ARC FAULT DETECTION DEVICES AND CORRESPONDING ELECTRICAL PROTECTION DEVICES

Abstract

A device (10) for detecting an arc fault in a polyphase electrical installation (2) comprises: - a high-frequency measurement system (14) coupled to at least two electrical phases (L1, L2, L3) of the installation, said measurement system being configured to extract a first signal representative of high-frequency components of electrical currents flowing in said phases; - a plurality of low-frequency measurement systems (20), each coupled to an electrical phase of the installation, each being configured to acquire a second signal representative of the alternating line current flowing in the corresponding phase; - a data processing module (22), programmed to detect an arc fault from the second signals and the first signal.

Description

[0001] Aspects of the invention relate to devices for detecting an electric arc fault, particularly in an electrical installation. The invention also relates to electrical protection devices incorporating such a detection device.

[0002] In general, the invention is applicable to the field of electrical protection, and aims in particular to enable the detection of arc faults in a polyphase alternating current (AC) electrical installation.

[0003] Electrical protection devices, such as circuit breakers, are sometimes configured to detect arc faults that may occur in a multiphase electrical installation. This detection is based on a measuring device comprising low-frequency current sensors and high-frequency current sensors, associated with the different phase conductors of the electrical installation. An arc fault on one phase generates specific variations in the low-frequency (LF) and high-frequency (HF) currents that are most strongly detectable on the faulty phase.

[0004] However, existing detection devices do not always provide satisfactory results, particularly in terms of the number of sensors and the complexity of the associated processing circuits. There is therefore a need for an arc fault detection device in an AC system that offers satisfactory performance while being simple to manufacture.

[0005] To this end, one aspect of the invention relates to a device for detecting an electrical arc fault in a polyphase electrical installation, this device comprising: a high-frequency measurement system coupled to at least two of the electrical phases of the installation, said measurement system being configured to extract a first signal representative of high-frequency components of electrical currents flowing in said phases, particularly in the event of the presence of an arc fault; a plurality of low-frequency measurement systems, each coupled to an electrical phase of the installation, each being configured to acquire a second signal representative of the alternating line current flowing in the corresponding phase; a data processing module, programmed to detect an arc fault from the second signals and the first signal.

[0006] Thus, a single high-frequency measurement system is used for all electrical phases. Therefore, it is unnecessary to use a separate high-frequency measurement system for each phase, as this would multiply the number of current sensors and signal processing chains, increasing the complexity and manufacturing cost of the detection device. Nevertheless, this solution allows for sufficiently reliable and efficient detection of arc faults.

[0007] Depending on advantageous but not mandatory aspects, such a detection device may incorporate one or more of the following characteristics, taken individually or in any technically permissible combination: The measuring device comprises a plurality of single-phase current sensors, each configured to be associated with an electrical phase of the electrical installation. The high-frequency measuring system is configured to combine the high-frequency measurement signals from the current sensors to form a composite signal, from which the initial signal is extracted. The outputs of the current sensors are connected to an input of the high-frequency measuring system via capacitors. The outputs of the current sensors are connected to an input of the high-frequency measuring system via resistors.The outputs of the current sensors are connected to the high-frequency measurement system via a magnetic coupling device. Each output is connected to a primary winding, and these primary windings are magnetically coupled to a secondary winding connected to an input of the high-frequency measurement system. The high-frequency measurement system includes a dedicated current sensor, such as a current transformer, configured to be coupled to at least two of the electrical phases and configured to generate a composite signal from which the first signal is extracted. The sensing device comprises a plurality of single-phase current sensors, each configured to be associated with an electrical phase of the circuit. Each single-phase current sensor is associated with one of the low-frequency measurement systems. The single-phase current sensors are current transformers.Each current sensor comprises a magnetic core and a measuring coil wound around the core and configured to provide a broadband measurement signal at its terminals. The measuring coil has fewer than forty turns or, preferably, fewer than twenty turns. The high-frequency measurement system includes a bandpass filter configured to eliminate from the acquired signal components with a frequency below a predefined threshold. The high-frequency measurement system includes a demodulator, such as a logarithmic amplifier or a heterodyne mixer, configured to demodulate the first representative signal before transmitting it to the processing module. High frequencies are frequencies greater than or equal to 1 MHz, or greater than or equal to 5 MHz, preferably frequencies between 5 MHz and 40 MHz.

[0008] According to another aspect, an electrical protection device includes an electrical switching device capable of interrupting the flow of current in a polyphase electrical installation upon receipt of a tripping signal, and a detection device as described above and coupled to the switching device.

[0009] The invention will be better understood and other advantages thereof will become more apparent in the light of the following description of an embodiment of a detection device given solely by way of example and with reference to the accompanying drawings, in which: [ Fig 1 ] there figure 1 is a schematic representation of an arc fault detection device for an electrical installation according to one embodiment; [ Fig 2 ] there figure 2 is an electrical diagram of an embodiment of a high-frequency measurement stage of the detection device figure 1 ; Fig 3 ] there figure 3 is a schematic representation of another embodiment of the arc fault detection device of the figure 1 ; Fig 4 ] there figure 4 is a schematic representation of another embodiment of the arc fault detection device of the figure 1 ; Fig 5 ] there figure 5 schematically illustrates a comparison between an arc fault detection device conforming to embodiments and another detection device; Fig 6 ] there figure 6 is an expanded view of the graph of the figure 5 .

[0010] There figure 1 represents a polyphase electrical installation 2, such as an electricity distribution installation 2 or, more generally, an alternating current (AC) electrical system.

[0011] Installation 2 includes several electrical conductors 4, each associated with an electrical phase, or pole, to allow the flow of polyphase current, in particular the flow of three-phase current.

[0012] In the examples described below, installation 2 comprises three phases, labeled L1, L2 and L3, with optionally a "neutral" conductor ( figure 3 ).

[0013] This example is not limiting, and alternatively, a different number of phases can be considered. The embodiments described below can be transposed to a polyphase system other than three-phase, for example, a two-phase system, or a four-pole system with three phases and a neutral line.

[0014] For example, conductors 4 are connected to an electrical load 6, labeled "LOAD", intended to be supplied by polyphase electric current.

[0015] In many embodiments, an electrical protection device is associated with the installation 2 to protect it against arc faults. For example, such arc faults can occur between two phases, or between a phase and the protected electrical load, or between a phase and earth.

[0016] For example, the protective device may include an electrical switching device 8 and a detection device 10 coupled to the switching device 8.

[0017] The switching device 8, noted "TRIP", is configured to interrupt the flow of current in the installation 2, and more specifically in the conductors 4, upon receipt of a tripping signal, here noted "TRIP_SIGNAL".

[0018] For example, the switching device 8 includes separable electrical contacts coupled to a mechanical or electromechanical release mechanism.

[0019] The detection device 10 is specifically configured to detect an arc fault in installation 2.

[0020] In accordance with many embodiments, the detection device 10 comprises: current sensors 12; a measurement and / or processing system 14 called high frequency (HF), this system 14 being coupled to at least two of the electrical phases L1, L2, L3 of the installation, or even to all of said phases, said measurement system 14 being configured to extract, in particular by demodulation, a first signal representative of high frequency components of electrical currents flowing in said phases, this measurement system 14 here comprising a device 16 for combining the high frequency measurement signals from the different sensors to form a high frequency composite signal from which said representative signal will subsequently be extracted, and a pre-processing stage 18; a plurality of low-frequency measurement systems 20, each coupled to an electrical phase of the installation, each configured to acquire a second signal representative of the line alternating current flowing in the corresponding phase; a data processing module 22, configured to detect an arc fault from the second signals and the first high-frequency signal.

[0021] In practice, when an arc fault occurs in installation 2, high-frequency current components, and more specifically high-frequency noise, are superimposed on the line current flowing in phases L1, L2 and L3 of installation 2.

[0022] In many examples, as illustrated on the figure 1 The current sensors, here collectively designated by reference 12 and individually noted CT1, CT2 and CT3, are single-phase current sensors. For example, each of these sensors is associated with an electrical phase L1, L2, L3, for example by each being mounted around a corresponding conductor 4.

[0023] For example, system 10 has a current sensor 12 for each of the phases L1, L2 and L3. In other words, system 10 has three sensors 12.

[0024] Preferably, each of the sensors 12 is configured to measure an alternating current flowing in the phase to which it is associated, with a wide frequency measurement band, in particular to measure high-frequency components of the alternating current, such as high-frequency noise generated in the event of an arc fault present on the phase.

[0025] For example, for the purposes of this description, "high frequencies" are frequencies greater than or equal to 1 MHz, or greater than or equal to 5 MHz, preferably frequencies between 5 MHz and 40 MHz, or even frequencies between 10 MHz and 20 MHz.

[0026] Low frequencies are, for example, frequencies less than or equal to 50kHz, or less than or equal to 10kHz, or even less than or equal to 1kHz.

[0027] For example, sensors 12 have a wide frequency measurement band and can thus measure both high-frequency components and other components, including low-frequency components of line currents flowing in conductors 4.

[0028] Preferably, the measurement frequency band of sensors 12 is between 50Hz and 50MHz.

[0029] In this example, the device 10 comprises three low-frequency measurement systems, individually labeled 24, 26 and 28, each of them being associated with an electrical phase L1, L2, L3, with the current sensors CT1, CT2 and CT3 being connected respectively to systems 24, 26 and 28.

[0030] This example is not exhaustive, and alternatively, the number of current sensors 12 could be chosen differently; for example, only two current sensors 12 could be used. The same applies to the number of low-frequency measuring systems 20.

[0031] In practice, the device 10 can include as many low frequency measurement systems 20 as current sensors 12. It is understood in particular that each low frequency measurement system 20 is associated with a single phase L1, L2 or L3 of the installation.

[0032] It is also understood that the system 10 here comprises a single high-frequency measurement system 14, which is common to all phases L1, L2 and L3 of the installation, or at least to all phases for which a measurement of the high-frequency component of the current is carried out.

[0033] In many embodiments, the current sensors 12 are current transformers, or Rogowski coils. For example, each current sensor 12 provides at its output a broadband measurement signal, such as an electrical voltage, representative of the low-frequency electrical current flowing in the conductor 4 to which the current sensor 12 is coupled, superimposed with the high-frequency signal also present in the same conductor.

[0034] For example, each current sensor 12 has a magnetic toroid and a measuring coil wound around the magnetic toroid, preferably of ferrite material, and configured to provide a measuring signal at its terminals.

[0035] Preferably, the measuring coil of each current sensor 12 has less than forty turns or, preferably, less than twenty turns, which limits parasitic capacitances and avoids accidentally eliminating high-frequency components of the measured signal, thereby improving the quality of the measured signal.

[0036] In embodiments, as illustrated on the figure 1 , the sensors 12 are common to the high-frequency measuring system 14 and the low-frequency measuring systems 20. In other words, the outputs of the sensors 12 are connected both to the input of the high-frequency system 14 and to the respective inputs of the low-frequency systems 24, 26 and 28.

[0037] It is therefore understood that the system 14 is configured to extract the high-frequency component of the signals measured by the sensors 12 and, more specifically, to perform this extraction on the composite signal from the device 16.

[0038] In practice, each low-frequency measurement system 24, 26, 28 is configured here to collect the signal measured by one of the current sensors 12 and to shape this signal before providing it to the processing module 22.

[0039] In other words, in this example, current measurements are taken by current sensors 12 and each of the systems 24, 26 and 28 processes the signals measured by the current sensor 12 specific to a phase L1, L2 or L3 with which it is associated.

[0040] For example, each low frequency measurement system 24, 26, 28 may include active integrators which are capable of amplifying and / or filtering and / or reconstructing the evolution of the line currents flowing in the corresponding conductors 4, from the low frequency measurement signals coming out of the current sensors 12, or at the very least of reconstructing the evolution of the low frequency components of these line currents.

[0041] In many embodiments, the data processing module 22 is implemented by one or more electronic circuits.

[0042] For example, module 22 includes a processor, such as a programmable microcontroller or microprocessor.

[0043] The processor is coupled to a computer memory, or any computer-readable data storage medium, which includes executable instructions and / or software code designed to implement a method for detecting an electrical arc fault when these instructions are executed by the processor.

[0044] Alternatively, module 22 may include a digital signal processor (DSP), or a field-programmable gate array (FPGA), or an automatic system integrated circuit (ASIC), or any equivalent element configured and / or programmed to implement said detection method.

[0045] Module 22 includes a first interface 30 for acquiring the first representative signal at the output of the high-frequency measurement system 14. Module 22 also includes one or more second interfaces 32, 34 and 36 respectively configured to receive the second signals at the output of the low-frequency measurement systems 20.

[0046] For example, interfaces 30, 32, 34 and 36 each include an analog-to-digital converter configured to acquire and sample a corresponding signal.

[0047] Embedding methods for device 16 are now described with reference to figures 1 , 2 And 3 .

[0048] The device 16 enables the high-frequency measurement system 14 to combine the high-frequency measurement signals from the different sensors 12, to form said composite signal common to the different phases, from the electrical currents measured for each of the phases to which sensors 12 are associated.

[0049] More specifically, device 16 allows the high-frequency measurement signals from the different sensors 12 to be added together to form said composite signal.

[0050] Preferably, this summation is carried out in an analog manner, that is to say with discrete electrical or electronic components, such as impedance dipoles, without resorting to a digital processing electronic circuit, which allows for a less expensive implementation and does not consume computing resources of module 22.

[0051] It is understood that, in general, device 16 is connected downstream of sensors 12 and upstream of the pre-processing stage 18. For example, sensors 12, together with device 16, form a measurement stage for the measurement system 14, this measurement stage being coupled to said phases L1, L2, L3.

[0052] According to a first example, illustrated on the figure 2 , the outputs of the current sensors 12 are connected to a common point 42 by resistors arranged in a star configuration, the common point 42 being connected to the input of the measuring system 14.

[0053] Thus, device 16, bearing the reference 40 in this particular embodiment, comprises resistors Z C1, Z C2 and Z C3, each connected between the common point 42 and the sensor CT1, CT2 and CT3, respectively.

[0054] In this example, the impedance ZIN denotes the input impedance of the preprocessing stage 18, measured between the common point 42 and the system's ground (GND). The impedances ZM1, ZM2, and ZM3 denote the output impedances of sensors CT1, CT2, and CT3, respectively.

[0055] According to a second example, not illustrated, device 16 is a magnetic coupling device.

[0056] For example, the outputs of the current sensors 12 are connected to the high-frequency measuring system 14 via a magnetic coupling device comprising primary and secondary windings. Each sensor output 12 is connected to a primary winding. The primary windings are magnetically coupled to the secondary winding, which is itself connected to an input of the measuring system 14.

[0057] To improve coupling, the device 16 may include a magnetic core around which are wound the respective primary windings of the current sensors 12 and the secondary winding.

[0058] According to a third example, illustrated on the figure 3 , the outputs of the current sensors 12 are connected to a common point 52 by capacitors 54 arranged in a star configuration, the common point 52 being connected to the input of the measuring system 14.

[0059] Thus, the device 16, bearing the reference 50 in this particular embodiment, comprises capacitors 54, preferably identical, each capacitor 54 being connected between the common point 52 and a sensor CT1, CT2 and CT3, respectively.

[0060] It is advantageous to use capacitors 54 to combine the signals measured by the current sensors 12, because the impedance of the capacitors is inversely proportional to the frequency, so that the high-frequency impedance is relatively low, which favors high-frequency coupling, while ensuring good isolation between the different line current signals for low frequencies.

[0061] The reference U IN_HF designates the composite signal obtained at the output of the device 16 from the electrical currents measured by the current sensors 12.

[0062] In some embodiments, the composite signal U IN_HF corresponds to the combination of the high-frequency contributions for the different phases L1, L2, and L3 of the installation. In other embodiments, the composite signal U IN_HF corresponds to the combination of only the currents measured for the different phases L1, L2, and L3 of the installation, without distinction of frequency, the extraction of the high-frequency contributions being achieved only by subsequent processing (such as filtering) in the preprocessing stage 18.

[0063] For example, the composite signal U IN_HF is an electrical voltage.

[0064] Note that, in the example of the figure 3 The electrical installation 2' differs from installation 2 in that the electrical conductors 4' also include, in addition to the three phases L1, L2 and L3, a neutral line, here noted N. This neutral line N can however be omitted without changing the operation of the detection system 10', nor changing the operation of the device 16.

[0065] According to variants not illustrated or described in detail, device 16 could be made differently again, for example by using more complex circuits, such as one or more bandpass filters in the frequency domain used for arc fault detection.

[0066] Embodiments of the pretreatment stage 18 are now described with reference to the figure 3 .

[0067] In many embodiments, and not only that of the figure 3 , the pre-processing stage 18 is configured to extract, notably by demodulation, the first signal representative of high-frequency components of electrical currents flowing in said phases, from the composite signal U IN_HF before acquisition by the processing module 22.

[0068] For example, the preprocessing stage 18 includes at least one filter 56 configured to eliminate from the acquired composite signal U IN_HF components having a frequency below a predefined threshold, such as a predefined threshold of 5MHz or 1MHz.

[0069] In the illustrated examples, filter 56 is a bandpass filter. This bandpass filter can be configured to only allow frequencies of the composite signal U IN_HF between 1 MHz and 50 MHz, or preferably between 5 MHz and 40 MHz, or even frequencies between 10 MHz and 20 MHz.

[0070] Thus, filter 56 allows the high-frequency components to be extracted from the composite signal from the measurements made by the current sensors 12.

[0071] The preprocessing stage 18 also includes a demodulator 58, such as a logarithmic amplifier or a heterodyne mixer, configured to demodulate said first signal before transmitting it to the processing module 22. For example, the preprocessing stage 18 is connected downstream of the filter 56.

[0072] Specifically, demodulator 58 allows the envelope of the first U IN_HF signal to be extracted. A corresponding envelope signal, here denoted RSSI on the figure 3 is then sent to input 30 of processing module 22.

[0073] The preprocessing stage 18 therefore makes it possible to extract, in particular by demodulation, from the first signal, resulting from the combination of the signals measured individually by the current sensors 12, information on the power value or on the effective value of the amplitude (the envelope) of said first signal.

[0074] Compared to the composite U IN_HF signal, the waveform of the demodulated signal (RSSI) evolves more slowly, i.e., at frequencies significantly lower than 1 MHz, for example, at least one hundred times lower than 1 MHz. The waveform of the demodulated signal is simpler to sample and requires fewer computing resources than sampling the composite U IN_HF signal. Nevertheless, the waveform alone contains enough useful information to allow for reliable arc fault detection. Therefore, the processing module 22 does not need to acquire the entire initial signal.

[0075] Thanks to the invention, a single high-frequency measurement system 14 is used for all electrical phases L1, L2, and L3. Therefore, it is not necessary to use a separate high-frequency measurement system for each phase, as this would multiply the number of signal processing and preprocessing components in the detection device. However, the components required to process high-frequency signals are generally expensive. Such a multiplication would thus increase the complexity and manufacturing cost of the detection device.

[0076] The different embodiments of the detection device 10 or 10' nevertheless allow the detection of arc faults in a sufficiently reliable and efficient manner, even using only a single high-frequency signal processing chain common to several phases and based on the first signal U IN_HF without directly using the signals measured individually for each phase.

[0077] Indeed, the occurrence of an arc fault in one of the phases L1, L2, or L3 generates noise in the currents flowing through the different phases. This noise is randomly phase-shifted between the different phases at high frequencies and can also be randomly amplified or attenuated from one phase to another, such that the sum of the high-frequency components of these currents is not zero. Conversely, no such phase shift is present in the low-frequency components of these same currents, which remain correlated with each other from one phase to the next. Thus, the sum of the low-frequency components of these same currents is zero.

[0078] Measuring high-frequency noise on electrical currents flowing in phases L1, L2, L3 therefore makes it easy to identify an arc fault, without needing to use, for high frequencies, excessively complex measurement and signal processing means dedicated to each of the phases.

[0079] According to embodiments given by way of example, the detection of an electric arc fault can be carried out by a detection algorithm implemented in the processing module 22 by comparing the measured signals from the low frequency measurement chain with the first signal associated with the high frequency components.

[0080] In particular, module 22 can be configured to detect if the sum of the low-frequency currents is zero while at the same instant, the sum of the high-frequency components of these same currents (given by the first signal, or by its envelope, or by any appropriate representative quantity constructed by the preprocessing stage 18) is not zero.

[0081] The waveform of the high-frequency composite signal can be advantageously used as an arc fault indicator. The presence of an arc fault is detected by a processing algorithm implemented in module 22. In response to the detection algorithm, module 22 can be configured to send a TRIP_SIGNAL trigger signal to the switching device 8, in order to interrupt the current flow in the conductors 4.

[0082] Otherwise, no such signal is emitted, and the system continues to operate.

[0083] However, other detection methods can be used.

[0084] There figure 4 represents a detection device 10" according to another embodiment, which differs from the embodiments previously described in that the high-frequency measuring system 14 includes a dedicated current sensor 60, such as a measuring torus.

[0085] The current sensor 60 is configured to be coupled to at least two of the electrical phases L1, L2, L3, or even to all of the electrical phases, and replaces the sensors 12 and the device 16. In other words, in this embodiment, the device 16 is omitted, as are the current sensors 12.

[0086] In other words, the sensor 60 serves both to measure the electrical currents flowing in said phases, and to combine the components specific to each phase to form the composite signal U IN_HF.

[0087] It is therefore understood that, in this embodiment, the single current sensor 60 forms a measurement stage for the high-frequency measurement system 14. The preprocessing stage 18 is connected to the output of the current sensor 60.

[0088] For example, the sensor 60 is a differential measuring toroid, such as those used in residual current circuit breakers. In the illustrated example, the sensor 60 comprises a magnetic toroid surrounding said phases and a measuring coil 62, connected to the input of the pretreatment device

[0089] In the illustrated example, the detection device 10" also includes a plurality of single-phase current sensors LFS1, LFS2, LFS3 and collectively noted 64, which are analogous to the sensors 12 previously described.

[0090] However, in this embodiment, the current sensors 64 are not connected to the high-frequency measuring system 14, since the latter has its own current sensor 60.

[0091] In practice, each of the 64 current sensors is configured to be associated with an electrical phase of the circuit while being connected to one of the 20 low-frequency measurement systems.

[0092] In this example, the device 10" comprises three low-frequency measuring systems 24, 26 and 28 as described previously, each of them being associated with an electrical phase L1, L2, L3, the current sensors LFS1, LFS2 and LFS3 being connected respectively to the measuring systems 24, 26 and 28. On the other hand, the current sensors LFS1, LFS2 and LFS3 are not connected to the high-frequency measuring system 14.

[0093] Apart from these differences, the operation of the detection device 10" is analogous, or even identical, to the operation of the detection devices 10 and 10' previously described, particularly with regard to the role and operation of the processing module 22 and the pre-processing device 18.

[0094] It is understood in particular that, in this embodiment, the detection device 10" also includes a single measurement system 14 common to all phases L1, L2 and L3 of the installation, or at least to all phases for which a measurement of the high-frequency component of the current is carried out.

[0095] There figure 5 This illustrates an example of a comparison of the results obtained for detecting an arc fault between, on the one hand, a detection device 72 conforming to embodiments as described above and, on the other hand, another detection device 74 in which each of the phases 76 of the installation 70 is associated with a sensor and a dedicated high-frequency measuring system, respectively labeled "HF Circuit 1", "HF Circuit 2" and "HF Circuit 3". By contrast, the detection device 72 comprises a single high-frequency measuring system, labeled "HF Circuit", for all phases of the installation.

[0096] In the illustrated example, it is assumed, for illustrative purposes, that arc fault 78, labeled "Arc-Fault," occurred on the second phase L2 between said phase and ground. This example is not exhaustive, and in practice, an arc fault can be detected on any phase.

[0097] Graph 80 illustrates the evolution, as a function of time (x-axis, in milliseconds, denoted "time"), of the amplitude of the signals from the two devices 72 and 74. figure 6 shows an enlarged view of area 82 of graph 80.

[0098] In the illustrated example, the signal noted "RSSI MAX" corresponds to the signal delivered by device 72, and here corresponds to the first RSSI signal representative of high-frequency components of electric currents flowing in said phases, as defined in previous embodiments.

[0099] The other signals “RSSI 1”, “RSSI 2” and “RSSI 3” correspond, respectively, to the signals delivered by each of the high-frequency measurement systems of the other device 74.

[0100] On the graph, the RSSI 2 signal associated with the second phase L2 has a maximum amplitude after the fault appears (shortly after the instant equal to 1 second), while the amplitude of the RSSI 1 and RSSI 3 signals, associated with the neighboring phases L1 and L3, is less.

[0101] The amplitude of the first RSSI MAX signal from the unique measurement system 14 of device 72, is close to that of the RSSI 2 signal.

[0102] Thus, the first signal from the measurement system 14 can replace the demodulated RSSI 1, RSSI 2 and RSSI 3 signals for each phase, without compromising the detection of an arc fault.

[0103] Any feature of one of the embodiments or variants described above can be implemented in the other embodiments and variants described.

Claims

1. Device (10; 10'; 10") for detecting an arc fault in a polyphase electrical installation (2), this device comprising: - a high-frequency measurement system (14) coupled to at least two electrical phases (L1, L2, L3) of the installation, said measurement system being configured to extract a first signal (RSSI) representative of high-frequency components of electrical currents flowing in said phases; - a plurality of low-frequency measurement systems (20), each coupled to an electrical phase of the installation, each being configured to acquire a second signal representative of the alternating line current flowing in the corresponding phase; - a data processing module (22), programmed to detect an arc fault from the second signals and the first signal.

2. A device according to claim 1, wherein the measuring device comprises a plurality of single-phase current sensors (12; CT1, CT2, CT3), each configured to be associated with an electrical phase (L1, L2, L3) of the electrical installation, and wherein the high-frequency measuring system is configured to combine the high-frequency measuring signals from the current sensors to form a composite signal (U IN_HF ) from which the said first signal (RSSI) is extracted.

3. Device according to claim 2, wherein the outputs of the current sensors (12; CT1, CT2, CT3) are connected to an input of the high-frequency measuring system by capacitors (54).

4. Device according to claim 2, wherein the outputs of the current sensors (12; CT1, CT2, CT3) are connected to an input of the high-frequency measuring system via resistors (Z C1 , Z C2 and Z C3 ).

5. Device according to claim 2, wherein the outputs of the current sensors (12; CT1, CT2, CT3) are connected to the high-frequency measuring system via a magnetic coupling device, each of said outputs being connected to a primary winding, said primary windings being magnetically coupled to a secondary winding connected to an input of the high-frequency measuring system.

6. Device according to claim 1, wherein the high-frequency measuring system (14) comprises a dedicated current sensor (60), such as a measuring toroid, configured to be coupled to at least two of the electrical phases and configured to generate a composite signal (U IN_HF) from which said first signal (RSSI) is extracted, and in which the detection device (10") comprises a plurality of single-phase current sensors (64; LFS1, LFS2, LFS3) each configured to be associated with an electrical phase of the circuit, each single-phase current sensor being associated with one of the low-frequency measurement systems (20).

7. Device according to any one of claims 2 to 6, wherein the single-phase current sensors (12; CT1, CT2, CT3; 64; LFS1, LFS2, LFS3) are current transformers.

8. Device according to claim 7, wherein each current sensor (12; CT1, CT2, CT3; 64; LFS1, LFS2, LFS3) comprises a magnetic core and a measuring coil wound around the magnetic core and configured to provide a broadband measuring signal at its terminals, the measuring coil having less than forty turns or, preferably, less than twenty turns.

9. Device according to any one of the preceding claims, wherein the high-frequency measurement system (14) includes a bandpass filter (56) configured to eliminate from the acquired signal components having a frequency below a predefined threshold.

10. Device according to claim 1, wherein the high-frequency measurement system (14) includes a demodulator (58), such as a logarithmic amplifier or a heterodyne mixer, configured to demodulate said first representative signal before transmitting it to the processing module.

11. Device according to any one of the preceding claims, wherein the high frequencies are frequencies greater than or equal to 1MHz, or greater than or equal to 5MHz, preferably frequencies between 5MHz and 40MHz.

12. Electrical protection device (8+10), comprising an electrical switching device (8) capable of interrupting the flow of current in a polyphase electrical installation (2) upon receipt of a tripping signal, and a detection device (10; 10'; 10") conforming to any one of the preceding claims and coupled to the switching device.