Abstract:
A protection device for an electrical circuit having a load includes a sensor operatively associated with the electrical circuit to sense current changes and voltage fluctuations in the electrical circuit. A detector receives input from the sensor and compares the input to known arc fault signatures and arc fault mimicking signatures to determine what category of arc fault or mimicked arc fault occurs. The detector then produces an encoded output signal indicative of the category of arc fault or mimicked arc fault. Categories of arc faults include upstream or downstream series, downstream parallel, downstream line to line, and downstream line to ground.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority from U.S. Provisional Application Ser. No. 60/254,730 filed Dec. 11, 2000 and entitled ARC FAULT DETECTOR WITH DIAGNOSTIC INDICATOR, incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     This invention relates generally to the field of arc fault detectors, and more particularly to an arc fault detector that indicates what type of arc fault is detected. 
     BACKGROUND OF THE INVENTION 
     The Underwriters Laboratories requirements for the family of arc fault circuit interrupters, as defined in their standard 1699, require the device to sense a variety of arcing conditions within a branch circuit of an AC electrical power distribution system and in appliance conductors receiving power therefrom, to be referred to as an electrical circuit, and to interrupt the flow of electrical current before an arcing condition causes flammable ignition of nearby combustibles. The ability to locate the arcing condition in the electrical circuit to mediate repair is often difficult since the arcing condition could be occurring in a portion of the electrical circuit that is hidden behind sheet rock or that is in a remote space. Even if the arcing condition is occurring in a visible portion of the electrical circuit, visibility of the arc could be denied by the arc fault circuit interrupter itself because of interrupting the arc before the arc becomes visible. 
     Arc faults known as “A-type” are those in which the arcing condition occurs across a discontinuity in the line or neutral conductor of the electrical circuit. Such discontinuities include a broken conductor, a frayed cord set, a loose terminal, or a poor connection within a wire nut. An A-type arc fault occurs when load current conducts intermittently through the discontinuity, commonly known as “sputtering current.” Since the current through the A-type fault is limited by the impedance of the load itself, because the fault is in series with the load, an A-type fault is also known as a “series fault.” 
     Arc faults known as “B-type” are a second type of arc fault condition. In a B-type arc fault, the arc occurs across two conductors in the branch circuit or any extension cords plugged into it, at a site where the insulating media separating the two conductors has been compromised. The arc may occur across the line and neutral conductors or the line and ground conductors, or in the case of reverse polarity where the line and neutral conductors are connected to the supply voltage in reverse, the arc may occur across the neutral and ground conductors. The current through the B-type fault is not limited by the impedance of the load, but instead by the available current from the supply voltage as limited by the loop impedance of the conductors and terminals between the source of supply voltage and the position of the parallel fault, i.e., specifically by the impedance of the conductive members carrying the fault current. Since B-type faults are effectively across the line, they have been known as “parallel faults.” 
     The arc fault circuit interrupter may be incorporated in various housings associated with electrical circuits including receptacles, circuit breakers, boxes devoid of receptacles, or plugs. Each device has a line side, also known as the upstream side, from which electrical power is received from the electrical power distribution system, and a load side, also known as the downstream side, from which electrical power is conveyed to a load. 
     Various circuit interrupters protect wiring circuits at different locations. Underwriters Laboratories requires downstream parallel arc faults to be interrupted by these devices: branch feeder arc fault circuit interrupter, combination arc fault circuit interrupter, outlet branch circuit arc fault interrupter, and outlet plug arc fault circuit interrupter. Loop currents in upstream parallel arc faults are not interruptible by the arc fault circuit interrupter because interrupting the circuit downstream of a parallel arc fault has no effect on the fault. 
     The arc fault devices must detect parallel arc faults in which the available current to the parallel fault is as high as 500 amperes, above which the overcurrent device (fuse or circuit breaker) has been determined to afford protection. Since the parallel arc fault current is established by the value of the loop impedance, the lowest value of parallel arc fault current is typically considered to be 75 amperes. 
     The combination arc fault circuit interrupter, the outlet branch circuit interrupter, and outlet arc fault circuit interrupter are required by UL to detect series faults in which the load is as low as 5 amperes, which was determined by UL to be the lowest current at which the risk of ignition of nearby combustibles is likely to occur. The highest series arc fault current slightly exceeds the rating of the upstream overcurrent device required by code to protect the branch circuit, for example, 30 amperes. For each of these types of arc fault circuit interrupters, the discontinuity, or series fault, can be upstream or downstream of the device. 
     Considering both series and parallel arc faults, the AFCI&#39;s must be able to cover a range of fault currents from 5 amperes to 500 amperes. The test methodologies in the UL standard for generating series and parallel arc faults differ in order to establish the two different types of faults. The standard allows for a longer interrupting time of the AFCI for lower energy series arcs than for higher energy parallel arcs, without sacrificing the protective benefit or risking ignition of nearby combustibles, further emphasizing that there are different types of arc faults. 
     Arc faults have been detected on the basis of monitoring the current or voltage of the electrical circuit to be protected. It is important to distinguish signals from arcing conditions that would result in the ignition of combustibles from arc-mimicking signals caused in normal everyday use, such as arcs produced by motor brushes or the toggling of wall switches, or by environmental factors such as lightning. The arc fault circuit interrupter may inadvertently trip in response to high energy arc-mimicking signals, occurring either upstream or downstream of the arc fault circuit interrupter, that present a signal to the arc fault detector that is normally unique to true A-type or B-type arcing conditions. 
     Many methods are well known in the prior art for identifying the type of arc, de-sensitizing detection of arc-mimicking noise, and determining whether the arcing condition or arc-mimicking condition is upstream or downstream, such as, for example, are disclosed in U.S. patent application Ser. No. 09/828,622 filed Apr. 6, 2001 and entitled AFCI DEVICE WHICH DETECTS UPSTREAM AND DOWNSTREAM SERIES AND PARALLEL ARC FAULTS; U.S. patent application Ser. No. 09/788,206 filed Feb. 16, 2001 and entitled ARC FAULT CIRCUIT INTERRUPTER RECOGNIZING ARC NOISE BURST PATTERNS; U.S. patent application Ser. No. 09/776,582 filed Feb. 2, 2001 and entitled AFCI WHICH DETECTS AND INTERRUPTS LINE SIDE ARCING; U.S. patent application Ser. No. 09/990,809 filed Nov. 16, 2001 and entitled ARC FAULT CIRCUIT DETECTOR HAVING TWO ARC FAULT DETECTION LEVELS; and U.S. patent application Ser. No. 09/992,055 filed Nov. 14, 2001 and entitled UPSTREAM/DOWNSTREAM ARC FAULT DISCRIMINATOR, each of which is incorporated herein by reference. 
     SUMMARY OF THE INVENTION 
     Briefly stated, a protection device for an electrical circuit having a load includes a sensor operatively associated with the electrical circuit to sense current changes and voltage fluctuations in the electrical circuit. A detector receives input from the sensor and compares the input to known arc fault signatures and arc fault mimicking signatures to determine what category of arc fault or mimicked arc fault occurs. The detector then produces an encoded output signal indicative of the category of arc fault or mimicked arc fault. Categories of arc faults include upstream or downstream series, downstream parallel, downstream line to line, and downstream line to ground. 
     According to an embodiment of the invention, a device for detecting an electrical fault in a power line having electrical faults includes detection means for detecting a category and location of an occurring fault; and output means for outputting a unique code associated with each different fault category and location detected. 
     According to an embodiment of the invention, a protection device for an electrical circuit having a load includes a sensor operatively associated with the electrical circuit which senses current changes and voltage fluctuations in the electrical circuit; and a detector which receives input from the sensor and compares the input to known arc fault signatures to determine what category of arc fault occurs; wherein the detector produces an encoded output signal indicative of the category of arc fault. 
     According to an embodiment of the invention, a plurality of arc fault protective devices protective of an electrical circuit includes an array of sensors disposed at least two different locations in the electrical circuit for sensing a variety of arc fault signatures; an array of detectors operatively associated with the array of sensors for detecting which category of arc faults are indicated by the sensed arc fault signature; wherein the array of detectors produces encoded output signals indicative of the category of arc fault. 
     According to an embodiment of the invention, a protection device for an electrical circuit having a load includes a sensor operatively associated with the electrical circuit which senses ranges of current to ground; and a detector which receives input from the sensor, wherein the detector produces encoded output signals unique to each range. 
     According to an embodiment of the invention, a testing device for testing an electrical circuit having a load and an electrical protector therein that protects the electrical circuit from a variety of arc faults is equipped to receive encoded signals from the electrical protector for identifying a category of arc fault. 
     According to an embodiment of the invention, a protection device for an electrical circuit having a load includes a sensor operatively associated with the electrical circuit which senses current and/or voltage fluctuations in the electrical circuit; and a detector which receives input from the sensor for detecting signatures associated with glowing connections, wherein the detector produces a unique encoded output signal indicative of the glowing connection. 
     According to an embodiment of the invention, a testing device for testing an electrical circuit having a load and an electrical protector therein responsive to arc faults and/or arc mimicking faults is equipped to receive encoded signals from the electrical protector for identifying an upstream or downstream location of the arc or arc-mimicking fault. 
     According to an embodiment of the invention, a method for detecting an electrical fault in an electrical circuit includes the steps of (a) sensing current changes and voltage fluctuations in at least one location in the electrical circuit; (b) detecting what category of fault occurs by comparing the current changes and voltage fluctuations to known arc fault signatures; and (c) outputting a unique code associated with each different fault detected. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a schematic diagram of a fault detector and indicator device according to an embodiment of the invention. 
     FIG. 2 shows a schematic diagram of a fault detector and indicator device according to an embodiment of the invention. 
     FIG. 3 shows a schematic diagram of a fault detector and indicator device according to an embodiment of the invention. 
     FIG. 4A shows a the sinusoidal current through a load produced by the supply voltage of the electrical distribution system without an arcing fault condition. 
     FIG. 4B shows the sputtering current through the load associated with an arc that involves carbon. 
     FIG. 4C shows the sputtering current through the load associated with an arc that does not involve carbon. 
     FIG. 5 shows a block diagram of a remote monitoring system according to an embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIG. 1, an arc fault circuit device is shown generally at  1 . A power source from the electrical circuit having line and neutral conductors are connected respectively to line terminals  2  and  4  of the device. The circuit between the voltage source and line terminals  2 ,  4  is commonly designated “upstream” or “hitherward.” The device is optionally provided with a set of normally closed contacts  14 ,  16  for connecting the power source to load terminals  6 ,  8  of the device for connection to a load  12 , and/or to a receptacle  10  integral to the housing of the device, either of which are designated as “downstream” or “thitherward.” Terminals  2  and  4  are optionally receptacle blades if device  1  is arc fault plug. 
     Device  1  is provided with a current sensor  18  for sensing current to load  12 . Current sensor  18  is connected to an input  22  of a detector  24 . Arc fault circuit device  1  is powered from the power source generally as shown at a terminal  3  of detector  24 . Detector  24  is preferably a microprocessor with appropriate input and output buffering circuits that is programmed to recognize the salient characteristics of arc fault signals and optionally ground fault signals. Detector  24  can be implemented as software programmed into hardware, as firmware, or as hardware. The supply voltage across line input terminals  2  and  4  is optionally attenuated by a voltage divider shown here as including resistors  20  and  26  at an input  28  to detector  24 . 
     Detector  24  is responsive to current and voltage signals at detector inputs  22  and  28  respectively. Detector  24  includes a code output terminal  30  that produces a signal indicative of the conditions observed at inputs  22  and  28  of detector  24 . Such code is optionally saved by detector  24  after a reset button  33  is manually depressed, thus allowing the condition to be read out at a later and/or more convenient time by a computer, portable testing device, monitoring device, or remote monitoring device connected to a monitoring port integral to the arc fault circuit interrupter or through the conductors of the electrical distribution system by way of a modem, with the monitoring device receiving its signal from output terminal  30  of detector  24 . Thus, a person monitoring the electrical distribution system at a remote location or a serviceman affixing the portable testing device to output terminal  30  can determine the category and location of the fault. 
     The electrical distribution system may contain an array of arc fault devices in circuit breaker, box, or receptacle housings. If more than one arc fault device responds to a given arc fault condition, the plurality of encoded signals received by the remote monitor would provide additional insight for locating the fault to facilitate repair. Alternatively, output  30  is connected to a lamp indicator  32  as shown, which may either complement the remote monitor or replace the need for a remote monitor. 
     Reset button  33  is optionally fully electronic as shown, producing a signal at an input  42  of detector  24 . Alternatively, a solenoid  38  along with contacts  14  and  16  comprise a mouse-trap type mechanism, with a reset button to effect closure of contacts  14  and  16  through a set of mechanical linkages, in which case a load voltage sensor  46  is optionally employed. Voltage sensor  46  establishes the open or closed status of contacts  14  and  16  by the presence or absence of voltage, respectively, at terminal  6 , and communicates the status to an input  44  of detector  24 . The encoded signal at output  30  of detector  24  is preferably saved until the contact closure signal is detected at input  44  of detector  24 . The reset button may be integral to the arc fault device housing or located in the remote monitor. 
     Detector  24  is optionally equipped with an output  34  to trigger a switch such as SCR  36  in response to the stated conditions to enable solenoid  38  to open contacts  14  and  16 , thereby disconnecting load  12  from the source of power. Detector  24  combined with SCR  36  and solenoid  38  is known as an arc fault circuit interrupter. 
     The code at output  30  is determined by the relationship between the signals at inputs  22  and  28  of detector  24 , as determined by the relationships of the current sensed by sensor  18  and fluctuations in the supply voltage, respectively, across terminals  2  and  4 . If there is a fluctuation in the supply voltage proportionally exceeding the change in current sensed by sensor  18 , detector  24  establishes that the cause of the fluctuating voltage is on the line side of the device, producing a distinctive code at output  30  to designate the fault location. Conversely, if there is a change in current from sensor  18  but the line voltage is unchanged, detector  24  establishes that the cause of the fluctuation is on the load side of the device. If detector  24  is equipped with output  34 , either of these conditions optionally causes a signal at output  34  of detector  24  for operating SCR  36 , causing solenoid  38  to open contacts  14  and  16 . 
     A test button  40  optionally provides a signal to an input  48  of detector  24 . Closing test button  40  preferably produces a simulated arc fault signal for testing the operative status of sensor  18 , detector  24 , SCR  36 , and solenoid  38 . Proper response to the test button is optionally demonstrated by a unique code indication at output  30  of detector  24 . 
     The invention as described is useful in an arc fault circuit device where it is desirable to physically locate the series or parallel arc fault or arc mimicking fault condition to facilitate repair. Series faults  100  and  102  are shown in located upstream and downstream, respectively, of the arc fault device. As previously described, arc faults produce a sputtering condition in the current. Whereas the current sensed by sensor  18  is the same in either case, the voltage variation at input  28  to detector  24  is entirely different. Since the current through series fault  102  is limited by the impedance of load  12  to thirty amperes or less (because otherwise the overcurrent protection device, e.g., fuse or circuit breaker, will have already tripped if the current exceeds 30 amperes) the presence or absence of a 30 ampere sputtering current has little effect on the supply voltage, wherein the supply voltage is able to source at least 500 amperes. Since series arc fault  100  is on the line side of the arc fault device, sputtering arcs from the fault randomly produce an alternating conductive and non-conductive condition, thereby causing a wide fluctuation in the supply voltage across line terminals  2  and  4  as sensed at input  28  to detector  24 . Line and load series arc faults are discernable thereby, allowing differing and associative codes to be produced at output  30  of detector  24 . If interrupting contacts  14 ,  16  are provided, SCR  36  is triggered which energizes solenoid  38  to open contacts  14 ,  16 , thereby interrupting the current to load  12  to terminate arc current  100  or  102 . In this manner, an arc fault is safely terminated to prevent the occurrence of a fire, and the location of the fault is identified through the code signal at output  30  of detector  24  to facilitate repair of the fault. 
     A parallel arc fault  104  occurring across load  12  is discernable by a sputtering current exceeding 75 amperes, which is sensed by current sensor  18 . The high current above the handle rating of the protective device preferably establishes yet another code at output  30  of detector  24  which is indicative of yet another fault condition, thereby facilitating the location and repair of the parallel fault condition. 
     Detector output  24  is optionally connected to an indicator lamp  32  as previously described. An example of code at detector output  30  is for a single blink of lamp  32  on two second intervals to indicate downstream series arc faults, a double blinking pattern to indicate downstream parallel arc faults, a triple blinking pattern to represent depression of the test button  40 , and a quadruple blinking pattern to represent upstream series arc faults. Output  30  could alternatively be used to trigger an audio tone. Or the signal at output  30  could be a voltage pulse, with the type of fault and its location encoded in the width of the voltage pulse. Regardless of the encoding method, the variety of code patterns is particularly useful for an outlet branch AFCI as described in standard 1699 which must detect and interrupt a plurality of conditions, but is also useful for other arc fault circuit interrupter embodiments that may not be required to respond to as many conditions. 
     Referring to FIG. 2, a schematic of another embodiment of an arc fault device is shown in which components that provide the same function as in FIG. 1 bear like identifications. Series and parallel arc faults can be considered to be two broad classifications of arc faults each representing a variety of arc fault conditions having individual arc fault signatures. The more that the arc fault characteristics can be differentiated by the arc fault device and interpreted by a local indicator, a remote monitor or an arc fault tester, the easier it becomes to locate the arcing condition to facilitate repair of the electric circuit. As previously described, parallel arc faults may occur between line to neutral or line to ground. These two types of parallel arc faults can be distinguished and given distinctive codes at code output  30  of detector  24 . Current sensor  18  senses the current through load  12  as previously described, by specifically sensing the current through one of the line conductors of the electrical circuit. A current sensor  200  senses current on another of the line conductors and provides a signal to an input  202  of detector  24  in the same manner as current sensor  18  provides a signal to input  22  of detector  24 . A line to neutral parallel arcing condition  104  is identifiable by detector  24  as a presence of signal from both current sensors  18  and  200 . A line to ground parallel arcing condition  204  is identifiable by detector  24  as a signal from only one of sensors  18 ,  200 . 
     Referring to FIG. 3, an alternate embodiment to FIG. 2 is shown in which the two sensors  18 ,  200  are replaced by a single toroidal transformer  300 , known as a “differential transformer” surrounding the two line conductors  2 ,  4 . A parallel arcing condition  104  between the line conductors produces equal and opposite currents on the line conductors through toroidal transformer  300  so that there is signal cancellation and absence of signal at an input  302  of detector  24 . A parallel arcing condition  204  from line conductor  2  to ground produces a current on only one of the line conductors, resulting in the presence of signal at input  302  of detector  24 . Alternately, the asynchronous transformer as described in U.S. Pat. No. 6,266,219 “Combination Ground Fault And Arc Fault Circuit Interrupter”, incorporated herein by reference, may be used to detect ground faults, line to ground arc faults, and line to line arc faults. Types of parallel arcing conditions are thereby distinguished. 
     As yet another alternative to the two current sensors shown in FIG. 2, sensors  18  and  200  could be replaced by a small current viewing series resistance placed in series with either the hot, neutral, or both wires, and commonly referred to as a shunt, and shown as series resistors  206 ,  208  in conductors  2 ,  4 , respectively, as disclosed in part in U.S. patent application Ser. No. 09/990,809 filed Nov. 16, 2001 and entitled ARC FAULT CIRCUIT DETECTOR HAVING TWO ARC FAULT DETECTION LEVELS, previously incorporated herein. Shunt  206  in the hot wire located between terminals  2  and  6  produces a signal in response to current flow in the hot wire. The signal is applied to an input of an operation amplifier (not shown) floating above the circuit ground. The amplified signal is then coupled to detector  24  through an isolation means (not shown) such as an opto-isolator coupler. 
     In addition, the signal from transformer  300  can be used to determine whether a ground fault occurs. UL standard  943  requires a ground fault circuit interrupter (GFCI) to trip when a ground fault current equals or exceeds 6 milliamps. Based on the signal from transformer  300 , detector  24  can determine the amplitude of any ground fault current and trip interrupting contacts  14 ,  16  when the ground fault current equals or exceeds 6 milliamps. Detector  24  can also send a unique code to output  30  indicative of the type of fault, as well as the amplitude or range of amplitudes of the ground fault current. If the ground fault current is less than 6 milliamps, a unique code at output  30  can indicate that condition as well. The location of any ground fault sensed by transformer  300  is downstream of device  1 . 
     FIG.  2  and FIG. 3 are representative of only a few ways for distinguishing types of parallel arc faults, including faults on multi-wire circuits. 
     Referring to FIGS. 4A-4C, the broad classification of series arc faults also represents a variety of conditions that can be distinguished. FIG. 4A represents the sinusoidal current through load  12  produced by the supply voltage of the electrical distribution system without an arcing fault condition. FIG. 4B represents the sputtering current through load  12  associated with an arc that involves carbon, in which there are distinctive arc start edges  402  following at random the zero crossing, and arc cessation edges  404  preceding the next zero crossing. The carbon in the arcs associated with carbon develops through the carbonization of flammable materials, which typically involve wire nuts or frayed electrical cords. FIG. 4C represents the sputtering current through load  12  associated with an arc that does not involve carbon, in which there are distinctive arc start edges  406  following at random the zero crossing but without arc cessation edges. Arcs in the absence of carbon typically involve loose-metal-against-metal terminals which can maintain an arc across a small series arc fault gap until very close to the following current zero cross, which action causes the weak arc cessation edges, as opposed to arcing carbon which tends to increase the arcing air gap as carbon is oxidized by the arc, or blown clear by the sputtering action of the arc. Arcs in the absence of carbon also manifest as a phenomenon known as glowing connections in which a terminal becomes resistive and glows while conducting current. 
     A glowing connection typically requires many hours of operation before the fault causes a fire. During this time, a significant percentage of these normally undetectable faults break into series arcing from physical vibration of the loose connection. These vibrations can be caused by movement of a plug attached to a receptacle undergoing a glowing connection or by vibrations caused by such actions as a closing door. When this occurs, the momentary series arc is detected by the embodiments of this invention, which causes tripping and opening of interrupter contacts  14  and  16 , thereby breaking the circuit and extinguishing the glowing connection. The various signals produced by current sensors  18  or  200  or the shunts described above are interpreted by detector  24  to identify the type of fault and provide a family of coded signals to detector  24  code output  30 . Other signatures are known to those skilled in the art. 
     Referring to FIG. 5, a block diagram shows how a remote monitoring system could be established according to an embodiment of the invention. A building main M 1  shows two feeder circuits providing power to overcurrent protection devices breaker B 1  and breaker B 2 . Breaker B 1  is shown with two branch circuits, one protected with protection devices PD 1 , PD 2  with the other protected with protection devices PD 3 , PD 4 . Similarly breaker B 2  is shown with two branch circuits, one protected with protection devices PD 5 , PD 6  with the other protected with protection devices PD 7 , PD 8 . Protection devices PD 1 -PD 8  are preferably AFCI&#39;s or AFCI/GFCI&#39;s according to the embodiments of the invention described above. 
     Building main M 1 , breakers B 1 -B 2 , and protection devices PD 1 -PD 8  are preferably connected to a remote monitoring device RM 1  as shown in FIG. 5 by the dashed lines. Remote monitoring device RM 1  is preferably located in the building within a security monitoring room or co-located with the building&#39;s fire alarm control panel (FACP). The connections can be via signal wires in similar fashion as FACP&#39;s are connected to fire alarm pull boxes and smoke detectors. Alternately, each main, breaker, and device could be connected via wireless transmitters to remote monitor RM 1 . Another optional connection could be done via power line communication technology, although this method of connection has the disadvantage that the arc fault itself can disrupt the signal. The signals are the encoded output signals from detector  24 , which can be binary, hex, or ASCII coded signals. 
     A remote monitor RM 2  is shown connected to remote monitor RM 1  via the Internet. ASCII coded signals from detector  24  sent via the Internet would permit monitoring the status of the various devices anywhere in the world by a monitoring or security service. In this case, remote monitor RM 1  preferably acts as the Internet interface. Thus, the encoded output signal from detector  24  permits diagnosing the type and probable location of the fault at remote monitor RM 1  and/or remote monitor RM 2 . 
     While the present invention has been described with reference to a particular preferred embodiment and the accompanying drawings, it will be understood by those skilled in the art that the invention is not limited to the preferred embodiment and that various modifications and the like could be made thereto without departing from the scope of the invention as defined in the following claims.