Abstract:
An apparatus includes a plurality of contacts for interrupting current flow when an overcurrent condition occurs, each contact including a mating face displaced at an angle with respect to a pivot point of at least one of the contacts, where the displacement of the mating faces is configured to minimize a repulsion force moment arm from the pivot point of at least one of the contacts.

Description:
BACKGROUND 
       [0001]    The disclosed embodiments relate to contacts that conduct current, and in particular, contacts that experience repulsion forces when mating as a result of the amount of current conducted by the contacts. 
         [0002]    Circuit breakers are generally used to protect equipment from overcurrent situations caused, for example, by short circuits or ground faults. When an overcurrent condition occurs, electrical contacts within the circuit breaker are designed to open, interrupting current flow through the circuit breaker to the equipment. Circuit breakers may be designed for high quiescent currents and high withstand currents. To maintain a high withstand current rating, the contacts must be locked closed at the current withstand rating and be able to withstand the large electrodynamic repulsion forces generated by the current flow. 
         [0003]    Circuit breakers have a variety of designs including blow open and non-blow open contact arms, overcentering and non-overcentering contact arms, single contact pair arrangements with the contact pair at one end of a contact arm and a pivot at the other end, double contact pair arrangements, also referred to as rotary breakers, with a contact pair at each end of a contact arm and a contact arm pivot intermediate the two ends, single housing constructions with the circuit breaker components housed within a single case and cover, and cassette type constructions, also referred to as cassette breakers, with the current carrying components of each phase housed within a phase cassette and each phase cassette in turn housed within a case and cover that may also include an operating mechanism. Multipole circuit breakers are generally available in two, three, and four pole arrangements, with the two and three pole arrangements being used in two and three phase circuits, respectively. Four pole arrangements are typically employed on three phase circuits having switching neutrals, where the fourth pole operates to open and close the neutral circuit in a coordinated arrangement with the opening and closing of the primary circuit phases. 
         [0004]    When current carrying contacts of a circuit breaker are closing on a fault, the current through the contacts is very high resulting in significant electromagnetic repulsion forces between the contacts. These electromagnetic repulsion forces impede breaker closing. 
         [0005]      FIG. 1  shows a diagram of an exemplary circuit breaker  100 . Breaker  100  includes a fixed contact assembly  105  and a movable contact assembly  110  that pivots about a rotation point  115 . The movable contact assembly  110  may include one or more first arcing contacts  120  and one or more first main contacts  125 . Correspondingly, the fixed contact assembly  105  may include one or more second arcing contacts  130  and one or more second main contacts  135 . 
         [0006]    The fixed and movable contact assemblies  105 ,  110  are generally constructed to withstand closing on a fault. When closing on a fault, as the first and second arcing contacts  120 ,  130  contact each other, the currents flowing through the first and second arcing contacts  120 ,  130  are close to each other and cause an electromagnetic repulsion force represented by vector  140  due to a constriction effect. The electromagnetic repulsion force acts opposite the applied closing force and applies a torque in a direction opposite the closing rotation of the movable contact assembly  110 . The electromagnetic repulsion forces are directly proportional to the magnitude of the current and indirectly proportional to the distance between the contacts when the current flow follows a path of a loop between the contacts. 
         [0007]    Thus, the repulsion force  140  is essentially perpendicular to a moment arm  145  representing a distance from the rotation point  115  to the center of the force vector  140 . In this embodiment, the moment arm has a significant magnitude resulting in a significant additional closing force required to close the fixed and movable contact assemblies  105 ,  110 . 
         [0008]    It would be advantageous to provide a circuit breaker with reduced or redirected repulsion forces. 
       BRIEF DESCRIPTION OF THE DISCLOSED EMBODIMENTS 
       [0009]    The following are non limiting exemplary embodiments. 
         [0010]    In one embodiment, an apparatus includes a plurality of contacts for interrupting current flow when an overcurrent condition occurs, each contact including a mating face displaced at an angle with respect to a pivot point of at least one of the contacts, where the displacement of the mating faces is configured to minimize a repulsion force moment arm from the pivot point of at least one of the contacts. 
         [0011]    In another embodiment, a method includes displacing mating faces of a plurality of contacts at an angle with respect to a pivot point of at least one of the contacts, and configuring the displacement to minimize a moment arm from the pivot point of at least one of the contacts to reduce electromagnet repulsion forces between the contacts when an overcurrent condition occurs. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0012]    The foregoing aspects and other features of the presently disclosed embodiments are explained in the following description, taken in connection with the accompanying drawings, wherein: 
           [0013]      FIG. 1  shows a diagram of an exemplary circuit breaker; 
           [0014]      FIG. 2  shows an exemplary circuit breaker  200  suitable for practicing the embodiments disclosed herein; 
           [0015]      FIG. 3  shows an expanded view of exemplary first and second arcing contacts; and 
           [0016]      FIG. 4  shows an expanded view of another embodiment of exemplary first and second arcing contacts. 
       
    
    
     DETAILED DESCRIPTION  
       [0017]      FIG. 2  shows an exemplary circuit breaker  200  suitable for practicing the embodiments disclosed herein. Although the presently disclosed embodiments will be described with reference to the drawings, it should be understood that they may be embodied in many alternate forms. It should also be understood that In addition, any suitable size, shape or type of elements or materials may be used. 
         [0018]    The disclosed embodiments may include a plurality of contacts with characteristics that operate to minimize electromagnetic repulsion forces between the contacts. 
         [0019]    Circuit breaker  200  may include a fixed contact assembly  205  and a movable contact assembly  210  that pivots about a rotation point  215 . The movable contact assembly  210  may generally include one or more first arcing contacts  220  and one or more first main contacts  225 . The fixed contact assembly  205  may include one or more second arcing contacts  230  and one or more second main contacts  235 . The fixed and movable contact assemblies  205 ,  210  may be constructed to withstand closing on fault. Upon closing, the first and second arcing contacts  220 ,  230  may be configured to contact each other before the first and second main contacts  225 ,  235 . 
         [0020]    While the disclosed embodiments are described in terms of arcing contacts and main contacts in a circuit breaker, it should be understood that the disclosed embodiments may be utilized with any contacts that are subject to repulsion forces during closing. 
         [0021]      FIG. 3  shows an expanded view of first and second arcing contacts  220 ,  230 . The first and second arcing contacts  220 ,  230  may have any suitable shape and configuration for minimizing arcing as they contact each other. For example, the first and second arcing contacts  220 ,  230  may each have a rounded or arcuate contact face  305 ,  310  having a portion  330 ,  340  that extends, for example, away from the fixed and movable contact assemblies  205 ,  210 . The shape of the first and second arcing contacts  220 ,  230  may be a complex shape configured to direct any arcing away from the contacts and towards, for example, an arc quenching device such as a screen or plate located adjacent the first and second arcing contacts  220 ,  230 . The first and second arcing contacts  220 ,  230  may each have a base  335 ,  340  for coupling the arcing contacts to the respective fixed and movable contact assemblies  205 ,  210 . Each base  335 ,  340  may have an L-shape or each base may have any suitable shape. 
         [0022]    In this embodiment, the first arcing contact  220  may have a first mating face  305  and the second arcing contact  230  may have a second mating face  310 . The first and second mating faces  305 ,  310  may be disposed at an angle that reduces or minimizes a moment arm  315  from rotation point  215 . Due to the angular orientation of the first and second mating faces  305 ,  310  the currents flowing through the first and second arcing contacts  220 ,  230  may generally travel further away from each other, or may travel an extended distance through the first and second arcing contacts  220 ,  230 . The electromagnetic repulsion forces may be reduced by introducing a larger loop into the current path as the forces are indirectly proportional to the distance between the contacts when the current flow is in a loop formation. 
         [0023]    This may operate to reduce or minimize an electromagnetic repulsion force  320  resulting from the current flowing through the first and second arcing contacts  220 ,  230 . 
         [0024]    The angular orientation of the first and second mating faces  305 ,  310  may also operate to change the direction of the electromagnetic repulsion force  320  applied to the first and second arcing contacts  220 ,  230 . As shown in  FIG. 3 , the direction of the electromagnetic repulsion force  320  may be directed toward the pivot point  215 , and may result in a reduced or minimized moment arm  325 . As a result, the electromagnetic repulsion forces may be reduced or minimized. 
         [0025]      FIG. 4  shows an expanded view of another embodiment  400  of the first and second arcing contacts. This embodiment may include a fixed contact assembly  405  and a movable contact assembly  410  that pivots about a rotation point  415 . Similar to other embodiments, the movable contact assembly  410  may generally include one or more first arcing contacts  420  and one or more first main contacts  425 . The movable contact assembly  410  may include a finger  440  on which the first arcing contact  420  is mounted. The fixed contact assembly  405  may include a main conductor  450  on which one or more second arcing contacts  430  and one or more second main contacts  435  are mounted. In this embodiment, a first physical gap  445  may be provided between the finger  440  and the first arcing contact  420 . The first gap  445  may operate to extend or lengthen a current path  465  through the first arcing contact by causing the current to travel a longer distance through the first arcing contact  420 . A second physical gap  455  may be provided between the main conductor  450  and the second arcing contact  430 . Similar to the first gap  445 , the second gap  455  may operate to extend or lengthen a current path through the second arcing contact by  430  causing the current to travel a further distance through the second arcing contact by  430 . 
         [0026]      FIG. 4  shows an exemplary current path  460  that current may travel through the fixed contact assembly  405  and the movable contact assembly  410  in the absence of gaps  445 ,  455 . Current path  465  shows an exemplary current path that may result from the inclusion of gaps  445 ,  455 . Current path  455  may generally have a longer length than current path  445  and may produce a reduced electromagnetic repulsion force between the first arcing contact  420  and the second arcing contact  430 . 
         [0027]    It should be understood that the foregoing description is only illustrative of the present embodiments. Various alternatives and modifications can be devised by those skilled in the art without departing from the embodiments disclosed herein. Accordingly, the embodiments are intended to embrace all such alternatives, modifications and variances which fall within the scope of the appended claims.