Synthetic ester and mineral oil dielectric fluids with increased stability

Abstract

The present invention provides a dielectric fluid comprising oil and one or more compounds selected from the group consisting of phosphite compounds. It has been found that adding one or more compounds selected from the group consisting of phosphite compounds to a dielectric fluid comprising oil imparts a stabilizing effect that reduces, inhibits or prevents the formation of stray gases in the dielectric fluid during normal use.

Description

[0001] This application is a divisional application of international application date March 20, 2019, international application number PCT / US2019 / 023152, which entered the Chinese national phase on October 23, 2020, application number 201980027870.9, and invention name “Synthetic ester and mineral oil dielectric fluids with increased stability”. Technical Field

[0002] In one aspect, the present invention is directed to dielectric fluid compositions, including insulating oils, for use in electrical power distribution and power equipment including transformers, switch gears, and cables. Background Art

[0003] Dielectric (or insulation) fluids used for power distribution and power equipment (comprising transformer, switch gear and cable) perform two kinds of important functions.These fluids are used as electrical insulating medium, that is, show dielectric strength, and they are used as cooling medium by the heat transmission of generation.For example, when used in transformer, dielectric fluid transfers heat to cooling surface from winding and the core of transformer or circuit connected.Except having dielectric strength and cooling capacity, the ideal dielectric fluid for electrical equipment also shows very little adverse effect or no adverse effect to environment, is compatible with the material used to construct equipment, and is relatively non-flammable.

[0004] Dielectric oils have many specific functional properties. The dielectric breakdown or dielectric strength of an oil provides an indication of its ability to resist electrical breakdown and is measured as the minimum voltage required to cause an arc discharge between two electrodes at a specified gap immersed in the oil. The pulse dielectric breakdown voltage provides an indication of the ability of the oil to resist electrical breakdown under transient voltage stresses such as lightning and surges. The dissipation factor of an oil is a measure of the dielectric losses in the oil; a low dissipation factor indicates low dielectric losses and low concentrations of soluble polar contaminants. The gassing tendency of an oil measures the tendency of the oil to emit or absorb gas under conditions of partial discharge. Similarly, stray gassing can occur due to thermal stress of dielectric oils (such as transformer oils), resulting in the release of hydrogen, methane, ethane, ethylene, etc.

[0005] Since one function of a dielectric fluid is to carry and dissipate heat, factors that significantly affect the relative ability of a fluid to function as a dielectric coolant include viscosity, specific heat, thermal conductivity, and coefficient of expansion. The values ​​of these properties must be weighed when selecting an appropriate dielectric fluid for a particular application, especially over the operating temperature range of a fully rated device.

[0006] In addition to the above properties that affect heat transfer, the dielectric fluid should also have a relatively high dielectric strength, a low dissipation factor, a dielectric constant compatible with solid dielectrics, a low outgassing tendency, and it must be compatible with the electrical equipment materials to which it is exposed. Control of stray outgassing prevents the accumulation of explosive gases in the headspace of electrical equipment.

[0007] Dielectric fluids containing vegetable oils or blends of vegetable oils and containing one or more antioxidant compounds for use in electrical equipment are described in US Patent No. 7,651,641 to Corkran et al. Summary of the invention

[0008] The preparation dielectric fluid is to add an antioxidant based on di-tert-butylphenol with the typical practice of reducing the oxidation degradation effect.These antioxidants are by extracting hydrogen free radicals from the peroxide formed during oxidation, and chelating this free radical and working.Gained quinone methide and stilbenequinone are highly painted, which are considered to be harmful in some dielectric fluid applications or in the situation where color disturbs oiliness visualization.In addition, passivating agent such as aryl triazine is added in the dielectric fluid to reduce the catalysis of dissolved metal and metal surface to oxidation degradation, thereby prolonging the life-span of antioxidant.

[0009] The oil used as dielectric fluid, for example mineral oil, synthetic ester and particularly biologically derived oil, has the limitation of stability when used as dielectric fluid.Thermal degradation is confirmed by the generation of stray gases, which are selected from hydrogen, methane, ethane and ethene.The stray outgassing is measured according to ASTM D3612-02, and method C is measured.Specifically, oxidative degradation has increased hydrogen and ethane concentration of thermal degradation, and is usually accompanied by the generation of organic acid, alcohol and superoxide.Hydrogen and methane confirm the ionization deterioration caused by partial discharge (electron leakage), and arc discharge and electrostatic discharge are accompanied by the generation of hydrogen and acetylene.

[0010] It has been found that adding a phosphite component comprising one or more phosphite compounds to a dielectric fluid comprising oil imparts a stabilizing effect that reduces, inhibits or prevents the formation of stray gases in the dielectric fluid during normal use. Without being bound by theory, it is believed that adding one or more compounds selected from the group consisting of phosphite compounds to the dielectric fluid imparts a stabilizing effect prior to the formation of peroxides, thereby advantageously preventing the formation of gases.

[0011] On the one hand, a dielectric fluid is provided, which comprises oil and one or more compounds selected from the group consisting of phosphite compounds. On the one hand, a dielectric fluid is provided, which comprises oil and one or more compounds selected from the group consisting of phosphite compounds, and also comprises a non-phosphite antioxidant component selected from one or more non-phosphite antioxidant compounds.

[0012] In one aspect, a dielectric fluid formulated for use in power distribution or power plants is provided, the dielectric fluid comprising an oil and one or more compounds selected from the group consisting of phosphite compounds.

[0013] In one aspect, a method of insulating an electrical power distribution or power device is provided, the method comprising incorporating a dielectric fluid as described herein into the electrical power distribution or power device.

[0014] In one aspect, there is provided an electrical power distribution or power device comprising a dielectric fluid as described herein. DETAILED DESCRIPTION

[0015] The various aspects of the present invention described below are not intended to be exhaustive or to limit the present invention to the exact forms disclosed in the detailed description below. On the contrary, the purpose of the various aspects selected and described is to facilitate the understanding and appreciation of the general principles and practices of the present invention by other persons skilled in the art by way of illustration or example.

[0016] In one aspect, the dielectric fluid comprises an oil selected from the group consisting of biologically derived oils, synthetic ester oils, mineral oils, and mixtures thereof.

[0017] On the one hand, the dielectric fluid comprises an oil of biological origin. For the purposes of the present disclosure, an oil of biological origin is an oil derived from a plant or animal source. On the one hand, an oil of biological origin is refined, bleached and deodorized ("RBD") oil. On the one hand, the dielectric fluid comprises an oil of biological origin of at least 75 % by weight. On the one hand, the dielectric fluid comprises an oil of biological origin of at least 85 % by weight. On the one hand, the dielectric fluid comprises an oil of biological origin of at least 90 % by weight. On the one hand, the dielectric fluid comprises an oil of biological origin of at least 95 % by weight. On the one hand, the dielectric fluid comprises an oil of biological origin of at least 98 % by weight. On the one hand, only oil in the dielectric fluid is an oil of biological origin.

[0018] The oil of biological origin is especially expected to be used in the dielectric fluid of the present invention, because they derive from renewable resources and are generally easy to biodegradation.On the one hand, the oil of biological origin has the additional characteristic that increases the paper stability in transformer application.Different from mineral oil, the oil of biological origin brings the benefit of high flash point and ignition point characteristic, low flammability and low flame propagation.Flash point, ignition point and the ignitability of synthetic esters are highly dependent on composition.Under certain conditions, mineral oil stands explosion and flame propagation, and its effect is similar to gasoline around the ignition source.The oil of biological origin with unsaturation provides useful flow characteristics, and the unsaturation that wherein reduces the viscosity of oil is relevant to increase.

[0019] On the one hand, the oil in the dielectric fluid is the oil of natural biological origin, which means that it derives from plant or animal origin, and this plant or animal origin is not yet modified by reaction chemistry (for example, by transesterification or forming oil derivative product).For the sake of clarity, it should be understood that the modified vegetable oil or animal oil by transesterification (that is, the redistribution of the fatty acid moiety present in the triglyceride oil on its glycerol moiety) is considered to the oil of natural biological origin.In addition, it should be understood that the vegetable oil or animal oil obtained by extracting is considered to the oil of natural biological origin.

[0020] On the one hand, the dielectric fluid comprises vegetable oil.On the one hand, the dielectric fluid comprises vegetable oil, and this vegetable oil is selected from the group consisting of the following: castor oil, coconut oil, corn oil, cottonseed oil, crambe (crambie) oil, linseed oil, jojoba oil, macadamia oil, lesquerer oil, flax seed oil, olive oil, palm oil, peanut oil, pine nut oil, rapeseed oil, safflower oil, sunflower oil, soybean oil and Veronica oil and their mixture.On the one hand, only oil in the dielectric fluid is vegetable oil.On the one hand, only oil in the dielectric fluid is vegetable oil, and this vegetable oil is selected from the group consisting of the following: castor oil, coconut oil, corn oil, cottonseed oil, crambe (crambie) oil, linseed oil, jojoba oil, macadamia oil, lesquerer oil, flax seed oil, olive oil, palm oil, peanut oil, pine nut oil, rapeseed oil, safflower oil, sunflower oil, soybean oil and Veronica oil and their mixture. On the one hand, only oil in the dielectric fluid is a vegetable oil.On the one hand, the dielectric fluid that comprises vegetable oil can provide the oil composition that can be commercially obtained, and this oil composition is further modified by adding phosphite compounds.For example, Envirotemp FR3 is the natural ester fluid that is made of soybean oil and additive (di-tert-butylphenol antioxidant, pour point additive, dyestuff).Other similar fluids that can derive from renewable resources comprise MideleN (based on Semen Brassicae Campestris).These materials can be modified to reduce stray outgassing by adding phosphite compounds.

[0021] In one aspect, the dielectric fluid comprises natural oils obtained from microorganisms, algae, and similar organic sources.

[0022] In one aspect, the dielectric fluid comprises an animal oil. In one aspect, the only oil in the dielectric fluid is an animal oil. Representative examples of animal oils include tallow, lard, fish oil, or chicken fat.

[0023] On the one hand, dielectric fluid comprises synthetic oil.On the one hand, synthetic oil is the oil as the product of chemical reaction, this chemical reaction relates to by making polyol and saturated or undersaturated straight and branched carboxylic acid react and form ester, aryl ester, C5-C12 saturated or undersaturated straight and branched ester, and their mixture, or by reaction chemistry (for example by transesterification or forming oil derivative product) carry out the chemical modification of source oil.Therefore, for the purpose of this discussion, the oil obtained from plant or animal source by the chemical modification of transesterification is synthetic oil.On the one hand, dielectric fluid comprises synthetic oil, and this synthetic oil is prepared by the reactant of the oil that only derives from plant or animal biological source.

[0024] In one aspect, the synthetic ester oil comprises a synthetic ester of a polyol selected from glycerol, pentaerythritol, trimethylolpropane (TMP), hydroxylated fatty acids, and polyglycerols. In one aspect, the synthetic ester is formed by reacting a polyol with a compound selected from the group consisting of C5-C25 saturated or unsaturated straight and branched carboxylic acids, C5-C12 saturated or unsaturated straight and branched carboxylic acids, aryl esters, C5-C12 saturated or unsaturated straight and branched esters, C5-C25 saturated or unsaturated straight and branched esters, and mixtures thereof.

[0025] In one aspect, the dielectric fluid comprises a synthetic ester selected from the group consisting of esters of C5 to C24 branched and straight chain aliphatic carboxylic acids with pentaerythritol, dipentaerythritol, 2,2-dimethylpropylene glycol, 2,2-dimethyl-3-isopropyl-1,3-propanediol, trimethylolpropane, glycerol, neopentyl glycol, 2,2-dimethylolbutane, trimethylolethane, sorbitol, (C2 to C12 glycols)ethylene glycol, propylene glycol, 1,4-butanediol and 2-methylpropylene glycol, and mixtures thereof.

[0026] In one aspect, the dielectric fluid comprises a synthetic ester selected from the group consisting of esters of C5 to C24 branched and straight chain aliphatic alcohols and acids selected from the group consisting of adipic acid, suberic acid, azelaic acid, sebacic acid, phthalic acid, oxalic acid, glycolic acid, fumaric acid, and mixtures thereof.

[0027] In one aspect, the only oil in the dielectric fluid is a synthetic oil.

[0028] On the one hand, the dielectric fluid comprises mineral oil. On the one hand, the dielectric fluid comprises mineral oil, and the mineral oil is selected from the group consisting of straight and branched aliphatic paraffin hydrocarbons, and it has a molecular weight of about 220 to about 700, or about 500 to about 700. On the one hand, the dielectric fluid comprises mineral oil, and the mineral oil has a fire point of about 120 ℃ to about 250 ℃, or has a fire point of about 140 ℃ to about 200 ℃. On the one hand, the dielectric fluid comprises mineral oil, and the mineral oil has a fire point higher than 200 ℃. On the one hand, the dielectric fluid comprises mineral oil, and the mineral oil is selected from the group consisting of a mixture of cycloparaffin oil and aforementioned paraffin and cycloparaffin with similar characteristics, such as described in U.S. Patent No. 4082866, and its disclosure is incorporated herein by reference. On the one hand, the only oil in the dielectric fluid is mineral oil.

[0029] On the one hand, the dielectric fluid comprises a mixture of oil from biological origin and mineral oil. On the one hand, the dielectric fluid comprises a mixture of vegetable oil and mineral oil. On the one hand, the dielectric fluid comprises a mixture of synthetic ester oil and mineral oil. On the one hand, the dielectric fluid comprises a mixture of synthetic ester oil and oil from biological origin. On the one hand, the dielectric fluid comprises a mixture of synthetic ester oil and vegetable oil. On the one hand, the dielectric fluid comprises a mixture of synthetic ester oil, oil from biological origin and mineral oil. On the one hand, the dielectric fluid comprises a mixture of synthetic ester oil, vegetable oil and mineral oil.

[0030] Have found that the unsaturation degree that increases in oil is associated with the stray outgassing of increase with branching.In the oil with the unsaturation degree of significant amount and branching, adding phosphite compounds to reduce stray outgassing becomes more important.It should be noted that the oil with relatively low unsaturation degree or without unsaturation degree (for example having less than 50 iodine value) greatly benefits by mixing phosphite compounds as described herein.But the oil with the unsaturation degree of relatively high amount even more significantly benefits from adding phosphite compounds to reduce stray outgassing.On the one hand, dielectric fluid comprises the oil with 50 to 200 IV.On the one hand, dielectric fluid comprises the oil with 80 to 200 IV.On the one hand, dielectric fluid comprises the oil with 100 to 200 IV.On the one hand, dielectric fluid comprises the oil with 110 to 200 IV.

[0031] For purposes of this disclosure, "iodine value" (IV) is defined as the number of grams of iodine that will react with 100 grams of the material being measured. Iodine value is a measure of the unsaturation (carbon-carbon double bonds and carbon-carbon triple bonds) present in a material. Iodine value is reported in grams of iodine (I2) / 100 grams of material and is determined using the procedure of AOCS Cd Id-92.

[0032] On the one hand, the dielectric fluid does not contain organosilicon compounds, or does not contain phosphatide, or does not contain pigment, or does not contain lecithin, or does not contain fatty acid, or does not contain monoglyceride and diglyceride, or does not contain acid, or does not contain alcohol, or does not contain color impurities, or does not contain sulfur compounds, or does not contain cresols, or does not contain polycyclic aromatic hydrocarbons, or does not contain acid, or does not contain halogenated compounds, or does not contain amine.On the one hand, the dielectric fluid comprises the oil in natural biological source and does not contain phosphatide, or does not contain pigment, or does not contain lecithin, or does not contain fatty acid, or does not contain monoglyceride and diglyceride.On the one hand, the dielectric fluid comprises synthetic ester oil and does not contain acid, or does not contain alcohol, or does not contain color impurities.On the one hand, the dielectric fluid comprises mineral oil and has sulfur compounds, or does not contain cresols, or does not contain polycyclic aromatic hydrocarbons, or does not contain acid, or does not contain halogenated compounds, or does not contain amine.

[0033] On the one hand, the dielectric fluid comprises highly purified oil. For the purposes of this disclosure, an oil is "highly purified" if it is treated on a clay medium (such as silicates, aluminates, etc.) to remove polar compounds and impurities and then filtered to substantially remove particles that would be retained by a 1 micron filter. On the one hand, the dielectric fluid comprises highly purified oil of biological origin.

[0034] Have been found that, when selecting to be used in the oil of dielectric fluid, advantageously this oil has low initial peroxide value, makes it possible to avoid undesirable side reaction and gaseous escape from the beginning.Preferably, the peroxide value in transformer oil is kept lower by degassing and maintaining inertia (nitrogen sealing) head space, makes additive be used in target oil maintenance during use, and need not be corrected on the oil condition produced before they are introduced into the application.Along with the time that dielectric fluid is exposed to atmosphere or oxidizing conditions, the peroxide value of oil in dielectric fluid can for example be increased to about 8 or 10 or even higher higher peroxide value from the very low initial peroxide value being less than about 1.Have been found that phosphite compounds especially effectively suppress the gas generation in dielectric fluid, wherein oil has the initial peroxide value being less than 5, or wherein oil has the initial peroxide value being less than 3, or wherein oil has the initial peroxide value being less than 2, or wherein oil has the initial peroxide value being less than 1. On the one hand, the oil used in the dielectric fluid has an initial peroxide value of about 0.01 to 5, or has an initial peroxide value of about 0.01 to 3, or has an initial peroxide value of about 0.01 to 2, or has an initial peroxide value of about 0.01 to 1, or has an initial peroxide value of about 0.1 to 1. For purposes of this disclosure, "peroxide value" is determined by AOCS method Cd 8b-90. However, it should be noted that the dielectric fluid with high initial peroxide value shows the minimizing of stray outgassing by adding phosphite compounds as described herein.

[0035] In one aspect, the dielectric fluid comprises one or more compounds selected from the group consisting of phosphite compounds.

[0036] On the one hand, compared with the similar dielectric fluid composition that does not comprise the phosphite component, the phosphite component is enough to be present in the amount of hydrogen (H2) of the dielectric fluid determined by dissolved gas analysis (ASTM D3612-02, method C) reducing by at least 60% outgassing.On the one hand, compared with the similar dielectric fluid composition that does not comprise the phosphite component, the phosphite component is enough to be present in the amount of H2 outgassing of the dielectric fluid determined by dissolved gas analysis reducing by at least 70%.On the one hand, compared with the similar dielectric fluid composition that does not comprise the phosphite component, the phosphite component is enough to be present in the amount of H2 outgassing of the dielectric fluid determined by dissolved gas analysis reducing by at least 80%.

[0037] On the one hand, compared with the similar dielectric fluid composition that does not comprise the phosphite component, the phosphite component exists with the amount that is enough to reduce the ethane outgassing of the dielectric fluid determined by dissolved gas analysis (ASTM D3612-02, method C) by at least 60%.On the one hand, compared with the similar dielectric fluid composition that does not comprise the phosphite component, the phosphite component exists with the amount that is enough to reduce the ethane outgassing of the dielectric fluid determined by dissolved gas analysis by at least 70%.On the one hand, compared with the similar dielectric fluid composition that does not comprise the phosphite component, the phosphite component exists with the amount that is enough to reduce the ethane outgassing of the dielectric fluid determined by dissolved gas analysis by at least 80%.

[0038] On the one hand, compared with the similar dielectric fluid composition that does not comprise the phosphite component, the phosphite component exists in an amount that is enough to reduce the methane outgassing of the dielectric fluid determined by dissolved gas analysis (ASTM D3612-02, method C) by at least 60%.On the one hand, compared with the similar dielectric fluid composition that does not comprise the phosphite component, the phosphite component exists in an amount that is enough to reduce the methane outgassing of the dielectric fluid determined by dissolved gas analysis by at least 70%.On the one hand, compared with the similar dielectric fluid composition that does not comprise the phosphite component, the phosphite component exists in an amount that is enough to reduce the methane outgassing of the dielectric fluid determined by dissolved gas analysis by at least 80%.

[0039] On the one hand, compared with the similar dielectric fluid composition that does not comprise the phosphite component, the phosphite component exists with the amount that is enough to reduce the ethylene outgassing of the dielectric fluid determined by dissolved gas analysis (ASTM D3612-02, method C) by at least 60%.On the one hand, compared with the similar dielectric fluid composition that does not comprise the phosphite component, the phosphite component exists with the amount that is enough to reduce the ethylene outgassing of the dielectric fluid determined by dissolved gas analysis by at least 70%.On the one hand, compared with the similar dielectric fluid composition that does not comprise the phosphite component, the phosphite component exists with the amount that is enough to reduce the ethylene outgassing of the dielectric fluid determined by dissolved gas analysis by at least 80%.

[0040] On the one hand, compared with the similar dielectric fluid composition that does not comprise the phosphite component, the phosphite component is enough to reduce the hydrogen outgassing of the dielectric fluid determined by dissolved gas analysis (ASTM D3612-02, method C) by at least 60%, and the ethane outgassing of the dielectric fluid determined by dissolved gas analysis (ASTM D3612-02, method C) is reduced by at least 60% in addition and exists.On the one hand, compared with the similar dielectric fluid composition that does not comprise the phosphite component, the phosphite component is enough to reduce the hydrogen outgassing of the dielectric fluid determined by dissolved gas analysis by at least 70%, and the ethane outgassing of the dielectric fluid determined by dissolved gas analysis is reduced by at least 70% in addition and exists.On the one hand, compared with the similar dielectric fluid composition that does not comprise the phosphite component, the phosphite component is enough to reduce the hydrogen outgassing of the dielectric fluid determined by dissolved gas analysis by at least 80%, and the ethane outgassing of the dielectric fluid determined by dissolved gas analysis is reduced by at least 80% in addition and exists.

[0041] On the one hand, the phosphite component is present in the dielectric fluid in an amount of 0.05 to the solubility limit. On the one hand, the phosphite component is present in the dielectric fluid in an amount of 0.1 to the solubility limit. On the one hand, the phosphite component is present in an amount of 0.05 weight % to 4 weight %. On the one hand, the phosphite component is present in an amount of 0.05 weight % to 3 weight %. On the one hand, the phosphite component is present in an amount of 0.05 weight % to 2 weight %. On the one hand, the phosphite component is present in an amount of 0.05 weight % to 1.5 weight %. On the one hand, the phosphite component is present in an amount of 0.05 weight % to 1 weight %. On the one hand, the phosphite component is present in an amount of 0.05 weight % to 0.5 weight %. On the one hand, the phosphite component is present in an amount of 0.1 weight % to 4 weight %. On the one hand, the phosphite component is present in an amount of 0.1 weight % to 3 weight %. In one aspect, the phosphite component is present in an amount of 0.1 wt % to 2 wt %. In one aspect, the phosphite component is present in an amount of 0.1 wt % to 1.5 wt %. In one aspect, the phosphite component is present in an amount of 0.1 wt % to 1 wt %. In one aspect, the phosphite component is present in an amount of 0.1 wt % to 0.5 wt %.

[0042] In one aspect, the dielectric fluid comprises one or more compounds selected from the group consisting of water-stable phosphite compounds. For purposes of this disclosure, a phosphite compound is defined as being water-stable if, when a solid sample of the phosphite compound is placed in a chamber at 60° C., 85% relative humidity and sampled to determine the % hydrolysis over time, the sample does not hydrolyze more than 30% within 80 minutes.

[0043] In one aspect, the dielectric fluid comprises one or more compounds selected from the group consisting of phosphite compounds selected from the group consisting of phosphites, triarylphosphites, trialkylphosphites, cyclic phosphites, diaryl pentaerythritol cyclic phosphites, and the like.

[0044] On the one hand, the phosphite component is selected from the group consisting of phosphite compounds or selected from phosphite compounds, and the phosphite compounds have one to three aryloxy groups. On the one hand, the phosphite component is selected from aryl phosphite compounds. On the one hand, the phosphite component is selected from triaryl phosphite compounds. On the one hand, the phosphite component is selected from the group consisting of phosphite compounds or selected from phosphite compounds, and the phosphite compounds are cyclic esters and diaryl pentaerythritol phosphite cyclic esters. On the one hand, the phosphite component is selected from the group consisting of the following: cyclic aryl phosphites, cyclic alkyl-aryl phosphites, aryl cyclic phenoxy phosphites, diaryl phosphites, alkyl aryl phosphites and mixtures thereof.

[0045] In one aspect, the phosphite component is selected from the group consisting of tris-(2,4-di-tert-butylphenyl)phosphite (commercially available, for example, as Irgafos 168); bis(2,4-dicumylphenylpentaerythritol diphosphite (commercially available, for example, as Doverphos S-9228); trisnonylphenylphosphite (commercially available, for example, as Adela ADK stabilizer 1178 or Doverphos 4); 1,3,7,9-tetra-tert-butyl-11-(2-ethylhexyloxy)-5H-benzo[d][1,3,2]-benzodioxaphosphane (commercially available, for example, as Amfine HP-10); 3,9-bis(2,6-di-tert-butyl-4-methylphenoxy)-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5]undecane (commercially available, for example, as Amfine PEP-36A is commercially available); bis(2,4-di-tert-butylphenol)pentaerythritol diphosphite (commercially available as Irgafos 126); 4,4'-isopropyldiphenol C12-15 alcohol phosphite (commercially available, for example, as Amfine 1500); 3,9-diphenoxy-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5]undecane; 3,9-bis(octadecyloxy)-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5]undecane (commercially available, for example, as Amfine PEP-8); triphenylphosphite (commercially available, for example, as Amfine TPP or Doverphos 10); isodecyl diphenylphosphite (commercially available, for example, as Adela ADK stabilizer 135A or Doverphos 8); phenyl diisodecyl phosphite (commercially available, for example, as Doverphos 7); diisodecyl pentaerythritol diphosphite (commercially available, for example, as Doverphos 1220); distearyl pentaerythritol diphosphite (commercially available, for example, as Doverphos S-680); trilauryl phosphite (commercially available, for example, as Doverphos 53); alkyl (C 12 -C 15 ) bisphenol A phosphite (commercially available, for example, as Doverphos 613); alkyl (C 10 ) bisphenol A phosphite (commercially available, for example, as Doverphos 675); 2-ethylhexyl diphenyl phosphite (commercially available, for example, as Amfine C); 5,5-dimethyl-2-phenoxy-1,3,2-dioxaphosphinane; methyl diphenyl phosphite; and mixtures thereof.

[0046] On the one hand, the dielectric fluid comprising the phosphite compound also comprises a non-phosphite antioxidant component, and the non-phosphite antioxidant component comprises one or more non-phosphite antioxidant compounds. It has been found that in the dielectric fluid comprising the phosphite compound, one or more non-phosphite antioxidant compounds are mixed to supplement and further enhance the protection of the dielectric fluid to prevent oxidative degradation. In addition, compared with similar compositions not comprising the non-phosphite antioxidant component, on the one hand, it has been found that in the dielectric fluid comprising the phosphite compound, one or more non-phosphite antioxidant compounds are mixed to suppress the viscosity increase over time. On the one hand, it has been found that the non-phosphite antioxidant component, and especially the presence of phenolic antioxidant compounds is conducive to providing oxidation stability in the composition exposed to oxygen. Therefore, on the one hand, the composition comprising both the phosphite component and the non-phosphite antioxidant component in the composition shows good stray gas suppression characteristics and oxidation stability, as determined by measuring oxidation induction time (" OIT ") (measured according to ASTM D6186-98 at the temperature). The OIT test was conducted at an air pressure of 500 + / - 25 psig and an air flow rate of 100 + / - 10 ml / min.

[0047] It should be noted that the presence of conventional antioxidants (non-phosphite antioxidant compounds, particularly phenolic antioxidants) does not prevent the formation of peroxides, but is used to degrade peroxides after peroxide formation. In addition, the peroxide value of the biologically derived oil with air in the headspace will increase over time. Can be by replacing the oxygen atmosphere with an inert gas (such as nitrogen or argon) and reducing oxidation by degassing the fluid. However, conventional antioxidants will not effectively reduce peroxide accumulation at ambient temperature usually. The temperature increased is effective in increasing the interaction between conventional antioxidants and peroxides, but also increases the thermal degradation rate of oil. At about 120 ℃, the peroxide degradation rate increases to exceed the peroxide formation rate. In the presence of conventional antioxidants, alcohol is the byproduct of peroxide degradation. In the absence of antioxidants, peroxide substances degrade to form acid.

[0048] It has been observed that increased peroxide content also contributes to increased stray gassing. However, by using phosphite compounds as described herein, stray gassing produced by degradation through peroxide formation and this form of degradation is significantly reduced.

[0049] When the oil used is mineral oil, it has been found that peroxide formation and degradation of mineral oil dielectric compositions tends to accelerate at about 120° C. For this reason, heating mineral oil based dielectric compositions for the purpose of controlling peroxides by interaction with conventional antioxidants in the composition is not a preferred approach.

[0050] In one aspect, the additional non-phosphite antioxidant component is selected from phenolic antioxidants, and in one aspect is a di-tert-butylphenol analog. In one aspect, the non-phosphite antioxidant component is selected from the group consisting of butylated hydroanisole (BHA), butylated hydrotoluene (BHT), tert-butylhydroquinone (TBHQ), tetrahydrobutyrophenone (THBP), ascorbyl palmitate (rosemary oil), propyl gallate, and alpha-tocopherol, beta-tocopherol or delta-tocopherol (vitamin E) and mixtures thereof.

[0051] In one aspect, the additional non-phosphite antioxidant component is selected from the group consisting of: pentaerythritol tetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate) (commercially available, for example, as Iganox L101, Irganox 1010, BNX1010); hexamethylene bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (commercially available, for example, as Irganox L109); octadecyl-[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (commercially available, for example, as Irganox 1076); ethylene bis(oxyethylene) bis-(3-(5-tert-butyl-4-hydroxy-m-tolyl) propionate) (commercially available, for example, as Irganox 2,6-di-tert-butyl-4-(4,6-bis(octylthio)-1,3,5-triazin-2-ylamino)phenol (commercially available, for example, as Irganox 565); N,N′-hexane-1,6-diylbis(3-3,5-di-tert-butyl-4-hydroxyphenylpropionamide) (commercially available, for example, as Irganox 1098); 4,6-bis(octylthiomethyl)-o-cresol (commercially available, for example, as Irganox 1520); 4,4′-methylene-bis-2,6-di-tert-butylphenol (commercially available, for example, as Ethanox 4702); and 2,6-di-tert-butyl-4-methylphenol (BHT).

[0052] On the one hand, it has been found that within a specific range, the amount of the phosphite component in the composition, the amount of the non-phosphite antioxidant component in the composition, and the relative ratio of the phosphite component to the non-phosphite antioxidant component exhibit particularly excellent properties in terms of inhibiting the generation of stray gases and controlling redox. On the one hand, it has been found that incorporating too much non-phosphite antioxidant component relative to the amount of the phosphite component may adversely affect the inhibition of stray gas generation.

[0053] In one aspect, the phosphite component is present in the dielectric fluid composition in an amount from about 0.05 weight percent to the solubility limit of the phosphite component, and the non-phosphite antioxidant component is present in an amount such that the ratio of the phosphite component to the non-phosphite antioxidant component is 1 part phosphite component to 0 to 1.2 parts non-phosphite antioxidant component.

[0054] In one aspect, the phosphite component is present in the dielectric fluid composition in an amount from about 0.2 weight percent to the solubility limit of the phosphite component, and the non-phosphite antioxidant component is present in an amount such that the ratio of the phosphite component to the non-phosphite antioxidant component is 1 part phosphite component to 0 to 1.2 parts non-phosphite antioxidant component.

[0055] In one aspect, the phosphite component is present in an amount from about 0.2 weight percent to about 1 weight percent, and the non-phosphite antioxidant component is present in an amount such that the ratio of the phosphite component to the non-phosphite antioxidant component is 1 part phosphite component to 0 to 1.2 parts non-phosphite antioxidant component.

[0056] In one aspect, the phosphite component is present in the dielectric fluid composition in an amount from about 0.4 weight percent to the solubility limit of the phosphite component, and the non-phosphite antioxidant component is present in an amount such that the ratio of the phosphite component to the non-phosphite antioxidant component is 1 part phosphite component to 0 to 1.2 parts non-phosphite antioxidant component.

[0057] In one aspect, the phosphite component is present in an amount from about 0.4 weight percent to about 0.6 weight percent, and the non-phosphite antioxidant component is present in an amount such that the ratio of the phosphite component to the non-phosphite antioxidant component is 1 part phosphite component to 0 to 1.2 parts non-phosphite antioxidant component.

[0058] In one aspect, the phosphite component is present in the dielectric fluid composition in an amount from about 0.05 weight % to the solubility limit of the phosphite component, and the phosphite component is present in the dielectric fluid composition in an amount from about 0.05 weight % to the solubility limit of the non-phosphite antioxidant component; and further, provided that the ratio of the phosphite component to the non-phosphite antioxidant component is 1 part phosphite component to 0 to 1.2 parts non-phosphite antioxidant component.

[0059] In one aspect, the phosphite component is present in the dielectric fluid composition in an amount from about 0.2 weight percent to the solubility limit of the phosphite component, and the phosphite component is present in the dielectric fluid composition in an amount from about 0.05 weight percent to the solubility limit of the non-phosphite antioxidant component; and further, provided that the ratio of the phosphite component to the non-phosphite antioxidant component is 1 part phosphite component to 0 to 1.2 parts non-phosphite antioxidant component.

[0060] In one aspect, the phosphite component is present in an amount from about 0.2 weight percent to about 1 weight percent, the phosphite component being present in the dielectric fluid composition in an amount from about 0.05 weight percent to the solubility limit of the non-phosphite antioxidant component; and further, provided that the ratio of the phosphite component to the non-phosphite antioxidant component is 1 part phosphite component to 0 to 1.2 parts non-phosphite antioxidant component.

[0061] In one aspect, the phosphite component is present in the dielectric fluid composition in an amount from about 0.4 weight percent to the solubility limit of the phosphite component, and the phosphite component is present in the dielectric fluid composition in an amount from about 0.05 weight percent to the solubility limit of the non-phosphite antioxidant component; and further, provided that the ratio of the phosphite component to the non-phosphite antioxidant component is 1 part phosphite component to 0 to 1.2 parts non-phosphite antioxidant component.

[0062] In one aspect, the phosphite component is present in an amount from about 0.4 weight percent to about 0.6 weight percent, the phosphite component being present in the dielectric fluid composition in an amount from about 0.05 weight percent to the solubility limit of the non-phosphite antioxidant component; and further, provided that the ratio of the phosphite component to the non-phosphite antioxidant component is 1 part phosphite component to 0 to 1.2 parts non-phosphite antioxidant component.

[0063] In one aspect, the phosphite component is present in the dielectric fluid composition in an amount of about 0.4 weight % to the solubility limit of the phosphite component, and the phosphite component is present in the dielectric fluid composition in an amount of about 0.2 weight % to the solubility limit of the non-phosphite antioxidant component; and further, provided that the ratio of the phosphite component to the non-phosphite antioxidant component is 1 part phosphite component to 0 to 1.2 parts non-phosphite antioxidant component.

[0064] In one aspect, the phosphite component is present in an amount from about 0.4 wt. % to about 0.6 wt. %, the phosphite component being present in the dielectric fluid composition in an amount from about 0.2 wt. % to the solubility limit of the non-phosphite antioxidant component; and further, provided that the ratio of the phosphite component to the non-phosphite antioxidant component is 1 part phosphite component to 0 to 1.2 parts non-phosphite antioxidant component.

[0065] In one aspect, the phosphite component is present in the dielectric fluid composition in an amount from about 0.4 weight % to the solubility limit of the phosphite component, and the phosphite component is present in the dielectric fluid composition in an amount from about 0.3 weight % to the solubility limit of the non-phosphite antioxidant component; and further, provided that the ratio of the phosphite component to the non-phosphite antioxidant component is 1 part phosphite component to 0 to 1.2 parts non-phosphite antioxidant component.

[0066] In one aspect, the phosphite component is present in an amount from about 0.4 weight percent to about 0.6 weight percent, and the phosphite component is present in the dielectric fluid composition in an amount from about 0.3 weight percent to the solubility limit of the non-phosphite antioxidant component; and further, provided that the ratio of the phosphite component to the non-phosphite antioxidant component is 1 part phosphite component to 0 to 1.2 parts non-phosphite antioxidant component.

[0067] On the one hand, dielectric fluid also comprises metal passivator.It has been found that mixing metal passivator can be used in dielectric fluid, especially those dielectric fluids comprising synthetic ester oil.Not bound by theory, it is believed that metal passivator is used to reduce the catalysis of metal and metal surface to oxidative degradation dissolved in dielectric fluid use environment.In addition, it has been found that the dielectric fluid composition comprising metal passivator in addition as described herein also shows low fluid dissipation factor value (and therefore reducing electrostatic charging trend) under the condition of long-term oxidative stress.

[0068] In one aspect, the metal deactivator is selected from benzotriazole or a derivative thereof. In one aspect, the metal deactivator is selected from N,N-bis(2-ethylhexyl)-arylmethyl-1H-benzotriazole-1-methylamine (commercially available, for example, as Irgamet 39); N,N-bis(2-ethylhexyl)-1H-1,2,4-triazole-1-methylamine (commercially available, for example, as Irgamet 30); 1H-benzotriazole (commercially available, for example, as Irgamet BTZ); methyl-1H-benzotriazole (commercially available, for example, as Irgamet TTZ); butyl-1H-benzotriazole; and 2,2'-[[(methyl-1H-benzotriazol-1-yl)methyl]imino]bis-ethanol (commercially available, for example, as Irgamet 42).

[0069] On the one hand, metal passivator exists with the amount of about 0.001 % by weight to 2 % by weight of dielectric fluid. On the one hand, metal passivator exists with the amount of about 0.005 % by weight to 1 % by weight of dielectric fluid. On the one hand, metal passivator exists with the amount of about 0.005 % by weight to 0.4 % by weight (that is, 50ppm to 4000ppm) of dielectric fluid.

[0070] On the one hand, when the oil of the dielectric fluid is a synthetic ester, the metal passivator is present in an amount sufficient to control the dissipation value of the dielectric fluid determined by IEC 60247 (120° C.) to be equal to or less than 0.10 (10%) in a 164-hour oxidation stability test evaluated according to IEC 61125 Method C. On the one hand, when the oil of the dielectric fluid is a synthetic ester oil, the metal passivator is present in an amount sufficient to control the dissipation value of the dielectric fluid determined by IEC 60247 (120° C.) to be equal to or less than 0.30 (30%) in a 164-hour oxidation stability test evaluated according to IEC 61125 Method C. On the one hand, when the oil of the dielectric fluid is a synthetic ester oil, the metal passivator is present in an amount sufficient to control the dissipation value of the dielectric fluid determined by IEC 60247 (120° C.) to be equal to or less than 0.50 (50%) in a 164-hour oxidation stability test evaluated according to IEC 61125 Method C.

[0071] In one aspect, when the oil of the dielectric fluid is a synthetic ester, the metal deactivator is present in an amount sufficient to control the dissipation value of the dielectric fluid as determined by IEC 60247 (120° C.) to be equal to or less than 0.30 (30%), or equal to or less than 0.60 (60%), or equal to or less than 0.90 (90%), or equal to or less than 1.0 (100%) in an 800 hour oxidation stability test evaluated according to IEC 61125 Method C.

[0072] In one aspect, when the oil of the dielectric fluid is a synthetic ester oil, the metal deactivator is present in an amount sufficient to control the dissipation value of the dielectric fluid determined by IEC 60247 (120° C.) to be equal to or less than 0.60 (60%) in a 164 hour oxidation stability test evaluated according to IEC 61125 Method C.

[0073] In one aspect, when the oil of the dielectric fluid is a synthetic ester oil, the metal deactivator is present in an amount sufficient to control the dissipation value of the dielectric fluid determined by IEC 60247 (120° C.) to be equal to or less than 0.90 (90%) in a 164 hour oxidation stability test evaluated according to IEC 61125 Method C.

[0074] In one aspect, when the oil of the dielectric fluid is a synthetic ester oil, the metal deactivator is present in an amount sufficient to control the dissipation value of the dielectric fluid determined by IEC 60247 (120° C.) to be equal to or less than 1.0 (100%) in a 164 hour oxidation stability test evaluated according to IEC 61125 Method C.

[0075] In one aspect, when the oil of the dielectric fluid is an oil of biological origin, the metal passivator is present in an amount sufficient to control the dissipation value of the dielectric fluid determined by IEC 601125 (120° C.) to be equal to or less than 0.50 (50%) in a 48 hour oxidation stability test evaluated according to IEC 61125 Method C.

[0076] In one aspect, when the oil of the dielectric fluid is a mineral oil, the metal passivator is present in an amount sufficient to control the dissipation value of the dielectric fluid determined by IEC 60247 (120° C.) to equal or below 0.50 (50%) in a 500 hour oxidation stability test evaluated according to IEC 61125 Method C.

[0077] In one aspect, the oil selected dielectric fluid component, phosphite compound, optional non-phosphite antioxidant component, and optional metal passivator are selected to provide specific physical properties such as:

[0078] In one aspect, when the oil of the dielectric fluid is an oil of biological origin or a synthetic ester oil, the dielectric fluid has a flash point greater than 250° C. as determined by ISO 2719. In one aspect, when the oil of the dielectric fluid is an oil of biological origin or a synthetic ester oil, the dielectric fluid has a flash point greater than 270° C. as determined by ISO 2719. In one aspect, when the oil of the dielectric fluid is a mineral oil, the dielectric fluid has a flash point greater than 135° C. as determined by ISO 2719.

[0079] In one aspect, the dielectric fluid has a fire point greater than 300°C as determined by ISO 2592. In one aspect, the dielectric fluid has a fire point greater than 310°C as determined by ISO2592.

[0080] In one aspect, the dielectric fluid has a pour point less than -5°C, as determined by ISO 3016. In one aspect, the dielectric fluid has a pour point less than -10°C, as determined by ISO 3016. In one aspect, the dielectric fluid has a pour point less than -20°C, as determined by ISO 3016.

[0081] In one aspect, the dielectric fluid has a pour point of less than -25°C, as determined by ISO 3016. In one aspect, the dielectric fluid has a pour point of less than -30°C, as determined by ISO 3016. In one aspect, the dielectric fluid has a pour point of less than -45°C, as determined by ISO 3016. In one aspect, when the oil of the dielectric fluid is an oil of biological origin or a synthetic ester oil, the dielectric fluid has a pour point of less than -10°C, as determined by ISO 3016. In one aspect, when the oil of the dielectric fluid comprises soybean-based oil, the dielectric fluid has a pour point of less than -15°C, as determined by ISO 3016, or has a pour point of less than -20°C, as determined by ISO 3016. In one aspect, when the oil of the dielectric fluid comprises rapeseed oil, the dielectric fluid has a pour point of less than -30°C, as determined by ISO 3016. In one aspect, when the oil of the dielectric fluid is a synthetic ester oil, the dielectric fluid has a pour point of less than -45°C, as determined by ISO 3016. In one aspect, when the oil of the dielectric fluid is a mineral oil, the dielectric fluid has a pour point of less than -40°C, as determined by ISO 3016, or has a pour point of less than -60°C, as determined by ISO 3016.

[0082] In one aspect, the dielectric fluid has a water content of less than 750 mg / kg, as determined by IEC 60814. In one aspect, the dielectric fluid has a water content of less than 200 mg / kg, as determined by IEC 60814. In one aspect, the dielectric fluid has a water content of less than 100 mg / kg, as determined by IEC 60814. In one aspect, the dielectric fluid has a water content of less than 60 mg / kg, as determined by IEC 60814. In one aspect, the dielectric fluid has a water content of less than 50 mg / kg, as determined by IEC 60814. In one aspect, the dielectric fluid has a water content of less than 30 mg / kg, as determined by IEC 60814. In one aspect, the dielectric fluid has a water content of less than 25 mg / kg, as determined by IEC 60814. In one aspect, the dielectric fluid has a water content of less than 20 mg / kg, as determined by IEC 60814. In one aspect, the dielectric fluid has a water content of about 5 mg / kg to 25 mg / kg as determined by IEC 60814.

[0083] In one aspect, the dielectric fluid has a chromaticity of less than 200 Hazen as determined by ISO 2211.

[0084] In one aspect, the dielectric fluid has a relative humidity of less than 1000 kg / dm at 20°C. 3 Density as determined by 3675, ISO12185.

[0085] In one aspect, the dielectric fluid has a thermal conductivity of about 1 mm at 100°C. 2 / s to 15mm 2 / s, or a kinematic viscosity of about 1 mm at 40°C 2 / s to 35mm 2 / s kinematic viscosity, or about 20 mm at 40 °C 2 / s to 35mm 2 / s kinematic viscosity, or about 100mm at -20°C 2 / s to 3000mm 2 / s kinematic viscosity as determined by ISO 3104. In one aspect, the dielectric fluid comprises mineral oil and has a kinematic viscosity of about 3 mm at 40°C. 2 / s to 12mm 2 In one aspect, the dielectric fluid comprises an oil of biological origin and has a kinematic viscosity of about 9 mm at 40°C. 2 / s to 50mm 2 In one aspect, the dielectric fluid comprises a vegetable oil and has a kinematic viscosity of about 9 mm at 40°C. 2 / s to 50mm 2 In one aspect, the dielectric fluid comprises a synthetic oil and has a kinematic viscosity of about 7 mm at 40°C. 2 / s to 40mm 2 / s kinematic viscosity.

[0086] On the one hand, dielectric fluid has the acidity less than 0.06mg KOH / g, as determined by AOCS method Cd-63. On the one hand, dielectric fluid has the acidity less than 0.03mg KOH / g, as determined by AOCS method Cd-63. On the one hand, dielectric fluid has the acidity less than 0.02mg KOH / g, as determined by AOCS method Cd-63. On the one hand, when the oil of dielectric fluid is mineral oil, dielectric fluid has the acidity less than 0.01mg KOH / g, as determined by AOCS method Cd-63.

[0087] In one aspect, the dielectric fluid has a breakdown voltage greater than or equal to 35 kV, as determined by IEC 60156. In one aspect, the dielectric fluid has a breakdown voltage greater than 45 kV, as determined by IEC 60156. In one aspect, the dielectric fluid has a breakdown voltage greater than 55 kV, as determined by IEC 60156. In one aspect, the dielectric fluid has a breakdown voltage greater than 65 kV, as determined by IEC 60156. In one aspect, the dielectric fluid has a breakdown voltage greater than 75 kV, as determined by IEC 60156. In one aspect, when the oil of the dielectric fluid is a mineral oil, the dielectric fluid has a breakdown voltage greater than 30 kV, as determined by IEC 60156. In one aspect, when the oil of the dielectric fluid is a mineral oil, the dielectric fluid has a breakdown voltage greater than 70 kV, as determined by IEC 60156.

[0088] In one aspect, the dielectric fluid has a DC resistivity at 90°C, as determined by IEC 60156, greater than 2 GΩm. In one aspect, the dielectric fluid has a DC resistivity at 90°C, as determined by IEC 60156, greater than 20 GΩm.

[0089] On the one hand, dielectric fluid is used in the device as electrical system, and this electrical system needs electrical insulation and cooling.On the one hand, dielectric fluid is used for transferring heat from the generating point and insulating conductive element (such as wire coil) from adjacent conductive element.On the one hand, dielectric fluid is used in the device as electrical network, and this electrical network provides the interconnection of electrical components, such as for calculating, power distribution, power generation or power conversion.On the one hand, dielectric fluid is used in the device including the parts selected from the following: capacitor, voltage stabilizer, voltage compensator, and phase shifter.On the one hand, dielectric fluid is used in the device selected from liquid insulation electrical equipment such as electronic circuit and liquid insulation electrical board and panel.On the one hand, dielectric fluid is used in the device as switch gear.On the one hand, dielectric fluid is used in the device as data center computer module.On the one hand, dielectric fluid is used in the device selected from transformer, and this transformer comprises shell, shell in core / coil assembly, and wherein dielectric fluid at least partially surrounds core / coil assembly. On the one hand, dielectric fluid is used in the device selected from transformer, this transformer is such as autotransformer, generator step-down and step-up transformer, interconnection transformer, flexible AC transformer, distribution transformer (pole mounted, base mounted, vault / underground unit, submersible, substation), phase shifting transformer, static voltage compensator, HVDC transformer, furnace and other industrial transformer, traction transformer and grounding transformer.On the one hand, dielectric fluid is used in the device selected from reactor, battery and battery system.

[0090] On the one hand, the method for insulating the device as the electrical system that needs electrical insulation and cooling includes any dielectric fluid as described herein (including the selected dielectric fluid containing the specific specified material or component or amount of dielectric fluid as described herein) mixed in the device as the electrical system that needs electrical insulation and cooling.On the one hand, the method for insulating the device is carried out on the device as an electrical network, and the electrical network provides the interconnection of electrical components, such as for calculating, power distribution, power generation or power conversion.On the one hand, the method for insulating the device is carried out on the device including the parts selected from the following: capacitor, voltage stabilizer, voltage compensator, and phase shifter.On the one hand, the method for insulating the device is carried out on the device selected from liquid insulation electrical equipment such as electronic circuit and liquid insulation electrical board and panel.On the one hand, the method for insulating the device is carried out on the device as a data center computer module.On the one hand, the method for insulating the device is carried out on the device selected from transformer, and the transformer includes shell, core / coil assembly in shell, and wherein dielectric fluid at least partially surrounds core / coil assembly. In one aspect, the method of insulating a device is performed on a device selected from transformers, such as autotransformers, generator step-down and step-up transformers, interconnection transformers, flexible AC transformers, distribution transformers (pole mounted, base mounted, vault / underground units, submersible, substations), phase shifting transformers, electrostatic voltage compensators, HVDC transformers, furnace and other industrial transformers, traction transformers, and grounding transformers. In one aspect, the method of insulating a device is performed on a device selected from reactors, battery packs, and battery systems.

[0091] In one aspect, a device is provided as an electrical system requiring electrical insulation and cooling, the device being composed of any of the dielectric fluids described herein (including selected dielectric fluids containing specifically specified materials or components or amounts of the dielectric fluids described herein).

[0092] In one aspect, the device is selected from a device comprising a component selected from the group consisting of: a capacitor, a voltage regulator, a voltage compensator, and a phase shifter.

[0093] On the one hand, the device is selected from liquid insulated electrical equipment such as electronic circuits and liquid insulated electrical boards and panels. On the one hand, the device is a data center computer module. On the one hand, the device is selected from a transformer, and the transformer includes a core / coil assembly in a housing, a housing, wherein the dielectric fluid at least partially surrounds the core / coil assembly. On the one hand, the device is selected from a transformer, such as an autotransformer, a generator step-down and step-up transformer, an interconnection transformer, a flexible AC transformer, a distribution transformer (pole-mounted, base-mounted, vault / underground unit, submersible, substation), a phase-shifting transformer, an electrostatic voltage compensator, an HVDC transformer, a furnace and other industrial transformers, a traction transformer and a grounding transformer. On the one hand, the device is selected from a reactor, a battery pack and a battery system.

[0094] Example

[0095] program : Unless otherwise specified, the test fluid used in the examples of the present invention is untreated refined, bleached and deodorized ("RBD") soybean oil ("SBO") treated with 0.5% by weight of a reagent for evaluation in a stray gassing test. If a dissolved reagent is required, the fluid is warmed under nitrogen. The treated fluid is drawn into a 50 mL syringe, capped to prevent fluid loss and introduction of air, and placed in an oven at 80°C or 120°C for 48 hours. The syringe is removed from the oven to cool. The fluid is then tested for dissolved gases according to ASTM method D-3612 to determine the level of stray gassing.

[0096] Example 1: Comparison of RBD-SBO fluid containing 0.5% phosphite (Irgafos 168) with a control sample .

[0097] The test results to determine the outgassing levels are presented in Table 1 below:

[0098] Table 1

[0099] Phosphite compounds Hydrogen (ppm) <![CDATA[% H2 reduction]]> Ethane (ppm) <![CDATA[%CH3CH3 reduction]]> Irgafos 168 158 73.6 14 94.3 none 599 n / a 246 n / a

[0100] Irgafos 168 = tris-(2,4-di-tert-butylphenyl)phosphite

[0101] Results and Discussion :

[0102] At 80° C., the two gases indicative of thermally induced stray gas degradation were hydrogen and ethane. Significant reductions in stray gas release of both gases were observed in the RBD-SBO fluid containing phosphite compared to the control.

[0103] Example 2: RBD-SBO dielectric fluid, RBD-SBO dielectric fluid containing phosphite compound, and RBD-SBO dielectric fluid containing non-phosphite compound Comparison of RBD-SBO Dielectric Fluids with Phosphate Compound Antioxidants .

[0104] The non-control compositions all contained 0.5 wt % of the specified additive (phosphite compound or non-phosphite antioxidant).The RBD-SBO dielectric fluid of this example had a peroxide value of 10.

[0105] The test results to determine the outgassing levels are presented in Table 2 below:

[0106] Table 2

[0107]

[0108]

[0109] Results and Discussion :

[0110] The dielectric fluid containing the phosphite compound (Sample B) significantly reduced the outgassing of both hydrogen and ethane compared to the dielectric fluid containing the non-phosphite antioxidant. Notably, the phenolic-based antioxidant containing the metal passivator (i.e., di-tert-butylphenol benzotriazole with additional metal surface inhibition function - Samples D, E, F, I, L, M and N) actually showed an increase in stray outgassing compared to similar compositions without the metal passivator.

[0111] Generally speaking, phosphites are considered to be secondary antioxidants with significantly lower antioxidant strength relative to antioxidants based on di-tert-butylphenol. Comparisons with antioxidants of other categories show that the effect of phosphites is more than just an antioxidant effect. Together with the difference in the oxidative stability results, this shows that the mechanism of action that suppresses stray outgassing may be a mechanism other than antioxidant properties. Without being bound by theory, it is believed that stray outgassing is the result of thermal free radical degradation. Therefore, phosphites are suppressing stray outgassing mechanisms in an effective manner. It is expected that the removal of peroxides will cause a certain degree of stray gas reduction. Non-phosphite materials will not effectively reduce two gases, and some materials have increased the outgassing trend of oil.

[0112] Example 3: RBD-SBO low peroxide value dielectric fluid, RBD-SBO low peroxide value dielectric fluid containing phosphite compound Comparison of low peroxide value dielectric fluids and RBD-SBO low peroxide value dielectric fluids containing non-phosphite compound antioxidants .

[0113] The non-control compositions all contained 0.5 wt % of the specified additive (phosphite compound, non-phosphite antioxidant, or other additive type).The RBD-SBO dielectric fluid of this example had a peroxide value of 0.6.

[0114] The test results to determine the outgassing levels are presented in Table 3 below:

[0115] Table 3

[0116]

[0117]

[0118] Results and Discussion :

[0119] Compared with the dielectric fluid comprising non-phosphite antioxidant, the dielectric fluid comprising phosphite compound (sample BJ) significantly reduces the outgassing of hydrogen and ethane. Sample K shows the increase of hydrogen outgassing, but shows the minimizing of ethane outgassing. However, these data are only run based on a single experiment, and it is believed that the integrity of the phosphite sample may have been compromised.

[0120] In contrast, low peroxide value dielectric fluids containing di-tert-butylphenol antioxidants or other types of additives increased both hydrogen and ethane gassing. This test confirms that the incorporation of phosphite compounds prevents gassing in dielectric fluids when other additives do not prevent gassing in similar dielectric fluids that do not contain a phosphite component.

[0121] In all subsequent examples, RBD-refined, bleached and deodorized vegetable oils or synthetic ester oils were purified by clay treatment prior to use to obtain dielectric grade fluids. Stray outgassing tests were performed by keeping the air-saturated oils in an oven at 80°C or 120°C for 48 hours or 168 hours, as indicated.

[0122] Example 4: Compared with other stabilizers, antioxidants, and passivators, phosphites have a higher Effectiveness of controlling stray outgassing

[0123] Table 4 shows how RBD soybean oil that has been heated to 80°C for 48 hours is affected by various additives. The main indicators are hydrogen and ethane. In these examples, the levels of other gases are not significant. Sample 4-1 is an RBD-SBO without additives and heat treatment to compare the basic levels of stray gases, which are analyzed by dissolved gas analysis (DGA). Sample 4-2 is an RBD-SBO without additives after heat treatment. Among all categories of antioxidants tested, phosphite compounds showed a significant reduction in two stray gases. Other examples show no significant change or increase in either or both of the stray gases.

[0124] Table 4: Preliminary data demonstrates that phosphite has a higher degradation rate at 80°C (48 The effectiveness of controlling stray gassing under the 24-hour test). RBD-SBO was used with 0.5 wt% of the additive .

[0125]

[0126] It is evident from this data that butylated phenol antioxidants do not control stray gassing, but can contribute to a significant increase in stray gassing in bio-derived oils. Passivator compounds, which are typically benzotriazole compounds (Examples 4-10, 4-12, and 4-15), also significantly increase stray gassing in bio-derived oils.

[0127] Example 5: Negative interaction of butylated phenol, Irganox L101 and passivating agent

[0128] The interaction of one of the most common antioxidants used in transformer oils, Irganox L101 (butylated phenols), and the most common passivating agent, Irgamet 39, is shown in Table 5 compared to or in combination with the phosphite compound Irgaphos 168.

[0129] Table 5: Butylated phenol, Irganox L101 and passivator Irgamet 39 against Irgaphos 168 phosphite Negative interactions for compensating effects of controlling spurious outgassing in RBD-SBO at 80 °C for 48 h .

[0130]

[0131]

[0132] Comparison of samples 5-16 and 5-17 shows that the incorporation of conventional butylated phenol increases stray gassing above that of purified soybean oil by increasing the release of hydrogen by 370%. In contrast, comparison of samples 5-16 and 5-18 shows that stray gassing is significantly reduced by the use of phosphite compounds, even reducing the content to a level below that of purified untreated oil. Samples 5-19 and 5-20 show that phosphite compounds even reverse the stray gassing effect of butylated phenol. Samples 5-20, 5-21, and 5-22 show the adverse effects of passivators on oil, where small amounts of passivators have a severe adverse effect on stray gassing on oil. Samples 5-24 to 5-28 demonstrate how the Irgaphos 168 phosphite compound overcomes the stray gassing effect of the combination of butylated phenol antioxidant and benzotriazole passivator.

[0133] Example 6: Effect of Typical Antioxidants on the Increase of Stray Gases

[0134] The general behavior of typical antioxidants in terms of increasing stray gases is shown in Table 6. These compounds are classified as butylated phenol, di-tert-butylphenol thiothiozine, di-tert-butylphenol mercaptan, di-tert-butylphenol benzotriazine, aminotriazole, benzamine, thiol diester, piperidinyl ester-N-alkoxide piperidinyl ester.

[0135] Table 6: Increase in stray gas in RBD-SBO by using 0.5 wt% antioxidant at 80 °C for 48 hours body .

[0136]

[0137] Example 7: Reduction of stray gassing in oil by phosphite compounds

[0138] Screening of phosphite compounds demonstrated the generality of these compounds' ability to reduce stray gassing in oils.

[0139] Table 7 demonstrates the benefits of treating purified, refined, bleached, deodorized soybean oil with 0.5% of the listed phosphites and then heating at 80°C in a sealed container for 48 hours and then testing the oil for dissolved gases.

[0140] Table 7: Screening of phosphite compounds to reduce spurious outgassing in RBD-SBO at 80 °C for 48 hours .

[0141]

[0142] Example 8: Butylated phenol with phosphorous acid in highly purified RBD-SBO at 80°C and 120°C for 18 hours Comparison of salt compounds

[0143] The spurious off-gassing of highly purified RBD-SBO containing either the butylated phenol Irganox L101 or the phosphite compound Irgaphos 168 was compared when the oil was held at 80°C or 120°C for 18 hours. The results are shown in Table 8.

[0144] Table 8: Comparison of stray offgassing of highly purified RBD-SBO containing butylated phenol or phosphite compounds

[0145] Sample No. Temperature ℃ Irgaphos 168 wt% Irganox L101 weight % Hydrogen ppm Ethane ppm 8-1 80 0 0.4 43 95 8-2 80 0.4 0 6 8 8-3 120 0 0.4 44 347 8-4 120 0.4 0 30 85

[0146] Example 9: Hybridization of Aliphatic Synthetic Ester Compositions Containing Various Levels of Benzotriazole Passivating Agent and Phosphite Evaluation of outgassing .

[0147] It is known that a temperature of 120°C can accelerate the degradation of natural and synthetic esters. This was confirmed in an 80°C oven test with untreated mineral oil and synthetic esters, where the higher stability of the aliphatic base oils was demonstrated with no stray gassing. The increased stability of the aliphatic compounds requires temperatures above 100°C to increase the rate of stray gassing. The samples were tested at 120°C for 48 hours and 168 hours. Table 9A shows the results after heat treatment at 120°C for 48 hours.

[0148] Table 9A: Spurious Outgassing of Aliphatic Synthetic Esters at 120°C for 48 Hours and Irgaphos 168 Phosphite The stabilizing effect .

[0149]

[0150] A commercial synthetic ester sample, Midel 7131, with undetermined levels of Irganox L101 and a passivator, was known to exhibit high levels of stray gassing over a shorter period of time than the synthetic ester fluids used in this study. At elevated temperatures where butylated phenol is known to act more rapidly on peroxide-induced stray gassing (compare samples 9-29 and 9-30), the effect of the benzotriazole passivator was shown to overcome any effect of butylated phenol and significantly increase hydrogen stray gas (sample 9-31). The phosphite compound, Irgaphos 168, significantly reduced hydrogen stray gassing in the synthetic esters in samples 9-32 and 9-33.

[0151] Increasing the severity of exposure by extending the time to 168 hours at 120°C (Table 9B) demonstrates the superiority of the phosphite compounds in controlling stray gassing under the challenge of other additives.

[0152] Table 9B: Spurious Outgassing of Aliphatic Synthetic Esters at 120°C for 168 Hours and Irgaphos 168 Phosphite The stabilizing effect .

[0153]

[0154] Example 10: Demonstration of Irgaphos 168 Phosphite Compound to Prevent Stray Gassing in Mineral Oil .

[0155] Temperatures of 120°C are known to degrade mineral oils. Table 10 shows the high stray gassing rates in mineral oil fluids without additives, and the ability of phosphite compounds to prevent stray gassing.

[0156] Table 10: Demonstration of Irgaphos 168 phosphite compound for preventing stray outgassing in mineral oils .

[0157]

[0158] Example 11: Oxidative Stability Test Results of RBD-SBO with and without Phosphite and Passivator

[0159] Oxidative stability testing of soybean oil formulations (Table 11) indicates that Irgaphos 168 can be used in formulations with improved total acidity (specification <0.3 total). However, it has been found that the use of a passivator with bio-derived oils significantly increases the viscosity and acidity of the fluid. For aliphatic synthetic esters, the passivator does not affect viscosity, but has an adverse effect on the acidity and dissipation factor (tan delta) of the fluid, as shown in Table 12.

[0160] Table 11: Oxidative stability test results of RBD-SBO (IEC 61125 method C, 48 hours, 120 ° C, 2.5 mL / min airflow) .

[0161]

[0162] Example 12: Oxidative Stability Test Results for Aliphatic Synthetic Esters

[0163] Aliphatic synthetic ester fluids formulated with Irgaphos 168 phosphite compound showed excellent properties in oxidation stability testing. When using Irgaphos 168, viscosity remained constant and the test results after 800 hours of oxidation stability testing at 120°C at 2.50 mL / min air flow exceeded the required specification for the 164 hour test according to IEC 61125 Method C. The results are summarized in Table 12.

[0164] Table 12: Oxidative stability test results for aliphatic synthetic esters (IEC 61125 method C, 120°C, 2.5 mL / min Air flow, 164 hours or 800 hours specified time) .

[0165]

[0166]

[0167] Note: Viscosity change in all cases was <1.0 wt% and <0.01 wt% for slurries.

[0168] Example 13: Reduction of stray off-gassing in natural oils with high peroxide values

[0169] Oils with high initial peroxide content also exhibit increased stray gassing, as seen in Table 13. However, this stray gassing is significantly reduced by using the Irgaphos 168 phosphite compound. It should be noted that the presence of conventional antioxidants (non-phosphite antioxidant components) does not prevent the formation of peroxides, but is used to degrade peroxides after peroxide formation. However, conventional antioxidants will not effectively reduce peroxide accumulation at ambient temperatures. Elevated temperatures are effective in increasing the interaction between conventional antioxidants and peroxides, but also increase the thermal degradation rate of the oil.

[0170] Table 13: Effect of high peroxide oil and Irganox 168 on reducing stray gassing (48 hours, 80°C) .

[0171]

[0172]

[0173] Example 14: Reduction of stray gassing in natural oils having low peroxide content

[0174] Experiments were conducted to demonstrate the reduction of stray gassing in natural oils that do not have high peroxide content. The test results are provided in Tables 14-1 and 14-2.

[0175] Table 14-1: Irganox 168 reduces stray gassing in oils of biological origin at 80°C for 48 hours Effectiveness .

[0176]

[0177] Table 14-2: Phosphite compounds (triphenylphosphite) on various oils kept at 80°C for 48 hours Examples .

[0178]

[0179]

[0180] Example 15: Confirmation that phosphites in oil do not interfere with transformer testing

[0181] It is important that phosphite compounds do not interfere with the diagnostic testing of the transformer where acetylene levels are used to determine if arcing or discharge conditions are occurring. To test this, the oil was subjected to greater than 65 kV and 50 kV discharges sent through a 2 mm gap into 350 mL of oil to demonstrate no difference in acetylene and DGA levels. It should be noted that the oil was not heat treated so no additional stray gases were expected to be generated by anything other than sparks passing through the oil.

[0182] Table 15: Non-diagnostic effects of the phosphite compound Irgaphos 168 on discharge of oil of biological origin (RBD-SBO) Confirmation of interference .

[0183]

[0184] As used herein, the term "about" or "approximately" means within an acceptable range of a particular parameter, which is determined by a person of ordinary skill in the art, and which depends in part on how the value is measured or determined, for example, the limitations of sample preparation and measurement systems. Examples of such limitations include different requirements for preparing samples in wet / dry environments, different instruments, sample height variations, and signal-to-noise ratios. For example, "about" may mean 1 / 10 of a specified value greater or less than a specified value or value range, but is not intended to limit any value or value range to only this broader definition. For example, a concentration value of about 30% means a concentration between 27% and 33%. Each value or value range preceded by the term "about" is also intended to cover embodiments of a specified absolute value or value range. Alternatively, particularly relative to measurements of logarithmic scales such as those seen in biological systems or processes, the term may mean within the order of magnitude of a value, preferably within 5 times, more preferably within 2 times.

[0185] Throughout this specification and claims, unless the context requires otherwise, the word "comprise" and variations (e.g., "comprising" and "containing") should be understood to imply the inclusion of the specified integers or steps or groups of integers or steps, but not the exclusion of any other integers or steps or groups of integers or steps. When used herein, "consisting of excludes any element, step, or ingredient not specified in the claim elements. When used herein, "consisting essentially of does not exclude materials or steps that do not materially affect the basis and novel characteristics of the claim. In the present invention of various embodiments, any of the terms "comprising," "consisting essentially of," and "consisting of" used in the description of the embodiments may be replaced with either of the other two terms.

[0186] For all purposes, all patents, patent applications (including provisional applications) and disclosures cited herein are incorporated by reference as if individually incorporated. Unless otherwise indicated, all parts and percentages are calculated by weight, and all molecular weights are weight average molecular weights. The above detailed description is given only for the purpose of clear understanding. It should be understood that there are no unnecessary limitations. The present invention is not limited to the exact details shown and described, because variations obvious to those skilled in the art will be included in the present invention defined by the claims.

Claims

1. A dielectric fluid, comprising: an oil selected from the group consisting of synthetic ester oils and mineral oils; a phosphite component containing one or more phosphite compounds; Metal passivators; and a non-phosphite antioxidant component selected from one or more non-phosphite antioxidant compounds, wherein the phosphite component is present in the dielectric fluid in an amount of 0.05 wt % to 0.4 wt %, wherein the phosphite component is present in an amount sufficient to reduce stray outgassing of the dielectric fluid as determined by dissolved gas analysis by at least 60% compared to a dielectric fluid composition not containing the phosphite component, wherein the stray outgassing is H2, methane, ethane or ethylene, wherein the dissolved gas analysis is performed by ASTM D3612-02, Method C.

2. The dielectric fluid of claim 1, wherein the phosphite component is present in an amount sufficient to reduce H2 gassing of the dielectric fluid by at least 70% compared to a dielectric fluid composition not comprising the phosphite component.

3. The dielectric fluid of claim 1, wherein the phosphite component is present in an amount sufficient to reduce ethane gassing of the dielectric fluid by at least 80% compared to a dielectric fluid composition not comprising the phosphite component.

4. The dielectric fluid of claim 1, wherein the phosphite component is selected from water-stable phosphite compounds.

5. The dielectric fluid of claim 1, wherein the phosphite component is selected from the group consisting of phosphites, triaryl phosphites, trialkyl phosphites, cyclic phosphites, and diaryl pentaerythritol cyclic phosphites.

6. The dielectric fluid of claim 1, wherein the phosphite component is selected from phosphite compounds having one to three aryloxy groups.

7. The dielectric fluid of claim 1, wherein the phosphite component is selected from triaryl phosphite compounds.

8. The dielectric fluid of claim 1, wherein the phosphite component is selected from the group consisting of cyclic aryl phosphites, cyclic alkyl-aryl phosphites, aryl cyclic phenoxy phosphites, bis-aryl phosphites, alkyl aryl phosphites, and mixtures thereof.

9. The dielectric fluid of claim 1, wherein the phosphite component is selected from the group consisting of: tris-(2,4-di-tert-butylphenyl)phosphite; bis(2,4-dicumylphenyl)pentaerythritol diphosphite; trisnonylphenylphosphite; 1,3,7,9-tetra-tert-butyl-11-(2-ethylhexyloxy)-5H-benzo[d][1,3,2]-benzodioxaphosphane; 3,9-bis(2,6-di-tert-butyl-4-methylphenoxy)-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5]undecane; bis(2,4- di-tert-butylphenol) pentaerythritol diphosphite; 4,4'-isopropylidene diphenol C12-15 alcohol phosphite; 3,9-diphenoxy-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5]undecane; 3,9-bis(octadecyloxy)-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5]undecane; triphenyl phosphite; isodecyl diphenyl phosphite; 2-ethylhexyl diphenyl phosphite; 5,5-dimethyl-2-phenoxy-1,3,2-dioxaphosphacyclohexane; methyl diphenyl phosphite; and mixtures thereof.

10. The dielectric fluid of claim 1, wherein the non-phosphite antioxidant component is selected from the group consisting of phenolic antioxidants.

11. The dielectric fluid of claim 1 , wherein the non-phosphite antioxidant component is selected from the group consisting of: butylated hydroanisole; butylated hydrotoluene; tert-butylhydroquinone; tetrahydrobutyrophenone; ascorbyl palmitate; propyl gallate; alpha-tocopherol, beta-tocopherol, or delta-tocopherol; and A mixture of them.

12. The dielectric fluid of claim 1, wherein the non-phosphite antioxidant component is selected from the group consisting of: pentaerythritol tetrakis (3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate); hexamethylene bis [3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate]; octadecyl-[3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate]; ethylene bis (oxyethylene) bis-(3-(5-tert-butyl-4-hydroxyphenyl) propionate); butyl-4-hydroxy-m-tolyl) propionate); 2,6-di-tert-butyl-4-(4,6-bis(octylthio)-1,3,5-triazin-2-ylamino)phenol; N,N'-hexane-1,6-diylbis(3-3,5-di-tert-butyl-4-hydroxyphenylpropionamide); 4,6-bis(octylthiomethyl)-o-cresol; 4,4'-methylene-bis-2,6-di-tert-butylphenol; and 2,6-di-tert-butyl-4-methylphenol.

13. The dielectric fluid of claim 1, wherein the metal passivator is selected from benzotriazole or its derivatives.

14. The dielectric fluid of claim 1, wherein the metal passivator is present in an amount sufficient to control the dissipation value of the dielectric fluid to be equal to or less than 0.50 (50%), or equal to or less than 0.60 (60%), or equal to or less than 0.90 (90%), or equal to or less than 1.0 (100%) in a 48-hour oxidation stability test.

15. The dielectric fluid of claim 1, wherein the metal passivator is present in an amount of 0.005 wt% to 1.0 wt%.

16. The dielectric fluid of claim 1, wherein the metal passivator is selected from the group consisting of: N,N-bis(2-ethylhexyl)-arylmethyl-1H-benzotriazole-1-methylamine; N,N-bis(2-ethylhexyl)-1H-1,2,4-triazole-1-methylamine; 1H-benzotriazole; methyl-1H-benzotriazole; and 2,2'-[[(methyl-1H-benzotriazole-1-yl)methyl]imino]bis-ethanol.

17. The dielectric fluid according to claim 1, wherein the dielectric fluid comprises at least 75% by weight of a synthetic ester oil; or wherein the dielectric fluid comprises at least 85% by weight of a synthetic ester oil; or wherein the dielectric fluid comprises at least 90% by weight of a synthetic ester oil; or wherein the dielectric fluid comprises at least 95% by weight of a synthetic ester oil; or wherein the dielectric fluid comprises at least 98% by weight of a synthetic ester oil; or The only oil in the dielectric fluid is a synthetic ester oil.

18. The dielectric fluid of claim 1, wherein the dielectric fluid comprises a synthetic ester oil comprising a synthetic ester of a polyol selected from the group consisting of glycerol, pentaerythritol, trimethylolpropane, hydroxylated fatty acids, and polyglycerol; or wherein the dielectric fluid comprises a synthetic ester oil comprising a synthetic ester formed by reacting the polyol with a compound selected from the group consisting of C5-C25 saturated or unsaturated linear and branched carboxylic acids, aryl esters, C5-C25 saturated or unsaturated linear and branched esters, and mixtures thereof; or wherein the dielectric fluid comprises a synthetic ester oil comprising a synthetic ester selected from the group consisting of esters of C5 to C24 branched and straight chain aliphatic carboxylic acids with pentaerythritol, dipentaerythritol, 2,2-dimethylpropylene glycol, 2,2-dimethyl-3-isopropyl-1,3-propanediol, trimethylolpropane, glycerol, neopentyl glycol, 2,2-dimethylolbutane, trimethylolethane, sorbitol, C2 to C12 glycols, ethylene glycol, propylene glycol, 1,4-butanediol and 2-methylpropylene glycol, and mixtures thereof; or wherein the dielectric fluid comprises a synthetic ester oil comprising a synthetic ester selected from the group consisting of esters of C5 to C24 branched and straight chain aliphatic alcohols and acids selected from the group consisting of adipic acid, suberic acid, azelaic acid, sebacic acid, phthalic acid, oxalic acid, glycolic acid, fumaric acid, and mixtures thereof.

19. The dielectric fluid of claim 1, wherein the dielectric fluid comprises a synthetic ester oil prepared from reactants derived solely from oils of plant or animal biological origin.

20. The dielectric fluid of claim 1, wherein the dielectric fluid comprises at least 75% by weight mineral oil; or wherein the dielectric fluid comprises at least 85% by weight of mineral oil; or wherein the dielectric fluid comprises at least 90 wt % mineral oil; or wherein the dielectric fluid comprises at least 95% by weight of mineral oil; or wherein the dielectric fluid comprises at least 98% by weight of mineral oil; or The only oil in the dielectric fluid is mineral oil.

21. The dielectric fluid of claim 1, wherein the dielectric fluid comprises a mineral oil selected from the group consisting of: Straight and branched chain aliphatic paraffins and cycloalkanes and mixtures thereof.

22. The dielectric fluid according to claim 21, wherein the straight chain and branched aliphatic paraffins and cycloalkanes and mixtures thereof have an average molecular weight of 220 to 700; or The linear and branched aliphatic paraffins and cycloalkanes and mixtures thereof have a flash point of 120°C to 250°C.

23. The dielectric fluid of claim 1, wherein the oil is selected from a mixture of synthetic ester oils and mineral oils.

24. The dielectric fluid of claim 1, wherein the dielectric fluid does not contain halogen compounds, organosilicon compounds, or sulfur compounds.

25. The dielectric fluid of claim 1, wherein the dielectric fluid has a peroxide value of less than 5; or wherein the dielectric fluid has a peroxide value of less than 3; or wherein the dielectric fluid has a peroxide value of less than 2; or wherein the dielectric fluid has a peroxide value of less than 1; or wherein the dielectric fluid has a peroxide value of 0.01 to 5; or wherein the dielectric fluid has a peroxide value of 0.01 to 3; or wherein the dielectric fluid has a peroxide value of 0.01 to 2; or wherein the dielectric fluid has a peroxide value of 0.01 to 1; or wherein the dielectric fluid has a peroxide value of 0.1 to 1.

26. A dielectric fluid formulated for use in power distribution or power generation, the dielectric fluid comprising: an oil selected from the group consisting of synthetic ester oils and mineral oils; a phosphite component comprising one or more phosphite compounds; and a non-phosphite antioxidant component selected from one or more non-phosphite antioxidant compounds, wherein the phosphite component is present in the dielectric fluid in an amount of 0.05 wt % to 0.4 wt %, wherein the phosphite component is present in an amount sufficient to reduce stray outgassing of the dielectric fluid as determined by dissolved gas analysis by at least 60% compared to a dielectric fluid composition not containing the phosphite component, wherein the stray outgassing is H2, methane, ethane or ethylene, wherein the dissolved gas analysis is performed by ASTM D3612-02, Method C.

27. Use of a dielectric fluid according to any one of claims 1 to 26 in power distribution or power plants.

28. A method of insulating an electrical power distribution or power plant, the method comprising incorporating a dielectric fluid according to any one of claims 1 to 26 into the electrical power distribution or power plant.

29. An electrical power distribution or power plant comprising a dielectric fluid according to any one of claims 1 to 26.

30. The power distribution or power device of claim 29, wherein the device is selected from a capacitor and a transformer.

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