Abstract:
In a high voltage circuit breaker having a contact system comprising a contact driven by a switch mechanism and a counter-contact opposite the contact and driven by an auxiliary gear, the parallel current path leading over the auxiliary gear is interrupted by using an insulation part between the counter-contact and a second terminal of the high voltage circuit breaker.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a high voltage circuit breaker having a contact system, a contact driven by a switch mechanism, and a counter-contact opposite the contact and driven by a transmission element. An auxiliary gear is formed by a multiple transmission elements. The contact is electrically connected to a first electric terminal of the high voltage circuit breaker. The counter-contact is electrically connected to a second electric terminal of the high voltage circuit breaker via a current path. 
     BACKGROUND INFORMATION 
     Such a high voltage circuit breaker is described in, for example, European Patent No. 0 313 813. This patent describes a contact driven by a switch mechanism, where a stud-shaped counter-contact can also be driven to increase the contact separation rate in a shutdown operation in particular. The motion of the driven contact is transmitted to the counter-contact by motion transmission elements or an auxiliary gear, driving the counter-contact in the direction of motion opposite that of the contact. 
     French Patent 2 491 675 also describes a high voltage circuit breaker where a driven contact and a counter-contact driven in the opposite direction by an auxiliary gear and by motion transmission elements are provided. 
     European Patent Application 0 25 833 A1 also describes a high voltage circuit breaker where a contact and a counter-contact are linked by a gear and can be driven in opposite directions in the event of shutdown. 
     SUMMARY 
     An object of the present invention is to provide a high voltage circuit breaker of the type defined in the preamble such that its lifetime is lengthened in comparison with that of conventional switches. 
     This object is achieved according to the present invention by the fact that a parallel current path which is electrically parallel to the current path and leads from the counter-contact to the second terminal of the high voltage circuit breaker by way of the transmission elements is interrupted by an insulation area. At least one of the transmission elements may be designed so that it is electrically insulating in order to interrupt a parallel current path formed in parallel to the main current path between the counter-contact and the second terminal of the high voltage circuit breaker. 
     Conventional high voltage circuit breakers have in common the fact that the counter-contact is driven by an auxiliary gear and transmission elements which are connected at least in part to stationary parts of the switch, e.g., for bearing purposes. For example, gearwheels or levers must be pivotingly mounted at a fixed point. 
     This fails to take into account the problem that a parallel current path is thus created from the counter-contact to the second terminal of the circuit breaker by way of the auxiliary gear or the motion transmission elements; this current path is parallel to the main current path leading from the counter-contact to the second terminal usually by way of slide contacts. 
     The drive mechanism for the counter-contact is destroyed or at least damaged after a few switching cycles due to the electric load, because motion transmission elements and auxiliary gear are not normally designed to carry high currents such as those occurring in the event of a short circuit, for example. 
     Due to the method of achieving the object of the present invention, current flow outside the main current path is completely prevented, so that mechanical parts cannot be damaged due to such a current flow. 
     Furthermore, this also prevents the effects of magnetic forces occurring due to parallel current-carrying current paths which can have a negative effect on the contact pressure in the case of slide contacts, for example, due to lifting of the contact fingers. 
     An advantageous embodiment of the present invention provides for the end of the counter-contact facing away from the contact to be made of insulating material in the area of the point of action of the transmission elements. 
     Thus, the auxiliary current path from the counter-contact over the auxiliary gear to the second terminal of the circuit breaker is interrupted at the point of action of the transmission elements on the counter-contact. 
     Another advantageous embodiment of the present invention provides for at least one bearing or one shaft of the auxiliary gear to be made at least partially of an insulating material. 
     Additional advantageous embodiments of the present invention provide for a stud of the auxiliary gear sliding in a sliding guide to be made at least in part of insulating material or a sliding guide of the auxiliary gear to be made of an insulating material. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows the pairing of an auxiliary gear with a fixed continuous current contact of a high voltage circuit breaker, namely in one end position. 
     FIG. 2 shows a cross section through an auxiliary gear. 
     FIGS. 3 through 5 show an auxiliary gear in two intermediate positions and in the other end position. 
    
    
     DETAILED DESCRIPTION 
     Following FIG. 2 of European Patent 0 383 813 B1, FIG. 1 shows details of the fixed continuous current contact  5  of a high voltage circuit breaker into which an axially driven continuous current contact  4  having insulation nozzle  8  attached to it and axially driven contact  9  projects from the left. The lower half of the figure shows the closed position of driven continuous current contact  4  and the upper half shows the position of insulation nozzle  8  in the open position. In the closed position, insulation nozzle  8  also surrounds counter-contact  7  which is driven in the opposite direction. In this position, first terminal  39  and second terminal  40  of the switch are conductively connected. Terminals  39 ,  40  are shown symbolically in FIG.  1 . Rod-like transmission element  27  is attached to insulation nozzle  8 ; it is designed here not as a gear rack but instead as a coupling rod and, to drive an auxiliary gear, it has a journal  28  arranged across the direction of thrust of coupling rod  27  having a U-shaped cross section. The coupling rod may also have an L-shaped or T-shaped cross section, with one part of the cross section forming a slideway to guide the coupling rod. In this embodiment, bottom  34  of the U-shaped cross section forms the slideway. 
     Unlike the conventional design, according to FIG. 2, coupling rod  27  is guided in two bearing cheeks  31  forming part of a casing  30 . This casing is attached to a contact bridge  32  which is attached to fixed continuous current contact  5  and carries stationary part  33  of a tubular slide contact in which oppositely driven counter-contact  7  is contacted by way of contact blades. Counter-contact  7  has a flat head  13  on the end facing away from the arc gap, head being guided in two slideways  35  of casing  30  formed by bearing cheeks  31 . Flat head  13  has an elongated hole  12  running vertically to coupling rod  27 . 
     A two-armed control lever  10  with a fork at one end and a journal  11  at the other end is mounted on a shaft  38  running in casing  30  vertically to the plane of the drawing. Journal  11  engages in elongated hole  12  on head  13 . The fork end has two prongs  16  and  17  forming a mouth-like opening  18  in which journal  28  of coupling rod  27  can engage. Two prongs  16  and  17  are provided on the outside with contact faces  19  and  20 , respectively, with which control lever  10  comes to rest on bottom  34  of U-shaped cross-sectional profile of coupling rod  27 , depending on the position of the control lever. Stops  36  and  37  in casing  30  guarantee that control lever  10  will remain in the respective stop position. The two stop positions are end positions between which control lever  10  moves under the influence of journal  28 . Coupling rod  27  in bottom  34  of U-shaped cross section has an elongated slot  29  so that the fork end can execute a rotational motion about axis  38 . 
     For example, head  13  may be made of an insulating material, e.g., fiberglass reinforced plastic to interrupt the current path from this end of counter-contact  7  over cheeks  31  and shaft  38  to casing  30  and to contact bridge  32 . For this purpose, shaft  38  and/or its bearing  100  or journal  28  may also be made of an insulating material. 
     Journal  28 , bearing cheeks  31  and control lever  10  are, as transmission elements, parts of the auxiliary gear converting the driving motion of driven contact  9  into an opposite driving motion of counter-contact  7 . 
     In a breaking motion, coupling rod  27  and thus journal  28  pass continuously through various intermediate positions, starting from the position illustrated in FIG. 1; FIGS. 2 and 3 illustrate the positions assumed by head  13  and thus also a respective driven counter-contact  7  shortly before and shortly after reaching maximum speed; FIG. 5 shows the other end position of control lever  10 . Following the position shown in FIG. 5, the coupling rod may move even further to the right without control lever  10  changing its position.