US3086075A - Electrical bushing with spaced conductor with metallic powder for thermally connecting the bushing and conductor - Google Patents

Description

Apnl 16, 1963 I. ,s. GARD 3,086,075

ELECTRICAL BUSHING WITH SPACED CONDUCTOR WITH METALLIC POWDER FOR THERMALLY CONNECTING THE BUSHING AND CONDUCTOR Filed March 1, 1960 INVENTOR. //VG J. cffleg A Tram W575 nited States atent 3,086,075 ELECTRICAL BUSHING WITH SPACED CONDUC- TOR WITH METALLIC POWDER FOR THER- MALLY CONNECTING THE BUSHING AND CONDUCTOR Inge S. Gard, Ludvika, Sweden, assignor to I-T-E Circuit Breaker Company, Philadelphia, Pa. Filed Mar. 1, 1960, Ser. No. 12,075 Claims priority, application Sweden Mar. 5, 1959 4 Claims. (Cl. 174152) This invention relates to an electrical bushing insulator of the type wherein an electrical conductor may be carried through some type of metallic housing in insulated relation with respect to the housing and more specifically relates to an electrical bushing insulator wherein the space between the outer diameter of the central conductor and the inner diameter of the outer insulator housing is filled with a compressible medium of relatively high thermal conductivity with respect to air.

In the past electrical bushing insulators have been formed of a tube of ceramic material such as porcelain, and these tubes receive a central conductor therethrough. The outer porcelain tube is then provided with a securing means so that the complete assembly of insulator and central conductor may be connected to a support structure which will be insulated with respect to the central conductor. Since the central conductor within the outer insulator housing will have a coetficient of thermal expansion substantially different from that of the insulator, it is normally necessary to provide space between the outer diameter of the central conductor and the inner diameter of the insulator housing so that the conductor may expand and contract responsive to temperature fluctuation without causing a fracture of the insulator housing. Note that the temperature change to which the assembly may be exposed can be of appreciable magnitudes as where the bushing assembly is used in the oil tank of an oil interrupter and is exposed to the hot ionization products of interruption when the oil circuit interrupter is operated to a circuit open position.

In view of this required spacing, there will be a cushion of air which surrounds the central conductor where this layer of air interferes with efiective cooling of the central conductor. The problem of cooling the central conductor is made worse since the circuit terminal which may have a relatively high resistance will be immediately adjacent the of end of this conductor so that a substantial amount of heat is generated in the central conductor and cannot be effectively removed to the outer insulator housing.

The principle of the present invention is to fill the aforementioned air space surrounding the central conductive member with a compressible medium having a relatively high thermal conductivity with respect to the thermal conductivity of air. By way of example, this space may be filled with copper filings or a powdered conductive material. By using a powder, the central conductor is still free to expand without transmitting substantial stress to the outer housing and at the same time the thermal conductivity of the powder will permit a conductive flow of heat from the central conductor to the housing. By way of example, since the heat is moved in this highly efiicient manner, the current conducting capacity of the bushing insulator may be substantially doubled for the same cross-sectional area of the central conductor.

Further advantages flow from this novel structure whereby it is no longer necessary to coat the inner surface of the insulator housing with a conductive material such as graphite in order to avoid corona between the conductor and the housing wall. That is to say, since the compressible medium is electrically conductive, the graphiting process may be eliminated. While the thermally conductive medium can be of any type of material, it is preferably of a nonmagnetic material in the case of an A.-C. bushing insulator to avoid heat generated by eddy current losses in the medium.

Accordingly, the primary object of this invention is to provide a novel electrical bushing insulator.

Another object of this invention is to provide a novel electrical bushing insulator having an increased current rating.

A further object of this invention is to provide a novel electrical bushing insulator wherein the central electrical conductor is thermally connected to its outer insulator housing through a relatively compressible medium having a relatively high thermal conductivity with respect to air.

A still further object of this invention is to fill the space between the central conductor and outer insulator housing of an electrical bushing insulator with a compressible medium having a relatively high thermal conductivity with respect to the thermal conductivity of air.

A further object of this invention is to replace the coating of the inner surface of the insulator housing of an electrical bushing insulator by filling the space between the insulator and its central conductor with a medium of relatively high conductivity with respect to air.

These and other objects of the invention will become apparent from the following description when taken in connection with the drawing which shows an electrical insulator bushing of the typical type wherein an outer insulator housing 1 which may be of porcelain or any other desired insulator material has an external flange 2 fastened thereto in any desired manner. The insulator housing 1 can be secured to flange 2, for example, in the manner shown in copending application Serial No. 853,185, filed November 16, 1959, now Patent 3,011,013, entitled Method for Joining Two Tubular Parts.

The central conductor 3 is carried centrally of the central opening within insulator housing 1 and may be of copper or any other desired material. More specifically, central conductor 3 may be held by means of the two clamping conductor members or support means 3a and 3b which are secured to conductor 3 in any desired manner and clamped into respective ends of insulator housing 1 as shown. Conductor 3 is then terminated at either end by terminal members 4 and 5 which can be of any standard construction.

The insulator described up to this point is typical of present commercially used electrical bushing insulators, and it will be noted that the external diameter of conductor 3 is less than the internal diameter of bushing insulator 1. This spacing is provided purposely because of the diiferent thermal coefficients of expansion of insulator 1 and conductor 3 and prevents the transmission of stress to insulator 1 under high temperature change conditions. This space, however, provides a thermal barrier where the space is filled with air so that the heat is nit efficiently conducted from conductor 3 to insulator In accordance with the present invention, the space between the conductor and housing is filled with a medium 6 of relatively good thermal conductivity with respect to the thermal conductivity of air. By way of example, medium 6 may be formed of a copper powder. With this novel medium 6 of relatively good thermal conductivity, it will be apparent that heat may be transmitted from conductor 3 to insulator 1 by conduction, whereby it has been found that the current carrying capacity of conductor 3 for the same size conductor and same temperature rise can be doubled with respect to the use of the conductor with a surrounding air space.

Furthermore, since the relatively good thermally conductive medium 6 will also be electrically conductive, the inner surface of insulator ll need not be coated with a conductive material such as graphite to control corona effects.

Although preferred embodiments of the novel invention have been described, many variations and modifications will now be obvious to those skilled in the art, and it is preferred, therefore, to be limited not by the specific disclosure herein but only by the appended claims.

What is claimed is:

1. An electrical bushing insulator; said electrical bushing insulator comprising an outer insulator housing having a central opening therein, a conductor passing through said opening and extending beyond either end of said outer insulator housing and a support means; said support means being connected between said insulator housing and said central conductor to support said conductor within said opening and in spaced relation with respect to the inner walls of said opening; and a compressible medium having a relatively high thermal conductivity with respect to the thermal conductivity of air being contained Within at least a portion of the space defined by the external area of said conductor and the internal area of the walls of said opening in said insulator housing; said medium comprising a conductive metal powder.

2. An electrical bushing insulator; said electrical bushing insulator comprising an outer insulator housing having a central opening therein, a conductor passing through said opening and extending beyond either end of said outer insulator housing and a support means; said support means being connected between said insulator housing and said central conductor to support said conductor within said opening and in spaced relation with respect to the inner walls of said opening; and a medium having a relatively high thermal conductivity with respect to the thermal conductivity of air being contained Within at least a portion of the space defined by the external area of said conductor and the internal area of the walls of said opening in said insulator housing; said medium being comprised of a copper powder.

3. An electrical bushing insulator; said electrical bushing insulator comprising an outer insulator housing having a central opening therein, a conductor passing through said opening and extending beyond either end of said outer insulator housing and a support means; said support means being connected between said insulator housing and said central conductor to support said conductor within said opening and in spaced relation with respect to the inner Walls of said opening; and a medium having a relatively high thermal conductivity with respect to the thermal conductivity of air being contained within at least a portion of the space defined by the external area of said conductor and the internal area of the Walls of said opening in said insulator housing; said medium comprising an electrically conductive material in particle form.

4. An electrical bushing insulator; said electrical bushing insulator comprising an outer insulator housing having a central opening therein, a conductor passing through said opening and extending beyond either end of said outer insulator housing and a support means; said support means being connected between said insulator housing and said central conductor to support said conductor within said opening and in spaced relation with respect to the inner walls of said opening; and a medium having a relatively high thermal conductivity with respect to the thermal conductivity of air being contained within at least a portion of the space defined by the external area of said conductor and the internal area of the walls of said opening in said insulator housing; said medium being comprised of a copper powder; said insulator housing being of porcelain; the walls of said opening in said insulator housing being rendered conductive through said medium.

References Cited in the file of this patent UNITED STATES PATENTS 1,079,352 Keyes Nov. 25, 1913 1,368,160 loutiret Feb. 8, 1921 1,703,409 Smith Feb. 26, 1929 1,899,752 Estorff Feb. 28, 9133 2,318,922 Carington May 11, 1943 2,351,964- Hill June 20, 1944 2,357,602 Peters et al Sept. 5, 1944 FOREIGN PATENTS 605,512 France Feb. 19, 1926 OTHER REFERENCES Deinema, George R.: Bushing Modifications Reduce Corona, Electrical World, June 2, 1952, page 104.

Claims (1)

1. AN ELECTRICAL BUSHING INSULATOR; SAID ELECTRICAL BUSHING INSULATOR COMPRISING AN OUTER INSULATOR HOUSING HAVING A CENTRAL OPENING THEREIN, A CONDUCTOR PASSING THROUGH SAID OPENING AND EXTENDING BEYOND EITHER END OF SAID OUTER INSULATOR HOUSING AND A SUPPORT MEANS; SAID SUPPORT MEANS BEING CONNECTED BETWEEN SAID INSULATOR HOSUING AND SAID CENTRAL CONDUCTOR TO SUPPORT SAID CONDUCTOR WITHIN SAID OPENING AND IN SPACED RELATION WITH RESPECT TO THE INNER WALLS OF SAID OPENING; AND A COMPRESSIBLE MEDIUM HAVING A RELATIVELY HIGH THERMAL CONDUCTIVITY WITH RESPECT TO THE THERMAL CONDUCTIVITY OF AIR BEING CONTAINED WITHIN AT LEAST A PORTION OF THE SPACE DEFINED BY THE EXTERNAL AREA OF SAID CONDUCTOR AND THE INTERNAL AREA OF THE WALLS OF SAID OPENING IN SAID INSULATOR HOUSING; SAID MEDIUM COMPRISING A CONDUCTIVE METAL POWDER.

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