Abstract:
A circuit breaker and a method of forming a current limiting circuit breaker are described. The circuit breaker includes a carrier assembly to supply current to a circuit through a fixed contact in a first operative state, a movable contact in physical contact with the fixed contact of the circuit, and a contact arm coupled to the movable contact, the contact arm including a pivot point. The contact arm moves about the pivot point responsive to a force transferred as a result of a fault condition in the circuit and the movable contact breaks the physical contact with the fixed contact of the circuit to put the circuit breaker in a second operative state. The circuit breaker also includes a mechanism to move the carrier assembly to put the circuit breaker in a third operative state responsive to a signal indicative of the fault condition.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The subject matter disclosed herein relates to a current-limiting circuit breaker. 
         [0002]    A circuit breaker is an automatically operated electrical switch that interrupts current flow when a fault is detected. This prevents an overload or short circuit that can damage the circuit being protected by the circuit breaker. Interruption of the current generates an arc which must be extinguished to prevent damage caused by the arc flash. In an air circuit breaker, the arc is broken by air (e.g., displaced air resulting from the contacts being moved into a closed chamber). The speed with which the arc is broken can affect the extent of damage. That is, a current limiting circuit breaker reduces the fault energy that flows into the circuit and, therefore, reduces any damage to the circuit caused by the fault. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0003]    According to one aspect of the invention, a circuit breaker includes a carrier assembly configured to supply current to a circuit through a fixed contact in a first operative state, the carrier assembly comprising a movable contact configured to be in physical contact with the fixed contact of the circuit to supply the current to the circuit in the first operative state; a contact arm coupled to the movable contact, the contact arm including a pivot point, the contact arm configured to move about the pivot point responsive to a force transferred as a result of a fault condition in the circuit and the movable contact configured to break the physical contact with the fixed contact of the circuit to put the circuit breaker in a second operative state responsive to movement of the contact arm; and a mechanism configured to move the carrier assembly to put the circuit breaker in a third operative state responsive to a signal indicative of the fault condition, wherein the movable contact of the carrier assembly is configured to break the physical contact with the fixed contact of the circuit to put the circuit breaker in the second operative state responsive to movement of the contact arm prior to the mechanism moving the carrier assembly to put the circuit breaker in the third operative state responsive to the signal. 
         [0004]    According to another aspect of the invention, a current limiting assembly includes a movable contact configured to be in physical contact with a fixed contact in a first operative state; and a contact arm coupled to the movable contact, the contact arm including a pivot point, the contact arm configured to move about the pivot point responsive to a force transferred as a result of a fault condition in the circuit and the movable contact configured to break the physical contact with the fixed contact of the circuit to establish a second operative state responsive to movement of the contact arm. 
         [0005]    According to yet another aspect of the invention, a method of developing a current limiting circuit breaker includes arranging a carrier assembly in physical contact with a circuit, the carrier assembly supplying current to the circuit through a fixed contact in a first operative state, the arranging the carrier assembly further comprising arranging a movable contact to be in physical contact with the fixed contact of the circuit in the first operative state arranging a contact arm to be coupled to the movable contact, the contact arm including a pivot point, the contact arm configured to move about the pivot point responsive to a force transferred as a result of a fault condition in the circuit and the movable contact configured to break the physical contact with the fixed contact of the circuit to put the circuit breaker in a second operative state responsive to movement of the contact arm; and arranging a mechanism coupled to the carrier assembly, the mechanism configured to move the carrier assembly to put the circuit breaker in a third operative state responsive to a signal indicative of the fault condition. These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0006]    The subject matter, which is regarded as the invention, is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
           [0007]      FIG. 1  details a circuit breaker according to an embodiment of the invention; 
           [0008]      FIG. 2  depicts the circuit breaker according to the embodiment shown in  FIG. 1 ; 
           [0009]      FIG. 3  depicts the circuit breaker according to the embodiment shown in  FIG. 1 ; 
           [0010]      FIG. 4  is a three-dimensional view of the circuit breaker according to an embodiment of the invention; 
           [0011]      FIG. 5  details the cam assembly according to an embodiment of the invention; 
           [0012]      FIG. 6  details the arrangement of the cam assembly and the latching bracket assembly according to an embodiment of the invention; 
           [0013]      FIG. 7  depicts aspects of the carrier assembly according to an embodiment of the invention; 
           [0014]      FIG. 8  depicts aspects of the carrier assembly according to an embodiment of the invention; 
           [0015]      FIG. 9  details a restrike control latch assembly according to an embodiment of the invention; 
           [0016]      FIG. 10  provides an exploded view of a restrike control latch assembly according to an embodiment of the invention; and 
           [0017]      FIG. 11  details the arrangement of the restrike control latch assembly and the latching bracket assembly according to an embodiment of the invention. 
       
    
    
       [0018]    The detailed description explains embodiments of the invention, together with advantages and features, by way of example with reference to the drawings. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0019]    As noted above, speed of operation of a circuit breaker is a key factor in limiting fault energy. Typically, a circuit breaker includes a trip mechanism that receives a fault signal and initiates operation of a carrier assembly that resides between the trip mechanism and the circuit to be protected. The operation of the carrier assembly by the trip mechanism creates the open condition in which current flow to the circuit is interrupted. Embodiments of the system and method described herein relate to a carrier assembly that additionally operates based on a force generated by the fault current. Specifically, the moving arm associated with the moving contact initiates the break in contact based on the force. 
         [0020]      FIG. 1  details a circuit breaker  100  according to an embodiment of the invention. The view shown in  FIG. 1  is a perspective side view showing one set of contacts. As shown in  FIG. 1 , the circuit breaker  100  is in a closed (“on”) position such that current is flowing to the circuit  110 . Based on a fault, the carrier assembly  120  between the circuit  110  and the mechanism  130  physically disengages from the circuit  110 , thereby disengaging the fixed contact  115  ( FIG. 2 ) of the circuit  110  from the moving contact  116  ( FIG. 2 ) of the carrier assembly  120 . The mechanism  130  receives a signal based on a fault condition being detected and pulls the carrier assembly  120  away from the circuit  110  to fully disengage contact between the circuit  110  and the carrier assembly  120 . The mechanism  130  and the carrier assembly  120  are connected via a pole coupler  140  which ends at the mechanism  130  in a lay shaft  132  and at the carrier assembly  120  at a pole coupler pin  127 . The mechanism  130  facilitates resetting the circuit breaker  100  (back to the position shown in  FIG. 1 ) following a fault detection and clearing procedure. The mechanism spring  135  facilitates this full opening. In a conventional selective circuit breaker, the mechanism  130  is the only initiator of a break in contact between the circuit  110  and the carrier assembly  120 . According to the embodiment shown in  FIG. 1 , the carrier assembly  120  disengages from the circuit  110  in less time than it takes for the mechanism  130  alone to break the contact, as detailed below. That is, the carrier assembly  120  breaks the contact to limit the flow of fault current and, subsequently, the mechanism  130  fully disengages the carrier assembly  120  in preparation for reset. The carrier assembly includes a contact arm  122  that includes the moving contact  116 . The contact arm  122  shares a pivot point (contact arm and carrier assembly pivot  121 ) with the carrier assembly  120 . A latch pin  124  keeps the cam assembly  123  within the latching bracket assembly  128  locked in position. The latch pin  124  is a spring-loaded pin that operates based on the latch spring  125 . 
         [0021]      FIG. 2  depicts the circuit breaker  100  according to the embodiment shown in  FIG. 1 . In  FIG. 2 , the contact between the circuit  110  and the carrier assembly  120  is broken (as indicated by “A”). This break (A) is caused by the force exerted in the direction B by the fault current. Thus, the carrier assembly  120  is said to be in the blow open position in  FIG. 2 . The moving contact  116  of the carrier assembly  120  is pushed away from the fixed contact  115  by the fault current force (B) in the following way. The force from the fault current pushes against the moving contact  116 . Because the contact arm  122  and the carrier assembly  120  share a pivot point (contact arm and carrier assembly pivot  121 ) that is as far as possible from the point of contact between the fixed contact  115  and the moving contact  116  (on the opposite end of the contact arm  122 ), torque acting on the contact arm  122  due to the fault force is maximized. As a result, when a fault occurs, the fault current exerts a force (B) pushing away the moving contact  116 , and the carrier assembly  120  pulls away from the circuit  110  by pivoting at the contact arm and carrier assembly pivot  121 . In alternate embodiments, the pivot of the contact arm  122  may be different from the pivot of the carrier assembly  120  but the fault force would affect movement at both pivots. Rotation of the contact arm  122  about the contact arm and carrier assembly pivot  121  based on the fault force pushes the latch pin  124 . The latch pin  124  is a spring-loaded pin in the illustrated embodiment. The latch pin  124  may be activated based on one or multiple contact arms  122 . Movement of the latch pin  124  de-latches the cam assembly  123 , which facilitates further movement of the carrier assembly  120  away from the circuit  110 . A comparison of the circuit breaker  100  in  FIG. 1  (which is in the closed position) with the circuit breaker  100  in  FIG. 2  (which is in the blow open position) indicates that the carrier assembly spring  126  is in the compressed state when the circuit breaker  100  is in the closed position and in the stretched state when the circuit breaker  100  is in the open position. 
         [0022]      FIG. 3  depicts the circuit breaker  100  according to the embodiment shown in  FIG. 1 . In  FIG. 3 , the carrier assembly  120  is in the open position in which it may be reset by the mechanism  130 . As a comparison of  FIG. 2  (showing the circuit breaker  100  in the blow open position) with  FIG. 3  (showing the circuit breaker  100  in the open position) indicates, the mechanism spring  135  around the lay shaft  132  aids in putting the carrier assembly  120 , which is already in the blow open position ( FIG. 2 ), into the open position. Specifically, the pole coupler  140  is positioned for a reset of the circuit breaker  100 . To be clear, the fixed contact  115  and moving contact  116  disengage, thereby limiting fault current, prior to action by the mechanism  130 . The disengagement is based on the configuration of the carrier assembly  120  as discussed with reference to  FIG. 2  above. However, in order for the mechanism  130  to be able to reset the circuit breaker  100 , the mechanism  130  must put the carrier assembly  120  in a fully disengaged position (referred to as the open position here). From the position shown in  FIG. 3 , the mechanism  130  may use the pole coupler  140  to put the circuit breaker  100  back in the closed position shown in  FIG. 1 . 
         [0023]      FIG. 4  is a three-dimensional view of the circuit breaker  100  according to an embodiment of the invention. As  FIG. 4  makes clear, multiple sets of contacts (fixed contact  115  and moving contact  116 ) may be affected with the carrier assembly  120 . A plurality of contact arms  122  correspond with the moving contacts  116 . While the exemplary circuit breaker  100  shown in  FIG. 4  includes four fixed contacts  115 , the circuit breaker  100  according to embodiments of the invention is not limited to any particular number and may have one, eight, or another number of fixed contacts  115 , for example. 
         [0024]      FIG. 5  details the cam assembly  123  according to an embodiment of the invention. The latch surface  510  indicates the portion of the cam assembly  123  that contacts the latch pin  124  when the circuit breaker  100  is in the closed position. The de-latch surface  520  indicates the portion of the cam assembly  123  that contacts the latch pin  124  when the circuit breaker  100  is in the blow open position. When the force of the fault moves the moving contact  116  based on a pivot at the contact arm and carrier assembly pivot  121 , the latch pin  124  moves from the latch surface  510  of the cam assembly  123  to the de-latch surface  520  to rotate the cam assembly  123  about the pole coupler pin  127  and further dissociate the moving contacts  116  from the fixed contacts  115 . 
         [0025]      FIG. 6  details the arrangement of the cam assembly  123  and the latching bracket assembly  128  according to an embodiment of the invention. As shown in  FIG. 6 , the pole coupler pin  127  is held by the latching bracket assembly  128  and goes through the cam assembly  123  such that the cam assembly  123  may rotate about the pole coupler pin  127  once the latch pin  124  moves to de-latch the cam assembly  123 . The latch pin  124  need not necessarily have a cylindrical surface and need not necessarily slide along a slot  610 . In alternate embodiments, the latch pin  124  may be pivoted in circular holes instead of slots  610  and may rotate instead of sliding. In addition, the exemplary latch pin  124  is shown as being spring-mounted based on a torsion spring (latch spring  125 ). In alternate embodiments, the latch pin  124  may be operated based on a different type of spring such as a tension spring, for example. The interface surfaces of the cam assembly  123 , the latch pin  124 , and the slot  610  may be provided with a heat treatment or surface finish or with bearing parts that minimize friction and facilitate smooth operation of the carrier assembly  120 . 
         [0026]      FIG. 7  depicts aspects of the carrier assembly  120  according to an embodiment of the invention.  FIG. 7  shows contact springs  710 . While shown as torsion springs in  FIG. 7 , the contact springs  710  may be extension, compression, or leaf springs in alternate embodiments.  FIG. 8  depicts aspects of the carrier assembly  120  according to an embodiment of the invention.  FIG. 8  shows a flexible component  810  which may be connected below the contact arms  122  in alternate embodiments.  FIG. 8  also includes the contact arms  122  and shows the contact springs  710  resting on the contact arms  122 . While the latching bracket assembly  128  is shown between the contact arms  122 , in alternate embodiments of the invention, the latching bracket assembly  128  may be arranged on the sides of the set of contact arms  122 , for example.  FIG. 8  also shows a restrike control latch assembly  900  at an opposite end of the latching bracket assembly  128  from the cam assembly  123 . 
         [0027]      FIG. 9  details a restrike control latch assembly  900  according to an embodiment of the invention. The restrike control latching assembly  900  includes fixing bracket  910  to attach the restrike control latching assembly  900  to the bottom terminal (see e.g.,  FIG. 4 ). The restrike control latching assembly  900  also includes a latch link assembly  920  with a latch link pin  925 , a biasing torsion spring  930 , and latch link assembly pivot pin  940 .  FIG. 10  provides an exploded view of a restrike control latch assembly  900  according to an embodiment of the invention.  FIG. 11  details the arrangement of the restrike control latch assembly  900  and the latching bracket assembly  128  according to an embodiment of the invention. The latch link pin  925  forms a cam-follower joint with the latching bracket surface  950  of the latching bracket assembly  128  such that the latch link pin  925  follows the latching bracket surface  950  and is always in touch with the surface  950 . When the carrier assembly  120  is pushed away from the circuit  110  based on a fault force and is about to re-bounce after hitting the bottom terminal ( FIG. 4 ), the latch link pin  925  slides along the dented area of the latching bracket surface  950  (ending up near “x”). After impact of the carrier assembly  120  with the bottom terminal ( FIG. 4 ), the carrier assembly  120  rotates in the opposite direction (back toward the circuit  110 ) but faces an opposing force from the biasing torsion spring  930  to overcome the dented area of the latching bracket surface  950 . As a result, bounce-back of the carrier assembly  120  into contact with the circuit  110  is restricted to prevent restrike of the electric arc. During the closing operation, the mechanism  130  supplies sufficient energy to overcome the force of the biasing torsion spring  930 . 
         [0028]    While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.