US2938095A

US2938095A - Electric circuit interrupter

Info

Publication number: US2938095A
Application number: US764641A
Authority: US
Inventors: Ralph J Baskerville
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1958-10-01
Filing date: 1958-10-01
Publication date: 1960-05-24
Anticipated expiration: 1977-05-24

Description

24, 1950 R. J. BASKERVILLE 2,938,095

ELECTRIC cmouxr INTERRUPTER 3 Sheets-Sheet 1 Filed Oct. 1, 1958 I I I I I I I I IIIIIIIIIIIII Inventors,

Ralph J. Baskerville,

by. His Attorney.

May 24, 1960 R. J. BASKERVILLE ELECTRIC CIRCUIT INTERRUPTER 3 Sheets-Sheet 2 Filed Oct. 1, 1958 Inventor. falph J. Baskerville u '7.

$5 At orneg 1959 R. J. BASKERVILLE 2,938,095

ELECTRIC CIRCUIT INTERRUPTER Filed Oct. 1, 1958 3 Sheets-Sheet 3 lnventor-z Ralph J. Baskerville by WM His Atborrleg.

United States Patent O 2,938,095 ELECTRIC CIRCUIT INTERRUPTER Ralph J. Baskerville, Drexel Hill, Pa., assignor to General Electric Company, a corporation of New York Filed Oct. 1, 1958, Ser. No. 764,641 13 Claims. (Cl. 200-164) This invention relates to electric circuit interrupters or breakers, and more particularly it relates to an improvement in the contact structure of a low voltage air circuit breaker.

It is a well known practice in designing the contact structure of circuit interrupters to provide for scrubbing or wiping action between the cooperating contact surfaces of the movable and relatively stationary contact members, respectively. This action, which serves to keep the contact surfaces clean and improve breaker operation, is usually obtained by designing the contact structure so that there is relative translational movement between the cooperating contact surfaces as the movable contact member moves from a position of initial engagement with the relatively stationary contact member, wherein the cooperating surfaces just touch, to a final, fully closed position. It is an object of the present invention to provide a relatively simple and inexpensive circuit breaker contact structure having means for conveniently and accurately adjusting the position of the movable contact member with respect to the relatively stationary contact member, whereby the desired amount of contact wiping action can be readily obtained with great precision.

A general object of the invention is to provide an improved circuit breaker contact structure of the character described hereinafter.

In carrying out my invention in one form, an electric circuit breaker is provided with a relatively stationary contact member, and a cooperating movable contact member is pivotally supported for rotation about an axis between open and closed circuit positions with respect to the stationary contact member. A generally cylindrical shaft disposed substantially parallel to the axis of rotation is rotatably connected to the movable contact member. The shaft has an eccentric portion of polygonal cross section, and an actuating member is adjustably coupled to this eccentric portion in order to move the movable contact member between its open and closed circuit positions. The adjustable coupling between the eccentric portion of the shaft to two or more different predetermined angular positions and the actuating member is arranged to permit controlled rotation of the shaft for precisely determining the closed circuit position of the movable contact member, whereby the amount of contact wipe between the movable and relatively stationary contact members may be varied.

My invention will be better understood and its various objects and advantages will be more fully appreciated from the following description taken in conjunction with the accompanying drawings in which:

Fig. 1 is a side elevation of a circuit breaker contact structure embodying a preferred form of my invention, with the movable contact member shown in its closed circuit position;

Fig. 2 is a front elevation of the contact structure illustrated in Fig. l, with the movable contact member moved to its open circuit position;

. 2,938,095 Patented May 24, 1960 by means of which actuating force is transmitted to the movable contact member; and

Fig. 6 is a view similar to Fig. 5 illustrating an alternative construction of the impelling shaft of the contact structure.

Referring now to Fig. 1, I have shown an electric circuit breaker or interrupter comprising a base member 11, a relatively stationary contact member 12 mounted on the base, an electroconductive bracket 13 mounted on the base in spaced relation to the stationary contact member, a movable contact member 14 pivotally supported by bracket 13 and disposed in cooperative relationship with the stationary contact member 12, and actuating means such as a crossbar 15 coupled to the movable contact member 14 for moving this member into and out of circuit-making engagement with the stationary contact member 12. The

components

12, 13 and 14 comprise the contact structure of one pole unit of an alternating or direct current circuit breaker or interrupter, and other similar pole units (not shown) can be mounted for gang operation on the base member 11 adjacent to the pole unit that has been illustrated in Figs. 1 and 2.

The base member 11 supports the current-conducting studs of the breaker and the other breaker parts directly connected to the studs. As illustrated in Fig. l, the base member comprises a sheet 16 of electric insulating material of substantially uniform thickness. The sheet 16 is shaped to form a channel-shaped section or depression at 17, and the bottom of this section is provided with an aperture for snugly admitting and partially supporting an upper breaker stud 18. For the purpose of the present description, the contact structure 12-14 will be considered mounted on the front of the base 11, and the upper breaker stud 13 is connected to a suitable electric power source or bus (not shown) located behind or to the rear of the base. The contact structure shown in the drawings and described herein to illustrate a preferred embodiment of my invention is designed for connection to an electric power bus rated 600 volts A.C. and capable of supplying as much as 25,000 amperes short-circuit current.

The stationary contact member 12 is mounted on the upper breaker stud 18. As can be seen in Fig. 1, the upper stud 18 is secured to the sheet 16 of base member 11 by suitable support means such as generally L-

shaped angles

19 and 20. The

angles

19 and 20 are respectively disposed above and below stud 18 and are fastened thereto by three copper rivets or the like. The lower angle 20 is provided with a pair of tapped holes, and a pair of appropriate bolts 21 is used to secure this angle to the base member 11. The supporting angle 19, which extends above the breaker stud 18 as is shown in Fig. 1, serves as a conventional arc runner in cooperation with the stationary contact member 12. This angle is provided with a stud 22 for securing it to the insulating sheet 16 of the base 11.

The end of breaker stud 18 extending forward from the base member is divided into two horizontally diverging branches, whereby this stud in plan view has a general ly Y-shaped appearance. In the preferred embodiment of my invention illustrated in Figs. 1 and 2, the stationary contact member 12 comprises at least one pair of elongated contaot elements or fingers 23, each finger 23 being pivotally supported intermediate its ends on the outer end of a different diverging branch of the breaker stud 18. For this purpose, the outer ends of the diverging contact surfaces 24 normally disposed in branches are respectively provided with generally cylindrical bearing surfaces having centerlines oriented inv a vertical direction as viewed in Figs. 1 and 2. Each hearing surface is recessed so that Shoulders are formed at its upper and lower ends to prevent vertical movement of the associated contact finger. If desired, the length of the bearing surface can be made suflicient to accommodate more than one contact finger 23 in side-by-side rel ation.

The bearing surfaces at the outer ends of the diverging branches of the breaker stud 18 provide fulcrums for a pair of contact fingers 23, and the pivotal connection between each contact finger and the breaker stud forms a current-conducting joint. The fingers are respectively supported on opposite bearing surfaces in opposing relationship with respect to each other for pivotal movement in a common horizontal plane. The opposing or inner ends of the contact fingers are movable in separate, relatively short arcuate paths, and the opposing ends are respectively provided with generally flat, complementary a common vertical plane as viewed in Figs. 1, 2 and 4.

The inner end of each contact finger 23 has an extension 25 (see Fig. 4) disposed to engage a common stop 26 for determining the limit of the arcuate movement of the contact surface 24 in one direction. The stop 26, as is indicated in Fig. 2, comprises a pin vertically disposed intermediate the divergent branches of the breaker stud 18 and fixedly connected to the upper and lower supporting

angles

19 and 20. Associated with the outer end 27 of each contact finger 23 is suitable spring means, for example, the illustrated tension spring 28 which may be anchored at one end to a fixed member such as pro- 'vided by a laterally extending lug 29 of the upper supporting angle 19. Thus, spring means 28 establishes a biasing torque in the contact finger 23 tending to move the contact surface 24 along its arcuate path in a forward direction away from the base member 11, and such movement by the finger is limited by the stop pin 26.

The above-described structure provides for arelatively limited deflection of each contact finger in a rearward direction.

The biasing torque is opposed and overcome and each contact finger 23 of the relatively stationary contact member 12 is tilted slightly on its fulcrum by the action of the movable contact member 14. As will be more fully explained hereinafter, the movable contact member 14 in the illustrated embodiment of the invention includes a pair of arms respectively provided with contact surfaces 47 which move in parallel planes disposed approximately perpendicular to the plane defined by the arcuate paths of the contact surfaces 24 of the fingers 23. The actuating means 15 provides actuating force for moving each contact surface of member 14 into and out of circuit-making abutting engagement with the contact surface 24 of a different contact finger.

During a circuit making operation, the contact surfaces 47 of the movable contact member 14 are jointly carried rearwardly from their open circuit position (Fig. 2) into substantially simultaneous engagement with both of the cooperating contact surfaces "24, and further rearward movement of the contact surfaces 47 to their fully closed position (Fig. l) forces the spring means 28 to yield as the relatively stationary contact fingers 23 tilt on their fulcrums. The arrangement is such that the cooperating

contact surfaces

24 and 47 follow different paths. of movement while in engagement with each other. Consequently one of the engaging surfaces is translated with respect to the other and there will be sliding or scrubbing movement therebetween. In this manner, conventional contact Wiping action is obtained, and the amount of wiping action can be adjusted with great precision in accordance with my invention soon to be described in detail.

- respectively,

Although for the sake of illustration I have shown and described cooperating contact members constructed and arranged for abutting circuit-making engagement, I do not wish to be limited to such an abutting type contact structure. It will soon become apparent that the successful application of my invention does not depend in any respect on the particular nature of the cooperating relationship between the movable and stationary contact members. In lieu of the abutting arrangement illustrated, the movable contact member could be, for example, a blade-like member disposed to slide between and spread apart a pair of generally parallel cooperating contact elements.

In Figs. 1 and 2 it can be seen that the electro-conductive bracket 13 for supporting the movable contact member 14 is mounted on base member 11 by means of a pair of suitable bolts 30 or the like. The bracket 13 has a lower lip 31 provided with a hole for the purpose ofconnecting a suitable current-conducting member or another breaker stud (not shown) to the bracket. Part of the bracket 13 is disposed adjacent the front surface of the insulating sheet 16 of base member 11, and a rigid reinforcing member 32 is disposed adjacent the rear surface of the sheet 16 in overlapping relationship with bracket 13 and the lower supporting angle 20, respectively. The reinforcing member 32 is provided so that the loading of the insulating sheet 16 in the area between the bracket 13 and the relatively stationary contact member 12 will be in compression rather than in flexure. A channel 33 of insulating material is disposed intermediate the reinforcing member 32 and the rear of sheet 16 to provide additional electrical insulation between the sides of member 32 and the fastening bolts 21 and 3G.

The bracket 13 includes a pair of spaced-apart upstanding lugs 34 and 35 projecting in front of base member 11. A removable pivot pin 36 is supported by the lugs 34 and 35, the axis of the pivot pin extending in a horizontal direction generally parallel to the plane of the base member 11 as viewed in Figs. 1 and 2. The pivot pin 36, which passes through both of the lugs 34 and 35 and protrudes from their outwardly facing sides, is retained in place by a releasable clamp 37 connected to the pin intermediate the lugs. The clamp 37 preferably comprises a resilient helical coil loosely encircling pin 36, the length of the helix corresponding approximately to the span between the lugs 34 and 35. The opposite ends of the coil of clamp 37 extend tangentially therefrom and are arranged for movement between first and second cooperating positions. In Fig. 2 the ends are shown in a position wherein they releasably engage each other, and in this self-locked position the circumference of the coil is contracted for firmly grasping the encircled pin and preventing axial movement and removal thereof. By separating the ends and permitting them to assume their other position in accordance with the resilience of the coil, the circumference of the coil can be expediently expanded for assembling or disassembling purposes.

The connection between the movable contact member 14 and the supporting bracket 13 will now be de scribed with particular reference to Figs. 2 and 4. The movable contact member 14 comprises a pair of

elongated contact arms

38 and 39 arranged in generally parallel relation for joint operation. One end 40 of the arm 38 is disposed adjacent the outwardly facing side of the upstanding lug 34 and is rotatably mounted on a protruding portion of pivot pin 36; and one end 41 of the other contact arm 39 is disposed adjacent the outwardly facing side of lug 35 for rotatable mounting on the opposite protruding portion of the pivot pin.

The connection between each

movable contact arm

38, 39 and the electroconductive bracket 13 is arranged to provide three separate current-conducting joints. The first such joint is provided by the bearing surfaces between the contact arm and the pivot pin 36 on which the movable contact arms it rotates, that is, between pin 36 and the periphery of a hole 42 which has been located in the one end 40, 41 to accommodate the pin 36. The surface of the pivot pin 36 and the periphery of hole 42 may be silver plated and burnished to ensure a wear-resistant, low electric resistance current-conducting path.

The second current-conducting joint is obtained by providing the outwardly facing side of each lug 34, 35 of the bracket 13 with a substantially fiat, smooth slide surface 44 disposed generally perpendicular to the axis of the pivot pin 36. Each slide surface 44 is contiguous to a smooth, pertaining slide surface 45 provided on the relatively broad inner side of the pivoted end 40, 41 of each

movable contact arm

38, 39, i.e., on the side of the contact arm facing the supporting bracket 13. Each slide surface 45 is disposed generally parallel to the respective adjoining slide surface 44 of the bracket 13, and therefore all of the slide surfaces 44 and 45 are substantially perpendicular to the axis of pivot pin 36 which corresponds to the axis of rotation of the

movable contact arms

38 and 39.

The slide surface 45 of each movable contact arm includes a raised section which, as can best be seen in Figs. 3 and 4, preferably comprises a portion of a cylinder. The crest of this raised section is oriented so that it extends in a direction substantially perpendicular to the longitudinal centerline of the contact arm, and it is intersected by the hole 42 provided for pivot pin 36. The crests of the raised sections of the two slide surfaces -45 respectively cooperate with and are contiguous to the .slide surfaces 44 of bracket 13, and pivotal movement .of the contact arms on pin 36 causes each crest to slide vover the associated slide surface of the relatively staztionary bracket 13. The contiguous portions of each ;pair of cooperating slide surfaces define a line contact which provides the second current-conducting joint between each movable contact arm and the supporting ibracket. Of course, as an alternative to the specific .arrangement illustrated and described aboev, a raised :section could be located on each of the slide surfaces 44 and the slide surfaces 45 could be made substantially zflat.

Contact pressure at the joints formed by the respective ,pairs of contiguous slide surfaces 44 and 45 is maintained by means of an electroconductive spring member 46 which preferably comprises a U-shaped spring clip. As indicated in Figs. 1 and 2, the resilient upstanding legs of the clip 46 are split for respectively bearing against :the outer sides of the pivoted ends 40 and 41 of the :contact

arms

38 and 39 at points disposed on opposite :sides of the pivot pin 36. The electroconductive spring :member 46 is secured to the bracket 13, and since it also is in engagement with each movable contact arm it provides the third current-conducting joint. In addition, spring member 46 applies a sidewise force which maintains contact pressure at the contiguous surfaces of both pairs of cooperating slide surfaces 44 and 45. This force is supplemented by an electromagnetic force whenever the movable contact member 14 is conducting current. Whenever the

parallel contact arms

38 and 39 conduct alternating current, a magnetic force is established tending to reduce the spacing between these two arms and thereby establishing additional contact pressure at the contiguous slide surfaces, the magnitude of this sidewise force being proportional to the square of the current magnitude.

The diameter of the hole 42 in the pivoted ends of is made slightly greater than the diameter of pivot pin 36. This arrangement permits the

contact arms

38 and 39 to rock on pivot pin 36. The crests of the raised sections of the slide surfaces 45 provide fulcrums for the rocking movement of the

arms

38 and 39, respectively. This arrangement allows for 'a certain degree of misalignment of the various parts and a liberal manufacturing tolerance without adversely 6 affecting the positiveness of the electric contact between the movable elements and the supporting bracket 13.

By utilizing three parallel current-conducting joints for each of the two parallel arms'of the movable contact member 14, the overall electric resistance of the pivotal connection has been efficiently reduced thereby significantly decreasing temperature rise. In this manner, it is possible to obtain a successful contact structure without the conventional flexible braids or conductors.

In the illustrated embodiment of my invention, the corresponding free ends of the

contact arms

38 and 39 are provided respectively with transverse contact surfaces 47 disposed for abutting engagement with the contact surfaces 24 of the relatively stationary contact fingers 23. Rotary movement of the contact arms on pivot pin 36 carries the contact surfaces 47 through arcuate paths which define vertical planes intersecting at approximately right angles the horizontal plane of movement of the relatively stationary contact surfaces 24, as viewed in Figs. 1, 2 and 4. This arrangement permits the convenient utilization of more than one stationary contact finger for each movable contact arm, whereby more than two separate points of circuit-closing engagement can be provided between the movable contact member 14 and the relatively stationary contact member 12.

The cooperating contact surfaces 24 and 47 preferably are made of silver tungsten carbide material which will successfully perform the continuous current-carrying function of the contacts and also the required circuit making and breaking duty, without appreciable contact erosion or pitting or contact welding as a result of electric arcing. Therefore it is not necessary to provide separate arcing and main contacts. With the various parts shown in Figs. 1 and 2 appropriately dimensioned, the contact structure will safely carry at least 225 amperes continuously at 600 volts A.C., and the same contact structure can be modified to carry at least 600 amperes continuously merely by changing the relatively stationary contact member 12 so that two additional contact fingers 23 are respectively disposed adjacent those shown and by appropriately extending the contact surfaces 47 of the movable contact arms.

In order to obtain a compact arrangement at the cooperating contact surfaces 24 and 47, the

contact arms

38 and 39 are spaced closer together at their corresponding free ends than at the pivot pin 36. As is shown in Figs. 2-4, this has been accomplished by axially offsetting the free ends of the contact arms with respect to the pivotally connected ends 40 and 41, respectively. In other words, each free end is disposed inside a plane normal to the pivot pin 36 that intersects the bearing area providing the pivotal connection between the associated movable contact arm (the periphery of hole 42) and pin 36. Thus, the center of the circuit-making surface area of the contact surface 47, that is, the center of the area of surface 47 which engages the contact surface 24 of the stationary contact finger 23, defines with the center of the pivotal connection to pivot pin 36 a straight line 48 which intersects the axis of rotation (the axis of pivot pin 36) at an oblique angle. See Fig. 3.

The

contact arms

38 and 39 have been oppositely offset at intermediate portions 49. As is indicated in Figs. 3 and 4, the offset portion 49 is provided with a transverse hole 50 the centerline of which is oriented parallel to the pivot pin 36. An actuating member such as a cylindrical impelling shaft 51 is rotatably disposed in hole 50, and by this means actuating force is applied to the movable contact member 14 for jointly moving the

contact arms

38 and 39 between open and closed circuit positions. The offset portion 49 of each of the contact arms is so arranged that the line of action of the resultant actuating force intersects the straight line 48. In other words, a common plane of action and reaction is defined by the center of the bearing surface between the impelling shaft 51 and the offset portion 49 of the holes 50 in the offset portions contact arm, the center of the pivotal connection between pivot pin 36 and the pivoted end of the arm, and the center of the engaging area of contact surface 47. This plane will include the intersection of the respective planes of movement of the cooperating movable and relatively stationary contact surfaces 47 and 24. As a result, there is no net component of actuating force having a moment arm with respect to the straight line 48, and there is substantially no torsion or twisting tendency in the contact arm in its closed circuit position. Such a tendency would be undesirable because it would cause uneven forces along the length of the crest of the raised section of slide surface 45 with respect to the contiguous slide surface 44, whereby the effectiveness of this current-conducting joint between the movable contact member 14 and the supporting bracket 13 would be seriously impaired.

In the vicinity of the offset portions 49 of the

contact arms

38 and 39, protrusions 52 are formed. These protrusions 52, which preferably are in the form of curved embossments on the inner sides of the contact arms, are respectively disposed to extend in overhanging relationship with the lugs 34 and 35 of bracket 13. In this manner, the current-conducting joints formed by the two pairs of contiguous slide surfaces 44 and 45 are shielded from the electric arc and are products which may be produced during circuit breaking action of the contact structure. The protrusions 52 will prevent particles of foreign matter produced during circuit breaking action from entering these joints by straight-line paths from the area of arc interruption. Such foreign matter, if permitted to enter the joint, could cause excessive wear and increased contact resistance.

The impelling shaft 51 fits relatively loosely in the 49 of the

movable contact arms

38 and 39, whereby each arm can slide on shaft 51while rocking on pivot pin 36. Thus the contact surface 47 of each arm is free to move in a lateral or transverse direction, and such lateral movement is controlled by resilient means associated with the contact arm. As is shown in Figs. 2 and 4, the resilient means preferably comprises a helical spring 53 disposed on impolling shaft 51 intermediate the

contact arms

38 and 39. The spring 53 applies a transverse force to each contact arm and establishes in the arm a relatively weak biasing torque with respect to the pivot provided by the line contact at the joint formed by the contiguous slide surfaces 44 and 45. This biasing torque is in a direction tending to spread apart the contact arms. Such movement of each contact arm is stopped and its normal position is determined by a bushing 54 disposed on shaft 51 between a retaining ring 55 or the like and the circular outer side of the offset portion 49 of the arm.

During circuitmaking action of the contact structure, each contact surface 47 comes into abutting engagement with the contact surface 24 of a relatively stationary contact finger 23, and as the cooperating contact surfaces wipe the contact finger 23 is tilted on its fulcrum in opposition to its biasing torque. The arrangement is such that a transverse force is supplied to contact surface 47 by contact surface 24 as the contact finger 23 moves pivotally on its fulcrum. Due to the resilient means 53, the movable contact arm yields to this transverse'force and the contact surface 47 is able to move laterally while following the arcuate path of the contact surface 24. As a result, the'relative movement or translation between the cooperating contact surfaces 24 and 47 in this lateral direction is reduced, thereby reducing the amount of fric- 'tion between these cooperating surfaces and improving the performance of 'the contact structure.

:The movable contact member 14 is coupled to the actuating means or crossbar by means of an actuating member 56 which is coupled to the impelling shaft 51 and which preferably comprises a generally U-shaped link securely fastened to the crossbar. Eachleg of the link56 is provided with an extension 57 connected to the first and second relatively fixed positions.

pivot pin 36 as shown in Fig. 1, and thus the crossbar 15 is supported for pivotal movement by pin 36. The crossbar is connected to a circuit breaker operating mechanism by means of another link 58 and a connecting member 59. The operating mechanism, which has not been shown, may be of any suitable type for moving the connecting member 59 in a generally horizontal direction (as viewed in Figs. 1 and 2) and thereby reciprocally moving the crossbar 15 about its pivot between As a result of this action, a shoulder 60 of the actuating member or link 56 is carried through a predetermined arcuate path with respect to pivot pin 36.

As is clearly shown in Figs. 2 and 4, the impelling shaft 51, which is disposed in generally parallel axial relationship to the pivot pin 36, has opposite end portions 61 extending laterally from opposite sides of the

movable contact arms

38 and 39, respectively. In accordance with my invention, each portion 61 is made eccentric with respect to the cylindrical body of shaft 51, and the eccentric portions 61 are adjustably coupled to the actuating member 56 in a manner permitting controlled rotation of the shaft. The adjustable coupling has been obtained in the illustrated embodiment of the invention, for example, by making each eccentric portion 61 a polygon having at least two flat sides and by providing a slot in each leg of the actuating member 56 for receiving the associated eccentric portion. As seen in Fig. 1, the two lengthwise sides of each slot in the actuating member 56 are respectively defined by the shoulder 60 and by a. relatively stiff cantilever flat spring 62 which is carried by the member 56 in spaced reiation to shoulder 60 for resiliently bearing against the polygonal eccentric portion 61. In a preferred form of the invention, the cross section of each eccentric end portion 61 of shaft 51 comprises an equiangular hexagon, and the parallel fiat sides of the hexagon are positively but resiliently locked between shoulder 60 and the fiat spring 62. See Figs. 1, 5 and 6. Thus the slots in the actuating member 56 permit controlled rotation of shaft 51, and the slots are disposed also to permit radial movement of the eccentric portion 61 with respect to the axis of pivot pin 36.

By means of a conventional open-end wrench applied to the hexagonal eccentric portions 61, and without the necessity of disassembling or reassembling any parts, the impelling shaft 51 may be conveniently rotated in steps of 60 degrees to any one of six different angular positions disposed at intervals of 60 degrees. In each of these six positions, the movable contact member 14 is located in a different relative angular position with respect to the crossbar 15 and with respect to the relatively stationary contact member 12. The purpose of this adjustrnent is to accurately establish the fully closed position of the movable contact member regardless of liberal manufacturing tolerances, whereby the desired amount of contact wipe can be precisely obtained. More specifically, this adjustment is used to vary in inverse relationship the distances which the free end of each

movable contact arm

38, 39 travels along its arcuate path from its open circuit position to a point which circuit-making engagement with the relatively stationary contact member 12 is initially established and from said point of initial engagement to its fully closed position, respectively, during a circuit closing operation of the contact structure. The total distance traveled by each free end between open and fully closed positions will, of course, remain constant.

In order to obtain the six different angular positions of the movable contact member 14 mentioned above, the eccentric hexagonal portions 61 have been oriented in an unsymmetrical relationship with respect to a diameter 63 of the cylindrical body of shaft 51 that passes through the center e of the cross-section of eccentric portion 61. See Fig. 5. In other words, the flats of the hexagonal portion 61 are not symmetrically disposed with respect to diameter 63, and the maximum degree of asymmetry has been obtained in the illustrated embodiment of my invention by shifting each hexagonal portion fifteen degrees from a symmetrical position. As a result, the distance b from the axis of rotation c of the cylindrical portion of shaft 51 to each flat side of the hexagonal portion measured along a line normal to the side is different than the correspondingly measured distance from the axis to any other side, and accordingly the fully closed position of the movable contact member 14 will be different for each of the six different angular positions of the impelling shaft 51.

For the sake of expedient adjustment of contact wipe, it is desirable to vary the wipe in uniform steps. In other words, the position of the movable contact member 14 should be changed a uniform amount for each discrete step in the adjustment process. With the construction illustrated in Fig. 5, wherein the cross-section of the eccentric portion 61 of impelling shaft 51 is a regular or equal-sided hexagon, this desirable result is approached but not fully realized. The construction illustrated in Fig. 6, however, enables the result to be obtained. Here the eccentric portion 61a of the shaft 51 has a hexagonal cross-section the sides of which are not equal in length and are not equidistant from the center e of the crosssection. The arrangement is such that the normal distances (b) between the axis of rotation c of the shaft and the respective sides of the hexagon differ from each other by multiples of a constant increment K, and consequently the amount of position change experienced by the movable contact member 14 is constant when the shaft 51 is rotated from one' angular position of shaft 51 to another. The six normal distances in 'Fig. 6 have been identified in ascending order of their lengths as follows: b b b b b and b and the sides of hexagonal cross-section are disposed in relation to the axis of rotation c so that b =b +K, b =b +K or b =b +2K, etc.

As is clearly shown in Fig. 5, the impelling shaft 51 is constructed so that the eccentricity of the hexagonal portion 61 (i.e., the distance from c to e) is less than the dimension d which is one-half the length of the fiat side of the hexagonal portion '61 and hence onetwelfth the perimeter of this portion. With this arrangement, the net effective crank arm of the eccentric portion 61 always lies within the limits of the flats so that the inherent tendency on the part of the impelling shaft 51 to rotate from the angular position to which it has been adjusted is positively and successfully resisted. This proposition is illustrated in Fig. 5 where the vector F represents the resultant of the actuating force applied to the eccentric end portion 61 in order to hold the contact structure closed and the vector R represents the resultant of the reactive force experienced by the impelling shaft 51. The net effective cran'k arm of the eccentric portion 61 is equal to a for the particular angular position of the impelling shaft 51 shown in Fig. 5. It will be apparent that the couple created by forces F and R cannot of itself rotate the shaft 51 from the position shown as long as a is less than d.

The crossbar 15 may be extended across the width of the circuit breaker for connection in a similar manner to other pole units of a multipole circuit breaker. An isolating barrier 64 of insulating material is shown mounted on the crossbar 15 in Fig. 2. Other barriers 65 are provided for the purpose of isolating the various current-conducting parts of the illustrated pole unit from the corresponding parts of adjacent pole units and from ground. A suitable arc chute, not shown in the drawings, may be mounted on the base member 11 to enclose the cooperating contact surfaces 24 and 47 for the conventional purpose of arc extinction.

While I have shown and described a preferred form of my invention by way of illustration, many modifications will occur to those skilled in the art. Therefore, I con- 7 1O template by the concluding claims to cover all such modi fications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In the contact structure of an electric circuit interrupter: a base member; a relatively stationary contact member mounted on the base; a bracket mounted on the base in spaced relation to the stationary contact member; an elongated movable contact arm pivotally supported by the bracket for rotation about an axis, one end of the arm being disposed for arcuate movement between open and closed circuit positions with respect to the stationary contact member; a cylindrical shaft rotatably connected to the movable contact arm and disposed substantially parallel to said axis, the shaft having an eccentric, polygonal end portion extending laterally from said arm; and an actuating member movable in a predetermined arcuate path between first and second relatively fixed positions and adjustably coupled to the end portion of the shaft for moving the one end of the contact arm between its open and closed circuit positions, the adjustable coupling comprising a slot in said actuating member for receiving said end portion and permitting radial movement thereof with respect to said axis, one side of the slot being disposed resiliently to bear against said end portion thereby permitting rotation of the shaft for determining the closed circuit position of said one end.

2. In the contact structure of an electric circuit interrupter: a base member; a relatively stationary contact member mounted on the base; a movable contact member mounted on the base in spaced relation to the stationary contact member for pivotal movement about an axis between open and closed circuit positions with respect to the stationary contact member; an impelling shaft disposed substantially parallel to said axis comprising a cylindrical portion rotatably connected to the movable contact member and an eccentric portion having a hexagonal cross-section; and an actuating member reciprocally movable between first and second relatively fixed positions and adjustably coupled to the eccentric portion of the impelling shaft for moving said movable contact member between its open and closed circuit positions, the adjustable coupling being arranged to permit controlled rotation of the shaft to any one of six different angular positions thereby to determine the closed circuit position of the movable contact member.

3. The contact structure of claim 2 in which the crosssection of the eccentric portion of the impelling shaft comprises an equiangular hexagon, whereby the six different positions to whichthe shaft can be rotated are disposed at angular intervals of sixty degrees.

4. The contact structure of claim 2 in which the crosssection of the eccentric portion of the impelling shaft comprises an equiangular, equal-sided hexagon and in which the eccentricity of the eccentric portion is less than one-half the length of each side of the hexagon.

5. In the contact structure of an electric circuit interrupter: a base member; a relatively stationary contact member mounted on the base; a movable cont-act member pivotally mounted on the base in spaced relation to the stationary contact member for movement between open and closed circuit positions with respect to the stationary contact member; an impelling shaft comprising a cylindrical portion rotatably connected to the movable contact member, the axis of rotation of said cylindrical portion being disposed substantially perpendicular to the plane of movement of the movable contact member, and an eccentric portion having a hexagonal cross-section encompassing said axis of rotation, the six sides of the hexagonal cross-section being disposed in relation to the axis of rotation so that the distance from the axis to each side measured along a line normal to the side is different than a correspondingly measured distance from the axis to any other side;

and an actuating member reciprocallymovable between first and second relatively fixed positions and adjustably coupled to the eccentric portion of the impelling shaft for moving said movable contact member between its open and closed circuit positions, the adjustable coupling being arranged to permit controlled rotation of the shaft to any one of six different angular positions thereby to vary the closed circuit position of the movable contact member.

6. The contact structure of claim in which the sides of the hexagonal cross-section of the eccentric portion of the impelling shaft are not equidistant from the center of said cross-section and the normal distances between the axis of rotation and the respective sides of the crosssection differ from each other by multiples of a constant increment.

7. In the contact structure of an electric circuit interrupter: a base member; a relatively stationary contact member mounted on the base; a bracket including a pivot pin mounted on the base in spaced relation to the stationary contact member; a movable contact member comprising a pair of generally parallel arms mounted for pivotal movement on the pivot pin, said arms having corresponding free ends disposed for joint arcuate movement between open and closed circuit positions with respect to the stationary contact member; a cylindrical shaft disposed in generally parallel axial relationship to the pivot pin and rotatably connected to both of the movable contact arms, the shaft having at least one eccentric portion; and an actuating member pivotally connected to said pivot pin for movement between first and second relatively fixed positions and adjustably coupled to the eccentric portion of the shaft for pivotally moving. both of said movable contact arms.

8. In the contact structure of an electric circuit interrupter: a base member; a relatively stationary contact comprising an electroconductive member mounted on the base and a contact finger pivotally supported by said electroconductive member for relatively limited movement in an arcuate path; a bracket mounted on the base in spaced relation to the stationary contact; an elongated movable contact arm pivotally supported by the bracket for movement at one end in an arcuate path, said arm being disposed in relation to the contact finger so that the respective arcuate paths define intersecting planes; a cylindrical shaft rotatably connected to the movable contact arm and disposed substantially perpendicular to the plane defined by the arcuate path of said one end, the shaft being provided with an eccentric portion extending laterally from said arm; and an actuating member reciprocally movable between first and second relatively fixed positions and adjustably coupled to the eccentric portion of the shaft for moving the one end of said arm along its arcuate path between open and closed circuit positions with respect to the relatively stationary contact finger, the adjustable coupling being arranged to permit controlled rotation of the shaft thereby to vary the length of the arcuate path from the open circuit position of said one end to the stationary contact finger.

9. In the contact structure of an electric circuit breaker: a base member; a relatively stationary contact comprising an electroconductive member mounted on the base, a contact finger pivotally suported by said electroconductive member for movement in a first plane, and spring means for establishing a biasing torque in the contact finger; a bracket mounted on the base in spaced relation to the stationary contact; an elongated movable contact arm pivotally supported by the bracket for movement at one end in a second plane substantially perpendicular to the first plane, the one end being disposed for circuit-making engagement with said contact finger; resilient means associated with the movable contact arm to permit transverse movement of said one end with respect to said second plane; a rotatable shaft, having an axis disposed substantially perpendicular to said second plane, loosely connected to the movable contact arm and ineluding an eccentric end portion extending laterally from said arm; and an actuating member adjustably coupled to the eccentric portion of the shaft for pivotally moving said arm, the adjustable coupling being constructed and arranged to permit controlled rotation of the shaft thereby to determine the amount of contact wipe between the one end of said arm and the relatively stationary contact finger.

10. In the contact structure of an electric circuit interrupter: a base member; a relatively stationary contact member mounted on the base member; an electroconductive bracket mounted on the base member in spaced relation to the stationary contact member; an elongated movable contact arm pivotally connected to the bracket for rotation on an axis, one end of the arm being arcuately movable between open and closed circuit positions with respect to the stationary contact member, the connection between bracket and aim including contiguous slide surfaces disposed generally perpendicular to the axis of rotation to form a current-conducting joint; a generally cylindrical shaft rotatably connected to the movable contact arm and disposed substantially parallel to said axis, the shaft having an eccentric portion; and an actuating member adjustably coupled to the eccentric portion of the shaft for moving said arm on said axis, the adjustable coupling being arranged to permit controlled rotation of the shaft thereby to determine the closed circuit position of the one end of said arm. I

11. In the contact structure of an electric circuit interrupter: a base member; a relatively stationary contact member mounted on the base member; an electroconductive bracket mounted on the base member in spaced relation to the stationary contact member; an elongated movable contact arm pivotally connected to the bracket for rotation on an axis, one end of the arm being arcuately movable between open and closed circuit positions with respect to the stationary contact member, the connection between bracket and arm including contiguous slide surfaces disposed generally perpendicular to the axis of rotation to form a current-conducting joint, one of said surfaces being substantially fiat and the other surface being raised so that said current-conducting joint provides a fulcrum for rocking movement by the arm with respect to the axis; a cylindrical, rotatable shaft loosely connected to the movable contact arm and disposed substantially parallel to said axis, the shaft having an eccentric end portion extending laterally from said arm; and an actuating member reciprocally movable between first and second relatively fixed positions and adjustably coupled to the eccentric portion of the shaft for moving said am about said axis, the adjustable coupling being arranged to permit controlled rotation of the shaft thereby to determine the closed circuit position of the one end of said arm.

12. In the contact structure of an electric circuit inter rupter: a base; a bracket mounted on the base; a relatively stationary contact comprising an electroconductive member mounted on the base in spaced relation to the bracket and a contact finger pivotally supported by said electroconductive member for movement in an areaate path; a cooperating movable contact member con nected to the bracket for pivotal movement between open and closed circuit positions in a plane intersecting the plane defined by the arcuate path of said contact finger, the connection between bracket and movable contact member including contiguous slide surfaces disposed generally parallel to the plane of movement of the movable contact member to form a current-conducting joint; a cylindrical shaft rotatably connected to the movable contact member and disposed substantially perpendicular to the plane of movement of said movable contact member, the shaft being provided with an eccentric portion; and an actuating member adjustably coupled to the eccentric portion of the shaft for pivotally moving said movable contact member, the adjustable coupling being arranged to permit controlled rotation of the shaft thereby to determine the closed circuit position of said movable contact member.

13. In the contact structure of an electric circuit interrupter: a base; an electroconductive bracket mounted on the base; a relatively stationary contact comprising an electroconductive member mounted on the base in spaced relation to the bracket and a contact finger pivotally supported by said member for movement in a first plane; a cooperating movable contact arm pivotally connected to the bracket for rotation about an axis, one end of the arm being axially offset with respect to the pivotal connection and being arcuately movable between open and closed circuit positions in a second plane intersecting said first plane, said one end having at least one contact surface engaging in the closed circuit position at least one cooperative contact surface of the relatively stationary contact finger, the connection between arm and bracket and including contiguous slide surfaces disposed generally parallel to said second plane to form a current-conducting joint, one of said slide surfaces being substantially flat and the other slide surface having a raised section defining with the fiat surface a line contact; a cylindrical shaft rotatably connected to the movable contact arm and disposed substantially perpendicular to said second plane, the arm being constructed and arranged so that the center of the bearing surfaces between shaft and arm together with the center of the engaging area of the contact surface of the arm and the centre of the pivotal connection between arm and bracket are in a third plane disposed parallel to or including the intersection of said first and second planes, said shaft having an eccentric portion extending laterally from the arm; and an actuating member adjustably coupled to the eccentric portion of the shaft for moving said arm about said axis, the adjustable coupling being constructed and arranged to permit controlled rotation of the shaft thereby to determine the closed circuit position of the one end of said arm.

References Cited in the file of this patent UNITED STATES PATENTS