EP-4737917-A2 - DETECTION OF ELECTRIC DISCHARGES THAT PRECEDE FIRES IN ELECTRICAL WIRING

EP4737917A2EP 4737917 A2EP4737917 A2EP 4737917A2EP-4737917-A2

Abstract

Described herein are methods and systems for detecting electrical discharges that precede electrical fires in electrical wiring. One or more sensor devices coupled to a circuit detect one or more signal waveforms generated by electrical activity on the circuit. The sensor devices identify one or more transient signals within the one or more signal waveforms, and generate one or more transient characteristics based upon the identified transient signals. A server communicably coupled to the sensor devices receives the one or more transient characteristics. The server analyzes the one or more transient characteristics to identify one or more electrical discharge indications. The server generates one or more alert signals when one or more electrical discharge indications are identified.

Inventors

MARSHALL, ROBERT
SLOOP, CHRISTOPHER DALE
HECKMAN, STAN
BIXLER, Donnie
HOPPMANN, Eric

Assignees

Whisker Labs, Inc.

Dates

Publication Date: 20260506
Application Date: 20190320

Claims (15)

A computerized method of detecting electrical discharges that precede electrical fires in electrical wiring, the method comprising: detecting, by each of one or more sensor devices coupled to a circuit, a full voltage cycle waveform generated by electrical activity on the circuit, the one or more sensor devices sampling the full voltage cycle waveform at a frequency above 10 MHz upon detecting that the full voltage cycle waveform has reached a threshold value; identifying, by each of the one or more sensor devices, one or more transient signals within the full voltage cycle waveform; generating, by each of the one or more sensor devices, one or more transient characteristics based upon the identified transient signals; receiving, by a server computing device communicably coupled to the one or more sensor devices, the one or more transient characteristics from each sensor device; analyzing, by the server computing device, the transient characteristics to identify one or more electrical discharge indications; and generating, by the server computing device, one or more alert messages when one or more electrical discharge indications are identified.
The method of claim 1, wherein identifying one or more transient signals within the full voltage cycle waveform comprises: a) dividing the samples of the full voltage cycle waveform into a plurality of bins; b) determining a mean value and a maximum value for each of the plurality of bins; c) determining a difference between the mean value and the maximum value; d) repeating steps a)- c) for each of a plurality of other samples of the full voltage cycle waveform to determine an accumulated maximum value for each bin across all of the samples; and e) determining a derivative of each accumulated maximum value across the plurality of bins.
The method of claim 2, wherein generating one or more transient characteristics based upon the identified transient signals comprises: determining an average transient amplitude over a voltage cycle of the full voltage cycle waveform; and determining an average transient amplitude for a plurality of phase sections within the voltage cycle.
The method of claim 3, wherein analyzing the transient characteristics to identify one or more electrical discharge indications comprises: determining a ratio of average peak transients in one or more of the phase sections near a maximum voltage to average peak transients near a zero crossing of the voltage cycle; and identifying the average peak transients in one or more of the phase sections near a maximum voltage as electrical discharge indications, when the ratio is above a predetermined threshold.
The method of claim 4, wherein generating one or more alert messages when one or more electrical discharge indications are identified comprises: determining a count of the identified electrical discharge indications occurred within a predetermined amount of time; and generating an alert message based upon the count of the identified electrical discharge indications.
The method of claim 2, wherein identifying one or more transient signals within the full voltage cycle waveform comprises: a) determining a derivative of the samples of the full voltage signal waveform across a full voltage cycle; b) dividing the samples of the full voltage cycle waveform into a plurality of bins; c) determining a maximum value for each of the plurality of bins; d) repeating steps a)- c) for each of a plurality of other samples of the full voltage cycle waveform to determine an accumulated maximum value for each bin across all of the samples; and e) determining a derivative of each accumulated maximum value across the plurality of bins.
The method of claim 6, wherein generating one or more transient characteristics based upon the identified transient signals comprises: determining an average transient amplitude over a voltage cycle of the full voltage cycle waveform; and determining an average transient amplitude for a plurality of phase sections within the voltage cycle.
The method of claim 7, wherein analyzing the transient characteristics to identify one or more electrical discharge indications comprises: determining a ratio of average peak transients in one or more of the phase sections near a maximum voltage to average peak transients near a zero crossing of the voltage cycle; and identifying the average peak transients in one or more of the phase sections near a maximum voltage as electrical discharge indications, when the ratio is above a predetermined threshold, and preferably wherein: generating one or more alert messages when one or more electrical discharge indications are identified comprises: determining a count of the identified electrical discharge indications occurred within a predetermined amount of time; and generating an alert message based upon the count of the identified electrical discharge indications.
The method of claim 1, wherein identifying one or more transient signals within the full voltage cycle waveform comprises: identifying one or more samples of the full voltage cycle waveform that exceed a threshold value; and storing the identified one or more samples.
The method of claim 9, wherein generating one or more transient characteristics based upon the identified transient signals comprises, for each identified sample: determining a count of peaks in the identified sample; determining a rise time of the peaks in the identified sample; determining a pulse width of the identified sample; and determining an integral of the identified sample.
The method of claim 10, wherein analyzing the transient characteristics to identify one or more electrical discharge indications comprises categorizing the identified sample as an electrical discharge indication when the count of peaks in the identified sample is above a predetermined threshold and when the rise time of the peaks in the identified sample is above a predetermined threshold, and preferably wherein generating one or more alert messages when one or more electrical discharge indications are identified comprises: determining a count of the identified electrical discharge indications occurred within a predetermined amount of time; and generating an alert message based upon the count of the identified electrical discharge indications.
The method of claim 1, wherein the one or more sensor devices identify one or more transient signals within the full voltage cycle waveform and generate one or more transient characteristics based upon the identified transient signals using a transient detection profile stored in a memory module of the sensor device.
The method of claim 12, wherein the server computing device generates an updated transient detection profile based upon transient characteristics received from one or more of the sensor devices and transmits the updated transient detection profile to each of the one or more sensor devices and preferably wherein the one or more sensor devices apply the updated transient detection profile to identify subsequent transient signals within the one or more signal waveforms and generate the one or more transient characteristics.
A sensor device for detecting electrical discharges that precede electrical fires in electrical wiring, the sensor device coupled to a circuit, the sensor device comprising: a converter that detects a full voltage cycle waveform of the electrical activity on the circuit by sampling at a frequency above 10 MHz, wherein the converter samples the full voltage cycle waveform upon detecting that the full voltage cycle waveform has reached a threshold value; a processor that: identifies one or more transient signals within the full voltage cycle waveform; generates one or more transient characteristics based upon the identified transient signals; analyzes the transient characteristics to identify one or more electrical discharge indications; and generates one or more alert messages when one or more electrical discharge indications are identified.
The sensor device of claim 14, wherein: the processor transmits the one or more alert messages to a remote computing device; and/or the processor activates an alert indication device embedded in the sensor device when one or more electrical discharge indications are identified, and preferably wherein the alert indication device comprises a light emitting diode (LED).

Description

TECHNICAL FIELD The subject matter of the application relates generally to detection of early-stage electrical discharges, including arc faults, in electrical wiring. BACKGROUND According to statistics released by the United States Fire Administration National Fire Data Center (https://www.usfa.fema.gov/downloads/pdf/statistics/v14i13.pdf), electrical arcing in residential electrical wiring account for over 70% of electrical fires-which are one of the most dangerous threats to life and property. Arc faults (also called arcs) are high-power, continuous electric discharges between two or more conductors-typically occurring in residential buildings when the integrity of an electrical wire or insulation is compromised (e.g., through physical damage, water damage, corrosion, age, or loose connections, among others). Events such as lightning strikes and power surges can also initiate the breakdown of insulation and lead to a compromised wire. As a result of the compromised wire, small, sporadic electrical discharges begin to occur and the insulating material that surrounds the wire is carbonized. As the electrical discharges continue over time, the insulation is increasingly eroded, and the electrical discharges increase in intensity. Eventually, strong electrical discharges become continuous arc faults that form in the wire-resulting in large flow of current and large releases of energy (with correspondingly high temperatures). Due to the proximity of the wire to wood frame, insulation, and/or similar combustible materials, when the temperatures produced by the arcs are high enough, they are likely to produce fire. It would be a great advantage in preventing electrical fires if one could detect, and be warned about, the small electrical discharges that may occur for days, weeks, or months before they become large enough to create electrical arcing (as is described in Yereance, R. A., and Kerkhoff, T., Electrical Fire Analysis, 3rd ed., page 206, Charles C. Thomas, Springfield IL (2010)). The above-mentioned electrical discharges can occur in various ways, including: parallel, series, and line-to-ground discharges. A parallel electrical discharge occurs when current/electrons flows from one conductor to another through a gas or dielectric material because of a large voltage difference between the conductors-typically through damaged insulation or the air. FIG. 1A is a diagram of a parallel electrical discharge. The electrical circuit has two wires 102a, 102b, each of which is surrounded by an insulating material. If the insulation between the wires breaks down, then electrical discharges (such as discharge 104) can occur between the wires. Examples of parallel electrical discharges include carbonization (i.e., breakdown of the insulating material) and wet tracking (i.e., moisture on the surface of the wire that enables currents to form). A series electrical discharge occurs when a single conductor is damaged to an extent that resistance through the conductor is increased and creates voltage differences high enough for discharges to occur within the conductor and into the surrounding insulation (or even to external objects, if the conductor is exposed). FIG. 1B is a diagram of a series electrical discharge. The electrical circuit includes a damaged wire 106 that produces an electrical discharge 108. Examples of series electrical discharges include ground pyrolysis (i.e., current flowing from the conductor to nearby wood), and last strand (i.e., breakage of the wire resulting in increase in heat and ignitable gases). A special type of series discharges occurs in a phenomenon known as a glowing connection (as shown in FIG. 1C). In such cases electrical conductors are touching, but not firmly connected together. An oxide layer forms at the boundary of the interface which increases the resistance of the conductors at the junction. If current is flowing through the interface, the temperature can rise to dangerous levels (e.g., the white area 110 shows a high temperature at an electrical outlet) which can ignite nearby materials and cause a destructive fire. By the time an electrical discharge has progressed to the point that it causes a fire, it is too late to take corrective action and prevent loss. It is important to detect the occurrence of such electrical discharges in electrical wiring as early as possible so that remedial measures can be put in place. Technology such as arc-fault circuit interrupters (AFCI) currently exist to detect early-stage electrical discharges, such as arc faults. In electrical outlets equipped with AFCI technology, an AFCI detects arc faults in a circuit and breaks the circuit upon detection of such faults to prevent an electrical fire from happening. However, AFCIs are relatively expensive and must be installed on each circuit in a building to detect electrical discharges on the individual circuits. SUMMARY Therefore, what is needed is a method and system that detects early-stage electric