GOE of Example 3 with 10 wt% of commodity soybean oil.
  • the oxidative stability of the above blends in the absence of synthetic antioxidants was evaluated by OSI and compared with neat fluids in Table 5.
  • the amount of unsaturation in high oleic soybean and commodity soybean was determined from NMR and the unsaturation in the blend was calculated based on the amount natural ester present and are reported as iodine value.
  • Saturated polyol esters demonstrate higher OSI induction time compared to natural esters, and the genetically modified high oleic soybean oil had longer induction time when compared to conventional commodity soybean oil
  • blends were prepared by mixing renewably sourced synthetic saturated polyol ester fluids with natural esters without adding any additives and the gassing tendency of these blends was tested and compared with neat ester fluids.
  • the fluids of the present invention can be tailored to have good chemical stability with respect to oxidation and electric stress by blending synthetic polyol ester fluids with appropriate amounts of natural esters in particular with high oleic soybean oil.
  • An uninhibited blend fluid was formulated by mixing only 90 wt% TTCC and 10 wt% HOS oil and this fluid is essentially free from synthetic additives including aromatic anti-gassing additives, synthetic antioxidants, passivators and pour point depressants.
  • the properties of the formulated fluid are listed in Table 9.
  • Inhibited fluid formulations were also prepared by blending the renewably sourced synthetic polyol ester (purified TTCC) as a major basestock and natural ester (HOS) as a minor (additive) component.
  • the resulting fluids have excellent balanced properties as shown in Table 9 and are suitable as insulating fluids for use in transformers, in particular, in open breathing power transformers.
  • Table 9 Properties of Synthetic and Natural Ester Blended Fluids
  • Table 9 shows the flexibility to alter the properties of the fluids and thereby their performance as dielectric fluids by blending the renewably sourced synthetic ester with a natural ester.
  • An inhibited fluid formulation with improved properties was prepared by blending the natural ester, soybean oil, as a major component, a mixture of two synthetic polyol esters (TTCC & GTCC) as minor components, 0.2% antioxidant and 1 .0% pour point depressant.
  • this fluid in comparison with commercial fluid had excellent oxidative stability, low gassing tendency, superior low temperature fluid properties, and met the K fire safety class.
  • the oxidatively stable fluid has a low gassing tendency as well. This fluid is useful both in sealed and open distribution and power transformers.
  • formulations of the present invention are not limited to the
  • compositions described further optimization of the formulations can be done to improve the performance of the fluid .
  • Example 30 An uninhibited dielectric fluid was prepared by blending a severely hydrotreated uninhibited insulating mineral oil (80% by weight, Nytro Taurus), 16% by weight of polyol ester( trimethylolpropane tricaprylate/caprate), and 4% by weight of high oleic soybean oil. No synthetic additives were added to the fluid. The properties of the uninhibited dielectric fluid blend were tested and compared with the neat mineral oil (comparative example 13) in Table 1 1 .

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  • Physics & Mathematics (AREA)
  • Spectroscopy & Molecular Physics (AREA)
  • Lubricants (AREA)
  • Organic Insulating Materials (AREA)

Abstract

La présente invention se rapporte à des compositions qui conviennent pour être utilisées comme fluides diélectriques et qui sont obtenues à partir d'huiles d'origine renouvelable et de mélanges de ces dernières. Les esters synthétiques d'origine renouvelable, tels que ceux décrits dans la présente, sont préparés à l'aide de composants obtenus à partir de produits de départ naturels ou biologiques, les produits de départ pouvant être régénérés par l'intermédiaire de techniques d'agriculture classiques. Des fluides diélectriques qui peuvent satisfaire les normes industrielles, sont obtenus à l'aide d'un procédé permettant de combiner des pourcentages appropriés de composants sélectionnés parmi les esters de polyol synthétiques, les huiles naturelles et l'huile minérale afin de personnaliser les propriétés du fluide diélectrique obtenu. Quelques-unes des propriétés qui peuvent être manipulées dans la pratique de la présente invention, comprennent : l'intensité électrique, la résistivité, la résistance à la tension de choc, le facteur de dissipation, la permittivité, la chaleur spécifique, la conductivité thermique, la stabilité chimique, l'absorption de gaz, le point d'écoulement, la viscosité, la volatilité, le point d'éclair et de feu et la biodégradabilité.
PCT/US2013/068837 2012-11-13 2013-11-07 Compositions d'huile mélangée utiles comme compositions de fluide diélectrique et procédés de préparation de ces dernières WO2014078156A1 (fr)

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EP13792834.7A EP2920794A1 (fr) 2012-11-13 2013-11-07 Compositions d'huile mélangée utiles comme compositions de fluide diélectrique et procédés de préparation de ces dernières
CN201380059273.7A CN104798143A (zh) 2012-11-13 2013-11-07 可用作介电流体组合物的共混的油组合物及其制备方法

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US6790386B2 (en) 2000-02-25 2004-09-14 Petro-Canada Dielectric fluid
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CA2492565A1 (fr) 2005-01-13 2006-07-13 Oleotek Inc. Refrigerants dielectriques pour utilisation dans des appareils electriques
US20090270644A1 (en) * 2005-09-09 2009-10-29 Takaaki Kano Base agent for electrical insulating oil
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US7524440B2 (en) * 2003-10-02 2009-04-28 Cooper Industries, Inc. Method comprising additive for dielectric fluid
DE102004025939A1 (de) * 2004-05-27 2005-12-22 Cognis Deutschland Gmbh & Co. Kg Polyolester für Transformatoren
BRPI1006424B8 (pt) * 2009-03-27 2022-12-06 Du Pont uso de um óleo de soja como um fluído dielétrico de transferência de calor em um dispositivo, dispositivo para gerar, armazenar, converter e/ou distribuir energia elétrica e material dielétrico

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US5981781A (en) 1996-04-26 1999-11-09 E. I. Du Pont De Nemours And Company Soybean oil having high oxidative stability
US6790386B2 (en) 2000-02-25 2004-09-14 Petro-Canada Dielectric fluid
WO2006040888A1 (fr) * 2004-10-13 2006-04-20 Japan Energy Corporation Huile isolante électrique
CA2492565A1 (fr) 2005-01-13 2006-07-13 Oleotek Inc. Refrigerants dielectriques pour utilisation dans des appareils electriques
US20090270644A1 (en) * 2005-09-09 2009-10-29 Takaaki Kano Base agent for electrical insulating oil
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US20230121933A1 (en) * 2020-03-17 2023-04-20 Hitachi Energy Switzerland Ag Mfc in pressboards for hv devices
US11769608B2 (en) * 2020-03-17 2023-09-26 Hitachi Energy Switzerland Ag MFC in pressboards for HV devices

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