US2351964A - Filling compound for insulating conductors - Google Patents

Description

June 20, 1944. Q E HILL FILLING COMPOUND FOR INSULATING- CONDUCTORS Filed July 25, 1942 r .illlllliilll h r/ s FHi/l.

NVENTOR WITNESSES: 8.9

Patented June20, 1944 UNITED STATES PATENT OFFICE FILLING COMPOUND FOR INSULATING CONDUCTORS Vania Application July 25, 1942, Serial No. 452,260

4 Claims.

This invention relates to iilling compounds, particularly for electrical bushings exposed to the weather.

In high tension bushings, a porcelain casing is spaced about the conductor element to serve as a weather casing. The conductor element carries electrical insulation. In the space between the porcelain weather casing and the insulated conductor element, it is the practice to apply an electrically insulating liquid or plastic compound. heavier than water have been introduced into the bushing space for this purpose. the space between the porcelain casing and the insulated conductor element with these viscous liquids heavier than water, it was expected that the entry or passage of moisture or other Highly viscous, organic liquids By filling deleterious materials therethrough would be prevented. The viscous liquid filling thus was intended to maintain the dielectric properties and power factor or the bushing at some predetermined value.

Contrary to expectations, bushings in service ior some time have been discovered to contain moisture diffused throughout the viscous organic liquid filling compound in spite of the greater density of the latter. The distributed moisture reduces the dielectric resistance and increases the possibility of failure of the bushing.

From an examination of the bushings it was concluded that the moisture was diffused throughout the organic filling by means oi convectlve fiow set up therein by thermal gradients between the porcelain weather casing and the insulated conductor element. Even gum-dike filling compounds tend to iiow or circulate slowly within the bushing and thereby carry moisture or entrapped water to the bottom of the bushing space. In some cases, in a year or two of service operation, water, whichis present on the upper surface of the bushing filling, may be carried by circulation into every portion of the organic substance.

The object of this invention is to provide an insulating composition that is resistant to the difiusion of water by convective flow, which does not crack, and which adheres to porcelain when applied.

Other objects of the invention will, in part, be obvious, and will, in part, appear hereinafter.

For a fuller understanding of the nature and objects of the invention, reference should be had to the single figure of the drawing illustrating the application of the invention to a bushing.

Referring to the single figure of the drawing,

the invention is shown as applied to a bushing It). The bushing l0 comprises an electrical conductor 12 with insulation it applied thereto. A meal sleeve I6 is disposed tightly about the lower portion of the insulation l4 and supports the entire bushing. Attached to the sleeve I6 is a metal flange member l8.- At the upper end of the conductor 12, a metal cap 20 is adiustably attached thereto. 1

A porcelain weather casing 22 is held in spaced 4 relation to the conductor 12 and insulation H by the metal flange member l8 and the metal cap 20. Suitable means are provided for hermetically sealing the flange member and metal cap 20 to the porcelain casing 22. Between the porcelain bushing and conductor i2 there is present a space 26.

A plug 23 in the upper metal cap 20 may be removed to expose an opening through which filling compound may be introduced. In the flange member 88, the plug 24 may be taken out of an aperture to permit filling compound to be withdrawn.

As disclosed hereinbefore, viscous or gum-like organic bushing compoundsalone are subject to convective flow thereby diffusing water in a relatively short time in the normal course of operation of bushings. According to this invention, such convective flow is materially diminished. Water or moisture will be diffused throughout the bushing compound at a rate so low that the normal life of the bushing will be surpassed before an objectionable distribution of moisture will have taken place in the bushing filling compound. Such reduction of convective flow is attained by combining solid organic dielectric particles of predetermined size with organic bushing compound.

In constructing a bushing according to the invention, the space 25 between the porcelain casing 22 and the insulated conductor i2--l4 is initially filled with a granular, solid inorganic dielectric. Sand, quartz, crushed porcelain, crushed glass and equivalent materials are suitable for this purpose. The best results are obtained by the use of particles of from 4 to 10 mesh fineness; however, particles of from 2 to 40 mesh will serve the purpose.

The granular inorganic particles are introduced into space 25 through the opening left by removing plug 23. Suflicient granular dielectric is put in to fill the space 26 to the top of the porcelain casing 22. It is advisable to shake or vibrate the bushing to fully pack the space 26.

A liquid bushing filling compound having good electrical insulation and a density greater than that of water is introduced through the opening closed by plug 23 until the interstices between the inorganic particles have all been completely filled. Preferably, a layer 00, one or two inches high, of the insulating bushing compound is applied above the level of the inorganic particles.

A suitable compound for applying to the inorganic particles is one composed of asphalt substantlally free from mineral impurities combined with highly chlorinated hydrocarbons and a petroleum oil to provide for softness and flexing at low temperatures. A compound of this type has been disclosed in the U. r S. patent to McCulloch No. 2,154,276.

As set forth in that patent, a suitable petroleum asphalt is one having a ball and ring melta,ss1,os4 7 along the boundaries between the inorganic particles and the filling compound. This feature is important in producing a satisfactory bushing composition.

A further advantage derivable by adding solid inorganic material such as quartz sand is the reduction of temperature gradient through the compound. The reduction oi the temperature gradient retards or decreases convective fiow of the compound many times as compared to that present in the compound alone in the same space.

. In the example above, the thermal gradient is only a third of what it is with the compound alone.

The pull-away temperature of the compound for the porcelain is not materially increased by the addition of the relatively large amounts of ing point of 115 C., a penetration of 15 seconds at 25 C., a pouring temperature of 175 C..- a specific gravity of 1.02 to C., and is less than 0.0 insoluble in benzol.

A satisfactorychlorinated hydrocarbon for the purpose of this invention is one derived by chlorinating diphenyl or its derivatives to a chlorine content of from 55% to 70%. These materials are known as Aroclors and are characterized as non-crystalline, glassy resin-like solids at room temperature which are soluble in oil in all pro-- portions. The Aroclors having a boiling range of from 270 C. to 400 C. are suitable for the purpose of this invention. They will not affect the insulation ll wound about the conductor I! in case the insulation consists of varnished paper.

The petroleum oil employed in preparing the bushing compound is a refined petroleum prodnot known as transformeroil. This material has excellent electrical properties, low viscosity, low

pour point and it is stable, inert, non-volatile at ordinary temperatures. Other petroleum oils, however, may be used for this purpose.

In preparing the filling compound, the proportions of the ingredients should be selected to provide for a density greater than that of water. Using from 17% to 29% by weight of the "Aroclor will assure attainment of such density. A density of 1.05 at 20 C. will be satisfactory. As representative of suitable compounds which may be produced having a specific gravity greater than that of water and an adherence to porcelain such that the compounds do not separate or pull away therefrom until temperatures of from 40 F. to -85 F. are reached, the following table of satisfactory formulations is submitted:

Composition in percent Serial No. Aroclor Asphalt Oil 17 so m 11 as is so 26 1s 54 2s 20 40 4o inorganic particles therein. Tests have indicated that for a compound pulling away alone at -60 F., when loaded with 8 to 8 mesh sand, the

. pull-away temperature is about -40 F. Inorganic material finer than 40 mesh is not desirable for the purpose of this invention since the pullaway temperature would be greatly increased.

A further advantage of the presence of the inorganic particles is the greatly diminished reduction of leakage of the compound in case the lower seal 22 or plug 24 contains minute openings. It has been discovered that the reduction in flow of the compound by the introduction of the inorganic particles reduces the escape of the filling compound to a small percentage of the escape in case the filling compound were present in the space 28 alone. a

In cases where the bushing containing filling compound alone is exposed to a differential temperature between the conductor i2 and the weather casing II, the surface 32 of the compound is noticeably warped or elevated at the warmer zone. Water present on the surface tends to collect in the valley so produced and thereby penetration is facilitated. With the introduction of inorganic particles of the type specified, it has been discovered that under similar conditions the filling composition expands more nearly as the unitary body and a substantially horizontal surface is maintained whereby water does not tend to accumulate or penetrate as readily.

Furthermore, it is to be understood that the particular form of product shown and described and the particular procedure set forth are presented for the purposes of explanation and illustration, and that various modifications of said product and procedure can be made without departing from the scope of the appended claims.

I claim as my invention:

1. An electrically insulating filling composition for bushings comprising a substantial proportion of inorganic insulating solid particles of from 2 to 40 mesh fineness and a liquid compound of a density greater than water in amount suilicient to fill all the interstices between the solid particles, the compound comprising a petroleum asphalt, a chlorinated diphenyl having a chlorine content of from 55% to 70% and being a non-crystalline, glassy, resin-like solid at room temperature and a petroleum oil.

2. An electrically insulating filling composition for bushings comprising a substantial proportion of inorganic insulating solid particles of from 2 to 40 mesh fineness and a liquid compound in amount sufiicient to fill all the interstices between of chlorinated diphenyls having from 55% to 70% chlorine and 23% to 40% of petroleum oil.

3. In a bushing comprising an exterior poi-eelain weather casing and an interior lead-in bushing spaced therefrom, a filling composition for the space between the porcelain and lead-in bushing comprising a substantial proportion of inorganic insulating solid. particles of from 2 to 40 mesh fineness and a liquid compound of a density greater than water in amount sufllcient to fill all the interstices between the solid particles, the compound comprising a petroleum asphalt, a chlorinated diphenyl having a chlorine content'of from 55% to 70% and being a non-crystalline, glassy, resin-like solid at room temperature and a petroleum oil, the inorganic solids greatly reducing the convective flow of the composition and thereby preventing the penetration of water therethrough.

4. In a bushing comprising. an exterior porce- .iain weather casing and an interior lead-in bushing spaced therefrom, a filling composition for the space between the porcelain and lead-in bushing comprising a substantial proportion of inorganic insulating solid particles of Irom 2 to 40 mesh fineness and a liquid compound in amount sufficient to fill all the interstices between the solid particles, the compound comprising 40% to 60% oi petroleum asphalt, 17 to 2 9% of a chlorinated diphenyl having from 55% to 70% chlorine and 23% to 40% of petroleum oil, the inorganic solids greatly reducing the convective flow of the composition and thereby preventing the penetration of water therethrough, CHARLES F. HILL.

Images