FR2827675A1 - Power supply monitoring system detects series arcs from ultrasonic vibration - Google Patents

Abstract

A power supply monitoring system uses ultrasonic vibration sensors (2) on a conductor (3) to detect characteristic signals (8) from a series arc (7) with envelope detector (12) and filtering (15, 17) in the processor (1) converting the input signal (S1) to an arc indication signal (S2) by comparison with an adaptive threshold.

Description

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DEVICE AND METHOD FOR MONITORING AN ELECTRICAL NETWORK, AND INSTALLATION COMPRISING SUCH A DEVICE.

The invention relates to an electrical network monitoring device comprising means for detecting a series arc in at least one electrical conductor. The invention also relates to an electrical installation comprising electrical devices connected by rigid electrical conductors and an electrical network monitoring device.

The invention also relates to a method for monitoring the electrical network.

There are network monitoring devices with parallel arc detectors. Parallel arcs are generally high energy electrical discharges occurring between a conductor and ground or between two conductors. Parallel arc or discharge detectors generally include electromagnetic radiation sensors or sound sensors to detect electromagnetic or sound waves conducted in the air.

Such devices do not make it possible to detect series arcs produced by the opening of an electrical circuit, in particular when the opening is due to a faulty connection between two electrical conductors. Some monitoring devices include thermal sensors to detect connection failures between conductors. However, such devices require a large number of sensors. In addition, detectors of this type do not detect frank connection breaks which do not generate heating.

The object of the invention is a device and a method for monitoring the electrical network making it possible to detect a series arc, and an installation comprising such a device.

In an electrical network monitoring device according to the invention comprising means for detecting a series arc in at least one electrical conductor, the detection means comprise:

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 - at least one input intended to be connected to a vibration-sensitive sensor disposed on an electrical conductor, for picking up signals representative of series electric arcs, - processing means connected to the input for detecting signals representative of series electric arcs in an input signal received by the input and supplied by said vibration-sensitive sensor, and - at least one output for supplying an output signal representative of the detection of a series electric arc.

Advantageously, the processing means include envelope detection means receiving a signal representative of the input signal and providing an analysis signal.

Preferably, the envelope detection means comprise first high-pass or band-pass filtering means for filtering the signal representative of the input signal, rectification means for rectifying a signal supplied by the first filter means, and second low-pass filtering means for filtering a rectified signal supplied by the rectifying means, the second filtering means providing said analysis signal.

Advantageously, the processing means comprise amplification means connected between the input of the monitoring device and the envelope detection means.

In a preferred embodiment, the processing means comprise means for analyzing a signal representative of an input signal to provide the output signal representative of the detection of a series electric arc.

Preferably, the analysis means comprise means of detection with an adaptive threshold.

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Advantageously, the processing means include signal sampling means for sampling a signal supplied by envelope detection means and supplying said analysis means with a sampled signal representative of an input signal.

In a particular embodiment, the analysis means comprise at least one buffer for storing signal samples during an analysis window, the storage being validated or controlled by the detection means with adaptive threshold.

Advantageously, the analysis means comprise means for controlling the energy of a signal supplied by at least one signal storage buffer to supply a signal representative of the detection of a serial arc.

Advantageously, the analysis means comprise means for controlling the shape of a signal supplied by at least one signal storage buffer to supply a signal representative of the detection of a serial arc.

Advantageously, the analysis means comprise means for controlling the frequency of a signal supplied by at least one signal storage buffer to supply a signal representative of the detection of a serial arc.

A device according to a preferred embodiment, comprises at least one sensor sensitive to vibrations connected to said at least one input, said sensor being intended to be disposed on an electrical conductor.

Preferably, the vibration sensitive sensor is an ultrasonic sensitive sensor.

An electrical installation according to the invention comprising electrical devices connected by rigid electrical conductors comprises at least one monitoring device as defined above, at least one vibration-sensitive sensor connected to an input of said monitoring device and disposed on a rigid conductor of the installation for detecting vibrations conducted in said conductor.

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An electrical network monitoring method according to the invention comprises a phase of detecting a series arc in at least one electrical conductor comprising: - a step of determining an adaptive threshold, - a step of comparing a representative signal of an input signal with said adaptive threshold, - a step of loading at least one buffer with samples of a signal representative of said input signal, and - an analysis phase of at least one buffer for detecting the presence of a signal representative of a series arc in said signal representative of said input signal.

Advantageously, the analysis phase includes an energy control step.

Advantageously, the analysis phase includes a form control step.

Advantageously, the analysis phase includes a frequency control step.

In a preferred embodiment, the monitoring method comprises a management phase for filling at least two buffers, said management phase comprising at least one initialization step and at least one step for filling two buffers.

- la figure 3 représente un schéma bloc de l'analyse du signal dans un traitement du signal selon la figure 2 ; - la figure 4 représente un schéma bloc du déclenchement de l'analyse du signal dans un traitement du signal selon la figure 2 ; Other advantages and characteristics will emerge more clearly from the description which follows, of particular embodiments of the invention, given by way of nonlimiting examples, and represented in the appended drawings in which: - Figure 1 represents a device electrical network monitoring implementing the invention; - Figure 2 shows a block diagram of signal processing in a device according to Figure 1;

- Figure 3 shows a block diagram of the signal analysis in a signal processing according to Figure 2; - Figure 4 shows a block diagram of the triggering of the signal analysis in a signal processing according to Figure 2;

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- la figure 7 illustre l'analyse d'un signal dans un dispositif de surveillance selon un second mode de réalisation de l'invention ; - la figure 8 montre un organigramme d'un procédé de surveillance de réseau électrique mettant en oeuvre l'invention ; - la figure 9 montre un organigramme de gestion de tampons pour un procédé selon la figure 8 ; - la figure 10 montre un organigramme d'analyse d'un signal pour un procédé selon la figure 8 ; -les figures llA, llB, 12A et 12B illustrent des signaux pouvant être reçus par un dispositif de surveillance selon des modes de réalisation de l'invention ; et - la figure 13 représente une installation comportant un dispositif de surveillance selon un mode de réalisation de l'invention.

- Figure 5 shows a particular block diagram of a signal analysis circuit for a device according to the invention; - Figure 6 illustrates the analysis of a signal in a monitoring device according to a first embodiment of the invention;

- Figure 7 illustrates the analysis of a signal in a monitoring device according to a second embodiment of the invention; - Figure 8 shows a flowchart of a method of monitoring the electrical network implementing the invention; - Figure 9 shows a flow chart of buffer management for a method according to Figure 8; - Figure 10 shows a flowchart for analyzing a signal for a method according to Figure 8; FIGS. 11A, 11B, 12A and 12B illustrate signals which can be received by a monitoring device according to embodiments of the invention; and - Figure 13 shows an installation comprising a monitoring device according to an embodiment of the invention.

A network monitoring device shown in FIG. 1 comprises a device 1 for detecting serial arcs comprising an input connected to a vibration-sensitive sensor 2 disposed on a conductor 3 of an electrical network 4 to be monitored. The conductor 3 is preferably rigid, it can be constituted in particular by a bar, a tube, a cable or a distributed electrical distribution conduit. The sensor 2 detects mechanical or acoustic vibrations which propagate in the conductor 3. The conductor 3 can be connected to another conductor 5 by a connection or connection device 6, in particular by clamping screws. In this case, it is possible that failures in the fastening systems generate series 7 arcs between conductors 3 and 5.

The arcs 7 then cause vibrations 8 which are conducted by the conductors 3 and 5.

These vibrations are generally in the field of sound or ultrasonic frequencies. The sensor 2 receives the vibrations 8 and provides an input signal SI representative of the vibrations propagating in the conductor 3 to an input of the detection device. The sensor 2 can be an acoustic sensor or, preferably, an ultrasonic sensor, in particular piezoelectric type.

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 The vibrations passing through the conductors can be very diverse and sometimes have much greater amplitudes than those which can be generated by a series arc. For example, they can be due to mechanical devices, resonances, electrical or electromagnetic stresses on conductors, mechanical shocks or acoustic couplings. To avoid the influence of parasitic vibrations in the signal supplied by the sensor, the detection device 1 comprises processing means for detecting signals representative of series electric arcs in the signal supplied by the sensor.

The detection device 1 has at least one output for supplying an output signal S2 representative of the detection of a series electric arc. This output signal can control, for example, a relay 9, communicate with a supervisor or a remote central unit 10, and / or trigger an alarm.

FIG. 2 shows an embodiment of a signal processing in a detection device 1. The input signal SI supplied by the sensor is applied for example to an amplifier 11, then an amplified signal SI A representative of the signal SI is applied to the input of an envelope detector 12. The envelope detector 12 provides an analysis signal S3 which can be sampled by a sampler 13 and analyzed by analysis means 14.

The envelope detector comprises a first high-pass or band-pass filter 15 for filtering the signal representative of the input signal, a rectifier 16 for rectifying a signal supplied by the first filter, and a second low-pass filter 17 for filter a rectified signal supplied by the rectifier. The filter 15 eliminates or reduces the signals in the very disturbed frequencies for example it attenuates the signals of frequencies close to the frequency of the network 50Hz or 60Hz as well as certain harmonics. Preferably the filter 15 will allow signals of frequency greater than 10 kHz or 20 kHz to pass, in particular the signals in the ultrasonic frequencies. The rectifier 16 is preferably a rectifier without threshold. The envelope detector allows to extract the modulation of the high frequency input sound signal and to have a signal to analyze low frequency. So the analysis of signal S3 or

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 of a sampled signal S3A can be done quickly and efficiently, in particular with a limited number of samples.

An embodiment of the analysis means is shown in FIG. 3. In this figure, the signal S3A or S3 is applied to a detector 18 with an adaptive threshold which evaluates the threshold as a function of previous signal values. When the detector 18 detects a threshold being exceeded, it commands the validation of the loading of a buffer 19 with samples of the analysis signal S3A. Then, when the buffer 19 is loaded during an analysis window, the content of the buffer is analyzed by a control circuit 20.

An embodiment of a threshold detector is shown in FIG. 4. Advantageously, an adaptive threshold detector comprises a module 21 for determining an adaptive threshold to supply an adaptive threshold value S4. Then, this threshold value S4 is timed or delayed in a module 22 to use the adaptive threshold with following signals S3 or S3A. The delayed threshold value S4 is compared to the signal S3A by a comparator 23 to validate the filling of at least one buffer if the threshold is exceeded.

Thus, the adaptive threshold is determined on a signal portion, a threshold determination window, or a number of predetermined samples of the signal S3 or S3A which precede the signal S3 or S3A to be analyzed. When the adaptive threshold is exceeded, the filling of a buffer is validated. The filling of a buffer is carried out during an analysis window of predetermined duration. This analysis window can start as soon as the threshold is detected or preferably before the threshold is detected with portions of the signal or samples prerecorded and then validated by the detection of exceeding an adaptive threshold. This configuration makes it possible to analyze a signal window taking into account the evolution of the signal before and after the threshold is exceeded by a pulse.

FIG. 5 shows a block diagram of a particular embodiment of the analysis means. In this embodiment, the adaptive threshold detector 18 controls a buffer manager 24 to manage the filling of two buffers 19A and 19B with signals S3A. The filling of a first buffer will be validated by a first threshold crossing and a second buffer will be validated by a second threshold crossing.

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If the two threshold crossings are very close, the two buffers can be filled in an offset manner with an identical signal portion.

The diagram in FIG. 5 also shows an exemplary embodiment of a control circuit 20 for analyzing a signal supplied or contained in at least one of the storage buffers. This circuit 20 includes an energy controller 25, a shape controller 26, and a frequency controller 27. The controllers 25, 26, and 27 can operate in parallel or consecutively. Advantageously, a decision module 28 makes it possible to decide on the detection of a series arc and on the output of a signal S2. Preferably, two out of three positive controls provide sufficient certainty to decide on the presence of a series arc. In a preferred embodiment, three out of three positive controls ensure very high decision reliability for the monitoring device.

FIG. 6 illustrates an envelope detection signal S3 to be analyzed and a position of a buffer analysis window 19. The signal S3 shown comprises a first part 30 noised without useful signal, a second part 31 with a high amplitude peak, and a third signal portion 32 having waves of lower amplitude. In this figure, a first window 33 of signal duration Tl makes it possible to determine an adaptive threshold value S4. This threshold is determined during the noisy part 30 of the signal S3. Then, during a delay 34 of duration T2, the value of the adaptive threshold S4 is kept to avoid taking into account in the threshold value rapid variations of the signal S3 during the appearance of a peak. Preferably, the durations T1 and T2 have values between 1 and 2 milliseconds (mS), for example 1.25 milliseconds.

At a time t1 0, for example, the signal S3 exceeds the threshold S4. Then samples of the signal S3 or S3A fill the buffer 19 during an analysis window 35 of duration T3. The duration T3 is preferably between 30 and 100 milliseconds, for example around 50 milliseconds. To avoid a shift in the analysis period due to successive triggers, there is no further triggering of the filling validation as long as the signal S3 is continuously above the threshold. If the signal S3 drops below the threshold S4, the triggering of the filling can be validated when a new one appears.

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 peak exceeding threshold S4. When the buffer 19 is filled, at the end of the period 35, the samples are supplied to a control circuit 20.

If parasitic pulses 37 occur in the frequency spectrum of the envelope detector 12, it is possible that these pulses exceed the adaptive threshold and trigger validation of the filling of the buffers. To avoid an erroneous analysis due to successive initiations of the filling, a device according to an embodiment shown in FIG. 7 advantageously comprises at least two buffers 19A and 19B for recording samples to be analyzed. The filling of the buffers is triggered in turn each time the threshold is exceeded at times t21 and t22. Thus, at least one buffer will provide a correct signal to analyze.

FIG. 8 shows a flow diagram for processing samples of an S3 or S3A signal.

A step 40 makes it possible to load into an adaptive threshold window samples preceding a current signal to be analyzed. In a step 41, an adaptive threshold S4 is determined with the preceding signals. Then, a step 42 makes it possible to compare a current signal S3 or S3A with the threshold S4. If the threshold S4 is exceeded, a step 43 validates the loading and a step 44 makes it possible to load the following samples into one or more buffers, preferably two buffers. The content of the buffer (s) is then analyzed in a step 45.

When at least two buffers are used, management of the initialization of the buffers makes it possible to optimize the loading of the signal samples S3 or S3A. FIG. 9 shows a flowchart for initializing and managing the loading of the buffers. When an adaptive threshold is exceeded in a step 50, a step 51 makes it possible to detect whether a first buffer 19A is empty. If the condition of step 51 is true, the storage is initialized in the buffer 19A at a step 52. If the condition of step 52 is not true, a step 53 makes it possible to detect if a second buffer 19B is empty. If the condition of step 53 is true, the storage is initialized in the buffer 19B at a step 54. A buffer which was empty and which is initialized by one of the steps 52 or 54 becomes a buffer being filled until at the moment when its content is supplied to the analysis, in particular at a step 45. If the step 50 is not detected with a current sample, said sample can fill a buffer during filling.

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A step 55 detects if the first buffer 19A is being filled and continues to fill the said buffer 19A with a current signal sample at a step 56. A step 57 detects if the second buffer is being filled and continues to fill the of said buffer 19B with a current sample in a step 58. When one of the buffers is filled, its content is transferred to an analysis step and said buffer becomes in an empty state to be initialized again in steps 52 or 54 If none of the buffers are being filled, a current sample will not be stored in steps 56 and 58 for analysis.

FIG. 10 shows a flowchart for analyzing the signal stored during an analysis window, in particular for analyzing the content of the storage buffers 19, 19A and / or 19B. In a step 60, an adaptive threshold is detected. Then, in a step 61, there is a management of the buffers, in particular the management of the initialization and of the filling. The analysis of the signal comprises a step 62 of controlling the energy of the signal stored in a buffer during an analysis window, a step 63 of controlling the shape of said stored signal and a step 64 of controlling the frequency of said stored signal . In this particular embodiment, if the conditions of the three steps 62, 63, 64 are fulfilled, a signaling step 65 signals the detection of a series arc. In other embodiments, it is possible to use two of the three steps 62, 63, 64 for the analysis.

The control of the energy of the signal carried out, for example, in step 62 or by the controller 25 notably consists in checking the maintenance of a sustained energy after the first peak. For example, in FIG. 11A a curve 70 represents a serial arc signal detected by a sensor 2 and in FIG. 11B a curve 71 represents a shock signal propagating a sound signal. The arc detection signal 70 has an energy maintained by different ignitions represented by lobes 72. The signal 71 has an energy peak which decreases exponentially or continuously and reaches a low value after a few tens of milliseconds. Advantageously, for this control it is possible to determine the energy of the signal during a control window and to compare this energy with a threshold.

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The shape control carried out, for example, in step 63 or by the controller 26 notably consists in verifying the shape of the signal between the first peak following the crossing of the adaptive threshold and the signal in a period which follows. In a series arc signal, the contrast is very high between the first peak and the following peaks whereas in a parasitic shock signal, there is a decay without contrast. In FIG. 12A a curve 80 represents a serial arc signal and in FIG. 12B a curve 81 represents a signal representative of a parasitic shock. The signal 80 has a part 82 of predetermined duration following the threshold detection with a high amplitude and a part 83 succeeding the part 82, of substantially equal duration and of lower average amplitude than the amplitude of the part 82. The signal 81 has parts 84 and 85 consecutive and succeeding the detection of adaptive threshold of little different amplitudes. Thus, the shape control can advantageously consist in determining the ratio between a first part of the signal succeeding the detection with an adaptive threshold and a second part of the signal succeeding the first part of the signal, then in comparing said ratio with a threshold. Periods 86 and 87 corresponding respectively to the first part and to the second part of the signal are shown in FIG. 6 illustrating a signal S3 supplied by an envelope detection. In FIG. 6, the peak of part 31 has a higher amplitude than the waves of part 32.

The frequency control carried out, for example, in step 64 or by the controller 27 notably consists in checking the frequency of the signal in the part 32 posterior to the peak 31.

If this part has a main spectral component with a frequency double that of the electrical network, there is a very high probability of the presence of a series arc. In FIGS. 11 A and 12A, the lobes of the signals 72 have fundamental modulation frequencies similar to twice the frequency of the electrical network, for example 50 Hz or 60 Hz.

The controls described above are preferred controls, however other controls may also allow detection of a serial arc signal. For example, another control can consist in controlling the change in polarization of the series arc signal by controlling a succession of waves of different amplitudes alternating. Indeed, as in FIG. 11 A, a wave 73 of high amplitude is preceded and followed by waves 74 of lower amplitude.

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 FIG. 13 shows an installation comprising a monitoring device with a device 1 for detecting serial arcs connected to sensors 2A and 2B arranged on rigid conductors 3A and 3B of two portions of network to be monitored, respectively 4A and 4B. These conductors 3A and 3B are connected to electrical devices 90, 91 and 92, for example by other conductors 5 and by connection devices 6. The devices 90, 91 and 92 can be, for example, circuit breakers arranged with the device 1 in a cabinet or an electrical cell 93. If a series arc appears in part 4A of the electrical network, following in particular the deterioration of an electrical connection 6, signals 8, sound, ultrasound or mechanical vibrations propagate in the rigid conductors 3A and reach the sensors 2A. The serial arc detection device 1 receives signals from the sensors and performs processing before signaling the presence of a serial arc. The device 1 can supply a signal S2A to control the opening of the circuit breaker 90 upstream of the part of the network presenting a fault, it can also send a signal S2C on a communication bus 94. If a serial arc occurs in the part 4B of the network at least one of the sensors 2B supplies a signal to the device 1. In this case, a signal S2B supplied by the device 1 can command the opening of the circuit breaker 91 upstream of the fault.

The signals and mechanical vibrations propagating in the rigid conductors can be stopped or attenuated by an electrical device such as a circuit breaker comprising flexible electrical conductors, in particular in the form of braids. Thus a circuit breaker 91 disposed between the parts 4A and 4B of the network can isolate the transmission of signals 8 of mechanical vibrations. Such characteristics also make it possible to locate a fault by sector.

The serial arc detection device can include processing circuits produced in analog, digital, and / or mixed form, certain functions being able to be in programmed form and integrated into microprocessors or microcontrollers.

Claims (20)

CLAIMS 1. Electrical network monitoring device comprising means for detecting a series arc in at least one electrical conductor (3) characterized in that the detection means comprise: - at least one input intended to be connected to a sensor (2) sensitive to vibrations arranged on an electrical conductor (3), for picking up signals (8) representative of series electric arcs, - processing means (11,12,13,14) connected to the input for detecting signals representative of series electric arcs in an input signal (S 1) received by the input and supplied by said sensor (2) sensitive to vibrations, and - at least one output for supplying a signal (S2) output representative of the detection of a series electric arc (7). 2. Device according to claim 1 characterized in that the processing means comprise means (12) of envelope detection receiving a signal (SI, SI A) representative of the input signal and providing a signal (S3) of analysis. 3. Device according to claim 2 characterized in that the envelope detection means comprise first means (15) of high-pass or band-pass filtering to filter the signal (SI, SI A) representative of the input signal , rectifying means (16) for rectifying a signal supplied by the first filtering means, and second low-pass filtering means (17) for filtering a rectified signal supplied by the rectifying means, the second filtering means providing said analysis signal. 4. Device according to one of claims 2 or 3 characterized in that the processing means comprise means (11) of amplification connected between the input of the monitoring device and the means (12) of envelope detection. 5. Device according to any one of claims 1 to 4 characterized in that the processing means comprise means (14) for analyzing a signal (S3, S3A) <Desc / Clms Page number 14>  representative of an input signal to provide the output signal (S2) representative of the detection of a series electric arc. 6. Device according to claim 5 characterized in that the analysis means comprise means (18,21, 22,23) of detection with adaptive threshold. 7. Device according to claim 6 characterized in that the detection means with an adaptive threshold include means (23) for comparing a signal (S3, S3A) representative of an input signal with an adaptive threshold (S4) . 8. Device according to any one of claims 5 to 7 characterized in that the processing means comprise signal sampling means (13) for sampling a signal (S3) supplied by envelope detection means and supplying audits means of analysis a sampled signal (S3A) representative of an input signal. 9. Device according to any one of claims 6 to 8 characterized in that the analysis means comprise at least one buffer (19,19A, 19B) for storing signal samples during an analysis window (35) , the storage being validated or controlled by the adaptive threshold detection means (18). 10. Device according to claim 9 characterized in that the analysis means comprise means (25,62) for controlling the energy of a signal supplied by at least one signal storage buffer to supply a signal representative of serial arc detection. 11. Device according to one of claims 9 or 10 characterized in that the analysis means comprise means (26,63) for controlling the shape of a signal supplied by at least one signal storage buffer to supply a signal representative of the serial arc detection. 12. Device according to any one of claims 9 to 11 characterized in that the analysis means comprise means (27,64) for controlling the frequency of a signal <Desc / CRUD Page number 15>  provided by at least one signal storage buffer to provide a signal representative of the serial arc detection. 13. Device according to any one of claims 1 to 12 characterized in that it comprises at least one sensor (2) sensitive to vibrations connected to said at least one input, said sensor being intended to be disposed on a conductor ( 3) electric. 14. Device according to claim 13 characterized in that the sensor sensitive to vibrations is a sensor sensitive to ultrasound. 15. Electrical installation comprising electrical devices (90, 91, 92) connected by rigid electrical conductors (3,5) characterized in that it comprises at least one monitoring device (1) according to any one of claims 1 to 14, at least one sensor (2,2A, 2B) sensitive to vibrations connected to an input of said monitoring device and arranged on a rigid conductor (3,3A, 3B) of the installation for detecting vibrations (8) pipes in said conductor. 16. Method for monitoring the electrical network, characterized in that it comprises a phase of detection of a series arc in at least one electrical conductor comprising: - a step (41) of determining an adaptive threshold (S4), - a step (42) of comparing a signal (S3, S3A) representative of an input signal with said adaptive threshold (S4), - a step (44) of loading at least one buffer (19, 19A , 19B) with samples of a signal representative of said input signal, and - an analysis phase (45,62-65) of at least one buffer to detect the presence of a signal representative of an arc series in said signal representative of said input signal. 17. The method of claim 16 characterized in that the analysis phase comprises a step (62) of energy control. 18. Method according to one of claims 16 or 17 characterized in that the analysis phase comprises a step (63) of shape control. <Desc / Clms Page number 16> 19. Method according to any one of claims 16 to 18 characterized in that the analysis phase comprises a step (64) of frequency control. 20. Method according to any one of claims 16 to 18 characterized in that it comprises a phase (50-58,61) of management of filling of at least two buffers (19A, 19B), said management phase comprising at least one initialization step (52,54) and at least one step (56,58) for filling two buffers.