Dielectric fluids having reduced streamer speed

Abstract

The present invention relates to a liquid composition for electrical insulation including a dielectric fluid and an additive, the additive being dissolved in the dielectric fluid and having a 1.sup.st excitation energy which is lower than the 1.sup.st excitation energy of the dielectric fluid.

Claims

1. An apparatus selected from the group consisting of electrical apparatuses and power applications, comprising a liquid electrically insulating composition comprising a dielectric fluid and an additive in a concentration of between 1 and 10 wt % of the composition, wherein the additive is dissolved in the dielectric fluid and has a 1.sup.st electron excitation energy within the range of from 1 to 4 eV which is lower than the 1.sup.st electron excitation energy of the dielectric fluid.

2. The apparatus of claim 1, wherein the additive is selected from azo compounds, of formula (I):
R.sup.5NNR.sup.6(I) wherein R.sup.5 and R.sup.6 are both independently selected from aryl or heteroaryl, which is unsubstituted or substituted in one, two or three positions with substituents independently selected from C.sub.1-10 alkyl, C.sub.2-10 alkynyl, OH, CHO, C.sub.1-10 acyl, C.sub.1-10 alkoxy, C.sub.1-6 alkanoyloxy, C.sub.1-10 alkylthio, C.sub.1-10 alkylamino, CN, nitro, amino, amido, sulfonyl, arylsulfonyl, halo, halo C.sub.1-10 alkyl, C.sub.1-10 alkyl aryl, and aminoaryl; or a five-membered carbocyclic or heterocyclic ring, which is unsubstituted or substituted in one, two or three positions with substituents independently selected from C.sub.1-10 alkyl, C.sub.2-10 alkynyl, OH, CHO, C.sub.1-10 acyl, C.sub.1-10 alkoxy, C.sub.1-6alkanoyloxy, C.sub.1-10 alkylthio, C.sub.1-10 alkylamino, CN, nitro, amino, arylamino, amido, sulfonyl, arylsulfonyl, halo, halo-C.sub.1-10 alkyl C.sub.1-10 alkyl aryl, and aminoaryl.

3. The apparatus of claim 1, wherein the dielectric fluid is an ester-based dielectric fluid.

4. The apparatus of claim 1, wherein the additive is selected from the group consisting of colour dyes.

5. The apparatus of claim 2, wherein R.sup.5 is selected from phenyl, 2-oxazolyl, 2-thiazolyl and 2-imidazolyl; and R.sup.6 is selected from phenyl and 2-thiazolyl.

6. An apparatus selected from the group consisting of electrical apparatuses and power applications, comprising a liquid electrically insulating composition comprising a dielectric fluid and an additive in a concentration of between 1 and 10 wt % of the composition, wherein the additive is dissolved in the dielectric fluid and has a 1.sup.st electron excitation energy within the range of from 1 to 4 eV which is lower than the 1.sup.st electron excitation energy of the dielectric fluid, and wherein the additive is selected from formula (II), (III) and (IV), ##STR00013## wherein X is selected from S, O and N; and R.sub.1, R.sub.2, R.sub.3, and R.sub.4, are each independently selected from H, C.sub.1-10 alkyl, CHCH.sub.2, halogens, OH, C.sub.1-10 alkoxy, OCHC.sub.1-10 alkyl, CN, and NH.sub.2.

7. The apparatus of claim 6, wherein X is selected from S and O; R.sub.1 is selected from H, C.sub.1-4 alkyl, OH, C.sub.1-4 alkoxy, CN, and NH.sub.2; R.sub.2 is selected from H or CN; R.sub.3 is selected from H, CHO, CHCH.sub.2; and R.sub.4 is selected from H and Cl.

8. The apparatus of claim 7, wherein R.sub.1 is selected from H, CN, CH.sub.3, OH, OCH.sub.3, and NH.sub.2.

9. An apparatus selected from the group consisting of electrical apparatuses and power applications, comprising a liquid electrically insulating composition comprising a dielectric fluid and an additive in a concentration of between 1 and 10 wt % of the composition, wherein the additive is dissolved in the dielectric fluid and has a 1.sup.st electron excitation energy within the range of from 1 to 4 eV which is lower than the 1.sup.st electron excitation energy of the dielectric fluid, and wherein the additive is of the following formula (V) ##STR00014## wherein X.sub.1, X.sub.2, Y.sub.1 and Y.sub.2 are each independently selected from H, C.sub.1-10 alkyl, C.sub.2-10 alkenyl, C.sub.2-10 alkynyl, OH, CHO, C.sub.1-10 acyl, C.sub.1-10 alkoxy, C.sub.1-6 alkanoyloxy, C.sub.1-10 alkylthio, C.sub.1-10 alkylamino, CN, nitro, amino, amido, sulfonyl, arylsulfonyl, halo, halo C.sub.1-10 alkyl, C.sub.1-10 alkyl aryl, and aminoaryl.

10. An apparatus selected from the group consisting of electrical apparatuses and power applications, comprising a liquid electrically insulating composition comprising a dielectric fluid and an additive in a concentration of between 1 and 10 wt % of the composition, wherein the additive is dissolved in the dielectric fluid and has a 1.sup.st electron excitation energy within the range of from 1 to 4 eV which is lower than the 1.sup.st electron excitation energy of the dielectric fluid, and wherein the additive is selected from 4-anilino-4-nitroazobenzene and p-dimethylamino-azobenzenesulfonic acid.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention is now described, by way of example, with reference to the accompanying drawings, in which:

(2) FIG. 1 is an experimental graph presenting a comparison in streamer velocity between a natural ester oil and a mineral oil as a function of applied voltage, of the prior art.

(3) FIG. 2 schematically illustrates the concepts of excitation energy and ionization potential of a compound.

(4) FIG. 3 is an experimental graph presenting a comparison in streamer velocity between a natural ester oil and the same ester oil comprising an additive according to the present invention.

(5) FIG. 4 is an experimental graph presenting a comparison in streamer velocity between a natural ester oil and the same ester oil comprising another additive according to the present invention.

DETAILED DESCRIPTION

(6) The invention will now be described more fully hereinafter with reference to certain embodiments of the invention. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided by way of example so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

(7) All words and abbreviations used in the present application shall be construed as having the meaning usually given to them in the relevant art, unless otherwise indicated. For clarity, some terms are however specifically defined below.

(8) The term fluid is used herein for the group comprising of oils, emulsions, suspensions and other liquids.

(9) The dielectric fluid of the present invention may be a non-mineral oil, such as a vegetable fluid or oil.

(10) Further, vegetable fluids and/or oils may for instance be selected from the group comprising, but that is not limited to, peanut, rapeseed, castor, olive, corn, cotton, canola, soybean, sesame, linseed, safflower, grapeseed, palm, avocado, pumpkin kernel, macadamia nut, sunflower, and any combinations and/or mixtures thereof. Additionally, fluids and/or oils may be obtained from essentially any organisms being a suitable fluid and/or oil source. Fluids and/or oils derived from animal sources may be selected from the group comprising beef tallow, fish oils, lard, and any combinations and/or mixtures thereof. Naturally, various combinations of the above fluids and/or oils may be utilized, irrespective of the source.

(11) It should be noted that the composition may comprise other additives which are not specifically related to the reduction of streamers, e.g. mixed with or dissolved in the dielectric fluid. Such additives may e.g. be additives for increased oxidation stability or improved pour point of the composition.

(12) In an aspect, the present invention relates to a composition suitable for electrical apparatuses comprising a dielectric fluid, wherein the composition has a slow LI streamer speed that is comparable to mineral oil. The dielectric fluid may be an ester-based dielectric fluid.

(13) In some embodiments of the present invention, the LI streamer speed of the composition is reduced by at least 50%, preferably from 50% up to and including 80%, when compared to the LI streamer speed of any of the commercially available ester-based dielectric oils today, for example triglycerides from rapeseed, soybean and sunflower oils, for a fixed applied test voltage. In yet a further embodiment, the LI streamer speed of the composition is almost similar to the LI streamer speed in mineral oil for the same applied test voltage.

(14) In some embodiments of the present invention, the acceleration voltage (V.sub.a) of the composition is increased by at least 25%, when compared to the acceleration voltage of the dielectric fluid without additive, such as any of the commercially available ester-based dielectric oils today, for example triglycerides from rapeseed, soybean and sunflower oils.

(15) In some embodiments of the present invention the composition comprises a dielectric ester-based fluid and one or more additives capable of lowering the LI streamer speed of the fluid. Preferably, the additive is capable to reduce the LI streamer speed of the fluid with at least 50%. More preferably the to additive is capable to reduce the LI streamer speed of the fluid from 50% up to and including 80%, preferably 60-80% or preferably 70-80%. More preferably the additive is capable to reduce the LI streamer speed of the fluid with at least 75%. In some embodiments, the additive is capable of increasing the acceleration voltage of the fluid by at least 25%. More preferably, the additive is capable of increasing the acceleration voltage of the fluid from 25% up to and including 80%, preferably 5-80%. More preferably, the additive is capable of increasing the acceleration voltage of the fluid by at least 75%.

(16) In some embodiments, the breakdown voltage of the composition is increased, often in combination with increased acceleration voltage. The breakdown voltage may e.g. be increased by at least 5% by means of the additive as compared with the dielectric fluid without additive, more preferably by at least 10% or by at least 25%. In some embodiments, the breakdown voltage is increased from 25% up to and including 100%, preferably 50-80%. More preferably, the additive is capable of increasing the breakdown voltage of the fluid by at least 50%, or by at least 75%.

(17) In some embodiments, it is convenient to use a concentration of the additive in the composition of at least 1 wt %, such as between 1 and 10 wt % or between 3 and 8 wt %, e.g. about 5 wt %.

(18) In some embodiments, the additive is a combination of a plurality of different additive compounds, such as the additive compounds additives discussed herein.

(19) Suitable additives are able to absorb the energy of the electrons emitted during streamer propagation, without the additive molecule itself getting ionized. This property of the additive molecule helps in reducing the streamer development in the case of LI Voltage or other applied voltage with high enough amplitude to introduce a streamer. Preferably, the additive added to the composition has a lowest or 1.sup.st electron excitation energy that is lower than the lowest or 1.sup.st excitation energy of the dielectric fluid. An excited state is obtained if one electron (at least) is excited from its ground state position to an unoccupied energy level. The 1.sup.st excitation energy is the lowest energy required to move one electron from the ground state configuration to an unoccupied energy level. In some embodiments, the additive has a 1.sup.st excitation energy of less than 7 eV, such as from 1 to 7 eV, from 1 to 5 eV, or more preferably from 1 to 4 eV.

(20) In one embodiment of the present invention the time to de-excitation of the excited state of the additive is shorter than the time to ionization. In one embodiment, the time to de-excitation of the excited state of the additive is shorter than 10.sup.9 sec.

(21) As per another embodiment, the time to ionization of the excited state is longer than 10.sup.9 sec. Ionization from the excited state requires less energy compared to ionization from a molecule in its electronic ground state. A long time to ionization can compensate for long life time of the excited state.

(22) The concepts of 1.sup.st excitation energy and ionization potential are explained with reference to FIG. 2. A molecule is in its ground state if all electrons are in the lowest possible energy levels, the ground state configuration. A cation is created if an electron is completely removed (above vacuum level). The minimum energy to create a cation is the ionization potential. An excited state is obtained if at least one electron is excited from its ground state position to an unoccupied energy level. The 1.sup.st excitation energy is the lowest energy required to move one electron from the ground state configuration to an unoccupied energy level. The excited states are unstable and will deexcite after some time.

(23) The additive is dissolvable in the dielectric fluid. Before being added to the insulating liquid composition, the additive may e.g. be in liquid form or in solid, such as particulate, form. If in liquid form, the additive is mixable with the dielectric fluid such that a two-phase liquid system is not formed, and is thus dissolved in the dielectric fluid. If in solid form, the additive is dissolvable in the dielectric fluid such that the additive occur as dissolved, preferably fully dissolved, molecules in the dielectric fluid, and does preferably not occur as particulate matter in a suspension with the dielectric fluid/liquid. However, the composition may also comprise a particulate streamer reducing additive in addition to the dissolved additive, such as nanoparticles e.g. nanoparticles of any of the additive compounds discussed herein.

(24) Suitable additives include dimethyl aniline (DMA) or are selected from the group consisting of azo compounds or color dyes, such as triarylmethane dyes, cyanines and quinone-imine dyes. Further examples of color dyes suitable as additives are selected from the group consisting of alcian yellow GXS, alizarin, alizarin red S, alizarin yellow GG, alizarin yellow R, azophloxin, bismarck brown R, bismarck brown Y, brilliant cresyl blue, chrysoidine R, chrysoidine Y, congo red, crystal violet, fuchsin acid, gentian violet, janus green, lissamine fast yellow, martius yellow, meldola blue, metanil yellow, methyl orange, methyl red, naphthalene black 12B, naphthol green B, naphthol yellow S, orange G, rose bengal, sudan II, titan yellow, tropaeolin O, tropaeolin OO, tropaeolin OOO, victoria blue 4R, victoria blue B, victoria blue R, and xylene cyanol FF. In some embodiments, the additive is selected from transitional metal compounds, such as oxides and carbo monoxides of transition metals. Examples of transition metal compounds are MnO.sub.4.sup., Mn.sub.2(CO).sub.10 and Ni(CO).sub.4.

(25) The term transition metals as used herein denotes the elements in group 3 to 12 of the periodic table. Examples of transition metals are titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, silver, cadmium, tungsten, iridium and gold.

(26) In this specification the term alkyl includes both straight and branched chain alkyl groups, but references to individual alkyl groups such as propyl are specific for the straight chain version only. For example, C.sub.1-6alkyl includes C.sub.1-4alkyl, C.sub.1-3alkyl, propyl, isopropyl and t-butyl. However, references to individual alkyl groups such as propyl are specific for the to straight chained version only and references to individual branched chain alkyl groups such as isopropyl are specific for the branched chain version only. A similar convention applies to other radicals, for example phenyl-C.sub.1-6alkyl would include phenyl-C.sub.1-4alkyl, benzyl, 1-phenylethyl and 2-phenylethyl. Alkyl groups may be optionally substituted as defined herein. Examples of alkyl groups include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, pentyl, iso-amyl, hexyl, octyl, noyl and the like. The term alkylene, as used herein, alone or in combination, refers to a saturated aliphatic group derived from a straight or branched chain saturated hydrocarbon attached at two or more positions, such as methylene (CH.sub.2). Unless otherwise specified, the term alkyl may include alkylene groups.

(27) The term halo refers to fluoro, chloro, bromo and iodo.

(28) Where optional substituents are chosen from one or more groups it is to be understood that this definition includes all substituents being chosen from one of the specified groups or the substituents being chosen from two or more of the specified groups.

(29) The term acyl, as used herein, alone or in combination, refers to a carbonyl attached to an alkenyl, alkyl, aryl, cycloalkyl, heteroaryl, heterocycle, or any other moiety were the atom attached to the carbonyl is carbon. An acetyl group refers to a C(O)CH.sub.3 group. An alkylcarbonyl or alkanoyl group refers to an alkyl group attached to the parent molecular moiety through a carbonyl group. Examples of such groups include methylcarbonyl and ethylcarbonyl. Examples of acyl groups include formyl, alkanoyl and aroyl.

(30) The term alkenyl, as used herein, alone or in combination, refers to a straight-chain or branched-chain hydrocarbon group having one or more double bonds and containing from 2 to 20 carbon atoms. In certain embodiments, said alkenyl will comprise from 2 to 6 carbon atoms. The term alkenylene refers to a carbon-carbon double bond system attached at two or more positions such as ethenylene [(CHCH),(CC)]. Examples of suitable alkenyl groups include ethenyl, propenyl, 2-methylpropenyl, 1,4-butadienyl and the like. Unless otherwise specified, the term alkenyl may include alkenylene groups.

(31) The term alkoxy, as used herein, alone or in combination, refers to an alkyl ether group, wherein the term alkyl is as defined below. Examples of suitable alkyl ether groups include methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, iso-butoxy, sec-butoxy, tert-butoxy, and the like.

(32) The term alkylamino, as used herein, alone or in combination, refers to an alkyl group attached to the parent molecular moiety through an amino group. Suitable alkylamino groups may be mono- or dialkylated, forming groups such as, for example, N-methylamino, N-ethylamino, N,N-dimethylamino, N,N-ethylmethylamino and the like.

(33) The term alkylidene, as used herein, alone or in combination, refers to an alkenyl group in which one carbon atom of the carbon-carbon double bond belongs to the moiety to which the alkenyl group is attached.

(34) The term alkylthio, as used herein, alone or in combination, refers to an alkyl thioether (RS) group wherein the term alkyl is as defined above and wherein the sulfur may be singly or doubly oxidized. Examples of suitable alkyl thioether groups include methylthio, ethylthio, n-propylthio, isopropylthio, n-butylthio, iso-butylthio, sec-butylthio, tert-butylthio, methanesulfonyl, ethanesulfinyl, and the like.

(35) The term alkynyl, as used herein, alone or in combination, refers to a straight-chain or branched chain hydrocarbon group having one or more triple bonds and containing from 2 to 20 carbon atoms. In certain embodiments, said alkynyl comprises from 2 to 6 carbon atoms. In further embodiments, said alkynyl comprises from 2 to 4 carbon atoms. The term alkynylene refers to a carbon-carbon triple bond attached at two positions such as ethynylene (C:::C, CC). Examples of alkynyl groups include ethynyl, propynyl, hydroxypropynyl, butyn-1-yl, butyn-2-yl, pentyn-1-yl, 3-methylbutyn-1-yl, hexyn-2-yl, and the like. Unless otherwise specified, the term alkynyl may include alkynylene groups.

(36) The terms amido and carbamoyl, as used herein, alone or in combination, refer to an amino group as described below attached to the parent molecular moiety through a carbonyl group, or vice versa. The term C-amido as used herein, alone or in combination, refers to a C(O)NR.sub.2 group with R as defined herein. The term N-amido as used herein, alone or in combination, refers to a RC(O)NH group, with R as defined herein. The term acylamino as used herein, alone or in combination, embraces an acyl group attached to the parent moiety through an amino group. An example of an acylamino group is acetylamino (CH.sub.3C(O)NH).

(37) The term aryl as used herein refers to a totally unsaturated, monocyclic, bicyclic or tricyclic carbon ring system containing 3-14 ring atoms, wherein such polycyclic ring systems are fused together. Preferably aryl is a monocyclic ring containing 5 or 6 atoms or a bicyclic ring containing 9 or 10 atoms. Suitable values for aryl include, but are not limited to phenyl, naphthyl, anthracenyl, and phenanthryl. Particularly aryl is phenyl.

(38) A heteroaryl as used herein as used herein, alone or in combination, refers to an unsaturated heteromonocyclic ring, or a fused monocyclic, bicyclic, or tricyclic ring system in which at least one of the fused rings is aromatic, containing 3 to 14 ring atoms of which at least one atom selected from the group consisting of oxygen sulphur or nitrogen. In certain embodiments, heteroaryl refers to a monocyclic ring containing 5 or 6 atoms or a bicyclic ring containing 8, 9 or 10 atoms of which at least one atom is chosen from nitrogen, sulphur or oxygen. The term also embraces fused polycyclic groups wherein heterocyclic rings are fused with aryl rings, wherein heteroaryl rings are fused with other heteroaryl rings, wherein heteroaryl rings are fused with heterocycloalkyl rings, or wherein heteroaryl rings are fused with cycloalkyl rings. Examples of heteroaryl groups include pyrrolyl, pyrrolinyl, imidazolyl, pyrazolyl, pyridyl, pyrimidinyl, pyrazinyl, pyridazinyl, triazolyl, pyranyl, furyl, thienyl, oxazolyl, isoxazolyl, oxadiazolyl, thiazolyl, thiadiazolyl, isothiazolyl, indolyl, isoindolyl, indolizinyl, benzimidazolyl, quinolyl, isoquinolyl, quinoxalinyl, quinazolinyl, indazolyl, benzotriazolyl, benzodioxolyl, benzopyranyl, benzoxazolyl, benzoxadiazolyl, benzothiazolyl, benzothiadiazolyl, benzofuryl, benzothienyl, chromonyl, coumarinyl, benzopyranyl, tetrahydroquinolinyl, tetrazolopyridazinyl, tetrahydroisoquinolinyl, thienopyridinyl, furopyridinyl, pyrrolopyridinyl and the like. Exemplary tricyclic heterocyclic groups include carbazolyl, benzidolyl, phenanthrolinyl, dibenzofuranyl, acridinyl, phenanthridinyl, xanthenyl and the like.

(39) The term heterocyclyl, as used herein, refers to a saturated, partially saturated or partially unsaturated, or fully unsaturated, monocyclic, bicyclic or tricyclic ring system containing at least one ring atom chosen from nitrogen, sulphur or oxygen, which may, unless otherwise specified, be carbon or nitrogen linked, wherein a CH.sub.2 group can optionally be replaced by a C(O) or a ring sulphur atom may be optionally oxidised to form the S-oxides. Preferably a heterocyclyl is a saturated, partially saturated or fully unsaturated, mono or bicyclic ring containing 5 or 6 atoms of which at least one atom is chosen from nitrogen, sulphur or oxygen, which may, unless otherwise specified, be carbon or nitrogen linked, wherein a CH.sub.2 group can optionally be replaced by a C(O) or a ring sulphur atom may be optionally oxidised to form S-oxide(s). Heterocycloalkyl and heterocycle are intended to include sulfones, sulfoxides, N-oxides of tertiary nitrogen ring members, and carbocyclic fused and benzo fused ring systems; additionally, both terms also include systems where a heterocycle ring is fused to an aryl group, as defined herein, or an additional heterocycle group. Examples of heterocycle groups include aziridinyl, azetidinyl, 1,3-benzodioxolyl, dihydroisoindolyl, dihydroisoquinolinyl, dihydrocinnolinyl, dihydrobenzodioxinyl, dihydro[1,3]oxazolo[4,5-b]pyridinyl, benzothiazolyl, dihydroindolyl, dihydropyridinyl, 1,3-dioxanyl, 1,4-dioxanyl, 1,3-dioxolanyl, isoindolinyl, morpholinyl, piperazinyl, pyrrolidinyl, tetrahydropyridinyl, piperidinyl, thiomorpholinyl, and the like. The heterocycle groups may be optionally substituted unless specifically prohibited.

(40) A carbocyclyl is a saturated, partially saturated or unsaturated, mono or bicyclic carbon ring that contains 3-12 atoms; wherein a CH.sub.2 group can optionally be replaced by a C(O). Preferably carbocyclyl is a monocyclic ring containing 5 or 6 atoms or a bicyclic ring containing 9 or 10 atoms. Suitable values for carbocyclyl include cyclopropyl, cyclobutyl, 1-oxocyclopentyl, cyclopentyl, cyclopentenyl, cyclohexyl, cyclohexenyl, phenyl, naphthyl, tetralinyl, indanyl or 1-oxoindanyl. Particularly carbocyclyl is cyclopropyl, cyclobutyl, 1-oxocyclopentyl, cyclopentyl, cyclopentenyl, cyclohexyl, cyclohexenyl, phenyl or 1-oxoindanyl.

(41) An example of C.sub.1-6alkanoyloxy and C.sub.1-4alkanoyloxy is acetoxy. Examples of C.sub.1-6alkoxycarbonyl and C.sub.1-4alkoxycarbonyl include methoxycarbonyl, ethoxycarbonyl, n- and t-butoxycarbonyl. Examples of C.sub.1-6alkoxy and C.sub.1-4alkoxy include methoxy, ethoxy and propoxy. Examples of C.sub.1-6alkanoylamino and C.sub.1-4alkanoylamino include formamido, acetamido and propionylamino. Examples of C.sub.1-6alkylS(O).sub.a wherein a is 0 to 2 and C.sub.1-4alkylS(O).sub.a wherein a is 0 to 2 include methylthio, ethylthio, methylsulphinyl, ethylsulphinyl, mesyl and ethylsulphonyl. Examples of C.sub.1-6alkanoyl and C.sub.1-4alkanoyl include C.sub.1-3alkanoyl, propionyl and acetyl. Examples of N(C.sub.1-6alkyl)amino and N(C.sub.1-4alkyl)amino include methylamino and ethylamino. Examples of N,N(C.sub.1-6alkyl).sub.2-amino and N,N(C.sub.1-4alkyl).sub.2-amino include di-N-methylamino, di-(N-ethyl)amino and N-ethyl-N-methylamino. Examples of C.sub.2-6alkenyl and C.sub.2-4alkenyl are vinyl, allyl and 1-propenyl. Examples of C.sub.2-6alkynyl and C.sub.2-4alkynyl are ethynyl, i-propynyl and 2-propynyl. Examples of N(C.sub.1-6alkyl)sulphamoyl and N(C.sub.1-4alkyl)sulphamoyl are N(C.sub.1-3alkyl)sulphamoyl, N-(methyl)sulphamoyl and N-(ethyl)sulphamoyl. Examples of N(C.sub.1-6alkyl).sub.2sulphamoyl and N(C.sub.1-4alkyl).sub.2sulphamoyl are N,N-(dimethyl)sulphamoyl and N-(methyl)-N-(ethyl)sulphamoyl. Examples of N(C.sub.1-6alkyl)carbamoyl and N(C.sub.1-4alkyl)carbamoyl are methylaminocarbonyl and ethylaminocarbonyl. Examples of N,N(C.sub.1-6alkyl).sub.2-carbamoyl and N,N(C.sub.1-4alkyl).sub.2-carbamoyl are dimethylaminocarbonyl and methylethylaminocarbonyl. Examples of C.sub.1-6alkoxycarbonylamino are ethoxycarbonylamino and t-butoxycarbonylamino. Examples of N(C.sub.1-6alkyl)ureido are N-methylureido and N-ethylureido. Examples of N(C.sub.1-6alkyl)ureido are N-methylureido and N-ethylureido. Examples of N,N(C.sub.1-6alkyl).sub.2ureido are N,N-dimethylureido and N-methyl-N-ethylureido. Examples of N(C.sub.1-6alkyl)-N(C.sub.1-6alkyl)ureido are N-methyl-N-methylureido and N-propyl-N-methylureido. Examples of N,N(C.sub.1-6alkyl).sub.2-N(C.sub.1-6alkyl)ureido are N,N-dimethyl-N-methylureido and N-methyl-N-ethyl-N-propylureido.

(42) Examples of triarylmethane dyes include methyl violet dyes, fuchsine dyes, phenol dyes and different bridged arenes.

(43) Examples of methyl violet dyes include methyl violet 2B, methyl violet 6B and methyl violet 10B (hexamethyl pararosaniline chloride).

(44) Examples of fuchsine dyes include pararosaniline ([4-[Bis(4-aminophenyl)methylidene]-1-cyclohexa-2,5-dienylidene]azanium chloride), fuchsine (4-[(4-Aminophenyl)-(4-imino-1-cyclohexa-2,5-dienylidene) methyl]aniline hydrochloride), new fuchsine and fuchsine acid.

(45) Examples of phenol dyes include phenol red (phenolsulfonphthalein), chlorophenol red (2-chloro-4-[3-(3-chloro-4-hydroxyphenyl)-1,1-dioxobenzo[c]oxathiol-3-yl]phenol) and cresol red (o-cresolsulfonephthalein).

(46) In this specification the term bridged arenes includes acridines, xanthenes, thioxanthenes, and derivatives thereof.

(47) Examples of cyanine dyes include streptocyanines or open chain cyanines, hemicyanines, or closed chain cyanines of the following formulas
RRN.sup.+CH[CHCH].sub.nNRR,
Aryl=N.sup.+CH[CHCH].sub.nNRR, and
Aryl=N.sup.+CH[CHCH].sub.nN=Aryl,
wherein the two nitrogens are joined by a polymethine chain, CH[CHCH].sub.n, and both nitrogens are each independently part of a heteroaromatic moiety. Examples of closed chain cyanines are Cy3 and Cy5.

(48) Examples of quinone-imine dyes include the groups selected from indamins; indophenols; azins, including the subgroups of eurhodins, safranins and indulines; oxazins, including gallocyanin, gallamin blue and celestin blue B; and thiazins, including methylene blue homologues.

(49) In some embodiments, the additive(s) used in the composition herein is selected from azo compounds, of formula (I)
R.sup.5NNR.sup.6(I)
wherein R.sup.5 and R.sup.6 are both independently selected from
aryl or heteroaryl, which is unsubstituted or substituted in one, two or three positions with substituents independently selected from C.sub.1-10 alkyl, C.sub.2-10 alkenyl, C.sub.2-10 alkynyl, OH, CHO, C.sub.1-10 acyl, C.sub.1-10 alkoxy, C.sub.1-6alkanoyloxy, C.sub.1-10 alkylthio, C.sub.1-10 alkylamino, CN, nitro, amino, amido, sulfonyl, arylsulfonyl, halo, halo C.sub.1-10 alkyl, C.sub.1-10 alkyl aryl, and aminoaryl; or
a five-membered carbocyclic or heterocylic ring, which is unsubstituted or substituted in one, two or three positions with substituents independently selected from C.sub.1-10 alkyl, C.sub.2-10 alkynyl, OH, CHO, C.sub.1-10 acyl, C.sub.1-10 alkoxy, C.sub.1-6alkanoyloxy, C.sub.1-10 alkylthio, C.sub.1-10 alkylamino, CN, nitro, amino, arylamino, amido, sulfonyl, arylsulfonyl, halo, halo-C.sub.1-10 alkyl C.sub.1-10 alkyl aryl, and aminoaryl.

(50) In some embodiments, R.sup.5 and R.sup.6 are each independently selected from the group consisting of phenyl, furyl, thiophenyl, pyrrolyl, oxazolyl, thiazolyl, imidazolyl and furan;

(51) wherein R.sup.5 and R.sup.6, each independently may be unsubstituted or substituted in one or two positions with OH, N(R.sup.7).sub.2, NO.sub.2, sulfonyl, or anilino, and wherein R.sup.7 is selected from H, or C.sub.1-6-alkyl, preferably H.

(52) In some embodiments,

(53) R.sup.5 is selected from phenyl, 2-oxazolyl, 2-thiazolyl and 2-imidazolyl; and

(54) R.sup.6 is selected from furyl, pyrrolyl, thiophenyl, 2-oxazolyl, 2-imidazolyl, 2-thiazolyl, phenyl, benzofuryl, indolyl, and benzothiophene;

(55) wherein R.sup.5 and R.sup.6 are each independently unsubstituted or substituted in one or two positions with H, C.sub.2-10 alkenyl, C.sub.2-10 alkynyl, OH, CHO, C.sub.1-10 acyl, C.sub.1-10 alkoxy, C.sub.1-6alkanoyloxy, C.sub.1-10 alkylthio, halo, halo C.sub.1-10 alkyl, C.sub.1-10 alkyl aryl, N(R.sup.7).sub.2, NO.sub.2, CN, amino, amido, sulfonyl, arylsulfonyl, and aminoaryl,
wherein R.sup.7 is selected from H, or C.sub.1-10-alkyl, preferably H.

(56) In some embodiments,

(57) R.sup.5 is selected from phenyl, 2-oxazolyl, 2-thiazolyl and 2-imidazolyl; and

(58) R.sup.6 is selected from phenyl and 2-thiazolyl,

(59) wherein R.sup.5 and R.sup.6 are each independently unsubstituted or substituted in one or two positions with OH, N(R.sup.7).sub.2, NO.sub.2, sulfonyl, or anilino,

(60) wherein R.sup.7 is selected from H, or C.sub.1-6-alkyl, preferably H.

(61) In some embodiments, the additive(s) is selected from the group of azo compounds having one of the following formulas (II), (III) and (IV),

(62) ##STR00001##
wherein
X is selected from S, O and N; and
R.sub.1, R.sub.2, R.sub.3, and R.sub.4, are each independently selected from H, C.sub.2-10 alkenyl, C.sub.2-10 alkynyl, OH, CHO, C.sub.1-10 acyl, C.sub.1-10 alkoxy, C.sub.1-6 alkanoyloxy, C.sub.1-10 alkylthio, C.sub.1-10 alkylamino, CN, nitro, amino, amido, sulfonyl, arylsulfonyl, halo, halo C.sub.1-10 alkyl, C.sub.1-10 alkyl aryl, and aminoaryl.

(63) In some embodiments,

(64) X is selected from S and O;

(65) R.sub.1 is selected from H, C.sub.1-10 alkyl, OH, C.sub.1-10-alkoxy, CN, and NH.sub.2;

(66) R.sub.2 is selected from H or CN;

(67) R.sub.3 is selected from H, CHO, CHCH.sub.2; and

(68) R.sub.4 is selected from H, OH and halo.

(69) In some embodiments,

(70) R.sub.1 is selected from H, C.sub.1-4-alkyl, OH, C.sub.1-4-alkoxy, CN, and NH.sub.2;

(71) R.sub.2 is selected from H or CN;

(72) R.sub.3 is selected from H, CHO, CHCH.sub.2; and

(73) R.sub.4 is selected from H and Cl.

(74) In some embodiments,

(75) R.sub.1 is selected from H, CH.sub.3, OH, OCH.sub.3, CN, and NH.sub.2;

(76) R.sub.2 is selected from H or CN;

(77) R.sub.3 is selected from H, CHO, CHCH.sub.2; and

(78) R.sub.4 is selected from H and Cl.

(79) In some embodiments, suitable additive(s) is of the following formula (V)

(80) ##STR00002##
wherein X.sub.1, X.sub.2, Y.sub.1 and Y.sub.2 are each independently selected from H, C.sub.1-10 alkyl, C.sub.2-10 alkenyl, C.sub.2-10 alkynyl, OH, CHO, C.sub.1-10 acyl, C.sub.1-10 alkoxy, C.sub.1-6 alkanoyloxy, C.sub.1-10 alkylthio, C.sub.1-10 alkylamino, CN, nitro, amino, amido, sulfonyl, arylsulfonyl, halo, halo C.sub.1-10 alkyl, C.sub.1-10 alkyl aryl, and aminoaryl.

(81) Preferably, X.sub.1 and X.sub.2 are each independently selected from H, C.sub.1-6 alkyl, CHO, NO.sub.2, NH.sub.2, and CN; and

(82) Y.sub.1 and Y.sub.2 are each independently selected from H, C.sub.1-6 alkyl, CHO, OH, NH.sub.2, and CN.

(83) In some embodiments,

(84) X.sub.1 and X.sub.2 are each independently is selected from H, NO.sub.2, NH.sub.2, and CN

(85) X.sub.2 is selected from H, NH.sub.2, and CN;

(86) Y.sub.1 is selected from H, OH, NH.sub.2, and CN; and Y.sub.2 is selected from H, OH, NH.sub.2, and CN

(87) In some embodiments, the additive is selected from 4-anilino-4-nitroazobenzene and p-dimethylamino-azobenzenesulfonic acid.

(88) In some embodiments of the present invention the dielectric fluid is an ester-based fluid such as an ester oil, preferably a triglyceride oil.

(89) In some embodiments, the dielectric, ester-based fluid has a fatty acid composition of between approximately 10% and approximately 100% fatty acids having at least one carbon-carbon double bond.

(90) The fatty acids may be of essentially any length, having essentially any number of unsaturations, either conjugated and/or unconjugated. Fatty acids may for instance be selected from the group comprising, but not limited to, oleic acid, linoleic acid, -linolenic acid, myristoleic acid, arachidonic acid, icosapentaenoic acid, palmitoleic acid, erucic acid, and docosahexaenoic acid, butyric acid, caproic acid, caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, vaccenic acid, gamma-linolenic acid, behenic acid, erucic acid, lignoceric acid, or any other fatty acids, suitably modified, if needed, in accordance with the requirements of the present invention.

(91) In an aspect, the present invention pertains to a method for preparing a composition suitable for electrical apparatuses, such as transformers. The composition may comprise a dielectric fluid (e.g. an ester-based fluid).

(92) In some embodiments, the method for providing the composition comprising a dielectric, ester-based fluid comprises the steps of providing a triglyceride composition having a fatty acid composition of between approximately 10% and approximately 100% fatty acids having at least one carbon-carbon double bond.

(93) In some embodiments, the method for providing the composition comprising a dielectric ester-based fluid comprises the steps of providing a triglyceride composition having a fatty acid composition of between approximately 10% and approximately 100% fatty acids having at least one carbon-carbon double bond, wherein the at least one carbon-carbon double bond is subsequently reacted with at least one conjugated diene, normally in the presence of a catalyst, resulting in the formation of said dielectric, triglyceride fluid.

(94) In an aspect, the present invention relates to an apparatus selected from the group consisting of electrical apparatuses and power applications, comprising a composition of the present invention. Preferably, the apparatus comprises a composition comprising a dielectric, ester-based fluid. More preferably, the apparatus comprises a composition that has a slow LI streamer speed that is comparable to mineral oil.

(95) In some embodiments, the electrical and/or power apparatus comprises a composition of the present invention, wherein said composition functions as an insulating medium.

(96) In some embodiments, the electrical and/or power apparatus comprising a composition of the present invention is selected from transformers, capacitors, switchgear, bushings, etc., as well components and/or parts utilized in power or electrical applications.

(97) In some embodiments, the electrical apparatus is a transformer.

(98) In an aspect, the present invention pertains to various uses of a composition of the present invention, in electrical apparatuses, and/or in apparatuses for power applications, and/or in components utilized in said apparatuses, wherein the composition comprises a dielectric, ester based fluid and has a slow LI streamer speed that is comparable to mineral oil. Apparatuses of interest as per the present invention may for instance be transformers, capacitors, switchgear, bushings, etc., as well components and/or parts utilized in power or electrical applications.

(99) The excited state of the additive may be determined with spectroscopy and/or calculations using quantum chemistry. The excited states of the additive is not expected to change when dissolved in the dielectric ester-based fluid.

Example 1

(100) N,N-dimethyl aniline, DMA, (Formula VI) was added to a natural ester dielectric to form a composition of the present invention.

(101) ##STR00003##

(102) The natural ester had an ionization potential (vertical) of 8.50 electron volts (eV), and a first excitation energy of 5.30 eV. DMA has an ionization potential (vertical) of 7.42 eV and a first excitation energy of 4.03 eV. Three different samples were prepared: the natural ester without the additive DMA, the natural ester with 1 wt % DMA and the natural ester with 5 wt % DMA. As can be seen in FIG. 3, the acceleration voltage is increased by about 10% with 1 wt % DMA and with about 80% with 5 wt % DMA. The streamer velocity is thus significantly reduced, especially with 5% additive but also with only 1% additive.

Example 2

(103) trans-Azobenzene (Formula VII) was added to a natural ester dielectric to form a composition of the present invention.

(104) ##STR00004##

(105) The natural ester had an ionization potential (vertical) of 8.50 eV, and a first excitation energy of 5.30 eV. Azobenzene has an ionization potential (vertical) of 7.82 eV and a first excitation energy of 2.29 eV. Three different samples were prepared: the natural ester without the additive azobenzene, the natural ester with 1 wt % azobenzene and the natural ester with 5 wt % azobenzene. As can be seen in FIG. 4, the acceleration voltage is increased by about 10% with 1 wt % azobenzene and with about 50% with 5 wt % azobenzene. The streamer velocity is thus significantly reduced, especially with 5% additive but also with only 1% additive.

Example 3

(106) Examples of additives which may conveniently be used according to the present invention include:

(107) compounds with PN double bonds

(108) ##STR00005##
for example N-(Triphenylphosphoranylidene)aniline

(109) ##STR00006##
pigments, for example tetraphenylcyclopentadienone

(110) ##STR00007##
or N-ethyl-1-(4-(phenylazo)phenylazo)-2-naphthylamine

(111) ##STR00008##
other compounds with aromatic groups, e.g. below

(112) ##STR00009##
where R.sub.1 and R.sub.2 are alkyl chains;
flavonoids, for example quercetin

(113) ##STR00010##
and compounds with furan substructure, for example furyl acrylic acid

(114) ##STR00011##
or 2-acetyl furan

(115) ##STR00012##

(116) The invention has mainly been described above with reference to a few embodiments. However, as is readily appreciated by a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the invention, as defined by the appended patent claims.