US3609218A

US3609218A - High voltage electrical insulators with flashover control means

Info

Publication number: US3609218A
Application number: US873216A
Authority: US
Inventors: Raymond G Herb; James A Ferry
Original assignee: NATIONAL ELECTROSTATICS
Current assignee: NATIONAL ELECTROSTATICS
Priority date: 1969-11-03
Filing date: 1969-11-03
Publication date: 1971-09-28
Anticipated expiration: 1988-09-28

Abstract

The disclosed insulator comprises a series of cylindrical insulating members with barrier cushions interspersed therebetween. Each barrier cushion comprises an insulating disk of greater diameter than the insulating members. Conductive disks are disposed between the insulating members and the insulating disks. Each barrier cushion comprises a pair of such conductive disks, having outer edge portions welded together along an annular joint. The barrier cushions prevent propagation of a spark along the length of the insulator. The conductive disks have laterally projecting convolutions of generally cylindrical curvature, forming spark gaps. The spacing between the adjacent convolutions represents the least spacing between the electrically conductive disks of adjacent barrier cushions.

Description

United States Patent Raymond G. Herb Madison;

James A. Ferry, Middleton, both of Wis. 873,216

Nov. 3, 1969 Sept. 28, 1971 National Electrostaties Middleton, Wis.

Inventors Appl. No. Filed Patented Assignee HIGH VOLTAGE ELECTRICAL INSULATORS WITH FLASHOVER CONTROL MEANS 4 Claims, 3 Drawing Figs.

U.S. Cl 174/141, 310/6, 313/63, 328/233 Int. Cl ..H0lb 17/48, H02n 1/00, HOSh 7/00 Field of Search 174/140.

References Cited UNITED STATES PATENTS 8/1959 Nash 315/36 3,126,439 3/1964 Denholm et a1. 174/142 X 3,473,064 10/1969 H61" 310/6 X FORElGN PATENTS 859,544 1/1961 Great Britain 313/249 Primary Examiner-- Laramie E. Askin Attorney-Burmeister, Palmatier & Hamby ABSTRACT: The disclosed insulator comprises a series of cylindrical insulating members with barrier cushions interspersed therebetween. Each barrier cushion comprises an insulating disk of greater diameter than the insulating members. Conductive disks are disposed between the insulating members and the insulating disks. Each barrier cushion comprises a pair of such conductive disks, having outer edge portions welded together along an annular joint. The barrier cushions prevent propagation of a spark along the length of the insulator. The conductive disks have laterally projecting convolutions of generally cylindrical curvature, forming spark gaps.

The spacing between the adjacent convolutions represents the least spacing between the electrically conductive disks of adjacent barrier cushions.

PATENTED SEP28 I97| FIG,

N VE/V T025 y Ja mond 6' Herb A. Harry M aiigs HIGH VOLTAGE ELECTRICAL INSULATORS WITH FLASHOVER CONTROL MEANS This invention relates to electrical insulators adapted to withstand extremely high voltages. For example, such insulators may be employed in high voltage electrostatic generators, adapted to produce several million volts.

It has been found that there is a tendency for high voltage insulators to break down due to the production of a minor electrical spark at some local point along the length of the insulator. The localized spark tends to be propagated along the surface of the insulator so that a general flashover, along the entire length of the insulator, is produced. Such a flashover can crack the entire insulator, or produce other severe damage so that it is necessary to shut down the generator to replace the insulator. Flashover sparks are particularly damaging if they pass along the surface of the insulator and thus produce intense heating of the adjacent portion of the insulator.

It is one object of the present invention to provide a high voltage insulator having barrier cushions which prevent the propagation of a spark along the surface of the insulator, so that the chance of producing a general flashover is greatly reduced.

A further object is to provide a high voltage insulator which is subdivided into a plurality of sections with cylindrically curved spark gap electrodes therebetween, so that any sparking is virtually certain to occur between the spark gap electrodes, spaced a considerable distance from the surface of the insulator, so that any sparks across the spark gaps will not damage the insulator in any way.

Briefly outlined, the present invention preferably comprises a high voltage insulator having a series of generally cylindrical insulating members, with barrier cushions interspersed therebetween. Each barrier cushion preferably comprises an insulating disk having a diameter substantially greater than that of the insulating members, so that any spark is forced outwardly and is prevented from being propagated along the entire length of the insulator. Electrically conductive disks or members are effectively wrapped around the outer portions of the insulating disks so as to force the spark currents outwardly, away from the insulating members. Preferably, each barrier cushion comprises a pair of electrically conductive disks, interposed between the insulating disk and the adjacent insulating members. The outer edge portions of the disks are welded or otherwise secured together. Any spark currents will be forced outwardly along the disks. The propagation of sparks is impeded by the effective inductance of the disks.

Each electrically conductive disk is preferably formed with a spark gap electrode in the form of a toroidal convolution, projecting laterally from each disk toward the next barrier cushion in the series. The convolutions are cylindrical in curvature and are wrapped around the entire insulator so that continuous annular spark gap electrodes of cylindrical curvature are provided on the barrier cushions. The spark gap electrodes on adjacent barrier cushions are much closer together than other portions of the barrier cushions, so that any sparks are forced to occur between the spark gap electrodes. The spark gaps are spaced a considerable distance outwardly from the surfaces of the insulating members so that any sparks will not damage the insulating members.

Further objects and advantages of the present invention will appear from the following description, taken with the accompanying drawings, in which:

F IG. 1 is a longitudinal section, taken through a high voltage insulator to be described as an illustrative embodiment of the present invention.

FIG. 2 is a cross section, taken generally along the line 22 in FIG. I.

'FIG. 3 is a view similar to FIG. 1, but showing a modified construction.

As just indicated, the drawings illustrate a high voltage insulator 10, adapted to be employed in a high voltage electrostatic generator, or in any other situation in which the insulator must withstand extremely high voltage gradients. The insulator 10 is sectionalized and thus comprises a series of insulating members 12, with barrier cushions l4 interspersed therebetween, The insulator 10 may be made as long as desired, simply by increasing the number of sections in the insulator.

The insulating members 12 are preferably cylindrical in shape. They may be either hollow or solid, as illustrated. The insulating members 12 may be made of any suitable electrically insulating material, such as various ceramic materials. it is particularly advantageous to employ a high alumina ceramic material. Such a ceramic material generally comprises in excess of percent aluminum oxide. However, it should be emphasized that other suitable insulating materials, particularly ceramic materials, may be employed.

Each barrier cushion 14 preferably comprises an insulating disk 16 and a pair of electrically conductive members 18. As shown, the insulating disk 16 is sandwiched between the conductive members 18 which are preferably made of metal. Each of the conductive members 18 is disposed between the insulating disk 16 and the adjacent insulating member 12.

The conductive members 18 are preferably formed with edge or peripheral portions 20 which are spot welded or otherwise secured together. Thus, the conductive members 18 are connected together both electrically and mechanically. However, the joint should preferably not be gastight, but rather should permit easy flow of the gaseous atmosphere around the insulator. Such atmosphere often comprises a high pressure insulating gas, such as sulfur hexafluoride, for example. It is desirable to enable the high pressure gas to fill the space between the conductive members 18.

The insulating disk 16 and the electrically conductive members l8 prevent any localized spark from being propagated along the entire length of the insulator 10. The insulating disk 16 and the conductive members 18 force the spark current outwardly, away from the outer surfaces of the insulating members 12. The effective inductance of the conductive members 18 impedes the propagation of any localized spark. Moreover, the insulating disk 16 is preferably larger in diameter than the insulating members 12, so as to prevent any spark from jumping between the inner portions of the conductive members 18.

. The conductive members 18 are preferably formed so as to provide spark gaps 22 between the adjacent barrier cushions 14. These spark gaps 22 are formed by toroidal convolutions 24 projecting laterally away from the conductive members 18. Each spark gap 22 is formed between the confronting convolutions 24 on adjacent barrier cushions 14. The spacing between the convolutions or electrodes 24 is considerably smaller than the spacing between other portions of the barrier cushions 14, so that any sparks are forced to jump across the gaps 22, between the convolutions 24.

The convolutions 24 are preferably cylindrical in curvature, but are wrapped around the insulator 10 so as to be annular in form. As viewed in cross section, the illustrated convolutions 24 are generally semicircular in form- The spark gap 22 between each pair of confronting convolutions 24 extends around the entire circumference of the insulator 10 so that any spark, however localized, will be forced to jump across the gap 22.

The electrically conductive members 18 are suitably bonded or otherwise secured to the insulating members 12 and disks 16. It is preferred to form each conductive member or disk 18 with a central aperture 26 so that the bonds between each member 18 and the insulating

elements

12 and 16 are not forced with the central portions of the insulating elements. The apertures 26 are of assistance in preventing any rocking movement between the conductive members [8 and the insulating

members

12 and 16, before and during the formation of the bonds.

Any suitable method may be employed to form the bonds between the metal and insulating members. Those skilled in the art will be familiar with various methods, such as soldering and the use of adhesives, for example. The bonding material is shown at 28 in FIGS. 1 and 3.

It will be appreciated that all of the elements of insulator 10 may be stacked and bonded together simultaneously in a single bonding operation. The resulting insulator will withstand exceptionally high voltages, because the barrier cushions l4 prevent the propagation of any localized spark. The insulating disks l6 and the metal members 18 of the barrier cushions 14 force any such spark outwardly, away from the surfaces of the insulating members 12. if any spark occurs, it will jump across one of the spark gaps 22, which are spaced outwardly from the insulating members 10, so that there will be no damage to any of the insulating members.

In order to utilize the high voltage insulators to best advantage, it is preferred to employ a potential distribution system, s that the voltage gradient along each insulator will be substantially constant. Fig. 1 shows a potential distribution system which may be employed when the insulators are used in a high voltage electrostatic generator. Normally, such a high voltage generator employs a plurality of the insulators, arranged to provide parallel supporting posts. Potential distribution rings 30 are preferably employed to interconnect the corresponding barrier cushions 14 of the various insulators. The rings 30 extend around the insulators and are suitably connected to the conductive members 18 of the barrier cushions 14. As shown in FIG. 1 for example, the rings 30 are welded to the outer flange portions of the barrier cushions 14.

In order to provide a substantially uniform potential gradient along the insulators, means are provided to cause a small current to flow along the insulators, between each pair of barrier cushions 14. In FIG. 1, corona gaps 32 are utilized to provide such currents. Each corona gap 32 is formed by a needle-point electrode 34 and a flat disk electrode 36. As shown, each disk 36 is circular in shape and is formed with rounded edges. The disks 36 are spot welded, riveted or otherwise secured to the corresponding barrier cushions 14. Specifically, as shown in FIG. 1, each disk 36 is spot welded to the outer flange portion 20 of one of the conductive members 18. The needle-point electrodes 34 may simply be press fitted into central openings 38 in the disks 36. Any other suitable arrangement may be employed to mount the needle-point electrodes on the disks 36.

Preferably, each needle point 34 provides the negative electrode of each corona gap 32, while the next disk 36, opposite the needle point 34, forms the positive electrode.

The needle-point electrodes 34 cause corona discharges to occur across the gaps 32. The resulting corona currents are small, but are sufficient to equalize the potential drops between the adjacent barrier cushions 14. For example, the voltage drop between the successive barrier cushions may amount to about 50 kilovolts.

FIG. 3 illustrates a modified arrangement in which resistors 40 are employed instead of the corona gaps 32 of FIG. 1. The resistors 40 are connected between the conductive members 18 of the successive barrier cushions 14. Those skilled in the art will be familiar with suitable resistors, adapted to withstand the high voltages which are developed between the adjacent barrier cushions. The resistors permit the flow of small cur rents which are sufficient to equalize the voltage drops between the successive barrier cushions. The resistors 40 are usually much longer then the interval between the successive barrier cushions l4 and are mounted diagonally between the barrier cushions of different insulators. This arrangement is made possible by the potential distributing rings 30 which insure that the corresponding barrier cushions of all the insulators are at the same potential.

We claim: 1. An insulator for high voltages, said insulator comprising a series of generally cylindrical insulating members, and a series of barrier cushions interspersed between said insulating members to prevent the propagation of a spark along the outer surfaces of said insulating members, each barrier cushion comprising an insulating CilSk having a diameter substantially greater than that of the adjacent insulating members,

and electrically conductive members extending around the outer sides of said insulating disks,

said electrically conductive members of each barrier cushion comprising a pair of electrically conductive disks disposed between said insulating members and said insulating disks,

said electrically conductive disks having outer annular portions welded together along an annular joint extending around the corresponding insulating disk.

2. An insulator according to claim 1 in which said electrically conductive disks are formed with laterally projecting toroidal convolutions of generally cylindrical curvature in cross section,

said convolutions of each pair of adjacent barrier cushions forming an annular spark gap therebetween.

3. An insulator for high voltages,

said insulator comprising a series of generally cylindrical insulating members,

and a series of barrier cushions interspersed between said insulating members to prevent the propagation of a spark along the outer surface of said insulating members,

each barrier cushion comprising an insulating disk having a diameter substantially greater than that of the adjacent insulating members,

said electrically conductive disks having outer annular portions engaging each other and rigidly secured together along an annular joint extending around the corresponding insulating disk.

4. An insulator according to claim 3,

in which said electrically conductive disks are formed with laterally projecting toroidal convolutions of generally cylindrical curvature in cross section,

Claims

1. An insulator for high voltages, said insulator comprising a series of generally cylindrical insulating members, and a series of barrier cushions interspersed between said insulating members to prevent the propagation of a spark along the outer surface of said insulating members, each barrier cushion comprising an insulating disk having a diameter substantially greater than that of the adjacent insulating members, and electrically conductive members extending around the outer sides of said insulating disks, said electrically conductive members of each barrier cushion comprising a pair of electrically conductive disks disposed between said insulating members and said insulating disks, said electrically conductive disks having outer annular portions welded together along an annular joint extending around the corresponding insulating disk.

2. An insulator according to claim 1, in which said electrically conductive disks are formed with laterally projecting toroidal convolutions of generally cylindrical curvature in cross section, said convolutions of each pair of adjacent barrier cushions forming an annular spark gap therebetween.

3. An insulator for high voltages, said insulator comprising a series of generally cylindrical insulating members, and a series of barrier cushions interspersed between said insulating members to prevent the propagation of a spark along the outer surface of said insulating members, each barrier cushion comprising an insulating disk having a diameter substantially greater than that of the adjacent insulating members, and electrically conductive members extending around the outer sides of said insulating disks, said electrically conductive disks having outer annular portions engaging each other and rigidly secured together along an annular joint extending around the corresponding insulating disk.

4. An insulator according to claim 3, in which said electrically conductive disks are formed with laterally projecting toroidal convolutions of generally cylindrical curvature in cross section, said convolutions of each pair of adjacent barrier cushions forming an annular spark gap therebetween.