US2143685A - Electric device and dielectric materials therefor - Google Patents

Description

Jan. 10, 1939. F. M. CLARK 2,143,685

ELECTRIC DEVICE AND DIELECTRIC MATERIALS THEIKEFOR Filed May 25, 1935 Inventor; Frank TT]. Clark,

by 7 6A9 His 'ttorney.

45 cule by decomposition.

Patented Jan. 10, 1939 UNITED STATES ELECTRIC DEVICE AND DIEIIlECTRIO MATERIALS THEREFOR Frank M. Clark, Pitt'sfield, Mass, assignor to General Electric Company, a corporation of New York Application May 25, 1935, Serial No. 23,404

9 Claims.

7 The present invention comprises a liquid dielectric and electrically insulating material.

In my prior Patent 1,931,455, patented October 17, 1933, I have described various non-inflammable dielectric and insulating compositions which consist of one or more aromatic hydrocarbons containing combined chlorine,-or other suitable halogen. When such halogenated material is decomposed, which may be the casewhen an electric arc strikes therethrough, as in a circuit breaker, then hydrogen halide gas is formed. In the presence of water vapor, which may be of atmospheric origin, some gaseous hydrogen halide tends to remain in the electrical apparatus as a fog. In some cases such halide and water may become emulsified in the halogenated hydrocarbon Where it may cause corrosion of metal parts or otherwise mayharmfully afiect the apparatus. While the halogen hydride gas may be removed by an external chemical absorber, as described in my prior U. S. Patent 1,964,684, patented June 26, 1934, its presence is in any event a source of difiiculty.

In accordance with my present invention I have provided new liquid compositions comprising as a preponderant ingredient one or more halogenated nitrile carbon compounds, and electric devices containing such compositions as insulating and heat transfer agents. By the term nitriles I include those materials in which one carbon atom combined with either an alkyl or an aryl group is combined with nitrogen, the general formula being RC:N.

The general or empirical formula for the halogenated nitriles is RXnCIN in which R represents an aromatic radical, or an aromatic derivative of an alkyl radical (as in the benzyl compounds), in which compound hydrogen atoms have been displaced by halogen (X) to an extent (n) preferably affording a chemical equivalency of hydrogen and halogen in the total mixture. Such materials are non-inflammable and possess the property of absorbing hydrogen halide which has been freed from its parent mole- The accompanying drawing illustrates somewhat conventionally difierent forms of electrical device in. which compositions embodying my present invention may beemployed for dielectric and insulating purposes. Fig. 1 is a side elevation partly in section of a transformer; Fig. 2 similarly illustrates a switch; Fig. 3 diagrammatically illustrates a capacitor; and Fig. 4 is a side view of a short section of cable the casing being shown in part removed to permit interior parts to be seen.

Among the compounds representative of the different classes of hydrocarbon compounds included in the term nitriles are the aromatic nitriles as benzonitrile and tolunitriles and phenylated aliphatic nitriles, as benzyl cyanide.

I prefer to employ either a halogenated phenyl nitrile compound, such, for example, as chlorinated benzonitrile, or chlorinated tolunitrile, or a halogenated phenylated aliphatic nitrile compound, such, for example, as chlorinated benzyl nitrile or tolylacetonitrile. In general halogenated aromatic nitrile compounds should be chosen in which the halogen content equals, or exceeds, the hydrogen content in order to insure non-inflammability. I

The halogenated nitrile compounds which are employed for the purpose of my invention need not be chemically pure material. The halogenated aromatic nitrile compositions most suitable for my invention are mixtures of halogenated nitrile isomers. Such isomeric mixtures have a desired property of remaining liquid down to low temperature which, as explained in my prior patents, is a highly desirable 'property in liquid dielectrics for high potential apparatus.

In the following example of the preparation of a nitrile dielectric composition, the halogen element is represented by chlorine. Other halogens may be substituted forchlorine without departing from my invention. Chlorinated benzyl cyanide, PhClnCHZCN (n being 1, 2, 3, 4 or 5), may be made by the chemical interaction of a chlorinated benzyl chloride, an alcohol and a cyanide. In the preparation of a trichlor benzyl cyanide composition the following mixture is heated to a reaction temperature, preferably while being agitated:

Parts by weight Technical mixture of trichlor benzyl chloride isomers 40 Ethyl alcohol Potassium cy 13 Water 12 Chlorinated benzyl chloride can be obtained from toluene, CcHsCHa by chlorination: first, introducing chlorine in the phenyl or ring part of the toluene in the presence of an iron catalyst at temperatures of the order of 25 to 50 C., and second, the CH3 side chain may be chlorinated in the presence of sulphur at a higher temperature, ordinarily at 140 to 150 C.

The product obtained,,when a technical mixture of the isomers of trichlorbenzyl chloride is used, is a clear liquid having a specific gravity at 155 C. (referred to water at the same temperature) of 1.53 and boiling in the range of185 to 215 C. at a pressure of about 25 millimeters of mercury. Its refractive index at 25 C. is 1.5850. Its electrical resistivity is higher than 1x 10 ohms per cm. cubed. The dielectric constant is high, being in the neighborhood of 20. It has a pour point of about minus 30 C. (determined by A. S. T. M. test procedure D97-27T) and a viscosity of about 47 seconds at 3'7.8 C. Saybolt Universal.

Tetrachlor benzyl cyanide may be prepared as a mixture of its isomers by a similar method to that already described for the preparation of the trichlor benzyl cyanide. In this case, however, the chlorination of the toluene at 25 to 50 C. in the presence of an iron catalyst is carried to such degree that four chlorine atoms are introduced into the phenyl or ring structure of the toluene molecule.

Tetrachlor benzyl cyanide as a mixture of its isomers is a more viscous liquid of higher pour point than the trichlor compound. It boils at 25 millimeters pressure within the range of 220 to 250 C., has a specific gravity (15.5/15.5 C.) of 1.58, a viscosity at 37.8 C. of 160 seconds, Saybolt Universal, a pour point (A. S. T. M.) of minus 5 C. and a refractive index of 1.598.

The phenyl nitrile compounds may be compounded or mixed dielectric materials, such for example as chlorinated diphenyl, chlorinated diphenyl oxide, chlorinated naphthalene, or other. chlorinated polyphenyls, chlorinated benzene and chlorinated polyphenyls containing an alkyl group, such as chlorinated diphenyl methane, thereby producing mixtures having a viscosity best suited for particular purposes.

Chlorinated diphenyl of 60% chlorine content is extremely viscous at room temperature, having a pour point of about 30 C. (A. S. T. M. standard), and, therefore, being capable of use only with 'difliculty for impregnating capacitors or other devices. Mixturesmay be prepared comprising this material and a nitrile such as trichlor benzyl cyanide, the product having pour points and viscosities as indicated below, the indicated proportions being by weight:

Per cent chlor Per cent diphenyl (60% trichlor Pour gggfii g chlorine benzyl point 37 8 C content) cyanide 0'. Seconds 75 25 Plus 2 v 740 50 60 Minus 10 123 75 Minus 27 65 pounds here under consideration is their aflinity for hydrogen chloride, no solid precipitate being formedand. no deleterious or poisonous gases with one or more other liquid being evolved. The hydrogen chloride gasformed from the chlorinated benzyl cyanide component of the above composition when decomposed by the electric arc is absorbed by the body of undecomposed cyanide. A harmless addition product is formed which dissolves in the benzyl cyanide.

In U. S. Patent No. 2,105,406 for Liquid insulating composition, patented January 11, 1938, I have described and claimed insulating and cooling compositions consisting of halogenated hydrocarbons, or mixtures thereof, and containing a fixative which may consist of halogenated nitrile whereby the evolution of hydrogen chloride from such compositions is inhibited.

Dielectric compositions consisting preponderantly of a halogenated nitrile may be used in various electrical devices of which four have been shown as illustrative. The transformer shown in Fig. 1 comprises a tank l, containing a magnetic core 2, and transformer windings 3, the latter being surrounded by a liquid halogenated nitrile composition 4. Only one high tension terminal 5 of the transformer windings is visible in the drawing. While the drawing shows also a pressure release conduit 6, such conduit is separated from the main tank I by a diaphragm 8 which will only be ruptured under such extraordinary circumstances in which the decomposition of the liquid 4 exceeds the gas-absorbing capability of the fixative in the composition. A solid gas-absorber 9 may be provided in the conduit 6 but ordinarily will not be necessary. No

gas release conduit has been shown for the circuit I breaker of Fig. 2, which comprises a tank ll, fixed contacts l2, l3, and cooperating movable contacts l4, IS. The latter are mounted on a support l6 which in turn is operatively-connected to actuating levers IT. The liquid arc-quenching material I8 embodies the present invention. The capacitor indicated in Fig. 3 comprises armatures or plates 20, 2| and an interposed porous dielectric layer 22 which may consist of paper. The layer 22 is impregnated by a composition made as herein described.

It has been found that capacitors having aluminum foil armatures and kraft paper spacers when impregnated with trichlor benzyl cyanide have a capacity of one microfarad for 2.28 square Letters Patent of the United States, is: a

1. In an electric device an insulating composition consisting essentially of a mixture of isomers of liquid chlorinated benzyl nitrile containing at least three combined chlorine atoms per molecule. 2. An electric device containing an insulating and heat transfer medium consisting essentially of a mixture of isomers of hydrocarbon compounds having the chemical formula RXnCN (R being an aromatic radical or an aromatic derivative of an alkyl radical, X being a halogen, n being equal to 3 or more, C being carbon, and

' N being nitrogen), said material being liquid, 76

sisting essentially of a liquid mixture of isomers of non-combustible, and being capable of absorbing liquid mixture of a hydrogen halide without forming precipitates.

3. In an electric device, an insulating composition of matter consisting of a liquid mixture of isomers of chlorinated phenyl nitrile, said mixture containing sufiicient chlorine to be noncombustible, evolving non-combustible gas upon decomposition by an electric arc, and being capable of absorbing hydrogen chloride.

4. In an electric device, a dielectric and insulating composition consisting essentially of a plurality of chlorinated benzyl cyanide isomers, said mixture being non-combustible and being capable of absorbing hydrogen chloride. v

5. In an electric device, a dielectric composition consisting essentially of a liquid mixture of isomers of trichlor benzyl cyanide. I

6. In an electric device, a dielectric composition consisting essentially of a liquid mixture of isomers of tetrachlor benzyl cyanide.

7. A dielectric and insulating composition contrichlor benzyl about -30 C., a visco 215 C., at a. pressure 0 cyanide having a pour point of sity of about 47 seconds at 0., and boiling in the range of about 185 to 1 about 25 mm. of mercury. 5

A dielectric and insulating composition consisting essentially of a. liquid mixture of isomers V of about 5 of tetrachlor benzyl cyanide having a pour point 0., a viscosity of about 160seconds at 37.8 C., and boiling in the range of about 220 10 to 250 C. at cury.

a. pressure of about 25mm. of mer- 9. In an electric device, a dielectric and insulating composition consisting preponderantly of a liquid mixture of halogenated aromatic nitrile l5 isomers, said composition containing halogen in an amount at least chemically equivalent to the hydrogen content th non-inflammable and hydrogen halide.

ereof, being substantially being capable of absorbing CLARK.

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