Abstract:
A mechanism for a circuit breaker contact arm that allows current limiting by reducing the opening time is disclosed. A secondary trip assembly is arranged to actuate due to magnetic forces generated during an undesirable electrical condition such as a short circuit. The secondary trip system releases a contact arm assembly allowing the contact arm to rotate to an open position that interrupts the flow of electrical power.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The subject matter disclosed herein relates to a mechanism for a circuit breaker. In particular, the subject matter disclosed herein relates to a mechanism coupled to a contact arm to provide current limiting functionality by reducing the opening time. 
         [0002]    Air circuit breakers are commonly used in electrical distribution systems. A typical air circuit breaker comprises an assembly of components for connecting an electrical power source to a consumer of electrical power called a load. The components are referred to as a main contact assembly. In this assembly, a main contact is typically either opened, interrupting a path for power to travel from the source to the load, or closed, providing a path for power to travel from the source to the load. In a particular type of circuit breaker, referred to as an air circuit breaker, the force necessary to open or close the main contact assembly is provided by an arrangement of compression springs. When the compression springs discharge, they exert a force that provides the energy needed to open or close the main contacts. Compression springs that provide a force to close the main contacts are often called closing springs. Compression springs that provide a force to open the main contacts are often referred to as contact springs. 
         [0003]    The mechanism for controlling the compression springs comprises a configuration of mechanical linkages between a latching shaft and an actuation device. The actuation device may be manually or electrically operated. An electrically operated actuation device generally operates when a particular electrical condition is sensed, for example, over-current or short-circuit conditions. The actuation device within the circuit breaker typically imparts a force onto a linkage assembly. The linkage assembly then translates the force from the actuation device into a rotational force exerted on the latching shaft. The latching shaft then rotates. This rotation is translated through the mechanical linkages to unlatch or activate either the closing springs or the contact springs. There is typically a first latching shaft mechanically linked to the closing springs called the closing shaft. A second latching shaft is mechanically linked to the contact springs called the tripping shaft. 
         [0004]    As each actuation device acts upon the latching shaft via a corresponding linkage assembly, the linkage assembly acts as a lever converting a linear force from the actuation device to a rotational force on the latching shaft. The time required for the actuation device to be electrically activated and initiate movement of the mechanism and the contact assembly can be lengthy. Where an undesirable electrical condition exists, this time period required to open the contact assembly may be longer than desired. 
         [0005]    While existing circuit breakers are suitable for their intended purposes, there still remains a need for improvements particularly regarding the operation of the circuit breaker and the time required to open the contacts under high current and short circuit conditions. 
       SUMMARY OF THE INVENTION 
       [0006]    A circuit breaker is provided having a contact structure movable between a closed and an open position. A contact carrier is coupled to the contact structure wherein the contract carrier has a slot. A first mechanism is coupled to the contact carrier by a shaft disposed in the slot. The shaft is rotatable and movable between a first position and a second position in the slot. A second mechanism is operably coupled to the shaft where the second mechanism includes a first linkage coupled to the shaft and an armature operably coupled to the first linkage. 
         [0007]    A magnetic trip device for a circuit breaker is also provided including an armature movable between an open position and a closed position. A first link is movable between a first position and a second position and is operably coupled to said armature. A shaft is coupled to rotate with the first link where the shaft has a cylindrical portion and a planar portion thereon. A contact arm carrier having a slot with a first end and a second end is positioned such that the shaft is arranged in the slot. 
         [0008]    A multi-pole circuit breaker is also provided having a mechanism movable between a first and second position. A first contact arm assembly including at least one contact arm and a contact arm carrier having a slot has a circular portion and an elongated portion. A first link is coupled between the mechanism and the contact arm carrier by a shaft positioned in the slot. Wherein said shaft is arranged to rotate between a first position and a second position in the slot circular portion. An armature is operably coupled to rotate the shaft from the first position to the second position. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    Referring now to the drawings, which are meant to be exemplary and not limiting, and wherein like elements are numbered alike: 
           [0010]      FIG. 1  is a top schematic illustration of a multi-pole circuit breaker of the exemplary embodiment; 
           [0011]      FIG. 2  is a side plan view illustration of a circuit breaker of  FIG. 1  in the closed position in accordance with the exemplary embodiment; 
           [0012]      FIG. 3  is a side plan view illustration of the circuit breaker of  FIG. 1  in the open position; 
           [0013]      FIG. 4  is a side plan view illustration of the circuit breaker of  FIG. 1  with the contact arm in a tripped position; 
           [0014]      FIG. 5  is a partial side plan view illustration of the contact arm mechanism of  FIG. 2 ; 
           [0015]      FIG. 6  is a perspective view illustration of the contact arm mechanism of  FIG. 5 ; 
           [0016]      FIG. 7  is a partial perspective view illustration of the contact arm carrier assembly of  FIG. 4 ; 
           [0017]      FIG. 8  is a plan side view illustration of the circuit breaker of  FIG. 1  where the secondary trip system is actuated; 
           [0018]      FIG. 9  is a partial perspective view illustration of the contact arm carrier assembly of  FIG. 8 ; and 
           [0019]      FIG. 10  is a partial plan view illustration of the contact arm carrier assembly of  FIG. 4  in the tripped position. 
       
    
    
     DETAILED DESCRIPTION 
       [0020]      FIG. 1  illustrates a multi-pole circuit breaker  20  having a main mechanism  22 . The mechanism  22  includes a lay shaft (“L/S”) assembly  24  that couples the mechanism  22  to the pole assemblies  26 ,  28 ,  30 . The mechanism provides a means for an operator to open, close and reset the pole assemblies  26 ,  28 ,  30  and will typically include an operator interface. The mechanism will further include a trip unit (not shown) that detects undesired electrical conditions and upon sensing of such a condition activates the mechanism  22 . As will be described in more detail herein, the pole assemblies  26 ,  28 ,  30  conduct electrical current through the circuit breaker  20  and provide the means for connecting and disconnecting the protected circuit from the electrical power source. 
         [0021]    In the exemplary embodiment, each pole of the multi-pole circuit breaker  20  carries a different electrical phase. Each of the pole assemblies  26 ,  28 ,  30  is coupled to a pair of conductors  32 ,  34  that connects the circuit breaker  20  to the protected load and the electrical power source. Typically, a housing  36  surrounds the mechanism  22  and the pole assemblies  26 ,  28 ,  30  to protect the components and prevent inadvertent contact by the operator with electrical current. 
         [0022]    The circuit breaker  20  is illustrated with the pole  26  in the closed position in  FIG. 2 . The lay shaft assembly  24  is coupled to a contact arm assembly  38  through a pin  40 . As will be described in more detail herein, the contact arm assembly  38  as illustrated in  FIG. 2  is in a locked position and transfers the energy from the mechanism  22  that is necessary to open and close a contact arm  44 . The contact arm assembly  38  is mounted in the circuit breaker  20  to pivot about a pin  42  to move between a closed, an open and a tripped position. Each of the other pole assemblies  28 ,  30  also includes a contact arm assembly  38  with each respective contact arm assembly coupled to the mechanism through the lay shaft assembly  24 . 
         [0023]    The contact arm assembly  38  includes the contact arm  44  having a movable contact  46  and an arcing contact  48  mounted to one end. A flexible, electrically conductive strap  50 , made from braided copper cable for example, is attached to the opposite end of the movable contact  46 . The flexible strap  50  electrically couples the contact arm  44  to the conductor  32  that allows electrical current to flow through the circuit breaker  20 . The electrical current flows through the contact arm assembly  38  and exits via movable contact  46 . The current then passes through stationary contact  52  and into conductor  34  where it is transmitted to the load. It should be appreciated that the terms “load” and “line” are for convenience, and the connections to the load and electrical supply may be reversed for certain circuit breaker applications. The contacts  46 ,  52  are typically made from Silver Tungsten and Silver Graphite composite to minimize resistance. Another arcing contact  54  is mounted to the conductor  34 . The arcing contacts  48 ,  54  assist the circuit breaker  20  in moving any electrical arc formed when the contact arm  44  is opened into an arc chute  56 . A compression spring  90  is mounted to the circuit breaker  20  to exert a force on the bottom side of the contact arm  44  and assist with the opening of the contact arm assembly  38 . It should be appreciated that the contact arm  44  may be a single component or may be composed of several parallel contact arms as illustrated in  FIG. 6 . In this embodiment, the contact arm assembly  38  will also include several contact arm carriers  58  that support and separate the individual contact arms  44 . 
         [0024]    The circuit breaker  20  also includes a secondary trip assembly  59 . The secondary trip assembly  59  includes a magnetic device that includes a fixed core  60  and a movable armature  62 . The fixed core  60  is electrically coupled to the conductor  32  and arranged to generate a magnetic field in proportion to the electrical current flowing through the conductor  32 . In the exemplary embodiment, the fixed core and movable armature are made from magnetic material, steel for example. As shown in  FIG. 6 , a pair of springs  63  separates and bias&#39; the armature  62  from the fixed core  60 . Alternatively, more than two springs may be utilized to bias the armature from the fixed core. In the exemplary embodiment, the armature  62  is coupled to a frame  57  that has one or more slots  67 . The slots  67  guide the motion of the armature during movement of the armature  62  caused by the magnetic field generated by fixed core  60 . 
         [0025]    The linkage assemblies  64 ,  65  are coupled to the armature  62 . Each linkage assembly includes a first link  78  that is coupled at one end to the armature  62  by a pin that allows rotation of the link  78  relative to the armature  62 . A second link  74  has a pivot  76  that is attached to the frame  57 . The second link  74  is coupled at one end to first link  78  and at the opposite end to a third link  72 . The third link in turn couples the second link  74  with a fourth link  70 . Fourth link  70  is attached to a shaft  66 . As will be described in more detail below, the linkage assembly  64  translates the linear motion of the armature  62  into a rotational movement of the shaft  66 . 
         [0026]    The shaft  66  couples the link  70 , the contact arm carrier  58  and the link  68 . Link  68  connects the contact arm assembly  38  to the lay shaft assembly  24  by pin  40 . The shaft  66  is arranged to rotate within the contact arm carrier slot  84 . The shaft  66  is attached to links  68 ,  70  such that there is no relative motion between the shaft  66  and links  68 ,  70 . As illustrated in  FIG. 7 , the shaft  66  includes a cylindrical portion  80  and a planar portion  82 . The shaft  66  is arranged to rotate in a slot  84  in the contact arm carrier  58 . The slot  84  includes a circular portion  86  and an elongated portion  88 . When the contact arm assembly  38  is in the locked position as shown in  FIG. 2  and  FIG. 3 , the shaft cylindrical portion  80  is positioned in the slot circular portion  86 . When in this locked position, any forces transmitted through the contact arm assembly  38  pass generally through the centers of shaft  66  and pin  40 . Due to this arrangement and the positioning of shaft  66  in slot circular portion  86 , movement of the contact arm assembly  38  independently from the movement lay shaft assembly  24  is prevented. Thus, during normal operation, the contact arm assembly  38 , the shaft  66  and the link  68  move, more or less, as a single rigid linkage when the mechanism  22  rotates the lay shaft  24 . This allows the main mechanism to open and close the contact arm assembly  32  without changing the position of the components in contact arm assembly  38  relative to the shaft  66 . 
         [0027]    During this opening operation, an operator may desire to remove electrical power from a protected circuit, to allow maintenance on equipment connected to the circuit for example. To accomplish this, the main mechanism  22  is activated, by an off push button for example, causing the lay shaft assembly  24  to rotate to an open position as illustrated in  FIG. 3 . The rotational movement of the lay shaft assembly  24  is translated into motion of the contact arm carrier  58  via link  68  causing the contact arm assembly  38  to rotate about pivot  42 . This rotation by the contact arm assembly  38  results in movable contact  46  separating from the stationary contact  52  and the halting of electrical current flow. To re-initiate flow of electrical power, the operator reactivates the main mechanism, by moving a closing push button for example, causing the lay shaft assembly  24  to rotate back to the position illustrated in  FIG. 1 . 
         [0028]    Under certain circumstances, the load connected to conductor  34  may experience an undesired condition, such as a short-circuit for example. Under these conditions, the level of current flowing through the circuit breaker will increase dramatically. For example, under normal operating conditions, circuit breaker  20  may carry 400-5000 A of electricity at 690V. Under short circuit conditions, the current levels may be many times the normal operating levels. For example, depending on the facility in which the circuit breaker  20  is installed, the current levels may reach more than 100 KA. These high levels of current are undesirable and the operator will typically desire to limit the amount of current that flows through circuit breaker  20  under these conditions. As discussed above, the fixed core  60  is arranged in electrical contact with the conductor  32  to generate a magnetic field. During an certain electrical fault conditions, such as the short circuit condition, the magnetic force is generated by fixed core  60  are sufficient to result in movement of armature  62 . 
         [0029]    The movement of the secondary trip assembly  59  and the contact arm assembly  38  will be described with reference to  FIGS. 7-10 . It should be appreciated the some of the components have been removed from  FIGS. 7-10  for clarity. The movable armature  62  and the linkage assembly  64  are arranged such that when the magnetic force between the fixed core  60  and the moveable armature  62  reaches a predefined level the armature  62  will move towards the fixed core  60 . For example, the armature  62  movement may initiate at the magnetic force level corresponding to 25 kA-100 kA and more preferably 50 kA. The different thresholds at which armature  62  moves will depend on selectivity of the circuit breaker  20  with other downstream feeder breakers (not shown). The movement of the armature  62  causes the link  78  to rotate the link  74  about the pivot  76 . This rotation in turn results in the link  72  rotating the link  70 , shaft  66  and link  68 . 
         [0030]    The secondary trip assembly  59  is arranged to rotate the shaft  66  until the planar portion  82  is generally parallel with the sidewalls of slot-elongated portion  88 . Upon reaching this position, any reaction force exerted by the shaft  66  on the contact carrier  58  in the direction of the elongated portion of the slot is removed, allowing the shaft  66  and contact carrier to move independently from each other. As the contact arm assembly  38  rotates from the closed position shown in  FIG. 2  to the tripped position of  FIG. 4 , the shaft  66  moves within the slot  84  from the circular portion  86  into the elongated portion  88 . Movement of the contact arm assembly  38  may be the result of the force generated by spring  90  or due to magnetic forces between the conductor  34  and the contact arm  44  generated by high current levels during a short circuit. The movement of the contact arm assembly  38  continues until the shaft  66  reaches the end of the slot-elongated portion  88 . This position, commonly known as the “tripped” position, is illustrated in  FIG. 4  and  FIG. 10 . In the exemplary embodiment, the end of the slot-elongated portion  88  is curved to match the curvature of shaft cylindrical portion  80 . The rotation of the contact arm assembly  38  causes the movable contact  46  to separate from the stationary contact  52 . Any electrical arc generated between the contacts  46 ,  52  is transferred via arcing contacts  48 , 54  to the arc chute  56  where the energy from the electrical arc is dissipated. 
         [0031]    To reset the positioning of the shaft  66  and allow the opening and closing of the contact arm assembly  38 , the operator activates the circuit breaker mechanism  22 . This rotates the lay shaft assembly  24  to the open position causing the link  68  and shaft  66  to rotate and move within the slot  84 . The link  68 , shaft  66  and slot  84  are arranged such that as the lay shaft assembly  24  reaches the open position, the shaft  66  is positioned within the slot circular portion  86 . Once the shaft  66  is positioned in the slot circular portion  86 , the link  68 , shaft  66  and contact arm assembly  38  are once again in the locked position allowing them to open and close as a single component. 
         [0032]    Allowing the contact arm assembly  38  to separate from the stationary contact  52  without the assistance of the mechanism  22  provides advantages in the operation of the circuit breaker  20 . The faster the circuit breaker  20  opens the contact arm assembly  38 , the less of electrical current is experienced by the protected load. By utilizing the armature  62  and secondary trip assembly  59 , the circuit breaker  20  can react to the undesired electrical condition faster than through the use of mechanism  22  alone. In the exemplary embodiment it is expected that the secondary trip assembly  59  will allow the contact arm assembly  38  to separate in 8-10 milliseconds versus upwards of 30 milliseconds for the mechanism  22 . In the exemplary embodiment, it is contemplated that the mechanism  22  will move to the open position after the tripping position is reached, allowing the other poles associated with the circuit breaker to open. 
         [0033]    This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.