Patent Publication Number: US-9899176-B2

Title: Self-resetting biasing devices for current limiting circuit breaker trip systems

Description:
BACKGROUND 
     The field of the disclosure relates generally to circuit breaker devices, and, more specifically, to self-resetting biasing devices for current limiting circuit breaker trip systems. 
     Known current-limiting circuit breakers interrupt circuit faults and limit the short-circuit current by utilizing a variety of electromechanical mechanisms to open the problematic circuit in a sufficiently short enough time to prevent damage to electrical components other than the circuit breaker. At least some known current-limiting circuit breakers impose an upper limit on the current that may be delivered to a load through the circuit breaker with the purpose of protecting the circuit generating or transmitting the current harmful effects due to a short-circuit or a similar problem in the load. Also, at least some known current-limiting circuit breakers utilize more than one method for sensing and reacting to increasing current (I) above a rated current and tripping the affected circuit. Further, at least some known current-limiting circuit breakers are designed to meet various requirements set forth by standards-making bodies. 
     In at least some known trip systems for current limiting circuit breakers, a biasing force on the trip lever increases linearly as the trip lever rotates. This results in a low biasing force for lower level current, and a large biasing force at high level fault current. In at least some known trip systems, the large biasing force at high current levels may make it difficult to trip the circuit breaker in 4-5 milliseconds (ms) in order to clear a fault in a half cycle of a fault current. As a result of the large biasing force at high current levels in at least some known trip systems, it is challenging to provide a current limiting circuit breaker device that satisfies both Underwriters Laboratories (UL) and International Electrotechnical Commission (IEC) requirements. 
     BRIEF DESCRIPTION 
     In one aspect, a circuit breaker having a case is provided. The circuit breaker includes a trip mechanism and a trip lever coupled to the case and configured to move between a first position and a second position. The trip lever includes a first end that selectively contacts the trip mechanism and a second end opposite the first end. The circuit breaker also includes a biasing device including a housing coupled to the case and a lever arm coupled to the housing. The lever arm includes an engagement surface in contact with the second end. The lever arm is configured to move between an initial position corresponding to the first position and a final position corresponding to the second position. The biasing device also includes a bias member extending between the housing and the lever arm and biasing the engagement surface against the second end, where the lever arm exerts a first torque upon the trip lever in the first position and exerts a second torque upon the trip lever in the second position, and where a value of the first torque is different from a value of the second torque. 
     In another aspect, a biasing device for a circuit breaker is provided. The circuit breaker includes a case, a trip mechanism, and a trip lever coupled to the case and configured to move between a first position and a second position. The trip lever includes a first end that selectively contacts the trip mechanism and a second end opposite the first end. The biasing device includes a housing coupled to the case and a lever arm coupled to the housing. The lever arm includes an engagement surface in contact with the second end. The lever arm is configured to move between an initial position corresponding to the first position and a final position corresponding to the second position. The biasing device also includes a bias member extending between the housing and the lever arm and biasing the engagement surface against the second end, where the lever arm exerts a first torque upon the trip lever in the first position and exerts a second torque upon the trip lever in the second position, and where a value of the first torque is different from a value of the second torque. 
     In still another aspect, a method of assembling a circuit breaker is provided. The method includes coupling a trip mechanism to a circuit breaker case. The method also includes coupling a trip lever to the circuit breaker case. The trip lever is movable between a first position and a second position. The trip lever includes a first end that selectively contacts the trip mechanism and a second end opposite the first end. The method further includes coupling a biasing device to the circuit breaker. The biasing device includes a housing coupled to the circuit breaker case and a lever arm coupled to the housing. The lever arm is movable between an initial position corresponding to the first position of the trip lever and a final position corresponding to the second position of the trip lever. The lever arm includes an engagement surface that contacts the second end. The biasing device also includes a bias member extending between the housing and the lever arm, where the bias member biases the engagement surface against the second end, where the lever arm exerts a first torque upon the trip lever in the first position and exerts a second torque upon the trip lever in the second position to facilitate self-resetting of the trip lever, where a value of the first torque is different from a value of the second torque, and where a torque characteristic of the trip lever is non-linear over a range of motion of the trip lever. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other features, aspects, and advantages of the present disclosure will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein: 
         FIG. 1  is a perspective view of an exemplary embodiment of a circuit breaker. 
         FIG. 2  is a perspective view of an exemplary embodiment of a biasing device that may be used in the circuit breaker shown in  FIG. 1 . 
         FIG. 3  is a perspective view of an alternative embodiment of a circuit breaker. 
         FIG. 4  is a perspective view of an alternative embodiment of a biasing device that may be used in the circuit breaker shown in  FIG. 3 . 
         FIG. 5A  is a side view of a portion of the circuit breaker shown in  FIG. 3  with a trip lever in a first position. 
         FIG. 5B  is a side view of the circuit breaker shown in  FIG. 3  with the trip lever in an intermediate position between the first position and a second position. 
         FIG. 5C  is a side view of a portion of the circuit breaker shown in  FIG. 3  with the trip lever in the second position. 
         FIG. 6  is a perspective view of an exemplary embodiment of an assembly that includes a trip mechanism, trip levers, and biasing devices that may be used in the circuit breaker shown in  FIG. 3 . 
         FIG. 7  is a plot of an exemplary simulation of biasing torque versus trip lever rotation from the first position to the second position for the circuit breaker shown in  FIGS. 3 and 5A-5C . 
         FIG. 8  is a flowchart of an exemplary method of assembling a circuit breaker that may be used to assemble the circuit breakers shown in  FIGS. 1 and 3 . 
     
    
    
     Unless otherwise indicated, the drawings provided herein are meant to illustrate features of embodiments of this disclosure. These features are believed to be applicable in a wide variety of systems comprising one or more embodiments of this disclosure. As such, the drawings are not meant to include all conventional features known by those of ordinary skill in the art to be required for the practice of the embodiments disclosed herein. 
     DETAILED DESCRIPTION 
     In the following specification and the claims, reference will be made to a number of terms, which shall be defined to have the following meanings. 
     The singular forms “a”, “an”, and “the” include plural references unless the context clearly dictates otherwise. 
     “Optional” or “optionally” means that the subsequently described event or circumstance may or may not occur, and that the description includes instances where the event occurs and instances where it does not. 
     Approximating language, as used herein throughout the specification and claims, may be applied to modify any quantitative representation that could permissibly vary without resulting in a change in the basic function to which it is related. Accordingly, a value modified by a term or terms, such as “about”, “approximately”, and “substantially”, are not to be limited to the precise value specified. In at least some instances, the approximating language may correspond to the precision of an instrument for measuring the value. Here and throughout the specification and claims, range limitations may be combined and/or interchanged, and such ranges are identified and include all the sub-ranges contained therein unless context or language indicates otherwise. 
     The self-resetting biasing devices and associated systems and methods of use thereof described herein provide non-linear opposing torque profiles to trip systems for current limiting circuit breakers. The embodiments described herein also facilitate meeting regulatory requirements that require circuit breakers to avoid tripping at lower level currents and to deliver tripping at higher level fault currents. The embodiments described herein are further suited to resetting a biasing system without manual user intervention. The self-resetting biasing devices and associated systems and methods of use thereof described herein are also suited to preventing a biasing force from being applied to trip levers after unlatching and thus, enable tripping the mechanism within a half cycle of the fault current (e.g., within 4-5 milliseconds (ms)). The embodiments described herein are further suited to enabling tuning specific circuit breaker performance characteristics including, without limitation, rated current value, time to trip when current flow exceeds rated current, and self-resetting of trip mechanisms. The embodiments described herein are further suited to providing a current limiting circuit breaker device suitable for applications demanding both Underwriters Laboratories (UL) and International Electrotechnical Commission (IEC) requirements. 
       FIG. 1  is a perspective view of an exemplary embodiment of a circuit breaker  100 . In the exemplary embodiment, circuit breaker  100  includes a case  102  providing structural support and protection for internal components of circuit breaker  100 . Circuit breaker  100  also includes terminal connectors  104  for connecting circuit breaker  100  to electrical power lines (not shown). Circuit breaker  100  further includes a trip indicator  106  which provides a visual indication of a switched state of circuit breaker  100  to a user (i.e., whether circuit breaker  100  is tripped or not). Circuit breaker  100  also includes a trip mechanism  108  rotatably coupled to circuit breaker  100  which rotates upon being contacted by a trip lever  110 . In other embodiments, trip mechanism  108  is not rotatably coupled to circuit breaker  100 , but rather is coupled to circuit breaker  100  to facilitate linear movement, rather than rotational movement of trip mechanism  108 . Trip lever  110  is also rotatably coupled to circuit breaker  100  and rotates about a trip lever rotational axis  112 . In other embodiments, trip lever  110  is not rotatably coupled to circuit breaker  100 , but rather is coupled to circuit breaker  100  to facilitate linear movement, rather than rotational movement of trip lever  110 . Trip lever  110  includes a first end  114  and a second end  116  opposite first end  114 . 
     Also, in the exemplary embodiment, circuit breaker  100  includes a biasing device  118  coupled to case  102 . Biasing device  118  contacts second end  116  of trip lever  110  and is configured to bias rotation of trip lever  110 , as described in further detail below with reference to  FIGS. 2-4 . In other embodiments, biasing device  118  contacts second end  116  of trip lever  110  and is configured to bias linear movement, rather than rotation, of trip lever  110 . In operation, in the exemplary embodiment, circuit breaker  100  is configured to enable flow of current between terminal connectors  104  within a range of current values, i.e., a rated current. As the current flow through circuit breaker  100  begins to exceed the rated current, a rotatable device, including, without limitation, a magnetic coil-based device (not shown), inside case  102  experiences a torque, including, without limitation, an electromechanically-generated torque, in proportion to the degree to which the current flow exceeds the rated current. The rotatable device is coupled to trip lever  110  and exerts a torque to rotate trip lever  110 . In other embodiments, the rotatable device exerts a torque to move trip lever  110  in a linear direction, rather than to rotate trip lever  110 . In the exemplary embodiment, prior to the current flow exceeding the rated current, an initial gap (not shown) exists between first end  114  of trip lever  110  and a portion of trip mechanism  108  proximate first end  114 , such that first end  114  is not in contact with trip mechanism  108 . At such times, trip lever  110  is in a first position representative of a low current condition of circuit breaker  100 . 
     Further, in operation of the exemplary embodiment, as current flow begins to exceed rated current, rotatable device begins to rotate trip lever  110 , e.g., in a counterclockwise direction relative to the view shown in  FIG. 1 , and the initial gap begins to close between first end  114  and trip mechanism  108 . As current flow exceeds rated current still further over a period of time, continued rotation of rotatable device and thus trip lever  110  causes first end  114  to contact trip mechanism  108 . Upon still further increases in current flow, continued rotation of trip lever  110  causes movement of trip mechanism  108  and eventual tripping of the circuit breaker  100  to disable current flow between terminal connectors  104 . In other embodiments, not shown, continued rotation of the rotatable device with increasing current flow above the rated current causes continued linear movement of trip lever  110 , leading to contact of first end  114  with trip mechanism  108 , and eventual tripping of the circuit breaker  100 . Upon tripping of circuit breaker  100 , trip lever  110  is in a second position representative of a tripped condition of circuit breaker  100 . 
     Furthermore, in operation of the exemplary embodiment, biasing device  118  is biased against second end  116  of trip lever  110 . Thus, biasing device  118  allows circuit breaker  100  to be tuned for specific performance characteristics including, without limitation, rated current value, time to trip when current flow exceeds rated current, as well as facilitating self-resetting of trip mechanism. As described in further detail below with reference to  FIGS. 2-4 , biasing device  118  facilitates a non-linear biasing torque characteristic as trip lever  110  transitions from first position to second position. This non-linear biasing torque characteristic facilitates self-resetting of trip lever  110  after circuit breaker  100  is tripped, as described herein. 
       FIG. 2  is a perspective view of an exemplary embodiment of biasing device  118  that may be used in circuit breaker  100  shown in  FIG. 1 . In the exemplary embodiment, biasing device  118  includes a housing  202  coupled to circuit breaker  100 , not shown. A lever arm  204  is rotatably coupled to housing  202  and rotates about a lever arm axis of rotation  205 . In other embodiments, lever arm  204  is not rotatably coupled to housing  202 , but rather is coupled to housing  202  to facilitate linear movement, rather than rotational movement, of lever arm  204 . Lever arm  204  includes an engagement surface  206  in contact with second end  116  of trip lever  110  (shown in  FIG. 1 ). Engagement surface  206  includes a first portion  208  and a second portion  210 . In the exemplary embodiment, first portion  208  is oriented at a different angle than second portion  210 . A rounded transition portion  212  extends between first  208  and second  210  portions. In other embodiments, engagement surface  206  may not include rounded transition portion  212 . 
     Also, in the exemplary embodiment, biasing device  118  includes a bias member  214  (including, without limitation, a coil spring) extending between housing  202  and lever arm  204 . Bias member  214  is secured between housing  202  and lever arm  204  by a housing bias member securement piece  216  and a lever arm securement piece  218  between bias member  214  and lever arm  204 , respectively. Bias member  214  biases engagement surface  206  against second end  116  of trip lever  110 . Also, in the exemplary embodiment, lever arm  204  includes a divider  220  which separates engagement surfaces  206  from a second engagement surface  221  to accommodate contact between bias member  214  and two trip levers  110 , for example as shown and described below with reference to  FIG. 6 . In other embodiments, lever arm  204  may include a single engagement surface  206 . In still other embodiments, lever arm  204  may not include divider  220 . 
     Also, in the exemplary embodiment, biasing device  118  includes a stop surface  222 . Lever arm  204  also includes a protrusion  224  configured to contact stop surface  222  to restrict a rotation of lever arm  204 . Biasing device  118  also includes an additional bias member  226  (including, without limitation, a leaf spring, a torsion spring, a ball catch mechanism, and a cam-biased spring mechanism) extending between housing  202  and lever arm  204 . Additional bias member  226  includes a bias surface  228  that contacts an extension  230  of lever arm  204 . Additional bias member  226  further biases (i.e., applies an amount of biasing torque in addition to biasing torque applied by bias member  214 ) lever arm  204  against second end  116  of trip lever  110 . In other embodiments, biasing device  118  may not include additional bias member  226 . 
     In operation, in the exemplary embodiment, as trip lever  110  rotates counterclockwise in response to current flow in circuit breaker  100  (not shown) exceeding rated current, trip lever  110  causes lever arm  204  to press against bias member  214 , thus compressing bias member  214 . In other embodiments, linear movement, rather than rotation, of trip lever  110  causes lever arm  204  to press against bias member  214 . Compressed bias member  214  biases engagement surface  206  against second end  116  of trip lever  110 . When present in the exemplary embodiment, additional bias member  226  further biases lever arm  204  against second end  116  of trip lever  110 . As trip lever  110  rotates from the first position to the second position, second end  116  of trip lever  110  traverses engagement surface  206  of lever arm  204  from first portion  208  to second portion  210 . The different orientations of first and second portions  208  and  210  cause different directions and magnitudes of a biasing force to be exerted upon second end  116  by engagement surface  206 . As such, in operation of the exemplary embodiment, lever arm  204  exerts a first torque having a first value (or a first range of values) upon second end  116  of trip lever  110  in the first position (i.e., with first portion  208  contacting second end  116 ), and lever arm  204  exerts a second torque having a second value (or a second range of values) upon second end  116  of trip lever  110  in the second position (i.e., with second portion  210  contacting second end  116 ), thus facilitating self-resetting of trip lever  110  and trip mechanism  108  (not shown), as described below. Also, in operation of the exemplary embodiment, the value of the first torque is greater than the value of the second torque. In other embodiments, the value of the second torque is greater than the value of the first torque. The torque characteristic exhibited by circuit breaker  100  with trip lever  110  and biasing device  118 , and with trip lever  110  transitioning through intermediate positions between first position and second position is a non-linear torque characteristic regardless of whether the value of the first torque is greater than or less than the value of the second torque. 
       FIG. 3  is a perspective view of an alternative embodiment of a circuit breaker  300 . In the alternative embodiment, circuit breaker  300  includes trip mechanism  108  (shown in  FIG. 1 ). Circuit breaker  300  also includes trip lever  302  rotatably coupled to circuit breaker  300 . Trip lever  302  rotates about a trip lever rotational axis  304 , similar to trip lever  110  of circuit breaker  100  (shown in  FIG. 1 ). Also, in the alternative embodiment, trip lever  302  includes a first end  306  and a second end  308  opposite first end  306 . In other embodiments, trip lever  302  is not rotatably coupled to circuit breaker  300 , but rather is coupled to circuit breaker  300  to facilitate linear movement, rather than rotational movement of trip lever  302 . 
     In the alternative embodiment, circuit breaker  300  includes a biasing device  310  coupled thereto. Biasing device  310  contacts second end  308  of trip lever  302  and is configured to bias rotation of trip lever  302 , as described in further detail below with reference to  FIGS. 4 and 5A-5C . In other embodiments, biasing device  310  contacts second end  308  of trip lever  302  and is configured to bias linear movement, rather than rotation, of trip lever  302 . Also, in the alternative embodiment, circuit breaker  300  includes two trip levers  302  that contact biasing device  310 . Further, in the alternative embodiment, a second biasing device  310  (not shown) may be coupled to a second side of circuit breaker  300  to contact a third trip lever (not shown). In other embodiments, circuit breaker  300  may include a single trip lever  302  contacting biasing device  310 . 
     In operation, in the alternative embodiment, circuit breaker  300  enables flow of current between terminal connectors  104  within a range of current values, as described above with reference to  FIG. 1 . Also, as described with reference to  FIG. 1 , if current flow exceeds rated current, a rotatable device (not shown) inside case  102  rotates trip lever  302  from a first position (representative of a low current condition) to a second position (representative of a tripped condition). In other embodiments, the rotatable device exerts a torque to move trip lever  302  in a linear direction, rather than to rotate trip lever  302 . Biasing device  310  is biased against second end  308  of trip lever  302 . In other embodiments, not shown, continued rotation of the rotatable device with increasing current flow above the rated current causes continued linear movement, rather than rotation, of trip lever  302 , leading to contact of first end  306  with trip mechanism  108 , and eventual tripping of the circuit breaker  300 . 
       FIG. 4  is a perspective view of biasing device  310  that may be used in circuit breaker  300  shown in  FIG. 3 . In the alternative embodiment, biasing device  310  includes a housing  402  coupled to circuit breaker  300  (shown in  FIG. 3 ). A lever arm  404  is rotatably coupled to housing  402  and rotates about a lever arm axis of rotation  406 . In other embodiments, lever arm  404  is not rotatably coupled to housing  402 , but rather is coupled to housing  402  to facilitate linear movement, rather than rotational movement of lever arm  404 . Lever arm  404  includes an engagement surface  408  in contact with second end  308  of trip lever  302  (shown in  FIG. 3 ). Engagement surface  408  is defined on a pawl  409  of lever arm  404 . Also, in the alternative embodiment, engagement surface  408  includes an arcuate surface. In other embodiments engagement surface  408  may not include an arcuate surface. 
     Also, in the alternative embodiment, biasing device  310  includes a bias member  410  (including, without limitation, a torsion spring, a tension spring, and a leaf spring) extending between housing  402  and lever arm  404 . Bias member  410  is secured between housing  402  and lever arm  404  by at least one housing bias member securement piece  412 . Bias member  410  biases engagement surface  408  against second end  308  of trip lever  302 . Further, in the alternative embodiment, biasing device  310  includes a stop surface  414 . Lever arm  404  also includes a protrusion  416  configured to contact stop surface  414  to restrict rotation of lever arm  404 . Moreover, in the alternative embodiment, biasing device  310  includes two lever arms  404  rotatably coupled to housing  402  on opposite sides of housing  402 , each lever arm  404  having an associated bias member  410 , for example to accommodate contact between biasing device  310  and two trip levers  302  (as shown and described below with reference to  FIG. 6 ). In other embodiments, biasing device  310  may include a single lever arm  404  and a single bias member  410 . In such other embodiments where biasing device  310  includes a single bias member  410 , biasing device  310  may include two lever arms  404  coupled independently to opposite sides of housing  402 , and the single bias member  410  extends through housing  402 , but provides spring action upon each of the two lever arms  404  independently. 
     In operation, in the alternative embodiment, as trip lever  302  rotates counterclockwise in response to current flow exceeding rated current, trip lever  302  causes lever arm  404  to press against bias member  410 , thus compressing bias member  410 . In other embodiments, linear movement, rather than rotation, of trip lever  302  causes lever arm  404  to press against bias member  410 . Compressed bias member  410  biases engagement surface  408  against second end  308  of trip lever  302 . Due to a shape of second end  308  of trip lever  302 , as further described and shown below with reference to  FIGS. 5A-5C , lever arm  404  exerts a first torque having a first value (or a first range of values) upon second end  308  of trip lever  302  in the first position, and lever arm  404  exerts a second torque having a second value (or a second range of values) upon second end  308  of trip lever  302  in the second position, thus facilitating self-resetting of trip lever  302  and trip mechanism  108  (shown in  FIG. 3 ). Also, in operation of the alternative embodiment, the value of the first torque is greater than the value of the second torque. In other embodiments, the value of the second torque is greater than the value of the first torque. The torque characteristic exhibited by circuit breaker  300  with trip lever  302  and biasing device  310 , and with trip lever  302  transitioning through intermediate positions between first position and second position is a non-linear torque characteristic regardless of whether the value of the first torque is greater than or less than the value of the second torque. 
       FIG. 5A  is a side view of a portion of circuit breaker  300  shown in  FIG. 3  with trip lever  302  in the first position.  FIG. 5B  is a side view of a portion of circuit breaker  300  shown in  FIG. 3  with trip lever  302  in an intermediate (i.e., transitional) position between the first position and the second position.  FIG. 5C  is a side view of a portion of circuit breaker  300  shown in  FIG. 3  with trip lever  302  in the second position. In the alternative embodiment, trip mechanism  108  rotates about a trip mechanism axis of rotation  502 . Further, in the alternative embodiment, trip mechanism  108  includes a hinged tip  504 . Hinged tip  504  is hingedly coupled to trip mechanism  108 . Furthermore, in the alternative embodiment, an initial gap  505  is defined between first end  306  and hinged tip  504  when trip lever  302  is in the first position. As such, in first position, first end  306  does not contact hinged tip  504 . 
     Also, in the alternative embodiment, second end  308  of trip lever  302  includes a first surface  506  and a second surface  508 . Second surface  508  is oriented substantially orthogonal first surface  506 . In other embodiments second surface  508  may have other orientations relative to first surface  506 . Further, in the alternative embodiment, second surface  508  is curved concavely and first surface  506  is substantially planar. In other embodiments, second surface  508  may be curved convexly. In still other embodiments, second surface  508  may be substantially planar. In yet other embodiments, first surface  506  may be curved concavely or curved convexly. 
     With trip lever  302  in the first position (as shown in  FIG. 5A ), engagement surface  408  of lever arm  404  contacts and is biased against first surface  506  of trip lever  302 . Also, in the first position, bias member  410  (shown in  FIG. 4 ) of biasing device  310  is in a relaxed (though not necessarily fully relaxed) position, and protrusion  416  of lever arm  404  contacts stop surface  414  of housing  402 . As such, lever arm  404  is in an initial position corresponding to the first position of trip lever  302 . With engagement surface  408  in contact with first surface  506 , an applied force  510  of magnitude F 1  (indicated by a vector arrow in  FIG. 5A  labeled F 1 ) is exerted by engagement surface  408  upon first surface  506 . An angle (θ 1 )  511  and a radius (r 1 )  512  from trip lever axis of rotation  304  determine a first value of bias torque (τ 1 ) associated with the first position according to the following equation:
 
τ 1   =r   1   F   1  sin(θ 1 )
 
where τ 1  acts upon trip lever axis of rotation  304  in a clockwise direction (indicated by a curved arrow in  FIG. 5A  labeled τ 1 ).
 
     As current flow in circuit breaker  300  begins to exceed rated current, trip lever begins to rotate as shown and described above with reference to  FIGS. 1 and 3 , and trip lever  302  rotates to an intermediate position in which first end  306  makes contact with hinged tip  504 , as shown in  FIG. 5B . Upon first end  306  making contact with hinged tip  504 , initial gap  505  is eliminated. In the alternative embodiment, hinged tip  504  is a biased hinge that introduces additional non-linearity to a bias torque characteristic curve (e.g., as shown and described below with reference to  FIG. 7 ). In other embodiments, hinged tip  504  may freely rotate. Further increases in flow of current through circuit breaker  300  causes further rotation of trip lever  302  and hinged tip  504  until hinged tip contacts trip mechanism  108 . 
     During rotation of trip lever  302 , engagement surface  408  contacts and traverses second surface  508  of second end  308 . At the intermediate position, engagement surface  408  applies a biasing torque upon second end  308  with an applied force  514  of magnitude F i  (indicated by a vector arrow in  FIG. 5B  labeled F i ) exerted upon second surface  508 . An angle (θ i )  516  and a radius (r i )  518  from trip lever axis of rotation  304  determine an intermediate value of bias torque (τ i ) associated with the intermediate position according to the following equation:
 
τ i   =r   i   F   i  sin(θ i )
 
where τ i  acts upon trip lever axis of rotation  304  in a clockwise direction (indicated by a curved arrow in  FIG. 5B  labeled τ i ).
 
     Upon contact of hinged tip  504  with trip mechanism  108 , and with a nominal amount of further rotation of trip lever  302 , trip mechanism  108  begins to rotate counter clockwise about trip mechanism axis of rotation  502 . Upon reaching a predetermined extent of rotation (which can be a nominal or negligible amount), trip lever  302  reaches the second position (as shown in  FIG. 5C ) and circuit breaker  300  trips, as described above with reference to  FIG. 1 . Thus, in the exemplary embodiment, the second position exists for a mere instance in time substantially simultaneously with tripping of circuit breaker  300 . At that time, lever arm  404  is in a final position corresponding to the second position of trip lever  302 . In other embodiments, the second position of trip lever  302  exists for more than a mere instant of time, including, without limitation, a predetermined amount of time. In the second position, engagement surface  408  applies a biasing torque upon second end  308  with an applied force  520  of magnitude F 2  (indicated by a vector arrow in  FIG. 5C  labeled F 2 ) exerted upon second surface  508 . An angle (θ 2 )  522  and a radius (r 2 )  524  from trip lever axis of rotation  304  determine a second value of bias torque (τ 2 ) associated with the second position according to the following equation:
 
τ 2   =r   2   F   2  sin(θ 2 )
 
where τ 2  acts upon trip lever axis of rotation  304  in a clockwise direction (indicated by a curved arrow in  FIG. 5C  labeled τ 2 ).
 
     Tripping of circuit breaker  300  releases stored potential energy from rotatable device inside case  102  (as described above with reference to  FIG. 1 ), which causes a forceful counter-rotation  526  of trip mechanism  108  in a clockwise direction (indicated by a curved arrow in  FIG. 5C  labeled  526 ). This counter-rotation  526  rotates trip lever  302  back to the first position, thereby self-resetting trip lever  302 . Substantially the same aforementioned sequence of positions (i.e., from first position through the intermediate position, from intermediate position to second position, and then tripping with subsequent self-resetting of trip lever  302 ) also applies to circuit breaker  100  with trip lever  110  and biasing device  118  as shown and described above with reference to  FIGS. 1 and 2 . 
       FIG. 6  is a perspective view of an exemplary embodiment of an assembly  600  that includes trip mechanism  108 , trip levers  302 , and biasing devices  310  that may be used in circuit breaker  300  shown in  FIG. 3 . In the exemplary embodiment, two biasing devices  310  are coupled to opposing sides of circuit breaker  300  (shown in  FIG. 3 ). Also, in the exemplary embodiment, circuit breaker  300  is configured to alternately enable and disable current flow between terminal connectors  104  (shown in  FIG. 3 ) in a multi-pole electrical circuit, for example a 3-pole circuit system used in a 3-phase alternating current (AC) power system. Thus, circuit breaker  300  includes three poles: a first pole  602 , a second pole  604 , and a third pole  606 . Each pole of the aforementioned three poles  602 ,  604 , and  606  includes a rotatable device  608 , including, without limitation, a magnetic coil-based device, rotatably coupled to respective trip levers  302 , as shown and described above with reference to  FIG. 1 . 
     In operation, in the exemplary embodiment, assembly  600  of circuit breaker  300  is configured to detect and respond to current flow exceeding rated current in individual poles of the three separate poles  602 ,  604 , and  606 . For this functionality, poles  602 ,  604 , and  606  are spaced apart (i.e., physically separated by a gap  610 ) from one another to ensure that one pole does not influence the other poles&#39; performance characteristics in circuit breaker  300 . Also, in operation of the exemplary embodiment, each pole of the three separate pole  602 ,  604 , and  606  is rotatably coupled to a respective rotatable device  608 , facilitating electromagnetic and/or electromechanical separation in addition to physical separation provided by gap  610 . 
     Also, assembly  600  may be used with both circuit breaker  100  and circuit breaker  300 . When used with circuit breaker  300 , assembly  600  does not sum electromagnetic forces from respective rotatable devices  608  of two or more of poles  602 ,  604 , and  606  experiencing increased current flow therethrough that is above the rated current. Therefore, tripping of circuit breaker  300  occurs less quickly than in circuit breakers not having assembly  600 . Also, use of assembly  600  with circuit breaker  300  improves efficiency and effectiveness of maintenance and calibration activities. Assembly  600  used with circuit breaker  100 , on the other hand, permits summing electromagnetic forces from respective rotatable devices  608  of two or more of poles  602 ,  604 , and  606  experiencing increased current flow above the rated current, thus enabling faster tripping relative to circuit breaker  300 . Furthermore, using assembly  600  with circuit breaker  100  or circuit breaker  300  provides additional options for tuning and calibration of circuit breaking performance characteristics, as described above with reference to  FIG. 1 . 
       FIG. 7  is a plot  700  of an exemplary simulation of biasing torque versus trip lever rotation from the first position to the second position for circuit breaker  300  shown in  FIGS. 3 and 5A-5C . In plot  700 , a y-axis represents values of bias torque as a percent (%) of a maximal torque attained during the exemplary simulation (i.e., 100%). Also, in plot  700 , an x-axis represents counterclockwise rotational angle (e.g., degrees) as a % of rotation of trip lever  302  from first position to second position (i.e., 0% represents trip lever  302  in first position and 100% represents trip lever  302  in second position). In the first position, first end  306  of trip lever  302  does not contact hinged tip  504  and initial gap  505  is present. Also, in the first position at a point  702 , circuit breaker  300  has current flow at or below rated current and biasing device  310  biases trip lever  302  with approximately 32% of the maximal torque attained during the exemplary simulation. 
     As shown by plot  700 , a roughly exponential growth in torque occurs between point  702  at 0% rotation and a point  704  at approximately 23% rotation as current flow increases above rated current and causes rotation of trip lever  302 . During this period of the exemplary simulation, initial gap  505  begins to close between first end  306  and hinged tip  504 . Also, during the period of the exemplary simulation between points  702  and  704 , engagement surface  408  traverses first surface  506  and bias member  410  biases engagement surface  408  against second end  308  at first surface  506  thereof. A roughly exponential decay in torque then occurs between point  704  and a point  706  at approximately 42% rotation. Between points  704  and  706 , engagement surface  408  is nearing, but has not yet reached second surface  508  of second end  308 , and torque decreases from approximately 81% of the maximal torque attained during the exemplary simulation at point  704  to approximately 26% maximal torque at point  706 . 
     Next, in the exemplary simulation, trip lever  302  experiences a rapid rise in torque between point  706  and a point  708  at approximately 43% rotation. During this period of the exemplary simulation, engagement surface  408  contacts second end  308  at an intersection region between first surface  506  and second surface  508 , and initial gap  505  closes completely. At point  708 , torque is at approximately 97% maximal torque and first end  306  continues to impinge upon hinged tip  504 . Trip lever  302  experiences a substantially linear decrease in torque to approximately 85% of maximal torque between point  708  and a point  710  at approximately 55% rotation, as engagement surface  408  traverses the intersection region between first and second surfaces  506  and  508  to reach second surface  508 . Moreover, in the exemplary simulation, trip lever  302  experiences a substantially linear increase in torque to 100% of maximal torque between point  710  and a point  712  at approximately 99% rotation. Between points  710  and  712 , first end  306  impinges upon hinged tip  504  still further, and hinged tip  504  is nearing, but has not yet contacted, trip mechanism  108 . 
     Next, in the exemplary simulation, trip lever  302  experiences a rapid decrease in torque to approximately 7% of maximal torque between point  712  and a point  714  at 100% rotation. At point  712 , hinged tip  504  makes contact with trip mechanism. From point  712  to point  714 , torque decreases from 100% of maximal torque to approximately 7% of maximal torque due to the counter-rotation  526  of trip mechanism  108  (as shown and described above with reference to  FIG. 5C ) and trip lever  302  returns to the first position (i.e., trip lever  302  self-resets). 
     Plot  700  is an exemplary plot of data obtained in an exemplary simulation of a particular exemplary embodiment of circuit breaker  300 , resulting in a non-linear torque characteristic as shown and described above with reference to  FIG. 7 . Depending on particular applications and design characteristics of features of circuit breaker  300 , and likewise, of circuit breaker  100 , particular torque characteristics may vary, but still maintain a non-linear torque characteristic curve (as shown in  FIG. 7 ) that results through substantially the same mechanisms described herein. For example, in other embodiments, simulation plots constructed as described above may have greater than or less than the number of points shown in  FIG. 7 , and may experience behavior between any pair of points  702 ,  704 ,  706 ,  708 ,  710 ,  712 ,  714 , and other points as applicable, that differs from that shown in  FIG. 7 , but still retain a non-linear torque characteristic between first position (0% rotation) and second position (100% rotation). In such other embodiments, for example, an approximately exponential growth or decay between points  702  and  704  and points  704  and  706 , respectively, may instead be a roughly linear growth or decay, respectively. Likewise, such periods of approximately exponential growth or decay may instead be periods of approximately logarithmic growth or decay, respectively. Similarly, in simulation plots of such other embodiments, periods of increasing or decreasing behavior of biasing torque may instead be periods for which the torque characteristic remains substantially constant. Furthermore, the torque characteristic exhibited by circuit breaker  300  with trip lever  302  and biasing device  310  (and likewise, by circuit breaker  100  with trip lever  110  and biasing device  118 ), and with trip lever  302  (or trip lever  110 ) transitioning through intermediate positions between first position and second position is a non-linear torque characteristic regardless of whether the value of the first torque at the first position is greater than or less than the value of the second torque at the second position. 
       FIG. 8  is a flowchart of an exemplary method  800  of assembling a circuit breaker that may be used to assemble circuit breaker  100  or circuit breaker  300  shown in  FIGS. 1 and 3 , respectively. Method  800  includes coupling  802  a trip mechanism, for example trip mechanism  108 , to a circuit breaker case (e.g., case  102  of circuit breaker  100  or circuit breaker  300 ). In the exemplary embodiment, the trip mechanism is rotatably coupled to the circuit breaker case. In other embodiments, trip mechanism is not rotatably coupled to circuit breaker case, but rather is coupled to circuit breaker case to facilitate linear movement, rather than rotational movement, of the trip mechanism. Method  800  also includes coupling  804  a trip lever, for example trip lever  110  (or trip lever  302 ) to the circuit breaker case to facilitate a movement of the trip lever between a first position corresponding to a low current condition of the circuit breaker and a second position corresponding to a tripped condition of the circuit breaker. In the exemplary embodiment, the trip lever is rotatably coupled to the circuit breaker case. In other embodiments, trip lever is not rotatably coupled to the circuit breaker case, but rather is coupled to circuit breaker case to facilitate linear movement, rather than rotational movement, of the trip lever. The trip lever includes a first end, for example first end  114  (or first end  306 ), that selectively contacts the trip mechanism. The trip lever also includes a second end, for example second end  116  (or second end  308 ) opposite the first end. 
     Method  800  further includes coupling  806  a biasing device, for example biasing device  118  (or biasing device  310 ), to the circuit breaker case. The biasing device includes a housing (e.g., housing  202  or housing  402 ) and a lever arm (e.g., lever arm  204  or lever arm  404 ) coupled to the housing to facilitate a movement of the lever arm between an initial position corresponding to the first position of the trip lever and a final position corresponding to the second position of the trip lever. In the exemplary embodiment, the lever arm is rotatably coupled to the housing. In other embodiments, lever arm is not rotatably coupled to housing, but rather is coupled to housing to facilitate linear movement, rather than rotational movement, of the lever arm. The lever arm includes an engagement surface (e.g., engagement surface  206  or engagement surface  408 ) that contacts the second end of the trip lever. The lever arm also includes a bias member (e.g., bias member  214  or bias member  410 ) extending between the housing and the lever arm, where the bias member biases the engagement surface against the second end of the trip lever. The lever arm exerts a first torque upon the trip lever (e.g., about trip lever axis of rotation  112  or trip lever axis of rotation  304 ) in the first position. The lever arm exerts a second torque upon the trip lever (e.g., about trip lever axis of rotation  112  or trip lever axis of rotation  304 ) in the second position, where a value of the first torque value is different from (i.e., is greater than or, alternatively, is less than) a value of the second torque. Furthermore, in the exemplary embodiment, a torque characteristic of the movement of the trip lever (i.e., movement of trip lever through intermediate positions between first position and second position as shown in  FIG. 7 , for example) is non-linear. 
     The above-described embodiments of self-resetting biasing devices and associated systems and methods of use thereof provide non-linear opposing torque profiles to trip systems for current limiting circuit breakers. The above-described embodiments also facilitate meeting regulatory requirements that require circuit breakers to avoid tripping at lower level currents and to deliver tripping at higher level fault currents. The above-described embodiments are further suited to resetting the biasing system without manual user intervention. The above-described embodiments of self-resetting biasing devices and associated systems and methods of use thereof are also suited to preventing a biasing force from being applied to trip levers after unlatching and thus, enable tripping the mechanism within a half cycle of the fault current (e.g., within 4-5 ms). The above-described embodiments are further suited to enabling tuning specific circuit breaker performance characteristics including, without limitation, rated current value, time to trip when current flow exceeds rated current, and self-resetting of trip mechanisms. The above-described embodiments are also suited to providing a current limiting circuit breaker device suitable for applications demanding both UL and IEC requirements. 
     Exemplary embodiments of the above-described self-resetting non-linear biasing devices and associated systems and methods of use thereof are not limited to the specific embodiments described herein, but rather, components of systems and/or steps of the methods may be utilized independently and separately from other components and/or steps described herein. For example, the methods, systems, and apparatus may also be used in combination with other systems requiring self-resetting non-linear biasing devices, and the associated methods are not limited to practice with only the systems and methods as described herein. Rather, the exemplary embodiments can be implemented and utilized in connection with many other applications, equipment, and systems that may benefit from using the above-described embodiments of the above-described self-resetting non-linear biasing devices and associated systems and methods of use thereof to improve the safety, reliability, versatility, and efficiency of operation for circuit breakers in electrical power systems and other related systems in various applications. 
     Although specific features of various embodiments of the disclosure may be shown in some drawings and not in others, this is for convenience only. In accordance with the principles of the disclosure, any feature of a drawing may be referenced and/or claimed in combination with any feature of any other drawing. 
     This written description uses examples to disclose the embodiments, including the best mode, and also to enable any person skilled in the art to practice the embodiments, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the disclosure 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 language of the claims.