Abstract:
A circuit breaker is disclosed that has a bi-stable display that maintains an indication of a fault condition after power is interrupted to the circuit breaker. The circuit breaker has a microcontroller that receives power derived from a line current that passes through the circuit breaker or the line voltage when the circuit breaker is in an on state. The bi-stable display is electrically coupled to and controlled by the microcontroller. A tripping mechanism trips the circuit breaker in response to detection of a fault condition. The tripping mechanism trips the circuit breaker in response to receiving a trip signal from the microcontroller. The microcontroller is programmed to modify the bi-stable display when sending the trip signal to the electronic switching device. The bi-stable display shows an indication of one of the several fault types that would have caused the circuit breaker to trip. The bi-stable display continues to display the fault-type indication after the circuit breaker has tripped and power is interrupted to the microcontroller.

Description:
FIELD OF THE INVENTION 
     Aspects disclosed herein relate generally to circuit breakers, and, more particularly, to a circuit breaker having a bistable display showing a fault condition after power is cutoff to the circuit breaker. 
     BACKGROUND 
     Circuit breakers provide automatic current interruption to a monitored circuit when undesired fault conditions occur. These fault conditions include, for example, arc faults, overloads, ground faults, and short-circuits. As is well-known, a circuit breaker is an automatically operated electromechanical device designed to protect branch wiring from damage caused by an overload or a short circuit. A typical circuit breaker has a load connector and a power connector with a break mechanism interposed between the load connector is (connected to a load device) and the power connector (connected to a power source such as a panel board). Various fault conditions trip the circuit breaker thereby interrupting power flow between the load and the power source. A circuit breaker can be reset (either manually or automatically) to resume current flow to the load. 
     An overcurrent may be detected when the fault current generates sufficient heat in a strip composed of a resistive element or bimetal to cause the bimetal to deflect and/or bend. The mechanical deflection triggers a trip assembly that includes a spring-biased trip lever to force a moveable contact attached to a moveable conductive blade away from a stationary contact, thereby breaking the circuit. When the circuit is exposed to a current above that level for a predetermined period of time, the trip assembly activates and tripping occurs thereby opening the circuit. 
     A circuit breaker may also include a solenoid coupled to electronic components that detect one or more fault conditions such as an arc fault in branch wiring or cord sets and are operable to cause the circuit breaker to electronically trip. The solenoid and the electronic components may be provided in addition to or in lieu of the thermal-magnetic tripping components. The electronic components process a signal output of a sensor that monitors current flowing in the circuit breaker. The electronic components may be configured to determine whether one of the fault conditions is present and to generate a fault signal and/or a trip signal. In response to the generation of a fault signal, a magnetic field is created around the solenoid, causing a plunger to move an armature relative to a yoke, which triggers a chain of mechanical actions that cause the circuit breaker to electronically trip. 
     The data on what fault conditions were present to trigger the trip condition is useful for fault diagnosis. Thus, a circuit breaker ideally includes an indication of the condition that leads to the tripping of the circuit breaker. However in many current mechanical or electrical circuit breaker designs, the event that led to the trip condition is not indicated by the circuit breaker. Thus, fault diagnosis is complicated by the lack of information to assist a technician. 
     One proposed solution uses light emitting diodes (LEDs) to indicate the cause of the trip condition. However, this solution requires the power to be enabled to the electronics of the circuit breaker in order to power the LEDs to display the causes of a trip condition. However, this requires power to be restored to power the LED fault display. Such restored power is also supplied to the load side terminals creating a potential hazard since the cause of the fault may still be connected to the load side terminals. Further, the fault condition must be stored in the memory of the circuit breaker thus taking up memory space. 
     The current circuit breaker designs therefore suffer from a problem of not having any indication of the fault that caused a tripped state when the power is turned off. 
     BRIEF SUMMARY 
     One disclosed example is a circuit breaker that includes a bi-stable display. A bi-stable display is a display that maintains an image without power. In this example, the bi-stable display maintains an indicator of a fault that caused the circuit breaker to trip regardless of whether power is maintained to the bi-stable display. In this manner, an electrician or homeowner may quickly tell the cause of the trip condition that caused the circuit breaker to interrupt power flow. This may aid in the diagnosis and solution of the problem that caused the power flow interruption. 
     An example circuit breaker has a load connector that is connected to a load that is sought to be protected and a power connector that is connected to a power line. The circuit breaker has a trip mechanism that when triggered interrupts current flow between the power line and the load. The trip mechanism typically includes an external handle and an actuating arm. If the trip mechanism is in an on condition (e.g., handle in an up position), current flows to the load. In order to protect the load, the circuit breaker can detect various faults such as ground fault or an arc fault on the load. On detecting a fault, a trip condition, interrupting current to the load, is triggered to protect the load. In this case, the handle is moved to a trip condition (e.g., handle is in a down position). The bi-stable display indicates the type of fault condition when the trip condition is triggered. When the trip condition is triggered, power is cutoff to the circuit breaker for safety reasons. However, the bi-stable display continues to indicate the fault condition thus showing an electrician or homeowner the cause of the trip condition without having to power up the circuit breaker. 
     The foregoing and additional aspects of the present invention will be apparent to those of ordinary skill in the art in view of the detailed description of various embodiments, which is made with reference to the drawings, a brief description of which is provided next. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing and other advantages of the invention will become apparent upon reading the following detailed description and upon reference to the drawings. 
         FIG. 1A  is a perspective view of a circuit breaker with a bi-stable display that maintains a fault indication after power is interrupted to the circuit breaker; 
         FIG. 1B  is a close-up view of the bi-stable display on the circuit breaker in  FIG. 1A ; 
         FIG. 2  is a cross section view of the internal components of the circuit breaker in  FIG. 1A ; 
         FIG. 3  is a block diagram of the electronic components of the circuit breaker in  FIG. 1A ; 
         FIGS. 4A-4C  are perspective views of the circuit breaker in  FIG. 1A  showing the various indications on the bi-stable display relating to different fault conditions tripping the circuit breaker in  FIG. 1A ; 
         FIGS. 5A-5C  are views of an alternative bi-stable display that may be used with the circuit breaker in  FIG. 1A ; and 
         FIG. 6  is a cross-section of an example bi-stable display of the circuit breaker of  FIG. 1A . 
     
    
    
     While the invention is susceptible to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and will be described in detail herein. It should be understood, however, that the invention is not intended to be limited to the particular forms disclosed. Rather, the invention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims. 
     DETAILED DESCRIPTION 
     Turning now to  FIG. 1A , a perspective view of a circuit breaker  100  is shown. The circuit breaker  100  includes a load side connector  102 , a power line connector  104 , a line neutral source wire  106  and a load neutral connector  108 . A handle  110  connected to a trip mechanism (detailed below) is mounted on a front panel  112 . The handle  110  may be placed in an on position (up position not shown in  FIG. 1A ) that causes the circuit breaker  100  to allow current flow between the power line connector  104  and the load side connector  102 . The handle  110  may be placed in a tripped condition (down position shown in  FIG. 1A ) cutting off current flow between the power side connector  104  and the load side connector  102 . A lens  114  is mounted below the handle  110  and shows an indication that the handle  110  is in a trip condition. A test button  116  is provided to test the internal electronics of the circuit breaker  100 . A bi-stable display  120  is also mounted on the front panel  112 . In this example, the circuit breaker  100  may be a miniature circuit breaker, such as the QO® and HOMELINE® family of circuit breakers available from Square D Company. However, it is to be understood that the principles discussed herein may be applied to other types of circuit breakers. 
     The example circuit breaker  100  shown in  FIG. 1A  allows the cause of the tripping event for the circuit breaker  100  to be displayed on the bi-stable display  120  without power to the electronics of the circuit breaker  100 . The bi-stable display  120  thus provides a fault-type indication indicative of which one of a plurality of fault types caused the circuit breaker  100  to trip and continues to display the fault-type indication after the circuit breaker  100  has tripped. As shown in  FIG. 1B , the bi-stable display  120  in this example has an AF area  130  and a GF area  132 . Printed indicia such as an “AF” graphic  134  and a “GF” graphic are located below each of the areas  130  and  132  respectively. In cases of a detected arc fault, the AF area  130  will be darkened indicating that an arc fault triggered the trip condition of the circuit breaker  100 . A darkened AF area  130  over the “AF” graphic  134  indicates an arc fault to a user. In cases of a detected ground fault, the GF area  132  will be darkened indicating that a ground fault s triggered the trip condition of the circuit breaker  100 . Neither the AF area  130  nor the GF area  132  will be darkened if the circuit breaker  100  is triggered by an event other than an arc fault or a ground fault. A darkened GF area  132  over the “GF” graphic  136  indicates an arc fault. The bi-stable display  120  does not consume power to maintain the display of the cause of a tripping event as either the GF or AF areas  130  and  132  remain darkened even after power is cutoff to the bi-stable display  120 . 
       FIG. 2  is cross section view of the internal components of the circuit breaker  100  in  FIG. 1A . Like elements from  FIG. 1A  have like element numbers in  FIG. 2 . The circuit breaker  100  contains a trip mechanism  200  and an electronics module  202 . The trip mechanism  200  includes a trip lever  204  connected to the handle  110 . The trip lever  204  is engaged with a is latch seat  206  of an armature  208 . The armature  208  is in a calibrated position such that a free end  210  of the armature  208  contacts a yoke hook  212 . The yoke hook  212  may be triggered by a bi-metal strip  214  that bends when a heat threshold is exceeded by current flowing through the b-metal strip  214 , thus causing the armature  208  to be released from the yoke hook  212  causing a spring  216  to drive the trip lever  204  and handle  110  to the trip position (shown in  FIG. 1 ). The movement of the trip lever  204  to the trip position breaks the electrical path between the line power connector  104  and the load power connector  102 . 
     The electronics module  202  includes a circuit board  220  that mounts a microprocessor  222 , a ground fault sensor  224 , a current sensor  226 , and a trip solenoid  228 . It is to be understood that the functions of the microprocessor  222  may be performed by a processor, microcontroller, controller, and/or one or more other suitable processing device(s) such as an application specific integrated circuit (ASIC), a programmable logic device (PLD), a field programmable logic device (FPLD), a field programmable gate array (FPGA), discrete logic, etc. 
       FIG. 3  is a block diagram of the electronic components of the electronics module  202  with like elements from  FIG. 2  having like element numbers. The electronics module  202  includes a power supply  300  that provides power for the electronic components in the circuit breaker  100 . The power supply  300  provides a regulated power supply and a reference voltage input to the microprocessor  222 . The microprocessor  222  may electronically cause the circuit breaker  100  to trip based on signals sensed by the ground fault sensor  224  or the current sensor  226  from the current flowing between the load connector  102  and the line connector  104 . On detection of a fault condition, the microprocessor  222  sends a signal to a trip circuit  302  that causes the trip solenoid  228  to activate a plunger  230  thus causing the armature  208  to release the yoke hook  212  causing the spring  216  to drive the trip lever  204  and handle  110  to the trip position thus breaking the electrical path between the line connector  104  and the load connector  102 . The microprocessor  222  analyzes the signals from the sensors  224  and  226  for indicators of fault conditions that may include, but are not limited to ground faults, arcing faults, overloads, and short-circuits. 
     The microprocessor  222  monitors the inputs from several input circuits including a zero crossing circuit and voltage monitoring circuit  310 , a differential current sensor circuit  312 , an integrator circuit  314 , a high frequency detection circuit  316 , a push to test circuit  318 , and a temperature sensor circuit  320 . In this example, the differential current sensor circuit  312  is coupled to the ground fault sensor  224 . The integrator circuit  314  and the high frequency detection circuit  316  are coupled to the current sensor  226 . The ground fault sensor  224  and differential current sensor circuit  312  provide an input to the microprocessor  222  indicating the presence of a ground fault or arcing ground fault from the load connector  102 . The current sensor  226  and the integrator circuit  314  provide an input to the microprocessor  222  indicating the presence of an arc fault on the load connector  102 . 
     The microprocessor  222  operates the bi-stable display  120  by sending signals to the bi-stable display  120  to change the display state to indicate the type of fault condition without delaying the tripping of the trip mechanism  200  by either the bi-metal strip  214  or the solenoid  228 . In this manner, the internal load side conductors coupled to the load connector  102  are brought to an electrically safe condition immediately. When power is removed from the electronic module  202  by the tripping process, the bi-stable display  120  maintains display of the fault that caused the trip condition. Electrical energy from the electronic module  202  may be used to change the state of the bi- stable display  120  once the handle  110  of the circuit breaker  100  is reset to the on position. 
     As shown in  FIGS. 4A-4C , the bi-stable display  120  may be used to inform a user as to the fault condition that existed on the load that caused the trip condition. Such information regarding the cause of the trip condition may be used for fault analysis. In the case of a normal circuit or overload condition, the thermal or magnetic systems of the circuit breaker  100  trips the trip mechanism. The handle position of the handle  110  and the bi-stable display  120  after a trip that does not involve an arc fault or a ground fault is shown by the circuit breaker  100  in  FIG. 4A . Neither the AF area  130  nor the GF area  132  is darkened, indicating that neither an arc fault nor a ground fault caused the trip condition. However, if there are certain specific conditions on the load connector  102  that caused the circuit breaker  100  to trip, the state of the bi-stable display  120  is changed by the electronics module  202  while simultaneously sending a trip signal to the trip solenoid  228 . The resulting state of the bi-stable display  120  indicates the type of fault that triggered the circuit breaker  100 . In  FIG. 4B , the bi-stable display  120  has darkened the “AF” area  130 , which is indicative of an arc fault. In  FIG. 4C , the bi-stable display  120  has darkened the “GF” area  132 , indicative of arc fault. In either case, the bi-stable display  120  maintains the indication of the trip state indefinitely until power is restored to the circuit breaker  100  and the bi-stable display  120  is reset via a reset or clear signal from the microprocessor  222 . In this example, the “AF” graphic  134  and the “GF” graphic  136  are printed below the bi-stable display  120 , but the graphics may be printed anywhere in proximity to the bi-stable display  120  in this example. It is to be understood that graphic indicators similar to the AF and GF graphics  134  and  136  may be displayed directly on the bi-stable display  120 . 
       FIGS. 5A-5C  show an alternate bi-stable display  520  that may display different text in a bi-stable state.  FIG. 5A  shows the bi-stable display  520  after a trip condition that was not caused by an arc fault or a ground fault. The bi-stable display  520  does not have any indicative text in  FIG. 5A , thus indicating that the trip condition has a cause other than an arc fault or a ground fault.  FIG. 5B  shows the bi-stable display  520  with a graphic indicator  522  that indicates an arc fault triggered the trip condition.  FIG. 5C  shows the bi-stable display  520  with a graphic indicator  524  that indicates a ground fault triggered the trip condition. As with the display  120  in  FIGS. 4A-4C , the graphic indicators  522  or  524  remain on the bi-stable display  520  after power is cutoff to the circuit breaker. 
     Alternatively, one of ordinary skill may modify the bi-stable display  120  to allow the display of additional information relating to the state of the circuit breaker  100  such as the level of ground fault (e.g., in mA) or the level of high frequency of the low current by segmenting the bi-stable display  120  and providing additional output signals to activate different parts of the display to show additional characters or text similar to the alternative bi-stable display  520  shown in  FIGS. 5A-C . 
     It is also to be understood that the bi-stable display  120  may be used during the on state of the circuit breaker  100  to indicate various operating parameters of the circuit breaker  100  or a monitored circuit coupled to the circuit breaker  100 . Such operating parameters may include the level of current flowing through the circuit breaker, level of high frequency, voltage, power factor, power, etc. The indication of the operating parameters may be text, bar graph, pulsating indicator (rate of pulse increase with current level, ground fault level, etc.), etc. The operating parameters displayed on the bi-stable display  120  may be transmitted by the microprocessor  222  along with suitable output signals for controlling the display  120 . 
     In the example shown in  FIG. 1A , the bi-stable display  120  is a bi-stable display device based on electrostatic charges used to affect “electronic ink” suspended in the display plane.  FIG. 6  shows a cross-section view of the bi-stable display  120  in  FIGS. 1A and 1B . The AF area  130  of the bi-stable display  120  includes an array of spheres  602  that each include a plurality of white subcapsules  604  and a plurality of black subcapsules  606  suspended in a clear fluid  608 . The bi-stable display  120  includes an array of back electrodes  610  and a corresponding array of transparent front electrodes  612 . Correspondingly, the AF area  132  of the bi-stable display  120  includes an array of spheres  622  that each include a plurality of white subcapsules  624  and a plurality of black subcapsules  626  suspended in a clear fluid  628 . The spheres  602  and  622  are electro-statically charged with the black subcapsules  606  and  626  carrying the negative charge and the white subcapsules  604  and  624  carrying a positive charge. In the example bi-stable display  120 , the array of electrodes  610  and  612  allows the color of each specific sphere such as the spheres  602  or  622  to be changed by changing the locations of the black and white subcapsules. Since the front electrodes  612  are transparent, the color of the different areas of the bi-stable display  120  may be seen by a user. 
     When a charge is placed across the electrodes  610  and  612  in a particular area defined by a sphere or spheres  602  or  622 , the subcapsules  604  or  624  and  606  or  626  move to align with the front to back charge gradient in that area. The subcapsules  604  or  624  and  606  or  626  are suspended in the clear fluid  608  or  628 . The clear fluid  608  and  628  is viscous and the subcapsules  604  or  624  and  606  or  626  remain in the position dictated by the charge between the electrodes  610  and  612  after the charge is removed from the electrodes  610  and  612 . For example, this makes the surface appear white at that area in the case of the AF area  130  in  FIG. 6 . At the same time, an opposite electric field pulls the black subcapsules  606  to the bottom of the spheres  602  where they are hidden. By reversing this process, the black subcapsules such as the black subcapsules  626  appear at the top of the spheres such as shown in the spheres  622 , which now makes the surface of the bi-stable display  120  appear dark at that spot. Therefore the bi-stable display  120  continues to show the color shown in the area when the power is cutoff. 
     The electronic module  202  in  FIG. 2  therefore will send an activation signal to the electrodes in the GF area  132  of the bi-stable display  120  simultaneously with energizing the trip solenoid  228  in the case of a detected ground fault. After power is shut off to the circuit breaker  100 , the black subcapsules  626  in the spheres  622  in the GF area  132  of the bi-stable display  120  as shown in  FIG. 6  will remain suspended near the transparent electrode  612  therefore providing an indicator of the ground fault independent of maintaining power to the circuit breaker  100 . Conversely, if an arc fault is detected by the electronic module  202  in  FIG. 2 , an activation signal will be sent to the electrodes of the AF area  130  of the bi-stable display  120  simultaneously with energizing the trip solenoid  228 . After power is shut off to the circuit breaker  100 , the black subcapsules  606  in the spheres  602  in the AF area  130  of the bi-stable display  120  will remain suspended near the transparent electrode  612  thereby providing an indicator of the arc fault independent of maintaining power to the circuit breaker  100 . The ability of the bi-stable display  120  to retain the indication of the fault does not require non-volatile memory, which if present may be allocated for other purposes. 
     There may be other types of bi-stable displays that may be used for the bi-stable display  120  in  FIG. 1 . For example, modified liquid crystal technology may be used for bi-stable displays. Such displays may include a cholesteric LCD technology that reflects almost all of the image light cast on it while attenuating most of the ambient light to produce a bright reflected display. For example, thin and flexible electronic paper may be used for the bi-stable display  120 . The electronic paper may use a liquid crystal dispersed in a polymer or a microcup structure to hold electronic ink stable on the paper. Another alternative is a nano-structure semi-conducting metal oxide film having a layer of viologen molecules creating black and white high contrast images. Another alternative is a micro-structured grating surface that controls liquid crystal alignment. 
     While particular embodiments and applications of the present invention have been illustrated and described, it is to be understood that the invention is not limited to the precise construction and compositions disclosed herein and that various modifications, changes, and variations can be apparent from the foregoing descriptions without departing from the spirit and scope of the invention as defined in the appended claims.