US3921116A

US3921116A - Sand filled - SF{HD 6 {B fused bushing

Info

Publication number: US3921116A
Application number: US465332A
Authority: US
Inventors: Harvey W Mikulecky
Original assignee: RTE Corp
Current assignee: Cooper Power Systems LLC
Priority date: 1974-04-29
Filing date: 1974-04-29
Publication date: 1975-11-18
Anticipated expiration: 1992-11-18
Also published as: CA1016617A

Abstract

A fused high voltage electric bushing for connecting a high voltage cable to an electrical apparatus within a casing, the bushing including a dielectric housing, an electrical terminal sealed to each end of the housing, a fusible element within said housing electrically connected to each of said terminals, a granular dielectric material within said housing and a gaseous insulating medium completely filling said housing, the medium being sulfur hexalfluoride (SF6). A layer of thermally insulating material can be provided on the inside surface of said housing.

Description

United States Patent [191 Mikulecky [451 Nov. 18, 1975 SAND FILLED SF FUSED BUSHING [75] Inventor: Harvey W. Mikulecky, Racine, Wis.

[73] Assignee: RTE Corporation, Milwaukee, Wis.

[22] Filed: Apr. 29, 1974 [21] Appl. No.: 465,332

[52] US. Cl. 337/202; 337/224; 337/279 [51] Int. Cl. H01H 85/18 [58] Field of Search 337/202, 273, 277, 279,

[56] References Cited UNITED STATES PATENTS v 2,539,261 l/l951 Miller 337/279 2,593,426 4/1952 Fahnoe 337/279 2,981,815 4/1961 Leeds et al. 174/31 R 3,633,141 l/l972 Ristuccia 337/202 3,648,211 3/1972 McKeithan 337/202 Primary Examiner-Harold Broome Attorney, Agent, or FirmRonald E. Barry [57] ABSTRACT A fused high voltage electric bushing for connecting a high voltage cable to an electrical apparatus within a casing, the bushing including a dielectric housing, an electrical terminal sealed to each end of the housing, a fusible element within said housing electrically connected to each of said terminals, a granular dielectric material within said housing and a gaseous insulating medium completely filling said housing, the medium being sulfur hexalfluoride (SP A layer of thermally insulating material can be provided on the inside surface of said housing.

A 10 Claims, 1 Drawing Figure US. Patent Nov. 18, 1975 3,921,116

I if, E

SAND FILLED SF FUSED BUSHING BACKGROUND OF THE INVENTION In my copending application entitled A Heat Insulating Fused High Voltage Bushing, Ser. No. 385,436, filed Aug. 3, 1973 and assigned tothe same assignee, and in the copending application of Edwin A. Link, Ser. No. 275,178, filed July 26, 1972 and assigned to the same assignee, current limiting fused bushings are disclosed which are designed for use at voltages of 8.3KV. This bushing also included a thermal insulating barrier which was used to protect the housing from thermal shock on vaporization of the fuse element. A resistive coating is placed on the inside surface of the bushing to minimize voltage stresses and to hold the radio influence voltage (RIV) down to an acceptable level. This type of bushing proved satisfactory at design voltage. However, the higher KV ratings provide higher voltage stresses which results in a further increase in the radio influence voltage.

SUMMARY OF THE PRESENT INVENTION hexafluoride (SE or one of a number of similar inert gases. These dielectric gases can withstand a much higher voltage stress without producing corona.

Other objects and advantages of the invention will become more apparent from the following description when read in conjunction with the drawing in which a sectional elevation view of the invention is shown.

DESCRIPTION OF THE INVENTION Referring to the drawing, the fused high voltage bushing 10 is shown mounted in an opening 12 in the casing 14 for an electrical device such as a transformer.

The casing 14 is normally filled with a dielectric fluid I or insulating oil 16 with the lower end of the bushing :10 extending into the oil 16'. The bushing 10 is retained close the passage 27 by means of a gasket 33. The bushing 10 is connected to the electrical apparatus by means of the electric terminal 32 provided at the inner end of the bushing. The terminal 32 is sealed to the inner end of the passage 27 by means of a gasket 38.

The voltage stress at the point of entrance of the bushing 10 through the casing 14 can be reduced by providing a layer of electrically conductive material on the inside of passage 27 as described in copending application Ser. No. 385,436. The material can be a conductive glaze or a conductive epoxy paint or any other conductive material which can be used for this purpose. The layer 40 extends through a portion of the length of the passage 27 and should pass through the opening 12 in the casing 14. Means can be provided for connecting the layer 40 to one of the

electrical terminals

30 or 32 in the form of a conductive member 42.

Means can also be provided for reducing the voltage stress in the opening 12 in the casing in the form of a conductive layer 42 provided on the outer surface of the housing 25. The layer 40 extends through the opening 12 a sufficient distance to be immersed in the dielectric fluid 16. The conductive layer 42 can be in the form of a conductive glaze or a conductive epoxy paint. The upper layer of the conductive layer 42 is grounded in casing 14 by means of the mounting assembly 18.

The passage 27 can be thermally insulated by means of a heat insulating layer 44 provided on the inside surface of the passage 27. The layer 44 is shown in the form of a sleeve which has an outer diameter substantially equal to the inner diameter of the passage 27. The passage 27 is filled with a granular dielectric material 34. The sleeve 44 is positioned between the granular dielectric material 34 and the inside surface of the passage 27 to insulate the housing from the heat of the are in the casing 14 by means of a mounting assembly 18 and is sealed in the opening by means of a gasket 20.

This is basically the same arrangement as shown in my copending application Ser. No. 385,436 except for an increase in fuse length in accordance with the higher voltage.

The bushing 10 includes an insulating housing 25 having a central passage 27 and a fuse assembly 22 po- 7 sitioned in the passage 27. The assembly 22 includes a first fusible element 24 generally in the form of a silver :wire or ribbon spirally wrapped around a spindle .28

and a second fusible element or expulsion fuse 26 connected in series with the element 24. The first fusible v element 24 provides a high current interruption capability. The second fusible element provides a low cur- I -rent interruption capability. The fuse assembly 22 is fusing of the

elements

24 and 26.

The bushing 10 is connected to a high voltage cable by means of a terminal casting 31 screwed onto the electric terminal 30 provided on the end of the housing 25. The terminal casting 31 is sealed to the housing to from the bushing. The passage is then back filled with produced on fusing of the element 24. The sleeve 44 can be formed from any of the known heat insulating materials such as asbestos.

In accordance with the invention, the radio influence voltage is reduced 'by providing a gaseous insulating medium of high dielectric strength within the passage 27. This is accomplished by removing the terminal casting 31 and gasket 33 from the housing 25 and pulling a vacuum within the passage 27 to remove all of the air sulfur hexafluoride (SP to equal or slightly higher pressure than normal atmospheric pressure. The terminal casting 31 and gasket 33 are then replaced'on the housing to seal the sulfur hexafluoride within the passage. I Y

7 Although sulfur hexafluoride has been shown as the preferred material, a number of other gaseous materials can also be used such as hexafluoroethane (C 1 perfluorocyclobutane (C F dichlorodifluoromethane (CF CL chloropentafluoroethane (CF CLCF and bromotrifluoromethane (CF BR).

I claim: I 1. A fused high voltage electrical bushing for connecting a high voltage cable to an electrical device housed within a casing, said bushing comprising:

a housing formed of a dielectric material having an axially extending passage, an electric terminal sealed to each end of said passage to define a closed chamber, a fusible assembly within said chamber electrically connected to each of said terminals,

a layer of conductive material on the inside surface of said passage for reducing the voltage stress at the point of entrance of the bushing through the casing, i

a granular dielectric material completely filling said chamber,

and an inert gaseous insulating medium completely filling said chamber to minimize the occurrence of corona within said granular dielectric material.

2. The bushing according to claim 1 wherein said fusible assembly comprises a first fusible element of high current interrupting capability and a second fusible element of low current interrupting capability, said first and second elements being connected together to form a series circuit, said layer of material on the inside surface of said passage enclosing only the first fusible element.

3. The bushing according to claim 1 wherein said insulating medium is sulfur hexafluoride.

4. The bushing according to claim 1 wherein said insulating medium is selected from the group consisting of sulfur hexafluoride, hexafiuoroet hane, perfluorocyclobutane, dichlorodifluoroethane, chloropentafluoroethane and bromotrifluoromethane.

5. The bushing according toclaim 3 including a layer of insulating material on the surface of said passage.

6. The bushing according to claim 5 includingmeanson the outside surface of the bushing for reducing voltage stress at the point of entrance of the bushing through the casing.

7. A fused high voltage electrical bushing for connecting a high voltage cable to an electrical device housed within a casing, said bushing comprising a housing formed of a dielectric material having an axially extending passage,

an electric terminal sealed to each end of said passage,

a fusible assembly positioned within said passage and electrically connected to each of said terminals, a layer of conductive material on the inside surface of said passage,

a layer of thermally insulating material on the inside surface of said conductive material,

a granular dielectric material completely filling said chamber,

and an inert gaseous medium completely filling said chamber to minimize the occurrence of corona within the granular dielectric material.

8. The bushing according to claim 7 wherein said fusible assembly comprises a first fusibleelement of high current interrupting capability and a second fusible element of low current interrupting capability, said first and second elements being connected together to form a series circuit, said layer of material on the inside surface of said passage enclosing only the first fusible element. I 1 v 9. The bushing according to claim 8 wherein said insulating medium is sulfur hexafluoride.

10. The bushing according to claim 8 wherein said insulating medium is selected from the group consisting of sulfur hexafluoride, hexafluoroethane, perfluorocyclobutane, dichlorodifluoroethane,

fluoroethane and bromotrifluoromethane.

chloropenta-

Claims

1. A fused high voltage electrical bushing for connecting a high voltage cable to an electrical device housed within a casing, said bushing comprising: a housing formed of a dielectric material having an axially extending passage, an electric terminal sealed to each end of said passage to define a closed chamber, a fusible assembly within said chamber electrically connected to each of said terminals, a layer of conductive material on the inside surface of said passage for redUcing the voltage stress at the point of entrance of the bushing through the casing, a granular dielectric material completely filling said chamber, and an inert gaseous insulating medium completely filling said chamber to minimize the occurrence of corona within said granular dielectric material.

4. The bushing according to claim 1 wherein said insulating medium is selected from the group consisting of sulfur hexafluoride, hexafluoroethane, perfluorocyclobutane, dichlorodifluoroethane, chloropentafluoroethane and bromotrifluoromethane.

5. The bushing according to claim 3 including a layer of insulating material on the surface of said passage.

6. The bushing according to claim 5 including means on the outside surface of the bushing for reducing voltage stress at the point of entrance of the bushing through the casing.

7. A fused high voltage electrical bushing for connecting a high voltage cable to an electrical device housed within a casing, said bushing comprising a housing formed of a dielectric material having an axially extending passage, an electric terminal sealed to each end of said passage, a fusible assembly positioned within said passage and electrically connected to each of said terminals, a layer of conductive material on the inside surface of said passage, a layer of thermally insulating material on the inside surface of said conductive material, a granular dielectric material completely filling said chamber, and an inert gaseous medium completely filling said chamber to minimize the occurrence of corona within the granular dielectric material.

8. The bushing according to claim 7 wherein said fusible assembly comprises a first fusible element of high current interrupting capability and a second fusible element of low current interrupting capability, said first and second elements being connected together to form a series circuit, said layer of material on the inside surface of said passage enclosing only the first fusible element.

9. The bushing according to claim 8 wherein said insulating medium is sulfur hexafluoride.

10. The bushing according to claim 8 wherein said insulating medium is selected from the group consisting of sulfur hexafluoride, hexafluoroethane, perfluorocyclobutane, dichlorodifluoroethane, chloropentafluoroethane and bromotrifluoromethane.