GB2033665A - Vacuum interrupter or spark gap envelope - Google Patents

Abstract

An envelope for a vacuum interrupter or spark gap comprises a plurality of aligned adjoining tubular sections, at least one of which is of conducting material and lies between two insulating sections. The conducting section has a central region of a diameter equal to that of the envelope, and has end regions of a reduced diameter, which lie within the respective adjoining insulating sections and which form vapour shields within the envelope. By employing extrusion or the like to form the conducting section, it may be formed as one integral piece.

Description

SPECIFICATION Vacuum interrupter and spark gap This invention relates to vacuum interrupters and vacuum spark gaps, and in particular to enclosures therefor.

The enclosure of a vacuum interrupter or vacuum spark gap usually takes the form of a substantially cylindrical tubular envelope closed off at both ends by endplates through which respective contact stems pass into the interior, the envelope, endplates and associated components being joined in a manner suitable to make the enclosure vacuum tight. The tubular envelope is made of, or incorporates, at least one circumferential section of electrically insulating material to achieve the required electrical insulation between the opposing contacts, and any conducting parts associated therewith such as e.g. the endplates and further sections of the envelope.Vacuum interrupters usually have one pair of opposing contacts, with one of the contacts being stationary and the other contact being movable, the vacuum tight seal between the movable contact and the associated end plate being provided by bellows. In vacuum spark gaps, both contacts are stationary, at a predetermined mutual separation. Alternatively, both vacuum interrupters and vacuum spark gaps may, of course, have more than one pair of opposing contacts within the same envelope.

To prevent the deposition of metal vapour, produced by arcing beween the opposing contacts, on the inner surface of the insulating section or sections of the envelope, it is the usual practice to place a tubular metal shield between the contacts and that inner surface so that any metal vapour will deposit on the shield rather than the insulating section.

In conventional vacuum interrupters or vacuum spark gaps there is commonly provided a mounting arrangement for the shield which consists of a support member interposed between the shield and the envelope, although the shield may in some cases consists of two tubular parts each having an outwardly projecting flange at one end and joined together by the welding of the flanges which thus form the support member, the latter engaging a recess or protuberance on the inside of the insulator by deformation of the metal, in the case of one insulating section, or being brazed or welded to or mechanically trapped between two insulating sections.

One problem encountered in manufacturing vacuum interrupters or spark gaps is the selection of materials which allow the joints to be made between the insulating sections and the shield while at the same time being subject to other constraints such as workability, cost etc.

Afurther difficulty is often experienced in mounting of the vapour shield within the envelope during the manufacture of conventional forms of vacuum interrupters and vacuum spark gaps on account of the necessity of soldering, brazing or welding a plur ality of closely spaced joints simultaneously in a vacuum tight manner and ensuring at the same time a fairly accurate alignment of the shield and adjacent section of the envelope.

It is an object of the present invention to provide a novel construction for the envelope of a vacuum interrupter or a vacuum spark gap, which avoids or at least mitigates some of the above mentioned difficu Ities.

In accordance with one aspect of the present invention an envelope for a vacuum interrupter or a vacuum spark gap comprises a plurality of adjoining substantially cylindrical tubular sections, at least one of which sections is of conducting material and lies intermediate two insulating sections, the conducting section having a central region of a first diameter and, connected thereto by respective annular webs, end regions of a second diameter smaller than the first diameter, with said annular webs providing shoulders to the outer surfaces of which the two adjoining insulating sections are secured in a vacuum tight manner, and such that each of the end regions lies within a respective one of the insulating sections thereby to provide a vapour shield extending along at least part of the inner surfaces of the respective insulating section.

By a suitable choice of the materials for the insulating sections and the intermediate conducting section it is possible to seal the insulating material sections directly to the webs of the intermediate section, with a consequent reduction in the number of components to be assembled.

Alternatively, by providing buffer rings of an appropriate conducting material on the appropriate ends of the insulating sections, the material for the intermediate section may be selected from a wide range of conducting materials, the appropriate ends of the adjoining insulating sections being sealed to the buffer rings and the latter being sealed to the webs of the respective intermediate sections.

A further advantage of the present invention resides in the fact that the vapour shield regions of the intermediate section form covers which prevent the contacts from being abraded on the respective insulating sections during their insertion into the envelope, which is undesirable since material abraded from a contact could form a conducting bridge across the insulating section.

The intermediate section is preferably made such as to form a single member prior to assembly of the envelope.

Alternatively the intermediate section may comprise a plurality of components, the envelope being formed by joining two of the components each to an end of a respective one of the adjoining insulating sections, and subsequently joining the components together. Thus the intermediate section may consist, for example, of two components, which may be identical, and each of which is joined separately to its associated insulating section, one of the last steps in the assembly of the envelope, or even a vacuum interrupter or vacuum spark gap of which it forms part, consisting in the vacuum tight joining of the two components along a circumferential seam, for example by brazing or welding.

Where the intermediate section is to form a single member prior to assembly, the intermediate section may either be formed as an integral part, e.g. by extrusion, pressing or casting, or it may be made up of two, or more, components joined together priorto being incorporated into the envelope. In accordance with a further aspect of the present invention, a vacuum interrupter comprises a set of opposing contacts, including at least one movable contact, within an evacuated enclosure, the enclosure consisting essentially of a tubular envelope closed off at both ends by endplates through which the contact stems of the opposing contacts pass, the envelope consisting essentially of five adjoining substantially cylindrical tubular sections the outermost ones of which are of conducting material and support the said endplates and are secured at their ends away from the endplates to respective insulating sections with an intermediate conducting section lying between these insulating sections and consisting of a central region of a first diameter and connected thereto by respective annular webs, end regions of a second diameter smaller than the first diameter, with said annular webs providing shoulders to the outer surfaces of which the two adjoining insulating sections are secured in a vacuum tight manner, and such that each of the end regions lies within a respective one of the insulating sections thereby to provide a vapour shield extending along at least part of the inner surface of the respective insulating section.

The invention will now be described further by way of example only and with reference to the accompanying drawing, which shows a simplified sectional view, sectioned along the major axis, of a vacuum interrupter in accordance with the present invention.

Referring now also to the Figure of the accompanying drawing the vacuum interrupter illustrated therein comprises an enclosure, consisting essentially of a tubular envelope 1 and endplate assemblies 5 and 16, and a stationary contact 7 and a movable contact 9 carried on contact stems 6 and 14 respectively.

The envelope 1 consists of a plurality of adjoining cylindrical sections 17, 18, 2,3 and 4, the two end sections 17 and 4, and the intermediate section 2 which lies between two insulating sections 18 and 3, being of conducting material. The intermediate section 2 of the envelope 1 is formed as an integral component and comprises a central region 2 which has approximately the same external diameter as the adjoining insulating sections 18 and 3, and end regions 11 having an external diameter less than that of the central region and also less than the internal diameter of the insulating sections 18 and 23. The transition between the central region 8 and the end regions 11 of the intermediate section is by way of annular webs 10.Thus, while the central regions form part of the envelope 1, the end regions 11 project into the insulating sections 18 and 3 respectively to form vapour shields on which any metal evaporating from the contacts 7 and 9 due to arcing between these contacts; e.g. upon interrupting a current flow, will deposit.

The insulating sections 18 and 3 are provided with buffer rings as shown at 19, which are of a ductile metal and suitable to form a vacuum tight joint with the insulating material of the insulating sections.

These buffer rings are, in turn, welded or brazed onto the section 2, the annular webs 10 providing a suitable abutment surface.

To the other end of each of the insulating sections 18 and 3 is secured a further metal ring 17 and 4 respectively, again by a vacuum tight metal insulator joint. The endplates 16 and 5 are attached to the outer ends of the corresponding metal rings, 17 and 4, by means of a circumferential weld 13.

The endplate 13 has a central aperture 21, through which the contact stem 14, carrying the movable contact 9, passes. Bellows 15, joined to the endplate 13 as well as to the auxiliary plate 20, which itself is fixed to the contact stem 14, allow movement of the movable contact between the open and the closed position, while at the same time ensuring a vacuum tight connection between the contact stem 14, or rather the plate 20 fixed thereto, and the end plate 16.

The stationary contact 7 is, through its contact stem 6, rigidly attached to the endplate 5.

The outer ends of the contact stems 6 and 14 are suitably shaped, as schematically indicated in the drawing, to accept the electrical and mechanical connections (not shown), which are necessary for the installation of the vacuum interrupter.

Suitable materials for the various components of the vacuum interrupter are: copper for the stems 6 and 14 and a suitable copper alloy for the contacts 7 and 9 respectively; nickel for the endplates 5 and 16 and the auxiliary plate 20; high aluminia ceramic for the insulating sections 18 and 3; Nilo-K for the end sections 17 and 4; copper for the buffer rings 19; and stainless steel for the bellows 15. The section 2 may be made from a wide range of metals, stainless steel being but one example, if buffer rings 19 are employed.

Alternatively, the section 2 may be formed from Nilo-K, so asto be secured directly to the insulating sections 18 and 3, making the buffer rings 19 superfluous.

The above list of materials is, of course, not intended to be exhaustive, and the criteria for choosing other suitable materials, such as workability, compatibility etc, will be readily appreciated by a person skilled in the art, as will be modifications to the detailed shape of the components such as, for example, using an intermediate section whose end regions are frusto-conical instead of cylindrical as illustrated in the drawing.

Moreover the central region of the intermediate section need not be of uniform diameter along its length, provided the diameter adjacent the webs is sufficiently greater than the diameter of the end regions adjacent the webs to provide the said shoulders to which the adjoining insulating sections may be secured in a vacuum tight manner.

Claims (10)

1. An envelope for a vacuum interrupter or a vacuum spark gap comprising a plurality of adjoining substantially cylindrical tubular sections, at least one of which sections is of conducting material and lies intermediate two insulating sections, the conducting section having a central region of a first diameter and, connected thereto by respective annu lar webs, end regions of a second diameter smaller than the first diameter, with said annular webs providing shoulders to the outer surfaces of which the two adjoining insulating sections are secured in a vacuum tight manner, and such that each of the end regions lies within a respective one of the insulating sections thereby to provide a vapour shield extending along at least part of the inner surfaces of the respective insulating section.

2. An envelope according to Claim 1 wherein the adjoining insulating sections are sealed directly to the webs of the intermediate section.

3. An envelope according to Claim 1 wherein the appropriate ends of the adjoining insulating sections are sealed to buffer rings which are themselves sealed to the webs of the respective intermediate section.

4. An envelope according to any preceding claim, wherein the intermediate section is formed as two separate components joined together and each joined to an end of a respective one of the adjoining insulating sections.

5. An envelope according to any preceding claim wherein the central region of the intermediate section has an external diameter which is approximately the same as that of the insulating sections.

6. A vacuum interrupter comprising a set of opposing contacts, including at least one movable contact, within an evacuated enclosure, the enclosure consisting essentially of a tubular envelope closed off at both ends by endplates through which the contact stems of the opposing contacts pass, the envelope consisting essentially of five adjoining substantially cylindrical tubular sections the outermost ones of which are of conducting material and support the said endplates and are secured at their ends away from the endplates to respective insulating sections with an intermediate conducting section lying between these insulating sections and consisting of a central region of a first diameter and connected thereto by respective annular webs, end regions of a second diameter smaller than the first diameter, with said annular webs providing shoulders to the outer surfaces of which the two adjoining insulating sections are secured in a vacuum tight manner, and such that each of the end regions lies within a respective one of the insulating sections thereby to provide a vapour shield extending along at least part of the inner surface of the respective insulating section.

7. A method of manufacturing an envelope according to any one of Claims 1 to 3 including the steps of forming the intermediate section and subsequently joining the intermediate section to the adjacent ends of the adjoining insulating sections.

8. A method of manufacturing an envelope according to any one of Claims 1 to 3, in which the intermediate section consists of a plurality of components, including the steps of joining two components each to an end of a respective one of the adjoining insulating sections, and subsequently joining the components together to form the intermediate section.

9. A vacuum interrupter or a vacuum spark gap having an envelope according to any one of Claims 1 to 5.

10. A vacuum interrupter having an envelope substantially as shown in and as hereinbefore described by reference to the accompanying drawing.