GB1573415A - Vacuum switch - Google Patents

Description

(54) VACUUM SWITCH (71) We, WESTINGHOUSE ELEC TRIC CORPORATION, a corporation organised and existing under the laws of the state of Pennsvlvania, United States of America. residing at Westinghouse Building, Gateway Center. Pittsburgh, Pennsylvania 15222. United States of America. do herebv declare the invention, for which we pray that a patent may be granted to us. and the method by which it is to be performed, to be particularly described in and by the following statement: - This invention relates to a vacuum switch.

which is compact and rugged, and is adapted for use in severe environments. such as in electrochemical processing plants.

Vacuum switches are well known and comprise an insulating body through which movable contacts are sealed. At least one of the contacts or contact supports have sorne sort of flexible member between the contact and the sealed switch body to permit contact movement.

Such switches are suitable for use in chlorine plants. The switch is connected between high current carrying buses which supply current through a chemical solution.

The buses pass through numerous chemical solution cells or tubs. and from time to time it is necessary to bypass a particular cell without interrupting the entire operation.

The switch permits shorting out the bus at selected location to permit maintenance operations.

It is important that opposed ends of the vacuum switch be easily connectable to the bus bars. with a large contact surface area to handle several thousand amperes of current.

The typical electrochemical plant application means that the switch is used in a highly corrosive environment. The flexible member used to permit contact movement must be able to withstand this corrosive environment. The flexible member must permit the requisite axial movement of the contacts to permit bringing the contacts together to their shorting or closed position. The flexible member should also permit some flexibility at an angle to the axis to facilitate breaking the contacts apart when opening them, and also to facilitate mounting of the switch between the bus bars.

According to the present invention a vacuum switch comprises an insulative body ring, a pair of end annular members, the outer perimeter of each annular member sealed to respective opposed ends of the insulative body ring, the annular members being disposed in a direction normal to the longitudinal axis of the body ring, a pair of cylindrical conductive support posts aligned along the insulative ring longitudinal axis, which posts pass through and are circumferentially sealed to the inner perimeter of the respective annular members through which the post passes, planar contacts disposed at each inwardly extending end of the support posts, which contacts are spaced apart within the evacuated switch when the switch is open. and which contacts are brought into contact by axial relative movement of the support posts, each annular member having a plurality of annular flexible corrugations and constituting a seal member formed therein, and that the annular flexible corrugated members being thin members of metal for axially flexing the annular seal member and permitting movement of the support posts to effect the opening and dosing operation of the switch.

The invention will now be described, by way of example. with reference to the only figure in a side elevational view partly in section of a vacuum shorting switch. The drawing depicts a switch 10 comprising the insulative ceramic body ring 12 which electrically isolates one end of the switch from the other. The opposed end surfaces of the insulative body ring are metallized, and a pair of thin. flexible, annular members 14 are sealed to the metallized end surfaces.

The annular members 14 and 12 mil thick "Monel" metal members which have a plurality of annular corrugations 16 formed therein. By way of example, the inner diameter of annular member 14 is about 2.375 inches and the outer diameter is 3.750.

The annular corrugations are about 0.06 inch deep. An outer perimiter portion 18 of the flexible annular member 14 is brazed to the metallized coating on the insulating body ring. An inner perimeter portion 20 of the annular flexible member 14 is brazed to a cylindrical conductive support post 22 which passes through the flexible annular member 14. The centrally disposed insulative body ring 12, the flexible annular members 14 and the cylindrical conductive support posts comprise a hermetically sealed envelope of the vacuum switch. The switch is assembled with rings of brazing material disposed between the seal surfaces, and the switch is placed in a vacuum furnace. The switch is evacuated and the temperature is raised above the brazing material melting point and then lowered to effect the hermetic seal.

Non-weld material contact discs 24 are disposed on the interior end surfaces of the support posts 22. The support posts are typically copper. and the contact discs are a copper-bismuth conventional non-weldable material. Planar mounting plates 26, having support post receiving apertures therethrough are brazed to the support posts proximate the exterior extending ends of the support posts. The support posts protrude a small distance from the planar mounting plates, for example about 0.02 inch. A plurality of threaded apertures (not shown) are provided in corners of the mounting Plates 26. Bolts which pass through the bus bar to which the switch is to be connected, are threaded into these threaded apertures to fasten the mounting plate to the bus bar.

It is the protruding support post which actually makes electrical contact with the bus bar. The support post is preferably of oxygen free high conductivity copper which is in a soft state to ensure mating of the end surface with the bus bar for good electrical contact.

An elastomeric, insulative member 28 is tightly fitted over the side walls of the mounting plates to effectively shield the ceramic body ring and the seal areas of the switch, particular the seals of the flexible annular members, from the corrosive en vironment of the processing plant.

An axial force is applied to the support posts to either move them together and close the contacts in mating engagement, or to move them apart. The corrugated flexible annular members provide the requisite flexi bility for such axial movement. The flexible annular members also permit some slight cocking of the support posts and contact surfaces to facilitate breaking welds which may form between the contacts. The fact that the annular members extend generally normal to the switch axis which is the direction of contact movement keeps this off axis cocking to a minimum but still permits it for breaking welds. With prior art bellows sealed switches it was possible for the contact surface to engage at a considerable angle, which is not desired, since such a premature small area of contact could be damaged by the large current density which would be present. High localized currents flowing in a small contact area could vaporize that portion of the contact damaging the contact and perhaps shorting the switch along the insulating ring.

The use of flexible annular members at both ends of the switch provides twice the travel for a given drive force. The annular corrugations reduce the axial force requirements and stresses while providing a stiff member in the transverse direction, i.e. the direction normal to the switch travel axis.

This reduces the need for positive alignment of the contact means.

A preferred method of fabrication of the vacuum switch of the present invention is to provide a small diameter chamber in the central inward terminal end of one support post, and to include a small titanium ribbon within this chamber. A small aligned aperture is provided through the contact disc which is brazed to the support post during sealing. The entire switch is placed in a vacuum furnace, and the air in the furnace is displaced with nitrogen, and the nitrogen then displaced with hydrogen. The hydrogen continues to flow through the system and enters the switch because the rings of brazing material separate the parts enough for gas to enter and be removed from the interior of the switch.The furnace is activated and as the system heats up the titanium ribbon absorbs a significant amount of hydrogen as the titanium passes through its gettering temperature range.

Thereafter, as the temperature is increased the titanium releases hydrogen resulting in a further purge of the interior of the switch so that essentially only hydrogen remains. The braze rings then melt and effectively seal the switch. The furnace temperature is then reduced and the hydrogen within the switch is again effectively gettered by the titanium to produce the resultant low vacuum in the sealed switch.

It has been the practice to braze a sintered thin disc of copper-bismuth non-weld contact material to the end of the copper support post. One problem is that the brazing material has a tendency to infiltrate into this thin contact material disc dimi nishing its non-weld characteristic. It has been discovered that providing a thin barrier layer on one side of the copper-bismuth disc will prevent infiltration of the brazing material into the contact. Such a barrier layer can be a thin deposit of nickel or copper of about a mil thickness, which can be vacuum or electro-deposited.

A preferred barrier is provided by pressing the admixed copper and bismuth powder upon a copper foil disc which is about 1-10 mils thick. This pressed compact on the foil can then be sintered as normally, and thereafter brazed to the support post during final sealing of the switch. The thin copper foil barrier layer prevents infiltration of the braze into the copper-bismuth contact.

WHAT WE CLAIM IS: 1. A vacuum switch comprising an insulative body ring, a pair of end annular members, the outer perimeter of each annular member sealed to respective opposed ends of the insulative body ring, the annular members being disposed in a direction normal to the longitudinal axis of the body ring, a pair of cylindrical conductive support posts aligned along the insulative ring longitudinal axis, which posts pass through and are circumferentially sealed to the inner perimeter of the respective annular members through which the post passes, planar contacts disposed at each inwardly extending end of the support posts, which contacts are spaced apart within the evacuated switch when the switch is open, and which contacts are brought into contact by axial relative movement of the support posts, each annular member having a plurality of annular flexible corrugations and constituting a seal member formed therein, the annular flexible corrugated members being thin members of metal for axially flexing the annular seal member and permitting movement of the support posts to effect the opening and closing operation of the switch.

2. A switch as claimed in claim 1, wherein a metallized coating is provided on the opposed ends of the insulative body ring and this metallized coating is brazed to the outer perimeter of the annular members.

3. A switch as claimed in claim 2, wherein a planar mounting plate having a centralized aperture therethrough is brazed on the end of each of the support posts, with the respective support posts extending through the mounting plate aperture.

4. A switch as claimed in claim 3, wherein an elastomeric, insulative member is tightly fitted over and between the sides of the planar mounting plates to shield the flexible annular members and the insulative body ring.

5. A switch as claimed in any of claims 1 to 4, in which each contact comprises a disc of sintered powdered contact material with a thin barrier-material layer disposed on one side of the disc.

6. A switch as claimed in claim 5, wherein the sintered powdered contact comprises a copper-bismuth mixture, and the barrier material layer is nickel or copper.

7. A method of manufacturing a vacuum switch as claimed in any of claims 1 to 6, including the steps of assembling an unsealed switch and including a titanium member within the switch, disposing the unsealed switch in a closed system and purging the system and the switch with inert gas, followed by purging the system with hydrogen gas, heating the switch within the hydrogen containing system whereby the titanium will initially getter hydrogen, with the heating continued above the titanium gettering temperature and until the brazing material constituting the seals are formed sealing the switch, and lowering the temperature of the switch, solidifying the brazing material of each seal, whereby the titanium getters the hydrogen gas within the switch to produce a high vacuum within the switch at ambient temperature.

8. A vacuum switch, substantially as hereinbefore described with reference to the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (8)

**WARNING** start of CLMS field may overlap end of DESC **. nishing its non-weld characteristic. It has been discovered that providing a thin barrier layer on one side of the copper-bismuth disc will prevent infiltration of the brazing material into the contact. Such a barrier layer can be a thin deposit of nickel or copper of about a mil thickness, which can be vacuum or electro-deposited. A preferred barrier is provided by pressing the admixed copper and bismuth powder upon a copper foil disc which is about 1-10 mils thick. This pressed compact on the foil can then be sintered as normally, and thereafter brazed to the support post during final sealing of the switch. The thin copper foil barrier layer prevents infiltration of the braze into the copper-bismuth contact. WHAT WE CLAIM IS:

1. A vacuum switch comprising an insulative body ring, a pair of end annular members, the outer perimeter of each annular member sealed to respective opposed ends of the insulative body ring, the annular members being disposed in a direction normal to the longitudinal axis of the body ring, a pair of cylindrical conductive support posts aligned along the insulative ring longitudinal axis, which posts pass through and are circumferentially sealed to the inner perimeter of the respective annular members through which the post passes, planar contacts disposed at each inwardly extending end of the support posts, which contacts are spaced apart within the evacuated switch when the switch is open, and which contacts are brought into contact by axial relative movement of the support posts, each annular member having a plurality of annular flexible corrugations and constituting a seal member formed therein, the annular flexible corrugated members being thin members of metal for axially flexing the annular seal member and permitting movement of the support posts to effect the opening and closing operation of the switch.

2. A switch as claimed in claim 1, wherein a metallized coating is provided on the opposed ends of the insulative body ring and this metallized coating is brazed to the outer perimeter of the annular members.

3. A switch as claimed in claim 2, wherein a planar mounting plate having a centralized aperture therethrough is brazed on the end of each of the support posts, with the respective support posts extending through the mounting plate aperture.

4. A switch as claimed in claim 3, wherein an elastomeric, insulative member is tightly fitted over and between the sides of the planar mounting plates to shield the flexible annular members and the insulative body ring.

5. A switch as claimed in any of claims 1 to 4, in which each contact comprises a disc of sintered powdered contact material with a thin barrier-material layer disposed on one side of the disc.

6. A switch as claimed in claim 5, wherein the sintered powdered contact comprises a copper-bismuth mixture, and the barrier material layer is nickel or copper.

7. A method of manufacturing a vacuum switch as claimed in any of claims 1 to 6, including the steps of assembling an unsealed switch and including a titanium member within the switch, disposing the unsealed switch in a closed system and purging the system and the switch with inert gas, followed by purging the system with hydrogen gas, heating the switch within the hydrogen containing system whereby the titanium will initially getter hydrogen, with the heating continued above the titanium gettering temperature and until the brazing material constituting the seals are formed sealing the switch, and lowering the temperature of the switch, solidifying the brazing material of each seal, whereby the titanium getters the hydrogen gas within the switch to produce a high vacuum within the switch at ambient temperature.

8. A vacuum switch, substantially as hereinbefore described with reference to the accompanying drawings.