GB2512161A

GB2512161A - Improvements in the manufacture of vacuum switching devices

Info

Publication number: GB2512161A
Application number: GB1321317.8A
Authority: GB
Inventors: Leslie Thomas Falkingham
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 2012-12-05
Filing date: 2013-12-03
Publication date: 2014-09-24
Also published as: GB201321317D0; GB2508623A

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 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 (figure 4), an electrode (figure 7) or an insulator (figure 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 (figure 6) that fits into a hole and is sealed by braze. The pumping port may also employ the principle of a U-bend or water trap (figures 9 & 10), whereby a passageway that dips down then up is filled by melted braze, sealing it against the passage of gases.

Description

Description:

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

A typical design of vacuum switching device is shown in figure L 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 evacuatcd envelope normally by means of a heflows 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.

The devices need to he made with a vacuum inside, and in manufacture nowadays they are generally assembled hy brazing inside a vacuum furnace. Assembled devices include braze material set in place, and the heat of the furnace causes the braze to run.

Before the furnace reaches brazing temperature, gases vent from the devices into the furnace and are pumped away. As well as fixing the components of the devices together, the brazing seals off the devices with vacuum inside.

Usually, as shown in Figure 2, a number of devices (f) are loaded at one time into (he hot zone (g) of a vacu ni furnace (h). The devices are presently always 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.

Vacuum furnaces are very expensive and the cycle time for pumping and brazing is long, so it is important to he ahe to load as many devices as possilie into a furnace of given size.

Due to constructional limitations and to simplify the loading and operation of the furnace in a clean room, the preferred type of vacuum furnace has a cylindrical vacuum container and is oriented with its cylinder axis horizontal (Figure 2). Such a furnace has a hot zone that is naturally thnger 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 with their axes vertical, as illustrated in figure 2. However there is a growing need for larger devices, to be manufactured in smaller quantities. If one or more larger devices are to lit with their axes vertical in the furnace, (he lurnace chosen will need a hot tone higher than the length of these larger devices. This can necessitate the use of a larger 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.

Horizontal loading could a'so sometimes he of advantage with sma'ler deviccs. For thcse there may he loading inefficiency with the axes of the devices vertical in that unless the height of the furnace hot zone is just a little more than a multiple of the length of the devices plus necessary jigs and stands, there is a significant part of the hot zone which cannot be used and so is wasted. Horizontal positioning of the devices may in some cases enable more devices to be loaded into the furnace at a time.

Unlèrtunately die arrangements made in present designs to allow gases to vent from a device into the vacuum furnace, and to enable subsequent seal-off to occur, will not work when the devices are laid horizontally.

According to the invention a vacuum switching device is designed so that there is a venting arrangement which is able to work when the device is laid with its axis in a horizontal orientation. The venting arrangement may be referred to as a pumping port.

The invention may be applied to the design of vacuum switching devices over a wide range of sizes and geometries. Pumping ports in the prior art are located on one of the end caps of (he device. The pumping port in the invention may be located on the insulator (a). end caps (b). or the stems (c) or d) or any other suitable place.

The invention could he impkmented 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.

A pumping port consists of a feature with one or more venting holes designed to be sealed by braze material when it melts. A suitable quantity of braze material is placed so that when the furnace reaches the right temperature the braze will flow under gravity and/or surface tension to seal the pumping port. The pumping port and braie material are sized and arranged so as to allow escaping gas to pass by the braze material before it is melted. 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 vent naturally into the furnace by means of the pumping ports. When the temperature is sufficiently high the braze nrntcrial 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.

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 (rn) has no holes and scaling 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 he on the rod part of an electrode. In a fourth implementation (figure 7) the pumping port consists of a tunnel (n) passing part way through one of the electrode rods and connecting 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 (k) 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.

In another class of pumping ports the principle of the U-bend or water trap is applied.

A passage that dips down and up again can be sealed against the passage of gases by filling die bottom of the bend with liquid to a level at which it blocks a part of the passage. In this aspect of the invention the liquid solidifies in position. In the implementations of figures 4 to 8. the hole sizes must he sufficiently small that they can retain molten braze by virtue of surface tension; the U-bend does not have this limitation and may be of any size, thus allowing more rapid venting of gases. Figure 9 shows an implementation in which holes drilled in the stem of the electrode from the vacuum side and the air side meet to provide a complete channel. A jig such as a small funnel (not shown) placed above one of the channel openings may he required to allow sufficient braze material (r) to flow into and block the bottom of the channel.

Figure 10 shows a cross section through a second implementation in which a horizontal slot (s) is formed on an end plate, and an L section of metal is attached to the end plate to form a trough (t) whose lip is substantially level with the bottom of the slot. A second L section (u) is attached to the end plate in such a way as to make a barrier reaching down to below the kvel of the lips of the trough. Sufficient braze is provided to fill thc trough to just above the bottom of thc barrier. Many other implementations of the U-bend principle niay be envisaged and will be obvious to one skilled in the art.

Claims

Claims: 1. A vacuum switching device consisting of an evacuated envelope which indudes an insulating component. a lixed electrode and a moving electrode which are designed to engage and disengage mechanically to perform the switching function and which incorporates a venting arrangement. 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 thc pumping port is attached to or part of one or more end caps.
3. A vacuum switching device as described in Claim 1 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 attachcd 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 surface 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 a 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 hy 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 device 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.
9. A vacuum switching device as described in Claim 1, 2, 3 or 4 whereby the pumping port consists of a passage that dips down and up and is formed so that it can be closed by filling with sufficient braze material.
10. A vacuum switching device as described in Claim 1. 2. 3 or 4 whereby the pumping port is formed as revealed in the description and any of figures 4 to 10.