Patent Publication Number: US-11385300-B2

Title: Differential current sensing bussing method

Description:
PRIORITY INFORMATION 
     The present application is a division of and claims priority to U.S. patent application Ser. No. 15/672,762, filed on Aug. 9, 2017, which is herein incorporated by reference as if fully set forth in this description. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to circuit interrupters that utilize ground fault sensing as part of the fault detection methods, including circuit breakers or receptacles, and particularly to ground fault sensing miniature circuit breakers and outlet receptacles found most commonly in residential use. 
     2. Discussion of the Art 
       FIG. 1  illustrates the basics of a known circuit breaker  10  of the Ground Fault Interrupter type with a schematic representation therein of the line power current path  11 . The line current path starts at the line power terminal  13  of the breaker  10  and continues through the separable contacts  15  and a toroidal current transformer current sensor  17  to the load terminal  18  which is wired out to the branch load  22 , here represented as a motor. A mechanical “side” or portion  16  of the circuit breaker  10  contains thermal and magnetic trip units  19 , typically a bimetal and a magnetic yoke assembly, respectively, which are components for tripping, i.e. separating, the contacts  15 , in the event of overcurrent conditions. 
     An electronic “side” or portion  20  of the arc fault sensing circuit breaker  10  contains the current sensor in the form of current transformer  17 , and associated electronics  21  for evaluation of Ground Fault events. The electronics  21  control an actuator  23 , typically a solenoid, whose function is also to trip the separable contacts  15  and remove power from the load  22 . 
     The return neutral current path  24  from the load  22  travels from the load  22  to the neutral terminal  28  through the current transformer current sensor  17  and out to the neutral return wire  26 . It will be appreciated that a plug on neutral type breaker will have a terminal clip rather than, or in addition to, the illustrated pigtail wire. 
     The current flow direction of the power conductors and the neutral conductors are in the opposite directions when they are routed through the Ground Fault current transformer  17  sensor housing. Each current carrying conductor will produce a magnetic flux which is in compliance with the “Right Hand Rule” used to determine flux direction. When the two conductors are carrying the same level of current in opposite directions, the flux of one conductor will cancel the flux from the other conductor. This then has a net flux value of zero. If there is an equal current exiting and then returning back through the Ground Fault circuit breaker, the Ground Fault sensor will output no signal. If there is an imbalance of current in the circuit wires, then the Ground Fault Interrupter sensor will output a current proportional to the current imbalance and if this imbalance exceeds a predetermined threshold, the Ground Fault circuit breaker will detect the presence of a ground fault and interrupt the electrical circuit. 
     A recognized problem with Ground Fault Interrupter sensors is that if the conductors are not located properly in the sensor, uneven magnetic fields throughout the current sensor assembly can cause an output current from the current sensor, even when the total current through the conductor paths are balanced. The result is an inaccuracy in the current sensor output known as load shift error. Typically this error is compensated for by twisting the main conductors (line and neutral) as they pass through the Ground Fault current transformer. It has been proposed, e.g. by U.S. Pat. No. 3,725,741 to Misencik, to replace the usual twisted pair of main conductors (line and neutral) with a rigid tubular outer conductor surrounding an insulated flexible conductor passing through the aperture of the Ground Fault Interrupter current transformer. 
     SUMMARY OF THE INVENTION 
     The line power and neutral conductors for a Ground Fault sensing interrupter are arranged as an improved rigid conductor surrounding and holding an insulated flexible conductor when passing through the current sensing transformer. The rigid conductor may be shaped to provide controlled current flow distribution for adjusting any ground fault load shift through the current transformer and more evenly distributing the magnetic field through the current transformer. Conversely, in some aspects of the invention a deliberate ground fault load shift may be provided by the apparatus if desired. 
     A Ground Fault current sensing package according to the present invention utilizes a so-called “faux coax bus bar” i.e. a rigid conductor encompassing and holding a flexible insulated conductor, passing through the current transformer core in place of twisted wires to help control ground fault load shift performance inside the Ground Fault current sensor. Aspects of the present invention can be used to control current distribution across the faux coax for a better output from the current sensor. The faux coax arrangement also provides for easier construction while also eliminating the need for a twisted wire assembly and maintaining a more consistent routing path for the Line and Neutral wires to obtain a more consistent load shift performance. 
     In one aspect, the present invention provides for a Ground Fault sensing miniature circuit breaker with line power and neutral power current paths within an apertured current transformer for the detecting of ground fault current anomalies, comprising: a rigid conductor surrounding and holding a flexible conductor; the rigid conductor and the flexible conductor passing through the aperture of the Ground Fault current transformer inside of the miniature circuit breaker with the rigid conductor being shaped to control current density, and resultant flux, within the core. 
     In some aspects of the present invention the rigid conductor is connected to and forms a part of the current path of the Neutral connection. Alternatively, the rigid conductor could form a part of the Line power connection and the neutral line could be connected through the flexible conductor encompassed and held by the rigid conductor. The rigid conductor may be formed from a flat blank having first and second terminal strips and a wider central portion which has been rolled into a substantially tubular form for fitting through the current transformer. The rigid conductor can also have current density directing features integrated therein to create increased resistance to the flow of current such as where the electrical resistance feature in the rigid conductor is created by a narrowed wall thickness or through hole in the section of the substantially tubular form. Also for example the tubular form might, e.g., be formed by a roll of 180 degrees or 270 degrees between input and output terminals to control current flow and flux patterns. 
     Other aspects of the present invention offer an improvement to a Ground fault interrupter apparatus of the differential transformer type such as a miniature circuit breaker of the ground fault sensing type comprising: a current transformer with an apertured magnetic core; a printed circuit board with electronics for detection of ground fault events; first and second primary conductors extending through the core; the first primary conductor being a substantially rigid conductor with a tubular portion located inside the core and further having nontubular second and third portions outside the core extending at angles to the tubular portion, one of the second or third portions secured to the printed circuit board; the second primary conductor being a flexible wire held inside the tubular portion of the first primary conductor in a substantially coaxial arrangement; the current sensor further having a secondary winding comprising a plurality of turns on the core; a trip circuit responsive to sensed signals on the secondary winding. In some aspects of the invention the rolled central portion does not necessarily form a fully closed tube. Other aspects of the present invention present an improvement comprising the rigid conductor being formed by starting from a flat conductive piece and having a rolled central portion of the flat piece thereby creating the tubular conductor and flat terminal strips. Again, features may be added to the structure of the rigid conductor to provide shaped current flow, wherein the features can include through-holes in the wall of the rolled central portion or include narrowed wall thickness in the wall of the rolled central portion. It will be appreciated upon understanding the present invention that the rigid conductor can provide other current routing advantages within the circuit interrupter such as the elimination of jumper wires. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing and other advantages of the disclosed embodiments will become apparent upon reading the following detailed description and upon reference to the drawings, wherein: 
         FIG. 1  is a schematic illustration of the working parts of an exemplary ground fault or dual function circuit breaker as known in the art. 
         FIG. 2  is a perspective view of the interior of the mechanical side of a dual function circuit breaker of the present invention; 
         FIG. 3  is a perspective view of the electronics side of the circuit breaker of  FIG. 2  of the present invention; 
         FIG. 4  is a perspective view of a Dual Function circuit breaker PCB with the integrated arc fault and ground fault current sensing package of the present invention utilizing one ground fault current transformer. 
         FIGS. 5-25  detail various alternative embodiments of the rigid conductor. 
     
    
    
     DETAILED DESCRIPTION 
     As an initial matter, it will be appreciated that the development of an actual commercial application incorporating aspects of the disclosed embodiments will require many implementation specific decisions to achieve the developer&#39;s ultimate goal for the commercial embodiment. Such implementation specific decisions may include, and likely are not limited to, compliance with system related, business related, government related and other constraints, which may vary by specific implementation, location and from time to time. While a developer&#39;s efforts might be complex and time consuming in an absolute sense, such efforts would nevertheless be a routine undertaking for those of skill in this art having the benefit of this disclosure. 
     It should also be understood that the embodiments disclosed and taught herein are susceptible to numerous and various modifications and alternative forms. Thus, the use of a singular term, such as, but not limited to, “a” and the like, is not intended as limiting of the number of items. Similarly, any relational terms, such as, but not limited to, “top,” “bottom,” “left,” “right,” “upper,” “lower,” “down,” “up,” “side,” and the like, used in the written description are for clarity in specific reference to the drawings and are not intended to limit the scope of the invention. 
     Words of degree, such as “about,” “substantially,” and the like are used herein in the sense of “at, or nearly at, when given the manufacturing, design, and material tolerances inherent in the stated circumstances” and are used to prevent the unscrupulous infringer from unfairly taking advantage of the invention disclosure where exact or absolute figures and operational or structural relationships are stated as an aid to understanding the invention. 
     The person of ordinary skill in the art will appreciate that the well known components of an electronic miniature circuit breaker unnecessary to the exposition of the present invention are not described in detail here, but will be understood to be present in a functioning circuit interrupter as briefly explained above. While shown here in the context of a miniature circuit breaker it will be appreciated by those in the art that the invention may be applicable to a variety of Ground Fault sensing apparatus, such as other forms of circuit interrupter devices, receptacles, or monitoring systems. 
       FIG. 2  illustrates the “mechanical side,” i.e. portion, of a partially constructed arc fault sensing circuit breaker  30  according to certain aspects of the present invention. The terms “side” and “portion” are used herein to convey the sense of a functional grouping which may or may not exist as discrete physical layouts within the design of the breaker. Further, some common reference numbering between  FIG. 1  and the remaining figures may be used herein where the component functionalities are substantially in common between the two. The line (power) current path starts at the line power terminal  13  of the breaker  30  and continues through the separable contacts  15  into the movable contact arm  70  and travels by wire  72  through the mechanical trip portions of the yoke  74 , latch plate  78 , and bimetal  76  which cause the mechanical trip by separating the latch plate  78  from the trip lever  80 . The current path then passes through the Ground Fault Interrupter current transformer  34 , as further explained below, before exiting to the load terminal  18  which is wired out to the branch load  22  ( FIG. 1 ). 
       FIG. 3  illustrates one possible electronic “side,” i.e. portion,  31  of the arc fault sensing circuit breaker  30  containing the current transformer current sensor  34 , and associated electronics  52  mounted to a PCB  50  for evaluation of Ground Fault and Arc Fault events. The electronics  52  control a solenoid actuator  53  whose function is also to move the latch plate  78  from the trip lever  80  to trip the separable contacts  15  and remove power from the load (not shown). The return (Neutral) current path from the load travels from the Neutral return terminal  28 , which is a second end of the rigid conductor  36 , through the current sensor current transformer  34 , as further explained below, and out to the neutral return wire (pigtail)  26  or the plug on neutral clip  82 , both of which are shown here for the sake of explanation. 
     Referencing particularly  FIG. 4 , as is understood in the art, the current transformer  34  includes a wound toroidal core within its case. Through the aperture  40  of the toroidal transformer core is passed a rigid conductor  36  surrounding and holding an insulated flexible conductor  38 , i.e. a wire, arranged here for carrying the line power current through the circuit breaker and ending at a load terminal  18  (in phantom) for connection to a branch load line. This arrangement creates a so-called “faux coaxial conductor” for the ground fault current sensing apparatus of the present invention. The rigid conductor  36  is connected to a neutral return wire  26 , sometimes known as a pig tail, at a first end  42  of the rigid conductor  36 , as part of the neutral current path through the circuit breaker  30 . The second end  44  of the rigid connector  36  is formed into the Neutral terminal  28  of the circuit breaker for connection to the neutral line of the branch load  22  ( FIG. 1 ). 
     The rigid connector  36  is mounted, e.g. soldered, to a printed circuit board (PCB)  50  along with the various electronic components, collectively  52 , necessary to perform the circuit interruption functions of the breaker  30 . Leads may be incorporated into the PCB  50  and make contact with the rigid conductor  36  where it is soldered to the board such as at one of its pins  57  (see  FIG. 24 ), to be connected for providing the current paths necessary to operate the breaker without excessive use of jumper wires. 
       FIG. 5  illustrates a first alternative version  110  of the rigid conductor which fits into the tubular opening inside the center of the current transformer and allows a second flexible conductor ( 38 ,  FIG. 4 ) to pass through the center tubular portion  111  of the rigid conductor  110 . 
       FIGS. 6 and 7  illustrate a current flow  114  through the rigid conductor  110 .  FIG. 7  shows the flat pattern of the conductor  110  before rolling of the center tubular portion  111  to create a tube. A pattern of holes, collectively  112 , at each end of the tubular portion  111  redirects the current flow through the center body area  113  to evenly distribute the current flow lines  114  about the entire width, resulting in a controlled current density and a substantially parallel direction of current flow. The well controlled current density and direction will produce a good flux pattern  115  for minimal load shift error. This controlled area  113  of the rigid conductor  110  will be located in the center of the GFI current transformer  34  ( FIG. 4 ) during operation. 
     The object of this design is to produce parallel paths of current flow to produce a well oriented flux pattern to offset the flux pattern of the flexible conductor wire inside the rigid conductor, with the resultant flux to be in line with the sensor core and windings. The current path of the captive flexible conductor (not shown) will produce flux lines in a direction that is in direct opposition to the rigid conductor current path. 
       FIG. 8  illustrates a basic construction second alternative  118  of rigid conductor wherein the unpierced broad central portion  119  of the flat conductor blank merely has its lateral edges folded into a tube with zero degrees of twist. However the current path in this basic embodiment was found to be fairly uneven and was generally concentrated in a straight line between the ends. 
       FIG. 9  illustrates a third alternative version  120  of the rigid conductor with a rolled central portion  121  of zero degrees twist similar to that of  FIG. 8  but with a slot  122  impressed in the tubular middle section  121  which redirects the current flow  123  to the outer edges of the tube. This design produced better flux patterns than the alternative of  FIG. 8 . 
       FIG. 10  illustrates a fourth alternative version  126  of the rigid conductor using three slots  127  instead of the one slot  122  in  FIG. 9 . These extra slots  127  provide a redirection of the current path  128  to achieve a different current distribution if desired. 
       FIG. 11  illustrates a fifth alternative version  130  of the rigid conductor.  FIG. 12  is a flat pattern of the rigid conductor of  FIG. 11  showing the general current path  134  and flux pattern  135 . The ends  131 ,  132  of the rigid conductor  130  are 180 degrees out from one another since the middle section  133  has been put through a half roll twist during formation from flat ( FIG. 12 ) to tubular ( FIG. 11 ). This embodiment was found to redirect the current flow for a good current density distribution and flux pattern  135  throughout the central portion. 
       FIGS. 13 and 14  illustrate a fifth alternative version  137  rigid conductor. The flat ends  138 ,  139  are not offset as the central tubular portion  140  was formed with a zero degree roll, i.e. without twisting. The wall areas of reduced cross sections  141  at each end of the rigid conductor tubular center  140  are an alternative to the holes of the alternatives shown in  FIGS. 5, 9 and 10 . These reduced cross sections  141  will create resistance to current flow and will cause the current to seek a wider path as shown by the current lines  142  of  FIG. 14 . 
       FIGS. 15 and 16  illustrate a sixth alternative version  145  of the rigid conductor similar to the fifth alternative but with the reduced cross sections  146  shaped to create different resistance values in the center  147  of the tubular body  148  versus the outer areas  149 . The resistance value varies to cause the current flow to be evenly distributed about the center portion  147  of the rigid conductor. Since current flows highest in the least resistance path, the area of resistance of the cross section is varied to be higher in the center  147  and to offer the least resistance on the outer areas  149  to achieve good distribution of current and flux path  150 . 
       FIGS. 17 and 18  illustrate a seventh alternative  152  version of the rigid conductor. The end tabs  153 ,  154  of the rigid conductor are 360 degrees out from one another since the middle section  157  has been put through a full roll twist during formation from flat ( FIG. 18 ) to tubular ( FIG. 17 ). This redirects the current flow  155  for a good density distribution throughout the part. Arrows  156  show the general flux direction which is noted to be at an angle to normal of the central axis of the conductor as a whole. 
       FIGS. 19 and 20  Illustrate an eighth alternative  158  of the rigid conductor. The end tabs, i.e. terminals  159 ,  160  of the rigid conductor are 270 degrees out from one another since the middle section  163  has been put through a three-quarter roll twist during formation from flat (FIG.  20 ) to tubular ( FIG. 19 ). Arrows  162  show the general flux direction which is noted to be at an angle to normal of the central axis of the conductor as a whole. 
       FIGS. 21 and 22  illustrate an ninth alternative  166  of the rigid conductor. The first end  167  of the center area  169  has a resistive area  170  shaped by a reduced cross sectional area. The first end  167  forces the majority of the current  171  to be routed around the outer edges of the pocket  170  to the outer edges of the center section  169 . After passing the pocket  170  the current  171  is then free to travel diagonally inward through the center section  169  to be brought together again at the opposite end  168  of the center section  169  to achieve a changed distribution of current  171  and flux  172  paths throughout the length of the rigid conductor  166 . This construction will result in a different flux output between the rigid conductor and captive flexible conductors, thus providing a different dispersion of flux to deliberately produce a current and consequent load shift output in the current transformer sensor winding. 
       FIGS. 23, 24, and 25  show three possible variants  36   a ,  36   b ,  36   c  of the rigid conductor  36  folded as if assembled into the faux co-axial conductors through the Ground Fault Interrupter current transformer. As will be understood from the foregoing discussion, each rigid conductor  36   a ,  36   b ,  36   c  can start as a flat plate-like part to be stamped, rolled and bent during the process of constructing the rigid conductor of the faux coax sensor package. In each variant, a first end  42  of the rigid conductor  36  is rolled to form an open cylinder tubular connection point  60  for a flexible wire within the breaker. While illustrated in the foregoing description as carrying the Neutral current, it will be appreciated that the rigid conductor  36  could just as well carry the line current in other arrangements. A central tubular portion  62 , unclosed here in all three variants, is formed by rolling a wider central portion of the plate. The central tubular portion  62  of  FIG. 23  is rolled and/or twisted 180 degrees. The central tubular portion  62  of  FIG. 24  is rolled and/or twisted through 90 degrees and the central tubular portion  62  of  FIG. 25  has a so-called “zero degree” twist where the edges of the central plate are merely turned up towards one another without a twist through the axis of the starting plate. The central portion  62  of  FIG. 25  further has a feature  64  for adding resistance to current flow stamped into the central portion as a reduced thickness of the wall section. 
     A multitude of variations for the faux coax concept could be utilized to optimize load shift performance using variations of geometries; some examples being coax shape, length, material thickness, etc.; to optimize voltage drop at both typical 60 Hz or 50 Hz as well as at higher frequency signatures during arcing faults. 
     The rigid conductor in conjunction with underlying PCB conductors might further be used to replace separate jumper wire connections to the module. For instance power and push-to-test (PTT) inputs could be incorporated through the rigid conductor rather than as jumper wires. It will also be appreciated that the body of the rigid conductor could be insulated to reduce dielectric concerns to surrounding components. Again it will be appreciated that the rigid conductor  36  could be connected through either the Line Power (hot) wire path or the Neutral Return wire path in the construction of the faux coax arrangement. 
     While particular aspects, implementations, and applications of the present disclosure have been illustrated and described, it is to be understood that the present disclosure is not limited to the precise construction and compositions disclosed herein and that various modifications, changes, and variations may be apparent from the foregoing descriptions without departing from the invention as defined in the appended claims.