GB2577376A

GB2577376A - Contact

Info

Publication number: GB2577376A
Application number: GB1910881.0A
Authority: GB
Inventors: Falkingham Leslie
Original assignee: S&C Electric Co
Current assignee: S&C Electric Co
Priority date: 2018-07-30
Filing date: 2019-09-30
Publication date: 2020-03-25
Anticipated expiration: 2039-09-30
Also published as: GB201812409D0; GB2577376B; GB2575990A; GB201910881D0

Abstract

A contact for an axial field vacuum switching device comprises a stem f for connection to a conducting rod, a cup-shaped support having a base conductively bonded to the stem, a disc for capping the cup-shaped support to form an enclosure, and one or more rings k placed within the enclosure to support the contact and/or the base from buckling. Angled slots are cut into the side of the cup. The rings placed within the cup are of a suitable length to provide support to the base against forces pushing the base inwards and fit sufficiently well into the cup that they keep each other in position. The number of rings may be between two and seven. At least one of the rings may be a split ring and/or may be larger than the other rings. The rings may be cylindrical or hexagonal tubes, spiral springs, or formed of flat metal strips. The rings may comprise holes I to facilitate the escape of gas during evacuation of the vacuum switching device. The electrical conductivity of the rings may be lower than that of the cup or the disc. The rings prevent the dishing of the disc and the distortion of the slotted cup.

Description

Contact

Field

This invention relates to a contact and in particular to a contact for an axial field vacuum switching device, which may include for example vacuum interrupters or vacuum switches.

Background:

A typical idealised construction of a vacuum switching device is shown in figure 1. These devices generally consist of an evacuated envelope which includes an insulating component (a) and end plates (b), together with a fixed electrode (c) and a moving electrode (d). The electrodes can be engaged and disengaged mechanically to perform the switching function. Normally this movement is permitted without breaking the seal of the evacuated envelope by means of a bellows or diaphragm arrangement (e). Each electrode (c or d) consists of a conducting rod (f) and a contact or contact assembly (g).

Vacuum switching devices that are designed to switch large currents have been produced for many years. These designs use self-generated magnetic fields to control electrical arcs that arise when the contacts are opened. A number of different designs of contact assemblies have been proposed for use under high current conditions. This invention concerns a type known as an Axial Magnetic Field (Amp contact assembly, in which the contact geometry produces a magnetic field that is substantially aligned with the axis of the contacts. With axial magnetic field geometries the contact faces are usually in the form of discs, and the effect of the axial field is to diffuse the current arc fairly evenly over the contact surfaces, thereby preventing overheating of points on these surfaces. Examples of such designs may be seen in EP 0349303, DE 3915519, DE 3610241, and GB 238111A.

A number of different designs of axial field contacts and contact assemblies have been proposed to switch the current on or off under load and fault current conditions. Examples of such designs may be seen in EP 0349303, DE 3915519, DE 3610241, and GB 238111A.

One form of axial field contact assembly is shown by US 6479779 B1 and shown in figure 2. The end of the contact stem (f) connects to a conical base component (g) which forms a closure to a cup shaped contact support component (h). These parts are made of a material of good electrical conductivity such as copper. Conductively bonded to the base of the cup is a contact disc (i) made of a layer of a material such as a copper-chromium material, which does not have such good electrical conductivity as copper, but does more effectively resist erosion by the electrical arc that forms during switching. Angled slots (j) are cut through the sides and base of the contact cup which force current passing from the contact stem to the contact disc to follow a path towards the contact edge which produces the desired form of magnetic field. Solid metal contacts are undesirable not least for the cost aspect, but also for the potentially undesirable dissipation of the formed electrical arcs.

This design of contact has been made in large numbers over a number of years, but when many switching operations have been performed two undesirable effects occur: a) The contact discs, together with the cup bases to which they are bonded, become dished inwards, as shown in figure 3, so that they are further apart towards the centre. This causes the diffused arc to concentrate at the edges of the contact discs, which increases the current density there, and so increases the rate of wear of the contacts at the edges, thus reducing the current carrying capacity and working life of the contacts.

b) Mechanical forces when the contacts are rapidly closed may also cause the slots in the side of the contact cup to become distorted to the detriment of the control of the current.

Patent US 6479779 B1 shows a form of support to prevent compression of the slots in the side of the contact cup, whereby a ring of strong metal, for example stainless steel, is placed against the inside of the slotted wall of the cup. This invention is effective, but requires an accurately made component and does not provide support to the centre of the contact disc.

Patent application GB2552839, illustrated in figure 6, shows a different form of axial field contact assembly in which the contact stem is joined to the base of a contact cup, and the open end of the cup is bridged by a disc (0 of contact material. The sides of the contact cup have angled slots (j) cut through them. In this type of contact assembly there is no copper layer under the contact disc (s).

GB2552839 proposes a support in the form of a thin-walled cone of poorly conducting material located centrally within the contact cup to oppose forces acting to dish the contact disc. This form of support is effective but has the disadvantages that a means to centralise the cone must be provided, and it only provides support in the central area of the contact disc.

It is an aim of the present invention to at least mitigate the above referenced issues with prior art devices.

Summary of the Invention

According to a first aspect of the present invention there is provided a contact for an axial field vacuum switching device, said contact comprising a stem for connection to a conducting rod, a cup-shaped support having a base conductively bonded to said stem; a disc for capping the cup-shaped support to form an enclosure; and one or more rings placed within the enclosure to support the contact and/or the base from buckling.

According to a second aspect of the present invention, there is provided a contact for an axial field vacuum switching device, said contact comprising a stem conductively bonded to the base of a cup-shaped support component, the open end of the cup being closed by a disc of contact material and the sides of the cup having angled slots cut through; and rings placed within the cup-shaped component of a suitable length to provide support to the inside of the base of the cup if forces push the cup base inwards, the rings fitting sufficiently well into the space that they keep each other in position.

In both aspects, the contact provides mechanical support to the inside of the base of the cup to oppose the forces which damage the contact.

The contacts may improve the design of contact assemblies for vacuum switching devices that utilise self-generated axial magnetic fields in the axis of the contact gap in order to be able to interrupt large currents. This makes this contact particularly suited to use in vacuum interrupter devices. As noted above, the contacts place a number of rings or short tubes of metal inside the contact cup to provide support to the contact disc against becoming dished away from the other contact disc or support, which may occur due to the large axial forces associated with such switching events.

According to the aspects there are provided a number of rings, or short tubes (hereby referred to as rings), which fill or partly fill the interior of the cup and may be of such a diameter that they almost touch each other and the inside of the cup wall, and may be of such a length that they span the distance from the face of the conical base component to the inner face of the base of the cup.

The number of rings may be two, three, four, five, six or seven. It can be appreciated that the number or rings may be higher if more support is desired, and may be in part determined by the size of contact (which may be determined by the size of the axial field vacuum switching device), the size of the rings, the degree of packing and the type of packing used.

The rings may be made of a strong material which is of relatively poor electrical conductivity, such as stainless steel, so that very little current passes directly to the contact face through the rings. The rings may be made cheaply by cutting lengths from suitable tube. It can be appreciated that the rings may be of unequal sizes, with for example a central larger or smaller ring being surrounded by smaller or larger rings to most efficiently pack the space or enclosure formed between the disc and the base of the cup-shaped contact.

In embodiments, one or more of the rings may be split rings that may ease manufacture and aid packing. One skilled in the art will appreciate that other numbers of rings may be used, and that this form of contact disc support need not be limited to cylindrical rings, but might be in the form for example of hexagonal tubes, structures in the form of spiral springs, or flat metal strip formed into shapes such as a cross or a honeycomb.

The rings may be made to the precise length needed to fit closely between the base of the cup and the underside of the contact disc, or they may be shorter so that less precision is needed in manufacture, which will permit a small amount of distortion of the contact disc.

The rings can be made fairly precisely to such a diameter that they fit closely into the space available, in which case they will provide support to each other against buckling under the axial load which causes the contacts to dish. This would allow them to be manufactured with thinner walls which in turn would increase the electrical resistance of the rings. Alternatively they can be a loose fit which reduces cost and assembly problems, but also reduces the mutual support.

It can be appreciated that the rings may comprise one or more holes to facilitate the escape of gas during vacuum evacuation of the vacuum switching device. This ensures that gas is not trapped within the rings if the device is used in an evacuated condition.

In embodiments the rings may be concentrically packed, such that rings sit within other rings. In alternative embodiments, the rings may be packed next to each other as described above.

In a third aspect of the present invention, there is provided an axial field vacuum switching device comprising the contact as defined in any embodiment of the preceding aspects. It can be appreciated that the axial field vacuum switching device may be a vacuum interrupter. Accordingly, the axial field vacuum switching device may comprise electrodes featuring the contacts, of which one or both of the electrodes may be moveable. Said contacts may couple either electrically or physically to conducting rods via the stem, or said stem may form part of the conducting rod. Furthermore, switchgear may be used to actuate the movement of the electrodes. Said electrodes and conducting rods may be housed within a vacuum evacuated housing. Bellows may be used to allow movement of the conducting rods through the vacuum evacuated housing, or alternatively bellows-free actuation may be used using magnetic actuation either within the vacuum evacuated housing such that no movement occurs outside or through said housing, or via magnetic coupling through said housing.

Detailed Description

Figure 4 shows a contact according to the aspects of the present invention. For convenience, this is shown in partial cutaway. The elements of the contact are as described in relation to Figures I to 3 above. In the example embodiment shown in Figure 4, there are three rings, and this is also shown as (n) in figure 5.

In figure 4, the rings sit within an enclosure formed between the disc and the base of the cup-shaped contact. In the example shown, each ring is provided with one or more holes (1) or notches to facilitate the escape of gas during vacuum pumping.

In figure 5 are illustrated the cases where there are (m) two rings, (n) three rings, (o) four rings, (p) five rings, (q) six rings and (r) seven rings. The rings are shown fitted within the slotted sides of the contact cup, with other parts omitted. The number of rings determines the degree to which support is provided at the centre of the contact disc and across its area, and the degree to which support is provided close to the inside of the slotted cup wall to oppose crushing of the slots.

It can be seen that the rings are typically self-locating because they keep each other in position well enough if they are a little loose but not too loose. This allows the rings to be easily packed into the enclosure and to provide the required support to prevent the contact and/or the base from buckling under the axial loads typically encountered during a switching event.

As shown in Figure 5, the rings may be arranged easily within the enclosure. It can be appreciated that the rings may be concentrically arranged. It is also appreciable that although circular rings are shown, the rings may be hexagonal, triangular or square, or may be a combination of shapes depending upon the support and packing requirements. Additionally, although shown as equal sizes, differing sized rings may be used as required.

The present invention can cooperate with the support structures described in the prior art, in particular that of GB 2552839 and shown in Figure 6, or may replace it.

Claims

Claims: 1. A contact for an axial field vacuum switching device, said contact comprising a stem for connection to a conducting rod, a cup-shaped support having a base conductively bonded to said stem; a disc for capping the cup-shaped support to form an enclosure; and one or more rings placed within the enclosure to support the contact and/or the base from buckling.
2. A contact for an axial field vacuum switching device, said contact comprising a stem conductively bonded to the base of a cup-shaped support component, the open end of the cup being closed by a disc of contact material and the sides of the cup having angled slots cut through; and rings placed within the cup-shaped component of a suitable length to provide support to the inside of the base of the cup if forces push the cup base inwards, the rings fitting sufficiently well into the space that they keep each other in position.
3. A contact as claimed in claim 1 or 2 in which the number of rings is two.
4. A contact as claimed in claim 1 or 2 in which the number of rings is three.
5. A contact as claimed in claim 1 or 2 in which the number of rings is four.
6. A contact as claimed in claim 1 or 2 in which the number of rings is five.
7. A contact as claimed in claim 1 or 2 in which the number of rings is six.
8. A contact as claimed in claim 1 or 2 in which the number of rings is seven.
9. A contact as claimed in any previous claim, wherein at least one of said rings is a split ring.
10. A contact as claimed in any previous claim, wherein at least one of said rings is larger than the other rings.
11. A contact as claimed in any previous claim, wherein the rings are cylindrical.
12. A contact as claimed in any previous claim, wherein the rings are hexagonal tubes.13. A contact as claimed in any previous claim, wherein the rings comprise one or more holes to facilitate the escape of gas during vacuum evacuation of the vacuum switching device.
13. A contact as claimed in any previous claim, wherein the rings are formed from flat metal strips.
14. A contact as claimed in any previous claim, wherein one or more of the rings is nested within one or more of the other rings.
15. A contact as claimed in claim 14, wherein the rings are concentrically packed within the enclosure.
16. A contact as claimed in any previous claim, wherein the rings are spiral springs.
17. A contact as claimed in any previous claim wherein the conductivity of the rings is lower than the conductivity of the cup-shaped support and/or the disc.
18. An axial field vacuum switching device comprising the contact as defined in any preceding claim.
19. An axial field vacuum switching device according to claim 14, wherein the axial field vacuum switching device is a vacuum interrupter.