EP0004425A1

EP0004425A1 - A method of insulating and transporting heat from the components of a transformer by means of a fluid and transformer impregnated with a fluid

Info

Publication number: EP0004425A1
Application number: EP79300352A
Authority: EP
Inventors: David Beretta; Frederick Charles Loveless; Walter Nudenberg
Original assignee: Uniroyal Inc
Current assignee: Uniroyal Inc
Priority date: 1978-03-09
Filing date: 1979-03-08
Publication date: 1979-10-03
Also published as: JPS5740601B2; CA1113707A; BR7901365A; JPS54132800A

Abstract

The use of transformer fluids comprising hydrogenated polyalphaolefins prepared from polymers and copolymers of alphaolefins having from six to twelve carbon atoms is disclosed. The fluids are characterised by outstanding dielectric, thermal and physical properties.

Description

The present invention relates to the use of transformer fluids comprising hydrogenated polyalphaolefins prepared from polyalphaolefins selected from the group consisting of polymers and copolymers of alpha-olefins having from six to twelve carbon atoms.
A transformer fluid has two principal functions. It acts as an electric insulating medium and it carries heat generated in the windings and core of the transformer to cooling surfaces. Transformer fluids must therefore have certain dielectric properties and heat transfer capabilities.
As the heat transfer capability of a fluid is dependent upon the viscosity, the viscosity must be kept within certain prescribed limits. A transformer fluid should not be carcinogenic or highly toxic and it should be biodegradable. It should exhibit low flammability and should not react chemically with the internal components of the transformer.
The application of liquid dielectrics is well known in the art, the most commonly used ones so far having been mineral (petroleum) oils, followed in recent years by halogenated aromatic hydrocarbons, fluorinated hydrocarbons, silicone oils and certain other materials. However, each of the above classes of materials has certain drawbacks.
In order for naturallty occurring mineral oils to function efficiently in transformers, they must be of low viscosity. This low viscosity insures good heat transfer properties and the adequately low pour point necessary in colder regions. Because of the structure of naturally occurring mineral oils, meeting the above requirements precludes use of high molecular weight oil which would be too viscous or tend to solidify. The fact that it is necessary to use. low molecular weight mineral oils creates a serious problem in that such oils are quite volatile and have low flash and fire points. That is, they are quite flammable. In contrast, the unique highly branched structure of the fluids of the present invention allows high molecular weight essentially non-flammable fluids to be produced which are still fluid enough at operating temperatures and lower to function as a heat transfer fluid. For a given viscosity, the vapor pressure (volatility) of the fluid of the present invention is much lower than mineral oil. Also, for a given molecular weight the viscosities and pour points are lower.
Balogenated aromatic hydrocarbons such as polychlorinated biphenyls (PCB) are outstanding dielectrics and heat transfer fluids and have been used for many years as a transformer fluid. However, recent analytical tests have shown that this transformer fluid produces many side effects which are detrimental to man and the environment.
Silicone oils have several drawbacks, one of them being cost, which prevents their being competitive with other transformer fluids. Because the silicone oils are not biodegradable, they tend to persist and accumulate and thus upset normally occurring equilibria in soil physics and chemistry. Silicones also impose problems when arcing occurs in transformers, which causes the formation of silicon oxides. These oxides deposit on sliding contacts and lead to abrasion problems. They also deposit on the surface of the oil and act as a wick, thus promoting burning of the silicone fluids which in turn forms more oxides. As the fluids of the present invention are hydrocarbons, no such harmful silicaceous side products can be formed.
The present invention relates to an improved transformer fluid, to the use of said fluid in transformers, and to transformers containing said fluid. The fluid of the present invention comprises hydrogenated polyalphaolefins prepared from polyalphaolefins selected from the group consisting of polymers and copolymers of alpha-olefins having from six to twelve carbon atoms.
Said hydrogenated polyalphaolefins should preferably have an iodine value equal to or less than 5, preferably equal to or less than 2.
The fluid of the present invention should preferably have the following properties; a fire point equal to or greater than 572°F., a flash point equal to or greater than 530°F., a kinematic viscosity at 210°F. equal to or less than 22 es (i.e., centistokes), a pour point equal to or less than -30°F., and a mumber average molecular weight between about 280 and 1,400. In other words, it is preferable that the fire point be at least 572°F., the flash point be at least 530°F., the kinematic viscosity at 210°F, not be greater than 22 cs and the pour point not be greater than -30°F.
The fluids of the present invention have high resistivity, high dielectric strength and a low dielectric constant. They have an excellent balance of both thermal (for example, high flash point, high fire point and high specific beat) and physical (for example, low viseosity low pour point and low spscific gravity) properties. The fluids of the present invention are also non-toxic and biodegradable.
The synthetic hydrocarbon fluids which can be used as transformer fluids are polymers, copolymers and blends of plymers and/or copolymers of alphs-olsfins having from six to twelve carbon atoms, such as hexene, heptene, octene, nonene, decene, undecene, and dodecene, which are polymerized and bydrogenated to produce a beat transfer fluid.
Polymerization of the alpha-olefins with peroside catalysts is preferably avoided because the presence of peroxide residues in the final product would be expected to decrease oxidative stability. Thus, any acidic catalyst would be preferred for the polymerization. Examples of such catalysts are aluminum chloride,boron trifluoride, and complexes of aluminum chloride or boron trifluoride with organic ligands.
The polyalphaolefins to be hydrogenated are preferably prepared as disclosed in U._S. Patent No. 4,041,098, the disclosure of which is hereby incorporated by reference.
For example, the polyalphaolefins to be hydrogenated may be prepared by generating in situ a soluble catalyst system by simultaneously adding with stirring to a reactor having an inert atmosphere and a temperature up to 200°C., a first feed comprising straight chain alpha-olefin monomers having at least 6 carbon atoms and a minor amount of a soluble aluminum alkyl halide and a second feed comprising straight chain alpha-olefin monomers having at least six carbon atoms and a minor amount of a soluble organic halide; wherein said soluble aluminum alkyl halide compound is selected from the group consisting of ethyl aluminum sesqui-chloride, ethyl aluminum dichloride and diethyl aluminum chloride, and said soluble organic halide is selected from the group consisting of a primary, secondary or tertiary aliphatic halide, an allylic halide or a benzylic halide, said soluble organic halide possessing a) at least one halogen-bearing carbon atom in the molecule and b) not more than one halogen atom attached to any single carbon atom in said molecule; said alkyl aluminum halide being present in said catalyst system in an amount of at least about 0.1% by weight of the total monomer content and in sufficient amount to provide a total Hal/Al ratio in said catalyst system of at least about 2.5/1.
As mentioned in U.S. Patent No. 4,041,098, optimum stability of polyalphaolefins toward oxidation is achieved by hydrogenating them to remove residual unsaturation. The importance of the degree of hydrogenation of a polyalphaolefin in determining stability to oxidation is illustrated In U. S. Serial No. 629,162, the disclosure of which is hereby incorporated by reference (see, for example, page 9, lines 6 - 14 (corresponding to West German OLS 2650580) Example II and Example XIV.
For optimum stability, the final iodine number of the polyalphaolefins is preferably 5 or less. Hydrogenation of the polyalphaolefins may be performed by known methods. For examples the polyalphaolefins may be subjected to a pressurized hydrogen atmosphere in the presence of a palladium, platinum or nickel catalyst, usually with heating in order to increase the rate of hydrogenation.
Normally, hydrocarbon polymers below C₂₀ are too volatile for use as heat transfer fluids whereas hydrocarbon polymers averaging much above C₆₀ have a pour point too high for certain low temperature applications. Accordingly, the synthetic hydrocarbon fluids preferably used herein are those having number average molecular weights essentially between about 280 and about 1,400, more preferably between 600 and 950.
In order to obtain a transformer fluid with the preferred number average molecular weight, it is generally necessary to follow polymerization of alpha-olefins and hydrogenation of the oligomers by distillative removal of lower boiling oligomers.
The fluids of the present invention may also be prepared by blending hydrogenated polyalphaolefins prepared as indicated above and then removing lower boiling polymers by distillation. Tnus, low viscosity and high viscosity fluids may be combined in order to obtain a desired balance of viscosity, low pour point and high flash and fire points. Two or more fluids prepared from different hydrogenated polyalphaolefins and/or comprising different homopolymers or copolymers may also be blended whether or not they have the same viscosity. It is also possible to blend two or more polyalphaolefin fluids and then bydrogenste them.
Although, in the preparations described above, low boiling fractions are removed after hydrogenation, it is also possible, though less convenient, to remove such fractions prior to hydrogenation.
Various antioxidant components may be added to the fluids of the present invention in order to prolong the life of said fluids during use. One usable antioxidant system is disclosed in U.S. Serial No. 629,162, filed November 5, 1975, (corresponding to West German Offenlegungsschrift 2650580, published May 18, 1977).
Another antioxidant system comprising a phenylated naphthylamine and a sulfoxide having two phenyl groups directly attached to the sulfur is disclosed in U.S. Serial No. 796,957, filed May 16, 1977. The particular naphthylamine is one of the formula:
or
where R₁ and R₂ may be hydrogen, alkyl with 1 to 12 carbon atoms, aryl with 6 to 20 carbon atoms, or aralkyl or alkaryl with 7 to 20 carbon atoms. Some of these phenylated naphthylamines are described in U.S. Patent No. 3,505,225, incorporated herein by reference. Preferably R₁ is hydrogen; tertiary pentyl; 1,1',3,3'-tetramethyl butyl; 1,1',3,3',5,5'-hexamethyl hexyl alpha, alphe, alpha-dimethyl benzyl; triphenyl methyl; and R₂ is hydrogen; alpha, alpha-dimethyl benzyl; alphamethyl benzhydryl; triphcnyl- methyl; or alpha, alpha, p-trimethyl benzyl. Particularly useful are phenyl-alpha-naphthylamine, N-(4-alpha, alpha- dimethylbenzylphenyl)-alpha-naphthylamine, p-octylphenyl- alpha-naphthylamine, and phenyl-beta-naphthylamine. Also, the oxidized forms of these phenylated naphthylamines may be used.
The sulfoxide compounds to be used in accordance with the present invention are compounds soluble in the oil and having at least one aryl group attached to the sulfoxide radical. The other group attached to the sulfoxide radical may be either an aryl group or an alkyl group which does not have any beta-hydrogen atoms. Preferably, this other group is phenyl, substituted phenyl, naphthyl, or methyl. The substituents on the phenyl group may be halogen, alkanoyloxy, nitro, nitrile, alkyl, alkoxy, derivatives of carboxy groups (salts, esters, amides., hydrazides, etc.), amino, aryl, aryloxy, keto, or aldehydo.
The first aryl group may likewise be phenyl, a substituted phenyl, or a naphthyl group. The substituents on the phenyl group may be the same as above.
In addition to the phenylated naphthylamine and the sulfoxide, the antioxidant composition further may optionally include an cligodynamic amount of copper or a copper salt.
A third antioxidant system comprising the reaction products of phenylnaphthylamine and mixed propylene trimers, said reaction having been conducted in the presence of a Friedel-Crafts catalyst, is disclosed in U.S. Serial No. 709,850, filed July 30, 1976. Formulae exemplifying these reaction products are:-
Where R = mixed propylene trimers
The preparation of such compounds may be performed by subjecting either α-or β-phenyl naphthylamine to the action of a mixture of propyle trimers and a Friedel-Crafts catalyst such as aluminum chloride or boron trifluoride. The reaction may be conducted at a temperature in the range of ambient temperature to 300°C.
It is preferably conducted in an inert atmospher, however, an inert atmosphere is not essential. The reaction product contains an alkylating moiety which comprise a multiplicity (e.g., at least 30) of isomers which are trimers of propylene. Typical of such structures are:

and
Phenolic type antioxidants which are well known in the art may also be used.
The following Examples illustrate the preparation and properties of fluids of the present invention. Table I depicts the properties of several fluids and compares the fluids of the present invention with other candidate transformer fluids. Table I shows that the fluids of the present invention have a superior balance of electrical, thermal, physical, toxicological and ecological properties.

EXAMPLE I

Octene-1 was polymerized by the teachings of U.S. Patent No.
4,041,098, and then hydrogenated to give a product having a crude viscosity of 10.4 cs at 210°F. Removal of the lower boiling components of the resultant polymers permitted an increase in fire point with a resultant decrease in flammability. The degree to which the lower boilers were removed affects the flash point, fire point, pour point and ultimate viscosity. Fluids IA and IB (both prepared from the original 10.4 cs material) illustrate this observation (see Table I).
By removal of even more of the lower boiling polymeric moieties, a fluid (IB) with an even higher fire point can be obtained (see Table I). Such combinatiors of high fire point and low pour point are difficult, if not impossible to attain by the use of naturally occurring mineral oils.

EXAMPLE II

Octene-1 was polymerized and hydrogenated as in Example I to give a polymer having a slightly higher crude viscosity at 210°F. (10.9 cs). Removal of the lower boiling fractions by distillation produced a fluid (II) having an excellent balance of properties (see Table I).

EXAMPLE III

Octene-1 was polymerized and hydrogenated as in Example I to give a product having an even higher crude viscosity (13.8 cs) than that of Example II. Removal of the lower boiling fractions by vacuum distillation produced, in high yield, material (fluid IIIA) again having an excellent balance of properties (see Table I). Fluid IIIB was prepared by removal of additional low boiling oligomers with an expected resultant increase in fire point (see Table I).
Octene-1 was polymerized and hydrogenated as in Example I, but to a lower crude viscosity (9.3 cs). Removal of low boiling oligomers from the crude product produced two fluids (IVA and IVB) corresponding to different degrees of distillation, but both having a desirably lower viscosity than previous examples coupled with high fire points (see Table I). The lower viscosities demonstrated by the products of Example IV make them superior as heat transfer fluids.

EXAMPLE V

Decene-1 was polymerized and hydrogenated as in Example I to give a product having a crude viscosity of 9.3 cs. The fluid was again subjected to vacuum distillation to remove lower boiling constituents. The resultant fluid (V) was similar to that of Example IV which had the same crude viscosity, but the pour point of the polydecene of this example was even lower, which is advantageous (see Table I).

EXAMPLE VI

Decene-1 was polymerized and hydrogenated as in Example I, but to a lower crude viscosity (7.3 cs). Removal by distillation of the lower boiling polymeric fractions produced product fluids (VIA and VIB) having an outstandingly good balance of properties (see Table I). VIA and VIB represent portions of the 7.3 cs material from which were removed different degrees of low boiling polymers.
This illustrates that fluids can be prepared with very high fire points, very low pour points and. very low
viscosities when decene-1 is used as the monomer for polymerization.

EXAMPLE VII

The fluids, one of 10 cs at 210°F. and the other of 40 cs at 210°F., were prepared according to the teachings of U.S. Patent No. 4,041,098 and were hydrogenated to insure oxidative stability. The 10 cs and 40 cs fluids were then blended in a 3/1 ratio and the blend was distilled under vacuum to remove low boiling substituents. The properties of the resulting fluid (VII) are shown in Table I.
It is obvious that by blending either different ratios or different viscosities of such fluids one can produce materials having a different balance of properties. For instance, a 4/1 blend of 10 cs and 40 cs fluids treated in the same manner will produce a fluid with lower viscosity and pour point. lower boiling fractions by vacuum distillation produced, in high yield, material (fluid IIIA) again having an excellent balance of properties (see Table 1). Fluid IIIB was prepared by removal of additional low boiling oligomers with an expected resultant increase in fire point (see Table I).
Octene-1 was polymerized and hydrogenated as in Example I, but to a lower crude viscosity (9.3 cs). Removal of low boiling oligomers from the crude product produced two fluids (IVA and IVB) corresponding to different degrees of distillation, but both having a desirably lower viscosity than previous examples coupled with high fire points (see Table I). The lower viscosities demonstrated by the products of Example IV make them superior as heat transfer fluids.

EXAMPLE V

EXAMPLE VI

Decene-1 was polymerized and hydrogenated as

EXAMPLE XI

In order to compare the flammability persistence of a fluid of the present invention with a silicone transformer fluid, a sample of silicone fluid (GE-SF-97-50, available from General Electric Co.) was placed in a Cleveland Open Cup flash and fire tester and heated to the point where flaming persisted (fire point), around 660°F. The test cup containing the burning fluid was transferred to an aluminum block and allowed to cool. Burning, accompanied by copious "soot" and smoke formation, persisted for 27 minutes and the flame then extinguished itself. During the burning, a sizeable volume loss occurred. The temperature of the fluid at the time that the flame extinguished itself was 178°F. The residual fluid contained large amounts of gelled and solid silicaceous matter.
A 16.5 cs fluid of the present invention was subjected to the same test. The fire point was 595°F., and once ignition was obtained, the test cup was placed on the same aluminum block. Flaming was slight and clean and persisted for only 3 minutes. The temperature of the fluid at the time of extinction was 455°F. The extinguished fluid had not changed in appearance.
This demonstrates that the hydrocarbon fluids of the present invention extinguish themselves much more rapidly than silicone fluids in this test. This property is of great safety value When transformer failure results in ignition of the transformer fluid.
It also shows that, although silicones must be heated to a higher temperature in order to become flammable (higher fire point), upon removal from the source of heat, they continue to burn for a much longer period of time. This occurs because silicon oxides, formed during burning, deposit on the surface of the silicon fluid and act as a wick.

Claims

1. A method of insulating and transporting heat from the components of a transformer comprising impregnating the transformer with a fluid characterised in that said fluid comprises hydrogenated polyalphaolefins prepared from polymers or copolymers of alphaolefins having from six to twelve carbon atoms.

2. A method according to claim 1, characterized in that said hydrogenated polyalphaolefins have an iodine value equal to or less than 5.

3. A method according to claim 2, characterized in that said iodine value is equal to or less than 2.

4. A method according to any one of the preceeding claims characterized in that said hydrogenated polyalphaolefins have a number average molecular weight between about 280 and about 1400.

5. A method according to claim 4, characterized in that said number average molecular weight is between about 600 and about 950.

6. A method according to any one of the preceeding claims characterized in that said fluid has a fire point equal to or greater than 572°F.

7. A method according to any one of the preceeding claims characterized in that said fluid has flash point equal to or greater than 530°F.

8. A method according to any one of the preceeding claims characterized in that said fluid has a kinematic viscosity at 210°F, equal to or less than 22 centistokes.

9. A method according to any one of the preceeding

claims characterized in that said fluid has a pour point equal to or less than -30°F.

10. A method according to any one of the preceeding claims characterized in that said fluid consists essentially of said hydrogenated polyalphaolefins.

₁₁. A method according to any one of the preceeding claims characterized in that said fluid has a flash point equal to or greater than 535°F., a fire point equal to or greater than 585°F., a kinematic viscosity equal to or less than 20 centistokes, and a pour point equal to or less than -35°F.

12. A method according to any one of the preceeding claims characterized in that said hydrogenated polyalphaolefins are prepared by polymerizing said alpha-olefins in the presence of an acid-catalyst and hydrogenating the resulting polyalphaolefins.

13. A method according to claim 13 characterised in that said acid-catalyst is aluminum chloride, boron trifluoride, a complex of aluminum chloride and an organic ligand, or a complex of boron trifluoride and an organic ligand.

14. A method according to any one of claims 1 to 11 characterized in that said hydrogenated polyalphaolefins are prepared by polymerizing said alpha-olefins in the presence of a soluble catalyst and hydrogenating the resulting polyalphaolefins.

15. A method according to claim l4 characterized in that said polyalphaolefins are prepared by a method comprising generating in situ a soluble catalyst system by simultaneously adding with stirring to a reactor having an inert atmosphere and a temperature up to 200°C., a first feed comprising straight chain alpha-olefin monomers having at least 6 carbon atoms and a minor amount of a soluble aluminum alkyl halide and a second feed comprising straight chain alpha-olefin monomers having at least six carbon atoms and a minor amount of a soluble organic halide; wherein said soluble aluminum alkyl halide compound is ethyl aluminum sesqui-chloride, ethyl aluminum dichloride or diethyl aluminum chloride, and said soluble organic halide is
a primary, secondary or tertiary aliphatic halide, allylic halide or a benzylic halide, said soluble organic halide possessing a) at least one halogen-bearing carbon atom in the molecule and b) not more than one halogen atom attached to any single carbon atom in said molecule; said aluminum alkyl halide being present in said catalyst system in an amount of at least about 0.1% by weight of the total monomer content and in sufficient amount to provide a total Hal/Al ratio in said catalyst system of at least about 2.5/1.

16. A method according to claim 15 characterized in that said alpha-olefin monomers are

monomers having from 6 to 12 carbon atoms, said organic halide is

t-butyl chloride, allyl chloride, benzyl chloride, or a halogenated oligomer having less than 25 carbon atoms prepared from alpha-olefins, and the reaction temperature is at least about 100°C.

17. A method according to claims 15 or 16 characterized in that products having a molecular weight of less than about 280 are removed by vacuum distillation.

18. A method according to claim 17 characterized in that the products removed are halogenated and then recycled as the organo halide compound.

19. A method according to any one of claims 15 to 18 characterized in that the yield of polymer obtained is at least about 56% based upon the weight of said alpha-olefins, and the number average molecular weight of said polymer is at least about 280.

20. A method according to any one of elaims 15 to 19 characterized in that the reaction temperature is between 23°C, and 200°C.

21. A method according to any one of claims 15 to 20 characterized in that said alphaolefin monomers are
octene-1 and decene-1.

22. A method according to any one of the preceeding claims characterized in that said fluid is a blend of at least two fluids, each of said fluids comprising hydrogenated polyelphaolefins, at least two of said fluids having different viscosities.

23. A method according to claim 22 characterized in that each of said fluids comprising hydrogenated equal polyalphaolefins has an iodine value/to or less than five.

24. A method according to claim 22 or 23 characterized in that at least two of said fluids are each prepared from alphaolefins having different numbers of carbon atoms.

25. A method according to any of the preceding claims characterised in that the number average molecular weight a of the halogenated polyalphaolefins is at least/710.

26. A method according to claim 25 characterised in that said number average molecular weight is at least about 800.

27. A transformer impregnated with a fluid, characterised in that the fluid is as defined in any of the preceding claims.