[0001] The present invention relates generally to dielectric fluids for use with electrical apparatus. In particular, the invention relates to dielectric fluids for use for electrical insulation and for the dissipation of heat in electrical apparatus such as electrical transformers. The invention also relates to a composition for adding to a dielectric fluid to enhance the performance of the dielectric fluid, as well as to a dielectric fluid containing the composition.

BACKGROUND ART

[0002] Dielectric fluids are typically used to insulate conducting wire windings in electrical transformers from one other. Dielectric fluids are also used in electric apparatus such as capacitors, switching gears, transmission components, distribution components, switches, regulators, circuit breakers, and autoreclosers. importantly, dielectric fluids also function to transfer heat generated during use.

[0003] There are several specific functional properties characteristic of dielectric fluids. The dielectric breakdown, or dielectric strength, for example, provides an indication of a dielectric fluid's ability to resist electrical breakdown and is measured as the minimum voltage required to cause arcing across a specified gap between two electrodes submerged in the fluid. The impulse dielectric breakdown voltage of a dielectric fluid provides an indication of its ability to resist electrical breakdown under transient voltage stresses such as lightning strikes and power surges. The dissipation factor of a dielectric fluid is a measure of the dielectric losses in the fluid; a low dissipation factor indicates low dielectric loss and a low concentration of soluble, polar contaminants.

[0004] Because one function of a dielectric fluid is to carry and dissipate heat, factors that significantly affect the relative ability of the fluid to function as a dielectric coolant include viscosity, specific heat, thermal conductivity, and the coefficient of expansion. The values of these properties, particularly in the range of operating temperatures for the equipment at full rating, must be weighed in the selection of suitable dielectric fluids for specific applications. [0005] When used in a transformer in particular, a dielectric fluid is required to withstand strong electromagnetic fields and increased temperatures for extended periods of time. In order to maintain their cooling properties, such fluids must also retain their fluid characteristics. However, exposure to such high voltages and variable heat causes deterioration of many dielectric fluids over time. Such deterioration results in the failure of the insulating and/or heat dissipation properties of dielectric fluids causing disruptive discharge and power loss.

[0006] An ideal dielectric fluid demonstrates chemical and thermal stability over a long service life of 20-30 years, good electric and thermal properties as described above, low flammability (i.e. high fire and flash points), low viscosity and low pour point, miscibility with existing transformer oils, and is non-corrosive and/or compatible with the electrical equipment material to which it is exposed.

[0007] Mineral oil has been used as a dielectric fluid for many years due to its high stability under transformer operating conditions and comparatively low cost. However, mineral oil does not biodegrade readily and therefore persists in the environment. The use of mineral oil as a dielectric fluid in transformers typically results in the production of large quantities of non-biodegradab!e waste which are costly to dispose of. Mineral oil is also relatively flammable and for this reason has regulatory restrictions imposed upon its use and containment.

[0008] Silicone has been used as an alternative dielectric fluid due to its relatively high flash point such that it is less flammable than mineral oil. However, silicone may contain methylpolysiloxanes which can generate the highly undesirable toxic by-product formaldehyde, at high temperature.

[0009] Increasingly, however, there has been concern that the idea! dielectric fluid should also be biodegradable, non-toxic and renewable so as to exhibit little or no detrimental impact on the environment. Mono-unsaturated fatty acid-containing oils may be obtained from renewable sources (such as vegetable oil, tallow, lard, milk fat, etc) and thus are attractive candidates for substituting petroleum-based dielectric fluids.

[0010] Advantageously, mono-unsaturated fatty acid-containing oils may have higher flash and fire point characteristics than mineral oils, which ensure better safety in operation, handling, storage and transportation of such oils and thus the operational safety of transformers using vegetable oil-based dielectric fluids. The excellent fire safety characteristics of mono-unsaturated fatty acid-containing oil-based dielectric fluids make them ideal candidates for high voltage transformers.

[0011] Notwithstanding the above advantages, mono-unsaturated fatty acid-containing oils are susceptible to oxidative degradation, and have a higher pour point, higher dissipation factor, higher acidity number, higher moisture content and significantly higher viscosity compared to mineral oils. Many of these deficiencies can be overcome by subjecting the mono-unsaturated fatty acid-containing oils to purification processes to remove water, acid, and conductive contaminants, and a winterization process to improve the mono-unsaturated fatty acid-containing oil's pour point. Additionally, antioxidants can be added to the purified mono-unsaturated fatty acid-containing oil to enhance its oxidative stability.

[0012] Plant-based and fatty acid ester oils are increasingly being used as dielectric fluids due to their ability to biodegrade and renewability of source. Currently available plant oil-based dielectric fluids include soy-based and canola-based fluids that are relatively less flammable than mineral oil. However, the use of these oils as dielectric fluids is often limited in terms of their dielectric strength, viscosity, and performance life.

[0013] The exposure of plant-based oils to high temperatures in the presence of oxygen causes oxidation and severely impacts on the insulating properties of the oil and its ability to remain in the liquid state. Over time, oxidation of plant oil-based dielectric fluids due to thermal and electrical stress causes the production of polymers or sludge precipitates which significantly compromise the dielectric strength of the fluid. Soy-bean oil, in its natural form, is oxidatively unstable and polymerises when used in a transformer, often thickening to the extent that it no longer possesses the fluid characteristics required for adequate heat dissipation. As such, soy-bean oil often requires costly modification before use as a dielectric fluid by, for instance, winterization, so as to improve its pour point in cold temperatures.

[0014] There remains a need for alternative high performing biodegradable bioelectric fluids from renewable sources for use in electrical apparatus, capable of withstanding the rigors of field use involving a wide range of temperatures and which exhibit good electric and thermal properties, chemical and thermal stability, low flammability, low pour point, miscibi!ity with existing transformer oils and long service life of 20-30 years comparable to existing dielectric fluids based on mineral oils.

[0015] It is against this background that the present invention has been developed. The present invention seeks to provide the consumer with a useful or commercial choice of bioelectric fluid for use in electrical apparatus.

[0016] The above discussion of the background art is intended to facilitate an understanding of the present invention only. The discussion is not an acknowledgement or admission that any of the material referred to is or was part of the common general knowledge as at the priority date of the application.

SUMMARY OF INVENTION

[0017] The present invention provides a dielectric fluid composition comprising a compound selected from the group defined by formula (I) and an unsaturated fatty acid- containing oil or oleochemical, wherein formula (I) is:

wherein

A is a 5 or 6 membered aromatic or heterocyclic ring;

R _a is OH, or C _m H _2m +i wherein m = 0 - 18, or a hydrocarbyl, or a hetero-substituted hydrocarbyl group;

R is OH, or C _m H2 _m+ i wherein m = 0 - 18, or a hydrocarbyl, or a hetero-substituted hydrocarbyl group;

R _c is OH, or a hydrocarbyl, or a hetero-substituted hydrocarbyl group, or (CH ₂ ) _a COOR _g where a = 1 - 10 and R _g is either H or hydrocarbyl; R _d - OH, or C _m H ₂ m ₊ i wherein m = 0 - 18;

X is a divalent bridging group such as S, O or N, or an optionally substituted or unsubstituted methylene group; and n has a value of at least 4.

[0018] There is also provided a dielectric fluid composition comprising a compound selected from the group defined by formula (II) and an unsaturated fatty acid-containing oil or oleochemical, wherein formula (II) is:

wherein

X is a divalent bridging group such as S, O or N or an optionally substituted methylene group;

R _a is a hydrogen, hydroxyl, hydrocarbyl or hetero-substituted hydrocarbyi group; R _b is a hydrogen, hydroxyl, hydrocarbyl or hetero-substituted hydrocarbyl group; R _c is a hydrogen, hydroxyl, hydrocarbyl or hetero-substituted hydrocarbyl group; R _d is a hydrogen, hydroxyl, hydrocarbyl or hetero-substituted hydrocarbyl group; and wherein either R _a is hydroxyl and R , R _c and R _d are independently either hydrogen, hydrocarbyl or hetero-substituted hydrocarbyl, or Rb and R _d are hydroxyl and R _a and R _c are independently either hydrogen, hydrocarbyl or hetero-substituted hydrocarbyl, or

Rb, Rc and Rd are hydroxyl and R _a is either hydrogen, hydrocarbyl or hetero-substituted hydrocarbyl, or

R _a and R _c are hydroxyl, and R _b and R _d are independently either hydrogen, hydrocarbyl or hetero-substituted hydrocarbyl; and n has a value of at least 4.

[0019] There is also provided a dielectric fluid composition comprising a compound selected from the group defined by formula (Hi) and an unsaturated fatty acid-containing oil or oleochemical, wherein formula (III) is:

wherein

Rc is C _m H ₂ m+i wherein m is 0 - 18;

R _h is C _m H _2m +i wherein m is 0 - 8; and n is 4, 5, 6, 7 or 8.

[0020] There is also provided a dielectric fluid composition comprising a compound selected from the group defined by formula (IV), and an unsaturated fatty acid- containing oil or oleochemical, wherein formula (IV) is:

wherein

R _a is C _m H ₂ m+i wherein m is 0 - 18; Rh is C _m H _2m +i wherein m is 0 - 8; and n is 4, 5, 6, 7 or 8.

[0021] There is also provided a dielectric fluid composition comprising a compound selected from the group defined by formula (V) and an unsaturated fatty acid-containing oil or oleochemical, wherein formula (V) is:

wherein

R _a is C _m H _2m +i wherein m is 0 - 18;

R _h is C _m H ₂ m+i wherein m is 0 - 18; and n is 4, 5, 6, 7 or 8.

[0022] There is also provided a dielectric fluid composition comprising a compound selected from the group defined by formula (VI) and an unsaturated fatty acid-containing oil or oleochemical, wherein formula (VI) is: wherein

R _c is C _m H _2m +i wherein m is 0 - 18, or S0 ₂ Y where Y is H, or an alkali metal; Rh is C _m H _2m +i wherein m is 0 - 8;

X is S, S0 ₂ , N, O or an optionally substituted methylene group; and n is 4, 5, 6, 7 or 8.

[0023] There is also provided a dielectric fluid composition comprising a compound selected from the group defined by formula (VII) and an unsaturated fatty acid- containing oil or oleochemical, wherein formula (VII) is;

wherein

Rc is C _m H ₂ m+i wherein m is 0 - 18, or NH ₂ , or S0 ₂ Y where Y is H or an alkali metal; R _h is C _m H _2m -M wherein m is 0 - 18;

R _a is (CH ₂ ) _a COOR _g where a - 1 - 12 and R _g is either H or hydrocarbyl; X is S, S0 ₂ , N, O or an optionally substituted methylene group; and n is 4, 5, 6, 7 or 8.

[0024] The unsaturated fatty acid-containing oil or oleochemical of the dielectric fluid composition of the present invention is preferably sourced from a naturally occurring or renewable source, including plants (including algae), animals, fungi, bacteria, etc. Preferably, the unsaturated fatty acid containing oil or oleochemical of the present invention is a mono-unsaturated fatty acid-containing oil or oleochemical.

[0025] The mono-unsaturated fatty acid content of the oil or oleochemical is preferably >60%, and most preferably about 80%. The mono-unsaturated fatty acid is preferably oleic acid.

[0026] The present invention also provides an antioxidant for use with an unsaturated fatty acid-containing oil or oleochemical to form a dielectric fluid, wherein the antioxidant is a compound selected from the group comprising: formula (I), formula (II), formula (Ml), formula (IV), formula (V), formula (VI), and/or formula (VII).

[0027] The present invention also provide a process for producing a dielectric fluid composition comprising the step of: a) blending a volume of unsaturated fatty acid-containing oil or oleochemical with a compound selected from the group comprising: formula (I), formula (II), formula (III), formula (IV), formula (V), formula (VI), and/or formula (Vil).

[0028] The present invention further provides a transformer having a housing which accommodates a transformer core/coil assembly and a dielectric fluid composition surrounding said core/coil assembly, wherein the dielectric fluid composition comprises a compound selected from the group comprising: formula (I), formula (II), formula (III), formula (IV), formula (V), formula (VI), and/or formula (VII), and a mono-unsaturated fatty acid-containing oil or oleochemical.

[0029] The present invention further provides a method of increasing the oxidative stabiiity of a dielectric fluid comprising an unsaturated fatty acid-containing oil or oleochemical, said method comprising the step of: blending the dielectric fluid containing an unsaturated fatty acid-containing oil or oleochemical with a compound selected from the group comprising: formula (I), formula (II), formula (III), formula (IV), formula (V), formula (VI), and/or formula (VII).

BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The description will be made with reference to the accompanying drawings in which:

Figure 1 is a diagram of a transformer 110 having a housing 112 which accommodates a transformer core/coil assembly 114. The transformer core-coil assembly 114 is arranged to be immersed in a dielectric fluid composition 116 of the present invention, such that the dielectric fluid composition 1 6 surrounds the transformer core-coil assembly 114 and performs according to desired electrical standards.

Figure 2 is a graph showing the power factor v oxidation time for an example dielectric fluid of the present invention comprising HOSO oil and Sample 6 (p-t- butyl calix[4]arene).

DESCRIPTION OF THE INVENTION

Detailed Description of the Invention

Dielectric Fluid

[0031] As discussed above, an important feature of a dielectric fluid is its oxidative stability. In order to improve the oxidative stability of unsaturated fatty acid-containing plant-based oils and oieochemicals, there is need for new additives, specifically designed for use with plant-based oils and oieochemicals. Many of the previously known additives for dielectric fluids were developed for use in mineral oils, and do not perform well in the new renewable oils. For example, the food industry adds certain antioxidants in small quantities (up to 0.02%) to oils used in food processing, such as BHT (Butylated Hydroxy Toluene, also known as DBPC used in transformer oil) and BHA (Butylated Hydroxy Anisole). However, Oommen et al (1997; "Biodegradable electrical insulation fluids" Electrical Insulation Conference and Electrical Manufacturing & Coil Winding Conference; Proceedings: 465-468 (Meeting date 22-25 Sept 1997)) undertook oxidations tests using such additives with plant based oils and found that none of the oils compared with regular mineral oil in stability. The use of very high concentrations of anti-oxidants in dielectric fluids is not desirable because of the marked increase in electrical conductivity. Furthermore, Oommen et al (2000; "A New Vegetable Oil Based Transformer Fluid: Development and Verification" Electrical Insulation and Dielectric Phenomena, 2000 Annual Report of Conference; Volume 1 : 308-312 (Meeting date 15- 8 Oct 2000)) found that oxidation inhibitors for mineral oils and plant based oils, such as BHT (a phenolic anti-oxidant) and TBHQ (a quinone antioxidant), were unable to protect the plant based oil from oxidation at concentrations as high as 3%. For transformer oil, the maximum level of known anti-oxidants used is generally about 0.3%.

[0032] The present invention therefore provides anti-oxidant additives for dielectric fluids that are suitable for use with unsaturated fatty acid-containing oils or o!eochemicals.

[0033] The antioxidant compounds of the present invention are preferably macrocyclic or cyclic oligomers with repeating units forming a ring. Examples of the compounds of the present invention include calixarenes.

[0034] In accordance with the present invention, there is therefore provided a dielectric fluid composition comprising a compound selected from the group defined by formula (I) and an unsaturated fatty acid-containing oil or oleochemical, wherein formula (I) is:

wherein

A is a 5 or 6 membered aromatic or heterocyclic ring;

R _a is OH, or C _m H _2m ÷i wherein m = 0 - 18, or a hydrocarbyl, or a hetero-substituted hydrocarbyl group; R _b is OH, or C _m H _2m+ i wherein m = 0 - 18, or a hydrocarbyl, or a hetero-substituted hydrocarbyl group;

R _c is OH, or a hydrocarbyl, or a hetero-substituted hydrocarbyl group, or (CH ₂ ) _a COOR _g where a = 1 - 10 and R _g is either H or hydrocarbyl;

R _d = OH, or CmH _2m +i wherein m - 0 - 8;

X is a divalent bridging group such as S, O or N, or an optionally substituted or unsubstituted methylene group; and n has a value of at least 4.

Preferably n is between 4 and 8.

[0035] The compound of formula (I) may be provided in a number of more specific forms. The compounds of formulas (II) to (VII) are provided as preferable sub sets of the compounds of formula (I).

[0036] There is therefor also provided a dielectric fluid composition comprising a compound selected from the group defined by formula (II) and an unsaturated fatty acid- containing oil or oleochemica!, wherein formula (II) is:

wherein

X is a divalent bridging group such as S, O or N or an optionally substituted me group;

R _a is a hydrogen, hydroxyl, hydrocarbyl or hetero-substituted hydrocarbyl group; R _b is a hydrogen, hydroxyl, hydrocarbyl or hetero-substituted hydrocarbyl group; Rc is a hydrogen, hydroxyl, hydrocarbyl or hetero-substituted hydrocarbyl group; R _d is a hydrogen, hydroxyl, hydrocarbyl or hetero-substituted hydrocarbyl group; and wherein either R _a is hydroxyl and R , R _c and Rd are independently either hydrogen, hydrocarbyl or hetero-substituted hydrocarbyl, or

Rb and Rd are hydroxyl and R _a and R _c are independently either hydrogen, hydrocarbyl or hetero-substituted hydrocarbyl, or

Rb, Rc and Rd are hydroxy! and R _a is either hydrogen, hydrocarbyl or hetero-substituted hydrocarbyl, or

R _a and R _c are hydroxy!, and R and R _d are independently either hydrogen, hydrocarbyl or hetero-substituted hydrocarbyl; and n has a value of at least 4.

[0037] In formula (II), X is preferably the substituted or unsubstituted methyl group (CR _e Rf)m in which R _e and Rf are independently either hydrogen or a hydrocarbyl of 1 - 6 carbons, and m is an integer which is at least one, preferably at least three, more preferably at least six. !f any of R _a to Rd is a heterosubstituted hydrocarbyl, preferably the heteroatom is O, or S, or NH, interrupting a chain of carbon atoms, such as an alkoxy-alkyl group of 2 - 20 carbons.

[0038] Preferably in formula (II) R _b and Rd are hydrogen; R _c is hydrocarbyl, preferably alkyl of greater than 3, preferably 4, more preferably t-Bu. Preferably, one of R _e and R is hydrogen and the other is either hydrogen or alkyl, preferably hydrogen.

[0039] Preferably, n is at least 4 and more preferably 4, 5, 6 or 8. [0040] The term "hydrocarbyl" as used herein describe organic compounds or radicals consisting exclusively of the elements carbon and hydrogen. These moieties include alkyl, alkenyl, alkynyi, and ary! moieties. These moieties also include alkyl, alkenyl, alkynyl, and aryl moieties substituted with other aliphatic or cyclic hydrocarbon groups, such as alkaryi, alkenaryl and alkynaryl. Unless otherwise indicated, these moieties preferably comprise 1 to 20 carbon atoms.

[0041] The "substituted hydrocarbyl" moieties described herein are hydrocarbyl moieties which are substituted with at least one atom other than carbon, including moieties in which a carbon chain atom is substituted with a hetero atom such as nitrogen, oxygen, silicon, phosphorous, boron, sulfur, or a halogen atom. These substituents include halogen, heterocyclo, alkoxy, alkenoxy, alkynoxy, aryloxy, hydroxy, protected hydroxy, keto, acyl, acyioxy, nitro, amino, amido, nitro, cyano, thiol, ketals, acetals, esters and ethers.

[0042] The term "heteroatom" shall mean atoms other than carbon and hydrogen.

[0043] Unless otherwise indicated, the alkyl groups described herein are preferably lower alkyl containing from one to eight carbon atoms in the principal chain and up to 20 carbon atoms. They may be straight or branched chain or cyclic and include methyl, ethyi, propyl, isopropyl, butyl, hexyl and the like.

[0044] The terms "heterocyclo" or "heterocyclic" as used herein alone or as part of another group denote optionally substituted, fully saturated or unsaturated, monocyclic or bicyclic, aromatic or nonaromatic groups having at least one heteroatom in at least one ring, and preferably 5 or 6 atoms in each ring. The heterocyclo group preferably has 1 or 2 oxygen atoms, 1 or 2 sulfur atoms, and/or 1 to 4 nitrogen atoms in the ring, and may be bonded to the remainder of the molecule through a carbon atom or heteroatom. Exemplary heterocyclo include heteroaromatics such as furyl, thienyl, pyridy!, oxazolyl, pyrrolyl, indolyl, quinolinyl, or isoquino!inyl and the like. Exemplary substituents include one or more of the following groups: hydrocarbyl, substituted hydrocarbyl, keto, hydroxy, protected hydroxy, acyl, acyioxy, alkoxy, alkenoxy, alkynoxy, aryloxy, halogen, amido, amino, nitro, cyano, thiol, ketals, acetals, esters and ethers.

[0045] The term "heteroaromatic" as used herein alone or as part of another group denote optionally substituted aromatic groups having at least one heteroatom in at least one ring, and preferably 5 or 6 atoms in each ring. The heteroaromatic group preferably has 1 or 2 oxygen atoms, 1 or 2 sulfur atoms, and/or 1 to 4 nitrogen atoms in the ring, and may be bonded to the remainder of the molecule through a carbon or heteroatom. Exemplary heteroaromatics include furyl, thienyl, pyridyl, oxazo!yl, pyrrolyl, indolyl, quinolinyl, or isoquinolinyl and the like. Exemplary substituents include one or more of the following groups: hydrocarbyl, substituted hydrocarbyl, keto, hydroxy, protected hydroxy, acyl, acyloxy, alkoxy, alkenoxy, aikynoxy, aryloxy, halogen, amido, amino, nitro, cyano, thiol, ketals, acetals, esters and ethers.

[0046] The term "acyl," as used herein alone or as part of another group, denotes the moiety formed by removal of the hydroxy] group from the group -COOH of an organic carboxylic acid, e.g., RC(O)- _t wherein R is R ¹ , R ¹ O-, R ¹ R ² N- or R ¹ S-, R ¹ is hydrocarbyl, heterosubstituted hydrocarbyl, or heterocyclo and R ² is hydrogen, hydrocarbyl or substituted hydrocarbyl.

[0047] As used herein, "tBu" and "t-Bu" means tert-butyl.

[0048] There is also provided a dielectric fluid composition comprising a compound selected from the group defined by formula (III) and an unsaturated fatty acid-containing oil or oleochemical, wherein formula (ill) is:

wherein

R _c is C _m H _2m +i wherein m is 0 - 18;

R _h is C _m H _2m +i wherein m is 0 - 18; and n is 4, 5, 6, 7 or 8. [0049] There is also provided a dielectric fluid composition comprising a compound selected from the group defined by formula (IV), and an unsaturated fatty acid- containing oil or oleochemicai, wherein formula (IV) is:

wherein

R _a is C _m H2m+i wherein m is 0 - 8; R _h is CmH ₂ m+i wherein m is 0 - 8; and n is 4, 5, 6, 7 or 8.

[0050] There is also provided a dielectric fluid composition comprising a compound selected from the group defined by formula (V) and an unsaturated fatty acid-containing oil or oleochemicai, wherein formula (V) is:

wherein

R _a is C _m H _2m +i wherein m is 0 - 18;

Rh is CmH ₂ m+i wherein m is 0 - 8; and n is 4, 5, 6, 7 or 8. [0051] There is also provided a dielectric fluid composition comprising a compound selected from the group defined by formula (VI) and an unsaturated fatty acid-containing oil or o!eochemical, wherein formula (VI) is:

wherein

R _c is C _m H _2m +i wherein m is 0 - 18, or S0 ₂ Y where Y is H, or an alkali metal; R _h is CmH ₂ m+i wherein m is 0 - 18;

X is S, S0 ₂ , N, O or an optionally substituted methylene group; and n is 4, 5, 6, 7 or 8.

[0052] There is also provided a dielectric fluid composition comprising a compound selected from the group defined by formula (VII) and an unsaturated fatty acid- containing oil or oleochemica!, wherein formula (VII) is:

wherein

R _c is C _m H _2m+ i wherein m is 0 - 18, or NH ₂ , or S0 ₂ Y where Y is H or an alkali metal; Rh is C _m H ₂ m+i wherein m is 0

R _a is (CH ₂ ) _a COORg where a = 1 - 12 and R _g is either H or hydrocarbyl; X is S, S0 _2] N, O or an optionally substituted methylene group; and n is 4, 5, 6, 7 or 8.

[0053] The present invention also provides a dielectric fluid composition comprising an ester or acid derivative of a compound selected from the group defined by any one or more of formulas (I) to (VII) and an unsaturated fatty acid-containing oil or oleochemical. Preferably, the acid substituent has the general formula: RCOOH, where R = (CH ₂ ) _n , with n ~ 1 to about 22. Preferably, the ester substituent has the general formula RCOOR', where R and R' = (CH ₂ ) _n , with n = 1 to about 22. For example, the compound may be an ester or acid derivative of formula (II), wherein the ester or acid is provided at position R _c of formula (II).

[0054] Preferably, the compound selected from formula (l)-(VII) is present in the dielectric fluid in a concentration of less than 0.3%. More preferably, it is present in a concentration of between about 0.001 % and 0.3%, between about 0.01 % and 0.25%, between about 0.02% and 0.2%, between about 0.025% and 0.15%, between about 0.025% and 0.1 %, between about 0.025% and 0.5%. The compound selected from formula (l)-(VIII) may be present in the dielectric fluid in a concentration of 0.3%, 0.275%, 0.25%, 0.225%, 0.2%, 0.175%, 0.15%, 0.125%, 0.1%, 0.075%, 0.05%, or 0.025%, 0.02%, 0.01 %, 0.005% or any value in between.

[0055] The dielectric fluids of the present invention may contain one compound selected from formula (i)-(Vll), or a mixture of two or more such compounds.

Oil or Oleochemical

[0056] The unsaturated fatty acid-containing oil or oleochemical of the dielectric fluid composition of the present invention is preferably sourced from a naturally occurring or renewable source, including plants (including algae), animals, fungi, bacteria, etc. The unsaturated fatty acid-containing oil or oleochemical of the present invention may be sourced from a single naturally occurring or renewable source, or may be a blend of two or more naturally occurring or renewably sourced unsaturated fatty acid-containing oils or oleochemical. [0057] Preferably, the unsaturated fatty acid containing oil or oleochemical of the present invention is a mono-unsaturated fatty acid-containing oil or oleochemical. However, the unsaturated fatty acid containing oil or oleochemical may alternatively be a poly-unsaturated fatty acid-containing oil or oleochemical.

[0058] In one embodiment of the invention, the unsaturated fatty acid-containing oil or oleochemical is a vegetable derived oil or oleochemical. However, it should be understood that non-vegetable sources of unsaturated fatty acid-containing oils and oleochemicals also fall within the scope of the present invention, such as animal fats and oils including tallow, lard, milk fat etc. The invention further contemplates that the unsaturated fatty acid-containing oil or oleochemical may be obtained from fungal sources or bacterial sources. In this respect, the fungal or bacterial source of the oil or oleochemical maybe a genetically modified organism that has been modified to produce an unsaturated fatty acid-containing oil or oleochemical that is substantially identical with an oil or oleochemical from another renewable source. For example, the bacterial source may be modified to produce an unsaturated fatty acid-containing oil or oleochemical that is substantially identical with a naturally occurring vegetable oil or oleochemical.

[0059] The oil or oleochemical from a naturally occurring or renewable source may also be combined with a minor amount of one or more mineral oils or synthetic oils, providing that the resulting blend demonstrates the beneficial properties of the naturally occurring or renewably sourced unsaturated fatty acid-containing oil or oleochemical.

[0060] While the present invention provides for the use of natural vegetable oils or oleochemical, the invention may use synthetic vegetable oils or oleochemical which have the same or similar compositional characteristics as natural vegetable oils or oleochemical, or genetically modified vegetable oils or oleochemical or a mixture thereof to provide the unsaturated fatty acid-containing oil or oleochemical.

[0061] Where the unsaturated fatty acid-containing oil or oleochemical is a vegetable derived oil or oleochemical, in one embodiment of the invention the vegetable oil or oleochemical is selected from the group comprising: natural vegetable oil, synthetic vegetable oil, genetically modified vegetable oil, oleochemicals derived from such oils and mixtures thereof. [0062] Typical examples of vegetable oils suitable for use in the present invention include, but are not limited to: castor oil, coconut oil, corn oil, cottonseed oil, linseed oil, olive oil, palm oil, peanut oil, grapeseed oil, canola oil, safflower oil, sunflower oil, meadowfoam oil and soybean oil, high oleic variants thereof, and mixtures thereof. One particular embodiment of the present invention employs RBD (Refined, Bleached, and Deodorised) vegetable oil. Alternatively, the vegetable oil may be RBDW vegetable oil (Refined, Bleached, Deodorised and Winterised). Oleochemical derivatives of these oils may be used in the present invention.

[0063] In the present application, the term "oleochemical" and "oleochemical derivative" encompasses basic oleochemical substances like fatty acids, fatty acid methyl esters (FAME), fatty alcohols, fatty amines and glycerols, derived from chemical modification of naturally occurring or renewable oils. Intermediate chemical substances may also be produced from these basic oleochemical substances; such intermediate chemical substances include alcohol ethoxy!ates, alcohol sulfates, alcohol ether sulfates, quaternary ammonium salts, monoacyiglycerols (MAG), diacylglycerols (DAG), structured triacylglycerols (TAG), sugar esters, and other oleochemical products derived from chemical modification of naturally occurring or renewable oils and/or from chemical modification of basic o!eochemica! substances derived from naturally occurring or renewable oils.

[0064] The physical and chemical stability (including oxidative stability) of any unsaturated fatty acid-containing oil or oleochemical is determined by the degree of unsaturation in the fatty acid content, while the freezing point of the oil or oleochemical is determined by chain length, degree of branching and unsaturation. While a unsaturated fatty acid-containing oil or oleochemical with a high saturated fatty acid content will demonstrate chemical stability to oxidation, it will also have a high freezing point. Typically, most fatty acids in oils such as vegetable oils have a chain length of between 16-22 carbon atoms. Therefore, a compromise between oxidative stability and freezing point characteristics is achieved by basing the dielectric fluid composition of the present invention on unsaturated fatty acid-containing oils or oleochemicals with a high (above 60%) unsaturated fatty acid content. Preferably, the high unsaturated fatty acid content is a high mono- unsaturated fatty acid content. However, the high unsaturated fatty acid content may alternatively be a high poly- unsaturated fatty acid content. [0065] The term "fatty acid" as used herein refers to a long chain (more than 8-10 carbon atoms) straight- or branched- saturated, mono-unsaturated or polyunsaturated hydrocarbon chain bonded to a terminal carboxyl group. It will be understood that the term "fatty acid" also encompasses the fatty acid moieties of mono-, di- and triglycerides which are the major constituents of renewable or naturally occurring oils, including vegetable oils, and oleochemicai derivatives of such oils.

[0066] Saturated fatty acids are stable under mild oxidative conditions; whereas mono- unsaturated and, even more so poly-unsaturated fatty acids, are susceptible to oxidation. The melting point of saturated fatty acids increases with chain length such that decanoic and longer chain saturated fatty acids are solids at ambient temperature. While it is also true that the melting point of mono-unsaturated and poly-unsaturated fatty acids .increases with chain length, the rise in melting point tends to be tempered by an increase in the degree of unsaturation throughout the chain length of the fatty acids or the extent of branching throughout the chain length of the fatty acids.

[0067] The physical and chemical stability of a dielectric fluid over prolonged periods of use is an important performance requirement. Thus, in one embodiment of the present invention the unsaturated fatty acid-containing oil or oleochemicai used in the dielectric fluid comprises a high unsaturated fatty acid content. Typically, the unsaturated fatty acid content is > 60%. In some forms of the invention, the unsaturated fatty acid content is > 65%. in some forms of the invention, the unsaturated fatty acid content is > 70%. in some forms of the invention, the unsaturated fatty acid content is > 75%. In one particular embodiment of the invention the unsaturated fatty acid-containing oil comprises about 80% unsaturated fatty acid content. In some forms of the invention, the unsaturated fatty acid content is > 80%.

[0068] The invention provides for the unsaturated fatty acid-containing oil or oleochemicai to comprise a high mono-unsaturated fatty acid content. Typically, the mono-unsaturated fatty acid content is > 60%. In some forms of the invention, the mono-unsaturated fatty acid content is > 65%. In some forms of the invention, the mono-unsaturated fatty acid content is > 70%. In some forms of the invention, the mono-unsaturated fatty acid content is > 75%. In one particular embodiment of the invention the mono-unsaturated fatty acid-containing oil or oleochemicai comprises about 80% mono-unsaturated fatty acid content. In some forms of the invention, the mono-unsaturated fatty acid content is > 80%. [0069] The invention also provides for the unsaturated fatty acid-containing oil or oieochemica! to comprise a high poly-un saturated fatty acid content. Typically, the polyunsaturated fatty acid content is > 60%, In some forms of the invention, the polyunsaturated fatty acid content is > 65%. In some forms of the invention, the polyunsaturated fatty acid content is > 70%. In some forms of the invention, the polyunsaturated fatty acid content is > 75%. In one particular embodiment of the invention the poly-unsaturated fatty acid-containing oil or oleochemical comprises about 80% poly-unsatu rated fatty acid content. In some forms of the invention, the polyunsaturated fatty acid content is > 80%.

[0070] Preferably the unsaturated fatty acid-containing oil or oleochemical is high in a single mono-unsaturated fatty acid (>94%) with <4 % saturated fatty acid, <2% di- unsaturated fatty acid and 0% tri-un saturated fatty acid. Preferably the oil is a safflower oil with a mono-unsaturated fatty acid content of >94%; <4 % saturated fatty acid; <2% di-unsaturated fatty acid and 0% tri-un saturated fatty acid.

[0071] The high unsaturated fatty acid content of the unsaturated fatty acid-containing oil or oleochemical may occur naturally or may be artificially enhanced. For example, an unsaturated fatty acid-containing oil or oleochemica s unsaturated fatty acid content may be enriched with additional unsaturated fatty acids or an oil containing high quantities of such, or the concentration of the unsaturated fatty acid increased by removal of other components from the unsaturated fatty acid-containing oil or oleochemical, or non-unsaturated fatty acid components of the oil or oleochemical may be chemicaily converted to unsaturated fatty acids.

[0072] The unsaturated fatty acid-containing oil or oleochemical is preferably a mono- unsaturated fatty acid-containing oil or oleochemical. The most common mono- unsaturated fatty acid found in vegetable oil is oleic acid. It is found in many naturally occurring vegetable oils, such as sunflower, olive and safflower oil in relatively high proportions, although other renewable and naturally sources of mono-unsaturated fatty acid-containing oils containing oleic acid exist. Genetic modification of certain oil seed stocks, such as canola and sunflower, can generate vegetable oils with an oleic acid content of above 80%. Mono-unsaturated fatty acid-containing oils or oleochemical with a high oleic acid content are particularly suitable for use in the present invention. [0073] Accordingly, in a preferred embodiment of the invention, the mono-unsaturated fatty acid-containing oil or oleochemicai comprises a high oleic acid content. Typically, the oleic acid content is > 60%. in some forms of the invention, the oleic acid content is > 65%, > 70%, > 75%, or > 80%. Preferably, the oleic acid content of the mono- unsaturated fatty acid-containing oil or oleochemicai is about 80%. Alternatively, the mono-unsaturated fatty acid-containing oil or oleochemicai may comprise other mono- unsaturated fatty acids such as eicosenoic acid, docosenoic acid, palmitoleic acid, or erucic acid.

[0074] The mono-unsaturated fatty acid-containing oil or oleochemicai may, for example, be daikon radish oil, meadowfoam seed oil, jojoba oil, meadowlactone, safflower oil or sunfiower oil.

[0075] in one of the embodiments of the invention the mono-unsaturated fatty acid- containing oil or oleochemicai used in the dielectric fluid is a high oleic sunflower oil (HOSO) or oleochemicai derivative of HOSO with 80% oleic acid and < 3% linoleic acid. This particular oil or oleochemicai often has the following fatty acid composition: 81 % mono-unsaturated fatty acid content, 1 1% saturated fatty acid content, and 8% polyunsaturated fatty acid content.

Antioxidant

[0076] The present invention also provides an antioxidant for use with an unsaturated fatty acid-containing oil or oleochemicai to form a dielectric fluid, wherein the antioxidant is a compound selected from the group comprising: formula (I), formula (II), formula (111), formula (IV), formula (V), formula (VI), and/or formula (VII).

[0077] The anti-oxidant may be an ester or acid derivative of the compound of formula (i), formula (II), formula (III), formula (IV), formula (V), formula (VI), and/or formula (VII). Preferably, the acid substituent has the general formula: RCOOH, where R = (CH ₂ ) _n , with n = 1 to about 22. Preferably, the ester substituent has the general formula RCOOR', where R and R' = (CH ₂ ) _n , with n = 1 to about 22.

Use

[0078] The present invention provides the use of a composition comprising: a) an unsaturated fatty acid-containing oil or oleochemicai; b) a compound selected from the group comprising: formula (]), formula (II), formula (III), formula (IV), formula (V), formula (VI), and/or formula (VII) as a dielectric fluid composition.

[0079] The compound may be an ester or acid derivative of the compound of formula (i), formula (II), formula (III), formula (IV), formula (V), formula (VI), and/or formula (VII). Preferably, the acid substituent has the general formula: RCOOH, where R = (CH ₂ ) _n , with n = 1 to about 22. Preferably, the ester substituent has the general formula RCOOR', where R and R' = (CH ₂ ) _n , with n = 1 to about 22.

[0080] The invention further provides for use of a compound selected from the group comprising: formula (i), formula (li), formula (III), formula (IV), formula (V), formula (VI), and/or formula (Vlf) as an additive for a dielectric fluid.

[0081] Preferably, the dielectric fluid to which the compound selected from the group comprising: formula (I), formula (II), formula (111), formula (IV), formula (V), formula (VI), and/or formula (VII) is added comprises an unsaturated fatty acid-containing oil or oleochemical.

Alkyl Esters

[0082] The dielectric fluid composition of the present invention may further comprise one or more alkyl esters. Preferably, the alkyl esters added to the dielectric fluid composition are able to act as viscosity modifiers of the dielectric fluid composition.

[0083] The alkyl esters of the present invention preferably comprise one or more fatty acid aikyi esters. The fatty acid alkyl esters are preferably organic compounds formed by an esterification or transesterification reaction between alcohols of 1 to 4 carbon atoms and fatty acids. Therefore, typically, the alkyl moiety has 1 to 4 carbon atoms. Generally, the most commonly available alkyl esters of fatty acids are produced by esterification or trans-esterification of unsaturated fatty acid-containing oils, such as mono-unsaturated fatty acid-containing oils, and other lipids with methanol or ethanol. In one embodiment of the invention the alkyl ester comprises one or more fatty acid methyl esters or fatty acid ethyl esters.

[0084] in one embodiment of the invention, the fatty acids are selected from the group comprising: saturated fatty acids, mono-unsaturated fatty acids, poly-unsaturated fatty acids, and mixtures thereof. Suitable examples of saturated fatty acids include, but are not limited to: butyric, valeric, caproic, caprylic, pelargonic, capric, lauric, myristic, palmitic, margaric, stearic, arachidic, behenic, lignoceric, cerotic, carboceric, montanic, melissic, lacceoic, psyilic. Suitable examples of mono-unsaturated fatty acids include, but are not limited to: obtusilic, caproleic, iauroleic, linderic, myristoleic, physeteric, tsuzuic, paimitoleic, petroselinic, oleic, vaccenic, gadoleic, gondoic, cetoleic, erucic, and nervonic. Suitable examples of polyunsaturated fatty acids include, but are not limited to: linoleic, y-iinolenic, dihomo-v-linolenic, arachidonic, a-linoleic, stearidonic 7,10,13,16- docosatetraenoic, 4,7,10,13,16-docosapentaenoic, 8,11,14,17-eicosatetraenoic, 5,8,11 ,14,17-eicosapentaenoic (EPA), 7,10,13,16, 9-docosapentaenoic (DPA), 4,7,10,13, 6,19-docosahexaenoic (DHA), docosadienoic acid and 5,8,11-eicosatrienoic (Mead acid).

[0085] Typically, the viscosity of most fatty acid alkyl esters, regardless of the degree of unsaturation in the fatty acid moiety, fall in a range of about 2-6 cSt at 40°C. While it will be understood that fatty acid alky! esters with any one of the above fatty acid moieties will be suitable for use in the dielectric fluid composition of the present invention, preferably as a viscosity modifier, a high mono-unsaturated fatty acid content of the fatty acid alkyl ester is preferred, in order to provide better chemical stability of the alkyl ester and/or to assist in protecting the dielectric fluid composition containing said alkyl esters against oxidation.

[0086] Preferably, the alkyl esters comprise a high unsaturated fatty acid content. Typically, sufficient chemical stability against oxidation is provided when the alkyl ester comprises above 60% unsaturated fatty acids. In some forms of the invention, the alkyl ester comprises above 65%, above 70%, or above 75% unsaturated fatty acids. In the preferred embodiment the alkyl ester comprises about 80% unsaturated fatty acids.

[0087] More preferably, the alkyl esters comprise a high mono-unsaturated fatty acid content. Typically, sufficient chemical stability against oxidation is provided when the alkyl ester comprises above 60% mono-unsaturated fatty acids. In some forms of the invention, the alkyl ester comprises above 65%, above 70%, or above 75% unsaturated fatty acids. In the preferred embodiment the alkyl ester comprises about 80% mono- unsaturated fatty acids. [0088] The alkyl esters employed in the present invention may be readily derived from high oleic mono-unsaturated fatty acid-containing oils which have a high concentration of mono-unsaturated fatty acids.

[0089] Preferably, the fatty acid moieties of the fatty acid alkyl esters are substantially homologous with the fatty acid content of the unsaturated fatty acid-containing oii or oleochemical of the dielectric fluid composition.

[0090] in a further embodiment of the present invention, the alkyl esters comprise fatty acid aikyl esters derived from the unsaturated fatty acid-containing oil or oleochemical of the dielectric fluid composition.

[0091] When the oil or oleochemicai in the fatty acid-containing oil or oleochemical of the dielectric fluid composition is a mono-unsaturated fatty acid-containing oil or oleochemical, the fatty acid moieties of the fatty acid alkyl esters are preferably substantially homologous with the fatty acid content of the mono-unsaturated fatty acid- containing oil or oleochemical of the dielectric fluid composition.

[0092] More preferably, when the oil or oleochemical in the fatty acid-containing oil or oleochemical of the dielectric fluid composition is a mono-unsaturated fatty acid- containing oil or oleochemical, the alkyl esters comprise fatty acid alkyl esters derived from the mono-unsaturated fatty acid-containing oil or oleochemical of the dielectric fluid composition.

[0093] To ensure that the alky! esters in the dielectric fluid composition conform to a similar or the same fatty acid content as the unsaturated fatty acid-containing oil or oleochemical, the alkyl esters may be conveniently be derived from the unsaturated fatty acid-containing oil or oleochemical of the dielectric fluid composition by subjecting the unsaturated fatty acid-containing oil or oleochemical to esterification or trans- esterification with the preferred alcohol.

[0094] Notwithstanding the preferred options described above, it will also be understood that the alky! esters employed by the present invention, either as the viscosity modifier or as one of the components of the dielectric fluid composition, may be derived from other sources of fatty acids, including vegetable- or animal-based fats and oils or oleochemicai and non-renewable sources of fatty acids such as mineral oils. [0095] Preferably, the addition of aikyl esters to the dielectric fluid composition of the present invention results in a viscosity of < 20 cSt at 40°C.

[0096] In one form, the viscosity of the composition is < 19 cSt at 40°C, < 18 cSt at 40°C, < 17 cSt at 40°C, or < 16 cSt at 40°C. In one form, the viscosity of the composition is between 1 and 20 cSt at 40°C, between 1 and 19 cSt at 40°C, 1 and 18 cSt at 40°C, between 1 and 17 cSt at 40°C or between 1 and 16 cSt at 40°C.

[0097] The dielectric fluid composition of the present invention may preferably comprise unsaturated fatty acid-containing oil or oleochemical in the range of 40 - 60 %v/v, and alkyi esters in the range of 60 - 40 %v/v. More preferably, the dielectric fluid composition comprises mono-unsaturated fatty acid-containing oil or oleochemical in the range of 40 - 60 %v/v, and aikyl esters in the range of 60 - 40 %v/v.

[0098] The present invention therefore provides a dielectric fluid composition comprising: a) an unsaturated fatty acid-containing oil or oleochemical; b) a compound selected from the group defined by formula (I); c) one or more fatty acid aikyl esters, each having a fatty acid moiety and an aikyl moiety, wherein the aikyl moiety of the fatty acid aikyl esters has 1 to 4 carbon atoms; wherein the oil or oleochemical is in the range of 40%-60% v/v of the dielectric fluid composition and the a fatty acid alkyi ester is in the range of 40%-60% v/v of the dielectric fluid composition, and wherein the viscosity of the dielectric solution is < 20 cSt at 40°C.

Additives

[0099] In another embodiment of the invention, the dielectric fluid composition further comprises at least one additive, to improve or further enhance the dielectric properties and characteristics of the dielectric fluid composition of the present invention. The or each additive may be selected from the group comprising: anti-oxidants, pour point depressants, corrosion inhibitors, anti-microbial compounds, and/or viscosity modifiers. [00100] The pour point of the dielectric fluid composition can be improved either by the addition of pour point suppressants to the dielectric fluid composition or winterization of the dielectric fluid composition.

[00101] The pour point depressant typically contains a branched polymethacrylate backbone which encourages inclusion of the pour point depressant molecule into a growing crystal of the unsaturated fatty acid-containing oil or oleochemicai in the dielectric fluid composition. By interfering with wax crystal growth patterns, the pour point depressant increases the operational range of the dielectric fluid composition so it remains fluid at much lower temperatures. Pour point depressants such as Viscoplex® 10-310, Viscoplex® 10-930, and Viscoplex® 10-950 are suitable examples.

[00102] Winterization is the process of removing sediment which appears in oils, such as unsaturated fatty acid-containing oils, at low temperatures. The sedimentation is accompanied by a decrease in the oil or oleochemical's viscosity. Winterization of the dielectric fluid composition is typically performed by slow cooling the dielectric fluid composition to 7°C, then filtering out any resulting crystals. The liquid filtrate subsequently undergoes another period of slow cooling in a manner as described above to remove any additional resulting crystals.

[00103] The oxidative stability of the dielectric fluid composition can be improved by addition of metal deactivators and/or supplementary anti-oxidants to the dielectric fluid composition. However, it is a benefit of the compounds of the present invention that they may be able to chelate metal ions. Therefore, it is believed that they may be able to provide a metal deactivating function as well as their antioxidant function. Given this, there may not be a need for additional metal deactivators to be added to the dielectric fluids. Nevertheless, the present compounds are compatible with known metal deactivators and therefore the compounds can be added to dielectric fluids already containing commercial or known metal deactivators.

[00104] Suitable examples of metal deactivators include, but are not limited to: copper deactivators such as benzotriazole and triazole derivatives. Typically, the dielectric fluid composition comprises less than 0.7 % metal deactivator.

[00105] Suitable examples of supplementary anti-oxidants include, but are not limited to: phenolic anti-oxidants such as Irganox® L109, Irganox® L64, lrganox® L94, and octylated/butyiated diphenyiamine antioxidants such as lrganox® L57. Typically, the dielectric fluid composition comprises less than 0.3 % anti-oxidant.

Transformer

[00106] The dielectric fluid composition developed by the inventors has comparable dielectric properties and performance to mineral oil, the standard dielectric fluid currently used in electrical distribution and power equipment, such as transformers, switching gear and electric cables. Existing transformers can be readily retro-filled with the dielectric fluid of the present invention comprising an unsaturated fatty acid- containing oil or oleochemical and an antioxidant compound and operated under standard conditions.

[00107] Accordingly, the present invention provides a transformer having a housing which accommodates a transformer core/coil assembly and a dielectric fluid composition surrounding said core/coil assembly, wherein the dielectric fluid composition comprises a compound selected from the group comprising: formula (I), formula (II), formula (111), formula (IV), formula (V), formula (VI), or formula (Vl!), and a mono-unsatu rated fatty acid-containing oil or oleochemical.

[00108] Referring to Figure 1 , there is shown a transformer 110 having a housing 112 which accommodates a transformer core/coil assembly 114. The transformer core- coil assembly 114 is arranged to be immersed in a dielectric fluid composition 116 of the present invention, such that the dielectric fluid composition 116 surrounds the transformer core-coil assembly 114 and performs according to desired electrical standards.

Method

[00109] The inventors have found that the compounds of formula (l)-(VII) of the present invention are able to increase the oxidative stability of dielectric fluids comprising unsaturated fatty acid containing oils or oleochemicals.

[00110] Thus, the present invention provides a method of increasing the oxidative stability of a dielectric fluid comprising an unsaturated fatty acid-containing oil or oleochemical, said method comprising the step of: blending the dielectric fluid containing an unsaturated fatty acid-containing oil or oleochemical with a compound selected from the group comprising: formula (I), formula (II), formula (III), formula (IV), formula (V), formula (Vi), or formula (VII).

[00111] The compound may be an ester or acid derivative of the compound of formula (I), formula (il), formula (III), formula (IV), formula (V), formula (VI), and/or formula (VII). Preferably, the acid substituent has the general formula: RCOOH, where R = (CH ₂ )n, with n = 1 to about 22. Preferably, the ester substituent has the general formula RCOOR', where R and R' = (CH ₂ )„, with n = 1 to about 22.

Oxidative Stability Modifier

[00112] The present invention also provides an oxidative stability modifier for an unsaturated fatty acid-containing oil or oleochemical -based dielectric fluid, comprising a compound selected from the list comprising: formula (I), formula (il), formula (Ml), formula (IV), formula (V), formula (VI), or formula (VII).

[00113] The oxidative stability modifier may be an ester or acid derivative of the compound of formula (I), formula (II), formula (III), formula (IV), formula (V), formula (VI), and/or formula (Vil). Preferably, the acid substituent has the general formula: RCOOH, where R = (CH ₂ ) _n , with n = 1 to about 22. Preferably, the ester substituent has the general formula RCOOR', where R and R' = (CH ₂ ) _n , with n = 1 to about 22.

Process for Producing a Dielectric Fluid Composition

[00114] The present invention also provide a process for producing a dielectric fluid composition comprising the step of: a) blending a volume of unsaturated fatty acid-containing oil or oleochemical with a volume of a compound selected from the group comprising: formula (I), formula (II), formula (III), formula (IV), formula (V), formula (VI), and/or formula (VII).

[00115] Preferably, the compound selected from formula (l)-(Vll) is present in the dielectric fluid in a concentration of less than 0.3%. More preferably, it is present in a concentration of between about 0.001 % and 0.3%, between about 0.01% and 0.25%, between about 0.02% and 0.2%, between about 0.025% and 0.15%, between about 0.025% and 0.1 %, between about 0.025% and 0.5%. The compound selected from formula (l)-(VI!l) may be present in the dielectric fluid in a concentration of 0.3%, 0.275%, 0.25%, 0.225%, 0.2%, 0.175%, 0.15%, 0.125%, 0.1%, 0.075%, 0.05%, or 0.025%, 0.02%, 0.01%, 0.005% or any value in between.

[00116] The compound may be an ester or acid derivative of the compound of formula (I), formula (II), formula (III), formula (IV), formula (V), formula (VI), and/or formula (VII). Preferably, the acid substituent has the general formula: RCOOH, where R = (CH ₂ )n. with n = 1 to about 22. Preferably, the ester substituent has the general formula RCOOR', where R and R' = (CH ₂ )„, with n = 1 to about 22.

[00117] The process for producing the dielectric fluids of the present invention may involve the blending of one compound selected from formula (l)-(VH) with a volume of unsaturated fatty acid-containing oil or oleochemical, or blending a mixture of two or more such compounds with a volume of unsaturated fatty acid-containing oil or oleochemical.

[00118] The unsaturated fatty acid-containing oil or oleochemical may be sourced from a naturally occurring or renewable source, preferably from the group comprising: natural vegetable oil, synthetic vegetable oil, genetically modified vegetable oil, animal fats and oils, oleochemica!s derived from such oils and mixtures thereof.

[00119] Preferably, the unsaturated fatty acid-containing oil is selected from the group comprising: castor oil, coconut oil, corn oil, cottonseed oil, linseed oil, olive oil, palm oil, peanut oil, grapeseed oil, canola oil, safflower oil, sunflower oil, and soybean oil, high oleic variants thereof, and mixtures thereof. Oleochemical derivatives of these oils may be used in the present invention.

[00120] In one form of the present invention, the unsaturated fatty acid-containing oil or oleochemical comprises a high unsaturated fatty acid content. Typically, the unsaturated fatty acid content is > 60%. In some forms of the invention, the unsaturated fatty acid content is > 65%, > 70%, > 75% or > 80%. In one particular embodiment of the invention the unsaturated acid-containing oil or oieochemical comprises about 80% unsaturated fatty acid content.

[00121] The invention provides for the unsaturated fatty acid-containing oil or oleochemical to comprise a high mono-unsaturated fatty acid content. Typically, the mono-unsaturated fatty acid content is > 60%. In some forms of the invention, the mono-unsaturated fatty acid content is > 65%, > 70%, > 75% or > 80%. In one particular embodiment of the invention the vegetable oil or oleochemicai comprises about 80% m on o-unsatu rated fatty acid content.

[00122] In a preferred embodiment of the invention the mono-unsaturated fatty acid-containing oil or oleochemicai comprises a high oleic acid content.

[00123] Typically, the oleic acid content is > 60%. In some forms of the invention, the oleic acid content is > 65%, > 70% or > 75%. In some forms of the invention, the oleic acid content is > 80%.

[00124] In one of the embodiments of the invention the mono-unsaturated fatty acid-containing oil is a high oleic sunflower oil (HOSO) or oleochemicai derivative of HOSO with 80% oleic acid and < 3% linoleic acid. In another embodiment, the mono- unsaturated fatty acid-containing oil is a safflower oil with a mono-unsaturated fatty acid content of >94%; <4 % saturated fatty acid; <2% di-unsaturated fatty acid and 0% tri- unsaturated fatty acid.

[00125] The dielectric fluid composition provided by the above process may additionally comprise an alkyl ester. Typically the a!kyl ester is blended with the unsaturated fatty acid-containing oil or oleochemicai in a percentage volume ratio of 40:60 to 60:40.

[00126] The dielectric fluid composition provided by the above process may additionally comprise at least one additive, the or each additive being selected from the group comprising: anti-oxidants, pour point depressants, corrosion inhibitors, anti- bacteriais, viscosity modifiers. Suitable examples of anti-oxidant additives comprise metal deactivators.

[00127] Therefore, there is provided a process for producing a dielectric fluid composition comprising the step of: a) blending a volume of unsaturated fatty acid-containing oil or oleochemicai with a volume of a compound selected from the group comprising: formula (I), formula (!l), formula (III), formula (IV), formula (V), formula (VI), or formula (Vil) to form a mixture; b) blending the mixture of step (a) with an alkyl ester. [00128] There is also provided a process for producing a dielectric fluid composition comprising the step of: a) blending a volume of unsaturated fatty acid-containing oil or oleochemical with a volume of a compound selected from the group comprising: formula (I), formula (il), formula (III), formula (IV), formula (V), formula (VI), or formula (VII); b) blending the mixture of step (a) with one or more additives.

[00129] There is additionally provided a process for producing a dielectric fluid composition comprising the step of: a) blending a volume of unsaturated fatty acid-containing oil or oleochemical with a volume of a compound selected from the group comprising: formula (!), formula (II), formula (III), formula (IV), formula (V), formula (VI), or formula (VII) to form a mixture; b) blending the mixture of step (a) with an alkyl ester and one or more additives

Purification of Oil

[00130] It is understood by the person skilled in the art that the dielectric fluid composition of the present invention comprising a compound of formula (I) and an unsaturated fatty acid-containing oil or oleochemical may need to undergo one or more purification processes in order to ensure that the dielectric fluid composition has the necessary performance characteristics to compare to existing mineral oil-based dielectric fluids.

[00131] For example, while it is envisaged that an oil such as RBD (Refined, Bleached and Deodorised) vegetable oil or or oleochemical derivative of RBD may be employed as the unsaturated fatty acid-containing oil component of the dielectric fluid composition of the present invention, it is acknowledged that RBD vegetable oil is typically unsatisfactory for use as a dielectric fluid. The RBD oil typically contains water and other conductive contaminants which degrade its performance properties as a dielectric fluid when used in electrical apparatus such as power and distribution transformers. For example, in respect to high oleic sunflower oil (HOSO), the dielectric breakdown voltage is typically > 55 kV (IEC 60156, 2 mm gap electrode), dielectric dissipation factor < 0.085 at 90 °C and 50 HZ (IEC 60247), initial acidity number < 0.12 mg KOH/g (iEC 60296), initial surface tension (IFT) > 21.0 dynes/cm (ISO 6295), pour point < -15 °C (iSO 3016), and a moisture content > 380 ppm. These values are outside of acceptable dielectric performance.

[00132) Therefore, the unsaturated fatty acid-containing oil or oleochemicai of the present invention and/or the dieiectric fluid composition of the present invention, may need to undergo one or more purification processes.

[00133] The process may comprise the step of depleting the dielectric fluid composition of water and other conductive contaminants such as acids.

[00134] Removal of water is effected with known dehydration processes. Suitable examples of dehydration processes include but are not limited to eluting the dielectric fluid composition under gravity through adsorption media such as molecular sieves, starches, and desiccants, centrifugal separation, and vacuum dehydration. Typically, the dehydration process employed in the present invention decreases the water content of the dieiectric fluid composition by more than 70%, preferably more than 80%.

[00135] Removal of other contaminants such as acids is typically accomplished by eluting the dielectric fluid composition under gravity through adsorption media including but not limited to Fuller's earth, activated clays, and attapulgite. Typically, elution of the dieiectric fluid composition through the above described adsorption media decreases the acid value of the dielectric fluid composition and increases the interfacial tension of the dielectric fluid composition to acceptable parameters.

[00136] It will be understood that the above described process may be conducted one or more times, depending on the original acid value and interfacial tension of the mono-unsaturated fatty acid-containing oil or oleochemicai.

[00137] Preferably, the dielectric fluid composition is dehydrated prior to treatment with adsorption media for removal of contaminants.

[00138] Advantageously, it has been found that sequential treatment of the dielectric fluid composition with the desiccant followed by elution through the adsorption media is an effective method for also significantly improving the dielectric voltage and dissipation factors of the dielectric fluid composition such that after said treatment these parameters fall within acceptable standards for dielectric fluids. In one example, the dielectric fluid composition is contacted with said adsorption media by eluting the dielectric fluid composition through a column of said adsorption media. In another example, the step of purifying the dielectric fluid composition comprises eluting the dielectric fluid composition through a first adsorption medium and removing water, and then eluting the dielectric fluid composition through a second adsorption medium and removing acid.

[00139] In an alternative example, the process comprises the step of purifying the unsaturated fatty acid-containing oil or oleochemical prior to blending the oil or oteochemical with the compounds of formula (I) to form the dielectric fluid composition. Typically, purifying the unsaturated fatty acid-containing oil or oleochemical prior to blending the oil or oleochemical with the compounds of formula (I) comprises eluting the unsaturated fatty acid-containing oil or oleochemical through adsorption media to remove water and acid.

General

[00140] Those skilled in the art will appreciate that the invention described herein is susceptible to variations and modifications other than those specifically described. It is to be understood that the invention includes all such variations and modifications. The invention also includes all of the steps, features, compositions and compounds referred to or indicated in the specification, individually or collectively and any and all combinations or any two or more of the steps or features.

[00141] The present invention is not to be limited in scope by the specific embodiments described herein, which are intended for the purpose of exemplification only. Functionally equivalent products, compositions and methods are clearly within the scope of the invention as described herein.

[00142] The entire disclosures of all publications {including patents, patent applications, journal articles, laboratory manuals, books, or other documents) cited herein are hereby incorporated by reference. No admission is made that any of the references constitute prior art or are part of the common general knowledge of those working in the field to which this invention relates. [00143] Each document, reference, patent application or patent cited in this text is expressly incorporated herein in their entirety by reference, which means that it should be read and considered by the reader as part of this text. That the document, reference, patent application or patent cited in this text is not repeated in this text is merely for reasons of conciseness.

[00144] Any manufacturer's instructions, descriptions, product specifications, and product sheets for any products mentioned herein or in any document incorporated by reference herein, are hereby incorporated herein by reference, and may be employed in the practice of the invention.

[00145] As used herein the term "derived" and "derived from" shall be taken to indicate that a specific integer may be obtained from a particular source albeit not necessarily directly from that source.

[00146] As used herein, the singular forms "a," "an" and "the" include plural references unless the context clearly dictates otherwise.

[00147] Throughout this specification, unless the context requires otherwise, the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.

[00148] Other than in the operating example, or where otherwise indicated, all numbers expressing quantities of ingredients, reaction conditions, and so forth used in the specification and claims are to be understood as being modified in all instances by the term "about". Accordingly, unless indicated to the contrary, the numerical parameters set forth in the specification and claims are approximations that may vary depending upon the desired properties sought to be obtained by the present invention. Hence "about 80%" means "about 80%" and also "80%". At the very least, each numerical parameter should be construed in light of the number of significant digits and ordinary rounding approaches.

[00149] Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical value; however, inherently contains certain errors necessarily resulting from the standard deviation found in their respective testing measurements

[00150] Other definitions for selected terms used herein may be found within the detailed description of the invention and apply throughout. Unless otherwise defined, all other scientific and technical terms used herein have the same meaning as commonly understood to one of ordinary skill in the art to which the invention belongs.

[00151] The following examples serve to more fully describe the manner of using the above-described invention, as well as to set forth the best modes contemplated for carrying out various aspects of the invention. It is understood that these methods in no way serve to limit the true scope of this invention, but rather are presented for illustrative purposes.

EXAMPLES

Example 1: Testing Samples of Formula I to VII

Materials

Oils

HOSO - Goodman Fielder Sunola® Envirotemp®FR3™ - Cargill

Sunflower Oil - Crisco® Sunflower

Additives

Sample No Additive Source

1 Irganox L57 BASF

2 Irganox L109 CIBA

3 Irgamet 30 CIBA

4 Irganox L135 BASF

5 Irgamet 39 BASF

73 Butyl a ted hydroxytoluene, DBPC Lanxess

74 2,6-Di-tert-butyiphenol Sigma Aldrich

76 4-tert-Butylphenol Sigma Aldrich Samples

[00152] Al! test compounds were provided in HOSO oil as described above. Those samples tested in the presence of a metal deactivator (Sample No + MD), were tested using Irgamet 30® as the metal deactivator.

Methods

[00153] The acceptable range of dielectric fluid properties for typical dielectric fluids used in power and distribution transformers is defined by the following standards: ASTM 6871 "Standard Specification for Natural (Vegetable Oil) Ester Fluids Used in Electrical Apparatus".

Method for Testing Dielectric Dissipation Factor, Resistivity at 20°C and Resistivity at 90/100°C

[00154] Testing of Dielectric Dissipation Factor (DDF), Resistivity at 20°C and Resistivity at 90/100°C was carried out on an Oil Tan-Delta and Resistivity Test System (Ajit Electronics; India). The DDF was tested at 90°C. [00155] To meet the ASTM 6871 criteria, the DDF at 60 Hz should be a maximum of 0.20% at 25°C and 4.0% at 100°C. The Resistivity at 20°C should be >10GOhms and Resistivity at 90/100°C should be >450MOhms.

Method for Testing Oxidative Stability

[00156] The oxidative stability of the dielectric fluid composition was tested using the Rancimat Oxidation Stability test EN14112 (2003). In this test, a volume of 10L per minute air is passed through the dielectric fluid at 110°C. The end point is determined when the production of acids begins, as indicated by a conductivity increase.

[00157] To meet the EN14112 (2003) criteria, the oxidative stability should be >6 hours.

Method for Testing Oxidative Stability IEC 61125 Method B

[00158] The oxidative stability of the dielectric fluid composition was tested using the IEC 61125 Method B. It measures the time taken for a phenolphthalein indicator to lose colour. At this point, volatile acidity is around 0.28mg KOH/g oil

Manufacture of Custom p-t-butyl calix[41arene

A. Preparation of "precursor. "

[00159] A mixture of 100 g (0.666 mol) of p-tert-butylphenol (Aldrich Chemical Company, Inc.), 62 mL of 37% formaldehyde solution (0.83 mol of HCHO) (Fisher Chemical Company), and 1.2 g (0.03 mol) of sodium hydroxide (corresponding to 0.045 equiv with respect to phenol) in 3 mL of water is placed in a 3-L, three-necked, round- bottomed flask equipped with a mechanical stirrer. The contents of the open flask are allowed to stir for 15 min at room temperature, and then heated for 2 hr at 100-120°C by means of a heating mantle. Care should be taken not to allow the heating mantle to get so hot as to char the solid materia! on the walls of the flask. The reaction mixture, which is clear and colourless at the beginning, becomes light yellow after 30 min, a somewhat deeper yellow after 2 hr, and eventually changing to a thick slurry as the water evaporates and finally turning to a deep yellow or brown-yellow very viscous mass. During this period there is considerable frothing, and the reaction mixture fills most of the flask before shrinking back to the original volume. Stirring is discontinued, the reaction vessel is removed from the heating mantle, and the reaction mixture is allowed to cool to room temperature. To dissolve the residue 800-1000 mL of warm diphenyl ether is added to the flask and the contents are stirred, the process generally requiring at least 1 hr.

B. Pyrolysis of the precursor.

[00160] The 3-L, three-necked flask is fitted with a nitrogen inlet. The contents of the flask are stirred and heated (110-120°C) with a heating mantle while a stream of nitrogen is blown rapidly over the reaction mixture to facilitate the removal of the water as it is evolved. During this period the colour of the solution changes from yellow to a grey or a light brown. When the evolution of water subsides and a solid starts to form (prior to attaining the reflux temperature), the flask is fitted with a condenser, and the contents of the flask are stirred and heated to ca. 150-160°C for a few minutes and then at reflux for 3-4 hr under a gentle flow of nitrogen. During this phase of the reaction the solid dissolves, and a clear dark-brown to greyish-black solution is formed. The reaction mixture is cooled to room temperature {some solid separates), and the product is precipitated by the addition ofl .5 L of ethyl acetate. The resulting mixture is stirred for 15-30 min and allowed to stand for at least 30 min. Filtration yields materia! that is washed twice with 00-mL portions of ethyl acetate, once with 200 mL of acetic acid, twice with 100-mL portions of water, and twice with 50-mL portions of acetone to yield ca. 66 g (61 %) of crude product. The white-to-beige-colored crude product is dissolved in ca. 1600-1800 mL of boiling toluene that is concentrated to ca. 700-900 mL. On cooling, 61 g (49%) of product is obtained as glistening white rhombic crystals, mp 342-344°C. The product of crystallization from toluene is a 1 :1 complex of p-tert- butylcalix[4]arene and toluene, from which the toluene can be removed by drying under high vacuum (< 1 mm) and high temperature (> 140°C) for an extended period of time (48 hr).

Results

[00161] Table 1 shows the properties of various base oils, without additives. Although the baseline stability of pure HOSO is variable, it is clear that the oxidation stability of HOSO does not exceed 7 hours.

[00162] In all Tables, where multiple values are provided for oxidation stability, the same samples were tested on multiple days. There was often a large difference in base oil and base oil plus sample oxidation stability values on different days, and so the base oil plus samples were generally tested concurrently with base oil alone each time. If multiple values appear in the Oxidative Stability", Oxidative Stability IEC 61125 Method B" and/or "Corresponding base oil stability" columns of the Tables, the values in line with each other were determined on the same day.

[00163] Table 2 shows the properties of commercial additives for dielectric fluids, tested using HOSO as the base oil. It can be seen that the commercial additive L109, when incorporated into a dielectric fluid composition at low concentrations, does not increase the performance of the dielectric fluid composition above that of HOSO alone in terms of oxidative stability.

[00164] 2,6-Di-tert-butyl-4-methyiphenol, 2,6-Di-tert-butyl~p-cresol (DBPC) and 4- tert-Butylphenol are non-macrocyclic analogues of the t-But calixraenes. Addition of these compounds to HOSO does not increase the oxidative stability performance of the dielectric fluid composition significantly beyond that of pure HOSO.

[00165] Tables 3 to 7 provide results for the testing of DDF, resistivity and oxidative stability of various compounds of formulas (I) to (VII).

Table 1 : Properties of Base Oiis

Table 2: Properties of Conventional Additives

Table 3: Testing of Compounds of Formula (1)

Table 4: Testing of compounds of formula (II)

Table 5: Testing of compounds of formula (IV)

Table 6: Testing of compounds of formuia (VI)

Table 7: Testing of compounds of formula (VII)

Example 2: Further testing ofp-t-butyl calix[4]arene

[00166] Further testing of Sample 6 (p-t-butyl calix[4]arene) in HOSO at 0.25g/L was carried out.

Method

Testing for Oxidation Stability of insulating Oil by Pressure Vessel

[00167] The procedure is performed according to ASTM test method D2112, with the modification that testing is carried out at 110°C for 64 minutes and water was not used in the sample preparation step. The test involves adding the test oil to a vessel and adding a copper catalyst. The pressure vessel was then charged with 95 psi of oxygen and rotated a specific angle in a bath set at a specific temperature. The termination of the test occurs when the pressure drops by 25 psi.

[00168] When tested using the unmodified ASTM test method D2112, the dielectric fluid comprising Sample 6 in HOSO lasted 25 minutes. When tested using the modified ASTM test method D2112, the dielectric fluid comprising Sample 6 in HOSO lasted 64 minutes.

Power Factor Valued Oxidation Testing (PFVO)

[00169] The Power Factor Valued Oxidation Testing (PFVO) periodically measures the power factor of an oil while it is being aged at 95°C in the presence of copper and air. Consequently, it indicates the dielectric-!oss characteristics of insulating oil as a function of accelerated aging conditions. The resulting graph of power factor versus time characterizes a given oil. It is applicable as a continuity test, as welt as a measure of oil quality. The test is run concurrently with the Doble Sludge-Free Life test which measures the time until the oil forms sludge.

[00170] The dielectric fluid of the present invention comprising HOSO oil and Sample 6 (p-t-butyl calix[4]arene) achieved a PVFO result as provided in Figure 2. Although the power factor rose above 4.5% at the end of the testing cycle, this is considered to be quite good for a natural ester insulating liquid Doble Sludge Free Life (SFL) Testing

[00171 ] The Sludge-Free Life of an oil, sampled at 8-hour intervals at 95°C during the PFVO test, is the number of hours which have elapsed between the start of the test and the time of taking the last sample which showed a sludge-free precipitation test. To date, standard parameters for sludge free oil life have only been developed for mineral oils, generally with BHT or DBPC included as an inhibitor. Table 8 provides the standards for such mineral oils.

[00172] Table 8: Sludge Free parameters

[00173] The test sample of dielectric fluid of the present invention comprising HOSO oil and Sample 6 (p-t-butyl calix[4]arene) provided a sludge free life of 88 hours.

Oxidation Stability Testing

[00174] The oxidation stability was performed in accordance to the modifications of the IEC61 125C method as defined in [EC 62770, Annex A. The temperature was 120°C, catalyst was copper, sparging gas was air and duration of test was 48hrs.

[00175] The test sample of dielectric fluid of the present invention comprising HOSO oil and Sample 6 (p-t-butyl calix[4]arene) had an oxidation stability within the limits of IEC 61 125 Method C (modified). Table 9: Results of Oxidation Stability Testing - Sample 6 in HOSO

Viscosity Increase Testing

[00176] The sample was aged for 4 days via conditions as outlined in IEC 61125C. Viscosity testing was performed at 40°C by using the criteria outline in ASTM D445.

Table 0: Viscosity testing results - Sample 6 in HOSO

[00177] Numerous variations and modifications will suggest themselves to persons skilled in the relevant art, in addition to those already described, without departing from the basic inventive concepts. All such variations and modifications are to be considered within the scope of the present invention, the nature of which is to be determined from the foregoing description.