Abstract:
A circuit breaker and a method of developing the 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. The carrier assembly includes a latch pin to move responsive to a force transferred to the latch pin as a result of a fault condition in the circuit, a cam assembly in contact with the latch pin to move responsive to movement of the latch pin, and a movable contact coupled to the cam assembly, the movable contact breaking the physical contact with the fixed contact to put the circuit breaker in a second operative state. The circuit breaker also includes a mechanism to move the carrier assembly responsive to a signal indicative of the fault condition to put the circuit breaker in a third operative state.

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 latch pin configured to move responsive to a force transferred to the latch pin as a result of a fault condition in the circuit; a cam assembly in contact with the latch pin and configured to move responsive to movement of the latch pin; and a movable contact coupled to the cam assembly and in physical contact with the fixed contact of the circuit to supply the current to the circuit in the first operative state, the movable contact configured to break the physical contact with the fixed contact of the circuit responsive to movement of the cam assembly to put the circuit breaker in a second operative state; and a mechanism configured to move the carrier assembly responsive to a signal indicative of the fault condition to put the circuit breaker in a third operative state, 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 latch pin and the cam assembly 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 latch pin configured to move responsive to a force transferred to the latch pin as a result of a fault condition in a circuit coupled to the assembly; a cam assembly in contact with the latch pin and configured to move responsive to movement of the latch pin; and a movable contact coupled to the cam assembly and in physical contact with a fixed contact of the circuit to supply current to the circuit in a first operative state, the movable contact configured to break the physical contact with the fixed contact of the circuit responsive to movement of the cam assembly to establish a second operative state. 
         [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 latch pin of the carrier assembly to move responsive to a force transferred to the latch pin as a result of a fault condition in the circuit; arranging a cam assembly of the carrier assembly to be in contact with the latch pin, the cam assembly moving responsive to movement of the latch pin; and arranging a movable contact of the carrier assembly to be coupled to the cam assembly and in physical contact with the fixed contact of the circuit in the first operative state, the movable contact breaking the physical contact with the fixed contact of the circuit responsive to movement of the cam assembly to put the circuit breaker in a second operative state; and arranging a mechanism coupled to the carrier assembly, the mechanism moving the carrier assembly responsive to a signal indicative of the fault condition to put the circuit breaker in a third operative state, wherein the movable contact breaking the physical contact with the fixed contact to put the circuit breaker in the second operative state is prior to the mechanism moving the carrier assembly to put the circuit breaker in the third operative state. 
         [0006]    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 
         [0007]    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: 
           [0008]      FIG. 1  details a circuit breaker according to an embodiment of the invention; 
           [0009]      FIG. 2  depicts the circuit breaker according to the embodiment shown in  FIG. 1 ; 
           [0010]      FIG. 3  depicts the circuit breaker according to the embodiment shown in  FIG. 1 ; 
           [0011]      FIG. 4  is a three-dimensional view of the circuit breaker according to an embodiment of the invention; 
           [0012]      FIG. 5  details the cam assembly according to an embodiment of the invention; 
           [0013]      FIG. 6  details the latching bracket assembly according to an embodiment of the invention; 
           [0014]      FIG. 7  details the arrangement between the latching bracket assembly and cam assembly according to an embodiment of the invention; and 
           [0015]      FIG. 8  details the arrangement between the contact arms, the latching bracket assembly, and the cam assembly according to an embodiment of the invention. 
       
    
    
       [0016]    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 
       [0017]    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 an electro dynamic force generated by the fault current. Specifically, the latch pin initiates the break in contact based on the force. 
         [0018]      FIG. 1  details a circuit breaker  100  according to an embodiment of the invention. The view shown by  FIG. 1  is a perspective side view showing one set of contacts. As shown in  FIG. 1 , the circuit breaker  100  is in the closed (“on”) position with current 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 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  (ending at a lay shaft  132  at the mechanism  130 ). The pole coupler  140  attaches to the mechanism  130  at the lay shaft pivot  124  and to the carrier assembly  120  at the pole coupler pin  123 . The mechanism  130  facilitates resetting the circuit breaker  100  (back to the position shown in  FIG. 1 ) following a fault detection and clearing procedure. In a conventional selective circuit breaker, the mechanism  130  is the only initiator of a break in contact. 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  120  includes a contact arm and cam pivot pin  121 . As illustrated by the discussion of  FIG. 2  below, the inclusion of the cam assembly  122  and the contact arm and cam pivot pin  121  facilitates the current limiting feature of the circuit breaker  100 . More particularly, the arrangement of the cam assembly  122  and the latch pin  125  allow the carrier assembly  120  to be pushed away from the circuit  110 .  FIG. 1  also shows the bottom portion of the contact arm  127  extending from the moving contact  116 , the carrier assembly pivot  126 , the carrier assembly spring  128 , and the latching bracket assembly  129 . The lay shaft resetting spring  135  facilitates resetting of the cam assembly  120  and lay shaft  132  as discussed with reference to  FIG. 3  below. 
         [0019]      FIG. 2  depicts the circuit breaker  100  according to the embodiment shown in  FIG. 1 . In  FIG. 2 , 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. The force may be an electro dynamic force. 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 is transferred to the pole coupler pin  123  through the contact arm and cam pivot pin  121  and cam assembly  122 . Because the lay shaft pivot  124  is rigid, a component of the force on the pole coupler pin  123  is transferred to the spring loaded latch pin  125  through the cam assembly  122 . As the fault current increases, this force also increases and pushes the latch pin  125  along a slot  610  (detailed in  FIG. 6 ). Movement of the latch pin  125  causes the cam assembly  122  to start rotating with the contact arm and cam pivot pin  121 . This causes the moving contact  116  of the carrier assembly  120  to start moving until the contact gap (A) is achieved. A comparison of  FIG. 1  (showing the circuit breaker  100  in the closed position) with  FIG. 2  (showing the circuit breaker  100  in a blow open position). 
         [0020]      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 off position. That is, in addition to the carrier assembly  120  being pushed away from contact with the circuit  110  based on force exerted by the fault current, the carrier assembly  120  is placed in the full disengagement position (readied for 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 off position) indicates, the lay shaft resetting spring  135  aids in the lay shaft pivot  124  moving down, thereby relaxing the mechanism spring  135  and the mechanism  130  being positioned for 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 off position here). From the position shown in  FIG. 3 , rotation at the pole coupler pin  123  based on force from the mechanism  130  puts the circuit breaker  100  back in the closed position shown in  FIG. 1 . 
         [0021]      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 . The moving contact arms  127  that correspond with the moving contacts  116  are shown in  FIG. 4 . 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. 
         [0022]      FIG. 5  details the cam assembly  122  according to an embodiment of the invention. The dent  510  in the cam assembly  122  prevents unwanted re-closure of the contacts (fixed contacts  115  and corresponding moving contacts  116 ). Because the fault force that creates the gap (A) between the fixed and moving contacts  115 ,  116  may generate enough inertia in carrier assembly  120  at a rate of speed that is sufficient to cause bounce back of the carrier assembly  120 , the dent  510  is designed to prevent any re-closure of the circuit breaker  100  based on its shape. The latch surface  520  indicates the portion of the cam assembly  122  that contacts the latch pin  125  when the circuit breaker  100  is in the closed position. The cam assembly  122  moves the latch pin  125  to disengage the fixed contacts  115  from the corresponding moving contacts  116 . The de-latch surface  530  is the surface that contacts the latch pin  125  during the blow open operation and during reset operation. 
         [0023]      FIG. 6  details the latching bracket assembly  129  according to an embodiment of the invention. The latch pin  125  need not necessarily have a cylindrical surface and need not necessarily slide along a slot  610 . In alternate embodiments, the latch pin  125  may be pivoted in circular holes instead of slots  610  and may rotate instead of sliding due to the force resulting from the fault condition. The latch pin  125  is spring-loaded. The latching spring  620  is wound around a latching spring mount  640  having a latching spring arm support  630 . The exemplary latch pin  125  is shown as being spring-mounted based on a latching spring  620 . In alternate embodiments, the latch pin  125  may be operated based on a different type of spring such as a tension spring, for example. The interface surfaces of the cam assembly  122 , the latch pin  125 , 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 . 
         [0024]      FIG. 7  details the arrangement between the latching bracket assembly  129  and cam assembly  122  according to an embodiment of the invention. As  FIG. 7  shows, the pole coupler pin  123  is held by the latching bracket assembly  129  and goes through the cam assembly  122  such that the cam assembly  122  may rotate about the pole coupler pin  123  to move the latching pin  125 . 
         [0025]      FIG. 8  details the arrangement between the contact arms  127 , the latching bracket assembly  129 , and the cam assembly  122  according to an embodiment of the invention.  FIG. 8  shows the arrangement of the latching bracket assembly  129  and cam assembly  122  shown in  FIG. 7  between the contact arms  127 . However, while the latching bracket assembly  129  is shown between the contact arms  127 , in alternate embodiments, the latching bracket assembly  129  (cam assembly  122  and pole coupler pin  123 ) may be on both sides of the circuit breaker  100  while the contact arms  127  are in the middle. 
         [0026]    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.