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EP-4492598-B1 - METHOD FOR CHECKING THE RESIDUAL CURRENT SUITABILITY OF DIFFERENTIAL CIRCUIT BREAKERS

EP4492598B1EP 4492598 B1EP4492598 B1EP 4492598B1EP-4492598-B1

Inventors

  • PALANCHE, DENIS
  • PILLIAS, Benoît

Dates

Publication Date
20260513
Application Date
20240617

Claims (10)

  1. A method for checking the adequacy at the residual currents passing through a differential circuit breaker (12) disposed at the head of an electrical installation (10), by means of a leakage current measuring clamp (30) gripping the active conductors exiting the differential circuit breaker to power a plurality of electrical appliances (14, 16, 18, 20), the method consisting in: - acquiring over a total acquisition duration (t end - t dstart ), 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 thus 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.
  2. The method according to claim 1, wherein the predetermined frequency bands are the following four: DC ; ]DC - 50Hz[ ; ]60Hz - 1kHz] and ]1kHz - 10kHz].
  3. The method according to claim 2, wherein the calculation of the FFT is reduced by determining it only up to 1kHz, the frequency band ]1kHz - 10kHz] being calculated by quadratic subtraction between the total effective current obtained over the entire frequency range [DC - 10kHz] and the sum of the residual current samples obtained in the frequency band ]DC - 1kHz].
  4. The method according to claim 3, wherein the calculation of the FFT is preceded by a Hanning or Hamming windowing applied to a determined number of residual current samples.
  5. The method according to any one of claims 1 to 5, wherein the 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 the following pictograms:
  6. The method according to claim 4, 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: DC ]DC - 50Hz[ ]60Hz - 1kHz] >1kHz Displayed pictograms >1mA and <6mA any any any ≥ 6mA and <10mA any any any ≥ 10mA any any any any >1mA any any any any >1mA any ≤ IΔn any any > IΔn any
  7. The method according to any one of claims 1 to 6, wherein the total effective current is calculated by simple quadratic addition of all the residual current samples.
  8. The method according to any one of claims 1 to 7, wherein the DC current is calculated by averaging the residual current samples.
  9. The method according to any one of claims 1 to 8, wherein each of the successive acquisition periods has a fixed duration of 100ms, the sampling frequency is 81.92kHz and the determined number of samples for the calculation of the FFT is 512.
  10. A leakage current measuring clamp including an AC+DC current sensor able to measure AC or DC currents from 1mA, over a frequency band comprised between 0Hz and 10kHz minimum, and a processing module specially configured to implement the method according to any one of claims 1 to 9.

Description

Technical Field The present invention relates to the field of monitoring electrical equipment and installations by differential protection consisting of comparing the currents entering and leaving these equipment and installations, in order to ensure the protection of persons against direct electrical contact resulting from a fault in these equipment or installations and it relates more particularly to a method for verifying the proper suitability of this differential protection with the leakage or residual currents emanating from these equipment and installations. Previous technique Differential protection is implemented in electrical installations through two families of devices, namely residual current switches and residual current circuit breakers, the latter being by nature very selective (i.e. sensitive but not too much) also integrating overcurrent detection in order to ensure both protection against earth fault and overloads. The increasingly widespread use of power electronics in power supplies, in their control but also in the products powered has led to the appearance of residual currents of complex nature and form, with, depending on the case, a DC component, low frequency components but also high frequency components. Also, the international standard IEC 60755 and its German equivalent VDE 0664-100 primarily define four families of residual current circuit breakers according to the nature of their tripping: type AC when this tripping is ensured by an alternating current without a DC component, type A when a pulsed current superimposed on a DC component of at most 6mA can also ensure this tripping, type F when this DC component is at most 10mA and Composite currents can also trigger this circuit, and type B/B+ allows for this triggering when a direct current or a high-frequency residual current (possibly exceeding 420mA for type B+) is also used. High frequency is defined as a frequency up to 1 kHz. In some cases, disturbances originating from the power grid or its environment can cause nuisance tripping of the residual current circuit breaker (RCCB), resulting in power outages even when there is no actual danger. This type of tripping, often repetitive, is very detrimental to the quality of the power supply and leads to operational losses for the user. These disturbances can also cause the breaker to fail to trip in the presence of a fault, and therefore a danger, due to a decrease in sensitivity in the detection of dangerous fault currents. This situation should not be overlooked as it affects safety. Among the main types of disturbances that can cause false alarms, the following should be particularly noted: Permanent leakage currents are higher the larger the electrical installation. In any electrical installation, there is a permanent leakage current to earth due either to imbalances in the natural leakage capacitances of the live conductors to earth (three-phase circuits), or to capacitances between a phase and earth for single-phase circuits which may originate from the filter capacitors connected to the ground of certain electronic equipment (automation, communication systems, computer networks, etc.). High-frequency leakage currents, present as harmonics or transients (resulting, for example, from switching operations during power-up), can originate from computer equipment power supplies, frequency converters, variable-speed motor drives, and fluorescent lighting systems. They can also result from proximity to medium-voltage switching devices and capacitor banks used for reactive power compensation. Among the main types of disturbances that can lead to a failure to trigger, the following are particularly noteworthy: Permanent currents with a direct current component, as well as permanent currents with a very low frequency component (typically less than a few Hz), while these currents inherently pose low or minimal risks to personal safety, their ability to saturate the magnetic core—the active element in detecting residual currents—leads to the ineffectiveness of some residual current circuit breakers due to blinding. The temperature can impact the mechanical components of the circuit breaker. Thus, in order to operate under optimal safety conditions without nuisance tripping or non-tripping, residual circuit breakers must be traversed by residual currents of very specific shapes depending on their type (AC, A, F, B/B+). However, to date, the only existing measurement devices are not capable of simply determining this adequacy. These are either simple portable devices, such as leakage current clamps without DC component management, or fixed devices, such as insulation testers, installed at the head of the electrical installation into which a control signal is injected, or even analysis and expertise centers that are particularly complex to use even for a seasoned technician. Examples of differential protection verification devices are disclosed in the publications JP 2006-184242 A , JP