Electric arc monitoring systems

Details Electric arc monitoring systems Electric arc monitoring systems

2002-02-13

2004-08-03

Hoff, Marc S. (Department: 2857)

Data processing: measuring, calibrating, or testing

Measurement system in a specific environment

Electrical signal parameter measurement system

C361S063000

Reexamination Certificate

active

06772077

ABSTRACT:

TECHNICAL FIELD
The technical field of the invention includes methods and apparatus for monitoring, detecting, indicating, evaluating and signaling electric arcs or sparks.
BACKGROUND
The chaotic electromagnetic emanations manifesting themselves as electric arcs or sparks are closely Linked to matter, wherein electromagnetic interactions bind electrons to nuclei in atoms and molecules and wherein the fundamental unit of electromagnetic radiation is the photon.
Indeed, spectra of electric arcs and sparks extend practically from DC through the entire radio-frequency spectrum and through microwave, infrared and light spectra.
Useful exploitations of the electric arc and spark phenomenon include the electric arc lamp, electric welding, the electric-arc-type of metallurgical furnace, the arc type of ion generator in satellite thrusters and for propulsion in outer space, the spark-plug-type of ignition in internal combustion engines, and electric spark ignition in gas appliances.
Unfortunately, the same quality of the electric arc or spark that led to electric lighting, electric arc welding and metallurgy, and ignition of internal combustion, has catastrophic effects in electrical faults that cause explosions or devastating fires through chaotic arcing or sparking.
A tragic example of this is seen in TWA flight 800 which on 17 Jul. 1996 exploded over the Atlantic Ocean shortly after taking off from John F. Kennedy Airport. That disaster, including its loss of all 230 persons aboard, sparked the most extensive governmental investigation in the history of aviation. As a result, it became known that the disaster started as a fuel/air explosion in the almost empty center fuel tank. After theories of sabotage were discounted, the most likely cause turned up as electric sparking or arcing in the fuel system. Indeed, such kind of sparking or its potential were found on other aircraft which thereupon were grounded for repair.
Conventional electric arc monitoring would, however, appear to be of little use in this respect, inasmuch as it manifestly is too late to recall an aircraft when an arc has sparked an explosion in the fuel system. In consequence, more is needed, or a different approach is required, than what the prior art suggests in terms of arc detection in aircraft electric current distribution systems in U.S. Pat. No. 5,185,684 by Beihoff et al., U.S. Pat. No. 5,185,685 by Tennies et al., U.S. Pat. No. 5,185,686 by Hansen et al., U.S. Pat. No. 5,185,687 by Beihoff et al., U.S. Pat. No. 5,206,596 by Beihoff et al., and U.S. Pat. No. 5,208,542 by Tennies et al., all issued to Eaton Corporation.
Electric arc detection aboard aircraft is also encumbered by the kind of electrostatic charge phenomena mentioned in U.S. Pat. No. 3,857,066, by Cline et al., issued to Dayton Aircraft Products, and disclosing electrostatic sensing probes, U.S. Pat. No. 4,262,254, by Eliasz Poss, issued to United Technologies Corporation, and disclosing a balanced corona electrostatic field sensor, and U.S. Pat. No. 4,323,946, by Robert L. Traux, disclosing techniques for reducing electrostatic charge storage.
By way of further example, electric arc monitors would be useful in garages, automobile or motorcar repair facilities, gasoline (British “petrol”) storage or dispensing facilities and in other areas where accidental electric arcing can cause disastrous explosions.
Moreover, fuses and circuit breakers are capable of preventing serious overload conditions, but they are generally ineffective to prevent electrical fires and other damage from accidental arcs and sparks which typically generate enough heat for a fire at electric current levels below the level at which the fuse will blow or the circuit breaker will trip. Reliable arc monitoring would thus be highly desirable in a large number and variety of electrical circuits.
These are, of course, only representative examples of fields where reliable arc or spark monitoring could be useful.
A major stagnating problem in this respect has been that prior-art development has run its course in its fear of false alarms. Of course, false alarms are the bane of alarm systems, as frequent occurrence of false alarms can nullify the utility of any alarm system.
Accordingly, in an effort to reduce the possibility of false alarms arising from radio broadcast and radio frequency security system signals, the arc detection system as disclosed in the International Patent Publication WO90/04278, by HAMPSHIRE, Michael John, rejects frequencies below about 160 kHz and above some 180 kHz of the arc signal signature, leaving for electrical fault detection only a narrow 20 kHz band at some 170 kHz center frequency. This, however, left a sample for arc detection that was dozens of times too small in the 100 kHz range for reliably detecting the occurrence of an arc signature while at the same time preventing the occurrence of false alarms equally reliably.
An arc detection system which avoids that drawback is apparent from PCT/US90/06113, filed 24 Oct. 1990 and published as WO92/08143, by Hendry Mechanical Works, inventors HAM, Jr., Howard M., and KEENAN, James J., and in its corresponding U.S. Pat. No. 5,373,241, issued 13 Dec. 1994, and U.S. Pat. No. 5,477,150, issued 19 Dec. 1995, all herewith incorporated by reference herein for the United States of America and for all other countries where incorporation by reference is permitted. Reference should also be had to their corresponding EPO 507 782 (90917578.8) and resulting European national patents, and to their corresponding Australian Patent 656128, Canadian Patent Application 2,093,420, Chinese Patent Application 92102453.3, Japanese Patent Application 500428/91, Korean Patent Application (PCT) 701219/93, and Mexican Patent 178914 (9201530), all herewith incorporated by reference herein for all countries where incorporation by reference is permitted. That system avoids false alarms by converting instantaneous arc signature frequencies into a combination frequency from which arc-indicative signals are detected in contradistinction to extraneous narrow-band signals that could cause false alarms.
Against this background, a frequency selective arc detection system of a subsequently filed prior-art application, appears as a typical representative of the prior-art approach to arc detection. It accordingly presents a variety of approaches to arc detection that mainly look at frequencies in the upper kilohertz range, such as from 100 kHz to one megahertz. This, however, covers not only major portions of the public A.M. radio broadcast band, also known as “long-wave” and “medium-wave” broadcast bands in some countries, but also the kind of control or security systems radio frequency band referred to in the above mentioned WO90/04278 reference. Depending on location, one thus had to contend with dozens of extraneous signal interferences.
The same in essence applies to another embodiment in that prior-art proposal that suggests using a comb filter arrangement composed of four bandpass filters each of which has a 50 kHz passband, and three of which have a center frequency of 225 kHz, 525 kHz, and 825 kHz, respectively. In the A.M. broadcast and above mentioned control and security systems radio frequency band portion of that spectrum, 50 kHz samples can only represent minor fragments of the chaotic arc signature, raising the danger of false alarms from coincidental extraneous signals. This also affects the efficacy of the 55 kHz bandpass filter in that comb filter arrangement, inasmuch as that prior-art proposal continuously rotates its detection process among the four filter components of that comb filter arrangement.
A prior effort at arc detection that ventured into low frequency regions effected monitoring in various low frequency bands that were too narrow for reliable arc detection as apparent from U.S. Pat. No. 5,578,931 and articles by B. D. Russell et al., entitled “An Arcing Fault Detection Technique Using Low Frequency Current Components—Performance Evaluation Using Recorded Field Data” and “Behaviour of Low Frequency Spectra Du

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