US3576961A

US3576961A - Vacuum switch with operating means for arresting contact in an intermediate position before complete opening

Info

Publication number: US3576961A
Application number: US749719A
Authority: US
Inventors: John L Turner
Original assignee: Turner Electric Corp
Current assignee: Turner Electric Corp
Priority date: 1968-08-02
Filing date: 1968-08-02
Publication date: 1971-05-04
Anticipated expiration: 1988-05-04

Abstract

Mechanism for operating a load interrupter switch responsive to opening and closing movements of an air break switch or a plurality of the latter. The load interrupter switch contacts are enclosed in a vacuum bottle preferably, one contact being fixed and the other movable axially away therefrom to open position and toward the fixed contact to closed position. The movable contact is biased toward open position and is normally held in closed position by a lever pivoted at one end and extending transversely of the direction of movement of the contact. The lever is normally maintained in the contact-closed position by a rotatable cam. A latch member extending transversely of the lever normally overlies one end of the lever and when the cam is rotated to permit initial movement of the lever the end of the latch becomes engaged with the end of the lever, permitting a slight initial opening movement of the lever and the associated contact for a period of two to three cycles. Further movement of the cam causes another projection on it to engage the latch, keeping it clear of the end of the lever and permitting the lever to move freely, thus freeing the contact to move under spring pressure to its full open position. This sequential opening of the contact permits harmless arcing to occur across the contacts within the vacuum bottles during initial opening of the contacts until the current reaches its zero value, thus avoiding interruption of the current at other than zero values and the consequent occurrence of high transient voltages.

Description

United States Patent .1 21 Inventor J L Turner 1,112,745 /1968 Great Britain 200/144 .2

[2 l A 1 No 52; Primary Examiner-Robert K. Schaefer 221 Fii e d Au 2 1963 Assistant Examiner-Robert A. Vanderhye 1 Patcmed May 4 1971 Attorney-Bedeli and Burgess [73] Assignee Turner Electric Corporation EastSt. Lou Ill.

ABSTRACT: Mechanism for operating a load interrupter switch responsive to opening and closing movements of an air [54] VACUUM SWITCH WITH OPERATING MEANS break switch or a plurality of the latter. The load interrupter FOR ARRFSTING CONTACTIN AN switch contacts are enclosed in a vacuum bottlepreferably, INTERMEDIATE POSITION BEFORE COMPLETE one contact being fixed and the other movab e aitially away OPENING therefrom to open position and toward the F1 ed contact to 11 Claims, 10 Drawing Figs. closed position. The movable contact is biased toward open position and is normally held in closed position by a lever [52] US. Cl pivoted at one end and extending transversely onhe direction [51] Int CL B01533, of movement of the contact. The lever is normally maintained Holh 3/52 in the contacbdosed position y a rotatable cam A latch Field 0 Search 200/144 2 member extending transversely of the lever normally overlies i one end of the lever and when the cam is rotated to permit inil48.6, 153.13, 148 (A), l53.i l, 78 (Cursory),

147 (C) 153 335/190 19 73 ual movement of the lever the end of the latch becomes engaged with the end of the lever, permitting a slight initial open- [56] Refergnces ci d ing movement of the lever and the associated contact for a UNYTED STATES PATENTS period of two to three cycles. Further movement of the cam causes another projection on it to engage the latch, keeping it g g l et clear of the end of the lever and permitting the lever to move 439 968 ran 200 2 freely, thus freeing the contact to move under spring pressure 3467'8o0 gasey a 200 to its full open position. This sequential opening of the contact 9 i l 6: permits harmless arcing to occur across the contacts within 3238328 l g g 90x the vacuum bottles during initial opening of the contacts until 3/ 9 arm 3 l the current reaches its zero value, thus avoiding interruption FOREIGN PATENTS of the current at other than zero values and the consequent l ,537.565 7/1968 France 200/144( .2) occurrence of high transient voltages.

PATENIEUMAY 4m: 3576.961

'T'TO EN -y;

VACUUM SWITCH WI'III OPERATING MEANS FOR ARRESTING CONTACT IN AN INTERMEDIATE POSITION BEFORE COMPLETE OPENING BACKGROUND OF THE INVENTION l. Field of the Invention The invention relates to sectionalizing switch gear and consists particularly in sequential actuating means, responsive to opening and closing of air break switches for a load interrupter switch.

2. Description of the Prior Art In some switch gear of this type, load interrupter switches of the vacuum type have been arranged to move from closed to full open position instantaneously. The efi'ect of this is to cause wave chopping with resultant high transient voltages and in such installations a shunt circuit around the load switches has been provided, incorporating a resistance to absorb the high transient voltages. In other switch gear of this general type, means are provided for slowing the rate of opening ofthe load switches.

SUMMARY OF THE INVENTION The invention provides means for preventing wave chopping and consequent occurrence of high transient voltages in a load interrupter switch of the vacuum bottle type by incorporating, in the actuating mechanism for such a switch, means whereby the contacts in the vacuum switch are initially opened a sufficient distance to provide arcing across the gap and positively retained in this position for 2 to 3 cycles, after which they are separated to their full opening.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a top view of a sectionalizing switch incorporating the invention.

FIG. 2 is an end elevation view of the switch illustrated in FIG. 1.

FIG. 3 is a side elevation view of the interrupter switch.

FIG. 4 is an enlarged top view, partially in section, of the interupter switch actuating mechanism, taken along line 44 of F1 5.

FIG. 5 is an enlarged partial side elevation view of the interrupter switch, taken along line 5-5 of FIG. 4.

FIG. 6 is a transverse vertical sectional view taken along line 6-6 of FIG. 4.

FIG. 7 is a transverse vertical sectional view along line 7-7 of FIG. 4.

FIGS. 8 and 9 are transverse vertical sectional views along lines 7-8 of FIG. 4.

FIG. 10 is a top view of interrupter switch mechanism arranged for use with a single air break switch.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring first to FIGS. 13, the letter P indicates a portion of a line pole to which is secured, at its midpoint, one leg 1 of a horizontal triangular framework to which are secured converging legs 3 and 5. Near the intersection of legs 3 and 5 with leg I the framework mounts vertical rotary insulators 7 and 9 each of which mounts at its upper end a horizontal air break switch blade 13 and 15 respectively. At the intersection of framework legs 3 and 5 a vertical fixed insulator 23 is supported. Insulator 23 mounts switch contact jaw members 25 27 circumferentially spaced with respect to each other about the axis of insulator 23 and adapted to receive respectively contact earns 31 and 33 mounted respectively on the ends of blades 13 and 15 for axial rotation thereon. The air break switches thus described are constructed in accordance with my US. Pat. No. 3,243,534 and are arranged so that, as viewed in FIG. 1, blades 13 and 15 are swung in opposite directions in their common horizontal plane during opening movement, blade 13 being swingable counterclockwise and blade 15 being swingable clockwise. In addition to their swinging movement in a common horizontal plane, blades 13 and 15 are also rotatable about their own axes so that their

contact cams

31 and 33 may be disengaged from the cooperating contact jaws 25 and 27 by such rotation, which is effected by the initial rotation respectively of insulators 7 and 9 and cranks 37 thereon which engage vertical cranks 39 on blades 13 and 15 to produce the initial rotation of blades 13 and 15 about their axes and thereafter swing blades 13 and 15 out of jaws 25 and 27. To prevent arcing upon disengagement of contact earns 31 and 33 from jaws 25 and 27, pairs of arcing horns 41 and 43 are mounted respectively on blades 13 and 15 normally are in engagement with contacts 47 and 49 supported on switch jaw members 25 and 27 respectively, so that after main switch contact earns 31 and 33 have been opened, as main switch blades 13 and 15 are swung about their vertical axis, arcing horns 41 and 43 will snap out of engagement with their contacts 47 and 49 and because of the speed with which this occurs, no arcing will take place.

For interrupting the load current in circuits controlled by the air break switches, above the air break switch jaws 25, 27 there is mounted a cylindrical housing 53 enclosing a plurality of vacuum bottle switches 55 arranged in end-to-end relation and connected in series with each other, the entire series being connected in parallel with

air break switches

25, 31 and 27, 33. Switches 55 are normally closed and the mechanism for actuating them will be described in detail below.

At its top, cylindrical housing 53 mounts a horizontally elongated housing 57 extending parallel to frame member I. At its ends, housing 57 is provided with hollow extensions 59, both horizontal, but inclined slightly in the horizontal plane away from frame member 1 so that their vertical planes are substantially transverse of blades 13 and 15 when the latter are closed. Each extension 59 mounts .a downwardly extending operating rod or lever 61 for rotation in a vertical radial plane with respect to cylindrical housing 53 and each rod 61 is normally biased inwardly radially by a spring 63 connected at one end to rod 61 and at its other end to structure within housing extensions 59, inward movement of rods 61 being limited by Y-shaped stop elements 65 clamped to cylindrical housing 53 and extending radially outwardly therefrom. Each of the main air break contact blades 13 and 15 mounts an upstanding element 67 on its inner end portion and each element 67 in turn mounts a hook member 69 open in the direction of opening swinging movement of the main air break switches and adapted to engage operating rods 61 after the main air break contacts are open but before disengagement of the arcing horns 43 and 45 from their contacts 47, 49 so as to cause current to pass through rods 61 and interrupter switches 55 prior to separation of the arcing horns and their contacts.

As best seen in FIGS. 3 and 6, interrupter switch operating mechanism housing extensions 59 are hollow and are downwardly open, and operating rods 61 are fulcrumed at 75 on axes extending transversely of extensions 59 so that the rods are swingable in the same vertical planes as extensions 59 and slightly transversely thereof. For transmitting movements of rods 61 to the interrupter switches 55, a short distance below fulcrum axes 75, rods 61 are pivoted at 76 to links 77 which extend axially of extensions 59 and are mounted for axial movement therein responsive to swinging movements of rods 61. Links 77 are each in two parts, 79 and 81, adjustably connected to each other by a turnbuckle 83. Springs 63, which are connected at their one end to rod 61, are connected at their other end to tumbuckles 83 by cotter keys 85 or other suitable connections so that springs 63 always bias rods 61 inwardly toward the interrupter switch column, similarly urging links 77 inwardly axially of extensions 59.

At their inner ends, inwardly of the trapezoidal-shaped upright wall 58 of mechanism housing 57, inner links 81 are connected to clevises 85, which in turn are pivotally connected at 87 to bellcrank arms 89 fulcrumed on vertical axis pivot members 91 fixed to the mechanism housing bottom wall 92. The other arms 93 of the same bellcranks extend substantially longitudinally of the housing and are connected by a universal pivot 95 to substantially horizontal links 97 extending transversely of the housing. Links 97 are connected, at theirends remote from pivots 95, by universal pivots 99 to the extremities of substantially vertical arms 101, rigidly mounted on the ends of operating shaft 105, which extends longitudinally of the housing 57 and is rotatably joumaled at 107, 107

' in rectangular framing 109 extending transversely of the housing between its upright walls.

A plurality of vacuum bottles 55 may be arranged in axially aligned positions within cylindrical column 53 which is made of dielectric material. Each vacuum bottle 55 encloses a lower fixed contact member 109 and an upper axially movable contact member 111. Movable contact member rod 111 extends upwardly from the top of each vacuum bottle into an actuating sleeve 113, the topmost of which is positioned within housing 57 directly below operating shaft 105. At its upper end rod 111 is threaded and mounts an enlarged head portion 115 of disc shape, and vertically spaced downwardly therefrom a shoulder is formed on rod 111 by a nut 117 threadably mounted on the threaded portion of the rod. lntermediate head portion 115 and nut 117, actuating sleeve 113 is formed with a horizontal inwardly directed annular rib 119. A spring 121, seated against the closed upper end 123 of actuating sleeve 113, acts against rod head portion 115 to bias contact rod 111 downwardly toward engagement with fixed contact rod 109. A second annular rib 122 inwardly of sleeve 113 and vertically spaced downwardly from first annular rib 119 abuts the upper end of a coil spring 123 seated on bottom wall 92 of housing 57 so as to bias sleeve 113 upwardly and, through engagement between first annular rib 119 and rod head portion 115, lift rod 111 out of engagement with fixed contact rod 109. For urging sleeve 113 downwardly in opposition to spring 123, so as to permit spring 121 to move movable contact rod 111 into current transmitting engagement with fixed contact rod 109, a lever 125 is pivoted at 127 to a sidewall of the housing. on an axis longitudinal of the housing 57 and extends transversely of the housing therefrom. Lever 125 is formed with a downwardly extending radial boss 131 engaging the upper surface of lever 125 and holding it in the position shown in FIG. 4, whereby sleeve 113 compresses spring 121 against the head portion of movable contact rod 111, biasing the latter downwardly into engagement with fixed contact rod 109, and at the same time compressing spring 123. Directly above the free end of operating lever 125 a latch member 133 is pivoted at 135 on an axis longitudinal of the housing to a bracket 137 on shaft mounting frame 109. Latch member 133 is vertically elongated and its surface facing shaft 105 and lever 125 is of irregular shape, the lower end being rabbeted as at 139 to fonn a horizontal shoulder opposing the upper surface of lever 12S and a vertical surface opposing the end surface of lever 125. A torsion spring 141 on pivot pin 135 biases latch 133 in a clockwise direction as viewed in FIG. 4, i.e., toward lever 125. When boss 131 on cam 129 is in the position illustrated in FIG. 6, in thirty-

second contact rods

111 and 109 are engaged, the horizontal shoulder 139 of latch 133 is slightly vertically spaced from the upper surface of lever 125 so that upon initial movement of shaft 105 caused by outward movement of operating rod 61, cam boss 131 will move clockwise permitting spring 123 to push sleeve 113 upwardly until the upper surface of lever 125 engages downwardly facing horizontal shoulder 139 of latch 125 as shown in FIG. 7, and contact rod 111 is lifted by sleeve rib 119 a slight distance sufficient to provide a gap in the order of one thirty-secondsto one-sixteenth inch between

contacts

109 and 111. Cam 129 is formed with a second boss 143 which, upon further rotation of the cam through a period of 2 to 3 wave cycles to the position shown in FIG. 8, will engage a protuberance 145 on latch 133,

forcing latch 133 to move counterclockwise about its fulcrum 135 so that shoulder 139 clears the end of operating lever 125, as shown in FIG. 8, and by this time cam projection 131 will be completely clear of operating lever 125, so that spring 123 is free to force sleeve 113 upwardly and the engagement between annular rib 119 and head portion 115 of movable contact rod 111 will permit the latter to move upwardly until it is spaced five thirty-seconds to three-sixteenths inch from the bottom fixed contact and the circuit through it is completely broken. The initial movement limited by the engagement of shoulder 139 and the upper surface of lever 125 to one thirtysecond to one-sixteenth inch during a period of 2 to 3 cycles is for the purpose of permitting arcing to occur between

contacts

109 and 111 in the vacuum bottles so that the current might continue to the zero ordinate of its wave cycle instead of being interrupted at some other value, i.e., chopped, thereby eliminating high transient voltages on low line current interruptions.

Additional vacuum switches55 mounted within housing 53 are spaced from each other axially of the housing by spacer frames 147, in which are included actuating sleeves 113 similar to that previously described. Each of the actuating sleeves 113 is formed with three radial legs 149, which are maintained in the same angular relation about the axis of the housing by an upstanding stud 151 which pass through holes in one of the legs 149 of each sleeve. For transmitting movement from the operating mechanism to the succeeding switch contact rods 111, vertical control rods 153 extend axially of the housing connecting the ends of corresponding sleeve arms 149.

The interrupter circuit comprises brackets 67 on air break blades 13 and 15, hooks 69, operating rods 61, links 77, wire 155 connecting the operating linkage to first movable contact rod 111, wire 157 connecting first fixed contact 109 to second movable contact rod 111, and wire 159 connecting the last or bottom switch 55 to the pedestal 24 of column 53. Since the interrupter mechanism carries the load current, to provide additional insulation, mechanism housing 57 and the annular space surrounding vacuum switches 55 within cylindrical housing 53 are filled with a gas of high dielectric strength. To prevent escape of this gas, and the admission of air, flexible bellows seals 161 are provided around rods 81 where they pass through housing wall 58, and suitable sealing gaskets are provided where required. I

Operation of the switch gear is as follows: By means of a suitable lever at ground level, selective rotation of any of the desired air break switch blades 13 or 15 to open position is initiated by rotating rotatable insulators 7 or 9. The initial rotation of insulator 7, for example, causes main switch blade 13 to rotate and with it contact cam 31 rotates out of engagement with jaws 25 before blade 13 begins to swing in a horizontal plane out of jaws 25, further rotation of shaft 7 initiating swinging movement. The current path is then through arcing horns 41 and their contacts 47. At approximately 5 of swinging movement of blade 13, pickup hook 69 engages operating rod 61, thereby placing the vacuum interrupter switches 109, 111 in the circuit. Arcing horns 41 remain in the circuit for another 10 of switch blade travel after which they are released. Meanwhile, hook 69 causes the engaged operating rod 61 to move outwardly, initiating rotation of shaft 105, causing cam projection 131 to move clockwise so as to permit the initial opening movement of contact rods 111 to approximately one thirty-second to one-sixteenth inch clearance from fixed contacts 109 in the interrupter switches, no further upward movement being permitted for a period of 2 to 3 cycles, approximately. It will be noted that movement of either rod 61 acts through shaft to cause similar movement of the other rod 61 away from its associated switch blades so that the other rod 61 is out of recovery voltage restrike range of its associated switch blade. Further outward movement of blade,

13, acting through bracket 67, pickup hook 69, operating rod 61, and operating shaft 105 causes further rotation of cam 129 until boss 131 is completely clear of lever and boss 143 engages protuberance 145 on latch member 133. This causes latch member 133 to rotate counterclockwise so that its shoulder clears the end of lever 125, permitting spring 123 to urge sleeve 113 upwardly so that rib 119 in sleeve 113 lifts movable contact rod 111, by means of its head portion 115, to a full open position, in which movable contact rods 111 are spaced from fixed contact rods 109 five thirty-seconds consequent high transient voltages-on low line current interruptions. The final full opening of

load interrupter contacts

109, 111 takes place at approximately 30 opening of air break switches 13 and 15. Main switch blade 13 can then be moved to its 90 full-open position and hook pickups 69 brush past the lower tip of operating rods 61, permitting springs 63 to return the operating rods to their normal position in which they are seated in Y-shaped stops 65. As operating rod 61 is moved inwardly by spring 63 about its fulcrum 65 it urges link 77 inwardly, which produces clockwise rotation of

bellcrank

89, 93 about its fulcrum 91 (right-hand side of FIG. 3). This movement of

bellcrank

89, 93 is transmitted by link 97 through arm 103 on operating shaft 105, producing counter-v clockwise rotation of the latter. This causes boss 131 of cam 129 to press downwardly on lever 125 which, through engagement with actuating sleeve 113, acts through spring 121 to bias movable contact rods 111 into engagement with fixed contact rods 109. Simultaneously boss 143 on cam 129 has rotated counterclockwise to clear protuberance 145 on latch 133 and permit torsion spring 141 to return latch 133 to its normal cocking position in which it engages the end of operating lever 125 and shoulder 139 overlies the upper surface of lever 125 in slightly spaced relation with respect thereto.

Although operation of arm 13 has been described as an illustrative example, it will be evident that thesame operating sequence will take place when either of the air break switches is opened. The only difference will be in the direction of rotation, i.e., blade 15 is rotated clockwise, as distinguished from the counterclockwise swinging of arm 13. However, irrespective of which operating rod is actuated, the operation of the interrupter switch actuating mechanism is the same.

A simplified fonn of the interrupter mechanism, for use with a single air break switch, is illustrated in FlG. 10. In this embodiment a smaller square housing 57A encloses the mechanism, which is essentially the same as the previously described embodiment, and bears the same reference numerals, except that in FIG. 10, the single operating rod 61 is mounted directly on shaft 105, and the intervening linkages are omitted.

Details of the switch gear and interrupter operating mechanism disclosed herein may be varied substantially without departing from the spirit of the invention and the exclusive use of such modifications as come within the scope of the appended claims is contemplated.

lclaim:

1. In a switch device, fixed structure including a fixed contact, a movable contact, operating mechanism comprising actuating means operatively connected to said movable contact, means biasing said actuating means away from said fixed contact, a lever fulcrumed to said fixed structure and extending transversely of the direction of movement of said movable contact and having a surface engaging said actuating means in opposition to said biasing means, a rotatable cam having a first projection normally engaging said lever and holding it against said actuating means to oppose said biasing means, a pivoted latch member having a transverse surface normally spaced from the longitudinal surface of said lever remote from said actuating means a distance proportional to a desired initial opening of said switch, said cam being rotatable to a position in which said first projection is at least as remote from said lever normal position as said latch transverse surface whereby to pennit said biasing means to move said lever into engagement with said latch surface upon initial rotation of said cam,

said cam having a second projection engageable with said latch upon further rotation of said earn a predetermined distance to urge said latch to a position clear of said lever and completely release the pressure exerted by said lever on said actuating means whereby to permit said movable contact to move away from said fixed contact to its fully open osition,

2. In a switch device according to claim 1, sm actuating means comprising a sleeve with a closed end engageable with said lever, said movable contact having an operating rod movable axially within said sleeve, opposing shoulders on said sleeve and on said rod, means within said sleeve biasing said rod toward the contact closed position and said shoulder therein, said first-named biasing means biasing said sleeve toward said lever and away from the contact closed position.

3. In a switch device according to claim 2, a plurality of said fixed and movable contacts arranged in pairs disposed axially with respect to each other and separate actuating means for each pair, each of said actuating means comprising similar sleeves having a plurality of radial arms, there being link members fixedly connecting the arms of all said actuating means whereby to transmit movement of said first-named actuating means to succeeding actuating means and cause simultaneous actuation of each of said movable contact means.

4. ln a switch device according to claim 3, each pair of fixed and movable contact means being enclosed in a sealed bottle.

5. In a switch device according to claim 1, a shaft rotatably journaled in said fixed structure and mounting said cam, a pair of rods angularly related to said shaft and extending outwardly from the ends thereof in a common plane, means for moving said rods axially, and means for converting the axial movement of said rods to rotational movement of said shaft whereby to cause opening movement of said movable contact upon application of axial forces to said rods.

6. In a switch device according to claim 5, said converting means comprising bellcranks fulcrumed on said fixed structure and each having one arm pivotally connected to one of said rods, arms on the ends of said shaft, and a link connecting each of said last-named arms to a second arm of each of said bellcranks.

7. ln a switch device according to claim 6, said means for moving said rods axially comprising levers fulcrumed to said fixed structure and pivotally connected at a point remote from their fulcrums to said rods respectively, means biasing said levers to the position in which said first-named lever holds said actuating means in contact closed position, a pair of air break switch blades each provided with a hooklike member engageable with said last-named levers for moving said last-named levers against said last-named biasing means toppen said contact means when said air break switch blades are moved away from their fully closed positions.

8. In a switch device according to claim 3, a shaft rotatably journaled in said fixed structure and rigidly mounting said cam, and a lever rigidly secured to said shaft and engageable by another member to rotate said shaft.

9. In a switch device according to claim 2, a sealed housing completely enclosing said operating mechanism.

10. In a switch device according to claim 9, a separate sealed housing enclosing said switch, said housings communicating with each other and being filled with gas having high dielectric strength.

11. In a switch device according to claim 4, a sealed housing completely enclosing said operating mechanism and a separate elongated sealed housing completely enclosing said sealed bottles in spaced relation thereto, said housings communicating with each other and being filled with agas having high dielectric strength.

7 3 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,576,961 Da May 4, 1971 Inventor(s) John L. Turner It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In the drawings, Sheet 2, FIG. 5, the reference numeral "85" applied to the cotter keys should read -84--.

Column 2, 11M 64, co'kter keys 85" should read --cotter keys 84-.

Column 3, line 54, "thirty-second" should read -whichline 62, "latch 125" should read --latch 133- Column 5, line 13, "fulcrum 65" should read --fulcrum 7 Signed and sealed unis lhth day of March 1972'.

(SEAL) Attest:

EDWARD M.FLETcHER,J1'=t. ROBERT GOTI'SCHALK Abtesting Officer Commissioner of Patents

Claims

1. In a switch device, fixed structure including a fixed contact, a movable contact, operating mechanism comprising actuating means operatively connected to said movable contact, means biasing said actuating means away from said fixed contact, a lever fulcrumed to said fixed structure and extending transversely of the direction of movement of said movable contact and having a surface engaging said actuating means in opposition to said biasing means, a rotatable cam having a first projection normally engaging said lever and holding it against said actuating means to oppose said biasing means, a pivoted latch member having a transverse surface normally spaced from the longitudinal surface of said lever remote from said actuating means a distance proportional to a desired initial opening of said switch, said cam being rotatable to a position in which said first projection is at least as remote from said lever normal position as said latch transverse surface whereby to permit said biasing means to move said lever into engagement with said latch surface upon initial rotation of said cam, said cam having a second projection engageable with said latch upon further rotation of said cam a predetermined distance to urge said latch to a position clear of said lever and completely release the pressure exerted by said lever on said actuating means whereby to permit said movable contact to move away from said fixed contact to its fully open position.

2. In a switch device according to claim 1, said actuating means comprising a sleeve with a closed end engageable with said lever, said movable contact having an operating rod movable axially within said sleeve, opposing shoulders on said sleeve and on said rod, means within said sleeve biasing said rod toward the contact closed position and said shoulder therein, said first-named biasing means biasing said sleeve toward said lever and away from the contact closed position.

4. In a switch device according to claim 3, each pair of fixed and movable contact means being enclosed in a sealed bottle.

7. In a switch device according to claim 6, said means for moving said rods axially comprising levers fulcrumed to said fixed structure and pivotally connected at a point remote from their fulcrums to said rods respectively, means biasing said levers to the position in which said first-named lever holds said actuating means in contact closed position, a pair of air break switch blades each provided with a hooklike member engageable with said last-named levers for moving said last-named levers against said last-named biasing means to open said contact means when said air break switch blades are moved away from their fully closed positions.

11. In a switch device according to claim 4, a sealed housing completely enclosing said operating mechanism and a separate elongated sealed housing completely enclosing said sealed bottles in spaced relation thereto, said housings communicating with each other and being filled with a gas having high dielectric strength.