ARC DETECTION USING DISCRETE WAVELET TRANSFORMS

• US 20100020451A1
• Filed: 07/24/2008
• Published: 01/28/2010
• Est. Priority Date: 07/24/2008
• Status: Active Grant

• Current Assignee: ABB Schweiz AG (ABB Limited)
• Original Assignee: General Electric Company
• Inventors: Hooker, John Kenneth, Hall, Scott Jeffrey, Grigoryan, Konstantin Vladimir, Changali, Sriram
• Granted Patent: US 8,054,591 B2
• Time in Patent Office: Days
• US Class Current: 361/42
• CPC Class Codes: H02H 1/0015 Using arc detectors
• CPC Class Codes: H02H 1/0092 concerning the data processing means, e.g. expert systems, neural networks

Abstract

An apparatus to perform series and parallel arc fault current interruption (AFCI). The apparatus includes a resistive element configured to sense a load from which a current signal is generated, a first detection unit configured to output a first signal based on the current signal, and a microcontroller configured to decompose at least the first signal via discrete wavelet transforms to thereby obtain discrete wavelet coefficients, and to generate a trip signal when the discrete wavelet coefficients indicate that a threshold condition for trip signal generation are satisfied.

Claims

1. An apparatus to perform series and parallel arc fault current interruption (AFCI), the apparatus comprising:

a resistive element configured to sense a load from which a current signal is generated;

a first detection unit configured to output a first signal based on the current signal; and

a microcontroller configured to decompose at least the first signal via discrete wavelet transforms to thereby obtain discrete wavelet coefficients, and to generate a trip signal when the discrete wavelet coefficients indicate that a threshold condition for trip signal generation are satisfied.

2. The apparatus according to claim 1, further comprising a second detection unit disposed in parallel with the first detection unit and configured to output a second signal based on the current signal.

3. The apparatus according to claim 1, further comprising a current measurement unit disposed in parallel with the first detection unit and configured to output a measurement signal, which is based on the current signal, such that the threshold condition for trip signal generation are a function of the current measurement.

4. The apparatus according to claim 2, further comprising a current measurement unit disposed in parallel with the first and second detection units and configured to output a measurement signal, which is based on the current signal, such that the threshold condition for trip signal generation are a function of the current measurement.

5. The apparatus according to claim 1, further comprising a summing amplifier operably disposed between the resistive element and the first detection unit, wherein the microcontroller is coupled to the summing amplifier.

6. The apparatus according to claim 1, further comprising an ambient temperature sensor coupled to the microcontroller by which the microcontroller determines whether to compensate for temperature changes of the resistive element.

7. The apparatus according to claim 1, wherein the first detection unit operates at a sampling rate of 300 kHz and filters all but those sub-signals having frequencies of about 6 kHz-60 Hz from the current signal.

8. The apparatus according to claim 7, wherein the first detection unit comprises a series arc detection unit and includes a set of filters in series.

9. The apparatus according to claim 2, wherein the second detection unit operates at a sampling rate of 10 kHz and filters all but those sub-signals having frequencies of about 150-900 Hz from the current signal.

10. The apparatus according to claim 9, wherein the second detection unit comprises a parallel arc detection unit and includes a set of filters in series.

11. The apparatus according to claim 3, wherein the current measurement unit operates at a sampling rate of 10 kHz.

12. A method of performing series and parallel arc fault current interruption (AFCI), the method comprising:

sensing a load current;

sampling a signal based on the sensed load current at a high frequency;

when the high frequency sampling is complete and, if a zero cross is determined to have been sampled, computing zero cross discrete wavelet coefficients;

when the high frequency sampling is complete and, if the zero cross is determined to have not been sampled, computing non-zero cross discrete wavelet coefficients; and

issuing a trip signal if a threshold criterion is determined to have been met based on the zero and non-zero cross discrete wavelet coefficients.

13. The method according to claim 12, further comprising sampling a signal based on the sensed load current at a medium frequency.

14. The method according to claim 13, further comprising:

sampling the signal at a low frequency while the high frequency sampling is determined to not be complete; and

computing a rolling average of the low frequency filtered signal when the low frequency sampling is determined to be completed.

15. The method according to claim 14, further comprising:

when the high frequency sampling is complete and, if a zero cross is determined to have been sampled, computing zero cross discrete wavelet coefficients from at least the rolling average; and

when the high frequency sampling is complete and, if the zero cross is determined to have not been sampled, computing non-zero cross discrete wavelet coefficients from at least the rolling average.

16. The method according to claim 14, wherein, if the low frequency sampling is determined to not be complete or if the threshold criterion is determined to have not been met, continuing the medium and/or the high frequency sampling.

17. The method according to claim 14, wherein the sampling at the medium and/or the high frequency occurs in accordance with a conversion of the sensed load current into the signal, and a determination of whether a root mean square (RMS) length of the low frequency signal is sampled, and further comprising:

determining whether the signal registers a positive zero cross subsequent to the determination of whether the RMS length is sampled and before the sampling occurs.

18. The method according to claim 17, further comprising:

setting delays for negative zero cross for zero cross sampling and non zero cross sampling;

triggering the medium and/or the high frequency sampling, if the signal does not register a positive zero cross, or

setting delays for positive zero cross for zero cross sampling and non zero cross sampling; and

triggering the medium and/or the high frequency sampling, if the signal registers a positive zero cross.

20. The method according to claim 18, wherein the decomposing comprises decomposing the medium and/or the high frequency filtered current signal using discrete wavelet transforms obtained from the low frequency filtered current signal, and wherein the issuing of the trip decision comprises:

comparing the summed respective energies of the discrete wavelet coefficients with a threshold condition; and

determining whether the summed respective energies exceed the threshold condition for trip signal issuance.

19. A method of operating a current interrupter by detecting series and parallel arcs, the method comprising:

sensing a load current and generating a current signal therefrom;

low frequency filtering the current signal and determining a fundamental frequency and a zero-cross of the low frequency filtered current signal under different load conditions;

medium and/or high frequency filtering the current signal and decomposing the medium and/or the high frequency filtered current signal to predetermined levels to obtain discrete wavelet coefficients;

sampling the medium and/or the high frequency filtered current signal across the zero-cross and across a pre-determined non zero-cross region;

computing absolute values of the discrete wavelet coefficients for the sampled medium and/or the sampled high frequency current signal at the zero-cross and the non zero-cross thereof, and

summing respective energies of the computed absolute values of the discrete wavelet coefficients and issuing a trip decision based on the summed respective energies.