METHOD FOR CHECKING THE ADEQUACY AT THE RESIDUAL CURRENTS OF DIFFERENTIAL CIRCUIT BREAKERS

Abstract

A method is for checking the adequacy of the residual currents passing through a differential circuit breaker disposed at the head of an electrical installation. The method includes acquiring over a total acquisition duration, at a determined sampling frequency, residual current samples during successive acquisition periods; frequency-analyzing by FFT these residual current samples in predetermined frequency bands; determining for each frequency band and for each of the successive acquisition periods, a maximum effective current and, at the end of the total acquisition duration, recording the maximum value of the maximum effective currents; and disqualifying or not the differential circuit breaker depending on whether or not this maximum value of the maximum effective currents meets a predetermined compatibility condition and displaying this disqualification or non-disqualification in binary mode by a pictogram on the leakage current measuring clamp.

Claims

1-10. (canceled)

11. A method for checking adequacy at residual currents passing through a differential circuit breaker disposed at a head of an electrical installation, by means of a leakage current measuring clamp gripping active conductors exiting the differential circuit breaker to power a plurality of electrical appliances, the method comprising in: acquiring over a total acquisition duration (t.sub.end-t.sub.dstart), at a determined sampling frequency, residual current samples during successive acquisition periods, frequency-analyzing by FFT the residual current samples in predetermined frequency bands, determining for each frequency band and for each of the successive acquisition periods, a maximum effective current and, at an end of the total acquisition duration, recording a maximum value of maximum effective currents determined in each band frequency, and disqualifying or not the differential circuit breaker depending on whether or not this maximum value of the maximum effective currents meets a predetermined compatibility condition and displaying this disqualification or non-disqualification in binary mode by a pictogram on the leakage current measuring clamp.

12. The method according to claim 11, wherein the predetermined frequency bands are the following four: DC; DC-50 Hz; 60 Hz-1 kHz; and 1 kHz-10 kHz.

13. The method according to claim 12, wherein calculation of the FFT is reduced by determining it only up to 1 kHz, the frequency band 1 kHz-10 kHz being calculated by quadratic subtraction between the total effective current obtained over an entire frequency range of DC-10 kHz and a sum of the residual current samples obtained in the frequency band DC-1 kHz.

14. The method according to claim 13, wherein the calculation of the FFT is preceded by a Hanning or Hamming windowing applied to a determined number of residual current samples.

15. The method according to claim 11, wherein use of a differential circuit breaker of the AC, A, or F type which is not recommended is displayed on the leakage current measuring clamp respectively by at least one of the following pictograms: a crossed-out AC pictogram; a crossed-out A pictogram; and a crossed-out F pictogram.

16. The method according to claim 14, wherein the maximum current value in each of the frequency bands defining the predetermined compatibility condition and leading to the disqualification of the differential circuit breaker is given by the following table: TABLE-US-00004 Displayed DC DC-50 Hz 60 Hz-1 kHz >1 kHz pictograms >1 mA any any any a crossed-out and AC pictogram <6 mA any crossed-out AC and A 6 mA any any pictograms and <10 mA 10 mA any any any crossed-out AC, A, and F pictograms any >1 mA any any crossed-out AC and A pictograms any any >1 mA any crossed-out In AC and A pictograms any any >In any crossed-out AC, A, and F pictograms

17. The method according to claim 11, wherein the total effective current is calculated by simple quadratic addition of all the residual current samples.

18. The method according to claim 11, wherein DC current is calculated by averaging the residual current samples.

19. The method according to claim 11, wherein each of the successive acquisition periods has a fixed duration of 100 ms, the sampling frequency is 81.92 kHz and a determined number of samples for calculation of the FFT is 512.

20. A leakage current measuring clamp including an AC+DC current sensor able to measure AC or DC currents from 1 mA, over a frequency band comprised between 0 Hz and 10 kHz minimum, and a processing module specially configured to implement the method according to claim 11.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Other characteristics and advantages of the present invention will emerge from the description given below, with reference to the appended drawings which illustrate one exemplary embodiment devoid of any limitation and in which:

[0031] FIG. 1 illustrates a schematic example of a household electrical installation to which the method for checking differential circuit breakers according to the invention is applied,

[0032] FIG. 1A illustrates pictograms that can be displayed in a binary or on/off mode by the measuring clamp.

[0033] FIG. 2 shows the different steps of the method for checking differential circuit breakers according to the invention, and

[0034] FIG. 3 shows in detail the step of frequency-analyzing by FFT the residual currents of the method in FIG. 2.

DESCRIPTION OF THE EMBODIMENTS

[0035] The principle of the invention is based on a method for qualifying a standard differential protection of type AC, A, F, B/B+ implemented in an electrical installation, that is to say diagnosing or highlighting in this installation devoid of faults, an inadequacy of this differential protection with regard to the residual currents present in this installation.

[0036] This checking method consists, by gripping all the active conductors at the head of a differential circuit breaker, in identifying the differential circuit breakers not compatible with the measured residual currents and in providing, in the form of a pictogram, a simple binary indicator, an inadequacy (or non-compatibility) verdict of the installed differential protection. It will also be able to integrate the visualization of the main causes of inadequacy observed and/or measured.

[0037] FIG. 1 shows one example of a household electrical installation whose electrical panel 10 includes a differential circuit breaker 12 to be tested.

[0038] The differential circuit breaker is connected to various electrical appliances for which it ensures protection, for example: an electric oven 14, a refrigerator 16, a washing machine 18 all single-phase supplied and a three-phase supplied inverter heat pump 20. The installation is assumed to be in operation and without defects as mentioned previously (the invention has no meaning in a defective installation).

[0039] According to the invention, the method for checking the adequacy of this differential circuit breaker 12 at the residual currents passing therethrough is implemented in this installation by means of a measuring device 30 gripping all of the active conductors (phase(s)) +neutral) connected at the output of the differential circuit breaker. Such a measuring device is for example a leakage current measuring clamp as described in the Application FR2206239 filed in the name of the Applicant, including an AC+DC leakage current sensor able to accurately measure AC or DC currents from 1 mA, on a frequency band comprised between 0 Hz and 10 kHz minimum, whose measurement processing module is specially configured to implement this innovative method.

[0040] The different steps of this method are illustrated in FIG. 2.

[0041] Once the measuring clamp 30 has been placed by the operator so as to grip all the active conductors (phase(s)+neutral) exiting the differential circuit breaker 12, the first step 40 of the method consists in carrying out over a total acquisition duration set by the operator (as will be detailed below) successive acquisitions, for example per period of 100 ms, of the residual current present in the installation and circulating in this differential circuit breaker.

[0042] In a second step 42, the measured residual currents are subject to a frequency analysis in four predetermined frequency bands: DC; DC-50 Hz; 60 Hz-1 kHz; and 1 kHz-10 kHz. DC meaning the frequency 0 Hz and the open or closed brackets meaning respectively an exclusion or an inclusion of the boundary frequency of the associated frequency range.

[0043] Then, in a following step 44, for each acquisition period and in each frequency band, a maximum effective current (Imax.sub.DC, Imax.sub.DC-50Hz, Imax.sub.60 Hz-1kHz, Imax.sub.1kHz-10kHz) corresponding to the maximum value of the residual currents measured in a determined frequency band and for a determined acquisition period, is calculated and recorded in memory. At the end of the total acquisition duration, the maximum value (maximum maximorum) of these maximum effective currents is recorded in turn.

[0044] Finally, in a fourth and last step 46, this maximum value of the maximum effective currents obtained in each frequency band is used as a compatibility condition to segregate the different types of differential circuit breakers in accordance with the aforementioned standards and therefore disqualify a particular circuit breaker by informing the operator with a simple binary signal which can be typically indicated by a pictogram or an icon. However, in order not to keep the operator waiting if, for example, it is already known that the AC circuit breaker is not compatible, it is possible to carry out this segregation step and the pictogram display step which will be detailed further at the same time as the calculation of the maximum of maximums, that is to say in particular every 100 ms.

[0045] To avoid a problem of blinding on some differential circuit breakers in the presence of current >1 kHz, it is also possible to inform the operator about the value of the current in this band and, if this current is significant, to recommend that he not use the AC type circuit breaker.

[0046] The total duration of acquisition of the measurements (t.sub.end-t.sub.start) and therefore of the corresponding frequency analysis depends on the nature of the charges connected to the differential circuit breaker 12. It is up to the operator to estimate this duration because it is he who has knowledge of the nature of the charges connected to the differential circuit breaker. The objective is to be able to record all the operating modes of the appliances. Some illustrative examples are given in the table below:

TABLE-US-00002 Total acquisition Type of charge duration Home automation charge (computer, <1 minute luminaire, roller shutter . . . ) Compressor system: 10 minutes Refrigerator, freezer Older generation PAC Variable-frequency driven system: <1 minute Next generation PAC with inverter Next generation refrigerator with inverter Steam oven with inverter Car battery charger Electrical appliances 60 minutes Washing machine

[0047] The first step of acquiring the current measurements is more specifically detailed below.

[0048] The analog signals derived from the current sensor are sampled using an analog-to-digital converter in the measuring clamp processing module. The sampling frequency should be set so as to be able to acquire the highest frequency. For example, to accurately measure the 10 kHz, a sampling frequency of at least 50 kHz should be chosen. Likewise, the duration of the acquisition must at least be greater than one period of the electrical network (i.e. 20 ms for the 50 Hz and 16.66 ms for the 60 Hz). This duration can be variable depending on the network period measured, but it is preferably fixed for reasons of simplicity and robustness. Typically, a fixed duration equal to 100 ms is preferred because it represents an integer number of periods for both the 50 Hz (5 periods) and the 60 Hz (6 periods). Thus, a sampling at 50 kHz would allow collecting 5,000 measurement samples out of 100 ms.

[0049] The second frequency analysis step is now detailed with reference to FIG. 3. This is carried out by a Fast Fournier Transform (FFT) algorithm 50 which requires, for correct operation, a number of samples multiple of n=2.sup.p. The sampling frequency is therefore preferably chosen at 81.92 kHz thus making it possible to obtain 8,192 samples of the residual current (n=2.sup.13) over the period of 100 ms.

[0050] A windowing 52, of the Hanning or Hamming type for example, precedes the calculation of the FFT in order to obtain a smoother result of the FFT. The duration of the calculation depends on the number of samples and is proportional to n.log(n). The memory of the processing module needed for this calculation is also proportional to n. Also, to reduce the size of the memory necessary for storing the samples and save calculation time, it is chosen to perform this calculation of the FFT only up to 1Khz (block 56 of low-pass filtering) and also not to take that 1 sample out of 16 (decimation block 54) is only 512 samples out of the 8,192 collected.

[0051] Given that the calculation of the FFT must only relate to four frequency bands, this simplification of the calculation by the decimation module 54 and the use of low-pass filtering 56 determining the FFT only up to 1 kHz, makes it possible to calculate the frequency band 1 kHz-10 kHz by quadratic subtraction between the total effective current (calculation block 58) obtained over the entire frequency range DC-10 kHz and the sum of the samples of the FFT (calculation block 60) obtained in the frequency band DC-1 kHz. The total effective current is calculated by simple quadratic addition of all the samples. The DC current is also obtained from the FFT but can be calculated more accurately by averaging the samples (calculation block 62).

[0052] This innovative technique makes it possible to reduce the calculation time of the FFT by approximately 23 (to the initial saving in calculation time of the FFT of 170 due to decimation, it is necessary to add the calculation of the low-pass filter at 1 kHz and the quadratic subtraction that reduces this ratio to approximately 23) and therefore, as indicated previously, to reduce the size of the memory by 16.

[0053] The last step of the method allowing the information to the operator on the disqualification or non-disqualification of the tested differential circuit breaker is detailed below. Indeed, the calculation of the maximum value of the maximum effective currents in the four frequency bands allows, depending on its level, segregating the 4 types of differential circuit breaker according, for example, to the IEC 60755 standard (AC/A/F/B).

[0054] For this, and thus for simplifying the analysis result for the operator, the pictograms illustrated in FIG. 1A can be displayed in a binary or on/off mode: [0055] Crossed-out AC pictogram (70): the use of AC type differential circuit breaker is not recommended [0056] Crossed-out A pictogram (72): the use of A type differential circuit breaker is not recommended [0057] Crossed-out F pictogram (74): the use of F type differential circuit breaker is not recommended

[0058] The table below sets the maximum current value in each frequency band leading to the disqualification of some differential circuit breakers:

TABLE-US-00003 Displayed DC DC-50 Hz 60 Hz-1 kHz >1 kHz pictograms >1 mA XXX XXX XXX Crossed-out and AC pictogram <6 mA (70) >6 mA XXX XXX XXX Crossed-out and AC and A <10 mA pictograms (70, 72) 10 mA XXX XXX XXX Crossed-out AC, A, and F pictograms (70, 72, 74) XXX >1 mA XXX XXX Crossed-out AC and A pictograms (70, 72) XXX XXX >1 mA XXX Crossed-out In AC and A pictograms (70, 72) XXX XXX >In XXX Crossed-out AC, A, and F pictograms (70, 72, 74) XXX = any and In an uncertainty

[0059] A threshold exceeded on the DC current leads to a potential safety problem with the blinding and the non-tripping of the differential protection in the event of an insulation fault,

[0060] A threshold exceeded on the frequency bands DC-50 Hz and 60 Hz-1 kHz does not result in a safety risk but in unwanted potential tripping,

[0061] Too high a current in the band >1 kHz can lead to a potential safety problem on the differential circuit breakers with the blinding and the non-tripping of the differential protection in the event of an insulation fault.

[0062] It will be noted that, if in the aforementioned example, the frequency band greater than 1 kHz is not used for the selection of the differential circuit breakers, nothing prevents it from doing so if the need arises, in particular in the context of the VDE 0664-100 standard or any other to come.