GB2508623A

GB2508623A - Evacuation and sealing of vacuum switches

Info

Publication number: GB2508623A
Application number: GB1221902.8A
Authority: GB
Inventors: Leslie Thomas Falkingham
Original assignee: VACUUM INTERRUPTERS Ltd
Current assignee: VACUUM INTERRUPTERS Ltd
Priority date: 2012-12-05
Filing date: 2012-12-05
Publication date: 2014-06-11
Also published as: GB2512161A; GB201321317D0

Abstract

Vacuum switching or similar devices are loaded and sealed off in a vacuum furnace with their axes horizontal rather than in a vertical orientation, to allow more efficient use of a vacuum furnaces. The vacuum switch comprises an evacuated envelope; an insulating component; fixed and moving electrodes that mechanically engage to perform switching; and a venting arrangement or pumping port which allows the device to be vented and sealed in a vacuum furnace while the device is laid with its axis in a horizontal orientation. The pumping port can be attached to an end cap (fig 4), an electrode (fig 7) or an insulator (fig 8). The pumping port can comprise a recess having holes to allow gases to evacuate the device and braze to fill the holes; a separate part having holes that are sealed by braze; or a plug (fig 6) that fits into a hole and is sealed by braze.

Description

Description:

This invention relates to improvements in vacuum switching devices, which may include for example vacuum interrupters and vacuum switches.

A typical design ofvacum switching device is shown in figure 1. Vacuum switching devices generally consist of an evacuated envelope that includes an insulating component (a) and end caps (b) together with a fixed electrode (c) and a moving electrode (d) which are designed to engage and disengage mechanically to perform the switching function. This movement is permitted without breaking the seal of the evacuated envelope normally by means of a beflows or diaphragm arrangement (e).

Vacuum switching devices that are designed to switch large culTents have been produced for many years. A number of different designs have been used. In manufacture nowadays the devices are generally assembled by brazing inside a vacuum furnace. As weB as fixing the components of the devices together, the brazing seals the devices against loss of vacuum. Usually, as shown in Figure 2, a number of devices (f) are loaded at one time into the hot zone (g) of a vacuum furnace (h). The devices are presently loaded into the furnace with the axes of the devices vertical, which allows for the brazing of components to be assisted by gravity and is extremely reliable.

The preferred type of vacuum furnace has a cylindrical vacuum container and is oriented with its cylinder axis horizontal (Figure 2) due to constructional limitations and to simplify the loading of the furnace in a clean room. Such a furnace has a hot zone that is naturally longer than high. Vacuum switching devices are generally considerably longer than their diameter, but for the manufacture of relatively small devices a large number can be fitted into the furnace at one time as illustrated in figure 2. 1-lowever there is a growing need for larger devices, to be manufactured in smaller quantities. If one or more larger devices are to fit with their axes vertical in the furnace, the furnace chosen must have a hot zone higher than the length of these larger devices. This can necessitate the use of a large and more expensive furnace. If the devices could be laid horizontally in the furnace as shown in figure 3, and sealed off in that position, this problem would be avoided.

Another advantage of horizontal loading applies to smaller devices. For these there may be loading inefficiency with the axes of the devices vertical in that unless the height of the furnace hot zone is close to an even multiple of the length of the devices plus necessary jigs arid stands, then there is a significant part of the hot zone which cannot be used and so is wasted. Horizontal positioning of the devices may enable more to be loaded into the furnace at a time.

The present invention allows the devices to be sealed against loss of vacuum while in the horizontal position. The invention may be applied to the design of vacuum switching devices over a wide range of sizes and geometries.

According to the invention a vacuum switching device is designed so that there is a venting alTangement, referred to as a pumping port, which is able to work when the device is laid with its axis in a horizontal orientation. The pumping port consists of a feature with one or more venting holes designed to be sealed by braze material when it melts. A quantity of suitable braze material is placed in or on the pumping port. The port and braze material are sized arid arranged so as to allow escaping gas to pass by the braze material before it is melted.

The pumping port forms part of the enclosure of the vacuum switching device, and may be located on the insulator (a), end caps (b), or the stems (c or d) or any other suitable place. After one or a number of vacuum switching devices have been loaded into a vacuum furnace the furnace is evacuated and during this process the devices evacuate naturally into the furnace by means of the pumping ports. When the temperature is sufficiently high the braze material in or on a pumping port melts and the flow of braze material fills or covers the venting holes thereby sealing the vacuum switching device. Once the furnace cools the brazing material solidifies, forming a permanent vacuum seal.

It is clear that the invention could be implemented in many different ways, provided that the pumping port is oriented so that the sealing part is sufficiently horizontal as to allow the flow of braze material to effectively seal the venting hole or holes. It will be appreciated that in many designs the axis of the pumping port does not need to be exactly vertical, indeed almost any orientation above horizontal may allow the invention to work correctly.

According to one implementation of the invention (figure 4) the pumping port consists of an indent or recess (j) in the material of an end cap incorporating one or more holes together with braze material (k). In a second implementation (figure 5) the pumping port may be a plug with holes (I) fixed in an aperture in an end cap. In a third implementation (figure 6) the plug (m) has no holes and sealing is performed by sealing the plug to an end cap aperture using braze material (k) formed to allow escape of gas before it melts.

In other implementations the pumping port may be on the rod part of an electrode. In a fourth implementation (figure 7) the pumping port consists of a tunnel (n) through one of the electrode rods which connects to the interior of the device together with a hole (o) which connects from the tunnel to the outside.

In a fifth implementation (figure 8) the pumping port consists of a sloping tunnel (p) connecting the inside of the device with the outside and the braze material (1k) is shaped and placed so as to allow the gases to pass it freely. The tunnel is designed with a feature (q) which when the braze material melts allows the braze material to seal the tunnel.

Any of these implementations could also bc appfled in the insulating component (a).

Claims

Claims: 1. A vacuum switching device consisting of an evacuated envelope which indudes an insulating component, a fixed electrode and a moving electrode which are designed to engage and disengage mechanically to perform the switching function and which incorporates a venting alTangement. referred to as a pumping port. which is designed to allow the device to be vented and then sealed in a vacuum furnace when the device is laid with its axis in a generally horizontal onentation.
2. A vacuum switching device as described in Claim I whereby the pumping port is attached to or part of one or more end caps.
3. A vacuum switching device as described in Claim I whereby the pumping port is attached to or part of one or more electrodes.
4. A vacuum switching device as described in Claim I whereby the pumping port is attached to or part of one or more insulators.
5. A vacuum switching device as described in Claim 1, 2, 3 or 4 whereby the pumping port consists of an indentation or recess in the suitace of the component said indentation or recess having one or more holes to allow gases to evacuate the vacuum switching device and which is designed to allow braze material to seal the holes.
6. A vacuum switching device as described in Claim 1. 2, 3 or 4 whereby the pumping port consists of separate part which can be sealed to the surface of the component said part having one or more holes to allow gases to evacuate the vacuum switching device and which is designed to allow braze material to seal the holes.
7. A vacuum switching device as described in Claim 1. 2, 3 or 4 whereby the pumping port consists of a plug which fits into a hole in the surface of the component and which is sealed by means of braze material.
8. A vacuum switching device as described in Claim 1, 2, 3 or 4 whereby the pumping port consists a feature in the component having one or more holes to allow gases to evacuate the vacuum switching device and which is designed to allow braze material to seal the holes.