Method and circuit for detecting an electric arc in a circuit, and switching device using such a circuit

Patent metadata

Field	Value
Publication number	US-10211618-B2
Application number	US-201515116044-A
Country	US
Kind code	B2
Filing date	Feb 3, 2015
Priority date	Feb 3, 2014
Publication date	Feb 19, 2019
Grant date	Feb 19, 2019

Abstract

A method and a circuit for detecting an electric arc in an electric circuit supplied with AC current during a supply period includes measuring at least one input signal (S) among a current (I) and an input voltage (U) of the electric circuit, supplying a warning signal (A 1 ) to indicate that an electric arc occurs when the input signal (S) is constant over at least one portion of the supply period, digitally sampling the input signal (S) during the measurement thereof according to predetermined levels and, to identify that the input signal (S) is constant, determining the frequency at which each level is reached by the input signal (S) over a predetermined time window, comparing the frequency of each level with a predetermined warning threshold, and issuing the warning signal if the frequency of at least one of the levels is higher than the warning threshold.

First claim

The invention claimed is:

1. A method for detecting an electrical arc in an electrical circuit supplied with alternating current according to a power supply period, comprising:
operating a detection circuit to measure at least one input signal (S), from between a power supply current (I) measured by a current measurement device and a power supply voltage (U) measured by a voltage measurement device, to the electrical circuit;
operating the detection circuit to supply a warning signal (A 1 ) indicating that an electrical arc is occurring when the input signal (S) is constant over at least a part of the power supply period;
using a clock to digitally sample the input signal (S) when it is measured according to predetermined levels;
determining over a predetermined time window a respective frequency at which each respective level of the predetermined levels is reached by the input signal (S) to identify that the input signal (S) is constant;
comparing the frequency of each level with a predetermined warning threshold; and,
delivering the warning signal if the frequency of at least one of the levels is greater than the warning threshold and controlling an opening of the electrical circuit by a switch.

2. The method according to claim 1 , wherein the detection circuit comprises:
a frequency memory for storing the frequencies of the levels, the frequency memory comprising registers and a first address bus (Addr 1 ) receiving the sampled value of the input signal (S),
addition means for incrementing by 1 one of the registers to which the value supplied on the first address bus (Addr 1 ) points,
a first in-first out memory receiving the sampled value of the input signal (S) on an input and supplying a shifted value (D) on an output, a second address bus (Addr 2 ) of the frequency memory receiving the shifted value (D), and
subtraction means for decrementing by 1 the register to which the shifted value on the second address bus (Addr 2 ) points, the addition, the subtraction and the shift in the first in-first out memory being carried out within the same cycle.

3. The method according to claim 1 , further comprising:
establishing other warning signals according to at least one of detection by spectral analysis, detection by interpolation filter, or time differentiation method; and
combining the other warning signals to determine a turn-off command for the electrical circuit.

4. The method according to claim 3 , wherein the input signal (S) includes the current signal (I), the determination of the turn-off command (C) taking into account an intensity of the current signal (I) during the warning period, a frequency of the warning signals (N), and an average duration (t arc ) of the warning signal.

5. The method according to claim 4 , wherein a cut-out command is issued if a pair frequency (N) of the warning signals and average duration (t arc ) of the warning signals is above a first curve with a decreasing hyperbolic form, or if a pair warning current intensity and average duration is above a second curve with a decreasing hyperbolic form.

6. The method according to claim 1 , further comprising storing in a respective register of a frequency memory respective frequencies of the respective levels, wherein the comparing of the frequency of each level is performed by comparing the respective stored frequencies of the respective levels to respective warning thresholds to determine if the input signal is constant.

7. A detection circuit for detecting the presence of an electrical arc in an electrical circuit powered with alternating current according to a power supply period, the detection circuit comprising:
measurement means for establishing at least one input signal (S) from between a voltage signal (U) and a current signal (I) respectively representative of the voltage (U) and of the current intensity (I) supplying the electrical circuit, the detection circuit being configured for delivering a warning signal (A 1 ) indicating that an electrical arc is occurring when the input signal (S) is constant over at least a part of the power supply period,
sampling means for digitally sampling the input signal (S) when it is measured according to predetermined levels;
processing means for identifying that the input signal (S) is constant, determining a frequency at which each level is reached by the input signal (S) over a predetermined time window, comparing the frequency of each level with a predetermined warning threshold, and delivering the warning signal if the frequency of at least one of the levels is greater than the warning threshold.

8. An electrical switching device comprising:
switching means for opening and closing an electrical circuit powered with alternating current according to a power supply period: and
a detection circuit for controlling the switching means, wherein the detection circuit comprises:
measurement means for establishing at least one input signal (S) from between a voltage signal (U) and a current signal (I) respectively representative of the voltage (U) and of the current intensity (I) supplying the electrical circuit, the detection circuit being configured for delivering a warning signal (A 1 ) indicating that an electrical arc is occurring when the input signal (S) is constant over at least a part of the power supply period,
sampling means for digitally sampling the input signal (S) when it is measured according to predetermined levels; and
processing means for identifying that the input signal (S) is constant, determining a frequency at which each level is reached by the input signal (S) over a predetermined time window, comparing the frequency of each level with a predetermined warning threshold, and delivering the warning signal if the frequency of at least one of the levels is greater than the warning threshold.

Assignees

• Leach Int Europe Sa
• Univ De Lorraine

Inventors

• Andrea Jonathan
• Schweitzer Patrick
• Weber Serge
• Tisserand Etienne
• Bournat Marc

Classifications

• G01R31/333

  Testing of the switching capacity of high-voltage circuit-breakers {; Testing of breaking capacity or related variables, e.g. post arc current or transient recovery voltage} · CPC title

• H02H3/46

  responsive to frequency deviations · CPC title

• H01H9/50

  Means for detecting the presence of an arc or discharge · CPC title

• H02H1/0015 Primary

  Using arc detectors · CPC title

• H01H9/30

  Means for extinguishing or preventing arc between current-carrying parts · CPC title