US3702911A

US3702911A - Vacuum circuit breaker

Info

Publication number: US3702911A
Application number: US161772A
Authority: US
Inventors: Max-Josef Schonhuber
Original assignee: Siemens Corp
Current assignee: Siemens AG; Siemens Corp
Priority date: 1970-07-16
Filing date: 1971-07-12
Publication date: 1972-11-14
Anticipated expiration: 1989-11-14
Also published as: DE2036099A1; DE2036099C3; DE2036099B2; CH523591A; GB1296337A

Abstract

A vacuum circuit breaker has contacts and a cylindrically shaped electrode system. A switching arc passes from the contacts to the electrode system. The electrode system comprises an inner cylindrical electrode affixed to one of the contacts and an outer cylindrical electrode concentric with the inner electrode and having a double wall. Voltage is applied to the outer sleeve of the outer electrode. An additional electrode at the potential of the inner electrode is axially adjacent and faces the outer electrode forming a substantially annular canal between the additional and outer electrodes which extends radially at least in part.

Description

United States Patent Schonhuber [s41 VACUUM CIRCUIT BREAKER [22] Filed: July 12, 1971 [21] Appl. No.: 161,772

[30] Foreign Application Priority Data 1 Nov. 14, 1972 3,632,928 1/1972 Emmerich et al. .....200/144 B FOREIGN PATENTS OR APPLICATIONS 571,959 1/1958 Italy ..200/l44 B Primary Examiner-Robert S. Macon Attorney-Curt Avery et a1.

[ 7] ABSTRACT A vacuum circuit breaker has contacts and a cylindrically shaped electrode system. A switching arc passes y 16, 1970 Germany 20 36 0999 from the contacts to the electrode system. The electrode system comprises an inner cylindrical electrode [52] US. Cl. ..200/l44 B ffi d to one of the contacts and an outer cylindrical [51] Int. Cl. ..H0lh 33/66 electrode concentric with the inner electrode and [58] Field of Search ..200/144 B ing a double wall voltage is applied to the outer 56 R f sleeve of the outer electrode. An additional electrode 1 e erences at the potential of the inner electrode is axially ad- UNITED STATES PATENTS jace'nt and faces the outer electrode forming a substantially annular canal between the additional and 3,185,800 5/1965 Titus ..200/ 144 B outer electrodes whigh extends radially at least in part 3,541,284 11/1970 Wachta .'...200/l44 B 3,546,406 12/ 1970 Frink ..200/ 144 B 13 Claims, 5 Drawing Figures /l/l/l/l/l/ld w/l/l/m PATENTEB Nov 14 I972 SHEET 1 BF 5 :Fig.1'

P ATENTEI'JNnv 14 m2 SHEET 2 OF 5 Fly. 2

PATENTEBnuv 14 m2 SHEET 3 BF 5 Fig. 3

PATENTEDnuv 14 I972 I sum u or 5 VACUUM CIRCUIT BREAKER DESCRIPTION OF THE INVENTION The invention relates to a vacuum circuit breaker. More particularly, the invention relates to a vacuum circuit breaker for high voltages and high power ratings.

In the design of vacuum circuit breakers it has been attempted for a long time to influence the power handling capacity of the breakers and their operational properties by the selection of the contact material and the geometric configuration of the contacts. However, it has become known that the contacts may be associated with a separate electrode system to which the arc jumps after being ignited between the contact and in which it is finally quenched or extinguished (U.S. Pat. No. 3,509,404). This known arrangement comprises two concentrically disposed, substantially cylindrical electrodes, the outer of which carries a contact or the end face of which functions as the contact. The movable contacts pass through openings of a carrier to which the inner cylindrical electrode is affixed. The contact blocks which are otherwise customarily used in vacuum circuit breakers cannot be. utilized in the described arrangement.

An object of my invention is to provide an operationally reliable vacuum circuit breaker for high voltages and power ratings which uses simple disc contacts. An object of the invention is to provide a vacuum circuit breaker having an internal structure which contributes to the achievement of lower contact bum-off,.a lower quenching current and particularly also of a higher power handling capacity as well as a higher voltage rating over the specified life.

An object of the invention is to provide a vacuum circuit breaker which eliminates the need for a vapor shield and its drawbacks. I

Another object of the invention is to provide a vacuum circuit breaker which is efficient, effective and reliable in operation.

My invention comprises a vacuum circuit breaker with contacts, from which a switching arc passes over to an electrode system. The electrode system comprises a cylindrical inner electrode and an outer electrode concentric with the inner electrode and is having a double wall. Voltage is applied to the outer sleeve of the outer electrode. A housing surrounding the contacts and the electrode system comprises an insulating body and electrically conductive metal parts closing the insulating body off at its end faces. In accordance with the invention, one of the contacts is affixed to the inner electrode. Axially adjacent the double wall electrode is an additional outer electrode which is at the potential of the inner electrode and faces the outerelectrode, forming an at least partially radially extending substantially annular canal.

Although in the circuit breaker of the invention the arc is initially made to move away fast enough from the contacts, the life of which is increased thereby, it remains captive in a space completely enclosed by electrode surfaces until it is quenched or extinguished. The large electrode running area available to the arc outside the contacts immediately results in a substantial reduction of the quenching current. Due to the complete enclosure of the arc space by electrode surfaces, however, migration of the charge carriers from the electrodes or recombination of charge carriers at surfaces not serving as electrodes is especially prevented. This eliminates the need for an additional increase and collection of charge carriers via an anode spot. Anode spots havea tendency to dwell for extended periods at certain points and to erode them excessively. Anode spots do not occur in the circuit breaker of the invention, and the rapid failure of circuit breakers caused thereby does not occur below a relatively high critical current.

Since the double wall outer electrode is faced by the additional electrode, the arcs are prevented from travelling any distancein the electrode system, but are efi'ectively repelled after entering into the oppositely disposed sections of the outer and additional outer electrodes. The arcs may therefore be kept at a safe distance from the insulating body of the vacuum vessel,

whereby the insulating body is prevented from being sprayed with metal vapor. -A separate vapor shield, which is provided in known vacuum circuit breakers for the condensation of metal vapor, is therefore unnecessary and the drawbacks connected therewith are eliminated.

A more favorable stress of the insulating body of the vacuum vessel may be provided by the two outer mutually facing electrodes, and generally smaller electrode spacings may be provided within the entire vacuum vessel, as is hereinafter described.

To form the aforedescribed substantially annular canal between the two outer electrodes, the additional outer electrode may have an outer sleeve and be continued radially inward, starting from the end facing the other outer electrode. The radial configuration can be designed in different ways as hereinafter explained.

It is advantageous to the functioning of the electrode system if the current is supplied to the two outer electrodes at the ends of their outer sleeves. This, together with a practical arrangement of the outer electrodes, may be accomplished by afiixing the outer sleeves of said electrodes to the metal parts at the end faces of the housing of the vacuum circuit breaker.

In order to limit the bum-off of the contacts, it is desirable that the arc from the contacts to the electrode system as rapidly as possible. The speed of this operation may be increased by special design of the outer electrodes. To accomplish this, and in accordance with the invention, the inner sleeve and the outer sleeve of the first outer electrode may be separated by an insulating annular gap, and voltage may also be applied to the inner sleeve via the corresponding metal part at the end face. This leads to the formation of a loop in the current path, which propels the arc. The same effect is obtained if the inner electrode is designed as a hollow cylinder which surrounds the terminal stud and is connected with said stud only at the end provided with the contact. This design of the inner electrode may be provided in all the embodiments of the invention.

As mentioned, the invention permits the insuring of a favorable dielectric stress of the insulating body of the vacuum circuit breaker. This may be achieved by aligning the outer sleeve of the additional outer electrode with the outer sleeve of the first outer electrode and arranging the aligned sleeves with a gap parallel to the insulating body, the canal formed between the outer electrodes opening at about the center of the insulating body. Due to this arrangement, the electrostatic field builds up relatively uniformly over the middle part of the insulating body and his possible to stay within the stress limits of the insulating surfaces by a suitable selection of the radii of curvature. of the electrodes, while keeping the spacings within the vacuum vessel along the lines of the fringe field small. Information on the physical basis'for the arrangement of such high voltage electrodes may be found in Breakdown of Gases Below the Paschen Minimum, IEEE Paper 68 TP 647-PWR, 1968.

The desired direction of the switching arcs in the electrode system depends on the configuration of the current path. In the region of the additional outer electrode, the desired return of the arc may be improved by an insulating gap between the additional electrode and the inner electrode. Different design forms are hereinafter described for the location of the insulating gap. It is furthermore advantageous for the design of the vacuum circuit breaker if the additional electrode has a part approximately aligned with the inner electrode, and the insulating gap between the aligned parts is in the region of the end of the first outer electrode. The desired effect is achieved in the most reliable manner if, in conjunction with this position of the insulating gap a double wall first outer electrode is selected with the inner and outer sleeve separated from each other in the indicated manner.

The danger of spraying the insulating body with metal vapor is reduced by the prevention of the are from travelling unchecked in the electrode system even before it is within visual range of the insulating body. Additionally, however, such a configuration of the two outer electrodes may be selected so that they embrace each other in labyrinth fashion. If, furthermore, in another embodiment of the invention, no visual connection exists between the ends of the substantially annular canal which is then labyrinth-shaped, the metal vapor always present in the arc precipitates on the adjacent electrodes and may therefore no longer reach the insulating body. I

In order to' insure that arcs cannot be generated by so-called bypass discharges, it is recommended that the spacingsbetween electrodes be selected at different potentials about equal to, or partially smaller than, the spacing of the contacts in the open condition.

For proper operation of vacuum circuit breakers, a high vacuum must always be present. Within the scope of the invention, the vacuum may also be maintained by having at least one electrode, at least in part, comprise a getter material, without necessarily exerting an unfavorable effect on the material of the contact proper. By the partial sputtering of the getter material during switching operations immediately prior to the quenching or extinction of the arc, gases which are possibly present are then absorbed.

In order that the invention may be readily carried into effect, it will now be described with reference to the accompanying drawings, wherein:

FIG. 1 is a schematic diagram, partly in section of an embodiment of the vacuum circuit breaker of the invention in which the inner cylindrical electrode is affixed to the movable contact;

FIG. 2 is a schematic diagram, partly in section of another embodiment of the vacuum circuit breaker of the invention in which the inner cylindrical electrode is fixed in position;

FIG. 3 is a schematic diagram, partly in section, of a modification of the embodiment of FIG. 2 in which there is a gap between the inner and outer sleeves of the first inner electrode;

FIG. 4 is a schematic diagram, partly in section, of two other embodiments of the vacuum circuit breaker of the invention, one embodiment being shown to the right of the center line and the other embodiment being shown to the left of the center line; and

FIG. 5 is a schematic diagram, partly in section, of still another embodiment of the vacuum circuit breaker of the invention having an additional outer electrode of especially simple structure.

In the FIGS., the same components are identified by the same reference numerals.

In the embodiment of FIG. 1, the vacuum circuit breaker has a housing 2 comprising a pair of

discshaped metal parts

3 and 4, arranged at the end faces, and an insulating body 5 in the form of a hollow cylinder, positioned between the

metal parts

3 and 4 and afiixed to said metal parts. The insulating body 5 may comprise glass or ceramic material and may be smooth or provided with ribs.

In the housing 2, a fixed contact 6 and a movable contact 7 face each other. Each

contact

6 and 7 is of disc, plate or block configuration. The fixed contact 6 may be affixed to the metal part 4, for example, through which the current is supplied. 'A connecting stud 10 is affixed to the metal part 4 and functions as a connection to a bus bar, cable, or the like.

The movable contact 7 is affixed to the end face of an extended, hollow-cylindrical inner electrode 11 which is supported by an actuator rod 12. The actuator rod 12 also functions as the terminal stud-when it is in the closed condition and immediately after. The inner electrode 11 is connected to the actuator rod 12 only at the end at which the contact 7 is mounted. The actuator rod 12 extends from the housing 2 through an opening 13 formed through metal part 3 and is movably supported in said metal part in a manner not shown in the FIGS. The actuator rod 12 is connected to a suitable driving mechanism (not shown in the FIGS). Bellows 14 is provided between the metal part 3 and the actuator rod 12 to seal the housing 2 with respect to the surrounding atmosphere and to permit vacuum-tight motion of said actuator rod. To relieve the bellows 14 from carrying current a connecting strap 15 provides a direct electrically conductive metal connection between the actuator rod 12 and the metal part 3.

A first outer electrode 16 and an additional outer electrode 17 are positioned in the housing 2 axially adjacent each other and concentric to the inner electrode 11. The first outer electrode 16 and the additional outer electrode 17 direct the arc ignited between the

contacts

6 and 7 in a manner hereinafter described. The first outer electrode 16 has a double wall which in its cross-sectional configuration is approximately a U.

The open end of the first outer electrode 16 faces the metal part 4. The first outer electrode 16 has an inner sleeve 20 and an outer sleeve 21 which is affixed to the metal part 4 at the end face. The inner sleeve 20 is shorter than the outer sleeve 21. A current entering the electrode 16 therefore always flows through the sleeve 21 to the metal part 4. A step 22 is provided between the

sleeves

20 and 21 of the first outer electrode 16 in such a manner that there is a small space 22' between the

sleeves

20 and 21 at the upper end of the first outer electrode 16 which expands to a larger space 23 between said sleeves.

. The additional outer electrode 17 has essentially the same shape as the first outer electrode 16. The additional outer'electrode 17- thus has an inner sleeve 24 which surrounds the inner electrode 11 concentrically with a substantially annular gap 28, and an outer sleeve 25. A step 26 is provided between the sleeves 24 and of the electrode 17, similarly to the step 22 of the electrode 16. The outer sleeve 25 of the electrode 17 is affixed to the metal part 3 at the end face of the housing 2, whereby the potential of the inner electrode 11 is applied to the additional outer electrode 17.

It is essential for the arrangement of the

electrodes

16 and 17 that they engage in labyrinth fashion in such a manner that a substantially annular canal 27 having a substantially Z-shaped cross-section is formed; the canal 27 having two radially extending sections and one axially extending section. Since the operating voltage of the vacuum circuit breaker is applied to the

outer electrodes

16 and 17, the stress of the insulating body 5 is shifted to its central zone from the opening of the canal 27. A favorable distribution of the electrostatic field is provided. By appropriate dimensioning of the radii of

curvature

30 and 31 at the outer opening of the canal 27, as well as by suitably dimensioned

gaps

32 and 33 between the

outer sleeves

21 and 25, respectively, and the insulating body 5, electrical overstressing of the surface of said insulating body is avoided. Increasing the spacing of the electrodes along the lines of the electric field going substantially beyond the width of the contact opening is therefore unnecessary. Due to the aforedescribed favorable field distribution, a high dielectric strength is provided along the insulating body 5, and in conjunction with the reliable arc return from the canal 27 a very substantial reduction in the spraying of the inner surface of said insulating body 5 is achieved. This results in increased life of the circuit breaker of the invention even at the highest power ratings.

Upon switching off, the

contacts

6 and 7 arrive at the positions shown in FIG. 1. The are ignited between the

contacts

6 and 7 travels into the substantially annular gap between the inner electrode 11 and the first outer electrode 16 through the influence of the magnetic field. The are may travel in such gap upwards until it is taken over by the additional outer electrode 17, which is at the same potential as the inner electrode 11. If the arc is not yet quenched or extinguished by then, it may enter into the Z-shaped canal 27. There, however, a magnetic influence on the arc occurs in such a manner that it is repelled efiectively and immediately. The are can therefore not get within view of the wall of the insulating body 5 and damage it or spray it with metal vapor. This is aided particularly by the fact that there is no visual connection to the insulating body 5 from the entrance of the Z-shaped canal 27, which is situated between the topmost point 29 of the first outer electrode 16 and the step 26 of the additional outer electrode 17.

The vacuum circuit breaker of the embodiment of FIG. 2 is completely similar to the breaker of the em-' bodiment of FIG. 1 with respect to its basic design and operation. However, in the embodiment of FIG. 2 there is a change in the arrangement of the

contacts

6 and 7 since the inner electrode 11 is provided in fixed relation with the contact 7 and the contact 6 is movably mounted. Accordingly, the bellows 14 is provided at the metal part 4 at the end face, and the contact 6 is affixed to a movably-mounted carrier 36. As in the embodiment of FIG. 1, a connecting strap 15 functions to relieve the bellows 14' from carrying current. The first inner electrode 16 is provided with slots 35.

In the modified vacuum circuit breaker of FIG. 3, in contrast to the other embodiments, the inner sleeve 20 of the first outer electrode 16 is also affixed to the metal part 4 at the end face of the vacuum vessel 2, and an annular insulating gap 34 is formed in the region of the upper end 29 of said first outer electrode 16. The insulating gap 34 may be located directly at the topmost point or somewhat below such point on the side facing the inner electrode 11, or on the side facing away from it.

- The parts of the electrodes adjacent the annular insulating gap 34 may be rounded off by a bead, or an overlap can be provided in lieu of the rounding off, as indicated in the embodiment of FIG. 4. This structure of the first outer electrode 16 provides the advantage that after the arc leaves the vicinity of the

contacts

6 and 7 an intensive loop effect is exerted which moves the are rapidly toward the upper end 29 of said electrode. As soon as the arc passes to the additional outer electrode 17, however, and enters the canal 27, it is prevented from travelling further, by a strong loop effect, and is repelled.

In the embodiments hereinbefore described, a part of the additional outer electrode 17, which is at the potential of the inner electrode 11, extends parallel to said inner electrode, as the sleeve 24, to maintain the annular gap 28. FIG. 4 shows two modifications for the design of the

outer electrodes

16 and 17 and the inner electrode 11 which permit an additional influence on the arc.

In the left part of FIG. 4, another additional outer electrode 18 is provided. The other additional outer electrode 18 has an inner sleeve 24 which is modified in such a way that it protrudes radially inwardly as a linear continuation of the step 26 of the electrode 17 (FIG. 1). The inner electrode 11' is shortened and also drawn inward, so that the substantially annular gap 28' remains, but in a different position. This results in a reliable engagement of the are at the entrance of the canal 27'.

In the right part of FIG. 4, another additional outer electrode 19 is provided. The other additional outer electrode 19 has an inner sleeve 24", contrary to the embodiments of FIGS. 1 to 3, which is angled off downward from the metal part 3 on the end face, that is, in the direction of the metal part 4 on the end face. Furthermore, the inner electrode 11" is shortened so that the end of the shortened electrode 11" and the end of the inner sleeve 24' face each other in a manner similar to the inner and outer sleeve of the electrode 16 of FIG. 3. It is recommended, however, that the gap 28" be provided between the inner electrode 11" and the outer electrode 19 at a different height than the gap 34 of FIG. 3. The ends of the electrodes 11" and 18 or 19, respectively, facing each other may suitably overlap each other, as shown in FIG. 4.

The changed direction of the inner sleeve 24" of the outer electrode 19 in the right hand part of FIG. 4 causes an extension of the labyrinth-like overlap between the two outer electrodes 16' and 19. The chance that metal vapor might get on the insulating body 5 is therefore particularly small. This is aided by the fact that the different position of the gap 28 between the electrodes 11'. and 19 repels the arc after the arc enters the labyrinth-like overlap of the outer electrodes 16' and 19, even earlier than in the aforedescribed embodiments.

It is known to produce in vacuum circuit breakers a rotation of the are caused by its own magnetism by slots formed in the contacts or the electrodes associated with them. Such slots may also be used advantageously in the electrode system of my invention, extending at an angle to the axis. Under some conditions, a favorable effect may be obtained if only one of the electrodes is slotted simply in the axial direction; but all three electrodes may be provided with slots. In the embodiment of FIG. 2, the double wall first outer electrode 16 has slots 35 formed therein at inclinations to the axis. The slots 35 are formed in the outer sleeve 21 (FIG. 2).

Individual features of the described embodiments may also be combined with one another in order to correct the magnetic effect on the arc. For example, the design of the electrodes 11', 11", 18 and 19 may be utilized, regardless of whether the first outer electrode 16 is divided and has a gap 34 at its topmost point (FIG. 4).

FIG. 5 illustrates another embodiment of the invention having a particularly simple design of the double wall first outer electrode 40 and the additional outer electrode 39. The additional outer electrode 39, starting at its outer sleeve 25 extends radially inward at a right angle and then again at a right angle axially toward the metal part 4 on the end face. The double wall first outer electrode 40 is of simpler structure than in the aforedescribed embodiments.

The first outer electrode 40 is of U-shaped cross-section, except for the substantially annular gap 34 in the same position as in the embodiment of FIG. 4. The inner sleeve 41 and the outer sleeve 42 of the first outer electrode 40 are hollow cylinders positioned concentrically around the actuator rod 12 and connected by a radially extending part 43. The inner electrode 11" has the shortened configuration illustrated in the right hand part of FIG. 4 with a constriction at its upper end thereby forming a substantially annular gap 28" with the additional outer electrode 39.

In FIG. 5, the canal 44 between the

electrodes

39 and 40 is of simple angular configuration. There is no visual connection between the entrance of the canal 44, which is at the mutually staggered substantially annular gaps 28" and 34, and the opening at the insulating body 5, as in the aforedescribed embodiments. This is essential for the protection of the insulating body 5 from spraying with metal vapor.

While the invention has been described by means of specific examples and in specific embodiments, I do not wish to be limited thereto, for obvious modifications will occur to those skilled in the art without departing from the spirit and scope of the invention.

I claim:

- 1. A vacuum circuit breaker having a housing comprising an insulating body of substantially hollow cylindrical configuration and a pair of electrically conductive metal parts closing the insulating body at the end faces thereof, first and second contacts and an electrode system in the housing in which a switching arc passes from the contacts to the electrode system, the electrode system comprising an inner electrode of substantially hollow cylindrical configuration and a first outer electrode of substantially hollow cylindrical configuration having a double wall with an inner sleeve and an outer sleeve concentrically positioned around the inner electrode, means for applying a voltage to the outer sleeve of the first outer electrode, the vacuum circuit breaker comprising an additional outer electrode at the potential of the inner electrode axially adjacent the first outer electrode and forming therewith a substantially annular canal extending radially at least in part, one of said contacts being affixed to the inner electrode.

2. A vacuum circuit breaker as claimed in claim 1, wherein the additional outer electrode has an outer sleeve extending substantially parallel to the inner electrode and continuing radially inward from the portion thereof opposite the first outer electrode, and an inner sleeve.

3. A vacuum circuit breaker as claimed in claim 1, wherein the additional outer electrode has an outer sleeve affixed to one of the metal parts of the housing and extending substantially parallel to the inner electrode and continuing radially inward from the portion thereof opposite the first outer electrode, and an inner sleeve, and the outer sleeve of the first outer electrode is affixed to the other of the metal parts of the housing.

4. A vacuum circuit breaker as claimed in claim 1, wherein the first outer electrode has a substantially annular insulating gap formed therein separating the inner sleeve and the outer sleeve thereof, and further comprising means for applying a voltage to the inner sleeve of the first outer electrode via one of the metal parts of the housing.

5. A vacuum circuit breaker as claimed in claim 1, wherein the additional outer electrode has an inner sleeve and an outer sleeve aligned with the outer sleeve of the first outer electrode, the outer sleeve of each of the first and additional outer electrodes extending substantially parallel to the insulating body of the housing but spaced therefrom by a gap, and wherein the canal opens approximately at the center of the insulating body of the housing.

6. A vacuum circuit breaker as claimed in claim 1, wherein the electrode system further comprises a substantially annular insulating gap between the inner electrode and the additional outer electrode.

7. A vacuum circuit breaker as claimed in claim 1, wherein the additional outer electrode has a part extending substantially parallel to the inner electrode and forming therewith a substantially annular insulating gap in the area of the upper end of the first outer electrode.

8. A vacuum circuit breaker as claimed in claim 1, wherein the additional outer electrode embraces the first outer electrode in labyrinth fashion.

9. A vacuum circuit breaker as claimed in claim 1, wherein the additional outer electrode embraces the first outer electrode in labyrinth fashion with no visual connection between the ends of the canal.

10. A vacuum circuit: breaker as claimed in claim 1, wherein the first and second contacts are spaced a predetermined distance in open condition and each of the inner and first outer electrodes and the first and additional outer electrodes are spaced from each other by a distance having a maximum magnitude equal to the predetermined distance.

11. A vacuum circuit breaker as claimed in claim 1, wherein at least one of the inner electrode, first outer electrode and additional outer electrode at least partially comprises getter material.

12. A vacuum circuit breaker as claimed in claim 1,

Claims

1. A vacuum circuit breaker having a housing comprising an insulating body of substantially hollow cylindrical configuration and a pair of electrically conductive metal parts closing the insulating body at the end faces thereof, first and second contacts and an electrode system in the housing in which a switching arc passes from the contacts to the electrode system, the electrode system comprising an inner electrode of substantially hollow cylindrical configuration and a first outer electrode of substantially hollow cylindrical configuration having a double wall with an inner sleeve and an outer sleeve concentrically positioned around the inner electrode, means for applying a voltage to the outer sleeve of the first outer electrode, the vacuum circuit breaker comprising an additional outer electrode at the potential of the inner electrode axially adjacent the first outer electrode and forming therewith a substantially annular canal extending radially at least in part, one of said contacts being affixed to the inner electrode.

10. A vacuum circuit breaker as claimed in claim 1, wherein the first and second contacts are spaced a predetermined distance in open condition and each of the inner and first outer electrodes and the first and additional outer electrodes are spaced from each other by a distance having a maximum magnitude equal to the predetermined distance.

12. A vacuum circuit breaker as claimed in claim 1, wherein at least one of the electrodes has slots formed therein.

13. A vacuum circuit breaker as claimed in claim 1, further comprising a terminal stud extending into the housing through one of the metal parts thereof and having one of the first and second contacts mounted at one end of the stud in the housing, and wherein the inner electrode is concentrically positioned around the stud and is affixed to the stud only at the end mounting the one of the contacts.