US3801725A - Spacer construction for fluid-insulated transmission lines - Google Patents

Abstract

Improved spacer discs with voltage-control rings are provided to centrally locate the inner high-voltage conductor in fluidinsulated transmission lines. The streamer-control rings reduce the probability of initiation of a streamer across the spacer. Rings, in conjunction with corrugations provided on the surface of the insulating spacers, may additionally be provided for voltage control across the spacers. The spacing between a plurality of voltage-control rings, supported on the spacer, may accommodate the voltage-distribution pattern. The rings may be cast into the spacer as cylinders or cemented thereto, as desired. The rings may be located in somewhat close proximity to both the inner high-voltage conductor, and also to the inner wall of the outer grounded pipe enclosure. Bands of conducting paint, conducting rings of resinous material, such as epoxy, or rings of high-dielectric-constant material may alternatively be employed in place of solid metallic rings.

Description

United States Patent [1 1 Farish SPACER CONSTRUCTION FOR.

FLUID-INSULATED TRANSMISSION LINES [75] Inventor: Owen Farish, Glasgow, Scotland [73] Assignee: Westinghouse Electric Corporation,

Pittsburgh, Pa.

22 Filed: Nov. 14,1972 21 App1.No.:306,492

174/73 R, 73 SC, 142, 140 R, 140 C, 140 H,

140 s,140 CR, 29, 25 o- [56] References Cited UNITED STATES PATENTS 3,585,270 6/1971 Trump 174/28 X 3,621,109 11/1971 Nakata 174/28 X 3,448,202 6/1969 Whitehead... 174/28 3,328,515 6/1967 Vose 174/140 S 3,529,201 9/1970 Rudolph 174/140 R 1,735,560 11/1929 Austin 174/140 C 1,513,292 10/1924 Steinberger 174/140 S 2,082,474 6/1937 Van de Graaff.... 174/73 R 3,715,532 2/1973 Morva.. 174/28 FOREIGN PATENTS OR APPLICATIONS 202,948 7/1956 Australia...., 174/73 R Apr. 2, 1974 17,761 3/1913 Great Britain 174/142 Primary ExaminerBernard A. Gilheany Assistant Examiner-A. T. Grimley Attorney, Agent, or Firm-W. R. Crout [57]- ABSTRACT Improved spacer discs with voltage-control rings are provided to centrally locate the inner high-voltage conductor in fluid-insulated transmission lines. The streamer-control rings reduce the probability of initiation of a streamer across the spacer. Rings, in conjunction with corrugations provided on the surface of high-dielectric-constant material may alternatively be employed in place of solid metallic rings.

10 Claims, 1 .4 Drawing Figures ATENTEUAPR 21974 3801.725

SHEET 2 BF 3 FIG.5

MENIEBAPR 2 i974 3; 801.725

1 HIGH DIELECTRIC 4| CONSTANT MATERIAL FIG. I3 XIV-4- 11 SPACER CONSTRUCTION FOR FLUID-INSULATED TRANSMISSION LINES CROSS REFERENCES TO RELATED APPLICATIONS Reference may be made to U.S. Pat. application filed Nov. 14, 1972, Ser. No. 306,493 by Alan H. Cookson,

likewise assigned to the assignee of the instant application.

BACKGROUND OF. THE INVENTION 1. Field of the Invention My invention relates to electrical-power distribution systems of the type including a gas or fluid-insulated transmission line of the metal-enclosed gas or fluidinsulated type consisting of a tubular conductor, with a grounded metal housing somewhat similar to isolated phase bus, with the exception that the air inside the sealed enclosure is evacuated, and filled with a relatively low pressure high-dielectric-strength gas, such as sulfur-hexafluoride (SF gas or other suitable fluid even oil or vacuum, if desired. However, my invention is also adaptable to. various compressed gases, or even oil, where this is adesirable medium to use.

The basic elements of such a transmission system include, for example, a tubular metallic such as for exam-' ple aluminum inner conductor at line potential, a tubular metallic enclosure concentric with the inner conductor tube at ground potential, with insulating spacer s, located at spaced intervals along the length of the inner conductor to keep the inner conductor centered within the enclosure. Preferably, an electronegative gas, such as SF gas, for example, is provided to assure the proper insulation between the inner high-voltage conductor and .the outer grounded metallic'enclosure.

2. Description of the Prior Art In accordance with prior-art practice, gas insulated distribution systems have been provided for minimizing the dimensions required in overground, or underground electrical transmission.,Reference may be made to Whitehead U.S. Pat. No. 3,378,731 issued Apr. 16, 1968; to Whitehead U.S. Pat. No. 3,391,243, issued July 2, 1968; to Whitehead U.S. Pat. No. 3,448,202, issued June 3, 1969; to D. F. Shankle et al. U.S. Pat. No. 3,324,272, issued June 6, 1967, and to Whitehead U.S. Pat. No. 3,331,911, issued July 18, 1967, and, in addition, to Spindle U.S. Patent 3,345,450, issued October 3, 1967, and Upton, Jr., et a1 U.S. Patent 3,348,001, issued. October 17, 1967, for the General Field of Application, with which the present invention is concerned.

Prior-art practice has utilized spacer designs to centrally locate the inner high-voltage conductor concentrically within the outer grounded housing, or tube.

SUMMARY OF THE INVENTION In accordance with the invention, in one form, there is provided an improved spacer construction in which one or. more metallic control rings are provided to protect against streamers initiating from the grounded outer enclosure. Two such metallic rings may additionally be provided, one in somewhat closeproximity to the inner wall of the outer grounded enclosure, and the other metallic ring disposed in somewhat close proximity to the inner high-voltage conductor.

Another form of the invention utilizes a corrugated insulating spacer construction having a pair of metallic control rings secured, as by cementing, for example, to the spacer surface.

A further form of the invention utilizes a plurality of streamer metallic control rings spaced apart to correspondwith the voltage distribution between the inner high-voltage conductor and the outer grounded enclosure. Bands of conducting paint or conducting resinous rings or rings of high-dielectric-constant material may be alternatively used.

The invention will be more fully understood by reference to the following detailed description, taken in conjunction with the accompanying drawings, and its scope will be pointed out in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 illustrates a portion of a high-voltage gasinsulated transmission line, together with its termination point;

FIG. 2 is a sectional view taken through a three-phase gas-insulated high-voltage transmission line, which includes conductors below ground level;

FIG. 3 illustrates a commercial-type section of a type sold within the electrical industry;

FIG. 4 is an enlarged sectional view of a prior-art spacer in which rings are-painted upon the surface of the spacer, FIG. 10 being a sectional view taken substantially along theline x x of FIG. 9;

FIGS. 11 and 12 illustrate still a further modifiedtype of spacer construction in which rings made of a conducting epoxy material are utilized in substitution of metallic rings, FIG. 12 being a sectional view taken substantially along the line XIIXII of FIG. 11; and,

FIGS. 13 and 14 illustrate a further modified-type of construction in which relatively high-dielectricconstant bands are cast or otherwise secured onto the main epoxy spacer, the latter being made of a relatively low-dielectric-constant material.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 illustrates a portion of a high-voltage gasinsulated system 1, in which the outer grounded metallic enclosure, or pipe is illustrated and designated by the reference numeral 2. A terminal bushing, or terminator structure 3 is provided at the end of the pipe 2 to tallic pipes 2, housing inner high-voltage conductors 7 maybe used, as illustrated somewhat diagrammatically in FIG. 2 of the drawings.

FIG. 3 illustrates sections 9 of metal-enclosed gasinsulating systems, each of which comprises an inner high-voltage conductor 7 having a grounded outer metallic housing 2, somewhat similar to isolated phase bus, with the exception that the air within the sealed enclosure is evacuated, and filled with a low-pressure high-dielectric-strength gas, such as sulfur hexafluoride (SF gas, at a pressure say of 22 p.s.i.g., for example. However, my invention may be used with other fluids, such as electro-negative gases, or even with oil.

As well known by those skilled in the art, the use of such a gas-insulated bus section 9 makes possible a very dramatic reduction in the'size required by the use of the SF, gas-insulating medium. For example, a 138 KV,

1,600-ampere, air-insulated bus 9 has a diameter of 80 inches, whereas the 345 KV, 3,000-ampere, gas-filled bus requires a diameter of only 18 inches. The land area, required for SF gas-insulated siwtching stations, may be'drastically reduced, as set forth in the aforesaid patents set out above.

The bus section 9 may include a tulip-type plug-in female contact 4 and a tulip-type male contact 6, so that many bus sections 9 may be connected serially together. The outer grounded enclosure tubes 2 may, for example, be welded together, as at eight.

Demand for underground power transmission at higher ratings is ever increasing, as available land for I In compressed-gas insulated cables, or lines 1,one of thecritical factors is the performance of the insulating spacers 11, illustrated in FIG. 4, which support the innerhigh-voltage conductor 7. Several studies have been made of the performance of different designs of spacers 11, and these have established design criteria, which gives the most favorable stress distribution across the spacer 1 1, so that breakdown will not be initiated at the spacerterminations under normal conditions. However, contamination, in the form of dust, metallic particles, etc., is regarded as a serious problem in such systems, in that it can trigger breakdown across the spacer surface 11a. The objective of the present invention is to illustrate, as in FIG. 5, the use of concentric metallic rings 13 on the spacer surfaces 11a, which would prevent'the propagation of streamers initiated by contaminants, and thus prevent complete breakdown.

FIG.' 4 illustrates a prior-art spacer design, which is typical for compressed-gas insulated transmission systems l. The purpose of the shielding electrodes 15, I6 is to improve the voltage stress distribution at the inside and outside of the spacer l 1. These are intended to reduce the probability of initiation of a streamer; how- 4 ever, if a streamer is initiated, say by a free conducting particle at either electrode, there is nothing to prevent complete propagation across the spacer surface 11a.

' FIG. 5 illustrates the use of streamer control rings l3,

is reduced to a value dependent upon the ring diameter, and if this is below the critical value for streamer propagation, the discharge terminates at the ring 13 or 14. The metallic ring would be useful in preventing complete spacer flashover when a particle first initiates a discharge at a spacer 11. However, it is recognized that compressed-gas insulated systems 1, could not tolerate continuous discharges due to free conducting particles, because of the effects of discharge products on the insulation of the spacer, and if the particles present were not such that they would be destroyed during the discharge (dust, very fine metallic particles), then the system 1 would have to employ other means, such as a particle trap, such as suggested by Trump et al.. US. Pat. No. 3,515,939. In the latter case, the metallic streamer control rings 13, 14 would still be required to protect the system 1 until the particles were removed by the Trump trapT (not shown).

In some design of spacers, corrugations 18 are used to improve flashover characteristics, In this type of spacer, the corrugations 18 mightprove beneficial in improving the effectiveness of the metallic control rings 14, 14, as it has been found that a fillet of epoxy on the opposite sides of the ring from the streamer improves the performance. FIG. 6 illustrates the placement of metallic rings l3, 14 on a corrugated spacer 20.

The basic system, s uggested in the present invention, is a metallic ring 13 or 14 cemented, glued to, or cast into the spacer 11 near one or both conductors 2, 7.

Variations of this might include the use of a number of rings spaced so as to control the voltage distribution across the spacer 11, such as illustrated in FIGS. 7 and 8, and the use of bands of conducting paint or annular sections of conducting epoxy in place of metallic rings, although possible not as effective as the metallic rings, since they do not reduce the field in the direction of propagation as much as a circular cross-sectional metallic ring-l3, 14'. I f

FIGS. 9 and-"l0 illustrate a modified-type-construction 25 in which rings 26, 27 are painted upon the surface of the spacer 28. The conducting rings 26, 27 could be painted onto the spacer surface 28a in configurations similar to those utilized previously for the metallic rings l3, 14, 18, 19, 20 and 21. The conducting paint used could be, for example, a silicone-silver surface coating, such as Eccocoat CC-l0,. manufactured by the Emerson Cuming Company. Or, a silverepoxy paint, such as Eccobond solder 58C, manufactured by the Emerson Cuming Company, could, alternately, be used as a painted conducting ring upon the spacer.

While not as effective as a circular cross-section metal ring, since they do not reduce the field in the 'di-.

rection of propagation as much, such painted 'bands would be an inexpensive method for providing additional protection on the spacers 28.

FIGS. 11 and 12 illustrate a modified-type of construction 30 in which the rings 31, 32 are made of a conducting resinous material, such as epoxy. The metallic rings could be replaced by rings made from a metal-filled epoxy, such as-Stycast I970, manufactured by the Emerson Cuming Company, which could be cast onto the epoxy spacer 35.

FIGS. 13 and 14 illustrate still a further modifiedtype of construction 40 in which high- dielectricconstant epoxy bands 41, 42 are used. The spacer 45 would contain bands 41, 42 of high-dielectric-constant epoxy (without metallic filling), cast into the main epoxy spacer 45, which will normally be made of relatively low-dielectric-constant material. Such rings 41, 42 would again tend to reduce the electrical stress in the direction of propagation, and while not as effective as metallic rings, might be preferred for some applica- .tions.

From the foregoing description, it will be apparent that the propagation and initiation of streamers has been controlled by the utilization of one or more metallic rings 13, 14 which control streamer propagation.

It is to 'be understood that the application of the invention is not restricted to electrical systems insulated by a high dielectric strength gas or electronegative gas such as SP The technique could be used in any system where there is a spacer mechanically separating highvoltage and .ground electrodes, for example coaxial systems insulated by other gases, such as air, or helium, or by other insulants such as oil or a vacuum.

Although there have been illustrated and described specific spacer constructions utilizing control rings 13, 14, it is to be clearly understood that the same were merely for the purpose of illustration, and that changes and modifications may readily be made therein by those skilled in the art, without departing from the spirit and scope of the invention.

What is claimed is:

1. A high-voltage electrical system comprising a plurality of spaced electrodes, a dielectric spacer disposed between said electrodes, andat least one conducting ring disposed on the exposed lateral surface of said spacer and spaced radially away from each of said spaced electrodes.

2. The combination of claim 1, wherein two concentric conducting rings are disposed on the exposed lateral surface of said spacer with both of the concentric conducting rings spaced radially away from each of said spaced electrodes.

3, A high-voltage coaxial electrical system comprising a pair of coaxial electrodes, a disc-like spacer of insulating material separating said electrodes, and one or more conducting rings surrounding the central conductor yet spaced radially away therefrom and supported inside and outer edges of the spacer.

8. A high-voltage electrical system comprising a plurality of spaced electrodes, a dielectric spacer disposed between said electrodes, and one or more spaced rings painted upon the exposed outer lateral surface of the dielectric spacer in concentric relationship with respect to said spaced electrodes and spaced radially away from both electrodes.

9. A high-voltage electrical system comprising a plurality of spaced electrodes, a dielectric spacer of resinous material disposed between said electrodes, and one or more rings made ofa conducting epoxy material cast into the exposed lateral side of the dielectric epoxy spacer and spaced radially away from said spaced electrodes.

10. A high-voltage electrical system comprising a plurality of spaced electrodes, a dielectric spacer disposed between said electrodes, and one or more high-dielectric-constant epoxy bands cast onto the main epoxy spacer, said main epoxy spacer being made of a relatively low-dielectric-constant material.

Claims (9)

1. A high-voltage electrical system comprising a plurality of spaced electrodes, a dielectric spacer disposed between said electrodes, and at least one conducting ring disposed on the exposed lateral surface of said spacer and spaced radially away from each of said spaced electrodes.

2. The combination of claim 1, wherein two concentric conducting rings are disposed on the exposed lateral surface of said spacer with both of the concentric conducting rings spaced radially away from each of said spaced electrodes. 3, A high-voltage coaxial electrical system comprising a pair of coaxial electrodes, a disc-like spacer of insulating material separating said electrodes, and one or more conducting rings surrounding the central conductor yet spaced radially away therefrom and supported on the lateral exposed surface of said spacer.

4. The combination of claim 3, wherein two rings are utilized and are in concentric relation.

5. The combination of claim 1, wherein the dielectric spacers is corrugated.

6. The combination of claim 3, wherein the dielectric spacer is corrugated.

7. The combination of claim 1, wherein metallic shielding electrodes are provided peripherally on the inside and outer edges of the spacer.

8. A high-voltage electrical system comprising a plurality of spaced electrodes, a dielectric spacer disposed between said electrodes, and one or more spaced rings painted upon the exposed outer lateral surface of the dielectric spacer in concentric relationship with respect to said spaced electrodes and spaced radially away from both electrodes.

9. A high-voltage electrical system comprising a plurality of spaced electrodes, a dielectric spacer of resinous material disposed between said electrodes, and one or more rings made of a conducting epoxy material cast into the exposed lateral side of the dielectric epoxy spacer and spaced radially away from said spaced electrodes.

10. A high-voltage electrical system comprising a plurality of spaced electrodes, a dielectric spacer disposed between said electrodes, and one or more high-dielectric-constant epoxy bands cast onto the main epoxy spacer, said main epoxy spacer being made of a relatively low-dielectric-constant material.

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