MXPA06000548A - Electrical switching apparatus and method including fault detection employing acoustic signature - Google Patents

Abstract

A circuit breaker detects a fault, such as an arc fault or glowing contact, of a power circuit. The circuit breaker includes a first lug and a second acoustic lug adapted to be electrically connected to the power circuit. Separable contacts are electrically connected in series between the first lug and the second acoustic lug. An operating mechanism is adapted to open and close the separable contacts. An acoustic sensor is coupled to the second acoustic lug. The acoustic sensor is adapted to sense an acoustic signal from the second acoustic lug. The acoustic signal is operatively associated with the fault of the power circuit. A circuit inputs the sensed acoustic signal and is adapted to detect the fault therefrom.

Description

APPARATUS AND METHOD FOR ELECTRICAL INTERRUPTION INCLUDING DETECTION OF FAULTS USING ACOUSTIC SIGNATURE Background of the Invention Field of the Invention This invention relates to apparatuses for electrical interruption and, more particularly, to circuit breakers, such as, for example, circuit breakers providing protection against faults. The invention also relates to methods for detecting faults, such as arc faults and glowing contacts. Background Information An electrical interruption apparatus includes, for example, circuit interruption devices and circuit breakers such as circuit breakers, receptacles, contacts, motor starting devices, motor controllers and other load controllers. Circuit breakers are generally old and well known in the field. An example of a circuit breaker is disclosed in US Pat. No. 5,341,191. Circuit breakers are used to protect electrical circuits from damage due to an overcurrent condition, such as an overload condition or a short circuit or relatively high level fault condition. Molded-case circuit breakers, for example, include at least one pair of separable contacts which are operated either manually by a handle disposed outside the box or automatically by an internal trip unit in response to an overcurrent condition . In small circuit breakers, commonly referred to as miniature circuit breakers, used for residential and light commercial applications, such protection is typically provided by a thermal-magnetic firing device. This triggering device includes a bimetal, which is heated and bent in response to a persistent overcurrent condition. The bi-metal, in turn, unlocks a spring-loaded operation mechanism that opens the separable contacts of the circuit breaker to interrupt the flow of current in the protected power system. Arc formation is a light discharge of electricity through an insulating medium, usually accompanied by the partial volatilization of electrodes. An arc fault is an unintentional arcing condition in an electrical circuit. Arc faults can be caused, for example, by worn insulation between adjacent exposed conductors, by exposed ends between broken conductors, by faulty electrical connections, and in other situations where conductor elements are in close proximity. Arc faults in systems can be intermittent since the magnetic repulsive forces generated by the arc current force the conductors to separate to extinguish the arc. Mechanical forces then lead the drivers together again so that another arc springs up. During sporadic arc fault conditions, the overload capacity of the circuit breaker will not operate since the half-square (RMS) value of the fault current is too small to activate the automatic trip circuit. The addition of electronic arc fault detection to a circuit breaker adds one of the elements required for sizzling arc fault protection - ideally, the output of an electronic arc fault detection circuit directly triggers and, thus, opens to the circuit breaker. See, for example, US Pat. No. 6,710,688; 6,542,056; 6,522,509; 6,522,228; 5,691,869; and 5,224,006, which are related to detection of AC and AC arc faults. See, also, the patent US 6,720,872, which relates to a receptacle. Known technology for arc fault detection can employ a current signature. The problems associated with this methodology include false arc fault current signature detection from some electrical loads. Also, there are variations in the arc fault that depend on how the arc fault is created including, for example, its immediate environment.

A glowing contact is a high resistance connection, which can be formed at the interface of a copper cable and a screw terminal, for example, of a receptacle. The resulting temperature rise at this connection point can melt the insulation of the cable and damage the receptacle. High strength connections, such as sparkling contacts, are typically "behind the wall" and, therefore, hidden. Therefore, it is desirable to be able to detect this condition and interrupt the current before the glittering contact failure progresses to a dangerous condition. See, for example, patent US 6,707,652. US Pat. No. 5,608,328 discloses that scattered methods for accurately locating faults in power cables are based on acoustic detection of an arc in the fault. Typically, a peak generator or "kicker" is used to excite the power cable with a series of high-energy pulses which, in turn, point to audible spark and vibration in the fault. US Pat. No. 5,608,328 discloses that a series arc, once formed, tends to grow in length due to the thermal and electrochemical action of the arc. The arch literally erodes the adjacent contacts thereby ensuring, if there is no human intervention, that the once-marginal "opening" will become a fully developed space. This space will continue to hold an arc for hours or even months until it grows beyond a maximum arch support. During such periods, electrical and acoustic noise will be produced by the arc. In addition, substantial energy will be generated by the volt-ampere product associated with the space / arc that must be dissipated to maintain temperatures within safe limits. The arc is detected by detectors that receive electrical radio frequency (RF) noise. US patent 6,734,682 discloses a portable arc fault location and failure device employing an ultrasonic pick-up coil and an ultrasonic detector in combination with an audible pick-up coil and an audible detector. A circuit determines the correlation between ultrasonic sound characteristics and audible sound of an arc fault. Patent US 6,777,953 discloses a system for locating parallel arc faults in a set of cables. The system includes an ultrasonic handheld monitor to measure and indicate the distance from the operator to the arc. It measures both the electromagnetic pulse of the arc and the ultrasonic emission of the arc and uses the difference in arrival times to calculate the distance to the arc. US patent 6,798,211 discloses a fault distance indicator that locates a fault in an energy line by modeling pulses of reflected wave signals that are generated from electrical arcs that occur as a result of the failure. The fault distance indicator is mounted directly on a power line inside a transformer cover, energized by an energy signal obtained from a secondary transformer and includes a transceiver, such as an infrared transceiver, although transceivers of Radio or ultrasonic frequency can be used. The publication of patent application US 2003/0037615 discloses the generation and detection of acoustic guided waves to evaluate the insulation condition in electrical wiring. For example, suitable transducer and receiver transducers are piezoelectric transducers of broadband acoustic emission. The website at http://www.idiny.com/chafing.html states that an excoriation sensor is a passive solution to the problem of cable excoriation detection by listening to noise signatures on the cable. This also establishes that the system can detect cable abrasion, arcing and burn, and that pattern recognition software categorizes grades of galling. There is room for improvement in electrical interrupting apparatuses, such as, for example, circuit breakers and receptacles for arc faults, and in methods for detecting arc faults and glowing contacts. SUMMARY OF THE INVENTION These and other needs are met by the present invention, which employs an acoustic signature generated by an arc fault or glowing contact to detect a fault.

An acoustic sensor "listens" directly to the signature noise generated by a fault, regardless of the type of electrical load that is present or in what type of environment in which the fault is generated. The acoustic noise generated by an arc fault or a glowing contact has an acoustic signal at one or more specific bandwidths that are directly related to any of the basic characteristics of, for example, the arc and its resonance frequency or frequency modulated AC power source and its harmonics. The acoustic signal of an arc fault is detected by an acoustic sensor. The resulting signal can be a trigger signal, which is sent to a trigger mechanism to, for example, trigger to open separable contacts, to interrupt the arc fault In accordance with an aspect of the invention, an apparatus for electrical interruption for detecting a failure of an energy circuit comprises: a first ring, a second acoustic ring adapted to be electrically connected to an energy circuit, separable contacts electrically connected in series between the first ring and the second acoustic ring; operation adapted to open and close the separable contacts, an acoustic sensor coupled to the second acoustic ring, the acoustic sensor being adapted to detect an acoustic signal from the second acoustic ring, the acoustic signal being operatively associated with the failure of the circuit energy, and a circuit entering the detected acoustic signal and being adapted to detect the fault from it. The fault can be a glowing contact or an arc fault. The arc fault can be a parallel arc fault or a series arc fault. The electrical interruption apparatus may be an arc fault circuit interrupter. The operating mechanism may comprise a trigger mechanism, and the circuit may emit a trigger signal to the trigger mechanism upon detection of the arc fault from the detected acoustic signal. The second acoustic ring can be adapted to couple the acoustic signal from the power circuit to the acoustic sensor. The second acoustic ring may include a voltage adapted to be electrically emitted to the power circuit. The second acoustic ring may comprise an electrical insulator adapted to electrically isolate the acoustic sensor from the voltage. The second acoustic ring may comprise an acoustic insulator adapted to isolate the acoustic sensor from noise in the air. As another aspect of the invention, a method for detecting a fault in an energy circuit comprises: employing an acoustic ring adapted to be electrically connected to the power circuit; attach an acoustic sensor to the acoustic ring; detecting an acoustic signal from the acoustic ring with the acoustic sensor, the acoustic signal being operatively associated with the failure of the power circuit; and emitting the acoustic signal detected and detecting the fault from it. The method may comprise employing as the energy circuit a direct current energy circuit; detect the fault in the direct current energy circuit; detect a current flowing between the acoustic ring and the energy circuit; filter the detected current; determining a first arc fault condition from the filtered detected current; determining a second arc fault condition from the detected acoustic signal; and enforcing a trigger signal in response to the first arc fault condition being substantially concurrent with the second arc fault condition and, alternatively, discarding the detected acoustic signal and the detected current and re-detecting the acoustic signal and the current flowing between the acoustic ring and the energy circuit. The method can enter the detected acoustic signal to a bandpass filter; emit a filtered signal from the bandpass filter; and analyzing the filtered signal to detect a continuous acoustic signal at about a predetermined frequency.

The method may further comprise employing as the energy circuit an alternating current energy circuit; and detect the fault in the alternating current power circuit. The method can determine a frequency of the power circuit or at least one harmonic or at least one sub-harmonic of the frequency; filter by bandpass the detected acoustic signal to determine a filtered signal; and determining whether a sum of the acoustic signal intensities in the frequency of the power circuit or the at least one harmonic or the at least one sub-harmonic exceeds a predetermined amount. The method can determine an absolute value of the acoustic signal detected; and employing a fast Fourier transform of the absolute value to determine the frequency or the at least one harmonic or the at least one sub-harmonic. The method can enforce a trigger signal if the sum of the acoustic signal intensities in the frequency of the power circuit or the at least one harmonic or the at least one sub-harmonic exceeds the predetermined amount; and alternatively; discard the detected acoustic signal and re-detect the acoustic signal. The method may further comprise analyzing the acoustic signal detected to detect acoustic waves and to determine the duration of a half cycle of the current; and determining whether the measured time durations between successive pairs of the acoustic waves during a predetermined period of time equals multiples of the duration of the half cycle of the current. The method can determine equivalence and assert a trigger signal and, alternatively, discard the detected acoustic signal and re-detect the acoustic signal. The method can determine a frequency of the power circuit or at least one harmonic or at least one sub-harmonic of the frequency; filter by bandpass the detected acoustic signal to determine a filtered signal; determining whether a sum of the acoustic signal intensities in the frequency of the power circuit or at least one harmonic or at least one sub-harmonic exceeds a predetermined amount and enforcing a first signal in response; analyze the acoustic signal detected to detect acoustic waves and to determine the duration of a half cycle of the current; determining whether the measured time durations between successive pairs of the acoustic waves during a predetermined period of time equals multiples of the half-cycle duration and enforcing a second signal in response; and enforce a trigger signal in response to the first signal or the second signal. BRIEF DESCRIPTION OF THE DRAWINGS A full understanding of the invention can be obtained from the following description of the preferred embodiments when read in conjunction with the accompanying drawings, in which: Figure 1 is a block diagram of a circuit breaker employing an acoustic sensor for detecting a series arc fault condition in accordance with the present invention; Fig. 2 is a block diagram of a circuit breaker employing an acoustic sensor for detecting an arc fault condition in parallel according to another embodiment of the invention; Fig. 3 is a flowchart of an acoustic direct current (DC) arc fault detection algorithm for use by the circuit breakers of Figs. 1 or 2 according to another embodiment of the invention; Fig. 4 is a flowchart of an acoustic alternating current arc (AC) fault detection algorithm for use by the circuit breakers of Figs. 1 or 2 according to another embodiment of the invention; Fig. 5 is a flowchart of another acoustic AC arc fault detection algorithm for use by the circuit breakers of Figs. 1 or 2 according to another embodiment of the invention; Fig. 6 is a flow diagram of a portion of another acoustic AC arc fault detection algorithm for use by the circuit breakers of Figs. 1 or 2 according to another embodiment of the invention; Figure 7 traces acoustic and fast Fourier transform (FFT) signals of absolute value for the algorithm of Figure 4; Figure 8 traces the correlation between a line synchronization signal and the absolute value of the acoustic signal being above a suitable threshold for the algorithm of Figure 4; Figure 9 is an acoustic event trace at acoustic event time differences for an arc fault in series with a vacuum cleaner for the algorithm of Figure 5; and Figure 10 is a block diagram of a receptacle employing an acoustic sensor for detecting a glowing contact according to another embodiment of the invention. DESCRIPTION OF THE PREFERRED EMBODIMENTS As used herein, the term "acoustic" should expressly include, but not be limited to, one or more sounds that are sub-sonic, sonic and / or ultra-sonic. As used herein, the term "ring" shall expressly include, but not be limited to, a terminal or other electrically conductive attachment to which one or more electrical wires or other electrical conductors are electrically and mechanically connected. The present invention is described in association with an arc fault circuit breaker, although the invention is applicable to a wide range of electric breakers. Figure 1 shows an electrical interrupting apparatus, such as a circuit breaker 2, employing a suitable acoustic sensor 4, such as a piezoelectric sensor, to detect a fault, such as an arc fault condition in series 6, in an electrical conductor 8 of an energy circuit 10. There, an acoustic signal conducted by electrical conductor 12 from the arc fault condition in series 6 is detected by the acoustic sensor 4, to provide detection of arc fault in acoustic series, as will be described. The acoustic signal 12 is operatively associated with the arc fault condition in series of power circuit 6. The acoustic sensor 4 is suitably coupled to the electrical conductor 8 for "listening" by conducted sound. The circuit breaker 2 includes a first ring, such as the line terminal 13, and a second acoustic ring 14, such as the loading terminal. The second acoustic ring 14 is adapted to be electrically connected to the electrical conductor of the energy circuit 8, as shown. The circuit breaker 2 also includes separable contacts 16 electrically connected in series between the line terminal 13 and the acoustic ring 14, and an operating mechanism 18 adapted to open and close the separable contacts 16. The acoustic sensor 4 is appropriately coupled to the acoustic ring 14 and is adapted to detect the acoustic signal 12 from the acoustic ring 14. The circuit breaker 2 further includes a circuit 20 by entering a detected acoustic signal 22 from the acoustic sensor 4. The circuit 20 is adapted to emit a detected fault signal 24 therefrom, as will be described. Although the exemplary energy circuit 10 includes a neutral conductor 9 (N), the invention is applicable to power circuits which do not employ a neutral conductor and to electrical interruption devices that receive or do not receive the neutral conductor 9. Example The circuit breaker 2 can be, for example, an arc fault circuit interrupter, The operating mechanism 18 can include a trigger mechanism 26, and the circuit 20 can emit the detected fault signal 24 as a trigger signal to the mechanism. 26 before detection of the arc fault 6 from the detected acoustic signal 22. Example 2 The preferred acoustic ring 14 is structured to correspond to the acoustic waveguide provided by the electrical conductor 8. The ring acoustic 14 preferably includes suitable acoustic waveguide properties that couple the acoustic signal 12 from the power circuit 10 with the acoustic sensor 4. 3 The acoustic ring 14 includes a voltage (e.g., a line voltage from the terminal 13) adapted to be electrically emitted to the power circuit 10. The acoustic ring 14 preferably includes a suitable electrical insulator 28 (e.g., a relatively thin insulating polymer or ceramic) adapted to electrically isolate the acoustic sensor 4 from the voltage. Example 4 The acoustic ring 14 preferably includes a suitable acoustic insulator 30 (e.g., without limitation, a sound insulation foam board wrapped around the acoustic ring 14 and the acoustic sensor 4), such as a suitable mounting and adequate acoustic insulation, adapted to isolate acoustic sensor 4 from air noise. Example 5 In this example, the circuit breaker 2 also includes a current sensor 32, which can be used, as discussed below in connection with figures 3 or 4, or which need not be used, as discussed further. further in connection with Fig. 5. For example, the use of the current sensor 32 in Fig. 4 is used to identify the frequency of electrical power source when the power circuit 10 is an AC power circuit. This current sensor 32 may not be necessary since, more typically, the AC power frequency is known.

As will be discussed, below, in connection with Figures 3-5, the circuit breaker 2 measures the acoustic signature generated by a fault, such as the arc fault in series 6 of Figure 1, to detect it. This acoustic signature detection technique will generally not experience a false output due to electrical current, since, fortunately, the current flowing through a solid electrical conductor and electrical connections or terminations does not produce an acoustic output. Instead, the acoustic sensor 4"listens" directly to the mechanical noise generated by an electrical fault, such as the arc fault in series 6. Example 6 Noise resulting from interruption of power on / off is generally short duration and has a specific "figure", due to a relatively short interruption time and, also, due to mechanical rebound. The acoustic noise activity at the initiation of the arc fault, such as the arc fault in series 6, is due, in part, to mechanical separation of electrical contacts 34, 36 in the broken conductor 88 and, thus, preferably it is considered to be insufficient to indicate a trip with the detected fault signal 24. Figure 2 is a block diagram of a circuit breaker 2 ', which is the same as or similar to the circuit breaker 2 of figure 1. 2 'circuit breaker provides parallel arc fault detection and employs acoustic sensor 4 to receive an acoustic signal 12', to detect an arc fault condition in parallel 6 'between electrical contacts 34', 36 'arising of, for example, worn or broken insulation (not shown) of the power circuit 10 '. Otherwise, there need be no difference in the structure of the circuit breakers 2, 2 'of FIGS. 1 and 2 or the algorithms of FIGS. 3-6 for detection of arc fault in parallel or in series. Fig. 3 is a flowchart of an acoustic direct current (DC) arc fault detection algorithm 40 suitable for use by the circuit breakers 2, 2 'of Figs. 1 or 2. The output 41 of the acoustic sensor 4 is damped by a damper 42 and is thus input by an acoustic band pass filter 44. The output 45 of the current sensor 32 is damped by a damper 46 and is thus input by a current signal filter. 48. The output 49 of the acoustic bandpass filter 44 is analyzed, at 50, to determine whether a continuous acoustic signal at a predetermined frequency band is detected. If so, then a signal A 52 is asserted. The output 53 of the current signal filter 48 is analyzed, at 54, by conventional arc fault detection techniques. For example, the detected current signal 57 is an arc shape if a step change of the current noise signal exceeds a predetermined level in a predetermined frequency band. If so, then a C 56 signal is asserted. At 58, if both signal A 52 and signal C 56 are true, then a trigger signal 60 is asserted. Otherwise, the detected acoustic signal 22 and the detected current signal 57 are both discarded at 62 and then re-sampled for a subsequent test. This algorithm employs a combination of electric current (eg, a step detector and, therefore, is applicable to DC circuits) and the acoustic indication conducted by an electrical conductor, such as by using an "AND" function ( Y) 59, when the two signal indications 52, 56 are coincident in time within a suitable predetermined time interval. This improves performance as measured by indications of minimal discomfort and relatively high failure sensitivity. Example 7 The strategy for DC arc fault detection uses noise levels in certain frequency regimes and is based on the uniform persistence of the acoustic activity. In the DC arc fault detection algorithm 40, the acoustic band pass filter 44 is used in, for example, 12.5 kHz, 25 kHz or 50 kHz and it is determined if a low level acoustic noise persists for more than a suitable time (e.g., without limitation, about 0.1 seconds). Also, to generate the trigger signal 60, the detected current signal 57 essentially remains in the arcing state. There, this is determined by the signal C 56 and the detected current signal 57 is an arc shape since the pitch change of the current noise signal exceeds a predetermined level in a predetermined frequency band. Fig. 4 is a flowchart of an acoustic alternating current arc (AC) fault detection algorithm 70 suitable for use by circuit breakers 2, 2 'of Figs. 1 or 2. Output 41 of the acoustic sensor 4 is damped by the damper 42 and is then input by an acoustic bandpass filter 72. The output 45 of the current sensor 32 is damped by the damper 46 and is then input by a current signal filter. 74, which determines, at 76, the current signal frequency. That frequency is emitted to the acoustic band pass filter 72, which is applied to the particular frequency of the detected current signal 57 and its harmonics and sub-harmonics. The output 77 of the acoustic bandpass filter 72 is analyzed, at 78, to determine whether the sum of the acoustic signal intensities at the current frequency or at its harmonics or sub-harmonics exceeds a predetermined noise level. If so, then a trigger signal 84 is enforced. Otherwise, the detected acoustic signal 22 is discarded and, then, re-sampled, at 86, for a subsequent test. To distinguish an arc fault, such as series 6 arc fault, from vibration and other mechanical noise, it is possible to use the fact that an AC power source modulates the arc fault, thereby providing a signature acoustics that is relatively more unique. In addition, resplendent AC contacts (not shown), under many conditions, also express similar modulated noise. Example 8 In the frequency-based acoustic AC-arc fault detection algorithm 70 of FIG. 4, at 72, a fast Fourier transform (FFT) of the absolute value of the detected acoustic signal 22 (e.g. the absolute value of the sensor output voltage) identifies, for example, 120 Hz and / or its sub-harmonic (s) (eg, 60 Hz) or harmonics for a 60 Hz power circuit. Example traces of the detected acoustic signal 22 and the absolute-value FFT signal 88 are shown in Figure 7. Example 9 In connection with the frequency-based acoustic AC-arc fault detection algorithm 70 of the figure 4, FIG. 8 shows the correlation between the line synchronization signal from the detected current signal 57 and the absolute value of the detected acoustic signal 22 being above a suitable threshold for a series arc fault, such as 6, in connection with, for example, a vacuum cleaner (not shown). The trace 90 indicates when the absolute value of the output voltage of the detected acoustic signal 22 is above the predetermined threshold. The correlation, although not perfect, is indicated in Figure 8 and can be verified in the wave start domain method of Figure 5. Figure 5 is a flowchart of another arc fault detection algorithm. Acoustic AC 100 suitable for use by the circuit breakers 2, 2 'of Figures 1 or 2. The output 41 of the acoustic sensor 4 is damped by the damper 42 and is then analyzed, at 102 to detect the acoustic waves and the duration of the half cycle of current in the power circuit 10. In this example, the energy frequency is a known value. That information is then reviewed, at 104, to determine whether the measured time durations between successive acoustic waves during a predetermined period of time (e.g., without limitation, around 0.1 seconds) are equivalent to multiples of the half-cycle duration. This uses, for example, a wave start time domain analysis as discussed, below, in connection with Example 10 and Figure 9. The absolute threshold value and the acoustic sensor voltage rectified by half wave is They use and the digital output is correlated with pulse frequency. If an equivalence is determined, at 104, then a trigger signal 110 is asserted. Otherwise, the detected acoustic signal 22 is discarded and then re-sampled for a subsequent test at 112. Example 10 Figure 9 shows a trace 114 of acoustic event differences at acoustic event time for an arc fault in series, such as 6 in Figure 1, with, for example, a vacuum cleaner (not shown) for algorithm 100 of Figure 5. There, in this example, the duration of acoustic waves of arc formation indicate that Acoustic event time differences of% line cycle (eg, 8.33 ms to 60 Hz) and 1 line cycle (eg, 16.67 ms) predominate in the measured times from event to event. Fig. 6 is a flowchart of a portion of another acoustic AC arc fault detection algorithm suitable for use by the circuit breakers 2, 2 'of Figs. 1 or 2. This algorithm 120 employs a combination of the first algorithm for AC 70 of Figure 4 and the second algorithm for AC 100 of Figure 5 by using an OR (o) function 122 to decide "o" on the respective trigger signals 84, 110 to provide a signal of combined trigger 124. Example 11 The detected acoustic signal 22 which is detected by the acoustic sensor 4 of FIGS. 1 and 2 can be used to output a trigger signal, such as 60 of FIG. 3, 84 of FIG. 4, 110 of FIG. 5 and 124 of FIG. 6, to a trigger mechanism, such as 26 of FIG. 1, to increase an event counter or other device, to produce an alarm, and / or to interrupt a fault, such as arc fault in series 6. Example 12 Although figures 3-5 mu The arc fault in series 6 is also applicable to the parallel arc fault 6 'of FIG. 2. Example 13 Although examples including arc faults 6, 6' are disclosed in FIGS. invention is also applicable to glowing contacts. For example, the methods for glowing contacts are the same as those for detecting arc fault in the AC circuits as discussed above in connection with Figures 4-6. Figure 10 shows a receptacle 2"including an operating mechanism 18 ', the acoustic sensor 4 and the circuit 20 employing one of the algorithms 40, 70, 100 to detect a glowing contact 126 of an energy circuit 10". Example 14 If the glowing contact is in the neutral charge, then there are two possible solutions. First, if there is a glowing contact, then there is current flow, the power cable is connected and the acoustic signal will be conducted through the load to the acoustic sensor. Alternatively, another acoustic sensor (not shown) can be attached to the neutral for acoustic detection. It will be appreciated that the circuit 20 and the algorithms 40, 70, 100 disclosed herein may be implemented by analog, digital, and / or processor-based circuits. Although specific embodiments of the invention have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, particular arrangements disclosed are intended to be illustrative only and not limiting as to the scope of the invention which should be given the full scope of the appended claims and any and all of their equivalents.

Claims (28)

1. CLAIMS 1. An electrical interruption apparatus for detecting a failure of a power circuit, said electric interruption apparatus comprising: a first ring; a second acoustic ring adapted to be electrically connected to said power circuit; separable contacts electrically connected in series between said first ring and said second acoustic ring; an operating mechanism adapted to open and close said separable contacts; an acoustic sensor coupled to said second acoustic ring, said acoustic sensor being adapted to detect an acoustic signal from said second acoustic ring, said acoustic signal being operatively associated with the failure of said power circuit; and a circuit entering said detected acoustic signal and being adapted to detect said fault from it.
2. 2. The electrical interruption apparatus of claim 1, wherein said fault is a glowing contact.
3. 3. The electrical interruption apparatus of claim 1, wherein said failure is an arc fault.
4. 4. The electrical interrupting apparatus of claim 3, wherein said arc fault is an arc fault in parallel.
5. 5. The electrical interruption apparatus of claim 3, wherein said arc fault is an arc fault in series.
6. The electric interrupting apparatus of claim 3, wherein said electrical interrupting apparatus is an arc fault circuit interrupter, wherein said operating mechanism comprises a trip mechanism; and wherein said circuit emits a trigger signal to said trigger mechanism upon detection of said arc fault from said detected acoustic signal.
7. The electric interrupting apparatus of claim 1, wherein said second acoustic ring is adapted to couple said acoustic signal from said power circuit to said acoustic sensor.
8. The electric interrupting apparatus of claim 1, wherein said second acoustic ring includes a voltage adapted to be electrically emitted to said power circuit; and wherein said second acoustic ring comprises an electrical insulator adapted to electrically isolate said acoustic sensor from said voltage.
9. The electric interrupting apparatus of claim 1, wherein said second acoustic ring comprises an acoustic insulator adapted to isolate said acoustic sensor from air noise.
10. 10. The electrical interruption apparatus of claim 1, wherein said acoustic sensor is a piezoelectric sensor.
11. The electric interrupting apparatus of claim 2, wherein said electrical interrupting apparatus is a receptacle.
12. 12. A method for detecting a fault in an energy circuit, said method comprising: employing an acoustic ring adapted to be electrically connected to said power circuit; coupling an acoustic sensor to said acoustic ring; detecting an acoustic signal from said acoustic ring with said acoustic sensor, said acoustic signal being operatively associated with the failure of said energy circuit; and enter said detected acoustic signal and detect said fault from it.
13. The method of claim 12, further comprising: employing as said power circuit a direct current energy circuit; detecting said failure in said direct current energy circuit; detecting a current flowing between said energy ring and said energy circuit; filter said detected current; determining a first arc fault condition from said filtered detected current; determining a second arc fault condition from said detected acoustic signal; and enforcing a trigger signal responsive to said first arc fault condition being substantially concurrent with said second arc fault condition and, alternatively, discarding said detected acoustic signal and said detected current and re-detecting said acoustic signal and said current flowing between said acoustic ring and said energy circuit.
14. The method of claim 13, further comprising: entering said detected acoustic signal to a bandpass filter; emitting a filtered signal from said bandpass filter; and analyzing said filtered signal to detect a continuous acoustic signal at about a predetermined frequency.
15. The method of claim 14, further comprising: employing as said predetermined frequency one of 12.5 kHz, 25 kHz and 50 kHz; and determining if acoustic noise at about said predetermined frequency persists for more than a predetermined time.
16. 16. The method of claim 15, further comprising: using said predetermined time about 0.1 seconds.
17. The method of claim 12, further comprising: employing as said power circuit an alternating current energy circuit; and detecting said failure in said alternating current power circuit.
18. The method of claim 17, further comprising: determining a frequency of said energy circuit or at least one harmonic or at least one sub-harmonic of said frequency; filtering by bandpass said detected acoustic signal to determine a filtered signal; and determining whether a sum of the acoustic signal intensities at said frequency of said power circuit or said at least one harmonic or said at least one sub-harmonic exceeds a predetermined amount.
19. The method of claim 18, further comprising: determining an absolute value of said detected acoustic signal; and employing a fast Fourier transform of said absolute value to determine said frequency or said at least one harmonic or said at least one sub-harmonic.
20. The method of claim 18, further comprising: enforcing a trigger signal if said sum of said acoustic signal intensities at said frequency of said power circuit or said at least one harmonic or said at least one sub-harmonic exceeds said predetermined amount; and alternatively, discarding said detected acoustic signal and re-detecting said acoustic signal.
21. The method of claim 17, further comprising: analyzing said acoustic signal detected to detect acoustic waves and to determine the duration of a half cycle of said current; and determining whether measured time durations between successive pairs of said acoustic waves during a predetermined period of time equals multiples of the duration of said half cycle of said current.
22. The method of claim 21, further comprising: determining said equivalence and enforcing a trigger signal and, alternatively, discarding said detected acoustic signal and re-detecting said acoustic signal.
23. The method of claim 17, further comprising: determining a frequency of said power circuit or at least one harmonic or at least one sub-harmonic of said frequency; filtering by bandpass said detected acoustic signal to determine a filtered signal; determining whether a sum of the acoustic signal intensities in said frequency of said power circuit or said at least one harmonic or said at least one sub-harmonic exceeds a predetermined amount and assert in response a first signal; analyzing said acoustic signal detected to detect acoustic waves and to determine the duration of a half cycle of said current; determining whether measured time durations between successive pairs of said acoustic waves during a predetermined period of time equals multiples of the duration of said half cycle and in response to asserting a second signal; and enforcing a trigger signal in response to said first signal or said second signal.
24. The method of claim 13, further comprising: outputting said trigger signal to a trigger mechanism to interrupt said failure.
25. 25. The method of claim 20, further comprising: outputting said trip signal to a trip mechanism to interrupt said fault.
26. 26. The method of claim 13, further comprising: producing an alarm from said trigger signal.
27. 27. The method of claim 12, further comprising: employing as said fault a glowing contact. The method of claim 13, further comprising: employing as said failure an arc fault; and ignoring acoustic noise activity during the start of said arc fault.