Patent Publication Number: US-2010108484-A1

Title: Contact system, especially for a switchgear

Description:
The invention relates to a contact system for closing and opening a current path. Current path is hereby understood as a pole path of a single-pole or multi-pole switchgear and/or protective gear, in particular a power switch, for switching a load. 
     A contact system of this type typically includes at least one contact point having a moving contact and a fixed contact and allowing a current path to be manually closed and opened with a switch latch. In addition to the manual switching function, the contact system responds automatically, in particular when being used in a power switch, in the event of overcurrent or short-circuit to a thermo-magnetically or electronically triggered overcurrent which opens the contact of the at least one contact point in the current path by applying an external force. To control the high disconnect power levels, arc quenching chambers in the form of so-called blow-out plates are provided in the opening region of the contact point. 
     Moreover, two contact points can be provided in a contact system, wherein the moving contacts of the contact system are synchronously switched relative to the associated fixed contacts by a contact bridge. For example, DE 198 36 549 A1 discloses a contact bridge which can move translationally to close and open the contact points, whereby the moving contacts are moved simultaneously into the respective closed and open positions. EP 0 538 149 B1 discloses a contact system with a rotating contact bridge, likewise for simultaneous actuation of the moving contacts of two contacts points. 
     It is an object of the invention to provide an especially suitable contact system with two contact points. 
     The object is attained in accordance with the invention by the features of claim  1 . Accordingly, a contact bridge which is pivotable about a pivot pin is provided, wherein the pivot pin is arranged for movement along a guide track in the opening direction of the contact points. Under operating conditions, only a first contact point opens while an opposing second contact point is closed. Both the first and the second contact points open in the event of overcurrent or short-circuit. 
     According to a preferred variation, the contact bridge is coupled to a switch latch via a switch lever that is moving along the guide track. The switch lever engages hereby the pivot pin on the bridge side. The pivot pin can in principle also be arranged on the switch lever, in which case the guide track is suitably configured as an oblong guide mechanism, subsequently also referred to as slotted link, and provided on the contact bridge. Preferably, the slotted link is provided on the switch lever and the pivot pin is provided on the contact bridge. coupled and. 
     The slotted link forming the guide track has two opposing spaced-apart contact edges in opposite relationship with respect to the opening direction of the contact points. A first (upper) contact edge of the guide track represents an impact stop contacted by the pivot pin when the first contact point is closed. In this operating mode when the first and second contact points closed, a first spring element acts on the contact bridge as a compression spring, suitably in the region of the pivot pin. This spring element operates as a tension spring when only the first contact point is open during operation. 
     A second (lower) contact edge of the guide track represents a traction stop which the pivot pin contacts when the first contact point is open. This traction stop operates as a fixed support for the pivot pin in the event of overcurrent or short-circuit. 
     According to an important aspect of the invention, the second contact point is always closed, when the first contact point opens during normal operation. A suitably configured second spring element engages hereby on the second contact point and applies a spring force upon the corresponding moving contact in the closing position thereof. The spring force operating in the closing direction of the second contact point is preferably greater than the tension force of the first spring element. To easily and reliably open and close the first contact point during normal operation, a hinge bearing or pivot bearing is formed on the second contact point. The moving contact of the second contact point has hereby an arched or hemispherical contact surface. 
     According to a preferred development, the lever arm formed between the pivot pin and the moving contact of the first contact point is longer than the lever arm formed between the pivot pin and the moving contact of the second contact point along the contact bridge. 
     The fixed contact of the corresponding contact point is arranged on a leg of a busbar in facing disposition to the associated moving contact, wherein the busbar can be U-shaped, for example. The busbar, in particular as a result of its shape, reverses the current direction in the busbars on at least one contact point, however on both contact points. Consequently, in the event of overcurrent or short-circuit, a dynamic current force and a dynamic magnetic force is generated at the respective contact points which repulses the lever arm of the contact bridge supporting the corresponding moving contact. The spring element acting on the second contact point is dimensioned such that its spring or restoring force is smaller than the dynamic forces produced in the event of overcurrent or short-circuit. 
     When the protection function of the contact system is triggered by the dynamic forces, the pivot pin strikes the traction stop of the guide track. This produces a fixed support for the pivot pin, about which the contact bridge rotates automatically in the opening direction of the contact points. 
     The contact system is especially suited for single-pole or multi-pole switching gear used in AC current networks, or compact power switches rated for currents of, for example, 10 A to 2,500 A and interrupt ratings of 20 kA or higher. A spark quenching chamber associated with the opening region of each contact point. 
    
    
     
       An exemplary embodiment of the invention will now be described in greater detail with reference to a drawing. 
         FIG. 1  shows schematically a contact system arranged in a power switch and having different switch positions of a contact bridge at two contact points; 
         FIG. 2  the contact system in operating mode with closed contact points; 
         FIG. 3  the contact system in operating mode with one contact point open and one contact point closed; 
         FIG. 4  the contact system in the event of short circuit while the contact points are opening; and 
         FIG. 5  the contact system under short circuit conditions with completely open contact points. 
     
    
    
     Corresponding elements in all Figures are provided with the same reference symbols. 
       FIG. 1  shows a switching gear and/or protection gear, for example a modularly constructed compact power switch  1 , with a contact system  2  which is coupled to a switch latch  4  by a switch lever  3 . For closing and opening a schematically depicted current path  5 , the contact system  2  can be manually operated with the switch latch  4  by moving an actuating lever or a rocker button in a manner not illustrated in detail. The power switch  2  also includes a trigger unit  6 . 
     Inside the contact system  2 , the current path  5  leads to a busbar  7  of a first contact point K 1  and an opposing additional busbar  8  of a second contact point K 2 . Spark quenching chambers  9  and  10 , which are formed by so-called blow-out plates, are provided in the opening area of the two contact points K 1  and K 2 . The two busbars  7  and  8  are each U-shaped and form a first busbar leg  7   a,    8   a  facing the respective contact points K 1 , K 2  and another busbar leg  7   b ,  8   b  facing away from the respective contact point K 1 , K 2 . Fixed contacts  11   a,    12   a  of the contact point K 1  and K 2  are respectively arranged on the outside of the busbar legs  7   a,    8   a  facing the respective contact points K 1 , K 2 . Each of the moving contacts  11   b,    12   b  associated with a respective contact point K 1 , K 2  is supported on a bridge end  13  and  14 , respectively, of a contact bridge  15  of the contact system  2 . 
     The contact bridge  15  has a pivot pin  16  disposed in the region between the two moving contacts  11  b and  12   b.  The pivot pin  16  is guided along a guide track  17  implemented in the switch lever  3  as an oblong recess near the lever end  18  facing the contact bridge  15 . 
       FIG. 1  shows in form of a continuous line a contact bridge  15  in the closed operating state, wherein both the first contact point K 1  and the second contact point K 2  are closed. Shown in form of a dash-dotted line is the contact bridge  15 , on one hand, in the normal operating state with the contact point  1  open and the contact point  2  closed, and on the other hand, in the event of a short-circuit, where both contact points K 1  and K 2  are open. Depending on the setting or position of the contact bridge  15 , the switch lever  3  is positioned at different displacement positions along the opening and closing direction  19 , hereinafter also referred to as displacement direction. 
     These different positions, namely the position P 1  of the switch lever  3  and hence also of the pivot pin  16  when both contact points K 1 , K 2  are closed, and the position P 2  of the switch lever  3  and the pivot pin  16  when the contact position K 1  is open and the contact position K 2  is closed under normal operating conditions, are illustrated in  FIGS. 2 and 3 . 
     According to the embodiment of  FIG. 2 , a (second) spring element  20  configured in the exemplary embodiment as a compression spring engages the lever arm  14  of the contact bridge  15  at the second contact point K 2  on the bridge side distal to the corresponding moving contact  12   b.  An additional (first) spring element  21  has spring ends which are attached, on one hand, to the switch lever  3  and, on the other hand, to the pivot pin  16 . In the closed position P 1  of the contact bridge  15  illustrated in  FIG. 2 , the spring element  21  operates as a compression spring on the pivot pin  16  connected to the contact bridge  15 . In this position P 1 , the pivot pin  16  contacts a contact contour  22  configured as an impact stop of the slotted link  17  forming the guide track. 
     In the position P 2  of the pivot pin  16  illustrated in  FIG. 3 , the spring element  21  operates as a tension spring. In the position P 2 , the pivot pin  16  makes contact with a contact or link contour  23  of the slotted link  17  which is located opposite the contact or link contour  22  and operates as a traction stop. For the opening and closing motion of the content bridge  15  in the operating mode, the contact point K 2  forms a rotary or pivot bearing for the contact bridge  15 . For supporting the resulting rotary or pivoting motion of the contact bridge  15 , the moving contact  12   b  of the second contact point K 2  has an arched or hemispherical shape in the region of the contact surface facing the fixed contact  12   a.    
       FIGS. 4 and 5  illustrate the contact opening of both contact points K 1  and K 2  in the event of short-circuit or overcurrent. Because the current directions reverse due to the U-shaped configuration of the busbars  7  and  8 , as indicated by the arrows shown in the region of the busbars  7 ,  8 , the short-circuit current which tends to be many times higher than the current under normal operating conditions, generates corresponding dynamic forces F 1 , F 2  at the contact points K 1  and K 2  in the opening directions  19  of the respective moving contact  11   b  and  12   b.  The contact point K 1  opens first, whereafter the pivot pin  16  strikes the traction stop  23  along the guide track  17 . Accordingly, a fixed support for the pivot pin  16  is established at this position P 3 , about which the contact bridge  15  rotates into the open direction  19 . The dynamic forces F 1 , F 2  overcome the spring force of the spring element  20  at the second contact point K 2 , causing the contact bridge  15  to pivot into the completely open position while simultaneously opening both contact points K 1  and K 2 . 
     When the short-circuit is interrupted, the spring force exerted by the spring element  20  operating as a compression spring automatically closes the second contact point K 2 . 
     To support the dynamic forces F 1 , F 2 , the lever arms H 1  and H 2  of the contact bridge  15  formed between the first contact point K 1  and the pivot pin  16 , and between the pivot pin  16  and the second contact point K 2 , respectively, can have different lengths. Preferably, the lever arm H 1  is longer than the lever arm H 2 . 
     The spring elements  21  and  20  acting on the pivot pin  16  and on the second contact point K 2 , in conjunction with the contact bridge  15  and its lever arms H 1  and H 2 , therefore embody a lever arm mechanism for force transmission. With this lever arm system, or this lever arm mechanism, one of the contact points K 1 , K 2  can then remain closed in the operating mode, and both contact points K 1  and K 2  can reliably open in the event of a short-circuit. 
     Accordingly, a contact system  2  is provided for realizing double-break contact points K 1 , K 2  in the event of a short circuit, as well as a single-break contact, in particular of the first contact point K 1 , under normal operating conditions. 
     Such contact system  1  is particularly suited for a compact power switch  1  for switching as well as overcurrent triggering, and therefore protection of power components of the system, e.g., a motor. Power switches  1  equipped with such a contact system  2  are therefore particularly suited for interfacing to additional system components in a potentially complex energy distribution system.