DE2240106A1 - HIGH PERFORMANCE LEAD-THROUGH ENCLOSED VACUUM SWITCH - Google Patents

Description

High performance bushing with encapsulated vacuum switch

In the electrical power distribution field, it is well known to use vacuum breakers or switches, to perform a wide variety of different interruption or switching functions. The ones with the well-known vacuum switches associated costs, coupled with the relatively fragile construction of most vacuum switch bottles However, the applications of these switches have been limited to devices in which a large number of interrupt operations is required. This can justify the relative cost of the switches versus their useful life, common Well-known applications for vacuum switches are in high-voltage circuit breakers and low voltage circuits that require numerous open circuit operations.

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Besides the limitations on cost and relative Fragile switch structures are well known high-voltage vacuum switches limited by their inherently relatively large dimensions to applications that use the switches with the appropriate housing space and bracket. All of these characteristic features of the conventional vacuum switch led to its widespread use as a

en
Switching device ^ n underground power distribution systems are prevented. The normal requirements of a switching function in such a system are that it be competitively priced, stable in construction, and small enough to be conveniently installed in underground structures.

Some of these system requirements could be met by combining a vacuum switch with other components that perform different functions in the system. Indeed, attempts have been made to combine the features of high voltage vacuum circuit breakers and submersible oil-filled circuit breakers to provide vacuum switching properties for underground power distribution systems. For example, U.S. Patent 3,171,669 describes the use of a relatively high voltage vacuum switch in combination with an underground power distribution switch module that includes push-on connectors that facilitate connection of the underground power cable ends to the switch. However, the known encapsulated switch has the disadvantages that it is relatively expensive and large, as already mentioned in the introduction. Another of the known examples of such a combination is described in US Patent 2594 52 ¹ I. Again, an oil-filled tank is specified with a vacuum switch which is immersed in the oil and electrically connected between a pair of push-on bushings that are mounted on the tank.

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The object on which the invention is based therefore exists in creating a plastic bushing that is in a integral assembly is combined with an encapsulated vacuum switch, thereby reducing the total cost of the combined Reduce implementation and switching functions while at the same time the requirements of a smaller size and a minimized space for one Vacuum switching function are to be fulfilled in an underground power distribution system.

The present invention is in the field of switching and feed-through devices in electrical power distribution directed and, more precisely, includes a plastic bushing that goes into an underground power transformer or a similar device can be installed and the one encapsulated cheap vacuum switch. According to a preferred embodiment of the invention is an inexpensive vacuum switch encapsulated in the molded dielectric of a feedthrough that also has a feedthrough mounting flange that is encapsulated in its outer surface. The bushing mounting flange enables the implementation to be in the operating position on the wall of an underground transformer tank is rigidly attached to form a hermetic seal with this. The tension from one end to the other that the vacuum switch withstands is at least doubled by the encapsulating dielectric of the bushing. According to In a further embodiment of the invention, numerous vacuum switches are encapsulated in a pressed bushing, in order to achieve a combination of switching functions and Bringing circuit connections.

The invention will now be based on further features and advantages the following description and the accompanying drawings of two exemplary embodiments.

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Figure 1 is a side elevational view, partially in section, of a bushing and one encapsulated therein Vacuum switch according to the present invention.

Figure 2 is a side view showing, on a reduced scale, a combination of a bushing and a Vacuum switch similar to FIG. 1 and also shows a side view of an unencapsulated vacuum switch, similar to that included in the device shown in FIG.

Figure 3 is a schematic side view of a plurality of clamps having implementation with numerous vacuum switches encapsulated therein according to an alternative embodiment the invention.

In Fig. 1 is a high power electrical bushing with a vacuum switch encapsulated therein in accordance with the present invention Invention shown. The implementation 1 comprises an elongated, cast or pressed housing la made of electrically insulated Epoxy resin. The particular resin that is used to form the housing will be discussed later in conjunction with the particular Embodiments of the invention described in more detail. As can be seen from Fig. 1, the housing la is shaped so that it at one of its ends a frustoconical surface Ib on-r shows. The surface Ib can receive a housing, not shown, of a cable end connector that is connected to the surface forms a watertight connection.

The use of such slip-on end links is well known in the field of energy distribution, and the use of frustoconical cooperating sealing surfaces between adjacent conductor connections has been standardized. An example of such a cable joint coupling Is described in U.S. Patent 3,551,587.

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In order to firmly attach the bushing 1 in a desired operating position relative to a transformer tank or other structure through which the bushing is to conduct current, a stable fastening device with an annular steel flange 2 is fastened to the housing la at a point between the corresponding housing ends. The inner peripheral surface 2a of the flange 2 is cast watertight into the housing la, while the outer peripheral edge 2b of the flange can be welded to a support frame made of steel, such as. B. the part of a frame 3-3 ', which is shown in FIG. For the person skilled in the art, who is familiar with the production of plastic feedthroughs and their associated fastening devices, it becomes clear that it may be desirable to cover the inner surface 2a of the flange 2 with an elastic layer of cement or adhesive material, before the flange 2 is poured into the housing la. Such an elastic layer of adhesive material serves to protect the housing la from ₈ that it is torn open due to differences in the expansion coefficient between the flange 2 and the epoxy resin of the housing la _e

The vacuum switch * J, which during a suitable pressing process Built into the housing la contains various characteristic features that make it suitable for use with the one shown here Make plastic bushing 1 particularly suitable. More accurate said, switch * J includes a generally cylindrical one hollow ceramic wall part 5, which is much more stable than the wall parts made of glass or thin metal, which are usually used to form the vacuum flaps of vacuum switches were used. First and second end caps 5 and 6 made of metal have opposite ends of the wall part 5 sealed to thereby form a vacuum chamber ^ a. In this Embodiment of the invention, the end caps 6 and 7 are made of electrically conductive copper, in different However, embodiments can also have other dimensions

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materials are used.

According to the present invention, the ceramic material is the wall part 5 a high alumina-containing ceramic; H. its alumina content is in the range of 90-99 percent. In the preferred embodiment described herein, the alumina content is in the range of 91-96 percent since this particular composition helps ensure a high quality seal for the vacuum chamber. It it should be noted that a conventional ceramic / metal caulking process is used to create an airtight seal between the wall part 5 and the end caps 6 and 7 to form.

A first contact piece 8 is attached in an electrically conductive, fixed relationship to the first end cap 6 and a second Contact piece 9 is electrically conductive on a mechanically displaceable Actuating rod 10 attached, which is movable relative to the second end cap 7. As it is in the field of manufacture is common for vacuum switches, means are provided to form an opening 11 through the second end cap 7, in order to receive the actuating rod 10 passing through. To seal the opening 11 and thereby create a vacuum chamber with the Forming the wall part 5 and the end caps 6 and 7 is more flexible Bellows 12 attached, which forms a seal between the | second end cap 7 and the actuating rod 10 forms. Of course, the bellows 12 is flexible enough to for a To ensure relative movement between the actuating rod 10 and the second end cap 7, which is sufficient to the movable Contact piece 9 in relation to the fixed contact piece 8 öff-r and to be able to close. Such bellows are known in the field of vacuum switch technology and for their production any conventional material can be used.

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The operating rod 10 is mounted so that it projects a predetermined distance beyond both sides of the bellows 12, so that the contact piece 9 can be moved in a predetermined range with respect to the fixed contact piece 8 and thus a suitable operating linkage with the lower end 10a of the Actuating rod 10 can be connected, which brings about such a movement. To complete the electrical circuit formed by the bushing 1, a suitable electrical conductor 13, which in this embodiment of the invention is formed by a threaded copper rod, is placed in the bushing when the latter is being cast. The conductor 13 is connected between the first end cap 6 and the smaller diameter end of the frustoconical surface Ib. Thus, an electrical circuit is formed by the contact members 8 and 9 of the switch ¹ J, when these are engaged, and extends from the upper end of the passage through the rod 10 to the lower end of the bushing. Thus, it is apparent that a characteristic feature of the present invention is, from one end to another of the vacuum switch ¹ J to substantially increase the breakdown voltage rating above their rated voltage flashover in the unencapsulated state also. This is achieved in that the exposed electrical conductors 13 and 10 at opposite ends of the bushing 1 are at least twice as far apart, measured along the outer surface of the bushing 1, than these conductors in the air creep distance through the end caps 6 and 7 / the wall part 5 of the vacuum switch ¹ J would be separated. Accordingly, the nominal end-to-end flashover voltage of the inventive combination of bushing and vacuum switch is at least twice as great as the nominal voltage which vacuum switch 4 is able to withstand per se. This means that a smaller and therefore cheaper vacuum switch in manufacture can be used in this combination, thereby achieving part of a primary objective of inexpensive manufacture.

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In order to ensure the electrical integrity of the seal between the wall part 5 of the switch 4 and the pressed epoxy resin of the housing la, it is necessary to have a defect or
To form an air space-free seal between these components. It has been found that such a seal can be achieved through use
a "soft" epoxy resin can be obtained which has such a modulus of elasticity that expansion and contraction with the vacuum interrupter 4 allows without it being separated therefrom. Alternatively , a "hard" epoxy resin can be used to form the housing la around the switch ^ ,
when a thin layer of elastic material 13 is attached between the VJandteil 5 and the housing la , when the housing la is pressed. In order to form such a layer of elastic Ma material 13 , the wall part 5 can be coated with either a hardened or uncured layer of Verklttungs- or adhesive material, which is similar to that which has been described above in connection with the surface 2a of the steel flange before the housing la made of epoxy resin is pressed around the vacuum switch ^ l . If desired, a further description of a suitable elastic material for a
such layer can be found in U.S. Patent 3,388,211 .

For those skilled in the art of plastic compacts
clear that the range of elasticities of plastic resins
varies greatly. However, in order to further define the present invention , it should be noted that the above is used
The term "soft" epoxy is intended to mean an epoxy resin having a modulus of elasticity at 25 ° C that is in the range of ^ 90,5,620 kg / cm ² (7,000-80,000 PSI). An example of a
such epoxy is the Gepol family of resins manufactured by the General Electric Company in its Insulator Products Department in Baltimore, Maryland . In the described here are surrounded preferred embodiment, the term "hard" epoxy resins should having an elastic modulus at 25 ⁰ C Defi-

C ρ IC

kidneys, which are in the range of 0.189 x 10 kg / cm (2.7 x 10

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PSI) - on the order of 10. More generally, the materials referred to as "hard" epoxy resins are produced by reacting a commercially available epoxy resin such as e.g. B. those from Shell Chemical Company under the tradename Epon Resins or those from Geigy-Ciba Corp. Resins sold as Araldite Resins, made with a multipurpose hardener such. B. a polyamine or a dibasic acid anhydride. A typical example would be the technical grade reaction product of the diglycidyl ether of 2,2'-diphenylolpropane (Epon 826) with metaphenylenediamine or with hexahydrophthalic anhydride. After curing, such materials typically have a modulus of elasticity of voi
(5 x 10 ⁵ to 1 χ 10 ⁶ PSI).

a modulus of elasticity of 0.35 χ ⁵ to 0.07 χ 10 kg / cm ²

It is common to include high levels of inorganic fillers in such compositions, e.g. B, silica flour, which serve for useful purposes such as cost reduction, lowering the thermal expansion coefficient, increasing the thermal conductivity, etc. The inclusion of such inorganic fillers also increases the modulus of elasticity up to a range of more than 0.35 χ l-0 ^Ω kg / cm (5 10 PSI).

On the other hand, the materials described herein as "soft" epoxy resins are those obtained by reacting the same types of Epoxy resins are made with curing systems that promote flexibility. Examples of such curing systems are (1) acid terminated polyesters as described in U.S. Patent 2,712,535, and (2) combinations of dibasic Anhydrides such as B. hexahydrophthalic anhydride, with polyethylene or polypropylene glycols,

Many examples of "hard" epoxy resins (as the term is used herein) are given in the "Handbook of Epoxy Resins", Lee & Neville, Chapters 8, 9, 10, 11 and 12 described, and examples for "soft" epoxy resins see Chapter 16 of the same manual

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given in the book.

The coating of the flexible material 13 can be any of several resilient materials, for example the material disclosed in the above-referenced US Pat. No. 3,318,211 is specified. For the purpose of the present invention it is only necessary that the material be flexible and that it be both flexible on the holder 4 as well as on the encapsulating epoxy resin of the housing la clings. Furthermore, the layer 13 must be free of defects or air spaces in order to avoid corona problems. Further Examples of suitable materials that have proven successful in this application are polyurethane (3M-221 Comp.) And Polysulfld (Thiokol GZR). It is important to care point out that the thickness of the coating layer 13 for a successful Adhesive effect is critical. More specifically, it has been found that the thickness of the layer 13 over its entire surface area should be in the range between 0.075 mm and 1 mm (0.003 inches and 0.04 inches). An optimal thickness for the Layer of resilient material 13 is about 0.125 mm (0.005 inches). However, it has been found possible to use one Form a coating up to 6.35 mm (0.25 inch) thick and still get relatively airspace-free results. The power such a thick coating is that it can only be manufactured at a very high cost; thus he is for the present Invention not ideally suited.

Another important feature of the combination of bushing and switch according to the preferred embodiment of the invention is that the epoxy resin of the housing la should be at least 3.3 mm (0.13 inch) thick all over it Surface area which encapsulates the ceramic wall part 5, so that the high voltage present between the conductor 13 and the rod 10 does not pierce the synthetic resin and causes a short circuit of the switch 4. Just as important is the need that the implementation 1 has a stable structure so that it can withstand the strong mechanical forces that

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be applied to them when a cable connector is clamped onto the top of the grommet or when a contact closure force is applied to the rod 10. Thus, the above minimum thickness of the walls of the housing la around the vacuum switch H has been shown to be necessary.

In order to further simplify the construction of the vacuum switch k , whereby the objects underlying the invention are better achieved, it has been found that only one of the contact pieces 8 or 9 needs to be formed from a relatively expensive, welding-counteracting alloy in order for the switch ^J 4 has a reasonable lifespan when applied normally to an underground power distribution system. Therefore, in the preferred exemplary embodiment of the invention, the first contact piece 8 is made of copper, while the second contact piece 9 is made of an alloy of copper and one to five percent bismuth which counteracts the welding. This leads to a noticeable reduction in costs, which makes the invention further suitable for use in power distribution systems. Of course, other anti-weld alloys can also be used in alternative exemplary embodiments of the invention.

It has also been found that a novel shielding arrangement can be used within the vacuum switch 4 to provide adequate shielding at a desirable economical price. More particularly, it has been found that a single, generally cylindrical, hollow shield or screen Ik provides adequate shielding for the intended application of the invention. This is attached to the first end cap C in such a way that it extends beyond the inner end of the first contact piece 8 to a Ρμη ^, where it ends in a plane which is located between the contact pieces when the movable contact piece 9 is in its the largest AUatand to the fixed contact piece 8 having position. So far it has been common practice to

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borrowed to use more expensive bulkhead assemblies. For example it is in high-voltage vacuum switches such as those used for example used in power showers, so far and still It is common practice to use a relatively long protective element that wraps around both contact pieces on opposite ends of the Vacuum chamber is attached. Furthermore, it is relatively common to use a separate protective wall from the isolated one The side wall of the vacuum chamber hangs down, where it covers the entire arc area formed by the open contact pieces surrounds. Of course, such constructions are relatively expensive and are therefore not suitable for use in of the present invention.

Now that the main features of the preferred embodiment of the invention have been described, reference will be made to FIG. 2 in order to clearly visualize the relative overall size of the bushing 1 and the vacuum switch 4 which is encapsulated in the bushing 1 according to the invention. V / he can clearly be seen from this figure, the length from one end to the other of the bushing 1 is at least twice as great as the length from one end to the other of the ceramic wall part 5 of the switch ^J J, over which a high voltage flashover could occur if the switch ^ l is not encapsulated. This illustration was intended to graphically demonstrate one of the main advantages of the present invention, namely the increased flashover rating obtained for a relatively 1 illip vacuum switch when such a switch is encapsulated in a plastic dielectric grommet in accordance with the present invention.

For the specialist ;; _; From the foregoing description of a preferred embodiment of the invention, it will be apparent that various modifications and improvements can be made within the teachings given. An example of this is shown in FIG. 3. In this Fig. 3, the same reference numbers, which are provided with dashed symbols, are used.

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applies to denote the components that are in their puncture are equivalent to those shown in Pig, I. Embodiment have been described.

Mainly this contains in Pig. 3, a multi-pole high-performance bushing 1 ', in which two vacuum switches V and * J''are encapsulated. In addition, in the implementation of a gas circuit breaker 15 can be used, which is similar in structure and function to the US patent "quick buttons described in the 3 5 ^ 2 -986. It should be noted that the pressed Epoxyharzgehäuse la is made of a material ¹ is similar to any of the materials described above, and is shaped to have a pair of frustoconical surfaces Ib 'and Ib "which extend from an outer surface to spaced points so that these frustoconical surfaces are capable of electrical Cable end housing with the formation of a watertight seal, as described above with reference to the embodiment shown in Pig a steel tank l6 can be welded to one end of the pressed housing la inside the tank assign »This creates a gas-tight seal around the housing. In this embodiment, an electrically insulating gas, such as. B, Preon disposed in the tank 16 to the enclosed end of the housing la ',, around the mechanical actuating mechanisms 17 and 17 to isolate the _s in a corresponding manner with the contact-actuating rod ^10! and 10 '' are coupled.

Each of the switches 4 'and 4' includes a generally cylindrical, hollow ceramic wall portion 5 'and 5' ^! and first and second metallic end caps 6'-7 "and 6 ^9Ü -7" correspondingly connected to opposite ends of the wall parts 5. '

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- lh -

and 5 ¹ 'are sealed in order to thereby form vacuum chambers within these wall parts, as was described above with reference to FIG. V. 'Furthermore, each switch contains a first contact piece 8' or 8 '', which ^{are firmly attached to the end caps 6 'and 6 1} ', and a pair of second contact pieces 9 'and 9 *'> which are electrically conductive, mechanically operable rods 10 'and 10 ^fI for relative movement with respect to the second end caps 7' mounted and 7 'are ^1. Finally, two flexible bellows 12 'and 12 "are attached to form a seal between the corresponding second end caps 7' and 7" and the rods 10 'and 10 "in order to thereby ^{seal the openings 11' and II '1} , which are formed through the second end caps 7 'and 7 ". Furthermore, two electrical conductors 13 'and 13 "are attached in a corresponding manner in the frustoconical sections Ib' and Ib" of the cast housing la ^{1 in} order to connect the electrical circuits from the corresponding first end caps 6 'and 6 "to the to close smaller diameter ends of the surfaces.

It can be attached either mechanically actuated Fechanismus in the tank 16 and with the rods 10 - are connected 'to this for an opening and closing of the corresponding pairs of the contact pieces B' 10 '' - 9 'and 8' ¹ - 9 ¹ ' move. The significant feature of this embodiment of the invention is the provision of numerous vacuum switches within a single molded epoxy bushing to demonstrate the flexibility of the present invention for use in various underground power distribution systems. It is important to note that in this embodiment of the invention the end-to-end rated voltage of each of the encapsulated vacuum switches 4 'and ^l \ "is at least 200 percent of the rated voltage of such switches that they would have in their unencapsulated state . The reason for this lies in the end-to-end insulation of the conductors 13 '- 13' · and 10 · -10 ", which is achieved by the insulating housing 1 a 'and the insulating gas in the sealed tank 16.

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Claims (1)

Claim e Electrical high-performance bushing with a vacuum switch encapsulated therein, characterized by an elongated pressed housing (la) which is made of electrically insulating epoxy resin and has a frustoconical surface (Ib) on one end for receiving an end housing of an electrical cable with the formation of a water-tight seal, fastening means (2) _s which are attached to the housing at a point between the housing ends, to the fixed Konta ge of the housing (la) in an opening (at 3) _s and a vacuum switch (4) mounted in the housing (la) j> one generally cylindrical., hollow ceramic wall part (5) _s first and second end caps (6 _S 7) made of metal which are sealed in a corresponding manner with opposite ends of the wall part (5) to form a vacuum chamber (4a) within the wall part (5) _s a first contact _{piece (8) s} the electrically conductive and fixed on the first end cap (6) ang Ebracht is a double contact piece (9) j, which is mounted on an electrically conductive, mechanically actuatable rod (10) for a relative movement with respect to the second end cap (7), means for forming an opening (11) through the second end cap (7) through for receiving the rod (10), a flexible bellows (12) which is attached between the second end cap (7) and the rod (10) to form a seal so that the opening (11) and the vacuum chambers ('Ia) are sealed and a relative movement between the rod (10) and the second end cap (7) is nevertheless permitted, the rod (10) being attached in such a way that it extends over predetermined distances over the two sides of the bellows (12) extends out ₉ and comprises an electrical conductor (IJ), which in the bushing (l) 309809 / 10SO ' attached and connected between the first end cap (6) and the smaller diameter end of the frusto-conical surface (Ib), so that when the contacts (8, 9) of the switch (Ό are in engagement with one another, an electrical circuit from one end of the Implementation is formed on the other hand, the end-to-end length of the implementation (1) is at least twice as large as the length of the switch (4) between its first and second end caps (6, 7) and the dielectric strength of the den Switch ( ² O surrounding epoxy resin is sufficient so that an electrical breakdown of the epoxy resin is prevented when it is subjected to a voltage which is greater than the withstand voltage of the switch (4) in its unencapsulated state. 2. High-performance implementation according to claim 1, characterized characterized in that on the first end cap (6) a generally cylindrical hollow protective wall or Shielding (1 * 1) is attached, extending over the inner end of the first contact piece (8) also extends, and the inner end of the protective wall or shield (IA) in one Plane between the contact pieces (8, 9) lies when the movable contact (9) is in its of the first contact piece (8) is the furthest position. 3. High-performance implementation according to claim 1, characterized characterized in that the first contact piece (8) made of copper and the second contact piece (9) made of an anti-welding alloy made from copper and 1 to 5 percent bismuth 1st. ¹ J. high-performance implementation by one or more of claims 1-3, characterized in that the epoxy resin is a "soft" epoxy resin a fehlsteilen- or air space-free seal with the vacuum switch 309809 / 10S0 - • 17- forms. 5. High-performance implementation according to one or more of the claims 1-3 »characterized in that the epoxy resin is a" hard "epoxy resin and a layer (13) made of elastic sealing material, which between 'the bushing (1) and the wall part (5) of the switch (4) is attached so that a passage free of air space is formed between the implementation and the wall part. 6. High-performance implementation according to claim 5> thereby characterized in that the thickness of the layer (13) over its entire area is in the range of 0.075 mm to 1 mm. 7. High-performance implementation according to one or more of the claims 1-6, characterized in that the fastening means (2) have an annular steel flange include, the inner peripheral surface (2a) waterproof in the Housing (la) is cast and its outer peripheral edge (2b) can be welded to a support frame (3) made of steel, so that the implementation (1) and the switch (4) on the Frame (3) can be permanently mounted. 8. high-performance implementation according to claim 1 ,. through this characterized in that the epoxy resin is at least 3.3 mm over the entire surface of the ceramic wall part (5) is thick. 9. High-performance bushing according to one or more of claims 1-8, characterized in that a pair of vacuum switches '( ^l \ ·, V ¹ ) are encapsulated in the bushing (1) and the housing (Ia') with a pair of conical ump ff örmi ge r surfaces (Ib ¹ , Ib ") is formed, which are to be spaced from the outer surface of the housing 309809/1050 ten run on the surface, each of the surfaces being designed to accommodate a cable end housing forming a watertight seal with this, a steel flange (2 ') is partially cast into the housing and surrounds the outer circumference of the housing, a steel tank (16) is provided , to which the outer part of the steel flange (2) is welded, so that one end of the cast housing (la ¹ ) is arranged in the tank (16) and a gas-tight seal is formed around one end of the housing, an electrical one Insulating gas is arranged in the tank around one end of the molded housing and each of the vacuum switches has rods (10 *, 10 ") attached thereto, which protrude into the tank (16) and with a mechanically operable mechanism (17> .17a ) are connected, which moves them to open and close the pairs of contact pieces (8 '9 ^f , 8 "- 9"). 10. High-performance implementation according to claim 9 »characterized in that the vacuum switch (^ ', V ¹ ) in their encapsulated state have an end-to-end nominal voltage that their end-to-end nominal voltage in the unencapsulated state by a factor of exceeds at least 200 percent. 309809/1050 Blank page