Electrical and transformer oil composition

Abstract: The composition comprises a major amount of a paraffinic oil having a Cleveland open cup flash point of more than about 200°C and an effective amount of at least one hindered phenolic antioxidant and at least one tolyltriazole metal deactivator.

Description: This invention relates to an oil composition suitable as, or in, an electrical or transformer oil, more especially suitable for use in transformers operating at elevated temperatures. BACKGROUND OF THE INVENTION Present commercial practice is to use conventional naphthenic transformer oils in transformers designed to operate under normal use at a maximum oil temperature of 90°C with an expected life in the range of about 20 to about 30 years. By operating a transformer at elevated oil temperatures of about 140°C, more kilowatts of power can be generated at a higher load. Unfortunately, the conventional naphthenic transformer oils that are used in present commercial transformers have poor oxidation stability at this higher temperature and through oil oxidation become incompatible with the materials of construction of the transformer, thus significantly shortening the transformer life. Accordingly, there is a need for a transformer oil having an extended useful life at significantly higher temperatures than present oils. One object of the invention is to provide improved electrical and transformer oils which have low solvency for materials of construction at top oil temperatures of about 140°C. Another object of the invention is to provide electrical and transformer oils that have improved oxidation stability at top oil temperatures greater than about 140°C. Another object of the invention is to provide an additive system which will impart exceptional chemical and oxidative stability to the oil and maintain the high efficiency of the transformer by not adversely affecting the power factor. Another object of the invention is to provide electrical and transformer oils that have a negative gassing tendency. These and other objects of the invention will become apparent upon a reading of the description which follows. FR-A-2679246 and its counterpart WO93/0216 disclose and claim an oil composition which is useful as an electrical insulating oil comprising: (i) a base oil which does not contain any additional aromatic petroleum stream; (ii) an antioxidant additive comprising a mixture of (a) phenol or a derivative thereof; and (c) a triazole or a derivative thereof. US-A-5681797 discloses and claims an oxidatively stable, biodegradable lubricant composition, comprising: (A) at least one hydrogenated polyisoprene prepared by polymerizing isoprene such that polyisoprene is obtained wherein there are from 4 to 1000 isoprene units wherein the polyisoprene prior to hydrogenation has the formula or wherein n is the number of isoprene units and hydrogenating the polyisoprene to obtain a hydrogenated polyisoprene containing a residual olefinic unsaturation of not more than 10 percent based upon the unsaturation content prior to hydrogenation and; (B) at least one performance additive selected from the group consisting of (1) an alkyl phenol of the formula wherein R 3 is an alkyl group containing from 1 up to about 24 carbon atoms and a is an integer of from 1 up to 5; (2) an ether of the formula wherein R 80 is an alkyl group containing from one up to about 12 carbon atoms, R 3 is an alkyl group containing from one up to about 24 carbon atoms and a is an integer of from one up to 5; or wherein R 75 is an aliphatic group containing from one up to 8 carbon atoms, n and m are independently integers of from zero up to 100 with the proviso that n and m are not both zero; (3) a mixture of a mono- or di-substituted glyceride of the formula: wherein R 81 and R 82 are hydrocarbyl groups independently containing from about 8 up to about 24 carbon atoms; (4) a phosphorus-sulfur derivative of the formula wherein R 43 and R 44 are independently hydrocarbyl groups containing from about 3 to 20 carbon atoms and B is a mixture of in a ketone:alcohol weight ratio of from 1:0.10-0.50; (5) a benzotriazole of the formula wherein R 4 is hydrogen or an alkyl group of 1 up to about 24 carbon atoms; (6) a phosphorous amine salt; (7) a trihydrocarbyl phosphorothionate; (8) an aromatic amine of the formula wherein R 12 is and R 13 and R 14 are independently a hydrogen or an alkyl group containing from 1 up to about 23 carbon atoms; (9) a zinc salt of the formula wherein R 43 and R 44 are independently hydrocarbyl groups containing from about 3 to 20 carbon atoms; (10) an ester having pour point depressant properties characterized by low-temperature modifying properties of an ester of a carboxy-containing interpolymer; said interpolymer having a reduced specific viscosity of from about 0.05 to about 2 and being derived from at least two monomers, one of said monomers being a low molecular weight aliphatic olefin, styrene or a substituted styrene wherein the substituent is a hydrocarbyl group containing from 1 up to about 18 carbon atoms, and the other of the said monomers being an alpha, beta-unsaturated aliphatic acid, anhydride or ester thereof, said ester being substantially free of titratable acidity and being characterized by the presence within its polymeric structure of pendant polar groups which are derived from the carboxy groups of said ester; (a) a relatively high molecular weight carboxylic ester group, said carboxylic ester group having at least 8 aliphatic carbon atoms in the ester radical, optionally (b) a relatively low molecular weight carboxylic ester group having no more than 7 aliphatic carbon atoms in the ester radical, wherein the molar ratio of (a):(b) of the pour point depressant when (b) is present is (1-20):1, and optionally (c) a carbonyl-amino group derived from an amino compound having one primary or secondary amino group, wherein the molar ratio of (a):(b):(c) of the pour point depressant when (b) and (c) are present is (50-100):(5-50):(0.1-15); (11) a hydrogenated block copolymer comprising a normal block copolymer or a random block copolymer, said normal block copolymer made from a vinyl substituted aromatic and an aliphatic conjugated diene, said normal block copolymer having from two to about five polymer blocks with at least one polymer block of said vinyl substituted aromatic and at least one polymer block of said aliphatic conjugated diene, said random block copolymer made from vinyl substituted aromatic and aliphatic conjugated diene monomers, the total amount of said vinyl substituted aromatic blocks in said block copolymer being in the range of from about 20 percent to about 70 percent by weight and the total amount of said diene blocks in said block copolymer being in the range of from about 30 percent to about 80 percent by weight; the number average molecular weight of said normal block copolymer and said random block copolymer being in the range of about 5,000 to about 1,000,000; and (12) an acrylate polymer of the formula wherein R 9 is hydrogen or a lower alkyl group containing from 1 to about 4 carbon atoms. R 10 is a mixture of alkyl, cycloalkyl or aromatic groups containing from about 1 to about 24 carbon atoms, and x is an integer providing a weight average molecular weight (Mw) to the acrylate polymer of about 5,000 to about 1,000,000. US-A-5773391 discloses and claims a composition useful as a lubricant and a functional fluid comprising: a polyol ester derived from (A) an aliphatic or alicyclic polyol containing from 2 to about 10 hydroxyl groups and (B) an aliphatic monocarboxylic acid mixture derived from a high oleic vegetable oil wherein the oleic content is at least 72 percent and the vegetable oil is canola oil, sunflower oil or peanut oil; with at least one antioxidant selected from the group consisting of phenolics, aromatic amines and tocophenols and at least one metal deactivator selected from the group consisting of benzotriazole and benzotriazole derivatives and wherein all the hydroxyl groups of the polyol are esterified with the acid mixture. EP-A-0821053 discloses and claims an antioxidant composition for base oils used in lubricants and hydraulic fluids consisting of (1) amine salts of alkyl phosphate wherein the amine is selected from ammonia, primary and secondary alkylamines or mixtures thereof and (2) ammonium, ethylenediamine or metal salts of petroleum or aromatic sulfonate wherein the metal is selected from alkali or alkaline earth metals and the aromatic substituent is selected from alkylated benzenes and alkylated naphthalenes having 1 to 4 alkyl groups of 8 to 20 carbons each, and wherein phosphate to sulfonate is present in the ratio of about 14:1 to about 1:275. The present invention provides an oil composition comprising a major amount of a paraffinic oil having a Cleveland open cup flash point of more than about 200°C and a minor amount of: (i) at least one hindered phenolic antioxidant, and (ii) at least one tolytriazole diphenyl amine metal deactivator having the general formula given in claim 1. The composition of the invention is especially useful as an electrical and transformer oil. The composition of the present invention utilizes a major amount of a paraffinic oil having a Cleveland open cup flash point more than about 200°C, An example of such an oil is a solvent refined 145N paraffinic basestock sold by Exxon Corporation, Dallas, Texas, USA. Such an oil has lower solvency and better compatibility with seal and gasket materials than do naphthenic oils. Compatibility with seal and gasket materials has been generally found to correlate with the aniline point of the oil, with oils that have higher aniline points being more gasket and seal compatible than those with lower aniline points. The additive system of the present invention includes (i) at least one hindered phenol antioxidant, and (ii) a metal deactivator. Typical hindered phenolic antioxidants suitable in the compositions of the present invention may be represented by formula I and formula II: where R 1 and R 2 may be the same or different alkyl groups, especially branched alkyl groups, containing 3 to about 9 carbon atoms. Preferred phenolic antioxidants include 2,6 di-tert-butylphenol, 2,6 di-tert-butylparacresol and mixtures thereof. The additive system also includes the said tolyltriazole metal diphenyl amine deactivator(s). The said tolyltriazole diphenylamine(s) may be a reaction product of a tolyltriazole and an alkylated diphenyl amine. The tolytriazole diphenyl amine reaction product may be represented by the formula III: wherein R 1 and R 2 may be the same or different alkyl groups having from 3 to 15 and preferably from 4 to 9 carbon atoms. In general, the additive system in the composition is present in a minor but effective amount. For example, the hindered phenol or mixtures thereof typically will comprise from 0.05 to 3.0 wt.% based on the weight of the paraffinic oil, and preferably 0.5 wt.% to 2.0 wt.%. The metal deactivator typically will comprise from 0.01 to 1.5 wt.%, based on the weight of the paraffinic oil, and preferably from 0.10 to 1.0 wt.%. The pour point depressant will comprise from 0.10 to 1.0 wt.%, based on the weight of paraffinic oil and preferably from 0.4 to 0.8 wt.%. Finally, the composition of the present invention may also include optional additives such as a pour point depressant capable of lowering the pour point to below the lowest temperature expected for the climate in which the electrical oil is to be used. This would normally be a temperature in a range of from -30°C to -40°C. A particularly preferred class of pour point depressants is alkylated polystyrenes. Other illustrative pour point depressants include methacrylates and fumeric acid esters. Alternatively, this low temperature performance can be provided through the use of a dewaxed paraffinic oil having a Cleveland open cup flash point greater than about 200°C. EXAMPLE 1 An electrical and transformer oil was formulated using the base oil a Solvent Neutral 145N paraffinic basestock having a Cleveland open cup flash point of 220°C. This Solvent Neutral 145N is commonly referred to as 145 SSU @ 100°F paraffinic stock. The formulation contained 2,6 di-tert-butyl phenyl, 2,6 di-tert-butyl cresol and tolyltriazole diphenyl amine in the amounts shown in Table 1. The formulated oil was tested for life using the ASTM D 2112 Rotary Bomb Test and for oxidation stability using the ASTM D 2440 test. The results are shown in Table 2. FORMULATION FOR EXAMPLE 1 COMPONENT CONCENTRATION, WT% Solvent Neutral 145 98.45 Tolyltriazole diphenyl amine 0.30 2,6, di-tert-butyl phenol 0.75 2,6, di-tert-butyl paracresol 0.50 COMPARATIVE EXAMPLE 1 The ASTM specification for a Type II oil are presented as Comparative Example 1 in Table 2. COMPARATIVE EXAMPLE 2 In the properties of a commercially available transformer oil are shown in Table 2 as Comparative Example 2. DESCRIPTION ASTM TEST METHOD EXAMPLE I COMPARATIVE EXAMPLE I COMPARATIVE EXAMPLE 2 ASTM D 3487 Type II Oil Physical Properties Specific Gravity, 60/60°F D 1298 0.866 0.91 max 0.870 Viscosity @ 40°C, cSt D 88, D 445 29.21 12.0 max 7.9 Viscosity @ 100°C, cSt D 88, D 445 5.10 3.0 max 2.2 Viscosity @ 100°F, SSU D 88, D 445 150.9 66 max 53.5 Viscosity @ 210°F, SSU D 88, D 445 43.4 36 max 33.5 Aniline Point, °C D 611 103 63-84 74 Pour Point, °C D 97 -18 -40 max -54 Color, ASTM D 1500 L0.5 0.5 max L0.5 Flash Point (COC), °C D 92 220 145 min 158 Sulfur, wt% X-ray 0.12 - 0.12 Neut Number, mg KOH/g D 974 0.0 0.03 max 0.0 Water by KF. ppm D 1533 27 30 max 20 Interfacial Tension @ 25°C. dynes/cm D971 47 40 49 Chemical Properties Corrosive Sulfur D 1275 Noncorrosive Noncorrosive Noncorrosive Antioxidant Content, mass % D 2668, D 1473 1.25 0.30 max 0.25 Oxidation Stability @ D 2440 110°C 130°C ( ) 110°C 110°C 130°C ( ) 72 Hours: Sludge, wt% 0.068 0.080 0.10 max 0.01 - Neutralization No., mgKOH/g 0.022 0.077 0.30 max 0.02 - 164 Hours: Sludge, wt% 0.124 0.006 0.20 max 0.01 0.47 Neutralization No., mgKOH/g 0.022 0.173 0.40 max 0.08 0.73 336 Hours: Sludge, wt% 0.086 0.096 - 0.12 0.76 Neutralization No., mgKOH/g 0.067 0.714 - 0.37 0.90 Oxidation Stability Rotary Bomb Life,Minutes @ D 2112 140°C 851 195 300 150°C ( ) 488 - - 160°C ( ) 345 - 116 Electrical Properties Dielectric Breakdown Voltage @ 60 Hertz, KV D 877 61 30 min 47 Impulse Breakdown Voltage @ 25°C, KV Needle (negative) - to-s phere(grounded), @ 1-in Gap D3300 144 145 min 175 Power Factor @ 60 Hertz. %@ D 924 25°C 0.004 0.05 max 0.005 90°C 0.280 - - 100°C 0.460 0.30 max 0.120 Gassing Tendency @ 80°C, µL/minute D 2300B -2.8 ( ) +30 max -11.0 Static Charge Density, µC/m 3 none 20 50 max 5 EXAMPLES 3 to 5 Three oils were formulated with the additive system of this invention. The composition of each is given in Table 3. The formulated oils were tested using the ASTM Rotary Bomb Test and ASTM Test D2440. The results are shown in Table 3. Comparative Examples 3 to 5 Three oils were formulated using only one of the components of the additive system of this invention. These compositions are given in Table 3. The oils were also tested as in Examples 3 to 5 and the results are presented in Table 3. EFFECT OF ANTIOXIDANT COMBINATIONS ON OXIDATION STABILITY Comparative Examples Examples 3 4 5 3 4 5 Component, wt.% Tolyltriazole diphenyl amine (TTDPA) 1.55 -- -- 0.30 0.30 0.30 2,6 di-tert-butyl phenol (DTBP) -- 1.55 -- 1.25 -- 0.75 2,6, di-tert-butyl paracresol (DBPC) -- -- 1.55 -- 1.25 0.50 Solvent Neutral 145 98.45 98.45 98.45 98.45 98.45 98.45 Oxidation Stability ASTM D2440 Oxidation @ 130°C 164 Hours, Sludge, wt.% 0.108 0.008 0.010 0.005 0.003 0.060 Neut. No., mg KOH/g 0.447 0.048 0.420 0.075 0.091 0.173 336 Hours Sludge, wt.% 0.217 0.322 0.553 0.085 0.085 0.054 Neut. No., mg KOH/g 0.559 1.170 1.628 0.615 0.674 0.629 Rotary Bomb Oxidation Test @ 160°C, Minutes 335 290 150 437 256 345 As can be seen from the data in Table 3, the additive system of the present invention is better than the phenolic inhibitor or metal deactivator alone in lowering the level of sludge formed during oxidation. Also, the additive system of the invention provides better oxidation stability as determined in the Rotary Bomb Oxidation Test. Examples 6 and 7 The oils were formulated, each containing the additive system of the invention. The formulations are given in Table 4. The power factor for each formulation also was determined. As is known, the power factor is a measure of how much energy is absorbed by the insulating oil when placed in an alternating electric field such as would be found in a transformer. High power factors result in lower electrical efficiency as well as shorter transformer life. The measured power factors are given in Table 4. Comparative Examples 6 and 7 Two additional oil formulations were prepared using the same base oil as in Examples 6 and 7, i.e., Solvent Neutral 145, the same phenolic antioxidants but a benzotriazole metal deactivator. The compositions are given in Table 4. The power factors for these compositions was determined and are also given in Table 4. EFFECT OF METAL DEACTIVATOR ON ELECTRICAL PROPERTIES Comparative Example 6 Example 6 Comparative Example 7 Example 7 Component, wt.% Solvent Neutral 145 99.55 99.50 99.1 99.00 2,6 di-tert-butyl paracresol 0.12 0.12 0.24 0.24 3,5 di-tert-butyl-4- 0.12 0.12 0.24 0.24 hydroxyhydrocinnamic acid, C 7-9-branched Nonylated diphenylamine 0.16 0.16 0.32 0.32 N,N-bis (2-Ethylhexyl)-ar-methyl-1H-benzotriazole-1-methanamine 0.05 -- 0.10 -- Tolytriazole diphenylamine -- 0.10 -- 0.20 Power Factor, % @ 25°C 0.028 0.009 0.036 0.016 90°C 3.70 1.46 4.80 2.40 100°C 5.20 1.74 7.00 3.30 As can be seen the additive system of this invention results in an oil formulation having a power factor about half of that obtained in oil formulations using a conventional metal deactivator.

Claims: An oil composition comprising: a major amount of a paraffinic oil having a Cleveland open cup flash point of more than 200°C, and a minor amount of: (i) at least one hindered phenolic anti-oxidant, and (ii) at least one tolyltriazole diphenyl amine metal deactivator having the general formula: wherein R 1 and R 2 are the same or different alkyl groups each having from 3 to 15 carbon atoms. The composition of claim 1, wherein the, or each, hindered phenol is selected from phenols having the formulae: where R 1 and R 2 may be the same or different alkyl groups having 3 to about 9 carbon atoms. The composition of any preceding claim, wherein the hindered phenolic antioxidant(s) comprises in total from about 0.05 to about 3.0 wt.% based on the weight of the paraffinic oil. The composition of any preceding claim, wherein the tolyltriazole diphenyl amine metal deactivator(s) comprise(s) in total from 0.10 to 1.0 wt.% based on the weight of the paraffinic oil. The composition of any preceding claim comprising a pour point depressant in an amount in a range of from about 0.05 to about 3.0 wt.% based on the weight of paraffinic oil. The composition of claim 5, wherein the amount of pour point depressant is in a range of from 0.1 to 1.0 wt%. The composition of any preceding claim wherein the paraffinic oil is a dewaxed oil. The use of a composition as claimed in any preceding claim as, or in, an electrical or transformer oil. A method of improving the power factor of a paraffinic oil or paraffinic oil composition, the method comprising incorporating therewith at least one hindered phenolic anti-oxidant as described in any one of claims 1, 2, 3 or 4 and at least one tolyltriazole diphenyl amine metal deactivator as described in claim 1 or claim 4.

Inventors: ANGELO JACOB BEN, KENT CHRISTOPHER JEFFREY STILL, ANGELO, JACOB BEN, KENT, CHRISTOPHER JEFFREY STILL
Applicants: EXXONMOBIL RES & ENG CO, EXXONMOBIL RESEARCH AND ENGINEERING COMPANY (DELAWARE CORP)
Application year: 2000
Main classification: C10M169
IPC codes: C10M141, C10M169