WO2006074553A1 - Liquides de refroidissement dielectriques destines a s'utiliser dans un equipement electrique - Google Patents

Liquides de refroidissement dielectriques destines a s'utiliser dans un equipement electrique Download PDF

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Publication number
WO2006074553A1
WO2006074553A1 PCT/CA2006/000045 CA2006000045W WO2006074553A1 WO 2006074553 A1 WO2006074553 A1 WO 2006074553A1 CA 2006000045 W CA2006000045 W CA 2006000045W WO 2006074553 A1 WO2006074553 A1 WO 2006074553A1
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Prior art keywords
dielectric coolant
ester
polyol
mixture
esters
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PCT/CA2006/000045
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English (en)
Inventor
David Berthiaume
Josée LABRECQUE
Paul ANGERS.
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Oleotek Inc.
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Priority to CA002594765A priority Critical patent/CA2594765A1/fr
Publication of WO2006074553A1 publication Critical patent/WO2006074553A1/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
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
    • C09K5/00—Heat-transfer, heat-exchange or heat-storage materials, e.g. refrigerants; Materials for the production of heat or cold by chemical reactions other than by combustion
    • C09K5/08—Materials not undergoing a change of physical state when used
    • C09K5/10—Liquid materials
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F27/00—Details of transformers or inductances, in general
    • H01F27/08—Cooling; Ventilating
    • H01F27/10—Liquid cooling
    • H01F27/12—Oil cooling
    • H01F27/125—Cooling by synthetic insulating and incombustible liquid

Definitions

  • the present invention relates to a synthetic insulating fluid for use as a dielectric and cooling medium in power and distribution electrical apparatus, such as transformers, oil bath breakers and attendant equipment.
  • Oleochemistry is a broad science which finds application in multiple fields, such as lubricants, paints, plastics, fuels, cosmetics, food, and pharmaceutical products. Oleochemistry further finds an application in the field of transmission and distribution of electrical power, and particularly for transformers in which important quantities of dielectric coolant are used.
  • the dielectric coolants employed in the electric transformers are mostly of mineral and petrochemical origin. However, some electric transformers using vegetable oil based dielectric coolants are newly presented on the American and European markets. These new coolants have the advantage of being efficient, biodegradable and non-toxic according to the American regulation. Until today, these coolants are mostly used for installations located nearby ecologically sensitive sites, such as rivers and other natural places, or indoor locations, such as commercial buildings and towers.
  • Vegetable oil based dielectric coolants are efficient and environmentally friendly as they are biodegradable and non-toxic. However, they are limited in their utilisation because of their relatively high temperature operating range (usually limited to operating temperatures higher than -2O 0 C). This value, which corresponds to the coolant's pour point, is acceptable for the majority of the
  • the pour point of standard dielectric coolants for cold climates is of about -40 0 C.
  • the lowering of the pour point is limited by the nature of these coolants.
  • dielectric coolants in the art such as those sold by ABB inc (Biotemp ® ) and by Cooper Power Systems (Envirotemp ® ). These products are made of purified and treated vegetable oil combined with conservative agents and other additives. These oils are biodegradable, non-toxic and have increased flash points. However, as mentioned above, these oils have a pour point unsuitable for use in electrical equipments located in at most about - 40 0 C climates and usually require the presence of additives when intended for operation temperatures around -20 0 C. These treated vegetable oils also pose other problems - such as product variability instability, etc - when used as dielectric coolants in electrical equipment, depending on the source oil, fatty acid content and compositions.
  • dielectric coolants derived from natural sources such as vegetable oils.
  • United States patent application US 2002/00272219 describes high concentration oleic acid triglyceride compositions that also contain specific concentrations of diunsaturated, triunsaturated and saturated fatty acids.
  • synthetic esters such as polyol esters are added to the composition in varying concentrations. This patent shows that the compositions have various properties, including a pour point that may be brought to about -38°C.
  • the International patent application WO 2004/108871 A2 (HOANG et al.) describes mixtures of natural triglycerides and fatty acid esters of 2-ethyl- 1-hexanol.
  • This dielectric coolant is a blend of a vegetable oil and the aforementioned fatty acid esters, and may contain a high concentration of the esters.
  • Various physical properties are attainable with such blends, among which is a pour point between about -20 0 C and -3O 0 C.
  • this patent teaches that mono-esters are advantageous as well as the polyunsaturated fatty acids thereof should be used.
  • the International patent application WO 97/22977 describes a dielectric coolant including a vegetable oil, antioxidant and low temperature additive.
  • the vegetable based oil includes glycerides such as trigycerides having a variety of carbon chains, preferably those with at least one degree of unsaturation to mitigate oxidation and hydrogen gas release.
  • glycerides such as trigycerides having a variety of carbon chains, preferably those with at least one degree of unsaturation to mitigate oxidation and hydrogen gas release.
  • additives are required and are mixed in with the composition; otherwise different sources of oils are mixed together.
  • the United States patent US 4,812,262 (SHINZAWA et al.) describes an electric device and an insulating oil for use therein, the oil being composed of a fatty acid polyol ester having a high fire point 300 0 C blended with a small amount of phenolic compound to improve antioxidant ability and epoxy compound to improve stability.
  • this patent teaches a blend of phenolic compounds with an ester of trimethylolpropane (1) or, especially, with an ester of pentaerythritol (2) (thus esters having three or four alkoxycarbonyl groups). In the Examples, only pentaerythritol esters (four alkoxycarbonyl groups) are used in combination with the phenolic and epoxy compounds.
  • polyalphaolefins are blended with at least one of the aforementioned compounds to make the coolant composition.
  • the polyol esters are blended with polyalphaolephins or aromatics to give the dielectric coolant blend.
  • Some of these blends may pose problems involving biodegradability, renewability of resources required and the expense of producing at least two very different compounds of different chemical families.
  • the most preferred polyol ester is a pentaerythritol with four identical fatty acid chains of C 9 H 2O -
  • pentaerythritol is blended in varying amounts with phenyl ortho-xylyl ethane (Example Vl), polyalphaolefin
  • Example VIII and/or aromatics (Example IX), together with additives to optimize the performance of the compositions.
  • insulating oils used in the prior art comprise vegetable oils, which have pour points unsuitable for use in cold temperatures, and thus to further lower the pour point, pour point depressant additives are blended with the base vegetable oil.
  • the resulting blend has disadvantages when used as a dielectric coolant, as its properties may not be up to certain standards of the industry or up to the requirements of certain applications.
  • the present invention provides a dielectric coolant that overcomes some of the disadvantages and drawbacks of known fluids used in the art, which are mentioned hereinabove.
  • the inventive dielectric coolant is used in electrical equipment and presents numerous advantages over the prior art.
  • the dielectric coolant according to the present invention has a pour point of at most about -2O 0 C for use in power distribution equipment for cold climates.
  • a dielectric coolant consisting essentially of a mixture of polyol esters has advantageous properties enabling the mixture to be used as a coolant in low temperatures. More specifically, the dielectric coolant according to the present invention has at most a pour point of about -20 0 C.
  • the present invention provides a dielectric coolant for use in electrical equipment, consisting essentially of a mixture of polyol esters chosen from formula X:
  • Ri and R 2 are the same or different and are selected from branched or unbranched, saturated or unsaturated alkyl groups with a carbon chain length of C 4 to C 22 and alkoxycarbonyl groups of formula CR 3 R 4 C 2 H 2 OCOR 5 , wherein R 5 is selected from branched or unbranched, saturated or unsaturated alkyl groups with carbon chain lengths of C 4 to C22; and
  • R 3 and R 4 are the same or different and are selected from branched or unbranched, saturated or unsaturated alkyl groups with carbon chain lengths of Ci to C 5 and alkoxycarbonyl groups of formula CH 2 OCOR 6 , wherein R 6 is selected from branched or unbranched, saturated or unsaturated alkyl groups with a carbon chain length of C 4 to C 22 and alkoxycarbonyl groups of formula CR 3 R 4 C 2 H 2 OCOR 5 ;
  • said dielectric coolant having a pour point of at most -2O 0 C.
  • the dielectric coolant has at most a pour point of about -40 0 C and consists of a mixture of more than one compound chosen from the following:
  • NPG neopentylglycol
  • Ri and R 2 are the same or different and are selected from branched or unbranched, saturated or unsaturated alkyl groups with carbon chain lengths of C 4 to C 22 ; and/or
  • R 1 , R 2 and Re are the same or different and are selected from branched or unbranched alkyl groups with carbon chain lengths of C 4 to C 22 ;
  • R 1 and R 5 are the same or different and are selected from branched or unbranched alkyl groups with carbon chain lengths of C 4 to Czz-
  • the dielectric coolant consisting essentially of the mixture of polyol esters of formula X defined above, and having a pour point of at most about -2O 0 C is manufactured by a process comprising the following steps:
  • the first polyol ester with the second polyol ester to produce the mixture of polyol esters.
  • the preceding polyol esters are combined in proportions that enable a synergistic effect on certain properties of the dielectric coolant.
  • the different polyol esters are combined to unexpectedly lower the pour point of the resulting polyol ester mixture.
  • the pour point of the mixture of polyol esters is lower than the proportional average of the pour points of the individual polyol esters used in the mixture.
  • the mixture of the polyol esters has a pour point lower than any of the pour points of the individual polyol esters used in the mixture.
  • polyol esters may be used to produce mixtures having variety of compositions. It should also be made clear that though the pour point of the mixture is preferably lower than the proportional average of the individual polyol esters, that this is not necessary to the functioning of the invention and other embodiments are envisioned by the inventors, and will be dicussed here below.
  • the inventor has surprisingly found that the use of a mixture of polyol esters - of which neopentyl glycol ester (NPG ester), hydroxypivalic acid neopentylgiycol ester (HPN ester) and/or trimethylolpropane ester (TMP ester) are preferred - offers an efficient fluid as a dielectric coolant useful in power distribution equipment, such as transformers.
  • NPG ester neopentyl glycol ester
  • HPN ester hydroxypivalic acid neopentylgiycol ester
  • TMP ester trimethylolpropane ester
  • the dielectric coolant of the present invention consists of a mixture of polyol esters and has a pour point of at most -40 0 C.
  • a dielectric coolant of the present invention should possess at least one of the following characteristics. It should transfer heat effectively, have an appropriate dielectric strength, and/or should not include ingredients harmful to the environment. As mentioned above, it has been surprisingly found that a mixture of polyol esters, optionally including an HPN ester, and combinations thereof satisfy both the requirements for suitability as dielectric coolant in cold climates and the requirements relating to environmental compatibility. It will also be understood that a dielectric coolant contemplated by the invention comprises a mixture of the defined polyol esters, and thus encompasses a mixture of polyol esters of formula X, and more particularly and preferentially, of formula I and/or of formula Il and/or of formula III.
  • a "polyol ester” of the present invention refers to an ester compound having at least two ester functional groups. Normally, an ester is produced by reacting a compound having a carboxylic acid functional group with a compound having an alcohol functional group.
  • the polyol esters result from the chemical combination of polyalcohol compounds with organic acids containing a variety of alkyl groups. Though this reaction is the most common for producing polyol esters, the polyol esters of the present invention are not limited to those produced in this fashion. Esterification and transesterification are preferred reaction techniques, though others may be used.
  • the polyol esters defined in formula X may be extracted from naturally occurring oils, or derived from other natural or synthetic sources. Thus, polyol esters of synthetic or natural origin may be used in the present invention.
  • the "mixture" of polyol esters of the present invention refers to a mixture that includes any combination of one or more polyol esters defined in formula X.
  • the mixture is of polyol esters, it is understood that it may also include impurities. These impurities, which may be the result of the fabrication, reaction, transfer, transport, storage, etc, of the mixture, will be further discussed herebelow.
  • the mixture may also be a substantially pure fluid composed of a polyol ester, thus having each Ri, R 2 , R3, R4 R 5 and/or R 6 groups individually the same.
  • Such a mixture is a substantially pure fluid consisting of the polyol ester NPG- dicaprylate (where Ri and R 2 are both CH 3 -(CH 2 )S-, though keeping in mind that there are often other carbon chain lengths such as C6 and/or C8 mixed in with this substantially pure mixture), with impurities. Nevertheless, it is preferable to have a certain range of carbon chain lengths, and thus that at least one of Ri to Rs groups is different.
  • the mixture may alternatively consist of a single class of polyol esters, such as for example NPG esters.
  • Such a preferable mixture may include NPG esters having a variety of Ri and R 2 groups. For example, NPG-dicaprylate and NPG-trioleate could be mixed together to give a pure NPG ester mixture, that may include impurities.
  • Another example of a mixture of polyol esters is where two or more polyol esters of different classes are mixed together.
  • NPG esters and TMP esters may be used to make up the mixture.
  • the mixture of polyol esters may include those of different classes, each having a variety of R groups, in order to make up the mixture.
  • esters including polyol esters
  • the present invention may be distinguished from such blends in that the dielectric coolant is composed of select polyol esters of formula X, and that the dielectric coolant does not require substantial amounts of other compounds. Thus trace amounts of undesired compounds, as well as small quantities of other compounds such as biocides, stabilizers and antioxidants are permitted.
  • dielectric coolant may contain impurities common in the arts of dielectric coolants, polyol ester manufacturing, as well as chemistry in general. Also, depending on the given impurity, different levels may be acceptable. However, other impurities may be present in greater quantities. Dielectric coolant impurities may be introduced into the coolant at a variety of stages of the production, transport, storing and/or use of the coolant. In the production of polyol esters, trace amounts of organic acids and alcohol may be present. There may also be traces of by-products of alcohol - acid reactions.
  • the polyol ester mixture When the polyol ester mixture is manufactured using a solvent and a catalyst, trace amounts of these compounds may be present in the isolated polyol ester mixture. Also, depending on the source of the organic acids and alcohols (e.g. if the acids are derived from a natural source comprising a complex array of compounds), small amounts of these miscellaneous compounds is permissible. As some polyol esters may present a certain degree of degradation over time, these degradation products may be present in varying amounts according to the age of the dielectric coolant as well as the quality and conditions under which it was stored or used. In this context, an acceptable trace amounts will be understood to be an amount that does not significantly affect the functioning of the base mixture.
  • the term "at most" used to characterize the pour point indicates that the pour point of the dielectric fluid is below the indicated temperature.
  • the value of the pour point is a temperature equal to or below -40 0 C, such as -45°C, -55 0 C and -90°C.
  • the value of said pour point or flash point can vary within a certain range depending on the margin of error of the method used to evaluate such pour point or flash point.
  • the margin of error may also include factors such as the measurement apparatuses, measurement standards and/or measurement method used to evaluate the pour point or flash point, and would be known to a person skilled in the art.
  • the method to measure the pour point ASTM D97, measures in intervals of 3 0 C, and thus such a margin of error exists for these measurements.
  • the "pour point" of a fluid is the temperature at which the fluid stops flowing. It may be measured according to a variety of standards, including the ASTM D97 method and the ISO 3016 standard. This property is particularly important in the field of dielectric fluids for electrical equipment since the pourability of the fluid affects numerous aspects of heat transfer capacity. For instance, if a fluid can no longer flow, the convective heat transfer is all but eliminated. Convection is a very important heat transfer mechanism and is dependant on whether a medium can flow or not. Also, when handling dielectric fluids at low temperatures it is desirable to have an adequately low pour point so that the coolant may be changed, replenished, tested, etc.
  • the dielectric properties of a coolant may change depending on its pourability, i.e. a dielectric coolant that is above its pour point has different dielectric properties than the same coolant at or below its pour point.
  • the pour point of a mixture is not necessarily an average of the pour points of the individual constituents, but, due to a variety of complex chemical interactions, the pour point of the mixture may be higher or lower.
  • the pour point is a function of a variety of molecular factors and may not be predicted alone by other properties of given chemical compounds such as the fire point, flash point, viscosity, molecular mass, etc.
  • a “transformer” is a device that transfers electric power from one circuit to another by electrical magnetic means. Transformers are used extensively in the transmission of electrical power, both at the generating end and the user's end of the power distribution system.
  • a distribution transformer is one that receives electrical power at a first voltage and delivers it at a second, lower voltage.
  • the dielectric coolant of the present invention consists of a mixture of polyol esters chosen from formula X:
  • Ri and R 2 are the same or different and are selected from branched or unbranched, saturated or unsaturated alkyl groups with a carbon chain length of C 4 to C22 and alkoxycarbonyl groups of formula CR 3 R 4 C 2 H 2 OCOR 5 , wherein
  • R 5 is selected from branched or unbranched, saturated or unsaturated alkyl groups with carbon chain lengths of C 4 to C 22 .
  • R 3 and R 4 are the same or different and are selected from branched or unbranched, saturated or unsaturated alkyl groups with carbon chain lengths of
  • Ci Ci to C 5 and alkoxycarbonyl groups of formula CHbOCOR 6 , wherein Re is selected from branched or unbranched, saturated or unsaturated alkyl groups with a carbon chain length of C 4 to C 22 and alkoxycarbonyl groups of formula CR 3 R 4 C 2 H 2 OCOR 5 .
  • R 1 , R 2 , R 3 , R 4 , R 5 and R 6 may be selected to give various preferred embodiments of the polyol ester of formula X, and more notably, NPG ester, HPN ester and TMP ester.
  • the polyol ester mixture may also include pentaerythritol (PET) ester and/or di-hydroxypivalic acid neopentylglycol (dHPN), as will be further described herebelow.
  • PET pentaerythritol
  • dHPN di-hydroxypivalic acid neopentylglycol
  • the first preferred polyol ester is neopentyl glycol (NPG) having the following formula:
  • R 3 and R 4 of formula X have been selected to be the same and to be methyl groups.
  • R 1 and R 2 are the same or different and are selected from branched or unbranched, saturated or unsaturated alkyl groups with carbon chain lengths of C 4 to C-2 2 - Ri and R 2 preferably present chains of natural or synthetic origin that offer a good level of biodegradability. Even more preferably, R 1 and R 2 present chains obtainable from a biological source such as vegetable or animal oils.
  • R 1 and R 2 of the NPG ester are both or independently:
  • the dielectric coolant of the invention comprises a hydroxypivalic acid neopentylglycoi ester (HPN ester).
  • HPN ester hydroxypivalic acid neopentylglycoi ester
  • formula III corresponds to formula X that has been rotated about a planar axis and has the following characteristics.
  • R 3 and R 4 of formula X have been selected to be the same and to be methyl groups.
  • R 2 has been selected to be alkoxycarbonyl groups of formula CR 3 R 4 C 2 H 2 OCOR 5 , wherein R 5 is selected from branched or unbranched, saturated or unsaturated alkyl groups with carbon chain lengths of C 4 to C 22 .
  • R 1 may be selected from branched or unbranched, saturated or unstaurated alkyl groups with carbon chain lengths of C 4 to C 22 .
  • R 1 and R5 have the same meaning and preferred embodiments as R 1 and R 2 defined above.
  • R 1 and R 2 are both CH 3 -(CH2) 6 - .
  • the third preferred polyol ester is trimethylolpropane (TMP) having the following formula:
  • R 3 and R 4 of formula X have been selected to be an ethyl group and an alkoxycarbonyl group of formula CH 2 OCOR 6 respectively, and wherein R 6 is selected from branched or unbranched, saturated or unsaturated alkyl groups with a carbon chain length
  • R 1 , R 2 and R 6 are the same or different and are selected from branched or unbranched, saturated or unsaturated alkyl groups with carbon chain lengths of C 4 to C 22 .
  • Ri, R 2 and R 3 preferably represent chains of natural or synthetic origin that offer a good level of biodegradability. Even more preferably, Ri , R 2 and R 3 present chains obtainable from a biological source such as vegetable or animal oils.
  • R 1 , R 2 and R 3 may be each or individually:
  • PET esters may be a constituent of the polyol ester mixture.
  • R 3 and R 4 are alkoxycarbonyl groups, as referred to above.
  • dHPN esters may be used, in which case R 3 and R 4 are selected to be the same and to be methyl groups, while Ri and R 2 are selected to be alkoxycarbonyl groups of formula CR 3 R 4 C 2 H 2 OCOR 5 .
  • Re is selected as an alkoxycarbonyl group of formula CR 3 R 4 C 2 H 2 OCOR 5
  • the resulting polyol esters are hydroxypyvalic derivatives of PET and/or TMP.
  • the pour point of the mixture of polyol esters is lower than the proportional average of the pour points of the individual polyol esters used in the mixture. In other preferred embodiments, the mixture of the polyol esters has a pour point lower than any of the pour points of the individual polyol esters used in the mixture.
  • the pour point of the dielectric coolant is about -20 0 C or less, but is not lower than the proportional average of the pour points of the different individual polyol esters making up the mixture.
  • dielectric coolants are chosen according to properties other than the pour point - such as fire-point, biodegradability, stability, cost, etc - other factors may come into play when choosing the combination of polyol esters to use to make up the mixture. For example, some fatty acids are more abundant than others and therefore are less expensive, which may prefer such acids in the production (with alcohols) of the corresponding polyol ester product. Still, the advantageous pour point of less than about -20 0 C is possible, even when using a variety of polyols having a variety of factors and properties influencing their selection and use.
  • a dielectric coolant consisting essentially of a mixture of polyol esters may be composed of certain polyol esters selected for certain properties they may have.
  • the molecular mass, the pour point, the fire point, the flash point, the density, the stability, the viscosity, among others could be used to help a person skilled in the art to select the polyol esters to be used.
  • other factors may influence the choice of polyol ester.
  • different polyol esters have different production costs due to process design, reactant availability and market price of certain materials.
  • different polyol esters may be selected for the dielectric coolant mixture on the basis of their cost and/or chemical/physical properties.
  • the resulting mixture of polyol esters has the beneficial properties of being biodegradable, environmentally friendly, and able to be used in cold environments.
  • polyol esters may be used as the unique component of the mixture.
  • NPG esters, TMP esters or HPN esters alone in the mixture to produce the dielectric coolant.
  • a variety of carbon chains may be used for the above mentioned polyol esters.
  • the polyol ester mixture may be manufactured using various processes and starting materials. Esterification and/or transesterification are preferred reactions, which are known in the art. Also, animal and/or vegetable oils, from a variety of sources may be used as a starting material. Furthermore, a selection of the fatty acids to be used in the esterification and/or transesterification may be performed to include specific fatty acids or a select range thereof, to react with alcohols. On the other hand, it is also possible to have an extremely wide, non-selective range of fatty acids. Also, in the case of transesterification, triglycerides having a variety of carbon chains may be reacted with polyols to yield polyol esters. Also, specific carbon chain lengths, ramifications and saturations may be chosen for specific applications.
  • the pour point of a fluid such as a dielectric coolant depends on the inability of the molecules to configurationally fit together to form crystals. It has been surprisingly found that this inability of fitting polyol esters together may be taken advantage of to produce a dielectric coolant consisting essentially of polyol esters that may have functional properties at very low temperatures.
  • a dielectric coolant of the present invention has preferably a pour point of at most about -40 0 C, more preferably of at most about -60 0 C, and even more preferably of at most about
  • the pour point of a mixture depends on the individual constituents of said mixture and also on their interaction (synergistic effects). These interactions are often very complex, in terms of the chemistry in play.
  • the pour point of mono-ol-esters is often lower than that of polyol ester, and such esters are often used as additives to lower the pour point of a coolant.
  • certain polyol esters are advantageous for constituting a dielectric fluid with a very low pour point.
  • the pour point may also depend on the length, ramification
  • the dielectric coolant of the present invention contains no additional pour point depressants but consists simply of the polyol esters of formula X.
  • small amounts of compounds that may be considered pour point depressants may be included. However, they are included only to decrease the pour point below the already surprisingly low value of at most -2O 0 C.
  • a dielectric coolant of the present invention has a flash point of at least about 200 0 C. It will be understood that the flash point is the lowest temperature at which a flame will set light to the vapour of the oil or its degradation product. It represents a qualification test and is employed on a pre-industrial scale. The most common standard methods for measuring the flash point are ASTM D92 and ASTM D93.
  • the power factor is another preferred property of the invention in applications in electrical equipment as a dielectric coolant.
  • the higher the power factor the higher power losses.
  • lower percentages are preferred.
  • the power factor at 100 0 C of the dielectric coolant is equal to or lower than 14%. More preferably, the power factor of the inventive dielectric coolant is lower than 11 %, still preferably lower than 5%, and even more preferably equal to or lower than 2.85%.
  • the power factor depends on a variety of factors including impurities in the fluid. Also, different isolating oils have different power factor standards.
  • cold weather minereal oils should have a power factor equal to or lower than 0.5%
  • vegetable oils should have a power factor equal to or lower than 4.0%.
  • Power factor standards depend on the type of fluid being used.
  • the power factor of the present invention is acceptable for its application.
  • the 50-50 mixture of TMP-trioleate and NPG- tricaprylate formulation was subjected to standard purification steps and an advantageous power factor was obtained.
  • purification steps commonly known to someone in the art may be used after production of the polyol ester mixture in order to improve its power factor to down to a certain degree.
  • the polyol esters are preferably produced by reacting organic acids with alcohols.
  • the organic acids are preferably chosen from natural sources such as vegetable or animal oils.
  • organic acids may also be chosen from synthetic organic acids taken or derived from industrial greases, oils, distillation products and by-products, or manufactured synthetically according to any number of reaction processes.
  • additives can be further added to the dielectric coolant described above in relatively small amount.
  • additives are selected from the group consisting of antioxidants, stabilizers, and biocides.
  • additives are used for a variety of reasons to improve the properties of dielectric coolants.
  • Antioxidants for example, increase the stability of the coolant with regards to oxidation, which may be present.
  • biocides may prevent the growth of bacterias feeding on certain oil components during utilisation.
  • Other additives may capture degradation products that inevitably occur during use of the coolant.
  • the properties of the coolant may be altered or improved by adding such additives, even beyond what the surprising and advantageous results are obtained without such additives.
  • Preferred antioxidants include, but are not limited to, phenolic antioxidants, with 2,6-di-tert-butyl-paracresol (DBPC), BHA and BHT being particularly preferred antioxidants, having the formula:
  • Preferred stabilizers include, but are not limited to, epoxide additives.
  • epoxide additives used to prevent degradation of the esters are:
  • biocide compounds include, but are not limited to, pyrithione derivatives, halogenated pyridine derivatives, triazole derivatives, and tetrahydrofuran derivatives.
  • the dielectric coolant according to the present invention may be fabricated by a variety of methods. Principal among these preferred methods are the "formulation” mixture method and the "synthesis” mixture method.
  • the formulation mixture is made by producing a first polyol ester by esterification and/or transesterification, followed by producing a second polyol ester. These first and second polyol esters are thus produced separately (two different batches), after which they are mixed together to produce the mixture of polyol esters.
  • the "synthesis" mixture may be produced by producing a variety of polyol esters in a same batch. Thus polyol esters and carboxylic acids are provided and reacted together to produce a range of different polyol esters that are already mixed together. Furthermore, the synthesis method and the formulation method may be combined, thus providing a synthesis mixture to which another polyol ester or another synthesis mixture is mixed to produce the dielectric coolant mixture. Also, though batch processes are a preferred to produce the present invention, continuous processes may also be used and could be readily adapted by a person skilled in the art.
  • the polyol esters for the dielectric coolant mixture may be synthesized according to various other production methods. For example, they may be synthesized by reacting an alcohol with an acid halide, optionally in the presence of at least one certain catalyst; an alkyl halide with a carboxylic acid, optionally in the presence of at least one certain catalyst; an ester with an alcohol, optionally in the presence of at least one certain catalyst; and/or an alcohol with an acid anhydride, optionally in the presence of at least one certain catalyst.
  • the aforelisted reactions are described in the following reference: "Comprehensive Organic Transformations: A Guide to Functional Group Preparations", 2 nd Ed., Richard C. Larock, 1999, especially at pages
  • the polyol ester mixtures of the present invention were obtained by esterifying the appropriate polyol compound or mixture with the appropriate carboxylic acid compound or mixture with an acid catalyst in a Dean Stark apparatus and/or formulation of separate batches thereof.
  • polyol esters and HPN esters mixtures of the present invention could also be obtained by esterifying the appropriate polyol compound or mixture with the appropriate carboxylic acid compound or mixture with a determined amount of hydroxypivalic acid with an acid catalyst in a Dean Stark apparatus and/or formulation of separate batches thereof.
  • Caprylic acid (667,3 g; 4,53 mol) and trimethylolpropane (202,3 g; 1,46 mol) are placed in a Dean Stark apparatus with toluene (solvent; 3,2 liters) and p-toluenesulfonic acid (catalyst; 14,2 g; 73 mmol) and heated at reflux under mechanical agitation for 5 hours. The solvent is then evaporated and the remaining oil is washed with a sodium carbonate solution and water to remove catalyst and unreacted caprylic acid.
  • R 1 , R 2 and R 3 are CH 3 -(CH 2 )B-- EXAMPLE 2
  • Caprylic acid, oleic acid, and HPN are placed in a Dean Stark apparatus with toluene and benzenesulfonic acid (catalyst) and heated at reflux under mechanical agitation for 6 hours. The solvent is then evaporated and the remaining oil is quickly washed with a diluted sodium hydroxide solution and brine.
  • Caprylic acid, oleic acid, HPN and neopentylglycol are placed in a Dean Stark apparatus with toluene and benzenesulfonic acid (catalyst) and heated at reflux under mechanical agitation for 6 hours. The solvent is then evaporated and the resulting ester mix is quickly washed with a diluted sodium hydroxide solution and brine.
  • 2-EthyIhexanoic acid, neopentyl glycol and hydroxypivalic acid are placed in a Dean Stark apparatus with toluene and p-toluenesulfonic acid (catalyst) and heated at reflux under mechanical agitation for 6 hours. The solvent is then evaporated and the remaining ester mix is washed with a sodium carbonate solution and water.
  • R 2 , R3, R4, R5 and R 6 are independently:
  • neopentyl glycol dicaprylate 75 weight percent is blended with 25 weight percent of HPN-dioleate.
  • an oxidation inhibitor such as 2,6-di-tert-butyl-paracresol (DBPC).
  • the mixture has a pour point that is surprisingly lower than the proportional average of the individual polyol esters.
  • the polyol ester mixture of TMP-tricaprylate and NPG-dicaprylate was produced according to various volume ratios of the individual polyol esters, ranging from 25% to 75% v/v TMP-tricaprylate. In particular, the following pour point results were obtained: 100% TMP-tricaprylate -63°C
  • the mixture has a pour point that is surprisingly lower than the proportional average of the individual polyol esters, and even more surprisingly lower than the pour point of either of the individual polyol esters.
  • the polyol ester mixture of HPN-dicaprylate and NPG-dicaprylate was produced according to various volume ratios of the individual polyol esters, ranging from 25% to 75% v/v HPN-dicaprylate. In particular, the following pour point results were obtained: 100% HPN-dicaprylate -54°C
  • the polyol ester mixture of TMP-trioleate and HPN-dicaprylate was produced according to various volume ratios of the individual polyol esters, ranging from 25% to 75% v/v TMP-trioleate.
  • the following pour point results were obtained:
  • the mixture has a pour point that is surprisingly lower than the proportional average of the individual polyol esters, which would be about -49 0 C.

Abstract

L'invention concerne un liquide de refroidissement diélectrique destiné à s'utiliser dans un équipement électrique, qui est principalement constitué d'un mélange d'esters à base de polyol. Le liquide de refroidissement a un point d'écoulement d'environ -20 °C au maximum, et si possible même encore moins. Les esters à base de polyol sont choisis dans la formule (X): R1 et R2 sont sélectionnés dans une longueur de chaîne de carbone de C4 à C22 et un groupe alcoxycarbonyle ayant la formule CR3R4C2H2OCOR5, dans laquelle R5 représente des longueurs de chaîne de carbone de C4 à C22. R3 et R4 des longueurs de chaîne de carbone de C1 à C5 ou des groupes alcoxycarbonyles ayant la formule CH2OCOR6, où R6 est une longueur de chaîne de carbone de C4 à C22 ou un groupe alcoxycarbonyle correspondant à la formule CR3R4C2H2OCOR5. Il est préférable que l'ester à base de polyol soit sélectionné parmi les esters NPG, TMP et HPN.
PCT/CA2006/000045 2005-01-13 2006-01-13 Liquides de refroidissement dielectriques destines a s'utiliser dans un equipement electrique WO2006074553A1 (fr)

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WO2013159761A1 (fr) * 2012-04-26 2013-10-31 Fuchs Petrolub Ag Esters utilisés comme fluides de refroidissement et diélectriques liquides pour des transformateurs
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US8790553B2 (en) 2009-07-07 2014-07-29 3M Innovative Properties Company Electrical equipment containing erucic acid dielectric oil
US9028727B2 (en) 2011-09-23 2015-05-12 E I Du Pont De Nemours And Company Dielectric fluids comprising polyol esters
WO2016132156A1 (fr) * 2015-02-20 2016-08-25 M&I Materials Limited Compositions de fluide diélectrique à basse température
US9978477B2 (en) 2014-02-13 2018-05-22 M & I Materials Limited Dielectric fluids

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WO2014078156A1 (fr) 2012-11-13 2014-05-22 E. I. Du Pont De Nemours And Company Compositions d'huile mélangée utiles comme compositions de fluide diélectrique et procédés de préparation de ces dernières
US10448493B2 (en) * 2016-04-18 2019-10-15 Schlumberger Technology Corporation Control of discharge in high voltage fluid insulation

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US8790553B2 (en) 2009-07-07 2014-07-29 3M Innovative Properties Company Electrical equipment containing erucic acid dielectric oil
CN103890256A (zh) * 2011-08-26 2014-06-25 纳幕尔杜邦公司 包含非织造纤维网的绝缘材料
WO2013043311A1 (fr) * 2011-09-23 2013-03-28 E. I. Du Pont De Nemours And Company Fluides diélectriques comprenant des esters de polyol, procédés permettant de préparer des mélanges d'esters de polyol, et appareils électriques comprenant des fluides diélectriques à base d'esters de polyol
CN103827979A (zh) * 2011-09-23 2014-05-28 纳幕尔杜邦公司 包含多元醇酯的介电流体、制备多元醇酯的混合物的方法、以及包含多元醇酯介电流体的电气装置
US9028727B2 (en) 2011-09-23 2015-05-12 E I Du Pont De Nemours And Company Dielectric fluids comprising polyol esters
WO2013159761A1 (fr) * 2012-04-26 2013-10-31 Fuchs Petrolub Ag Esters utilisés comme fluides de refroidissement et diélectriques liquides pour des transformateurs
US20150090944A1 (en) * 2012-04-26 2015-04-02 Fuchs Petrolub Se Esters as Cooling and Insulating Fluids for Transformers
JP2015521341A (ja) * 2012-04-26 2015-07-27 フックス ペイトロルブ エスエー 変圧器のための冷却及び絶縁流体としてのエステル
US9666328B2 (en) 2012-04-26 2017-05-30 Fuchs Petrolub Se Esters as cooling and insulating fluids for transformers
US9978477B2 (en) 2014-02-13 2018-05-22 M & I Materials Limited Dielectric fluids
WO2016132156A1 (fr) * 2015-02-20 2016-08-25 M&I Materials Limited Compositions de fluide diélectrique à basse température
GB2548421A (en) * 2015-02-20 2017-09-20 M&I Mat Ltd Low Temperature Dielectric Fluid Compositions

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