ARC FAULT DETECTOR WITH CIRCUIT INTERRUPTER

• US 20080140354A1
• Filed: 02/15/2008
• Published: 06/12/2008
• Est. Priority Date: 10/03/2002
• Status: Active Grant

• Current Assignee: David Kolker, Roger M. Bradley, Ross Mernyk
• Original Assignee: David Kolker, Roger M. Bradley, Ross Mernyk
• Inventors: Kolker, David, Bradley, Roger M., Mernyk, Ross
• Granted Patent: US 7,925,458 B2
• Time in Patent Office: Days
• US Class Current: 702/185
• CPC Class Codes: G01R 31/1272 of cable, line or wire insulation, e.g. using partial discharge measurements locating faults in cables G01R31/083
• CPC Class Codes: G01R 31/52 Testing for short-circuits, leakage current or ground faults
• CPC Class Codes: H02H 1/0015 Using arc detectors
• CPC Class Codes: H02H 3/162 for ac systems
• CPC Class Codes: H02H 3/334 with means to produce an artificial unbalance for other protection or monitoring reasons or remote control H02H3/338 takes precedence
• CPC Class Codes: H02H 3/44 responsive to the rate of change of electrical quantities

Abstract

There is here disclosed a method and apparatus for detecting the occurrence of arcing of a conductor by monitoring the current on an AC power line. The signal detected is split and directed along four separate paths to generate four signals having separate characteristics which represent the current in the line. A first path is for a signal representative of the current flowing in the line. A second path is for a signal having a pulse for each occurrence of a positive step change in current that is significant and has a di/dt value above a predetermined value. A third path is for a signal having a pulse for each occurrence of a negative step change in current that is significant and has a di/dt value above a predetermined value. A fourth path is for a signal having a voltage level representative of the broadband noise signal on the line. Using at least one of five different methods in combination with one of three input signals, a reference signal designated as “SINE” is generated. The SINE signal generated in combination with a CURRENT input is used to produce a control waveform “DELTA”. DELTA can be represented as a relative value or as an absolute difference between the SINE and the CURRENT. Each occurring half cycle of the DELTA signal is analyzed by, for example, a micro-controller for specific identifiable characteristics found to indicate the presence of arcing. Upon the detection of arcing, an output signal can be generated to activate a circuit interrupting mechanism, sound an audio alarm and/or alert a central monitoring station.

Claims

1. A method in an arc fault detecting device capable of being electrically connected to an electrical wiring system between line side phase and neutral conductors and load side phase and neutral conductors, said method detecting the occurrence of arcing of a conductor by monitoring the current on an AC power line, said method comprising:

detecting current in said conductor of the electrical wiring system and generating a signal representative of the detected current;

generating at least one modified signal which represents the filtered or unfiltered current detected in the conductor; and

receiving the at least one modified signal by a micro-controller and performing the following by the micro-controller;

generating a SINE signal having half cycles and zero crossings from a raw input signal, or a signal from a finite impulse response (FIR) filter, or a signal from an infinite impulse response (IIR) filter;

comparing the generated SINE signal with the at least one signals generated from the signal modifying means to generate a DELTA signal;

analyzing the DELTA signal for at least one characteristic representative of the occurrence of an arc; and

generating an output signal upon detection of the at least one characteristic representative of the occurrence of an arc.

2. The method according to claim 1, wherein the step of detecting current provides for the use of a current transformer.

3. The method according to claim 2, wherein the step of generating at least one modified signal provides a CURRENT signal representative of the current in the line.

4. The method according to claim 3, wherein the CURRENT signal is used by the micro-controller to generate the SINE signal.

5. The method according to claim 4, wherein the CURRENT signal is fed to a multipoint running finite impulse response filter to smooth the signal prior to being used to generate the SINE signal.

6. The method according to claim 4, wherein the CURRENT signal is fed to an infinite impulse response (IIR) filter to smooth the signal prior to being used to generate the SINE signal.

7. The method according to claim 3, wherein the step of generating at least one modified signal for generating the CURRENT signal provides for the use of a programmable gain amplifier controlled by the micro-controller which scales the output signal to one of a number of scales.

8. The method according to claim 7, comprising a voltage follower located between the transformer and the programmable gain amplifier, and a low pass filter located between the programmable gain amplifier and the micro-controller, wherein the programmable gain amplifier and the low pass filter operate as a D/A converter for generating the CURRENT signal.

9. The method according to claim 2, wherein the step of generating at least one modified signal provides negative and positive di/dt signals of the detected current in the line.

10. The method according to claim 9, wherein the step of generating at least one modified signal provides a signal of the high frequency noise on the line.

11. The method according to claim 2, wherein either the phase or neutral conductor is coupled to the current transformer.

12. A method in an arc fault detecting device capable of being electrically connected to an electrical wiring system between line side phase and neutral conductors and load side phase and neutral conductors, said method detecting the occurrence of arcing of a conductor by monitoring the current on an AC power line, said method comprising:

detecting current in said conductor of the electrical wiring system and generating a signal representative of the detected current;

generating a CURRENT signal which represents the filtered or unfiltered current detected in the conductor; and

receiving the CURRENT signal by a micro-controller and performing the following by the micro-controller;

generating a SINE signal having half cycles and zero crossings from a raw input signal, or a signal from a finite impulse response (FIR) filter, or a signal from an infinite impulse response (IIR) filter, when generating the SINE signal,

locates a starting CURRENT zero crossing,

finds the average of following half cycles of the CURRENT signal,

finds a peal of the same polarity as the average in that half cycle,

multiplies the peak height by the CURRENT at that point,

assumes that real zero crossings are exactly 1/240 second on either side of the peak, and

lockouts ¼

cycle from the leading zero crossing when advancing to next zero crossing,

subtracts the CURRENT signal from the generated SINE signal and divides the result by the SINE signal to obtain a DELTA signal,

analyzes the DELTA signal for at least one characteristic representative of the occurrence of an arc, and

generates an output signal upon detection of the at least one characteristic representative of the occurrence of an arc.

13. The method according to claim 12, wherein the microcontroller analyzes the DELTA signal, continuously, a half cycle at a time to identifying arcing by detecting, in a half cycle, two peaks.

14. The method according to claim 13, wherein the micro-controller further analyzes the DELTA signal for the occurrence of a second peak that is lower than the first peak to further identify arcing.

15. The method according to claim 14, wherein the micro-controller still further analyzes the DELTA signal to obtain a further indication of arcing when a half cycle containing two peaks surrounds a period of one or more half cycles during low current flow.