US3778538A

US3778538A - Insulating arrangement for increasing breaking voltage stability of high voltage instrumentalities

Info

Publication number: US3778538A
Application number: US00210069A
Authority: US
Inventors: W Widmann
Original assignee: Transformatoren Union AG
Current assignee: Transformatoren Union AG
Priority date: 1970-12-18
Filing date: 1971-12-20
Publication date: 1973-12-11
Anticipated expiration: 1990-12-11
Also published as: CA936585A

Abstract

A high voltage instrumentality including electrodes having wide sparking distances and inhomogeneous field lines between them in air. An insulating arrangement provides a guided path for premature discharges in a direction from one of the electrodes to another of the electrodes. The insulating arrangement is substantially closed on all sides defining the guided path which is longer than the path which would be traversed without guidance. The premature discharges which develop whenever ionization field strength is exceeded are conducted within the insulating barrier arrangement.

Description

United States Patent 11 1 Widmann Dec. 11, 1973 INSULATING ARRANGEMENT FOR INCREASING BREAKING VOLTAGE STABILITY OF HIGH VOLTAGE INSTRUMENTALITIES Inventor:

Assignee:

Filed:

Appl. No.: 210,069

Werner Widmann, Stuttgart, 50 Germany Transiormatoren Union Aktiengesellschaft, Stuttgart-Cannstatt, Germany Dec. 20, 1971 Foreign Application Priority Data Dec. 18, 1970 Germany P 20 62 359.0 May 12, 1971 Germany P 21 23 566.5

U.S. Cl. 174/140 R, 174/144, 317/72,

Int. Cl H0111 17/46, H0lt 17/00 Field of Search 174/40 R, 140 R,

174/140 11,140 S, 140 CR, 141 R, 144; 200/149 B; 313/131, 204, 205, 325, 356, DIG. 5; 317/61, 72, 77, 78

References Cited UNITED STATES PATENTS 11/1962 Pittman 313/D1G. 5 UX FOREIGN PATENTS OR APPLICATIONS 1,394,332 2/1965 France 174/40 R 895,799 11/1953 Germany... 174/140 R 1,183,152 12/1964 Germany 174/14] R 371,471 4/1932 Great Britain 317/72 Primary ExaminerLaramie E. Askin Att0rneyGeorge H. Spencer et al.

[57] ABSTRACT A high voltage instrumentality including electrodes having wide sparking distances and inhomogeneous field lines between them in air. An insulating arrangement provides a guided path for premature discharges in a direction from one of the electrodes to another of the electrodes. The insulating arrangement is substantially closed on all sides defining the guided path which is longer than the path which would be traversed without guidance. The premature discharges which develop whenever ionization field strength is exceeded are conducted within the insulating barrier arrangement.

15 Claims, 10 Drawing Figures PATENTEI] DEC 1 I I975 SHEET 10F 4 PRIOR ART IIIIIIIIIII III/111111117 L IIIIIIIIIIII IIIIIIIIIIII73 fill/IIIIIIII INSULATING ARRANGEMENT FOR INCREASING BREAKING VOLTAGE STABILITY OFIIIGH VOLTAGE INSTRUMENTALITIES BACKGROUND OF THE INVENTION This invention relates to an insulating arrangement for increasing the breaking voltage stability of high voltage instrumentalities. The invention more particularly relates to an insulating arrangement which defines a guided path 'for premature discharges for increasing the breaking voltage stability of high voltage instru-- mentalities.

Ever increasing levels of operating voltages are employed for the transmission of electrical energy so that continuously rising energy requirements can be met in an economical manner. In the very high voltage installations required for this purpose, excess voltages occurring as a result of switching and during switching intervals can be handled only when very wide sparking distances are provided in the insulating paths. While for short time voltage stresses, as they are produced for example by lightning, the voltage stability of the air gaps in high voltage arrangements increases approximately linearly with the sparking distance, the dielectric strength increases more and more flatly with increasing sparking distance for the substantially longer voltage pulses as they are produced by switchingsurge voltages. Thus, for wide sparking distances the so-called breaking voltage strength may be less than one half of the so-called lightning surge voltage strength.

The explanation-for this phenomenoncan be found in the fact that the insulation arrangements in air for very high voltage systems are practically always so constructed that the electric field extends relatively inhomogeneously. This means that directly at theelec- 'trode surfaces the electrical field strengths are substantially higher than, for example, in the center region of the field. Thus, when a voltage is applied, the so-called ionization field strength of the air is exceeded initially only in the vicinity of the electrodes, when a predetermined voltage magnitude has been exceeded, at those points where the field strength is highest, while the remaining air space initially remains free of any discharge. With further increases in voltage, discharge channels develop from the initially ionized portions in the direction of the field which are also called stern bundles. Their length increases with increasing voltage until they finally reach the counterelectrode thus causing the final sparkover of the insulating path. When a lightning surge voltage is applied, experience has shown that generally a plurality of discharge channels are formed which extend from the highly charged electrodes in the direction of the field. In contradistinction thereto, the number of the simultaneously occurring discharge channels is substantially less for switching surge voltages, often only a single discharge channel is formed.

Since the number of discharge channels is relatively low for switching surge voltages, the individual channels obviously transport substantially higher charges than for lightning surge voltages where the number of discharge channels is substantially larger. Consequently with switching surge voltages a substantially stronger ionization occurs in the individual discharge channels so that the voltage drops across the discharge channels are substantially lower for switching surge voltages than for lightning surge voltages.

It has thus far not been possible to increase the breaking voltage strength of long insulating paths in the air, so that this value continues to play a decisive part in the dimensioning of very high voltage systems. It has been attempted to limit the magnitude of the excess switching surge voltages which occur in the very high voltage systems. This is possible only, however, up to a certain voltage magnitude with economically justifiable expenditures.

SUMMARY OF THE INVENTION It is an object of the present invention to provide in a high voltage instrumentality an arrangement which increases the breaking voltage strength between electrodes.

It is another object of the present invention to provide in a high voltage instrumentality an insulating arrangement which defines a guided path for premature discharges between electrodes.

The forgoing objects, as well as others which will be apparent from the text which follows, are accomplished according to the present invention in a high voltage instrumentality by including therein electrodes having a wide sparking distance and inhomogeneous field lines between them in air with an insulating arrangment. The insulating arrangement provides a guided path for premature discharges in a direction from one of the electrodes to another of the electrodes. The insulating arrangement is substantially closed on all sides defining the guided path. The guided path is longer than the path whichwould be transvered without guidance. The premature-discharges which develop whenever ionization is exceeded are conducted within the insulating arrangement. The path of the premature discharges within the insulating arrangement is in the direction toward another electrode, which may be designated a counterelectrode. Insulation barriers are disposed in the vicinity of the electrodes whose surfaces are under high stress which barriers prevent unimpeded development of the premature discharges in the direction of the field. The premature discharges must then travel along the surface of these insulation barriers in the form of sliding discharges. With suitable design of the insulation barriers it is possible to achieve a substantial extension of the path of the premature discharges from the starting electrode to the counterelectrode. With this extension of the premature discharge path the voltage drop across the path is increased so that the breakdown voltage of the entire arrangement is simultaneously increased.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional view of a high voltage instrumentality diagrammatically illustrating the premature discharge path between the electrodes.

FIG. 2 is a cross-sectional view of a high voltage instrumentality incorporating an insulating arrangement according to one embodiment of the present invention.

FIG. 3 is a cross-sectional view of a high voltage instrumentality incorporating an insulating arrangement according to a second embodiment of the present invention.

FIG. 4 is a diagrammatic view of a high voltage instrumentality incorporating an insulating arrangement according to a third embodiment of the present invention.

FIG. 5 is a cross-sectional view of a high voltage instrument incorporating an insulating arrangement according to a fourth embodiment of the present inven-v tion.

FIG. 6 is a view, partially in cross section, of a high voltage instrumentality incorporating an insulating and arc protection arrangement according .to a fifth embodiment of the present invention.

FIG. 7 is a view, partially in cross section, of a high voltage instrumentality incorporating an insulating and are protection arrangement according to a sixth embodiment of the present invention.

FIG. 8 is a view, partially in cross section, of a high voltage instrumentality incorporating an insulating and arc protection arrangement according to a seventh embodiment of the present invention.

FIG. 9 is a partial side view of a high voltage instrumentality incorporating an insulating arrangement according to a further embodiment of the present invention, the right half of FIG. 9 being shown diagrammatically.

FIG. 10 is a partial plan view of the high voltage instrumentality shown in FIG. 9, the upper half of FIG. 10 being shown diagrammatically.

DETAILED DESCRIPTION OF THE EMBODIMENTS In FIG. 1 a high voltage instrumentality according to the prior art is seen which includes a high voltage electrode 1 and a second electrode 2, shown as a ground electrode. It has been often observed that a premature discharge takes place along a path diagrammatically shown as an irregular line 3 upon the occurrence of switching surge voltages between the electrodes land 2. As shown, the premature discharge path 3 is short.

Referring to FIG. 2, a high voltage instrumentality incorporating an embodiment of the present invention, includes a high voltage electrode 1 and a ground electrode 2; a premature discharge path is diagrammatically shown as an irregular line 3. A plurality of discshaped insulating barriers 4 are arranged individually within a plurality of laterally extending chambers formed by an insulating housing 5. Insulating housing 5 encloses the high voltage electrode 1 in such a manner that premature discharges from the electrode surface of electrode 1 are always deflected by the insulating housing 5 and the disc-shaped insulating barriers 4 and conducted on the intended path 3 in the form of slide discharges.

In the embodiment of a high voltage instrumentality illustrated in FIG. 3 the premature discharge is conducted along a discharge path diagrammatically shown as an irregular line 3 through an insulating channel defined by a tube-like member 6 into which opens a high voltage electrode 1. The lateral cross section of the tube-like member 6 may be round, as shown, or oval, or angular or of any other cross-sectional shape. The intended extension of the discharge path 3 maybe effected, as shown, by a meander-type configuration of the tube-like member 6 or by an annular, a spiral, a helical or any number of other suitable configurations.

The significant prerequisite for the occurrence of the intended effect is that premature discharges will-.not occur at any point within the critical gap width region except in the area enclosed by the insulating barrier arrangement. This is accomplished in that all electrode surfaces where the initial field strength of the air can be exceeded are covered with an insulation barrier or barriers in the described manner. With the high degree of inhomogeneity of insulating arrangements, however, these insulation barriers would have to have very thick walls if it were to be assured that premature discharges could not also occur at the outer surfaces of these insulation barriers facing away from the electrodes, i.e., toward the outside. This would require insulation barriers with an uneconomically great wall thickness in insulation arrangements involving very high voltages.

According to a further preferred feature of the present invention, the occurrence of premature discharges outside of the insulating barrier arrangement is prevented in that the premature discharges which develop within the insulating barrier arrangement are utilized to disperse the field. For this purpose the premature discharges are so conducted that they act as advanced control electrode-like means with respect to the high voltage electrodes or a high voltage electrode and a ground electrode. An embodiment of a high voltage instrumentality incorporating such an arrangement is shown diagrammatically in FIG. 4. A voltage drop occurs in the discharge channel defined within an insulating housing 6, shown as a tube-like member having an oval lateral cross-section. A decreasing potential gradient is produced in the interior of this insulating housing 6 beginning with its upper end at a high voltage electrode 1 in the form of a ring and continuing in the direction toward a counterelectrode 2. The premature discharges bring the interior surface of the insulating tube-like member forming the housing 6 to the potential of the premature discharges belonging to this particular point, e.g., to the percentages indicated at the individual points shown in FIG. 4, with respect to the potential of the actual high voltage electrode 1. This capacitively influences the field lines outside of the insulating tube-like member 6, as shown by the equal potential contour lines (unnumbered). With the aid of field images or by means of high voltage experiments the shape of the insulating barriers, or the design of the insulating channels, respectively, can be determined in such a manner that the field strengths in the air space outside of the insulating barriers or insulating channels, respectively do not exceed the initial field strength of the air at any point. This can be realized most easily if the insulating channel is defined by a tube-like member having a circular or oval lateral cross section and if it is arranged in a ring, spiral or helix, as shown, for example, in FIG. 4. In order for the initial field strength of the air not to be exceeded at the outer surface of such insulating channels, it is necessary to make the diameter of the channel cross section as well as the diameter of the rings, spirals or helixes formed by the channel sufficiently large.

The measures proposed by the present invention are suited, inter alia, to prevent breakover of an open wire circuit which is connected with a very high voltage device as, for example, a suspension chain, a pin-type insulator, a switch, a measuring transformer or the like. If the gap width of the outgoing open wire circuit to the counterelectrode is small enough that sparkovers must be feared, the first 'portion of the line can be covered withinsulating barrier arrangements. Such an embodiment is shown in FIG. 5. In FIG. 5, a high voltage electrode l and a counterelectrode 2 are shown. FIG. 5

shows the hanging suspension insulator of an open wire circuit line, 1 meaning the high voltage electrodes, and

2 the ground electrode. In this-case the ground electrode is the cross arm of a overhead line tower.

The high votlage electrodes 1 are hung on the suspension insulator chain'l9. The high voltage electrodes consist of the overhead open wire circuit line 20, the hanging armature 21, and the shield ring 22. The shield ring 22 is surroundedon all sides by insulating material; it has a spheroidal advanced electrode 22a from which the insulation channels 6a leading the predischarges come.

By arranging these insulation channels according to this invention the voltage strength against high switching voltages will be improved along the insulation hanging chain. With the shield ring 22 and the insulating

channels

6 and 6a the voltage strength will be improved, the overhead lines being outside the area in which the electrical field is effected by the electrode 22 and the

insulator channels

6 and 6a. Therefore it can be possible that flashovers will happen between the line and the ground electrode 2, as an example along the way 23. In .order to prevent these flashovers the lines 20 are surrounded by insulation barriers 24 arranged on the hanging armature 21 in such manner that the flashover distance from the ends 25 of these insulation barriers to the ground electrode 2 will be enlarged sufficiently.

Since insulators and high voltage instrumentalities are usually connected between a high voltage terminal and ground, the breaking strength almost always has a more or less strong polarity effect, i.e., the breakdown voltage is lowest at that polarity where the electrode with the higher field strength has the positive polarity. In arrangements with a strongly defined polarity effect it is usually sufficient to take the measures according to the present invention for increasing the breaking strength only at the electrode with the higher field strengths. Generally, this is the electrode for the high voltage. In arrangements with symmetrical field lines, however, both electrodes must be provided with insulating barrier arrangements according to the present invention. Under certain circumstances it may be advisable to provide ribs or shields of insulating material along a portion or along the entire outer surface of the insulating barrier arrangements which ribs or shields extend the creeping path and thus assure sufficient voltage strength along the outer surfaces of the insulation barriers even under conditions of rain and of dirt. It has also been found advisable to seal the interior of the channels formed by the insulation barrier arrangements against water and dust. Where this cannot be done, it is advantageous to provide an inclination against the horizontal for the insulating channels along their entire path so that possibly entering water can readily run off as a result of gravitational forces.

To increase the voltage strength between parallel open wire circuits or open wire cables, respectively, the measures of the present invention can also be employed in that tubular insulating barriers are placed over the entire length of the open wire circuit which barriers may consist of individual parts inserted into one another which contain the insulating channels which conduct the premature discharges radially out- .wardly on a helical path or on a detour of sufficient and ceilings of high voltage vaults such as installations within a building and within test fields. The present invention can also be employed to produce substantially uniform spark paths, where the surge sparkover voltage lies only a little higher than the breakdown voltage.

To produce the insulating barrier arrangements according to the present invention or the insulating channels made therefrom, ceramic insulating materials, glass, mica-containing insulating materials, asbestos, rubber and also synthetics with the appropriate electrical and mechanical properties can be used.

If the insulating barrier arrangements according to the present invention are used in connection with very high voltage instrumentalities in which are sparkovers must be counted on during operation as this is the case, for example, for open air isolators, it is advisable to make the insulation barrier members of an are resistant insulating material. Since, however, many are resistant insulating materials cannot be readily shaped or only shaped with relative difficulties when they are in the hardened or fully polymerized state and since on the other hand the insulating barrier members must have in some portions a rather complicated shape in order to meet the requirements placed on them, their manufacture is not always very simple. According to a further idea of the present invention it is therefore proposed to make the insulating barrier arrangements at least partially of an arc resistant insulating material. The procedure may here be such that initially an inner insulating sheath is made of a thermoplastic material which is enclosed on the side accessible to the arc with a layer of are resistant material. This layer may be applied by painting, spraying, immersion or encapsulation. It is, however, also possible to enclose the thermoplastic insulating sheath in telescoped insulating cup-shaped members of arc resistant material. The insulating cupshaped members may be either glued together or welded together, and the separating points between the cup-like members may remain open since discharge of the predischarges are prevented by the inner thermoplastic insulating sheath. Thus leaving open the separating grooves between the are resistant insulating cuplike members does not adversely influence their actual function, i.e., that of protecting the inner insulating sheath from an arc.

A further possibility of protecting the insulating barrier arrangements proposed by the present invention to control premature discharges against an arc is shown in FIG. 6. In FIG. 6, a first electrode 2 and a second electrode 1 are surrounded respectively by a stack of porcelain insulators l3 and an insulating barrier arrangement 6. The insulating barrier arrangement 6 includes an insulating channel defined by a tube-like member 6a which opens into that part of the barrier arrangement which surrounds the second electrode 1. A sheath 7 of an arc resistant insulating material covers the insulating barrier 6 on the side toward the electrode 2 where an arc can be produced.

Under some circumstances, it may be advisable to provide the surface of insulating sheath 7 with ribs 8, as shown in FIG. 7, so that the creeping path is lengthened and sliding discharges are prevented, the remaining parts shown in FIG. 7 being identical to those shown in FIG. 6.

In some cases, arc protection may be accomplished in a high voltage instrumentality by the arrangement illustrated in FIG. 8. In FIG. 8, the high voltage instrumentality includes a first electrode 1 and a second electrode 2 surrounded respectively by an insulating barrier arrangement 6 and a stack of porcelain insulators 13. The insulating barrier arrangement 6 includes an insulating channel defined by a tube-like member 6a which opens into that part of the insulating barrier arrangement 6 which surrounds the electrode 1. No insulating sheath, such as the sheath 7 shown in FIGS. 6 and 7 is proposed. Instead, an electrically conductive ring 14 is positioned about the porcelain insulating stack 13 remote from the insulating barrier arrangement 6. A mechanically rigid, electrically conductive member 15 is connected between the ring 14 and an electrically conductive ball 16. An additional mechanically rigid, electrically conductive member 17 extends from the electrode 1, either directly or from a wire or the like conductively connected to the electrode 1, to a second electrically conductive ball 18 which is separated from the ball 16 by a spark gap. The

balls

16 and 18 are both radially and longitudinally displaced from the insulating barrier arrangement 6 and the tube-like member 6a, defining the spark gap. Full arcs, when they occur, are conducted between the

ball fittings

16 and 18 thereby protecting the insulating barrier arrangement 6 and the tube-like member 6a.

In each of FIGS. 6, 7 and 8, the portion of the insulating barrier 6 which surrounds the electrode 2 is connected to the downwardly extending tube-like member 6a, a portion of the surface of the electrode 1 being exposed to the bore of the tube-like member 6a. It is to be appreciated, however, that an extension of the elec trode 1, in each case, may extend downwardly within a portion of the tube-like member 6a which opens into that portion of the insulating barrier arrangement which surrounds the electrode 1.

The above-mentioned measures can be realized in an economically feasible manner only when the shape of the insulation barrier members is not too complicated since many are resistant insulating materials can not readily be shaped or can only be shaped with relative difficulties in their hardened or fully polymerized state. On the other hand, the insulating barrier members must have a partially rather complicated shape to fulfill their intended purpose which shape depends on a plurality of factors.

According to a further preferred embodiment of the present invention, the insulating barrier arrangements can be protected against arcs occurring during operation in that further bare electrodes are provided outside of the insulation barrier arrangements for conducting the arc. These additional bare electrodes are so designed and arranged so that the insulating barrier arrangements lie outside of the area covered by an arc and that premature discharges occur only at the electrodes disposed radially inwardly from the insulation barrier arrangements.

With insulating barrier members having a'very complicated design it may be advisable to provide a plurality of separated individually closed systems of insulation barrier members which are then protected against arcs by a common or a plurality of separate bare electrodes. Such an embodiment of the present invention is illustrated in FIGS. 9 and 10.

FIG. 9 is a partially diagrammatic side view and FIG. 10 a partially diagrammatic plan view of an insulating arrangement according to the present invention as it may be used, for example, for suspension insulators.

Electrodes 10' and '11 are fastened to a metallic ring 9. Whereas electrodes 10 are disposed within insulating barrier arrangements 12, the electrodes 11 which serve to conduct the arc towards a counterelectrode (not shown) remain bare. FIGS. 9 and 10 also show how the insulating barrier arrangement according to the present invention can be divided into two separate closed systems of insulation barriers between which the bare electrodes 11 are disposed.

It will be understood that the above description of the present invention is susceptible to various modifications, changes and adaptations, and the same are intended to be comprehended within the meaning and range of equivalents of the appended claims.

I claim:

1. In a high voltage instrumentality in which high switching voltages occur and which includes two electrodes having wide sparking distances and inhomogeneous field lines between them in air, the improvement comprising: insulating means having an interior defining a guided path, which is longer than the path which would be transversed without guidance, for premature discharges in a direction from one of said electrodes toward another of said electrodes, said insulating means being substantially closed on all sides defining said guided path and comprising means defining a plurality of laterally extending chambers connected one to the next via a vertical passageway and a plurality of disc-shaped insulating barriers, one of said disc-shaped insulating barriers being positioned within each one of said plurality of chambers, being spaced from its walls and being in substantially axial alignment with the vertical passage-ways; one of said electrodes being in direct communication with said guided path defined by said interior, the remainder of said guided path defined by said interior being free of electrode structure and the other of said electrodes being positioned at a distance from said insulating means, whereby the premature discharges developing whenever the ionization field strength is exceeded are conducted within a path defined by said insulating means and the possiblity of arcing between the electrodes during switching voltage surges is substantially reduced.

2. In a high voltage instrumentality in which high switching voltages occur and which includes two electrodes having wide sparking distances an inhomogeneous field lines between them in air, the improvement comprising: insulating means having an interior defining a tortuous guided path for premature discharges, which produce a decreasing potential gradient in said interior, in a direction from one of said electrodes toward another of said electrodes, said insulating means being substantially closed on all sides defining said guided path, with said guided path being longer than the path which would be traversed without guidance; one of said electrodes being in direct communication with said guided path defined by said interior with the remainder of said guided path defined by said interior being free of electrode structure; and the other of said electrodes being positioned at a distance from said insulating means, whereby the premature discharges developing whenever the ionization field strength is exceeded are conducted within a path defined by said insulating means, an improvement in the field lines outside of said insulating means is effected, and the possibility of arcing between the electrodes during switching voltage surges is substantially reduced.

3. An arrangement as defined in claim 2 wherein said insulating means comprises a tube-like member extending from said one of said electrodes toward said other of said electrodes, the bore of said tube-like member defining said guided path.

4. An arrangement as defined in claim 2 wherein said insulating means is constructed at least partially of arc resistant insulating material.

5. An arrangement as defined in claim 2 wherein said insulating means includes a coating of arc resistant material.

6. An arrangement as defined in claim 2 wherein said insulating means comprises a plurality of insulating barriers surrounded by a housing of arc resistant material.

7. An arrangement as defined in claim 2 further comprising shield means of arc resistant material adjacent areas of said insulating means which may be endangered by an arc.

8. An arrangement as defined in claim 2 further comprising additional electrode means spaced from said insulating means for conducting an arc.

9. An arrangement as defined in claim 8 wherein said insulating means is outside of the area covered by the arc.

10. An arrangement as defined in claim 9 wherein said additional electrode means are at least two spaced apart electrodes, the spacing between these electrodes being sufficient to assure them to be substantially free of premature discharge phenomena, premature discharges developing substantially exclusively within said guided path.

ll. An arrangement as defined in claim 10 wherein said insulating means comprises at least two systems of insulating barriers, each system being substantially closed on all sides defining separate guided paths for premature discharges and said guided paths all being longer than the path which would be traversed without guidance.

12. An arrangement as defined in claim 8 wherein said additional electrode means are at least two spaced apart electrodes, the spacing between these electrodes being sufficient to assure them to be substantially free of premature discharge phenomena, premature discharges developing substantially exclusively within said guided path.

13. An arrangement as defined in claim 12 wherein said insulating means comprises at least two systems of insulating barriers, each system being substantially closed on all sides defining separate guided paths for premature discharges and said guided paths all being longer than the paths which would be traversed without guidance.

14. An arrangement as defined in claim 8 wherein said insulating means comprises at least two systems of insulating barriers, each system being substantially closed on all sides defining separate guided paths for premature discharges and said guided paths all being longer than the path which would be traversed without guidance.

15. An arrangement as defined in claim 2 wherein said insulating means comprises at least two systems of insulating barriers, each system being substantially closed on all sides defining separate guided paths for premature discharges and said guided paths all being longer than the path which would be traversed without guidance.

Claims

1. In a high voltage instrumentality in which high switching voltages occur and which includes two electrodes having wide sparking distances and inhomogeneous field lines between them in air, the improvement comprising: insulating means having an interior defining a guided path, which is longer than the path which would be transversed without guidance, for premature discharges in a direction from one of said electrodes toward another of said electrodes, said insulating means being substantially closed on all sides defining said guided path and comprising means defining a plurality of laterally extending chambers connected one to the next via a vertical passageway and a plurality of disc-shaped insulating barriers, one of said discshaped insulating barriers being positioned within each one of said plurality of chambers, being spaced from its walls and being in substantially axial alignment with the vertical passage-ways; one of said electrodes being in direct communication with said guided path defined by said interior, the remainder of said guided path defined by said interior being free of electrode structure and the other of said electrodes being positioned at a distance from said insulating means, whereby the premature discharges developing whenever the ionization field strength is exceeded are conducted within a path defined by said insulating means and the possiblity of arcing between the electrodes during switching voltage surges is substantially reduced.

11. An arrangement as defined in claim 10 wherein said insulating means comprises at least two systems of insulating barriers, each system being substantially closed on all sides defining separate guided paths for premature discharges and said guided paths all being longer than the path which would be traversed without guidance.