US3555222A

US3555222A - Vacuum switch with cylindrical guide means and annular field deflector means

Info

Publication number: US3555222A
Application number: US710197A
Authority: US
Inventors: Julian Camacho
Original assignee: Deutsche ITT Industries GmbH
Current assignee: Thomas and Betts Holdings Inc
Priority date: 1968-03-04
Filing date: 1968-03-04
Publication date: 1971-01-12
Anticipated expiration: 1988-01-12
Also published as: FR2003185A1; BE731982A; CH522282A; GB1259501A

Abstract

A power switch in which a hermetically sealed envelope includes a tubular insulator section sealed to a cylindrical bearing assembly which surrounds the adjacent ends of contact rods fixedly mounted on end cap structures of the envelope. The bearing assembly includes two telescopically mounted cylindrical shells which provide large bearing surfaces for supporting the contact rods in axial alignment. An annular deflector having a convex inner surface is positioned in the insulator portion of the envelope adjacent to the bearing assembly to produce a uniform distribution of the voltage gradient or field over the insulator portion of the switch.

Description

United States Patent [72] Inventor Julian Camacho San Jose, Calif. [21] Appl. No. 710,197 [22] Filed Mar. 4, 1968 [45] Patented Jan. 12, 1971 73] Assignee International Telephone and Telegraph Corporation New York, N.Y. a corporation of Delaware. by mesne assignment [54] VACUUM SWITCH WITH CYLINDRICAL GUIDE MEANS AND ANNULAR FIELD DEFLECTOR Primary Examiner-Robert K. Schaefer Assistant Examiner-Robert A. Vanderhye i AtlorneysC. Cornell Remsen, Jr.; Walter J. Baum, Paul W.

Hemminger, Percy P. Lantzy and A. Donald Stolzy ABSTRACT: A power switch in which a hermetically sealed envelope includes a tubular insulator section sealed to a cylindrical bearing assembly which surrounds the adjacent ends of contact rods fixedly mounted on end cap structures of the envelope. The bearing assembly includes two telescopically mounted cylindrical shells which provide large bearing surfaces for supporting the contact rods in axial alignment. An annular deflector having a convex inner surface is positioned in the insulator portion of the envelope adjacent to the bearing assembly to produce a uniform distribution of the voltage gradient or field over the insulator portion ofthe switch.

PATENTEBJAmmsn 3555222 sum 1 or 2 INVENTOR J 0444/? CH0 PATENTED m 1 2 ram SHEU 2 OF 2 AZTOEA/fl/ VACUUM SWITCH WITH CYLINDRICAL GUIDE MEANS AND ANNULAR FIELD DEFLECTOR MEANS BACKGROUND OF THE INVENTION This invention relates to switches and more particularly to high power switches of the hermetically sealed and vacuum types for interrupting electrical currents of large magnitude.

In the conventional vacuum-type power switch the movable contact rod is mounted in an insulated bearing on one of the end plates of the switch one envelope. A metal bellows surrounds the insulated bearing and is fixed at one end to the end plate and the other end to the movable contact rod to accommodate axial displacement thereof with respect to the fixed contact rod of the switch. The insulated bearing is required in this form of switch to prevent welding of the rod and bearing surfaces during high current power interruptions, the welding being caused by the voltage gradient between the bearing and rod which causes a considerable heating efi'ect. While this form of switch is generally satisfactory, it is difiicult to provide accurate axial alignment between the contact rods of the switch and the mechanical life of the switch is limited to a certain degree. What is desired, therefore, and constitutes one object of the present invention is to provide a power switch which is constructed in a manner to provide a higher degree of axial alignment of the contact rods than is achieved in the conventional power switch and which embodies a bearing assembly that eliminates the use of an insulated bearing about the movable contact rod as employed in the conventional power switch.

A limiting factor in the conventional power switch is the use therein of a cylindrical metallic shield which surrounds the adjacent ends of the contact rods and is positioned radially inwardly from the insulator portion of the switch, the latter being typically formed of ceramic. This shield is provided to prevent vaporized contact metal from condensing on the inner surface of the insulator portion of the switch. Such a shield has the disadvantage that the lines of force of the voltage gradient or field produced upon opening of the switch concentrate about the ends of the shield and upon narrow areas of the surrounding ceramic portions of the envelope. This nonuniform distribution of the field imposes electrostatic stresses upon the ceramic envelope, resulting in nonuniform heating of the envelope with attendant power losses thereof and destruction of the switch after extended use thereof. In addition, this form of shield often results in an excessive amount of vaporized contact metal depositing upon limited areas of the ceramic envelope, thereby creating current leakage from the coated ceramic to the shield and reducing the hold-off voltage of the ceramic. Another object of the invention is to provide an improved switch structure in which means are provided for uniformly distributing the voltage gradient across the ceramic portion of the switch envelope and for minimizing the condensation of vaporized contact metal on the ceramic portion of the envelope.

SUMMARY OF THE INVENTION According to the principal aspect of the present invention, there is provided a power switch in which the hermetically sealed envelope of the switch includes a tubular insulator portion and a cylindrical bearing assembly mounted coaxially to the insulator portion, with the remote ends'of these two sections being closed by suitable end closure structures. Axially aligned contact rods are fixedly mounted in the end structures with the adjacent ends of the rods being positioned within the cylindrical bearing assembly. The bearing assembly includes a pair of cylindrical shells surrounding the contact rods and engaged in telescoping relationship, with one shell being fixedly mounted to the insulator portion of the envelope and the other shell being fixedly mounted on the end closure structure of the bearing assembly. The two telescopingly engaged shells provide the bearing surfaces which permit relative axial displacement of the'contact rods to make or break a circuit through the switch. Thus, in the present invention the insulated bearing normally utilized to support the movable contact rod in a switch end plate is replaced by the telescopingly engaged shells which, because they form a part of the outer wall of the switch envelope, provide a substantially larger bearing surface and, thus, permit improved axial alignment of the contact rods and increased mechanical life for the switch.

According to another feature of the invention, there is provided a switch in which a hermetically sealed envelope includes a tubular insulator portion and a tubular metallic portion hennetically sealed together at their adjacent ends and closed at their remote ends by end caps. Axially aligned contact rods are mounted in each of the tubular portions of the assembly with means being provided for permitting relative axial displacement on one of the rods with respect to the other to make a or break a circuit through the switch. The adjacent ends of the rods are disposed within the metallic portion of the envelope. A novel annular field deflector is concentrically mounted within the end of the insulator portion of the envelope adjacent to the metallic portion thereof. The deflector is provided with a smooth convex inner surface which extends a relatively short distance toward the end cap on the insulator portion of the envelope so as to leave the major portion of the interior of the insulator portion exposed to the voltage gradient or electrostatic field within the switch. The configuration and spacing of the annular deflector relative to the insulator portion of the envelope and to the adjacent ends of the contact rods are such that the field produced by opening of the switch will result in a substantially uniform distribution of the lines of force of the field over the exposed major portion of the insulator section of the switch envelope. As a consequence, the problems resulting from stress concentrations of the field on the ceramic envelope which exists in conventional power switches are overcome by the present invention. In addition, since the adjacent ends of the contact rods are disposed within the metallic portion of the envelope, the major portion of the contact vapors will deposit on the metallic rather than on the insulator portion of the envelope. Hence, current leakage to the insulator portion of the envelope is minimized and the hold-ofi' voltage thereof is maximized and maintained relatively constant.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a partial section taken through the longitudinal axis of one form of the invention;

FIG. 2 is a section taken along line 2-2 of FIG. 1;

FIG. 3 is a partial section taken through the longitudinal axis of another form of the invention; and

FIG. 4 is a fragmentary sectional view taken along line 4-4 of FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings in detail, wherein like reference characters designate like or corresponding parts throughout the various views, there is illustrated in FIG. I and 2 one form of the power switch of the present invention, generally designatedlO. The switch comprises a hermetically sealed envelope including an elongated tubular insulator portion 12, preferably fabricated from ceramic, coaxial with a cylindrical bearing assembly, generally designated 14. The respective ends of the insulator portion 12 are metallized in a well-known manner with the upper end being hermetically sealed to a metallic end plate 16 via an annular metallic sealing structure 18. A metallic closure structure 20 hermetically sealed to the lower end of the bearing assembly 14 closes the lower end of the envelope.

Coaxially mounted in the envelope are a pair of aligned

contact rods

22 and 24 terminating at their adjacent ends in

integral contact buttons

26 and 28. The contact rod 22 is fixedly mounted on the end plate 16 while the contact rod 24 is fixedly mounted on the closure structure 20, with the

contact buttons

26 and 28 at the adjacent ends of the rods being 36 and 38, all concentrically mounted with respect to each other and with respect to the longitudinal axis of the

contact rods

22 and 24. The lower peripheral edge of the shell 32 is shaped to provide a cylindrical flange 40 which is bonded to the lower edge 42 of the bellows 34, while the latter is bonded .to a cylindrical flange 44 formed at the lower peripheral edge of the cylindrical shield 38. The shield 38 is bonded to the outer periphery 46 of the closure structure which is shown in this embodiment of the invention as being a metallic end plate similar to the plate 16. The upper peripheral portion of the shell 30 is shaped to provide a cylindrical flange 48, which is bonded to the upper portion 50 of the bellows 34, while the latter is bonded to a cylindrical flange 52 formed at the upper peripheral portion of the cylindrical shield 36. The upper and lower mating edges of these metal parts are preferably bonded together and bonded to the closure structure 20 by means of heliarc welding so as to provide hermetic seals between the various parts. It can be seen that the

shells

30 and 32, bellows 34, and

cylindrical shields

36 and 38 are fixedly mounted together in such a manner as to provide a unitary bearing assembly 14. The upper portion of this assembly is hermetically sealed to the lower end of the tubular insulator portion 12 of the envelope by a generally semitoroidal shaped metallic field deflector 54 which includes an outer cylindrical flange 56 bonded to the inner surface of the upper peripheral edge 52 of cylindrical shield 36. The lower metallized end of the tubular ceramic portion 12 is brazed to a radially extending portion 58 of the deflector 54. Alternatively, the deflector may be formed of a metal having a coefficient of expansion approximating that of the ceramic envelope 12, such as Kovar. In this case, the lower end of the ceramic envelope is not metallized, and the Kovar shield is sealed directly to the ceramic. The detailed construction and purpose of the deflector 54 will be described in detail later.

As seen in the drawing, the

shells

30 and 32 of the bearing assembly 14 are mounted in telescoping relationship with the inner surface 60 of the outer shell 30 sliding upon the outer surface 62 of the inner shell 32. The

surfaces

60 and 62 constitute the bearing surfaces for permitting relative axial movement of either one of the

contact rods

22 or 24 toward the other to make or break a circuit through the switch 10. As best seen in FIG. 2, preferably the

shells

30 and 32 are deformed inwardly along the axial extent of the shells at circumferentially spaced locations, as indicated at 64, to prevent rotational movement between the shells.

The

metallic shields

36 and 38 are arranged in radially spaced relation with the

inner ends

66 and 68 of the shields overlapping sufiiciently to insure that a continuous cylindrical shield is provided about the

contact buttons

26 and 28 when the contact rods are axially displaced from each other to their maximum extent, as limited by the bellows 34. As a consequence, regardless of the position of the

contact rods

22 and 24, the

shields

36 and 38 will intercept and condense a large portion of the metal particles and vapor emanating from the

switch contact buttons

26 and 28, thus preventing damage by such particles or vapor to the bellows.

As can be appreciated, since the

contact buttons

26 and 28 of the switch are positioned in generally axial alignment within the center of the metallic bearing assembly 14, the major portion of the particles and vapor emanating from the switch contacts will strike and condense upon the

shields

36 and 38, rather than coating the interior surface of the insulator portion 12 of the envelope. Further, because the telescoping shells 30 ad and 32 of the bearing assembly 14 provide the bearing surfaces for allowing axial displacement of the

contact rods

22 and 24 with respect to each other, the insulator bearing normally employed for mounting the movable contact rod in the metal end plate of the conventional power switch is eliminated by the present invention. Due to the substantial cylindrical bearing surfaces afforded by the

shells

30 and 32, a construction is achieved which insures accurate axial alignment of the contact rods over extended operation of the switch. In addition, the

parts

30, 32, 34, 36, and 38 of the bearing assembly 14 may be inexpensively formed by stamping or otherwise forming appropriate metallic stock and the parts may be bonded together in a manner previously described in a single operation, thus minimizing manufacturing costs. Also, because the bellows is positioned outside of the current path of the switch, relatively high currents may pass through the switch without heating and, hence, causing deformation of the bellows as occurs in conventional switches in which the bellows are in the current path.

Turning again to the field deflector 54, it is seen that it includes an annular curved portion 70 which is concentric to the tubular insulator portion 12 of the envelope and the contact rod 22, and extends radially inwardly from the radial portion 58 of the deflector. The annular portion 70 of the deflector provides a relatively smooth curved inner surface 72 convex in the direction toward the longitudinal axis of the envelope and extending in a direction toward the upper end plate 16 a relatively short distance as compared to the axial length of the insulator portion 12 of the envelope. As a consequence, the major portion of the inner surface of the ceramic section 12 is exposed to the field produced by breaking of the circuit upon axial displacement of the

contact rods

22 and 24. As seen in FIG. 1, the adjacent ends of the

contact rods

22 and 24 are spaced a distance X from the deflector 54 greater than the radial dimension Y between the inner periphery of the curved surface 72 and the outer surface of the contact rod 22; however, such distance should not be greater than twice a said radial dimension. With the deflector 54 being disposed in the manner just stated relative to the ends of the contact rods, and if the ratio of the radial dimension Y between the inner curved surface 72 of the deflector and the outer surface of the contact rod 22 to the axial dimension 2 between the ends of the exposed portion of the tubular insulator section 12 of the envelope is approximately 1 to 3, it has been found that there results a near uniform distribution of the voltage gradient of the switch across the insulator section, as indicated by the dashed lines in FIG. 1 of the drawing which represent the lines of force of the voltage gradient. Thus, by use of the deflector 54 providing a curved inner surface for deflecting the lines of force of the voltage gradient, there are no stress concentrations formed in limited areas on the insulator section 12 of the envelope which otherwise would produce high leakage across the envelope and failure of the switch. In addition, because of the arrangement of the parts in the present invention any vaporized contact material which is not condensed on the

shields

36 and 38 will be uniformly distributed over the inner surface of the insulator section 12 so that the hold-off voltage of the insulator remains high and relatively constant.

A modified form of the invention l0 is illustrated in FIG. 3 and 4, which is identical to the switch 10 in FIG. 1 and 2 except that the closure structure 20' constitutes a second tubular ceramic section 12 closed at its lower end by a metal end plate 16'. The plate 16' is connected to the ceramic portion 12 by man means of a thin flexible annular metallic sealing structure 8. In this embodiment, the lower contact rod 24 is fixedly mounted to the end plate 16'. A second field deflector 54' identical to the deflector 54 is interposed between the upper end of the insulator section 12' and the bearing assembly 14. In this arrangement, the field emission characteristics of the switch are identical to that shown in FIG. 1 except that the field is uniformly distributed over the inner surfaces of both of the insulator portions 12 and 12'.

It is to be understood that the field deflector 54 could be employed in switch structures other than that shown in the drawings; for example, the deflector could be employed in a a switch in which the envelope thereof consists of a coaxial tuthe two sections closed by end caps, with one of the contact rods being fixedly mounted on one end cap and the other rod being mounted for relative axial movement on the other end cap. In addition, the deflector 54 need not take the exact form illustrated in FIGS. 1 and 3 if it is shaped to provide a curved inner surface such as the surface 72. For example, the deflector could be provideo by a metal toroid mounted concentrically within the insulator envelope or a semitoroid split vertically rather than longitudinally as is the semitoroid 54.

Although there has been herein shown and described the invention in what is conceived to be the most practical and preferred embodiments, it is recognized that departures may be made therefrom within the scope of the invention, which is not to be limited to the details disclosed herein but is to be accorded the full scope of the claims so as to embrace any and all equivalent structures and devices.

l claim:

l. A switch assembly comprising:

a hermetically sealed envelope including a tubular insulator portion, a cylindrical bearing assembly coaxial with said tubular insulator portion, and end plate and a closure structure;

means hermetically sealing adjacent ends of said tubular insulator portion and said bearing assembly to each other;

means hermetically sealing the ends of said tubular insulator portion and said bearing assembly to said end plate and said closure structure, respectively;

axially aligned contact rods fixedly mounted on said end plate and said closure structure and extending into said envelope;

a flexible bellows forming a part of said bearing assembly, said bellows being hermetically interposed between said tubular insulator portion and saidclosure structure to accommodate relative axial displacement of said contact rods to make or break a circuit through said switch;

a pair of cylindrical shells forming a further part of said bearing assembly, said cylindrical shells being engaged in telescoping relationship with one shell being fixed to said tubular insulator portion and the other shell being fixed to said closure structure, said shells providing the bearing surfaces for supporting said contact rods in axial alignment; and l a pair of cylindrical shields coaxial with said contact rods and interposed between said rods and said bellows forming a part of said bearing assembly, one of said shields being fixed to said tubular insulator portion and the other of said shields being fixed to said closure structure, the free ends of said shields being arranged in overlapping relationship, said cylindrical bearing assembly being metallic and surrounding the adjacent ends of said contact rods, and the remote ends of said shells, bellows, and shields being formed with concentric, axially aligned cylindrical flanges with adjacent flanges being hermetically bonded to each other to provide a unitary bearing assembly.

2. A switch assembly comprising: i

a hermetically sealed envelope including a tubular insulator portion, a cylindrical bearing assembly coaxial with said tubular insulator portion, an end plate and a closure structure;

a flexible bellows forming a part of said bearing assembly, said bellows being hermetically interposed between said tubular insulator portion and said closure structure to ac commodate relative axial displacement of said contact rods to make or break a circuit throu h said switch; a pair of cylindrical shells forming a urther part of said bearing assembly, said cylindrical shells being engaged in telescoping relationship with one shell being fixed to said tubular insulator portion and the other shell being fixed to said closure structure, said shells providing the bearing surfaces for supporting said contact rods in axial alignment; and

annular field deflector means concentrically mounted within the end of said tubular insulator portion which is sealed to said bearing assembly, a portion of said deflector means extending radially outward over said end of said tubular insulator portion, and said deflector means providing a relatively smooth curved surface convex in a direction toward the longitudinal axis of the envelope and extending rearwardly toward said end plate a relatively short distance so that the major portion of the inner surface of said tubular insulator portion is exposed to the field produced by breaking of said circuit, the adjacent ends of said contact rods being positioned within said bearing assembly and being axially spaced from said deflector means, and the ratio of the radial dimension between the inner periphery of said curved surface and the outer surface of the contact rod fixed to said end plate to the axial dimension between the ends of said major ex}- posed portion of said tubular insulator portion being such as to produce a uniform field distribution over said major exposed portion. l

Claims

1. A switch assembly comprising: a hermetically sealed envelope including a tubular insulator portion, a cylindrical bearing assembly coaxial with said tubular insulator portion, and end plate and a closure structure; means hermetically sealing adjacent ends of said tubular insulator portion and said bearing assembly to each other; means hermetically sealing the ends of said tubular insulator portion and said bearing assembly to said end plate and said closure structure, respectively; axially aligned contact rods Fixedly mounted on said end plate and said closure structure and extending into said envelope; a flexible bellows forming a part of said bearing assembly, said bellows being hermetically interposed between said tubular insulator portion and said closure structure to accommodate relative axial displacement of said contact rods to make or break a circuit through said switch; a pair of cylindrical shells forming a further part of said bearing assembly, said cylindrical shells being engaged in telescoping relationship with one shell being fixed to said tubular insulator portion and the other shell being fixed to said closure structure, said shells providing the bearing surfaces for supporting said contact rods in axial alignment; and a pair of cylindrical shields coaxial with said contact rods and interposed between said rods and said bellows forming a part of said bearing assembly, one of said shields being fixed to said tubular insulator portion and the other of said shields being fixed to said closure structure, the free ends of said shields being arranged in overlapping relationship, said cylindrical bearing assembly being metallic and surrounding the adjacent ends of said contact rods, and the remote ends of said shells, bellows, and shields being formed with concentric, axially aligned cylindrical flanges with adjacent flanges being hermetically bonded to each other to provide a unitary bearing assembly.

2. A switch assembly comprising: a hermetically sealed envelope including a tubular insulator portion, a cylindrical bearing assembly coaxial with said tubular insulator portion, an end plate and a closure structure; means hermetically sealing adjacent ends of said tubular insulator portion and said bearing assembly to each other; means hermetically sealing the ends of said tubular insulator portion and said bearing assembly to said end plate and said closure structure, respectively; axially aligned contact rods fixedly mounted on said end plate and said closure structure and extending into said envelope; a flexible bellows forming a part of said bearing assembly, said bellows being hermetically interposed between said tubular insulator portion and said closure structure to accommodate relative axial displacement of said contact rods to make or break a circuit through said switch; a pair of cylindrical shells forming a further part of said bearing assembly, said cylindrical shells being engaged in telescoping relationship with one shell being fixed to said tubular insulator portion and the other shell being fixed to said closure structure, said shells providing the bearing surfaces for supporting said contact rods in axial alignment; and annular field deflector means concentrically mounted within the end of said tubular insulator portion which is sealed to said bearing assembly, a portion of said deflector means extending radially outward over said end of said tubular insulator portion, and said deflector means providing a relatively smooth curved surface convex in a direction toward the longitudinal axis of the envelope and extending rearwardly toward said end plate a relatively short distance so that the major portion of the inner surface of said tubular insulator portion is exposed to the field produced by breaking of said circuit, the adjacent ends of said contact rods being positioned within said bearing assembly and being axially spaced from said deflector means, and the ratio of the radial dimension between the inner periphery of said curved surface and the outer surface of the contact rod fixed to said end plate to the axial dimension between the ends of said major exposed portion of said tubular insulator portion being such as to produce a uniform field distribution over said major exposed portion.