PARALLEL ARC DETECTION USING DISCRETE WAVELET TRANSFORMS

• US 20100165521A1
• Filed: 12/29/2008
• Published: 07/01/2010
• Est. Priority Date: 12/29/2008
• Status: Active Grant

• Current Assignee: ABB Schweiz AG (ABB Limited)
• Original Assignee: General Electric Company
• Inventors: CHANGALI, Sriram, Grigoryan, Konstantin V., Hooker, John Kenneth, Hall, Scott Jeffrey
• Granted Patent: US 8,170,816 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
• CPC Class Codes: H02H 3/08 responsive to excess current responsive to abnormal temperature caused by excess current H02H5/04

Abstract

An apparatus to perform parallel arc fault current interruption (AFCI). The apparatus includes a current sensing device disposed in the electrical circuit to sense an electrical load, the current sensing device configured to produce an output signal representative of a load current passing therethrough, a detection unit, in signal communication with the current sensing device and configured to receive the output signal produced by the current sensing device, the detection unit being configured and disposed to output a secondary signal based on the output signal, and a microcontroller coupled to the detection unit, being responsive to computer executable instructions which, when executed by the microcontroller, cause the microcontroller to receive and to decompose the secondary signal via discrete wavelet transforms to thereby obtain discrete wavelet coefficients, and to compute a sum of the discrete wavelet coefficients, and to compare the sum of the discrete wavelet coefficients to a predetermined threshold, and to generate a trip signal when the sensed load current is above a predetermined threshold and the sum of the discrete wavelet coefficients cooperatively indicate that predetermined threshold conditions for trip signal generation are satisfied

Claims

1. An apparatus for interrupting current in an electrical circuit, the apparatus comprising:

a current sensing device disposed in the electrical circuit to sense an electrical load, the current sensing device configured to produce an output signal representative of a load current passing therethrough;

a detection unit, in signal communication with the current sensing device and configured to receive the output signal produced by the current sensing device, the detection unit being configured and disposed to output a secondary signal based on the output signal; and

a microcontroller coupled to the detection unit, being responsive to computer executable instructions which, when executed by the microcontroller, cause the microcontroller to receive and to decompose the secondary signal via discrete wavelet transforms to thereby obtain discrete wavelet coefficients, and to compute a sum of the discrete wavelet coefficients, and to compare the sum of the discrete wavelet coefficients to a predetermined threshold, and to generate a trip signal when the sensed load current is above a predetermined threshold and the sum of the discrete wavelet coefficients cooperatively indicate that predetermined threshold conditions for trip signal generation are satisfied.

2. The apparatus of claim 1, further comprising:

a current measurement unit, configured to output to the microcontroller a measurement signal, which is related to a timing of the output signal and which is employed by the microcontroller in a determination of whether the threshold conditions are satisfied.

3. The apparatus of 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 current sensing device.

4. The apparatus of claim 1, further comprising a summing amplifier operably disposed between the current sensing device and the detection unit and in signal communication with the microcontroller,

wherein the summing amplifier includes a filter, and wherein the filter and the detection unit are configured to cooperatively filter components of the secondary signal having frequencies outside of a range of about 150-900 kHz from the secondary signal.

5. The apparatus of claim 1, wherein the discrete wavelet coefficients are obtained from components of the secondary signal having frequencies in a range of about 5-10 kHz.

6. The apparatus of claim 1, further comprising a detection circuit, disposed in signal communication with the microcontroller, wherein the detection circuit is further configured and disposed to detect a zero cross instance of the output signal and to instruct the microcontroller to subsequently decompose the secondary signal.

7. The apparatus of claim 6, wherein the microcontroller is further responsive to computer executable instructions which, when executed by the microcontroller, cause the microcontroller to decompose the secondary signal separately for positive and negative half cycles.

8. The apparatus of claim 1, wherein the microcontroller further comprises an integrator.

9. The apparatus of claim 8, wherein the sum of the discrete wavelet coefficients is integrated over a predetermined coefficient threshold.

10. The apparatus of claim 9, wherein the microprocessor issues a trip signal for use in interrupting an operation of the electrical circuit when the sensed load current is above a predetermined threshold and the value of the integrator is above a predetermined threshold condition.

11. A computer implemented method of performing arc fault current interruption (AFCI) for a circuit, the method comprising:

sensing a load current at a current sensing device in electrical communication with the circuit;

generating a secondary signal reflective of a current of the sensed load current at a detection unit in signal communication with the current sensing device;

sampling the secondary signal at a predetermined frequency at a microcontroller coupled to the detection unit;

determining the magnitude of the secondary signal;

computing discrete wavelet coefficients from components of the secondary signal;

computing a sum of the discrete wavelet coefficients;

comparing the sum of the discrete wavelet coefficients to a predetermined threshold;

determining if threshold criteria have been met based on the sum of the discrete wavelet coefficients and the magnitude of the secondary signal; and

if so,

issuing a trip signal to interrupt an operation of the circuit.

12. The method of claim 11, further comprising:

sensing an ambient temperature relative to the current sensing device; and

compensating for changes of the ambient temperature.

13. The method of claim 11, further comprising:

filtering the secondary signal to exclude frequencies outside of a range of about 150-900 kHz from the secondary signal.

14. The method of claim 11, wherein, if the sampling of the secondary signal at the predetermined frequency is determined to not be complete or if the predetermined threshold is determined to have not been met:

continuing the sampling of the secondary signal at the predetermined frequency.

15. The method of claim 11, further comprising:

triggering the sampling of the secondary signal when the secondary signal registers a positive or negative zero cross

16. The method of claim 15, further comprising:

decomposing the secondary signal separately for the positive and negative half cycles.

17. The method of claim 11, further comprising:

integrating, over a predetermined coefficient threshold, the sum of the discrete wavelet coefficients to determine an integrator value.

18. The method of claim 17, further comprising

reducing the integrator value at a predetermined rate;

and wherein the determining if threshold criteria have been met further comprises comparing the integrator value with a predetermined integrator value threshold.

19. The method of claim 17, wherein the determining if threshold criteria have been met further comprises:

comparing the integrator value with a predetermined integrator value threshold.

20. A computer implemented method of performing arc fault current interruption (AFCI) for a circuit, the method comprising:

decomposing portions of a secondary signal, which is generated at a detection unit as being based on a load current sensed by a current sensing device with which the detection unit is in signal communication, into detailed and approximate coefficients, respectively, using discrete wavelet transforms;

with the first portion of the secondary signal determined to have been zero cross sampled, computing a sum of absolute values of the discrete waveform coefficients for the positive and or negative half cycles of the secondary signal;

comparing the sum of the absolute values with a first predetermined threshold or, if a current of the sensed load is below a pre-selected magnitude, integrating the sum of the absolute values over a predetermined coefficient threshold;

comparing the value of the integrated sum of the absolute values with a predetermined integrator value threshold; and

issuing a trip signal to interrupt an operation of the circuit if a result of the comparison indicates that the corresponding one of the first and second predetermined thresholds is exceeded over a given period of time

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

sensing a load current and generating a current signal therefrom;

frequency filtering the current signal;

determining a fundamental frequency of the filtered current signal;

detecting a zero-cross of the voltage and/or current of the filtered signal;

determining the magnitude of the filtered current signal;

filtering the current signal and decomposing the filtered current signal to predetermined levels to obtain discrete wavelet coefficients;

sampling the filtered current signal during positive and negative half-cycles;

computing absolute values of the discrete wavelet coefficients for the sampled filtered current signal for the positive and negative half-cycles; and

summing the computed absolute values of the discrete wavelet coefficients of the sampled filtered current signal for the positive and negative half-cycles;

comparing the sum of the absolute values of the discrete wavelet coefficients of the sampled filtered current signal for the positive and/or negative half-cycles with a predetermined coefficient sum threshold level;

determining if threshold criteria for a parallel arc detection have been met based on the

     1) comparison of the sum of the absolute values of the discrete wavelet coefficients of the sampled filtered current signal for the positive and/or negative half-cycles with a predetermined coefficient sum threshold level, and

     2) the magnitude of the secondary signal; and

,

issuing a trip signal to operate the current interrupter.

22. The method of claim 21, further comprising:

integrating, over a predetermined coefficient threshold, the sum of the absolute values of the discrete wavelet coefficients of the sampled filtered current signal for the positive and/or negative half-cycles, to determine an integrator value; and

,

wherein the determining if threshold criteria have been met further comprises;

comparing the integrator value with a predetermined integrator value threshold.

23. The method of claim 22, further comprising:

reducing the integrator value at a predetermined rate, if the sum of the absolute values of the discrete wavelet coefficients of the sampled filtered current signal for the positive and/or negative half-cycles is less than a predetermined coefficient sum threshold level.