AU2021298110A1

AU2021298110A1 - Method for detecting leakage or fault currents in an electrical installation using a protective device providing at least differential protection and such a device suitable for implementing the method

Info

Publication number: AU2021298110A1
Application number: AU2021298110A
Authority: AU
Inventors: Bastien DOLISY; Patrice Joyeux; Michel Schneider
Original assignee: Hager Electro SAS
Current assignee: Hager Electro SAS
Priority date: 2020-06-23
Filing date: 2021-06-22
Publication date: 2023-02-16
Also published as: EP4169137A1; FR3111746B1; WO2021259922A1; FR3111746A1

Abstract

The present invention relates to a method for detecting leakage or fault currents in an electrical installation using a protective device, the electrical installation being supplied by a current flowing in at least two conductors of an AC or DC network. It consists in detecting an asymmetry in the alternating measurement signal between its positive alternation, or half-cycle, and its negative alternation, or half-cycle, generated by the presence of even order harmonics in the alternating measurement signal representative of a DC current relative to a fault current occurring in the network: either by determining, by frequency analysis of the alternating measurement signal, a measurement value representative of the occurrence of even order harmonics in the alternating measurement signal, then comparing the measurement value with a reference threshold comprised in the processing and control unit (3) in order to produce the control signal, depending on the result of the comparison, or by measuring a first value of a physical quantity of the alternating measurement signal in its positive alternation, or half-cycle, and a second value of the physical quantity in its negative alternation, or half-cycle, then calculating their difference and comparing it to a reference threshold in order to produce the control signal, depending on the result of the comparison. It also relates to such a protective device suitable for implementing the method.

Description

Title of the invention: Method for detecting leakage or fault currents in an electrical installation using a protective device providing at least differential protection and such a device suitable for implementing the method

[0001] The present invention concerns the field of safety protection circuits, more particularly the field of protective devices providing at least differential protection, such as differential circuit-breakers, in an electrical installation and using electric current detectors functioning with a clamp and has for object a method for detecting leakage or fault currents in an electrical installation using a protective device providing at least differential protection and such a device suitable for implementing said method.

[0002] Present-day protective devices providing at least differential protection are installed in domestic or tertiary sector electrical installations fed by an alternating or direct current supply and have for object mainly assuring the safety of persons by detecting as rapidly as possible a fault current representing a possible leakage to ground in one of the circuits or receivers to be protected of the electrical installation.

[0003] Leakage of this kind is cause for example by direct contact of persons with an uninsulated electrical conductor or indirect contact caused by ground defects. These electrical incidents are liable to cause accidents, sometimes fatal accidents, damage to equipment, starting of fires, localized or generalized malfunctions or the like.

[0004] In these protective devices the detection of a leakage or fault current is used to control directly or via dedicated electronics (signal processing stages) an actuator or the like (for example of relay type) that in turn controls an associated tripping, disconnector or breaker mechanism, or those of other protective devices of the installation.

[0005] Differential protection necessitates the use of a reliable and economical and sensor that is relatively insensitive to interference that can lead to untimely tripping. A clamp magnetic circuit including a clamp through which pass or surrounding electrical conductors powering the electrical installation is a known solution used by present-day protective devices because it enables measurement of the imbalance of the galvanically insulated input and output currents of a circuit in an intrinsic manner (Ampere's theorem). The conductors passing through the clamp form the primary. The clamp includes one or more secondary windings or coils forming one or more measuring windings and serves as a magnetic flux concentrator. Thus in the event of leakage, reflected in an imbalance of the input and output currents in said conductors, the flux created in the clamp by this imbalance at the level of the primary induces in the secondary coil, or measurement winding, a voltage that constitutes a current detection signal, where applicable imaging or representing a fault current.

[0006] These devices further include an electronic processing and control unit enabling processing of the current detection signal by comparing it to a reference threshold and, as a function of the result of the comparison, tripping the device by causing disconnector or breaker means to interrupt the circulation of the current in the conductor or conductors concerned.

[0007] Where the detection of leakage or fault direct currents is concerned, if the measurement clamp has such a current pass through it the magnetic field remains constant and no induced voltage can be measured or detected. To solve this problem protective devices further include a carrier generator enabling excitation of the measurement clamp, generally a soft magnetic clamp, by means of a voltage generated by said carrier generator at a frequency from a few hundred hertz to several kilohertz. The amplitude of the excitation current or of the excitation voltage must be sufficiently high to saturate the clamp in a symmetrical manner.

[0008] The document W019091740 has for object a differential protective device of this kind enabling detection of leakage or fault currents in an electrical installation powered either by at least two phase conductors of a supply or by at least one phase conductor of a supply and by a neutral conductor of said supply. The device includes at least one detection and control module that is functionally active or operational for frequencies of the fault signal from 0 Hz to a few tens of Hz. The module is fed by the supply and includes, on the one hand, a ferromagnetic material measurement clamp through which said conductors pass and, on the other hand, an excitation circuit of the clamp including an alternating current signal generator producing a periodic carrier, and, finally, a measurement winding able and intended to generate a fault signal (AC measurement signal) resulting from the appearance of a differential fault at the level of the supply, said measurement winding being connected to circuits for processing and evaluating the fault signal and sending a control signal for a disconnector or breaker means that is also part of the differential protective device. Said circuits then form the components of an operational electronic system that is part of said module. Moreover, these circuits include at least, on the one hand, a circuit supplying a signal corresponding to the rectified average value of the fault signal or a derived signal directly dependent on the latter and, on the other hand, a circuit comparing said rectified mean signal to a predetermined or preset threshold value and conditionally or selectively delivering a control signal for the disconnector or breaker means as a function of the result of said comparison.

[0009] However, if the differential protective device from the document WO19091740 enables detection of DC leakage or fault currents and conforms to differential protection standards such as those relating to the type B class enabling detection of smooth residual direct currents and high-frequency alternating currents, it does not, without major modifications, enable measurement of weak currents, in particular currents less than 15 mA. This device is therefore not able to comply with the standard of the type EV class that imposes that the differential protective device trips at between 3 and 6 mA. In fact, the clamp used in this type of device is subject to dispersion in the behavior of the magnetic material of the clamp such that a device of the type disclosed in this document is dependent on the characteristics of the clamp, commensurately limiting its sensitivity to weak currents. It is also dependent on variations due to the conditions of use (external temperature and magnetic field).

[0010] One solution to enable this type of device disclosed in the document W019091740 to conform to the standards and to address the problem of dispersion could be to modify the calibration of the device or to change the components or even to increase the size of the clamp. However, these modifications or adaptations would lead to a significant increase in the unit cost of the device and, where applicable, an increase in its volume and therefore in its overall size, which would go against objectives that manufacturers seek to achieve at present.

[0011] The present invention has for object alleviating these disadvantages whilst making it possible to obtain a device having a volume or overall size less than that of a device of the type described in the document WO19091740.

[0012] To this end the method according to the invention for detecting leakage or fault currents in an electrical installation using a protective device providing at least differential protection, said electrical installation being powered by a current circulating in at least two conductors of an AC or DC supply, said protective device including at least one detection, processing and control module including, on the one hand, a clamp detector able to generate as output an AC measurement signal and including a clamp through which said conductors pass and having a measurement winding and an AC voltage or current supply able to generate an AC excitation signal to saturate the clamp, where applicable said clamp detector including a resistance in series with said clamp, a processing and control unit connected to the output of the clamp detector and able to process the AC measurement signal to detect a leakage or fault current in the supply and to send a control signal as a function of the result of the processing to a disconnector or breaker control means that said protective device further includes, is essentially characterized in that it consists in detecting asymmetry of the AC measurement signal between its positive alternation, or half-period, and its negative alternation, or half-period, generated by the presence of even harmonics in said AC measurement signal representative of a direct current relating to a leakage or fault current in the supply:

[0013] - either by determining, by frequency-domain analysis of the AC measurement signal, a measurement value representative of the occurrence of even harmonics in said AC measurement signal and then comparing said measurement value with a reference threshold to send the control signal according to the result of the comparison,

[0014] - or by measuring a first value of a physical parameter of the AC measurement signal in its positive alternation, or half-period, and a second value of said physical parameter in its negative alternation, or half-period, and then determining the difference between said first and second values and comparing that difference with a reference threshold to send the control signal according to the result of the comparison.

[0015] The present invention also has for object a protective device providing at least differential protection against leakage or fault currents in an electrical installation, said electrical installation being powered by a current circulating in at least two conductors of an AC or DC supply, said protective device being suitable for implementation of the method according to the present invention and including at least one detection, processing and control module including, on the one hand, a clamp detector able to generate as output an AC measurement signal and including a clamp through which said conductors pass with a measurement winding and an AC voltage or current supply able to generate an AC excitation signal to saturate the clamp, where applicable said clamp detector including a resistance in series with said clamp, a processing and control unit connected to the output of the clamp detector and able to process the AC measurement signal to detect a leakage or fault current in the supply and to send as a function of the result of the processing a control signal to a disconnector or breaker control means that said protective device further includes, essentially characterized in that the processing and control unit is configured to detect asymmetry of the AC measurement signal between its positive alternation, or half-period, and its negative alternation, or half-period, generated by the presence of even harmonics in said AC measurement signal representative of a direct current relating to a leakage or fault current in the supply by determining:

[0016] - either by determining by frequency-domain analysis of the AC measurement signal a measurement value representative of the occurrence of even harmonics in said AC measurement signal and then comparing said measurement value with a reference threshold to send the control signal according to the result of the comparison,

[0017] - or by measuring a first value of a physical parameter of the AC measurement signal in its positive alternation, or half-period, and a second value of said physical parameter in its negative alternation, or half-period, and then determining the difference between said first and second values and comparing that difference with a reference threshold to send the control signal according to the result of the comparison.

[0018] The invention will be better understood thanks to the following description, which relates to a preferred embodiment provided by way of non-limiting example and explained with reference to the appended diagrammatic drawings, in which:

[0019] [Fig. 1] represents the electrical circuit diagram of the detection, processing and control module of a protective device according to the present invention suitable for implementing the detection method according to the present invention in an analog implementation of the processing and control unit of said module and in a configuration of said processing and control unit enabling detection of lack of symmetry of the AC measurement signal between its positive alternation, or half-period, and its negative alternation, or half-period, by detection of an asymmetry of amplitude between said alternations, or half-periods,

[0020] [Fig. 2] represents the electrical circuit diagram of the detection, processing and control module of a protective device according to the present invention suitable for implementing the detection method according to the present invention in an analog embodiment of the processing and control unit of said module and in a configuration of said processing and control unit enabling detection of asymmetry of the AC measurement signal between its positive alternation, or half-period, and its negative alternation, or half-period, by detection of asymmetry of saturation between said alternations, or half-periods,

[0021] [Fig. 3] represents the electrical circuit diagram of the detection, processing and control module of a protective device according to the present invention suitable for implementing the detection method according to the present invention in a digital implementation of the processing and control unit of said module and in a configuration of said processing and control unit enabling detection of asymmetry of the AC measurement signal between its positive alternation, or half-period, and its negative alternation, or half-period, by detection of asymmetry of amplitude between said alternations, or half-periods,

[0022] [Fig. 4] represents the electrical circuit diagram of the detection, processing and control module of a protective device according to the present invention suitable for implementing the detection method according to the present invention in a digital implementation of the processing and control unit of said module and in a configuration of said processing and control unit enabling detection of asymmetry of the AC measurement signal between its positive alternation, or half-period, and its negative alternation, or half-period, by detection of asymmetry of saturation between said alternations, or half-periods,

[0023] [Fig. 5] represents the electrical circuit diagram of the detection, processing and control module of a protective device according to the present invention suitable for implementing the detection method according to the present invention in a digital implementation of the processing and control unit of said module and in a configuration of said processing and control unit enabling detection of asymmetry of the AC measurement signal between its positive alternation, or half-period, and its negative alternation, or half-period, by analysis of the frequency of said signal,

[0024] [Fig. 6] represents an AC measurement signal generated by the clamp detector and processed by the processing and control unit of the module represented in figure 1 and in figure 3,

[0025] [Fig. 7] represents the frequency spectrum of the AC measurement signal represented in figure 6, said spectrum being processed by the processing and control unit of the module represented in figure 5,

[0026] [Fig. 8] represents an AC measurement signal with a high level of saturation greater than that of the AC measurement signal represented in figure 6 and processed by the processing and control unit of the module represented in figure 2 or in figure 4,

[0027] [Fig. 9] represents the frequency spectrum of the AC measurement signal represented in figure 8, said spectrum being processed by the processing and control unit of the module represented in figure 5,

[0028] [Fig. 10] represents the electrical circuit diagram of the detection, processing and control module of a protective device according to the present invention that further includes an additional processing and control unit connected in parallel with the processing and control unit represented in figure 2.

[0029] The figures show a protective device providing at least differential protection against leakage or fault currents in an electrical installation, said electrical installation being powered by a current circulating in at least two conductors of an AC or DC supply. A protective device of this kind is suitable for implementing the method according to the present invention and includes at least one detection, processing and control module including:

[0030] - a clamp detector 1 able to generate as output an AC measurement signal S and including a clamp la through which said conductors pass and provided with a measurement winding 10a,

[0031] - an AC current or voltage supply 2 able to generate an AC excitation signal to saturate the clamp la, where applicable said clamp detector 1 including a resistance lb in series with said clamp la, said resistance then forming at the terminals of said resistance the output S of the clamp detector 1,

[0032] - an analog and/or digital processing and control unit 3 connected to the output S of the clamp detector and adapted to process the AC measurement signal in order to detect a fault current in the supply and, as a function of the result of the processing, to send a control signal for a disconnector or breaker control means 4, for example of the relay or other actuator type, that said protective device further includes.

[0033] According to the present invention, a device of this kind is characterized in that the processing and control unit 3 is configured to detect asymmetry of the AC measurement signal between its positive alternation, or half-period, and its negative alternation, or half period, generated by the presence of even harmonics H2, H4, H6 in said AC measurement signal representative of a direct current Idc relating to a fault current in the supply:

[0034] - either, by frequency-domain analysis of the AC measurement signal, determining a measurement value representative of the occurrence of even harmonics H2, H4, H6 in said AC measurement signal and then comparing said measurement value with the reference threshold Hs to send the control signal according to the result of the comparison,

[0035] - or by measuring a first value VI, tl of a physical parameter of the AC measurement signal in its positive alternation, or half-period T/2, and a second value V2, t2 of said physical parameter in its negative alternation, or half-period T/2, and then determining the difference between said first value VI, ti and said second value V2, t2 and comparing that difference to the reference threshold Vs, ts to send the control signal according to the result of the comparison.

[0036] In such a manner as to be able to measure the first value VI and the second value V2, in a first embodiment (figures 1 and 3) the processing and control unit 3 is configured to detect an amplitude asymmetry by measuring the maximum amplitude of the positive alternation, or half-period T/2, of the AC measurement signal and the minimum value of its negative alternation, or half-period T/2, the first value VI being said maximum amplitude and the second value V2 being said minimum amplitude.

[0037] Referring to figure 6, and it will be understood that in this first embodiment, if a leakage or fault current coming from the supply is detected by the clamp detector 1, an amplitude peak forming the maximum or minimum amplitude in one of the alternations, or half periods T/2, of the AC measurement signal is accentuated relative to the amplitude peak of the other alternation, or half-period T/2. This difference is proportional to the value of the current detected by the clamp detector 1.

[0038] It can more particularly be seen in figure 1 that, in a first implementation of the processing and control unit 3 in thefirst embodiment, the latter is configured electronically in an analog manner and includes at least the following circuits electrically connected in series:

[0039] - an analog measurement circuit 3a connected to the output S of the clamp detector 1 and consisting of two branches 30a, 31a connected in parallel, namely a first branch 30a able to measure the first value VI and a second branch 31a able to measure the second value V2,

[0040] - an analog summation/subtraction circuit 3b connected to the output of said measurement circuit 3a and able to determine the difference between said first and second values VI, V2,

[0041] - an averaging and/or rectifier and/or filter circuit 3c connected to the output of said summation/subtraction circuit 3b, and

[0042] - a comparator and trigger circuit 3d connected to the output of said averaging and/or rectifier and/or filter circuit 3c and able to compare said difference and the reference threshold Vs to send the control signal according to the result of the comparison.

[0043] Referring to figure 3, it can be seen that in a second implementation of the processing and control unit 3 in the aforementioned first embodiment, the latter is configured electronically in a digital manner and consists in a microprocessor or microcontroller based processing and control circuit 3e able to execute the instructions of a program loaded into a memory of said processing and control unit 3 to measure the first value V Iand the second value V2 and then to establish the difference between said first and second values VI, V2 and to compare that difference to the reference threshold Vs.

[0044] So as to be able to measure the first value VI and the second value V2, in a second embodiment the AC voltage or current supply 2 is configured to generate an excitation signal with a current level creating in each positive or negative alternation, or half-period T/2, of the AC measurement signal saturation of its maximum or minimum amplitude over a measurable time period. Moreover, as can be seen in figures 2 and 4, the processing and control unit 3 is configured to be able to measure the first value tl and the second value t2 to detect asymmetrical saturation in the AC measurement signal by measuring a first duration of saturation of the maximum amplitude of the AC measurement signal in its positive alternation, or half-period T/2, and a second duration of saturation of the minimum amplitude of the AC measurement signal in its negative alternation, or half-period T/2. The first value tl is/corresponds to said first saturation duration and the second value t2 is/corresponds to said second saturation duration.

[0045] It will be understood that in this second embodiment the duration of saturation represents the time for which the clamp la is strongly saturated, that is to say saturated to a level greater than the level of excitation of the clamp la in the aforementioned first embodiment. Thus when a leakage or fault current coming from the supply is detected by the clamp detector 1 the AC measurement signal saturation duration differs between that measured in its positive alternation, or half-period T/2, and that measured in its negative alternation, or half-period T/2. This difference is proportional to the amplitude of the current detected by the clamp detector 1.

[0046] It can be seen more particularly in figure 2 that, in a first implementation of the processing and control unit 3 in the second embodiment, the latter is configured in an analog manner and includes at least the following circuits, preferably based on operational amplifiers, electrically connected in series:

[0047] - an analog measurement circuit 3a connected to the output S of the clamp detector 1 and consisting of two branches 30a, 31a connected in parallel, namely a first branch 30a able to determine the first value tl and a second detection branch 31a able to detect the second value t2,

[0048] - an analog summation/subtraction circuit 3b connected to the output of said detection circuit 3a and able to establish the difference between said first and second values tI, t2,

[0049] - an averaging and/or rectifier and/or filter circuit 3c connected to the output of said summation/subtraction circuit 3b, and

[0050] - a comparator and trigger circuit 3d connected to the output of said averaging and rectifier and/or filter circuit 3c and able to effect the comparison between this difference and the reference threshold ts to send the control signal according to the result of the comparison.

[0051] The averaging and/or rectifier and/or filter circuit 3c in each of the aforementioned embodiments essentially or preferably enables processing of the output signal of the summation/subtraction circuit 3b so as to be able to place said signal in a state that can be processed by the comparator and trigger circuit 3d. The rectifier part (see in particular figures 1, 2 and 10) of the averaging and/or rectifier and/or filter circuit 3c enables the comparator function of the comparator and trigger circuit 3d always to process a positive voltage (or a positive signal), which avoids the presence of two comparator and trigger circuits 3d, that is to say two comparators, one for the positive voltage and the other for the negative voltage.

[0052] It is clear that in each of the aforementioned embodiments the summation/subtraction circuit 3b may be either a subtraction circuit or a summation circuit 3b, according to the sign of the parameters. Thus in the situation where the positive half-period yields a positive parameter while the negative half-period yields a negative parameter, the present invention can provide a summation circuit 3b. In fact, the sum of the two parameters makes it possible to obtain the difference for the absolute value because one is positive and the other negative. In other words, the present invention can provide a subtractor circuit.

[0053] Referring to figure 4, it can be seen that in a second implementation of the processing and control unit 3 in the second embodiment, the latter is electronically configured in a digital manner and consists in a microprocessor or microcontroller based processing and control circuit 3e able to execute the instructions of a program loaded into a memory of said processing and control unit 3 to measure the first value tl and the second value t2 and then to establish the difference between said first and second values tI, t2 and to compare that difference to the reference threshold ts.

[0054] The method for detecting leakage or fault currents according to the present invention in an electrical installation using a protective device of the type described above in accordance with the present invention, said electrical installation being powered by a current circulating in at least two conductors of an AC or DC supply, consisting of detecting asymmetry of the AC measurement signal between its positive alternation, or half-period T/2, and its negative alternation, or half-period T/2, generated by the presence of even harmonics in said AC measurement signal representative of a direct current Idc relating to a fault current in the supply:

[0055] - either, by frequency-domain analysis of the frequency of the AC measurement signal, determining a measurement value representative of the occurrence of even harmonics in said AC measurement signal, and then comparing said measurement value with the reference threshold to send the control signal as a function of the result of the comparison,

[0056] - or by measuring a first value VI, tl of a physical parameter of the AC measurement signal in its positive alternation, or half-period T/2, and a second value V2, t2 of said physical parameter in its negative alternation, or half-period, and then determining the difference between said first and second values VI, ti, V2, t2 and comparing that difference with the reference threshold Vs, ts to send the control signal as a function of the result of the comparison.

[0057] So as to be able to measure the first value VI and the second value V2, in a first embodiment of the method (figures 1 and 3), for measuring the first value tl and the second value t2, the processing and control unit 3 detects asymmetry of the amplitude of the AC measurement signal and measures the maximum amplitude of its positive alternation, or half-period, and the minimum amplitude of its negative alternation, or half-period. The first value VI is/corresponds to said maximum amplitude and the second value V2 is/corresponds to said minimum amplitude.

[0058] To be able to measure the first value VI and the second value V2, in a second embodiment of the method (figures 2 and 4), said method generates an excitation signal with a current level creating in each positive or negative alternation, or half-period, of the AC measurement signal saturation of its maximum or minimum amplitude over a measurable duration. Moreover, to measure the first value tl and the second value t2 said method detects saturation duration asymmetry in the AC measurement signal by measuring a first saturation duration of the maximum amplitude of its positive alternation, or half period, and a second saturation duration of the minimum amplitude of its negative alternation, or half-period. The first value tl is/corresponds to said first saturation duration and the second value t2 is/corresponds to said second saturation duration.

[0059] The choice of the embodiment of the method or of the device enabling detection of amplitude or saturation asymmetry depends essentially on the level of saturation of the clamp la by the AC excitation signal generated by the AC current or voltage supply 2 and therefore the adjustment of the latter.

[0060] When the AC current or voltage supply 2 is set up so as to generate an excitation signal the effect of which is that the clamp la reaches a high saturation state (high excitation current or high current to be measured), the impedance of the clamp will be negligible, where applicable compared to the value of the resistance lb connected in series with said clamp la, and the whole of the voltage of the carrier formed by the excitation signal will be found at the terminals of the resistance lb. In this case the embodiment to enable detection of saturation asymmetry is preferred.

[0061] Detection or analysis of saturation asymmetry in the AC measurement signal between its positive and negative alternations, or half-periods, carried out in the second embodiment of the method or of the device is more precise than detection or analysis of amplitude asymmetry in the second embodiment of the method or device but necessitates high saturation of the clamp la, that is to say a level higher, or even significantly higher, than that of the excitation of the clamp la in the first embodiment, and therefore necessitating higher energy consumption by the electronics employed.

[0062] Moreover, as can be seen in figure 10, in one particular implementation of the method or the device for detecting very high currents the present invention may provide for a second detection to be carried out in parallel, that is to say for an additional processing and control unit 5 to be connected to the output S of the clamp detector 1 in parallel with the processing and control unit 3 regardless of the embodiment of the latter described above. An additional processing and control unit 5 may be based on rectification and calculation of the mean without using the asymmetry detection/analysis part, by frequency analysis or comparison of the positive and negative alternations, or half-periods, of the AC measurement signal by the processing and control unit 3. An additional processing and control unit 5 of this kind may be of the type of processing and control unit or circuit used in present-day protective devices, for example of the type of processing circuit of the device described in the document W019091740. This asymmetry detection/analysis part of the processing and control unit 3 forms as it were an analog or digital electronic filter situated in the operational subsystem.

[0063] The additional processing and control unit 5 may include circuits in series, on the one hand, a circuit 5a connected to the output S of the clamp detector 1 and able to supply a signal corresponding to the rectified mean value of the fault signal, or a directly derived signal depending on the latter and, on the other hand, the circuit 5b connected to the output of the circuit 5a and able to compare said rectified average signal to a predetermined or preset reference threshold and conditionally or selectively delivering a control signal to the disconnector or breaker means as a function of the result of said comparison.

[0064] Referring to figure 5, it can be seen that the method according to the present invention may, in its implementation determining the asymmetry in the AC measurement signal by frequency-domain analysis of the latter, may consist in carrying out said frequency-domain analysis by means of Fast Fourier Transform (FFT) processing of the AC measurement signal and comparing the voltage amplitude corresponding an even harmonic, for example at least one of the first three harmonics H2, H4, H6, with the reference threshold Hs. The processing and control unit 3 of the protective device can then be configured to carry out said frequency-domain analysis by means of Fast Fourier Transform (FFT) processing of the AC measurement signal and comparing the amplitude of the voltage corresponding to an even harmonic H2, H4 or H6 with the reference threshold Hs.

[0065] Figure 7 shows the frequency spectrum obtained for an AC measurement signal of the type represented in figure 6 and including a maximum or minimum amplitude peak in each alternation, or half-period. The even harmonics H2, H4, H6 in said frequency spectrum are representative of the presence of a direct current Idc relating to a fault current occurring in the network. It will be understood that, for an AC measurement signal of this kind the even harmonics can therefore be detected either by the aforementioned detection of amplitude asymmetry or by the frequency-domain analysis also described above.

[0066] Figure 9 shows the spectrum obtained for an AC measurement signal of the type represented in figure 8 and including a saturation duration in each alternation, or half-period. The even harmonics H2, H4, H6 in said frequency spectrum are representative of the presence of a direct current Idc relating to a fault current arising in the supply. In this case Idc is strictly greater than zero. It will be understood that the even harmonics of an AC measurement signal of this kind can therefore be detected either by the detection of saturation asymmetry as described above or by frequency analysis also as described above.

[0067] Each reference threshold Vs, ts, Hs can be preset or predetermined. In the analog form of the processing and control unit 3 (figures 1 and 2) the reference threshold Vs, ts is stored for example by a capacitor that the comparator and trigger circuit 3d may include. In the digital form of the processing and control unit 3 (figures 3, 4 and 5) the reference threshold Vs, ts, Hs can be stored in a memory that the processing and control unit 3 may include.

[0068] A method of this kind and a protective device of this kind suitable for its implementation therefore makes it possible to achieve at least one of the following advantages:

[0069] - measurement of weak currents, in particular currents less than 30 mA, complying with present-day standards and in particular the type B class standard imposing tripping of the differential protective device between 15 and 60 mA and the EV type class standard imposing tripping of the differential protective device between 3 and 6 mA,

[0070] - improvement of the accuracy of the clamp detector by eliminating the dispersion largely caused by the intrinsic characteristics of the clamp la and the variations caused by the conditions of use (for example: exterior magnetic fields and temperatures),

[0071] - fewer constraints on the clamp la (reduced unit price and easy procurement),

[0072] - no calibration after fitting the protective device,

[0073] - measurement and display of AC and DC current values to the user by means of a screen integrated into said device or in another device connected to the latter,

[0074] - small overall size or volume, in particular less than that of a device of the type described in the document WO19091740, whatever the value of the weak current measured.

[0075] Of course, the invention is not limited to the embodiments described and represented in the appended drawings. Modifications remain possible, in particular from the point of view of the composition of the various elements or through substitution of technical equivalents without this departing from the scope of protection of the invention.

Claims

Claims

[Claim 1] A method for detecting leakage or fault currents in an electrical installation using a protective device providing at least differential protection, said electrical installation being powered by a current circulating in at least two conductors of an AC or DC supply, said protective device including at least one detection, processing and control module including, on the one hand, a clamp detector (1) able to generate as output (S) an AC measurement signal and including a clamp (la) through which said conductors pass and having a measurement winding (1Oa) and an AC voltage or current supply (2) able to generate an AC excitation signal to saturate the clamp (la), where applicable said clamp detector (1) including a resistance (lb) in series with said clamp (la), a processing and control unit (3) connected to the output (S) of the clamp detector and able to process the AC measurement signal to detect a leakage or fault current in the supply and to send a control signal as a function of the result of the processing to a disconnector or breaker control means (4) that said protective device further includes, characterized in that it consists in detecting asymmetry of the AC measurement signal between its positive alternation, or half-period, and its negative alternation, or half-period, generated by the presence of even harmonics (H2, H4, H6) in said AC measurement signal representative of a direct current (Idc) relating to a leakage or fault current in the supply: - either by determining, by frequency-domain analysis of the AC measurement signal, a measurement value representative of the occurrence of even harmonics (H2, H4, H6) in said AC measurement signal and then comparing said measurement value with a reference threshold (Hs) to send the control signal according to the result of the comparison, - or by measuring a first value (VI, tl) of a physical parameter of the AC measurement signal in its positive alternation, or half-period, and a second value (V2, t2) of said physical parameter in its negative alternation, or half-period, and determining the difference between said first and second values (VI, tl, V2, t2) and comparing that difference with a reference threshold (Vs, ts) to send the control signal according to the result of the comparison.
[Claim 2] The method as claimed in claim 1, characterized in that, for measuring the first value (VI) and the second value (V2), it consists in detecting amplitude asymmetry in the AC measurement signal by measuring the maximum amplitude of its positive alternation, or half-period, and the minimum amplitude of its negative alternation, or half-period, the first value (VI) being said maximum amplitude and the second value (V2) being said minimum amplitude.
[Claim3] The method as claimed in claim 1, characterized in that it consists in generating an excitation signal with a level of intensity creating in each positive or negative alternation, or half-period, of the AC measurement signal saturation of its maximum amplitude or minimum amplitude over a measurable duration and in that, for measuring the first value (tl) and the second value (t2), it consists in detecting saturation asymmetry in the AC measurement signal by measuring a first saturation duration of the maximum amplitude of its positive alternation, or half-period, and a second saturation duration of the minimum amplitude of its negative alternation, or half-period, the first value (tl) being said first saturation duration and the second value (t2) being said second saturation duration.
[Claim 4] The method as claimed in claim 1, characterized in that it consists in carrying out the frequency-domain analysis by applying Fast Fourier Transform processing to the AC measurement signal and comparing the voltage amplitude corresponding to an even harmonic (H2, H4, H6) with the reference threshold (Hs).
[Claim 5] A protective device providing at least differential protection enabling the detection of leakage or fault currents in an electrical installation, said electrical installation being powered by a current circulating in at least two conductors of an AC or DC supply, said protective device being suitable for implementation of the method as claimed in any one of claims 1 to 4 and including at least one detection, processing and control module including, on the one hand, a clamp detector (1) able to generate as output (S) an AC measurement signal and including a clamp (la) through which said conductors pass with a measurement winding (1Oa) and an AC voltage or current supply (2) able to generate an AC excitation signal to saturate the clamp (a), where applicable said clamp detector (1) including a resistance (lb) in series with said clamp (la), a processing and control unit (3) connected to the output (S) of the clamp detector and able to process the AC measurement signal to detect a leakage or fault current in the supply and to send as a function of the result of the processing a control signal to a disconnector or breaker control means (4) that said protective device further includes, characterized in that the processing and control unit (3) is configured to detect asymmetry of the AC measurement signal between its positive alternation, or half- period, and its negative alternation, or half-period, generated by the presence of even harmonics (H2, H4, H6) in said AC measurement signal representative of a direct current (Idc) relating to a leakage or fault current in the supply by determining: - either by determining by frequency-domain analysis of the AC measurement signal a measurement value representative of the occurrence of even harmonics (H2, H4, H6) in said AC measurement signal and then comparing said measurement value with a reference threshold (Hs) to send the control signal according to the result of the comparison, -or by measuring a first value (VI, tl) of a physical parameter of the AC measurement signal in its positive alternation, or half-period, and a second value (V2, t2) of said physical parameter in its negative alternation, or half-period, and then determining the difference between said first and second values (VI, tl, V2, t2) and comparing that difference with a reference threshold (Vs, ts) to send the control signal according to the result of the comparison.
[Claim 6] The protective device as claimed in claim 5, characterized in that, to be able to measure the first value (VI) and the second value (V2), the processing and control unit (3) is configured to detect amplitude asymmetry by measuring the maximum amplitude of the positive alternation, or half-period, of the AC measurement signal and the minimum amplitude of its negative alternation, or half-period, the first value (VI) being said maximum amplitude and the second value (V2) being said minimum amplitude.
[Claim 7] The protective device as claimed in claim 6, characterized in that the processing and control unit (3) is electronically configured in an analog manner and in that it includes at least the following circuits electrically connected in series: an analog measurement circuit (3a) connected to the output (S) of the clamp detector (1) and consisting of two branches (30a, 31a) connected in parallel, namely a first branch (30a) able to measure the first value (VI) and a second branch (31a) able to measure the second value (V2), an analog summator/subtractor circuit (3b) connected to the output of said measurement circuit (3a) and able to determine the difference between said first and second values (VI, V2), an analog averaging and/or rectifier and/or filter circuit (3c) connected to the output of said summator/subtractor circuit (3b) and an analog comparator and trigger circuit (3d) connected to the output of said averaging and/or rectifier and/or filter circuit (3c) able to effect the comparison between said difference and the reference threshold (Vs) to send the control signal according to the result of the comparison.
[Claim 8] The protective device according to claim 6, characterized in that the processing and control unit (3) is electronically configured in a digital manner and in that it consists in a microprocessor or microcontroller based processing and control circuit (3e) able to execute the instructions of a program loaded into a memory of said processing and control unit (3) to measure the first value (VI) and the second value (V2) and then to determine the difference between said first and second values (VI, V2) and to compare that difference with the reference threshold (Vs).
[Claim 9] The protective device as claimed in claim 5, characterized in that the AC voltage or current supply (2) is configured to generate an excitation signal with a level of intensity creating in each positive or negative alternation, or half-period, of the AC measurement signal saturation of its maximum or minimum amplitude over a measurable duration and in that the processing and control unit (3) is configured to be able to measure the first value (tl) and the second value (t2) to detect saturation asymmetry in the AC measurement signal by measuring a first saturation duration of the maximum amplitude of its positive alternation, or half-period, and a second saturation duration of the minimum amplitude of its negative alternation, or half-period, the first value (tl) being said first saturation duration and the second value (t2) being said second saturation duration.
[Claim 10] The protective device as claimed in claim 9, characterized in that the processing and control unit (3) is configured in an analog manner and includes at least the following circuits electrically connected in series: an analog measurement circuit (3a) connected to the output (S) of the clamp detector (1) and consisting of two branches (30a, 31a) connected in parallel, namely a first branch (30a) able to determine the first value (tl) and a second branch (31a) able to detect the second value (t2), an analog summator/subtractor circuit (3b) connected to the output of the measurement circuit (3a) and able to establish the difference between said first and second values (tl, t2), an analog averaging and/or rectifier and/or filter circuit (3c) connected to the output of the summator/subtractor circuit (3b) and an analog comparator and trigger circuit (3d) connected to the output of the averaging and/or rectifier and/or filter circuit (3c) and able to effect the comparison between that difference and the reference threshold (ts) to send the control signal according to the result of the comparison.
[Claim 11] The protective device as claimed in claim 9, characterized in that the processing and control unit (3) is electronically configured in a digital manner and in that it consists in a microprocessor or microcontroller based processing and (3e) able to execute the instructions of a program loaded into a memory of said processing and control unit (3) to measure the first value (tl) and the second value (t2) and then to establish the difference between said first and second values (tl, t2) and to compare that difference with the reference threshold (ts).
[Claim 12] The protective device as claimed in claim 5, characterized in that the processing and control unit (3) is configured to carry out the frequency-domain analysis of the AC measurement signal by Fast Fourier Transform processing and comparing the voltage amplitude corresponding to an even harmonic (H2, H4, H6) with the reference threshold (hs).