GB2154065A

GB2154065A - Vacuum switch

Info

Publication number: GB2154065A
Application number: GB08501898A
Authority: GB
Inventors: Roy Edward Voshall
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1984-02-02
Filing date: 1985-01-25
Publication date: 1985-08-29
Also published as: GB8501898D0; DE3501603A1

Abstract

A low voltage, high AC vacuum switch is provided by arcing shields 42,48 positioned in a vacuum chamber about two tapered surface arcing contacts 24,26 each having a depression 40 in a flat contacting surface 30,32. The arcing shields prevent deposition of electrically conductive material from the tapered surface contacts on walls of a ceramic housing 12 and on bellows 14,16 fixed to each end of the housing 12. <IMAGE>

Description

SPECIFICATION Low voltage, high alternating current vacuum switch using diaphragm bellows and internal shielding This invention relates to a vacuum switch, for low voltage high alternating current switching, applicable in the field of vacuum switches generally and is directed specifically to a low voltage, high alternating current diaphragm bellows vacuum switch.

The most relevant prior art known is that set forth in the following specification of U.S.

Patent Nos. 4,216,360 and 4,216,361.

Both of these are directed to and limited to DC switches. The present invention is a low voltage, high current, AC version of the prior art switches.

According to the present invention, a vacuum switch, for low voltage high alternating current switching, comprises an annular ceramic envelope, diaphragm bellows, said bellows being affixed at opposite ends of said envelope to said envelope, said envelope and said bellows defining a vacuum chamber, two electrodes disposed within said vacuum chamber and aligned vertically along the switch axis, one end of a stem member affixed to one of said electrodes, another end of said stem member extending through said bellows, said electrodes being in a relative movable relationship to each other, aligned contacting surfaces of said electrodes having a central flat portion and a tapered outer portion, whereby when said electrodes are moved into physical contact with each other said central flat portions are substantially in physical contact and said tapered outer portions are spaced from each other by said taper, the flat portion of each of said electrodes contacting surfaces having walls forming a cup shaped depression therein, and arc shields disposed within said vacuum chamber between said electrodes and said annular ceramic enveloped and between said electrodes and said diaphragm bellows.

Conveniently, said bellows being affixed at opposite ends of said envelope to said envelope, said envelope and said bellows defining a vacuum chamber, two electrodes disposed within said vacuum chamber and aligned vertically along the switch axis, one end of a stem member affixed to one of said electrodes, another end of said stem member extending through said bellows, said electrodes being in a relative movable relationship to each other, aligned contacting surfaces of said electrodes having a central flat portion and tapered outer portion, whereby when said electrodes are moved into physical contact with each other said central flat portions are in physical contact and said tapered outer portions are spaced apart from each other by reason of said taper, the flat portion of each of said electrodes contacting surfaces having walls forming a cup shaped depression therein, and are shields disposed within said vacuum chamber between said electrodes and said annular ceramic enveloped and between said electrodes and said diaphragm bellows.

The invention will now be described, by way of example, with reference to drawings in which; Figures 1 to 3 are side views of vacuum switches.

Fig. 1 shows a side view in partial crosssection of a low voltage, high alternating current, diaphragm bellows vaccum switch 10.

The switch 10 is comprised of a ceramic envelope 1 2 with diaphragm bellows 1 4 and 1 6 brazed to the ceramic envelope 1 2 at each end by a transition piece 1 8.

The diaphragm bellows 1 4 and 1 6 normally consist of stainless steel.

The bellows 1 4 and 1 6 are also brazed to electrode stems 20 and 22 respectively which are used to support a pair of relatively movable electrodes or contacts 24 and 26 respectively shown in their separated or open circuit position.

The electrodes 24 and 26 may consist of from 50% to 80%, by weight, copper and from 20% to 50%, by weight, chromium. In the alternative, the electrodes 24 and 26 may consist of 99.5%, by weight, copper and 0.5%, by weight, bismuth.

The electrodes 24 and 26 are tapered from a point A, which is an approximate projection of the stems 20 and 22, denoted by dotted line, onto front surfaces 30 and 32 respectively of electrodes 24 and 26, to their end portions 34 and 36 respectively.

The degree of taper ranges from 3 to 5" so that arcing which results from the electrodes being moved apart will occur away from the central portion 38 of the electrodes The electrodes 24 and 26 also each have a cup shaped depression 40 centrally disposed in their opposed front surfaces 30 and 32 so that initial arcing will occur off center and magnetic loop force will move the arc outward away from the center. The depth of the depression ranges from 1/16 inch to 1/8 inch and the width is from 2 inch to an inch.

The electrodes should have either spiral or petal cuts in them to ensure that the arc is moved magnetically.

The electrodes 24 and 26 are movable relative to each other. Usually the upper electrode 26 is a stationary contact suitably secured to stem 22 and the bottom electrode 24 is a movable contact joined through stem 20 to a conductive operating rod to cause movement.

When the electrodes 24 and 26 are separated there is an arcing gap formed therebetween. The gap in a switch of this type is about 3mm or 0.118 inch.

If the pressure in the interrupter is 10 - 3 to 10-2 torr and the electrode stroke is 3mm, the pressure time distance is 3 x 10-3 to 3 x 10-2mm torr which is on the left-hand side of the Paschen curve and the breakdown voltage would be much greater than several kV. In fact, with this pressure range and this geometry, only a vacuum type of breakdown should occur.

A first arc barrier shield 42 having a horizontal portion 44 and a vertical portion 46 is affixed to stem 20 of electrode 24.

A second arc barrier shield 48 having a horizontal portion 50 and a vertical portion 52 is affixed to stem 22 of electrode 26.

The arc barrier shields are at the same electrical potential as the stem and electrodes to which they are affixed.

The arc barrier shields serve to prevent any vaporized metal from the electrodes being deposited on surfaces within the switch, especially the ceramic envelope 1 2 and diaphragm bellows 14 and 16, when the electrodes are moved apart or closed. The barrier shields also serve to prevent the arc itself from damaging any portion of the switch.

Vertical portion 46 of arc shield 42 extends upward from horizontal portion 44 to a point 51 which is at least in a horizontal plane with point 52 on electrode 26 when the electrodes 24 and 26 are separated and vertical portion 52 of arc shield 48 extends downward from horizontal portion 50 to a point 54 which is at least in a horizontal ptane with point 56 on electrode 24 when the electrodes 24 and 26 are separated.

As can be seen in Fig. 1, the iength of each of the vertical portions of the arc shields overlap thus any arc moving horizontally from the electrodes must pass through a circuitous "S" -shaped path and will be extinguished before it can reach the ceramic envelope 1 2 or either of the bellows 14 or 16.

The distance from edge 34 of electrode 24 to vertical portion 46 of arc shield 42 is equal to or greater than twice the stroke distance, i.e., the distance or gap between the two electrodes when fully separated.

The distance between vertical portion 46 of arc shield 42 and vertical portion 52 of arc shield 40 is equal to or greater than 1.5 times the gap distance.

The spacing between the electrodes and the vertical portions of the arc shields ensures that arcing will occur only between the electrodes 24 and 26 and not between the arc shields when the electrodes are either separated or closed.

Fig. 2 shows another low voltage, high AC current diaphgram bellows vacuum switch 110 illustrating another embodiment of the present invention.

In the switch 110 the ceramic envelope, bellows, electrodes and electrode stems are the same as described in the discussion of Fig. 1 and all similar parts are denoted by the same numerical designation used in discussing Fig. 1.

In the switch 110 of Fig. 2, there is a first arc shield 60 brazed to ceramic-metal joint 62 and a second arc shield 64 brazed to ceramicmetal joint 66.

The arc shields 60 and 64 extend from the respective ceramic-metal joints to a point 68 and 70 respectively which points are located approximately one-half the distance between vertical projections of end portions 36 and 34 of electrodes 26 and 24 denoted by a dotted line, and the respective stems 22 and 20.

The arc shields 60 and 64 prevent any metal vapors or particles from the electrodes 24 and 26, during arcing, from damaging or depositing on the bellows members 1 4 and 16.

A third arc shield 72 is brazed to shield 60 and extends vertically downward to a point 74 which is at least horizontally aligned with bottom surface 76 of electrode 24 when the electrodes 24 and 26 are fully gapped.

The arc shield 72 protects the ceramic envelope 1 2 against arc damage or the deposit of metal vapors or particles thereon.

The switches of Figs. 1 and 2 are capable of handling currents in excess of 7KA.

Fig. 3 shows switch 210 which is a low voltage, high AC current diaphragm bellows vacuum switch illustrating another embodiment of the present invention.

The switch of Fig. 3 is capable of handling currents up to 7KA.

In the embodiment of switch 210 the ceramic envelope, bellows, electrodes and electrode stems are the same as described in the discussion of Fig. 1 and all similar parts are denoted by the same numerical designation used in discussing Fig. 1.

In the switch 210 of Fig. 3 there is a first arc shield 80 affixed to electrode stem 22.

The shield 80 extends horizontally from the stem 22 for a distance approximately equal to the length of the electrode 26.

The arc shield 80 protects the bellows 1 6 from the arc and from metal vapor and particles.

A second arc shield 82 is affixed to stem 20. The shield 82 has a horizontal portion 84 and a vertical portion 86.

The horizontal portion 84 extends from the stem 20 a distance sufficient to ensure that the vertical portion 86, which extends vertically and perpendicular from end 88 of the horizontal portion 84, is at least twice the gap distance from edges 34 and 36 of electrodes 24 and 26.

The vertical portion 86 of shield 82 extends perpendicularly upward from the horizontal portion 84 of shield 82 for a distance such that its edge portion 90 extends at least to the midpoint 94 of the electrode 26 when the electrodes are fully gapped or open.

The horizontal portion 84 of shield 82 protects the bellows 14 and the vertical portion 86 protects the ceramic envelope 1 2.

This configuration of shielding is sufficient for switches in which the AC current is 7KA or less.

Claims

1. A vacuum switch, for low voltage high alternating current switching, comprising an annular ceramic envelope, diaphragm bellows, said bellows being affixed at opposite ends of said envelope to said envelope, said envelope and said bellows defining a vacuum chamber, two electrodes disposed within said vacuum chamber and aligned vertically along the switch axis, one end of a stem member affixed to one of said electrodes, another end of said stem member extending through said bellows, said electrodes being in a relative movable relationship to each other, aligned contacting surfaces of said electrodes having a central flat portion and a tapered outer portion, whereby when said electrodes are moved into physical contact with each other said central flat portions are substantially in physical contact and said tapered outer portions are spaced from each other by said taper, the flat portion of each said electrodes contacting surfaces having walls forming a cup shaped depression therein, and arc shields disposed within said vacuum chamber between said electrodes and said annular ceramic envelope and between said electrodes and said diaphragm bellows.

2. A switch as claimed in claim 1 in which a first arc shield is comprised substantially of a horizontal portion and a vertical portion, said vertical portion extending substantially perpendicular from said horizontal portion.

3. A switch as claimed in claim 2 in which said horizontal portion of said arc shield is affixed to the stem of one of the electrodes and the vertical portion is disposed annularly about the electrodes, said vertical portion being spaced horizontally from the electrode a distance equal to at least twice the gap distance of the switch.

4. A switch as claimed in claim 3 in which a second arc shield comprises substantially a horizontal portion and a vertical portion and in which the horizontal portion is affixed to the stem of the other electrode and the vertical portion is disposed annularly about the electrodes and between the vertical portion of the first arc shield and the ceramic envelope and the vertical portion of the second arc shield is spaced apart from the vertical portion of the first arc shield a horizontal distance equal to at least 1.5 times the gap distance of the switch.

5. A switch as claimed in claim 4 wherein the vertical portions of the first and second arc shields are arranged to overlap in the vertical direction.

6. A switch as claimed in any one of claims 1 to 5 in which said horizontal portion having one end affixed to a stem of one electrode, the vertical portion being affixed to the other end of the horizontal portion and extending vertically from said horizontal portion, and a second arc shield extending horizontally from and affixed to the other electrode stem.

7. A switch as claimed in any one of claims 1 to 5 in which a first and a second arc shield are affixed to joints between said ceramic envelope and said bellows, said arc shields extending in a horizontal direction toward said electrodes and another arc shield affixed to and extending from one of said either first or second arc shields in a vertical direction.

8. A vacuum switch, for low voltage high alternate current switching, constructed and adapted for use substantially as hereinbefore described and illustrated with reference to the accompanying drawings.