GB2095475A

GB2095475A - Electric vacuum switch

Info

Publication number: GB2095475A
Application number: GB8208178A
Authority: GB
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 1981-03-20
Filing date: 1982-03-19
Publication date: 1982-09-29
Also published as: DE3111791A1; JPS57168436A

Abstract

A vacuum switch includes an evacuated tube (4) into which there passes a first current-conducting member (10) that is movable to make or break contact, in the tube, with a second current-conducting member (9), and drive means (2) are coupled to the first member (10) for bringing about such movement. Releasable abutment means (34) are arranged to come into effect when the first member (10) has been moved away from the second current-conducting member (9), and serve then to inhibit unwanted return of the first member towards the second (9). The abutment means may be in the form of a catch (34) or a toggle joint (54, Figure 2, not shown) which reaches its "dead centre" when the first member (10) has been fully moved away from the second member (9). <IMAGE>

Description

SPECIFICATION Vacuum switching devices for electrical circuitbreakers This invention relates to vacuum switching devices for electrical circuit-breakers.

German Offenlegungsschrift 2818905 describes a vacuum switching device including a switching tube, a driving apparatus for the switching tube and a container surrounding the switching tube and filled with an insulating gas. In this respect, German Offenlegungschrifts 2 439 381 and 1881 349, and British Patent Specification 1 086, 179, are also of interest. If the pressure of the insulating gas in such a device is made greater than the ambient atmospheric pressure, as is desirable for good insulation, then the closure force on elecrical contacts in the switching tube will become correspondingly increased. A circuit-breaking spring used conventionally to bring about separation of the contacts will accordingly need to be stronger, as compared with a case in which the vacuum switching tube is operated in air at normal atmospheric pressure.The use of such a stronger spring may necessitate strengthening of other parts of the driving apparatus of the vacuum switching device.

However, even if such a circuit-breaking spring lacks sufficientstength to maintain a desired circuitbreaking gap between the electrical contacts, it is found that such full separation can be brought about momentarily, when the driving apparatus is actuated to separate the contacts, by relaxation of a contactpressure spring which is compressed to apply pressure between the electrical contacts when they are closed together but is released upon such actuation of the driving apparatus. Thus, momentum imparted to components of the driving apparatus by the relaxing contact-pressure spring can bring about full separation of the contacts, momentarily, whereafter they would normally return to an only partially separated disposition, or may even be closed together again if the insulating gas pressure in the container is sufficiently high.

It is an object of the present invention to provide means for inhibiting partial (or possibly even complete) closure of the contacts, after attainment of full separation thereof. Any necessary increase in strength of the circuit-breaking spring can then be restricted, if desired, to that necessary to ensure that full separation of the contacts can normally be achieved momentarily, with the aid of momentum imparted to driving means of such a switching device substantially as described above, when the insulating gas pressure in the container is at the maximum prssure normally to be expected during use of the switching device.

According to the present invention there is provided a vacuum switching device, including an evacuated tube (4) into which there passes a first current-conducting member (10) which is movable, relative to the tube, from a first to a second disposition thereof to make contact in the tube with a second current-conducting member of the device, and drive means coupled to the first currentconducting member and operable to bring about such movement of that member, wherein the device includes releasable abutment means (34) arranged to come into effect, upon movement of the firstconducting member from its second disposition to its first disposition, to prevent return of the first member to its second disposition.

Thus an embodiment of the invention may include a locking device to prevent closing of contacts carried by the said current-conducting members, which device is automaically effective when the contacts are opened and is released by means of the driving apparatus when the contacts are to be closed. Such a locking device can be provided in the form of a reasonably inexpensive and simple auxiliary attachment which can extend the usefulness of a driving apparatus designed primarily to apply only comparatively small contact-opening forces.

The locking device in such an embodiment may comprise a mechnical abutment member, which arrives behind a lever of the driving apparatus when the fully separated position of the contacts is reached and which can be released when a switching-force accummulator of the driving apparatus is released to bring about closure of the contacts. Thus, release of the abutment member can, for example, take place by means of an electromagnet employed primarily to release a catch holding a switch-on spring, constituting the swiching-force accumulator, in its stressed state.

Reference will now be made, by way of example, to the accompanying drawing, in which: Figure 1 shows a diagrammatic partially-sectioned side elevation of a vacuum switching device elevation of a second vacuum switching device embodying the present invention, and, Figure 2 shows a diagrammatic partially-sectioned side elevation of a second vacuum switching device embodying the present invention.

The vacuum switching device shown in Figure 1 comprises a switching unit 1 and a driving apparatus 2. The switching unit 1 comprises an evacuated switching tube 4 mounted within a container 3 of some suitable shape, for example cylindrical or box-like. The switching tube 4 can be connected to external conductors by way of busings 5 and 6. The switching tube 4 is surrounded by an inslating gas (not air), for example SF6, contained in the container 3 at a pressure above atmospheric pressure, but can be a vacuum switching tube of some kind conventionally used for operation in free air.

The switching tube 4 contains a fixed currentconduction bolt, having an electrical contact 9, to which electrical connection can be made by way of the bushing 5. A moveable current-conducting bolt 10, having an electrical contact 8, passes into the tube 4 in a sealed manner and is connected with the upper bushing 6 by a flexible current lead 11.

A lever device 12 includes a shaft 13 which passes through a wall ofthe container 3 in a sealed manner.

A lever arm 14 is carried fixedly by the shaft 13, within the container 3, and its free end is coupled to the movable bolt 10. Externally of the container 3 the shaft 13 carries fixedly a second lever arm 15, which is connected to the driving apparatus 2 by way of a contact-pressure spring 20 and a coupling rod 21.

The driving apparatus is represented in a simplified manner. It comprises a switching drive unit having a cam 22, driven in a manner not shown, and a roller lever 23 which cooperates with the cam 22 and drives a shaft 24. The shaft carries a crank arm 25 which is hingedly linked to the coupling rod 21.

The shaft 24 can carry additional crank arms 25, corresponding to further vacuum switching tubes (not shown). A further crank arm 26, fixed to the shaft 24, is connected to a circuit-breaking spring 27.

Figure 1 shows the switching unit 1 in an opencircuit condition, in which the contacts 8 and 9 in the switching tube 4 are fully separated from one another. The shaft of the cam 22 is acted upon by a switching-force accumulator (not shown). Closure of the contacts 8 and 9 is brought about by energizing an actuating magnet 30, which withdraws a catch 31 from abutment with a lever arm 32 projecting from the shaft of the cam 22, thereby releasing the cam 22 to rotate in the direction of the arrow 33. The rotating cam acts on the roller lever 23 so as to turn the latter anti-clockwise. This produces movement of the shaft 24, the crank arm 25, the coupling rod 21 and the lever device 12 such that the bolt 10 is moved downwardly in the switching tube 4 until the contacts 8 and 9 are closed together.The desired contact force therebetween is produced by compressing the contact-pressure spring 20.

The pressure of the insulating gas contained in the container 3 tends to increase the pressure between the contacts 8 and 9. To return the device to the open-circuit condition, advantage is taken of dynamic forces associated with the opening movements of the contact 8 and the drive means connected therewith. These dynamic forces can enable full separation of the contacts 8 and 9, as shown in Figure 1, to be achieved even if the circuit-breaking spring 27 is not itself powerful enough to maintain the contact 8 in its fully opened position. Closing movement of the contact 8, following momentary attainment of full separation of the contacts, is prevented by means of a locking device comprising a releasable catch 34. This catch 34 is pivotally mounted in the driving apparatus 2 and engages behind the crank arm 26, carried by the shaft 24, towards the end of the contact-opening movement.

The resulting abutment between the catch 34 and the crank arm 26 serves to lock the crank arm 25 and the lever device 12 so as to prevent a return towards the closed-circuit condition.

Subsequently, when it is desired to close the contacts 8 and 9, the catch 34 can, at the same time as the magnet 30 is energized, be swung out of the way of the crank arm 26. Such release of the catch 34 is brought about by means of an auxiliary lever 35 which is pivotally mounted adjacent to the catch 31 and is connected to the catch 34 in a suitable manner, for example by a rod as indicated to 36.

It will accordingly be appreciated that the inclusion of the auxiliary lever 35, the catch 34, and a connecting rod therebetween, allows the circuitbreaking spring 27 and therewith other associated portions of the driving apparatus to have smaller dimensions than might otherwise be considered necessary.

The device may be designed so that, as illustrated in Figure 1, the normal open-circuit disposition of the components leaves a clearances between the end of the crank arm 26 and the adjacent abutment portion of the catch 34. This provides free lifting of the arm 26 to a small extent, but only as far as is consistent with the maintenance of a minimum permissible clearance between the contacts 8 and 9 in the open-circuit condition of the device. The circuitbreaking spring 27 is chosen to be of such a size that it can maintain the clearances, by balancing out the contact-closing force due to the pressure of that insulating gas in the container 3, when the pressure of that insulating gas is at the lowest value permitted during noraml use of the switching tube 4.In this way it is possible to ensure that the catch 34 normally remains unloaded, enabling it to be released easily by actuatinfg magnet 30 of smaller dimensions than might otherwise be necessary, despite fluctuations of the insulating gas pressure between predetermined acceptable limits.

In the embodiment shown in Figure 12, the vacuum switching device comprises a switching unit 40 and driving apparatus 41. As in the device of Figure 1, the switching unit 40 includes a container 56, and an upper bushing 42 aligned with an evacuated switching tube 43 and a lower bushing 44. A movable current-conducting bolt 45 which passes into the switching tube 43 is coupled to a lever apparatus 46 which can be operated by the driving apparatus 41 through the intermediary of the contact-pressure spring 47. The lever apparatus 46 comprises a bell-crank lever 50, one arm 51 of which is coupled to the movable current-conducting bolt 45 and the other arm 52 of which is connected by means of a coupling rod 53 to a lever 55 mounted fixedly on a shaft 54. The shaft 54 passes out of the container 56 in a sealed manner and is suitably coupled to the driving apparatus 41.

The components of the lever apparatus 46 are so arranged that, when the movable current-carrying bolt is in its open-circuit position substantially as illustrated, the coupling rod 53 and the lever 55 form a knee, ortoggle joint, approximately in its "dead centre" disposition. Accordingly, when the movable contact reaches its completely open position in the course of a circuit-breaking operation, then the aforesaid toggle joint reaches its "dead centre" disposition and thereupon forms a locking device which prevents a complete or even partial return to the closed position of the contact. Subsequent closure of the contacts can be brought about only by .means of the driving apparatus 41, operating by way of the shaft 54. In this embodiment a circuit-breaking spring, included in the driving apparatus 41 but not shown in Figure 2, can again be smaller than would otherwise be considered necessary, because dynamicforces (momentum) can assist in the attainment of the fully open disposition atwhich locking is brought about by means of the aforesaid toggle joint.

Claims

1. A vacuum switching device, including an evacuated tube (4) into which there passes a first current-conducting member (10) which is movable, relative to the tube, from a first to a second disposition thereof to make contact in the tube with a second current-conducting member of the device, and drive means coupled to the first currentconducting member and operable to bring about such movement of that member, wherein the device includes releasable abutment means (34) arranged to come into effect, upon movement of the first current-conducting member from its second disposition to its first disposition, to prevent return of the first member to its second disposition.

2. A device as claimed in claim 1, wherein the evacuated tube is mounted within a container for pressurized insulating gas which surrounds the tube when the device is in use.

3. A device as claimed in claim 1 or 2, wherein the drive means include a lever arm, and the abutment means comprise a releaseable catch arranged to come into effect by moving into the path of the said lever arm so as to prevent such return of the said first member.

4. A device as claimed in claim 3, wherein retention means are arranged to hold the said lever apart from the releasable catch by a small clearance, after the catch has come into effect, so as to facilitate release of that catch.

5. A device as claimed in claim 4, wherein the retention means comprise a spring of sufficient strength to maintain such a clearance, against the closing effect of ambient gas pressure urging the first current-conducting member towards its second disposition, for all values of such ambient pressure in a preselected operating range.

6. A device as claimed in claim 1 or 2, wherein the said drive means include a coupling arrangement which provides the said abutment means by acting as a toggle joint which attains a "dead centre" condition, when the first current-conducting member is moved to its said first disposition, and thereupon prevents unwanted return ofthefirst member towards its second disposition.

7. A device as claimed in any preceding claim, wherein the abutment means are automatically released upon actuation of the drive means to bring about such movement of the said first member.

8. A device as claimed in any preceding claim, wherein the said drive means include a switchingforce accumulator which is held in a stressed state when the first current-conducting member is in its said first disposition and can then be released to drive that member to its second disposition.

9. A vacuum switching device as claimed in claim 1, substantially as hereinbefore described with reference to Figure 1 or 2 of the accompanying drawing.