Claims:1. A device for series arc fault detection in a power circuit, the device comprising:
a high frequency current transformer configured to sense load current flowing through the power circuit and provide the sensed load current;
a current sensor configured to receive a live input from the power circuit and produce a current signal;
an analog circuit comprising a peak detector configured to receive the sensed load current from the high frequency current transformer and compute a peak high frequency noise for every half cycle; and a precision rectifier configured to receive current signal from the current sensor and produce a charge content for every half cycle;
a microprocessor configured to receive input signals from the peak detector and the precision rectifier, and further configured to analyze the received signals to detect occurrence of a series arc fault;
wherein the microprocessor detects occurrences of a series arc fault based on ratio of the high frequency peak and the charge content for every half cycle.

2. The device of claim 1, wherein the microprocessor detects occurrences of an abnormal wave form based on absolute difference for successive positive and negative half cycles in the ratio of the high frequency peak and the charge content for every half cycle, wherein incidences of the absolute difference in the ratio of the high frequency peak and the charge content for successive half cycle exceeding a detection threshold are detected for a defined period and occurrence of a series arc fault is concluded when the number of such occurrences during the defined period exceeds a trip threshold.

3. The device of claim 2, wherein the microprocessor detects occurrences of the abnormal wave form based on absolute difference between median of the ratio and the current ratio.

4. The device of claim 2, wherein the microprocessor detects occurrences of the abnormal wave form based on square of difference between mean and the ratio.

5. The device of claim 1, wherein the high frequency current transformer has a high bandwidth to sense the load current flowing through the power line.

6. The device of claim 1, wherein the device further comprises a zero cross detector configured to generate a synchronized pulse related to phase angle of the power circuit.

7. The device of claim 1, wherein the the current sensor is selected from a group comprising a ferrite core current transformer, an open loop Hall Effect current sensor and a series resistor.

8. A method for series arc fault detection in a power circuit, the method comprising the steps of:
computing high frequency peaks and charge content for every half cycle of a signal for a defined period;
computing ratio of the high frequency peak and the charge content for every half cycle;
computing absolute difference in the ratio for successive positive and negative half cycles;
comparing the absolute difference in the ratio to a detection threshold;
incrementing an arcing flag if the absolute difference exceeds the detection threshold;
comparing flag value with a trip threshold; and
concluding that a series arc fault has occurred when the flag value for the defined period is more than the trip threshold.

9. The method of claim 8, wherein the computation of the high frequency peak and the charge content for every half cycle is carried out based on a synchronized pulse related to phase angle of the power circuit.

10. The method of claim 8, wherein the high frequency peaks and the charge content for every half cycle is stored in respective buffers of of predefined size.

11. The method of claim 10, wherein the buffers of predefined size serve the purpose of defining a time period for which occurrence of a series arc is detected.

12. A method for series arc fault detection in a power circuit, the method comprising the steps of:
computing high frequency peaks and charge content for every half cycle of a signal for a defined period;
computing ratio of the high frequency peak and the charge content for every half cycle;
computing median of the ratio of the high frequency peak and the charge content;
computing absolute difference between the computed mean and the ratio for current half cycle;
comparing the absolute difference to a detection threshold;
incrementing an arcing flag if the absolute difference exceeds the detection threshold;
comparing flag value with a trip threshold; and
concluding that a series arc fault has occurred when the flag value for the defined period is more than the trip threshold.

13. A method for series arc fault detection in a power circuit, the method comprising the steps of:
computing high frequency peaks and charge content for every half cycle of a signal for a defined period;
computing ratio of the high frequency peak and the charge content for every half cycle;
computing mean of the ratio of the high frequency peak and the charge content;
computing, based on the computed mean, square of difference between mean and the ratio for current half cycle;
comparing the variance to a detection threshold;
incrementing an arcing flag if the square of difference between mean and the ratio exceeds the detection threshold;
comparing flag value with a trip threshold; and
concluding that a series arc fault has occurred when the flag value for the defined period is more than the trip threshold.
, Description:TECHNICAL FIELD
[0001] The present disclosure relates generally to the field of low voltage power systems. In particular, it pertains to a system and method for identifying series arc faults.

BACKGROUND
[0002] Background description includes information that may be useful in understanding the present invention.It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.
[0003] An arc is a luminous discharge of electricity across an insulating medium. Arcing creates a high intensity heating at the point of the arc where temperature could be in the range of 5,000°F to 15,000°F,resulting in burning particles that may easily ignite the surrounding materials.
[0004] An arc can typically be caused by loose connections, damaged wiring or degrading insulation in a power distribution system which can create high‐intensity heat capable of igniting the surrounding material such as curtains, wood framing or insulation and if not interrupted can subsequently lead to an electrical fire causing huge damage to property and people.
[0005] Arc faults in power distribution systems can be categorized into two categories, viz., series arc faults and parallel arc faults. A parallel arc fault occurs between conductors and the surroundings, and the fault current is dictated by power source and therefore is easily detected. A series arc is a condition where the fault occurs in series with the load and the amount of fault current is limited by the load impedance and impedance offered by the arc thus the condition goes undetected as the conventional circuit breakers fail to detect it as overload or as short circuit dependent on the impedance.
[0006] A large number of prior art references exist in the field of arc detection. For example, US Patent No. 6,972,572 B2 provides an arc detection circuit to detect series and parallel arcing which includes a peak detector with delay and a microcontroller with edge timing logic. The derivative (di/dt) signal of the current is fed to the arc detector circuit which then gives the trip signal when arcing is present.
[0007] US Patent No. 20,140,104,731 A1 discloses arc detection based on four signals having different characteristics. The first signal is the low pass filtered output representing the fundamental component of line current, second & third signal represent the positive and negative peaks of derivative of current for any step change as a function of time. Peak detector circuit with RC n/w delay uses derivative (di/dt) as the input signal and the fourth signal is the integrated band pass filtered output representing the high frequencies present in the current signal.
[0008] US Patent No. 7,633,729 provides a method to detect series arc by adding the absolute values of positive and negative half cycles of current to form a current level and subtracting the same from the previous current level.
[0009] US Patent No. 5,561,605 discloses a method which samples one cycle of the current waveform and subtracts the same from the samples of the preceding cycle of current waveform and in case the difference crosses a threshold limit and the condition persists, circuit is isolated.
[0010] While the prior art references teach one or other method for arc detection, there is extra challenge because of the increased penetration of modern power electronic loads which produce nonlinear current waveforms which can be mistaken for arc fault current waveforms.
[0011] There is, therefore, a need for an improved series arc detector that provides a more accurate detection of occurrence of series arc in the connected load.
[0012] All publications herein are incorporated by reference to the same extent as if each individual publication or patent application were specifically and individually indicated to be incorporated by reference. Where a definition or use of a term in an incorporated reference is inconsistent or contrary to the definition of that term provided herein, the definition of that term provided herein applies and the definition of that term in the reference does not apply.
[0013] In some embodiments, the numbers expressing quantities of ingredients, properties such as concentration, reaction conditions, and so forth, used to describe and claim certain embodiments of the invention are to be understood as being modified in some instances by the term “about”. Accordingly, in some embodiments, the numerical parameters set forth in the written description and attached claims are approximations that can vary depending upon the desired properties sought to be obtained by a particular embodiment.In some embodiments, the numerical parameters should be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.Notwithstanding that the numerical ranges and parameters setting forth the broad scope of some embodiments of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as practicable. The numerical values presented in some embodiments of the invention may contain certain errors necessarily resulting from the standard deviation found in their respective testing measurements.
[0014] As used in the description herein and throughout the claims that follow, the meaning of “a,” “an,” and “the” includes plural reference unless the context clearly dictates otherwise.Also, as used in the description herein, the meaning of “in” includes “in” and “on” unless the context clearly dictates otherwise.
[0015] The recitation of ranges of values herein is merely intended to serve as a shorthand method of referring individually to each separate value falling within the range.Unless otherwise indicated herein, each individual value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context.The use of any and all examples, or exemplary language (e.g. “such as”) provided with respect to certain embodiments herein is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention otherwise claimed.No language in the specification should be construed as indicating any non-claimed element essential to the practice of the invention.
[0016] Groupings of alternative elements or embodiments of the invention disclosed herein are not to be construed as limitations.Each group member can be referred to and claimed individually or in any combination with other members of the group or other elements found herein. One or more members of a group can be included in, or deleted from, a group for reasons of convenience and/or patentability.When any such inclusion or deletion occurs, the specification is herein deemed to contain the group as modified thus fulfilling the written description of all Markush groups used in the appended claims.

OBJECTS OF THE INVENTION
[0017] A general object of the present disclosure is to provide a system, method and device for improved series arc fault identification.
[0018] An object of the present disclosure is to provide a system, method and device for series arc fault identification that can efficiently discriminate between normal arcing conditions and a fault arcing condition.

SUMMARY
[0019] Aspects of the present disclosure relate to system, method and device for series arc faults identification. In an aspect, the system, method and device of the present disclosure relies on randomness of the arc current signature for detecting an occurrence of an arc. When an electrical circuit is free from any fault, the load maintains a pattern where the measures ofroot mean square (RMS), time averages, high frequency (HF) noise or even current peaks do not have a cycle to cycle variation. This uniformity in the current waveform maintained by the load is disrupted when a series arc occurs in the system.
[0020] In an aspect, the disclosed system, method and device of the present disclosure can discriminate between a normal arcing andan arc fault condition and a normal arcing that may occur in various equipment viz., a motorized vacuum cleaner, a furnace motor, an air conditioner, a refrigerator, etc. In another aspect it can also discriminate nonlinear current waveforms produced by electronic loads and which can be mistaken for arc fault current waveforms.
[0021] In an aspect, the system, method and device of the present disclosure detect occurrence of a series arc based on randomness of the arc current signature. Arcing generates HF noise during current conduction. The spectrum of this noise can range from few Hz to about 1GHz. The HF noise can only be present during the conduction of current while the arc can be sustained, and the noise disappears as soon as the arc extinguishes.
[0022] In an aspect, the system, method and device of the present disclosure detects a series arc by computing the ratio of the peak HF noise and the charge content (HF peak to RMS ratio) over every half cycle for which it simultaneously computes RMS (charge content) and the corresponding high frequency peak for every half cycle of the current waveform.
[0023] In an aspect, incidence of an abnormal wave form can be detected based on ratio of the high frequency peak and the charge content for each half cycles, wherein absolute difference in the ratio of the high frequency peak and the charge contentfor successive positive and negative half cycles exceeding a set threshold is concluded as occurrence of an abnormal waveform. In an embodiment, when such occurrences during a defined period exceed a second threshold, occurrence of a series arc can be concluded.
[0024] In an alternate methodology, incidence of an abnormal wave form can be detected based on absolute difference between median of previously calculated ratios of the high frequency peak and the charge content and the current ratio exceeding a set threshold. When such occurrences during a defined period exceed a second threshold, occurrence of a series arc can be concluded.
[0025] In another alternate methodology, incidence of an abnormal wave form can be detected based on variance. The variance can be calculated based on mean of previously calculated ratios of the high frequency peak and the charge content and the current ratio and when the variance exceeds a set threshold, a disturbance in the waveform is concluded. When such occurrences during a defined period exceed a second threshold, occurrence of a series arc can be concluded.
[0026] In an aspect, detection of incidences of an abnormal wave form based on median can eliminate undesired detections due to transients in power line and detection of incidences of an abnormal wave form based on mean can help in identifying arcs by recognizing data points spread out from the mean.
[0027] In an aspect, a peak detector can be included in the circuit that can measure the maximum amplitude of HF noise separated from the current signal through a HF current transformer (CT) or high pass/band pass filter in positive and negative half cycles separately; and a precision rectifier can be included in the circuit for computing charge content in every half cycle of the sensed current signal.
[0028] In an aspect, a microcontroller based control unit can be used to analyze wave pattern for arc fault detection. The method of arc detection can beimplementedby the microcontroller in real time and upon detection of arc fault the trip signal can be issued through the trip mechanism to the circuit breaker to isolate the circuit.
[0029] In an aspect, an analogue processing of data can be performed since it accounts for the current spikes and transients that can occur in the arcing state, thus reducing loss of information due to digitization. An analog processing stage can integrate and provide the magnitude of the sensed waveform at the end of each cycle that can greatly reduce the processing requirements of the digital stage. An additional zero cross detector (ZCD) input can help identify the charge stored.
[0030] In an aspect,the system, method and device of the present disclosure meets the requirement of IEC62606 and UL1699 standards which stipulate arc fault detection for arc currents ranging from 2.5A to 63A, within a specified time. Thus, threshold selection in this invention can be based on the rated AC line current flowing through the system by continuously sensing the current from the ferrite core CT. Also, the sensitivity to series arc detection can be improved by observing the width of the signal which becomes active when no event indication can be available from the zero cross detector for period greater than the reference period.
[0031] Various objects, features, aspects and advantages of the inventive subject matter will become more apparent from the following detailed description of preferred embodiments, along with the accompanying drawing figures in which like numerals represent like components.

BRIEF DESCRIPTION OF THE DRAWINGS
[0032] The accompanying drawings are included to provide a further understanding of the present disclosure, and are incorporated in and constitute a part of this specification. The drawings illustrate exemplary embodiments of the present disclosure and, together with the description, serve to explain the principles of the present disclosure.
[0033] FIG. 1A to 1Cillustratetypical current waveform, high frequency noise and time integral of current diagrams respectively duringoccurrence of arcing.
[0034] FIG. 2 illustrates an exemplary system diagram indicating various functional modules of the proposed system for detecting series arc in accordance with embodiments of the present disclosure.
[0035] FIG. 3 illustrates an exemplary block diagram of disclosed device for series arc detection and protection in accordance with embodiments of the present disclosure.
[0036] FIG. 4 illustrates an exemplary method flow diagram for disclosed method for series arc detection in accordance with embodiments of the present disclosure.
[0037] FIG. 5A and 5B illustrate exemplary method flow diagrams for alternate methods for series arc detection in accordance with embodiments of the present disclosure.

DETAILED DESCRIPTION
[0038] The following is a detailed description of embodiments of the disclosure depicted in the accompanying drawings. The embodiments are in such detail as to clearly communicate the disclosure. However, the amount of detail offered is not intended to limit the anticipated variations of embodiments; on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present disclosure as defined by the appended claims.
[0039] Each of the appended claims defines a separate invention, which for infringement purposes is recognized as including equivalents to the various elements or limitations specified in the claims. Depending on the context, all references below to the "invention" may in some cases refer to certain specific embodiments only. In other cases it will be recognized that references to the "invention" will refer to subject matter recited in one or more, but not necessarily all, of the claims.
[0040] As used in the description herein and throughout the claims that follow, the meaning of “a,” “an,” and “the” includes plural reference unless the context clearly dictates otherwise. Also, as used in the description herein, the meaning of “in” includes “in” and “on” unless the context clearly dictates otherwise.
[0041] All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context.The use of any and all examples, or exemplary language (e.g., “such as”) provided with respect to certain embodiments herein is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention otherwise claimed.No language in the specification should be construed as indicating any non-claimed element essential to the practice of the invention.
[0042] Various terms as used herein. To the extent a term used in a claim is not defined, it should be given the broadest definition persons in the pertinent art have given that term as reflected in printed publications and issued patents at the time of filing.
[0043] Embodiments of the present disclosure relate to system, method and device for series arc faults identification wherein the detection of a series arc is based on randomness of the current signature during arcing. When an electrical circuit is free from any fault, the load will maintain a pattern such that the measures like RMS, time averages, high frequency noise or even current peaks do not have a cycle to cycle variation. This uniformity in the current waveform maintained by the load is disrupted when a series arc occurs in the system. In an aspect, the disclosed system, method and device can discriminate between normal arcing (during switching operations, arcing at motor brush etc.) from an arc fault condition. In another aspect, it can also discriminate nonlinear current waveforms produced by electronic loads and which can be mistaken for arc fault current waveforms.
[0044] In an embodiment, the disclosed system and method make use of HF noise generated during arcing in the current conduction. The spectrum of this noise can range from few Hz to about 1GHz. The HF noise can only be present during the conduction of current while the arc can be sustained, and the noise disappears as soon as the arc extinguishes.
[0045] In an embodiment, the system and method of the present disclosure detect a series arc by computing the ratio of the peak HF noise and the charge content (HF peak to RMS ratio) over every half cycle for which it simultaneously computes RMS (charge content) and the corresponding high frequency peak for every half cycle of the current waveform.
[0046] In an embodiment, the disclosed device for series arc detection can incorporate a peak detector that can measure the maximum amplitude of HF noise separated from the current signal through a HF current transformer (CT) or high pass/band pass filter in positive and negative half cycles separately. It can further incorporate a precision rectifier for computing charge content in every half cycle of the sensed current signal.
[0047] In an embodiment, the disclosed device for series arc detection can incorporate a microcontroller based control unit to analyze wave pattern for arc fault detection. The arc detection methodology can be implemented by the microcontroller in real time and upon detection of arc fault the trip signal can be issued through the trip mechanism to the circuit breaker to isolate the circuit.
[0048] In an embodiment,the disclosed device can be configured to carry outanalogue processing of data. In an aspect, analogue processing can reduce loss of information that may occur during digitization of data. An analog processing stage can integrate and provide the magnitude of the sensed waveform at the end of each cycle that can greatly reduce the processing requirements of the digital stage. An additional zero cross detector (ZCD) input can help identify the charge stored.
[0049] In an aspect, the system, method and device of the present disclosure meets the requirement of IEC62606 and UL1699 standards which stipulate arc fault detection for arc currents ranging from 2.5A to 63A, within a specified time. Thus, threshold selection in this invention can be based on the rated AC line current flowing through the system by continuously sensing the current from the ferrite core CT. Also, the sensitivity to series arc detection can be improved by observing the width of the signal which becomes active when no event indication can be available from the zero cross detector for period greater than the reference period.
[0050] FIG. 1A to 1C illustrate typical current waveform, high frequency noise and time integral of current diagrams respectively during occurrence of arcing. FIG. 1A shows the arcing peaks during normal current conduction. In an embodiment, a peak detector can measure the maximum amplitude of HF noise separated from the current signal through a high frequency current transformer or high pass/band pass filter in positive and negative half cycles separately. FIG. 1B shows the peaks of HF noise that can be highly intermittent during arcing while they can be relatively stable during normal current conduction. In an embodiment, a precision rectifier based circuit can compute the charge content in every half cycle of the sensed current signal. The charge stored can be given by ∫(𝒕)𝒅𝒕 for half cycle period of the waveform. FIG 1C indicates that the charge content in half cycles can be highly irregular during arcing while they can be relatively constant during normal current conduction.
[0051] FIG. 2 illustrates an exemplary system diagram indicating various functional modules of the proposed system 200 for detecting series arc in accordance with embodiments of the present disclosure.The system 200 can incorporate a zero cross detector module 202 configured to receive AC line input voltage and feed its output to anarc detection circuit module 214. A high frequency current transformer module 204 and a current sensor module 206 can be configured to sense the load current flowing through the input voltage and feed the current signal to an analog circuit module 208 that comprises peak detector module 210 and precision rectifier module 212. The arc detection circuit module 214 can be configured to receive the output from the peak detector module 210 and precision rectifier module 212 and can analyze in real time to detect arc faults, if any, and can issue a trip signal to the trip module 216 in case an arc condition can be found. The trip module 216 module can be configured to isolate the circuit by breaking the circuit.
[0052] In an embodiment, the AC line voltage can be fed to the a zero cross detector module 202 that can be configured to generate a sync pulse related to the AC voltage phase angle that can be fed to the arc detection circuit Module 214. The pulse occurs at 00, 1800 and 3600. In an embodiment, the high frequency current transformer module 204 and the current sensor module 206 can be configured to sense the load current flowing through the input voltage and feed the current signal to peak detector module 210 and precision rectifier module 212, respectively, of the analog circuit module 208 that can produce outputs optimum for the arc detection circuit module. In an embodiment, the peak detector module 210 can measure the maximum amplitude of HF noise separated from the current signal through a high frequency current transformer or high pass/band pass filter in positive and negative half cycles separately whereas the precision rectifier module 212 can compute charge content in every half cycle of the sensed current signal.
[0053] In an embodiment, the arc detection circuit module 214 can be configured to receive inputs from the zero cross detector module 202, the peak detector module 210 and the precision rectifier module 212. The arc detection circuit module 214 can use a microcontroller to analyse the wave pattern for arc fault detection. Any of the arc detection methodologiescan beimplementedby the microcontroller in real time and upon detection of an arc fault a trip signal can be issued to the trip module 216 that can trip the circuit breaker to isolate connectedload.
[0054] FIG. 3 illustrates an exemplary block diagram of disclosed device 300 for series arc detection and protection in accordance with embodiments of the present disclosure. As shown the device 300 can be configured between a source 302 and a load 306 that are connected through a circuit breaker 304. The device 300 can incorporate a zero cross detector 308, a current sensor 312, a high frequency current transformer 310 and an arc detection circuit 320. The device 300 can further incorporate a peak detector 316 and a precision rectifier 318 both of which can be implemented as analogue circuit 314.
[0055] In an embodiment, the zero cross detector 308 can be configured to receive AC line voltage and provide its output to the arc detection circuit 320. In an embodiment, the ZCD 308 can be configured to generate a sync pulse related to the AC voltage phase angle. The pulse can occur at 00, 1800 and 3600 respectively.
[0056] In an embodiment, the high frequency current transformer 310 canhave a high bandwidth (such as 5 KHz to 25 KHz) to sense the load current flowing through the power line and provide the sensed load current to the analog processing circuit 314. FIG. 1B shows the peaks of HF noise that can be highly intermittent during arcing while they can be relatively stable during normal current conduction.
[0057] In an embodiment, the current sensor 312 which can be a 50 Hz ferrite core current transformer or an open loop Hall Effect current sensor or a simple series resistor, can be configured to receive a live input from the AC line and provide its output to the to the analog processing circuit 314.
[0058] In an embodiment, the analog processing circuit 314, on receipt of two signals from the high frequency current transformer 310 and the current sensor 312, sends them to the peak detector 316 and the precision rectifier 318 respectively. The peak detector 316 can measure the maximum amplitude of the HF noise separated in the input current signal in positive and negative half cycles separately. Further, the precision rectifier 318 can be configured to compute the charge content in every half cycle of the sensed current input signal. The charge stored can be given by ∫(𝒕)𝒅𝒕 for half cycle period of the waveform. FIG 1C shows the charge content in half cycles that can be highly irregular during arcing while they can be relatively constant during normal current conduction.
[0059] In an embodiment, the arc detection circuit 320 can receive the three optimized signals from, the zero cross detector 308, the peak detector 316 and the precision rectifier 318 and analyze the wave pattern to detect occurrence of a series arc. In an embodiment, the arc detection circuit 320 can be a microcontroller based system and contain peripherals like ADCs and timers. The arc detection circuit 320 can execute any of the disclosed arc detection methodologies in real time and upon detection of arc fault, issue a trip signal toa trip mechanism 322 to trip the circuit breaker 304 to isolate the load 306 from the source 302.
[0060] FIG. 4 illustrates an exemplary method flow diagram for disclosed method 400 for analysis of the waveform and series arc detection of series arc in accordance with embodiments of the present disclosure.As stated earlier, the disclosed method 400 can be implemented by the arc detection circuit 320 of the device 300 or thearc detection circuit module 314 of the system 200. At step 402 of the method 400, the three optimized signals from the zero cross detector 308, the peak detector 316 and the precision rectifier 318 and compute HF peaks and charge content for each half cycle of the AC signal.In an embodiment, the analogue HF peak and the charge (equivalent RMS) received from the peak detector 316 and the precision rectifier 318 are processed along with the zero cross detector 308 output. On a non-inverting logic the falling edge of the zero cross detector indicates the end of a positive half cycle, which means the output of the positive peak detector and charge from the integrator circuit, is ready to be read. For the negative half cycle the same logic follows. The read values of each positive and negative half cycle for detection parameters i.e. the HF peaks and the charge content are stored in respective buffers of predefined size.
[0061] In an aspect the buffers of predefined size as would be clear from subsequent description, serve the purpose of defining a time period for which the occurrence of a series arc is detected, wherein a check if the buffer is full is made and a full buffer indicates that the defined period is over, and wherein if number of occurrences of unusual waveform during a defined time period exceeds a predefined threshold (referred to as a second threshold hereinafter), it is interpreted as an series arc and the trip unit is tripped.
[0062] In an embodiment, the detected HF peaks and the charge content for each half cycle are used to compute a ratioHF peak/ charge for every half cycle as shown at step 404. At step 408, difference in the ratio HF peak/ charge content is computed for the successive positive and negative half cycles. At step 408 a check is made if the absolute difference exceeds a first threshold (i.e detection threshold). If it is so, an arcing flag is incremented at step 410. The arcing flag is a direct indication of the number of disturbances i.e. unusual waveform, in a defined period. At step 412, the flag value is compared with a second threshold value (i.e. trip threshold). If the flag variable value is greater than the threshold, the condition is considered as a persistent series arc condition and a trip signal is issued at step 414.
[0063] In an embodiment, after step 408 and step 412 if the result of the respective checks is found to be NO, a check to see if the buffer is full can be carried out at step 416. If it is full the buffer and the flag can be reset at step 418 before returning to the step 406.
[0064] FIG. 5A and 5B illustrate exemplary method flow diagrams 500 and 550 of alternate methods for series arc detection wherein the alternate methods base detection of a disturbance in the waveform based on absolute difference in the ratio of HF peak/ charge for every half cycle and mean value and variance in the ratio respectively as against based on absolute difference in successive positive and negative half cycles in the method 400. As shown in flow diagram 500, step 406 of the method 400 that computed absolute difference in the ratio for successive positive and negative half cycles is replaced by steps 506 and 508 that pertain to first computing median of the earlier computed ratios (step 506) and thereafter computing difference between the current ratio and the computed median (step 508). In an embodiment, for computing the median the buffer containing values of the ratio of positive and negative half cycles can be arranged in ascending order and median calculated. Further, difference between median and ratio R for positive and negative half cycles can be calculated separately. At step 510 a check is made if the absolute difference exceeds a first threshold (i.e detection threshold). If it is so, an arcing flag is incremented at step 512 which is a direct indication of the number of disturbances i.e. unusual waveform, in a defined period.In an aspect, detection of incidences of an abnormal wave form based on median can eliminate undesired detections due to transients in power line.
[0065] FIG 5B illustrates an exemplary method flow diagram 550 of another alternate method for series arc detection wherein this alternate method bases detection of a disturbance in the waveform based on absolute difference in the ratio of HF peak/ charge for every half cycle and variance in the ratio. As shown in flow diagram 550, the method incorporates step 556 that pertains to computing mean of the earlier computed ratios,and step 558 that pertains tocomputing square of difference between mean and the ratio for the current ratio based on the computed mean.At step 560 a check is made if the computed square of difference between mean and the ratioexceeds a first threshold (i.e. detection threshold). If it is so, an arcing flag is incremented at step 562. In an aspect, detection of incidences of an abnormal waveform based on mean can help in identifying arcs by recognizing data points spread out from the mean.
[0066] While the foregoing describes various embodiments of the invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof. The scope of the invention is determined by the claims that follow. The invention is not limited to the described embodiments, versions or examples, which are included to enable a person having ordinary skill in the art to make and use the invention when combined with information and knowledge available to the person having ordinary skill in the art.

ADVANTAGES OF THE INVENTION
[0067] The present disclosure provides a system, method and device for improved series arc fault identification.
[0068] The present disclosure provides a system, method and device for series arc fault identification that can efficiently discriminate between normal arcing conditions and a fault arcing condition.