US3026394A - Vacuumized electric switch - Google Patents

Description

March 20, 1962 J. E. JENNINGS VACUUMIZED ELECTRIC SWITCH Filed Nov. l0, 1959 R. m 6\.\ ll 'l E 2 il V W. 2 2 /v/ 3 4 6 a/ n Q L l, ,/0 l 7 n E: u. .n ,v .d M l ,E 8 J 44 :E 2 m M y C 2 IW\ n 7 i 9i ll il 8/ 4 6 2 2( W miki a Y IIJ T1211 Unit@ States My invention relates to vacuum switches and especially to such switches of large diameter and very large capacity.

One of the principal objects of the invention is the provision of a vacuumized switch having an envelope large enough to hold the heavyl conductive structure and contacts required for carrying currents upto 10,000 amperes or more.

With the development and use of'electric power, there has been an increasing demand for larger and larger vacnum switches to handle the increasing current loads. Expanding the diameter and capacity of vacuum switches has been severely hampered by the inherent weakness of the metal-to-glass or conventional Housekeepers seal. Any increase in size of a vacuumized shell or envelope results in a directly proportional increase in total pressure exerted by the atmosphere on all exposed surfaces of the envelope; and on an eight inch generally cylindrical evacuated envelope, the pressure tending to crush in each end amounts `to more than 700 lbs. vThis is greatly in excess of pressures which can be borne by switches having conventional metal-toglass unions or seals.

In addition to stresses imposed by atmospheric pressure, the conventional seal must carry stresses imposed by the Weight, sometimes considerable, of operative parts mounted on the ends, and also, the impact shock of closing contacts and the outward jerk of the opening contacts.

-A primary object of my invention therefore is to pro- .vide means whereby a large vacuumized nonconductive cylindrical shell can be closedl hermetically at its ends, and possess strength amply sufcient to carry the heavy loads imposed by its size.

Because of the excellence of the conventional metal-toglass seal under ideal conditions of light loading, it also lis an important object of my invention to utilize the metalto-glass seal in cooperative relation'with a heavy load bearing structure so that the metal-to-glass joint performs its primary function of hermetic sealing, but is relieved of destructive pressures, torsions and other stresses, which tend to cause failure.

Because of the high cost of electrical implements of this character, another object of my invention is the provision of a vacuumized envelope which can readily be opened for replacement or repair, then resealed yand exhaustedV for further service.

Another object of my invention is the provision of an hermetic sealing structure for the ends of an evacuated non-conductive shell in which atmospheric pressure is utilized as `an aid to rigidly secure the ends in permanent assembly.

Since the cost of labor, measured in terms of the time required to produce a consumer product, is an important factor in determining the cost of the item to consumers, another object of the invention is to provide a switch structure in which fabrication and assembly of the parts is susceptible -to mass production techniques.

Still another object of the invention is the provision of a non-conductive sputter shield of novel design surrounding the switch contacts to prevent accumulation of vaporized contact metal on the envelope wall.

A still further object is the provision of Ia vacuum switch incorporating means for easily applying localized heat to the switch electrodes within the envelope during the degassing cycle in order to more effectively and rapidly degas the switch electrodes;

3,026,394 Patented Mar. 20, 1962 Another object of the invention is the provision in a switch of the character d-escribed of a detachable nonconductive bearing means for the movable electrode.

Other objects will be brought out in the following description of the invention. l do not limit myself to the showing made by said description and the drawings, since I may use variant forms of the invention within the scope of the appended claims.

With reference to the drawing, the FIGURE is a half sectional view of a switch embodying my invention, The scale is approximately two-thirds actual size.

In broadly descriptive terms, the switch of my invention and as illustrated in the drawing comprises a large glass cylindrical shell closed at each end by a heavy cover plate. Within the shell and cover plate at each end, a relatively thin two-part annular .copper membrane is joined hermetically to the shell in a conventional metalto-glass seal.

At the fixed contact end of the switch, the relatively large central aperture of the two-part annular membrane is hermetically closed by a pair of concentrically arranged and integrally united annular plates. The inner plate is detachably secured to the overlying cover plate. A iixed electrode extending into the glass shell-through and hermetically brazed to the inner periphery of the inner plate completes the seal at this end of the shell. VThus atmospheric pressure on the xed contact end of the switch is imposed only on the exposed area of the membrane, while the major pressure as well as the weight of the xed contact and its related concentric plate structure is borne by the cover plate abutting the end of the glass shell.

At the other end of the shell, which constitutes the mobile rcontact end of the switch, a similar annular metallic membrane is arranged in a mctal-to-gl-ass seal with the shell. In this case however, the inner rim or" the annular membrane is integrally united, through the medium of an annular plate and a collar, with the outer rim of a metallic bellows which extends into the envelope and is hermetically closed 'across its inner end by an operator stem. The mobile contact of the switch is fixed on the inner end of the stem within the vacuumized envelope and in axial alignment with the'xed contact. The

stem extends out of the open end of the bellows, for connection to a solenoid or other operator.

Atmospheric pressure tends to close the mobile contact upon the aligned fixed contact to close the circuit through the switch. The solenoid or other operator when energized, pulls the mobile contact away from the iixed contact to open the circuit. The bellows permits both movements without break in the vacuum of the enclosing envelope.

A dielectric bearing tube in which the stem is slidably journaled is iixed within the open end of the bellows by a detachable part of the cover plate at that end. Electrostatic shields or baiiics surround the inner end of the stem and the bellows; and to insure that vaporized contact metal will not adhere to the inner surface of the glass shell and thereby form a conductive path between the end assemblies, a sputter shield is mounted on'one of the end assemblies so as to surround the contact ends of the xed and movable contact electrodes.

The arrangement of parts and the membranes Iassociated with the mobile electrode is such that in the event a part within this end of the envelope must be replaced or repaired, the membranes at this end may be cut to give access, and then rejoined and the envelope again exhausted for further use. The use of glass for the shell also makes possible the division of the glass shell intermediate its ends to give access to the parts, after which the shell parts may be rejoined and the envelope exhausted.

' In detail my switch comprises a cylindrical glass shell .2 around the inside edges of which at each end is integrally fused a glass apron or flare 3, extending inwardly to a bead 4. Shell and flare are preferably of heavy Pyrex glass which, of various dielectric materials, has the desired transparency, mechanical and dielectric strength, and heat resistance.

Arranged around both upper and lower ends, is an annular two-part copper membrane comprising an inwardly extending outer flange 6, having a generally cylindrical integral inner return flange section 7 heliarc brazed thereon, the outer flange thinning down into the bead 4 in a conventional metal-to-glass seal; and the inner flange extending to the plane of the associated 'shell end. At the fixed electrode end of the switch this edge is integrally united by the heliarc weld 8 to the upwardly extending outer peripheral flange 9 on annular copper plate 12, the inner periphery of which is provided with an upwardly extending flange 13 which is integrally united to a second annular copper mounting vplate 14 concentrically arranged contiguous to the inner periphery of the annular plate 12. An outer peripheral flange 16 on plate 14 is heliarc brazed tothe flange 13 onV plate 12 to provide a hermetic seal capable of being subsequently opened. The inner peripheral edge lof the annular plate 14 snugly surrounds and is integrally and hermetically brazed to a fixed copper electrode 17 which extends into the envelope and terminates at its inner end in a relatively larger diameter tungsten contact point 18. As indicated in the drawing, the electrode 17 is provided with an axial bore 19 to accommodate a heating element during the degassing cycle. It has been found that the application of high heatto they electrodes during the degassing cycle helps to drive gas molecules from the electrode metal itself, so that such gas does not subsequently escape into the evacuated envelope. The other end of the fixed electrode extends out of the envelope beyond the shell in a terminal portion 21 which may be connected to a source of power by any suitable means.

Overlying the end of the shell is a heavy end plate 22, to which the mounting plate 14 is tightly held by the cap screw 23. To thicken the plate at the point where the cap screws engage, interiorly threaded copper plated steel caps 24 are brazed on the interior of the plate 14.

VMounting holes 26 are formed about the rim of the end plate; and for evacuation purposes a metal tubulation 27, brazed in the mounting plate 14 extends through the end plate as shown.

It Will be observed that this structure provides a hermetically tight end for the shell entirely within it and immediately below the end cover plate. So constructed only a relatively small area including the metal-to-glass seal is subjected to unsupported atmospheric pressure. A major portion of such stress is carried by the end plate, which in addition, supports the weight of the fixed contact, and receives the shock and thrust of the closing and closed contacts.

At the other or lower end of the shell is the mobile contact 28 of tungsten mounted on the centrally bored copper electrode stem 29. The stem is slidably journaled in a dielectric bearing tube 31, detachably fixed by snap ring 32 on the bearing collar 3-3, which is detachably fixed by cap screws 34 on the detachable steel cover plate 36, which overlies the end of the shell in abutting relation thereto. As with the fixed electrode, the mobile electrode or stem extends outwardly beyond the plate 36 in a terminal end 37 provided at its outer end with a threaded bushing 38 integrally brazed in the central bore for attachment of operating means, such as a solenoid (not shown).

As previously described, this end also is hermetically sealed by an annular copper membrane 6-7 lmaking a metal-to-glass union with the bead 4, and extending radially inwardly, where the outer edge of the flange 7 is integrally heliarc brazed as at 41 to the flange 42, formed on the outer periphery of the annular plate 43. The inner periphery of plate 43 is` also provided with a flange 44, the edge of which is brazed to a contiguous flange 46 formed on the collar 47, which in turn is hermetically brazed about the open outer end 48 of bellows 49, ar'- ranged coaxially around the stern and bearing 3l. As shown, this assembly is supported against atmospheric pressure tending to crush it inward by detachably seV Y curing the plate 43 to the overlying heavy cover plate 36 by means of cap screws 51, which, like the corresponding cap screws 23 at the other end of the switch, extend through the plate and engage hermetically brazed reiri forcing caps 52 on the inner surface of plate 435 The inner end 53 of thebellows is closed by and brazed to the hollow stem intermediate its ends, and thus continues the hermetic closure at this end of the shell while permitting axial movement ofthe stern. It will be apparent from the drawing that Vcylindrical flange 7 is proportioned to surround the bellows andprotects it from bombardment by particles emanating from the contact points. A horizontalY baffle or shield 54 sub= stantially closing the inner end of cylindrical flange 7 provides additional protection for the bellows and helps to disperse such particles toward thefixed end ofthe shell. Particles that migrate toward the mobile end of the switch are kept from reaching the bellows by the substantially closed chamber within which it is enclosed.

As a further aid in controlling the movement within the envelope of particles of contact metal, a spatter shield 56 is provided. The spatter shield is preferably fabricated from heat-resistant glassor other dielectric. In the embodiment shown, the glass shield is fixed at one end to the annular plates 12-14 at Ythe fixed electrode end of the switch, by means of a metallic shell having a feathered portion 57 joined to the shield in the conventional manner. p

The other end of the shell constitutes an integral cy'd lindrical portion 58 of smaller diameter and havin-g its end remote from the shield integrally brazed to the inner and outer peripheries, respectively, of the annular plates 12 and 14. portion 57 is relatively larger in diameter than its adjai cent Waist section, which is reduced in diameter as at 59 to form a restricted passage 61 through which the xed electrode 17 must extend. Immediately below the waist section and approximately opposite the contacts 18-28, the shield is abruptly increased in diameter to provide a large diameter chamber 62 surrounding the contacts. The lower free end 63 of the shield is reduced to about the same diameter as the waist section 59, so that while fast traveling vaporized contact metal is permitted to be impelled radially outwardly away from the contacts, the restricted passage 161 and restricted end y63 of the shield effectively prevent migration of such particles in objectionable amounts beyond the confines of the chamber 62. It will thus be seen that condensation of the vaporized contact metal on the interior of the shield cannot result in the formation of a conductive layer between opposed electrodes, and such condensation effectively prevents the formation of such a layer on the interior surface of the glass shell 2. It will also be apparent that the restricted open end 63 of shield 56 effectively cooperates with the closely adjacent baffle 5'4 and the cylindrical flange 7, to protect the bellows against rupture by flying particles.

An actuator for the switch, such as a solenoid (not shown) is connected by a link 64 to the hollow copper stem 29-37. The end of the link is threaded into the brass bushing 38 brazed into the free end of the stem as previously described. No means is provided for holding the end cover plates against the ends of the shell, since atmospheric pressure after vacuumization of the envelope is amply sufficient to fix them rigidly in place. While the structure of my invention has been explained above without reference to sequence of assembly, such The end of the shield where it joins the shell sequence is of great importance in realizing some ofthe objects of my invention. Essentially it is as follows:

The annular membranes 6-7 are -rst beaded, the flares 3 attached, and then the flares are fused to corresponding edges of two separate halves of the unitary shell shown. At the mobile electrode end the plate 43, bellows, baffle and stem are integrally brazed as a unit, and as a unit inserted through the flange 7 and heliarc brazed at 41 to fix this assembly to the associated half-shell. For convenience, and to protect the parts, cover plate 316, bearing 31 and bearing collar 33 may be applied at this time to complete this end of the switch.

To close the open upper end of the envelope, the brazed fixed assembly of membrane 6 7, joined to the associated half-shell, receives the previously assembled and integrally brazed annular plates 12, 14, electrode 17 and attached shield 56. Heliarc brazing as at 8 xes this assembly to the associated half-shell, after which the cover plate 22 may be attached. The two shell halves are now mounted in a glass lathe and the abutted ends of the half-shells integrally joined to form the unitary glass shell 2 as shown. Evacuation of the envelope thus formed completes the switch.

Because of the high cost of making a switch of the great size and capacity described, it is very desirable that they be so constructed that if need arise the envelope may be opened and inner parts be repaired or replaced. This is accomplished by removing the lower cover plate 36 and opening the heliarc welded joint 41, whereupon the mobile contact assembly may be lifted out. If it is necessary to remove the fixed contact assembly, the shell 2 is opened at about its midpoint and the assembly removed through the thus opened end of the half-shell. After repair and reclosing, the envelope is once more vacuumized and the switch is again ready for use.

I claim:

1. A vacuum switch constructed for ease of assembly and repair comprising a vacuumized envelope including a dielectric shell having annular inturned ends and first and second conductive end caps hermetically sealing opposite ends of the shell, each of said end caps including a cylindrical flange assembly comprising a cylindrical inwardly extending ange and an outwardly extending cylindrical flange integral hermetically at its inner end with lthe inner end of said rst mentioned flange and its outer end hermetically joined to an associated in turned end of the shell whereby the cylindrical flanges lie within the confines of the shell at the ends thereof, said first conductive end cap comprising in part an assembly of an annular plate, a bellows attached at one end to the inner.

annular opening of the end plate, a hollow elongated mobile `electrode stem extending through said annular plate and attached intermediate its ends to the other end of the bellows and having an electrode portion at the inner end thereof, said first conductive end cap assembly being inserted through one of said cylindrical flange assemblies and having the outer periphery of the annular plate brazed to the outer end of the cylindrical inwardly extending flange with a portion of the hollow open end stem of the electrode protruding outward from the shell, a rst annular cover plate received over said protruding hollow stem in abutting relation against the adjacent end of the shell and attached to said annular plate, said first conductive end cap in said part assembly being readily removable from said flange assembly by breaking its brazed connection therewith after removal of said first cover plate, said second conductive end cap comprising in part an assembly of an annular plate and a hollow elongated fxed electrode stem extending through said annular plate in axial alignment with said mobile electrode stem and brazed to the last mentioned annular plate intermediate its ends and having an electrode portion at its inner end adjacent the mobile electrode for contact there- 6 with, said second conductive end cap assembly being inserted through lthe other of said cylindrical flange assemblies and having the outer periphery of its annular plate brazed to the outer end of the adjacent cylindrically extending flange and a portion of the hollow open end stem of the fixed electrode protruding outward from the shell and a second annular cover plate received over said protruding hollow fixed electrode stem in abutting relation against the adjacent end of the shell and attached to said annular plate of the second end cap assembly, said second conductive end cap assembly being readily removable from said adjacent flange assembly by breaking its brazed connection therewith after removal of said second cover plate, said hollow electrode stems having a bore of a size to accommodate a heating element therein to be placed adjacent the electrode portion of the stem to help drive gas molecules from the electrode metal portions during degassing of said envelope.

2. A vacuum switch according to claim 1 wherein said first conductive end cap assembly has an annulai collar fitting within said first annular plate and the end of the bellows is brazed to said annular collar rather than to said first annular plate, an elongated dielectric bearing tube extending through said annular collar and bellows and receiving axially therewithin said mobile electrode stem for sliding movement, said first colver plate receiving at its center and having attached thereto an annular bearing collar which receives therewithin said bearing tube, means holding said bearing tube within said bearing collar, an annular baille plate received over said mobile electrode stern and extending transverse thereto and attached thereto inward of the end of the bellows attachment to said stem, said baffle plate having a diameter slightly less than the diameter of the adjacent cylindrical flange assembly and forming therewith a shield of said bellows to prevent sputter from said electrodes from reaching said bellows.

3. A vacuum switch according to claim 2 wherein said second conductive end cap includes a cylindrical metal sleeve attached at one end of the annular plate thereof and extending inwardly in the shell and in spaced relation within the adjacent cylindrical flange assembly and a cylindrical dielectric shield attached to the other end of said metal sleeve and extending freely about said electrode portions to prevent sputter therefrom reaching said surrounding shell.

4. A vacuum switch according to claim 3 wherein said electrode portion contact at a contact locus within the shell and wherein said cylindrical dielectric shield is provided with a radially constricted shield section axially spaced from the electrode contact locus and radially distended shield section opposite the contact locus.

5. A vacuum switch according to claim 4 wherein said cylindrical dielectric shield has a second radially constricted shield section axially -spaced inward from the first contricted portion and axially spaced beyond said contact locus from said first radially constricted section of the shield whereby the contact locus is substantially encompassed by the dielectric shield.

6. A vacuum switch according to claim 4 wherein said second conductive end cap has the `annular plate thereof comprising an inner and an outer coaxially arranged annular plate portion each having axially extending annular flanges thereon in abutting relation, said abutting flanges being connected by brazing, the outer of said annular plate portion having an outer peripherial annular flange brazed to said surrounding cylindrical flange assembly Iand wherein said cylindrical metal sleeve is connected to the second end cap assembly at the juncture of said first and second annular plate portions by brazing thereby permitting ease of manufacturing assembly and disassembly for repair.

(References on following page) References Cited in the le of this patent UNITED STATES PATENTS Mllikan et a1. Dec. 9, 1930 Jennings Apr. 3, 1956 5 Jennings M-ay 28, 1957 Jennings Dec. 2, 1958 Lee Dec. 16, 1958

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