DE1910633A1 - Vacuum circuit breaker with getter material housed in the switching chamber - Google Patents

Description

YJes feinghouse February 27, 1969

Electric Corporation
Pittsburgh

My reference: PLA 69/8002 'Eb / Win

Vacuum circuit breaker housed in the switching chamber em_Gj3ttermaterial__

For this application priority is claimed from the corresponding US patent application Ser.Iio. 714 197 of March 19, 1968,

The present invention is concerned with vacuum circuit breakers for V / echselstrora, where two in one housing relatively movable contact pieces and a getter material are arranged.

The reliable operation of vacuum circuit breakers depends largely on the fact that there is always a pressure of less than 10 Torr in the switching chamber. If the pressure rises significantly above this value, for example only briefly to 10 ϊογγ, the dielectric strength of the vacuum is impaired and the probability of a breakdown between the voltage-carrying cables of the switch increases significantly. The lack of vacuum switch disconnection is also reduced if the pressure is too high. When switching off, the arc may stand still, or reignition may occur when the recurring voltage settles, whereby twice the value of the nominal voltage can temporarily occur. In this case, the vacuum switch can be damaged or even unusable. In addition, failure of the vacuum switch can cause damage to the electrical circuit supplied by it or to the electrical devices in it.

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Pressure rises in the holding chamber of the vacuum switch partly caused by Case, which was influenced by the Arcing from the surfaces and from inside the contact pieces »Arcs occur both when switching off» but also when switching on when the contact pieces are starting from the distance, for example approximately 12 mm, in the open position, approximated to a distance at which the applied voltage can break through the spark gap = the subsequent arc remains exist until the contact pieces have reached the closed position »

The erosion of the contact materials caused by the arc releases gases that are bound on the surface of the contact pieces and in the contact piece material itself. This can be, for example, hydrogen, carbon monoxide and carbon dioxide. Incidentally, erosion of the contact pieces associated with the release of gas occurs not only when the contact pieces are closed and opened, but also when the contacts are closed under load. The released gases are partly deposited on the walls of the switching chamber and form a type of contamination which reduces the dielectric strength of the affected parts. Another part of the gases inagesamt increases the pressure in the switching chamber.

Careful degassing of the contact materials used can reduce the release of gases from arcing will. Degassing, for example by vigorous heating, until the contact material is of the desired purity 1: 1 mill, but it is very complex and difficult. In addition, the temperatures involved in degassing are not so high can apply as they are under the influence of the arc in

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Switch operation occur. The situation here is the opposite of that with electron tubes, in which the Electrode materials for degassing higher temperatures as they occur in the operation of the tubes. Difficulties with the release of yes therefore do not occur with electron tubes.

In the case of electron tubes, it is already known to use a getter material, e.g. barium, inside the To attach the tube »It is also known from US Pat. No. 3,090,852, inside a vacuum switch To arrange getter material that is activated by heating * The heating is done electrically by means of a Saturation transformer by the one above the switch flowing current is excited.

The invention improves the gas binding in vacuum switches that contain a getter material by simple means. According to According to the invention, this is done in that the getter material is arranged in such a way in the vicinity of the area of the arc formation is that when an arc is struck, it is vaporized or sprayed. In this finely divided form it is Getter material is particularly active and can therefore quickly bind gases released by the arc. The reaction of the gases with the Getter material happens both in the fresh getter layer on the inner walls of the switching chamber, for example a condensation screen formed during spraying and evaporation, as well as during the passage of the getter material from the getter supply to the points mentioned »As tests have shown, in vacuum switches with a Arrangement according to the invention considerably lower pressures than in other vacuum switches »

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As getter materials are suitable for the purposes of the invention above all the refractory metals of the group consisting of titanium, tantalum, columbium, zirconium, tungsten and molybdenum. These metals react as fresh elementary layers or as sprayed particles in a heated state with those from the arc released gases with the formation of stable compounds, for example of nitrides and oxides, if it is the Gases nitrogen and oxygen are involved. Even complex molecules such as hydrocarbons, are bound by the getter materials mentioned.

In the context of the invention, for example, a body made of a getter material of the type mentioned can be placed on the back side at least one of the contact pieces can be arranged. Another possibility is to use the getter material in the form of a Ring outside the contact surface of at least one of the contact pieces to be provided.

The latter type of attachment of the getter material can In a further development of the invention, it is also used in conjunction with a contact arrangement according to US Pat. No. 3,182,156 will. Me contact pieces according to this patent specification have a part made of a metal for arc ignition or an alloy with a low chopping current strength, such as copper, tin, antimony, lead, zinc, bismuth or other metals. Furthermore, the contact pieces have an outer area which is used to run the arc and which is the area of the arc ignition surrounds and is provided with spirally arranged grooves to replace the arc by magnetic blowing .η circulation to - ». In the context of the present invention, the getter material can be arranged in the area of the arc path.

However, the getter material can also be in one of the contact pieces even be included. This can be achieved within the scope of the invention by 'a structure of the contact pieces in which at least

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one of the contact pieces made of a highly conductive carrier metal and exist in this embedded getter material. In this way, a type of composite material is obtained whose conductivity is high and its contact resistance is low, while at the same time the abrasion resistance and tack resistance also meet the requirements. The getter material is located in the immediate vicinity of the area of the arc formation, namely where the arc occurs arises so that gases released by the arc are bound in place.

The fibers or wires mentioned are easiest to insert in this way the Iträgererv / erstoff be embedded that they have a random distribution on the surface of the contact piece. However the fibers or wires made of getter material can also be aligned parallel and perpendicular to the contact surface, /.la carrier materials are particularly suitable for the highly conductive ones Metals copper, silver and alloys based on these metals.

The invention is explained below using several exemplary embodiments in conjunction with the figures.

Fig. 1 is a vertical section of a vacuum circuit breaker, of which a contact piece in Fig. 2 in a greatly enlarged partial view is shown.

Fig. 3 shows another embodiment of a contact piece, the view partially in section along the line III-III 4 is shown. Fig. 4 is a plan view of the in Fig. 3 shown contact piece.

In Fig. 5 is a number of short fibers or wires of getter metal shown.

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Fig. 6 illustrates the fibers shown in Fig. 5 after "the Compression to form a contact piece.

Fig. 7 shows an induction furnace for impregnating compressed fibers according to FIG. 6 with a highly conductive carrier metal in the "Vacuum or in a hydrogen atmosphere.

Fig. 8 shows another embodiment of a contact piece «

Fig. 9 shows a contact piece, which by impregnating the compressed body of FIG. 6 with a highly conductive metal in | the device of FIG. 7 is made.

In Fig. 10 is a formed from getter material and carrier material Composite body shown divided into a number of contact members.

An enlarged view of one of the cut surfaces shown in FIG. 10 is shown in FIG.

Figures 12 and 13 illustrate composite bodies similar to that of FIG j? y. 10.

14 shows a section through a contact system at 'which is provided with an area serving for arc ignition and an area serving for arc passage. A perspective A view of one of the contact pieces of this contact system is shown in FIG.

16 serves to illustrate the production of contact pieces from metal powder by sintering in an induction furnace of the type shown in FIG.

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The -B'ig. 1 shows a highly evacuated housing 1, daa one Jacket 2 made of suitable insulating material, e.g. Close jacket 2. Seals 5 are provided between the end caps 3 and 4 and the jacket 2. The normal pressure in that Housing 1 is less than 10 Torr under static conditions, so that there is reasonable assurance that the mean free path of the electrons is greater than the breakdown paths is in the housing.

Within the housing 1 there are two disk-shaped contact pieces "7 and 8, which are movable relative to one another and which are in the Open position of the switch shown in solid lines are. If the contact pieces are separated, there is an arc gap 9 between them. The upper contact piece 7 is fixedly arranged and fastened in a suitable manner to a conductor bar 10 which is firmly connected to the upper end cap 3 is. The lower contact piece θ is movably arranged and connected to a conductive operating rod 11, which extends extends through an opening 12 in the lower end cap 4. A movable metal bellows 13 forms a seal between the End cap 4 and the operating rod 11.

With the lower end of the operating rod 11, a suitable drive device is coupled to the movable contact piece 8 up to the closed position indicated by a dash-dotted line. The stroke is here about 12 mm.

The schematically indicated arc 15> that in the space is formed between the contact pieces, evaporates when opening and also when closing the contact pieces 7 and 8 part of the Contact piece material which is distributed in the direction of the jacket 2. In the case of the switch shown, the isolating

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Surfaces of the housing 1 before the condensation of the metal vapor it is protected by a tubular metal screen 16 which is braced on the jacket 2 in a suitable manner and preferably isolated from the two end caps 3 and 4 is. In order to take away the possibility of the vapors to bypass the screen 16, there are at the opposite ends of the screen 16 special screens 17 and 18 are provided.

The gases released by the arc are removed by a getter material, e.g. titanium or zirconium. As in Fig. 1 and shown in Fig. 2 in an enlarged view, is located on the back of one or both Contact pieces 7 and 8, respectively, a disc 20 made of titanium. This arrangement of the getter material in a relatively protected Position is suitable for switches with rated currents above 8 or 10,000 A. By changing the distance between the Scneibe 20 and the contact piece 7 and 8, respectively, can prevent the release be influenced by getter material, since the surfaces 22 of the disc 20 are covered differently by the discharge. The contact piece according to FIG. 2 has switched off a total of 1,200,000 A in practical tests. The spray of. Titanium, which results in the disc 20 at the general discharge associated with a shutdown or turn-on exposed causes a fresh deposition 21 of titanium on the screen 16 and other surfaces of the vacuum interrupter, which has a very high gettering speed due to its large area and its initial cleanliness and freedom from absorbed gases having. Such a gettering process also takes place during the passage of the titanium ions and titanatorae to the walls of the vacuum switch instead.

The getter material can also be in another area of the vacuum interrupter be located where it is exposed to the heat of the arc. Suitable areas are the condensation screen 16 and the

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Band roof shields 17 and 18 as well as the contact pieces 7 and 8. Removed are, however, places of the vacuum switch, of which aua the getter material would be thrown against the cladding 2, since this would impair the dielectric strength of the cladding 2 and would cause premature flashovers. It is also recommended that the area χ in Fig. 2 and in Fig. 8 and the area 8 'in FIG. 3 and the area 19 in FIG. 14 to be excluded.

The parts that come directly into contact with the arc 15 can be made of copper and copper alloys, in order to avoid sticking of the contact pieces and to obtain low chopping currents.

The erosion of the contact pieces 7 exposed to the arc 15 and 8 and the amount of gas generated by them is a function of the cut-off current. The arrangement of getter material according to the invention thus has the peculiarity of self-adaptation, with the ability to gettering in relation to the Gettering requirement is increased.

Figures 5 and 4 illustrate a modified type of contact piece 24, in which a ring 25 made of titanium or zirconium is connected to the back of the button-like contact piece 8 by brazing. Since titanium alloys mix quickly with copper, it is important in the manufacture of the contact piece 24 not to expose the copper-titanium connection 26 to excessive temperatures. At 900 ° 0 a low-melting eutectic forms. When producing the contact piece 24, the procedure was that the titanium disk 25 was connected to the copper part 8 ¹ without solder by heating the copper-titanium arrangement 24 to 90O ⁰ C in a vacuum and then brazing the Contact surfaces approved eutectic was left. Both components of the contact piece 24 were before the described connection

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OBfGiHAL INSPECTED

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Process degassed at high temperature and pressure in the range of 10 "to 10" Torr. However, it is important to have the vacuum switch ao to construct that during operation in the range of the disconnection capacity no temperatures occur which the Exceed eutectic temperature.

The problem of solubility at high temperature associated with the use of copper-titanium assemblies does not exist Arrangements with copper and tantalum, molybdenum or tungsten, as these refractory metals have an extremely low level Have solubility for copper and vice versa. Therefore, the copper casting technique can be used when tantalum, tung-fram or molybdenum mixtures are provided as materials for the getter supply.

The low alloying tendency between copper and tantalum, tungsten and molybdenum contributes to the conductivity of the Keep copper's big.

In some cases it is in the interest of increasing the heat dissipation of the electrode system is desirable, instead of a single body of getter material, one of two or composite arrangement consisting of several metals. For example, the high thermal conductivity of copper can be achieved by a method be exploited in the case of molybdenum, tantalum or tungsten either in the form of thin wires or in powder form in copper as Carrier material are embedded, as will be described below.

A suitable method for producing a contact piece made of tantalum, tungsten or molybdenum impregnated with copper, proceeds as follows:

It is assumed that the proportion by weight of the highly refractory metal is $ 60. Using 0.12? Tantalum wire mm thickness

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one presses a ball of wire in a suitable device to a small button 23 '(JPIg. 7) »about 25 mm long and has a diameter of about 37 mm. The button 23 is then placed in a degassed crucible 28 made of graphite about 37 mm in diameter, as shown in FIG. 7. The desired amount of copper is then placed on button 23. It is heated Now the copper in a vacuum using suitable processes, e.g. high-frequency heating until it melts. If the copper melts, it soaks the button 23 by capillary action. By adjusting the percentage of getter material one can ensure the desired release of getter material as a function of the power rating of the switch. The percentage of the getter material in the conductive carrier material, which can be copper, silver or gold, lies between 5 and 97 #.

The tantalum-copper mixture described can also be used as a substitute the known contact parts 32 shown in FIGS. 14 and 15 are used, as they are in US Pat. No. 3,182,156 * is described. The contact pieces according to this patent specification have an area 19 serving for arc ignition a metal or an alloy with a low chopping current strength, e.g. copper with tin, antimony, lead, zinc, bismuth or other metals. On the other hand, the outer part 32 in FIG. 14 serving the arc path can be higher for the interruption Currents designed and manufactured as a tantalum-copper composite electrode as it is described here. The advantage of using such contact pieces is that the Getter allows less complex degassing processes in the manufacture of the switch.

In the following, methods for the production of contact pieces are described, the fibers or wires from one of the named contain refractory getter metals and a highly conductive metal such as silver or copper.

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As set forth in U.S. Patent No. 2,295,338, one can such a construction by pressing in a number of rods made of tantalum, tungsten, molybdenum or some other metal into a casting mold into which the molten impregnation metal is poured. The following examples use combinations of silver and tungsten are given as examples. A preferred combination of materials is copper and tantalum.

In Fig. 10 a rod is shown which contains a number of wires 36 of a getter metal, for example made of tantalum, Tungsten or molybdenum. The wires 36 are in a base body made of highly conductive metal 37, for example copper or silver embedded. One suitable method for making contact members 34 in Pig. 10 consists in bundling the wires 36 in generally parallel alignment, the distance between the wires being merely due to mutual contact is determined. The bundled wires 36 are then by a not shown wrapping with wires or fibers or other suitable means held together in several places «. The bundled strands 36 are then passed through a bath of molten Impregnation metal pulled through evenly. The impregnation metal 37 is allowed to cool and solidify, whereupon the rod 35, as in Pig. 10, into individual contact members by means of a cutting disk or some other suitable tool 34 can be cut up. The wires 36 protruding from the outer ends of the outer contact members 39 are then separated with a grinding tool, so that each of the outer contact members 39 receives a Kontaktflache 38 at both ends =

Pig. 11 depicts one of the contact surfaces 38 in Pig. 10 shown Contact members 34, for the manufacture of which wires 36 made of tungsten with a diameter of 0.127 mm were used. That in Pig. The contact member shown in Figure 11 contains about 25 weight percent silver and 75 weight percent tungsten. This relationship

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can be done by changing the degree of packing of the bundle of tungsten wires and / or can be varied by changing the diameter of the tungsten wires.

A further method for producing the contact members 34 shown in FIG. 10 consists in placing a certain amount of a highly conductive metal in one piece or in powder form in a casting mold (not shown). A plurality of wires 36 are then bundled in generally parallel alignment and then placed in the casting mold on the highly conductive metal, to which about 1 $> nickel in powder form can be added in order to improve its wetting properties. This assembly is then loaded in a melting furnace having a temperature at which the highly conductive metal melts, for example, about 1 1QO ⁰ O. Huh cooling, the rod is cut into pieces 35, as Fig. 10 shows.

Another method of making the contact members of FIG. 10 is to assemble the bundle of wires 36 into a Insert the mold and pour a molten impregnation metal into the mold.

FIGS. 12 and 13 show modifications of the rod according to FIG. The parts in FIGS. 12 and 10 that correspond to FIG are provided with the same reference numerals as in Fig. 10, with the difference that the characters in Fig. 12 are simply deleted and are double-crossed in FIG.

The contact members 34 ', as shown in FIG. 12, can be produced according to the method already described. she differ eich from the contact members 34 according to FIG. 10 only in that the bundled metal wires 36 before the impregnation with the highly conductive metal wrapped with a wire,

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which also consists of one of the getter metals mentioned. The wrapping wire 40 forms a collar around the bundle which provides additional strength to the finished contact members 34 ' gives and holds the fibers 36 'together during the impregnation process O

The contact members 34 ″ shown in FIG. 13 can likewise be produced by means of the methods described. The wires 36 "in Fig. 13 are surrounded by a number of wires or fibers that are connected to each other before being soaked with the highly conductive metal are intertwined or stranded. This embodiment is of particular importance for the manufacturing process, in which the bundle of fibers through the. Melted highly conductive metal 37 "is pulled. During this process, the stranding holds the fibers 36" together.

Another embodiment of contact pieces violate the Fig. 5, 6 and 7. Figure 5 shows a cluster 42 of short pieces of lofty wires or fibers 43. These short fibers 43 are placed in a die, such as those used for pressing metal powders, and given the desired shape and density compressed. Fig. 6 illustrates a body 44 pressed from the fibers of Fig. 5. This body becomes placed in a casting mold together with a highly conductive metal 37 in lump or powder form. The semolina shape is then in exposed to a melting furnace at a temperature which is above the melting temperature of the metal 37 and below the melting temperature of the high-melting metal lies. The good conductive metal a small percentage of jingle powder can be added, in order to support the wetting ability of the metal 37. The finished contact piece 46 is shown in FIG. 7.

Another method of making that shown in FIG Contact member 46 is that one in Fig. 5

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short fibers 43 shown in loose form in a container on highly conductive metal 37 in lump or powder form and introduces the container into a melting furnace, whereby a finished contact member 46 is obtained as a composite body.

The crucible 28 shown in FIG. 7 can also have a greater depth. Rods similar to that in Fig. 10 shown rod with the composition of the contact member 46 in Fig. 9, which can be divided into individual contact members.

The short wires 43 (Fig. 5) made of refractory metal, which are used to make the contact members 46, can be remnants of wire that would otherwise be considered waste ο This is an advantage of the manufacturing process described in that otherwise wasted material can be used to make high quality contact members 46.

A further modification can consist in that a part of the short fibers 43 up to 80 $ by high-melting getter metal is replaced in powder form with a grain size of 100 mesh. The more or less homogeneous mixture of fibers and the powder can be compressed in the manner already described to form a compact, similar to the compact 44 in FIG and soaked in the manner described with a highly conductive metal. The fibers that are in the finished contact member and are present in a random distribution on its surface, prevent thermal breakage of the contact piece operational.

The following are examples of contact members made in accordance with the invention.

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Example I

Neat and smooth drawn tungsten wire 0.254 mm thick was on a double spindle reel 2U. an elongated one, about TO cm long bobbin. Both ends of the spool were cut open and the two halves were folded together to form a bundle of fibers approximately 16 ram in diameter and tightly wrapped with tungsten wire., This bundle of fibers was placed in a ceramic crucible, the silver powder with an addition of 1 percent by weight of Hickel The composite body formed in the melting furnace in a dry hydrogen atmosphere at 1100.degree. C. was converted into individual contact elements divided up. One of these contact elements was machined to a diameter of 12.7 mm and a height of 6.4 mm. An examination of the composition showed a content of 25 percent by weight silver and 75 percent by weight Tungsten.

Example II

Another contact element was made in the same way as that in Example I treated contact element produced, however with the difference that the tungsten wires had a diameter of 0.127 mm »in the resulting contact element a ratio of 20 percent by weight silver and 80 percent by weight tungsten was found »

Example III

Tungsten fibers 36 having a diameter of 0.254 mm were cut into short pieces, similar to the pieces shown in FIG. 5, 43 cut. These pieces of fiber were placed in a cavity made in a graphite block, 25.4 mm deep and about 16 mra Diameter poured »The fibers were poured together with silver

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powder in a melting furnace in a hydrogen atmosphere for one stand at 1 100 ⁰ C kept. The cooled contact member was machined to a bead of 6.3 mm and a diameter of 12.7 mm. The examination of the contact member showed a content of 80 percent by weight silver and 20 percent by weight tungsten.

Example IY

Tungsten fibers 36 with a diameter of 0.127 mm were cut into short pieces and placed in a die with a Die hole with a diameter of 12.7 mm and a pressure of approx

10 t processed into a compact, which has a height of about 12.7 mm and contained about 65 "percent by volume tungsten fibers. The compact was along with a disk made of silver with a weight of 4 g in a cavity of a graphite block for 30 minutes at a temperature of 1150 ° 0 under a hydrogen atmosphere exposed. The contact member machined to the desired dimensions contained 25 percent by weight silver and 75 weight percent tungsten.

.Figur 16 shows a contact member which consists of particles 21 'of a getter material and particles 37' of a highly conductive metal. The mixture of these ü _'e ilchen was heated in a melting furnace to the lower melting material 37' to melt. In this way, a contact piece was obtained purely by powder metallurgy.

11 claims
16 figures

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Claims (11)

Pat sntansorüche (1. Vacuum circuit breaker for alternating current with a housing, In the zv / ei relatively movable contact pieces and a getter material are arranged, characterized in that that the getter material (20) in the area of the. arcing (15) is arranged such that it is evaporated or sprayed when an arc is burning (Fig.1). 2. Vacuum circuit breaker according to claim 1, characterized in that that a metal from the group as a getter material which is made of titanium, tantalum, columbium, zirconium? Consists of tungsten and molybdenum. 3. Vacuum circuit breaker according to claim 1, characterized in that the getter material is arranged in the form of a body (20) on the back of at least one of the contact _{pieces (7 9} 8) (Fig.l). 4o vacuum circuit breaker according to claim 1, characterized in that the getter material is arranged in the form of a ring (25) outside the contact surface of at least one of the contact pieces (8 ¹ ) (Figs. 3, 4). 5. Vacuum circuit breaker according to claim 1, characterized in that that at least one of the contact pieces (7, 8) has a region (19) serving for arc ignition and one of these Area (19) surrounding area serving the arc path (32) and that the getter material in the for the Liehtbogenlauf provided area (32) is arranged (Fig = 14 »15) · - 19 - 009841/0937 PiA 69/8002 - 19 - 6. vacuum line switch according to claim 1, characterized in that that around the contact pieces (7,3) a condensation screen (16) is made of metal (Fig. 1), 7o vacuum circuit breaker according to claim 1, characterized in that that at least one of the contact pieces made of a highly conductive carrier metal and getter material embedded in this consists. 8. Vacuum circuit breaker according to claim 7, characterized in that that the getter material in the form of fibers or B. Wires (36) is embedded in the carrier metal (37). (Fig. 10). 9. Vacuum circuit breaker according to claim 8, characterized in that that the fibers (43) on the surface of the contact piece (66) have a random distribution (Fig. 5 and 9). 10. Vacuum circuit breaker according to claim 8, characterized in that that the fibers (36) are arranged essentially parallel to one another and perpendicular to the contact surface (38) (Fig. 10). 11 ο vacuum circuit breaker according to claim 7 »characterized by that the carrier metal is a metal from the group consisting of copper, silver and alloys on the basis of these Metals. Empty soap