Load Break Switch Arc Suppression

The invention relates to an improved electrical switching system and particularly to an improved load break switch.

Electric loads drawing high alternating current from a source of high voltage are commonly connected to the source through load break switches, also termed interrupter switches. These switches are specially designed to interrupt the high load and magnetizing currents when the load is interrupted. Load break switches commonly include a main, blade like, moveable contact member adapted to rapidly close and make contact with a main stationary contact member and to rapidly open so as to break this contact. Load interruption at high voltage and high currents is subject to substantial and potentially dangerous and destructive arcing, including sustained arcing from phase to phase. One common arrangement for preventing these deleterious effects is to add auxiliary contact members to the switch. The auxiliary members briefly continue to make electrical connection across the switch while the main contact members commence opening. Thus, the main contact members do not open under power and arcing between the main contact members is prevented.

The auxiliary members generally include a movable contact member, e.g. a flipper blade, pivotally coupled to the main moveable contact member, and an auxiliary stationary contact member that is electrically connected to the main stationary contact member. When the switch is opened the main, contact members break contact while the auxiliary contact members briefly continue to make contact. Thereafter the auxiliary contacts rapidly break contact. Disengagement of the auxiliary moveable contact member, e.g. the flipper blade, from the auxiliary stationary contact member mechanically draws an arc in an arc chute. The hot arc is blown away from the rapidly moving flipper blade and cooled by contact with the large area of the chute sides and the auxiliary moveable member opens to produce a sufficient air gap to isolate the terminals of the switch.

The auxiliary stationary member frequently comprises a pair of contact members that are spring biased to abut each other. When the breaker switch is closed, the flipper blade is moved from its open position with sufficient force to stab through the abutting pair of contact members. When the switch is opened the auxiliary moveable member, e.g. the flipper blade, is briefly restrained by this pair of contact members while the main contact members break contact. The flipper blade thereafter breaks through the pair of contact members and moves to its open position.

Reliable stabbing action upon switch closure is thus required to assure that the main contact members do not open under power when the switch is opened. Many designs also rely on proper stabbing action to assure that the auxiliary moveable contact member, e.g. flipper blade, opens at a sufficiently high velocity. This rapidly extinguishes the arc when the switch is opened and thus reduces arc chute erosion. The high velocity opening results from a spring that is precharged during the brief interval when the blade is restrained. In many designs proper stabbing action is required to assure that the spring is properly precharged.

The auxiliary stationary means, therefore, have a carefully designed contact contour to insure proper stabbing. The lead in of the stationary contact members is designed to assure that the moveable member, e.g. flipper blade, properly stabs into the contact members whenever the switch is closed.

However, when the auxiliary contact members separate upon switch opening, an arc is generated in the area of the lead in contour of the stationary contact members. The severity of the arc is related to the amplitude of load current. It is particularly severe at maximum rated current. This arcing causes some erosion, e.g. pitting, of the auxiliary stationary contact members. The resulting contact erosion accumulates with repetitive use, i.e. make-break cycling, of the switch. With repeated cycling this erosion could prevent proper interfacing, e.g. stabbing, between the moveable and stationary auxiliary contact members.

A primary object of the present invention is to provide an improved load break switch.

Another object is an improved arrangement for minimizing arc erosion of the contact members of a load break switch.

A further object is an arrangement for preventing the arc erosion of auxiliary contact members provided to prevent opening of the main contact members under power.

Other objects of this invention together with ways and means of attaining the various objects will be apparent from the following description and accompanying illustrations thereof.

FIG. 1 is a perspective view of a simplified version of a conventional type of load break switch;

FIG. 2 is a plan view of moveable main and auxiliary contact members of such a load break switch;

FIG. 3 is a front elevation view of the contact members illustrated in FIG. 2;

FIG. 4 is a side elevation view of the auxiliary stationary member and arc supporting means of the preferred embodiment of the invention;

FIG. 5 is a front elevation view of the auxiliary stationary member and arc supporting means illustrated in FIG. 4;

FIG. 6 is a side elevation view of an assembly of the arc chute and of the components illustrated in FIGS. 4 and 5;

FIG. 7 is a front elevation view of the assembly illustrated in FIG. 6, and a schematic representation of the auxiliary moveable member in latched and unlatched positions;

FIG. 8 is a side elevation view of an alternative embodiment of the auxiliary stationary member and arc supporting means; and

FIG. 9 is a side elevation view of another alternative embodiment of the auxiliary stationary member and arc supporting means.

In general the objects of the invention are accomplished in a load breaker switch of the type comprising an auxiliary moveable contact member adapted to disengage from auxiliary stationary means upon disengagement of main contact members and to move to an open position. Means are generally provided for preventing premature disengagement of the auxiliary means. At least one arc supporting means is positioned intermediate the stationary member and the open position, but displaced from the path of motion of the moveable member, to provide for rapid transfer of arc attachment from the auxiliary stationary contact member upon disengagement of the moveable member. The moveable contact member may comprise a pivotally mounted blade and the stationary member may comprise a pair of contact members that are supported by planar spring members arranged on opposing sides of the plane of pivotal motion of the moveable member. The preferred embodiment utilizes arc supporting means comprising a first member secured at one end to the conducting base member, which also supports the planar spring members, and a second member extending orthogonally to the first member. These arc supporting members are disposed intermediate the stationary contact member and the open position of the moveable contact member such that the arc is rapidly transferred from the stationary contact member to the arc supporting member. Alternative embodiments include, for example, attaching the arc supporting means to one or both of the planar members supporting the stationary contact members.

FIG. 1 is a simplified representation of a known type of load break switch. The switch selectively makes or breaks contact between base terminals 12 and 16. A main moveable contact member 10 comprising parallel blades 10a and 10b is pivotally mounted at one end to base terminal 12 by bushing 14. The opposite ends of blades 10a and 10b are adapted to engage main stationary contact 18 which is secured to and electrically connected to base terminal 16. The main contact member 10 is pivoted by a rod and crank arrangement so as to open and close the main contact members. This arrangement comprises a rotatable crankshaft 24 having a rigidly connected crank arm 22 that is pivotally, connected by pin 26, to one end of operating rod 20. The other end of operating rod 20 is pivotally connected, by pin 28, to the main contact blades 10a and 10b intermediate their ends.

The auxiliary moveable contact member 30 is pivotally mounted, by member 32, to the main blade assembly. The switch is closed by imparting clockwise rotation to shaft 24. The resulting motion of crank 22 and rod 20 rapidly pivots the main moveable contact 30 clockwise to quickly engage stationary contact 18. Load break switch assemblies generally utilize a plurality of switches of the type illustrated in FIG. 1 arranged in a parallel configuration in a housing and actuated by a common shaft. One switch is utilized for each electrical line. Thus a three phase system utilizes three switches. The shaft rotation may be actuated by a stored energy mechanism (which is not illustrated) comprising a spring which is charged manually by an operating handle or by an electric motor so as to provide for snap action motion of the shaft. For example, an operating handle is coupled to a compression spring. Rotation of the handle from its open to its closed position causes the overcenter spring to compress and go over the toggle position. The spring is coupled, e.g. via a drive crank, to crank shaft 24, such that the shaft snaps through a few degrees of rotation, and the main moveable contact member 10 snaps to engage the main stationary contact member 18. The mechanism 1perates in a similar manner to open the switch and thus provides for both rapid make and break operation.

During switch closure, the main moveable contact member rapidly pivots from its open to its closed position. As described subsequently, the auxiliary moveable contact member 30 moves in parallel with the main moveable contact member to engage the auxiliary stationary contact member, which is located within the assembly schematically identified as 34 in FIG. 1. The main and auxiliary members are designed so that the main members make contact prior to engagement of the auxiliary contact members. When the switch is opened, the mechanism comprising members 20, 22 and 24, pivots main moveable contact member 10 to its open position. As shown in FIG. 1, the auxiliary moveable contact member 30 briefly remains in its closed position so as to make contact with the auxiliary stationary contact member. After the main contact members have broken contact and have separated by a substantial distance, the auxiliary moveable contact member 30 rapidly disengages from the auxiliary stationary contact member. Member 30 then quickly flips to an open position. Member 30 thus rapidly draws out the arc generated when the auxiliary members break contact. An arc chute is arranged about the auxiliary stationary contact member and extends from the base terminal 16 in the direction of the open position of the contact member 30. The arc, drawn by the opening of member 30 impinges on the chute and the evolving gas blows the arc away from the contact. In FIG. 1 the assembly 34 schematically represents the arc chute assembly, the auxiliary stationary contact member, and the novel arc supporting means arranged within the arc chute.

The above described components are now described in more detail. The moveable contact members 10 and 30 of the preferred embodiment which utilize features known in the art, are shown in FIGS. 2 and 3. The main moveable contact member 10 comprises parallel blades 10a and 10b secured to one another with appropriate separation by previously referenced pin members 14 and 28, and by member 40. Each of these comprise a bolt having its head on the outer surface of one blade member and secured by a nut on the outer surface of the other blade member. The bolts support a bushing or spacer (14a, 28a and 40a, respectively) intermediate the blade members. One end of member 10 is pivotably mounted to base terminal 12 by bushing 14a. Silver rings 14c located at the interface of blades 10a and 10b and bushing 14a provide for current transfer from base terminal 12 to member 10. These rings may be formed by coining the rings as indicated by line 14d of FIG. 3. The hinge pressure of member 10 can be set by adjustment of the take up nut on the bolt of member 14. For this purpose a coiled compression spring 14b is secured intermediate washers between blade 10a and the take up nut of member 14. The operating rod is pivotally mounted to member 10 by bushing 28a. The opposing end of blades 10a and 10b have indented portions providing contact terminals 43 whose heavily silvered surface is adapted to engage the main stationary member 18, shown in FIG. 1. Member 40 has a compression spring arrangement, including spring 40b, like that of member 14, for adjustment of contact pressure between members 10 and 18. Referring to FIG. 3, switch closure results in clockwise motion of member 10 and downward movement of the end bearing the contact terminals 43. Special arcing contacts 45 of suitable material, such as copper tungsten, are preferably provided at the blade portions that initially touch stationary contact member 18.

The auxiliary moveable contact assembly 30 comprises the flipper arm 42 and flipper support 46. Flipper arm 42 is fastened by bolts 44 to one arm of U-shaped flipper support 46. Support 46 is pivotally connected to blade 10a, by bolt 32 which extends through blade 10a and the two arms of the support. For this purpose washers are interposed, respectively, between blade 10a and the adjacent arm of support 46 and between the other arm of the support and the retaining nut. The arm of support 46 adjacent to blade 10a has a rectangular notch 52 adjacent to its outer edge. Stop pin 50 is secured to blades 10b and 10a and extends orthogonally outward from blade 10a into notch 52. When the switch is closed and blades 10a and 10b pivot clockwise pin 50 abuts against the lower edge of notch 52. Accordingly neither support 46 nor flipper blade 42 pivot in respect to blades 10a and 10b. The flipper blade thus pivots in parallel with the main blades 10a and 10b during switch closure. Because of the configuration of the flipper and main blades, the latter contact the main stationary contact 18 before the flipper blade makes contact with the auxiliary stationary contact member.

During opening of the switch, blades 10a and 10b pivot counterclockwise to break contact with the main stationary contact 18. As described subsequently the flipper arm 42 is restrained from moving until the main contact members 10 and 18 have broken contact. Thus there is relative rotation between main member 10 and auxiliary moveable member 30, i.e. flipper 42 and support 46. This is enabled by motion of pin 50 within notch 52. However subsequent to a predetermined small rotation of main member 10 in respect to auxiliary member 30, pin 50 strikes and engages the upper wall of notch 52. As the main member 10 continues its counterclockwise rotation, the auxiliary moveable member 30 is thus forced to move counterclockwise and break its contact with the auxiliary stationary member.

A torque spring 54 is coiled on a bushing secured by bolt 32 between the two arms of support 46. One end 56 of the spring engages the bight of the U-shaped support 46 and the other end, 58, of the spring engages stop pin 50. When the switch is opened, main moveable contact member 10 initially pivots counterclockwise in respect to auxiliary moveable contact member 30. The resulting upward motion of pin 50 in notch 52 charges spring 54. When the pin 50 engages the top wall of notch 52 and releases flipper arm 42, the torque spring forces support 46, and thus flipper 42, to rapidly move counterclockwise in respect to stop pin 50 and member 10. This results in the flipper arm 42 snapping upward in a counterclockwise pivotal motion until pin 50 reengages the lower edge of notch 52. This snap action provides for rapid extinction of the arc generated when the auxiliary contact members break contact.

Reference is now made to FIGS. 4 and 5. The auxiliary stationary contact member comprises abutting contact members 60a and 60b each secured by a planar support member 62a and 62b respectively, to a support bracket 64 which is adapted to be secured to base terminal 16 (which is shown in FIG. 1). Thus electrical contact is established between the base terminal and the contact members 60a and 60b. The support bracket is a right angle bracket having a horizontal plate portion 66, adapted to be fastened to the base terminal and a vertical plate portion 68. The rectangular planar support members are fastened, adjacent to one of their longitudinal ends, to opposing sides of plate portion 68 by bolt 70. The rectangular contact members 60a and 60b are secured to the inward, i.e. adjacent, faces of the support members at, or near, their other longitudinal ends. The contact members 60a and 60b are of substantially identical thickness such that they abut one another. The planar supports 62a and 62b are spring members adapted to maintain the pair of contact members in abutting relation but to permit their lateral separation to permit entry and exit of the flipper arm. Supports 62a and 62b may, for example, comprise a lamination of steel and phosphor bronze. The above described assembly is mounted such that the stationary contact members and the planar supports are arranged so that plate portion 68 extends in the plane of motion of the flipper blade 42 and the stationary contact members are arranged on opposite sides of this plane. When the switch is closed the flipper blade decends with sufficient force to stab through the normally abutting contact members 60a and 60b until it attains a latched, i.e. engaged, position intermediate supports 62a and 62b, contact members 60a and 60b and support bracket portion 68. This latched position of the flipper blade is illustrated by "A" in FIG. 7. When the switch is opened, and main moveable contact member 10 pivots counterclockwise, the flipper blade initially pivots until it is temporarily restrained by contact members 60a and 60b. This position, assumed by the flipper arm just prior to unlatching, is illustrated by "B" in FIG. 7. In this position the auxiliary contact members make contact while the main contacts break contact. Finally, as previously described, the flipper blade stabs through the abutting contact members 60a and 60b and rapidly flips toward the open, i.e. unlatched position. "C" of FIG. 7 illustrates the flipper blade in a position intermediate the latched and open positions. In order to facilitate the described stabbing action, the abutting edges of the pair of contact members 60a and 60b are canted. The contour of these canted surfaces is selected to assure that the flipper arm will reliably and repetitively stab through contact members 60a and 60b.

As illustrated by FIGS. 6 and 7 an arc chute 80 extends upward from the support bracket 64 toward the open position of the flipper blade 42. The arc chute of the preferred embodiment comprises two plates, 84 and 86, extending in parallel on opposing sides of the plane of pivotal motion of the flipper blade. The plates are bolted to the opposing sides of portion 68 of the support bracket by bolts 88 and 90. They are thus separated sufficiently to provide for unrestricted passage of the flipper blade. The plates 84 and 86 are made of ablative and gas evolving substance such as an acrylic material. The arc chute is closed at the rear by spacer member 92 and at the bottom by spacer member 94. An arc is generated when the auxiliary contact members open. The gases evolved from the plastic arc chute blow the arc away from the moving flipper blade. The arc is drawn out and extinguished as the flipper blade snaps away from stationary contact members 60a and 60b.

Arc supporting means 100 is located within the arc chute 80 adjacent the path taken by the auxiliary moveable member, i.e. flipper blade, as it opens so as to be intermediate the position where it engages the auxiliary stationary contact members 60a and 60b and its open position. The means 100 is displaced from the open position of the flipper blade by a sufficient distance to assure that an arc will be properly extinguished. The arc supporting means is thus positioned close to the auxiliary stationary contact means, i.e. the pair of contacts 60a and 60b. This is desirable since it provides for rapid arc transfer from contacts 60a and 60b to means 100 as the flipper blade is unlatched and commences to flip to the open position. Arc transfer results as soon as the distance from the auxiliary moveable contact means, i.e. the flipper blade, to the arc support means 100 becomes less than the distance from the flipper blade to the auxiliary stationary contact means, i.e. contacts 60a and 60b. However, the separation between the arc transfer means and the auxiliary stationary contact means should be sufficient to prevent the arc from jumping back from means 100 to contact members 60a and 60b. The arc supporting means 100 must also be separated sufficiently from the path of motion of the flipper blade to provide for unobstructed movement of the latter. With repeated switch cycling means 100 will become pitted. Accordingly the above referenced separations should be sufficient even when the arc supporting means acquires some deformation of the surface to which the arc adheres.

The arc supporting means of the preferred embodiment utilizes an L-shaped member comprising a first leg 102 and a second leg 104 extending orthogonally in respect to the first leg. The L-shaped member 100 is fastened to portion 68 of support bracket 64. This provides a low impedance circuit between contact members 60a and 60b and the arc supporting means so that these components are maintained at substantially the same potential. This enhances arc transfer. The L-shaped arc supporting means is fastened to the support bracket near the end of leg 102, that is remote from leg 104, by bolt 106. Leg 102 extends adjacent to and parallel to planar support 62 such that leg 102 is preferably displaced from support 62 toward the open position of the flipper blade. Leg 104 extends adjacent, and parallel, to contact member 60 such that it is displaced from the latter along the path of the opening flipper blade. This relationship is shown in FIG. 7. A small gap distance is maintained between contact member 60 and leg 104, and between planar support 62, as well as leg 104, and leg 102. The L-shaped member is also displaced from the plane of pivotal motion of the flipper blade by a distance slightly greater than the distance from that plane to planar member 62. This spacing is attained by interposing a shim 108 intermediate plate portion 68 and leg 102. Accordingly adequate clearance is provided for unobstructed motion of the flipper blade and for unobstructed lateral motion of planar spring members 62a and 62b. The preferred embodiment utilizes one L-shaped member on each side of the plane of pivotal motion of the flipper blade. The arc supporting assembly members 102a and 104a are located on one side of plate portion 68 and are spaced therefrom by shim 108a. Arc supporting members 102b and 104b are located on the opposite side of plate portion 68 and are spaced therefrom by shim 108b. Components 102a, 102b and 108a, 108b are secured to plate portion 68 by bolt 106. This arrangement is particularly desirable since it provides arc supporting means adjacent to each of contact members 60a and 60b. It is also believed to be desirable because the L-shaped arc supporting means is adjacent to both the top and side edges surfaces of the contact member that are adjacent to the path of the flipper blade as it opens.

However, various alternatives may be utilized. For example, only one arc supporting member may be utilized instead of two. Such a single member could be located on either side of plate portion 68.

Various alternative forms of arc supporting means may be utilized which provide advantageous features of the inventive concept. Two of these are illustrated in FIGS. 8 and 9. In the arrangement of FIG. 8 the planar spring members 262a and 262b are secured by bolt 270 to opposing sides of the plate portion 268 of a support bracket. The pair of normally abutting contact members 260a and 260b are secured on the inboard sides of members 262a and 262b in the manner illustrated in FIG. 4. However planar members 262a and 262b extend longitudinally beyond the contact members. Arc support members 204a and 204b are secured to the inboard sides and near the longitudinal ends of members 262a and 262b. The arc supporting members thus extend inwardly toward the plane of motion of the flipper blade. However the width of arc supporting members 204a and 204b is sufficiently less than the width of contact members 260a and 260b to assure clearance between the adjacent faces of members 204a and 204b. This provides for the required unobstructed passage of the flipper blade.

The arrangement of FIG. 9 utilizes conductive support members 302a and 302b for arc supporting members 304a and 304b. The support members 302a and 302b are arranged on opposing sides of the planar spring members 362a and 362b that bear the contact members. Support members 302 and planar spring members 362 can be secured to plate portion 368 of the support bracket by a single bolt 370. The planar spring members are secured intermediate the conductive support members. These members are sufficiently displaced from each other by shim members 308a and 308b to provide for unobstructed lateral motion of the planar spring members. Because of the resulting displacement of members 302 from the plane of motion of the flipper blade it is desirable for arc supporting members 304a and 304b to have a greater width than the width of the arc supporting members 204a and 204b utilized in the arrangement of FIG. 8.

The arc supporting means in all of the described embodiments constitute a consumable arcing contact made of a conductive material preferably having a high melting point temperature, e.g. steel, copper or brass. The arc support means are preferably connected in a low impedance circuit so as to maintain them at the same potential as the stationary contact members.

It should be noted that the invention is not limited to the specific type of load break switch assembly described herein. Although this invention has been described with reference to specific embodiments thereof, numerous modifications are possible without departing from the invention, and it is desirable to cover all modifications falling within the spirit and scope of this invention.