WO2003003326A1

WO2003003326A1 - Arcing source position detector

Info

Publication number: WO2003003326A1
Application number: PCT/KR2001/001107
Authority: WO
Inventors: Chang-Jong Kim; Young-Soo Kim
Original assignee: Saturn Information & Communication Corporation
Priority date: 2001-06-27
Filing date: 2001-06-27
Publication date: 2003-01-09

Abstract

An arcing source position detector which can identify an electrical fire indication due to electrical arcs occurring in the electrical wiring, facilitates the tracking and detecting an arcing source position, and providing audible alarms highly correlated with the high frequency noise signal due to the arcs when arcs are being generated. The magnetic field sensor (10) senses the high frequency magnetic field generated by the high frequency noise due to arcing occurring in an electrical wiring and outputs a detection signal. The preamplifier (12) preamplifies the detection signal to output a preamplified signal. The filtering means (16) filters the preamplified signal to selectively pass frequency components in a predetermined frequency band and output a filtered signal. The sound converting means (22) converts the filtered signal into sound. The displaying means (26) visually displays the level of the filtered signal.

Description

ARCING SOURCE POSITION DETECTOR

Technical Field The present invention relates to an electrical fire warning apparatus and method and, more particularly, to an apparatus and method for identifying an electrical fire indication due to electrical arcing and detecting an arcing source position.

Background Art

Of the three primary contributing factors to a fire, fuel, heat and oxygen, the typical heat sources in office buildings or dwellings are arcing in electrical connections and overheating of the electrical connections due to overload conditions. Even though arcing is an inherently unstable phenomenon and does not usually persist long enough to start a fire, the arcing occasionally can develop temperatures well above the ignition level of most common flammable materials and therefore poses a significant fire hazard. While fuses and circuit breakers are capable of preventing serious overload conditions, they have been generally ineffective to prevent electrical fires caused by accidental arcs which frequently occur and persist at current levels below the level at which the fuse will blow or the circuit breaker has been set to trip.

Accordingly, various devices have been contemplated for detecting a pre-fire condition caused by electrical arcing in the electrical wiring. In U.S. Patent No. 5,434,509 issued 18 July 1995 to Fredrick H. Blades and entitled METHOD AND APPARATUS FOR DETECTING ARCING IN ALTERNATING-CURRENT

POWER SYSTEMS BY MONITORING HIGH-FREQUENCY NOISE, Blades describes a method and apparatus for detecting arcing in electrical connections by monitoring high frequency noise to provide the user with visual and audible alarm indications. Also, U.S. patent No. 5,831,538 issued 3 November 1998 to Robert G. Shena and entitled ELECTRICAL FLRE HAZARD

DETECTOR discloses a detector which senses an arcing condition in AC power distribution systems by sensing RF radiation generated by arcing to activate a visual and audible alarm. When electrical arcing is generated in the electrical wiring, an operator who checks, repairs, and maintains the electrical wiring wishes to know at which position the electrical arcing is being generated. Since the high frequency noise signal propagates to the whole wiring, however, it is difficult to determine the arcing source position when only the high frequency noise signal is analyzed. In this regard, the U.S. Patent No. 5,434,509 discloses an apparatus for detecting the arcing source position by sensing the high frequency noise radiated by the arcing from the electrical wiring while the operator moves along the electrical wiring. However, the audible alarm indication provided by the apparatus is not directly proportional to the high frequency noise but may be a recorded voice message or a uniform beep. Thus, the operator cannot intuitively determine the status of the high frequency noise based on the audible alarm indication.

Disclosure of the Invention

To solve the above problems, one object of the present invention is to provide an arcing source position detector which can identify an electrical fire indication due to electrical arcs occurring in the electrical wiring, facilitates the tracking and detecting an arcing source position, and providing audible alarms highly correlated with the high frequency noise signal due to the arcs when arcs are being generated. Another object of the present invention is to provide a method for easily detecting an arcing source position by providing audible alarms highly correlated with the high frequency noise signal due to arcs when the arcs are being generated and determining the position based on the audible alarms. Generally, when arcing break out in electrical wiring, a high frequency current flows through the wiring. Even though the line voltage does change little in spite of the arcing, the high frequency current is tens through hundreds times larger than that in a normal state. Such an increased high frequency current forms a high frequency magnetic field in the vicinity of the arcing source point. The inventor of the present inventors discovered that most of power of the high frequency current is distributed in the band of 1 KHz - 100 KHz and, more specifically, in 2 KHz - 20 KHz. Accordingly, the magnetic field originating from the high frequency current is outstanding in the above frequency band. The above band corresponds to the audible frequency band of human being. The arcing source position detector according to the present invention detects the magnetic field in the above frequency band and changes the detected magnetic field signal into sound, so that the user can determine the electrical fire indication and trace and detect the arcing source position. The arcing source position detector for achieving one of the above objects comprises a magnetic field sensor, a preamplifier, filtering means, sound converting means, and displaying means. The magnetic field sensor senses the high frequency magnetic field generated by the high frequency noise due to arcing occurring in an electrical wiring and outputs a detection signal. The preamplifier preamplifies the detection signal to output a preamplified signal. The filtering means filters the preamplified signal to selectively pass frequency components in a predetermined frequency band and output a filtered signal. The sound converting means converts the filtered signal into sound. The displaying means visually displays the level of the filtered signal. In a preferred embodiment, the filtering means comprises a notch filter for suppressing a frequency of the electrical power distributed through the electrical wiring. Also, it is preferable that the arcing source position detector further comprises a main amplifier, coupled to said filtering means, for amplifying the filtered signal. Further, the arcing source position detector preferably includes a peak level detector for receiving an amplified signal from the main amplifier and detect peak levels of the amplified signal to output a peak detection signal comprising the peak levels. The peak level detector may include a rectifier for rectifying the amplified signal. Displaying means of the detector receives the peak detection signal to display the peak levels.

In order to facilitate the determination process, the arcing source position detector may further include a memory and comparing means. In such a case, the comparing means receives the peak levels to store in the memory and compares an instantaneous peak level with a maximum value among the peak levels stored in the memory to display a comparison result on the displaying means. Here, the displaying means may include a first display for displaying the peak levels and a second display for displaying the comparison result.

The arcing source position detection method for achieving another one of the above objects, (a) a high frequency magnetic field signal is measured at each position while moving a plurality of positions, (b) the magnetic field signal is transformed into an electrical signal. The electrical signal is amplified and filtered to selectively pass frequency components of a predetermined band. Then the filtered signal is transformed into sound, and a level of the filtered signal is displayed on a display device, (c) Finally, one of the positions is determined as a position closest to the arcing source based on the sound and displayed level for the positions. The predetermined band preferably includes a band of 2 KHz - 20 KHz.

Brief Description of the Drawings

The above objectives and advantages of the present invention will become more apparent by describing in detail preferred embodiments thereof with reference to the attached drawings in which:

FIG. 1 is a block diagram of a preferred embodiment of the arcing source position detector according to the present invention; and FIG. 2 is a flowchart showing the process of detecting the arcing source position using the detector of FIG. 1.

Embodiments In FIG. 1, a coil-type sensor 10 senses a change of the magnetic field in the surrounding space and converts the change into an electric signal. A preamplifier 12 preamplifies the electric signal from the coil-type sensor 10. The preamplified signal from the preamplifier 12 includes a component of the power line frequency, e.g., 60 Hz, which acts as a noise in the measurement of the magnetic field generated by the arcing. Thus, a notch filter 14, which is a band stop filter having a very narrow stop band around the power line frequency, removes the power line frequency component from the preamplified signal from the preamplifier 12. A band pass filter 16 filters the output of the notch filter 14 to selectively pass the arc frequency component. In a preferred embodiment, the band pass filter 16 has a pass band of 1 KHz ~ 100 KHz which is a frequency band in which most of power of the high frequency noises due to the arcing generated in the electrical wiring is distributed. More preferably, the pass band of the band pass filter 16 is 1 KHz - 50 KHz. In a most preferred embodiment, the pass band of the band pass filter 16 is 2 KHz - 20 KHz. Meanwhile, in an alternative of the present embodiment, the band pass filter may be replaced with a low pass filter or a combination of a low pass filter and a high pass filter.

A main amplifier 18 amplifies the filtered signal from the band pass filter 16 to provide an amplified signal to a matching resistor 20 and a peak level detector 24. A speaker 22 receives a voltage level across the matching resistor 20 and transforms the voltage level into sound to provide an audible alarm. Since the high frequency noise is output through the speaker 22 just following the filtering and amplifying steps, the audio sound from the speaker sufficiently reflects the unsteady property of the arcing. Thus, the operator can intuitively inspect the occurrence and intensity of the arcing. In an alternative of the present embodiment, another type of audible warning means such as an earphone and a headphone may be employed instead of the speaker 22. In order to allow the use of the earphone or the headphone at least selectively, the preferred embodiment of the arc source position detector includes a connector jack on the outer surface of its housing for receiving an earphone jack or the headphone jack.

A peak level detector 24 receives the amplified signal from the main amplifier 18 and detects the peak level of the amplified signal to output an envelope signal of the amplified signal. Such a peak level detector 24 can easily be implemented by use of a low pass filter, e.g., a capacitor-input filter. On the other hand, the amplified signal from the main amplifier 18 is an alternating current (AC) signal in which the positive polarity portion and the negative polarity portion are unbalanced. Particularly, when arcing breaks out in the electricity distribution wiring, the negative polarity current frequently has larger magnitude than the positive polarity current. Thus, it is necessary to reflect both the maximum absolute levels of the positive polarity current and the negative polarity current in order to detect boh the maximum magnitudes of positive and negative high frequency noise. Therefore, the peak level detector 24 preferably includes a rectifying circuit for rectifying the amplified signal to output a rectified signal having the positive polarity only. Such a rectifying circuit can be implemented using an operational amplifier and a fast and high-conductance diode.

A first display 26 visually displays the level of the peak detection signal or the envelope signal from the peak level detector 20. In the preferred embodiment, the first display 26 includes ten light emitting diodes (LEDs) to express the level of the peak detection signal in 10 steps. In other words, the larger the level of the peak detection signal is, the more LED is turned on. Also, as the level of the peak detection signal varies, the number of turned-on LED's changes with time continuously. On the other hand, the first display 22 may include a 7-segment LED rather than the multiple LED lamps as well. An analog-digital converter (ADC) 28, a microprocessor 30, a ROM 32, a RAM 34, and a second display 36 store the level of the peak detection signal in digital data form, and compares the stored value with a present value so that the operator identifies the location showing the highest level. Here, the ADC 28, the microprocessor 30, the ROM(32), and the RAM(34) may be implemented using an embedded core chip.

The ADC 28 converts the output of the peak level detector 24 into digital data and provides the peak level data to the microprocessor 30, so that the microprocessor 30 stores the data in the RAM 34. The microprocessor 30 continuously compares the peak level data from the ADC 28 with a maximum data stored in the RAM 34. In the case that the peak level data from the ADC 28 is greater than the maximum data stored in the RAM 34, the microprocessor 30 shows a message such as "Arcing is maximum at this position. " on a second display 36, which preferably is a LCD panel. At this time, the microprocessor 30 may output a warning beep through the speaker 22 or control the first display so that the LED lamps flicker. In FIG. 1, the ROM 34 stores program codes for operating the microprocessor 30, and the input key is used for the user to input an operation command to the detector.

FIG. 2 is a flowchart showing the process of detecting the arcing source position using the detector of FIG. 1. The method generally includes steps 100 through 106 of detecting magnetic field while moving the detector, steps 108 through 116 of generating and outputting audible and visual warning according to the intensity of the magnetic field and determining the presence of arcing based on the warning, and a step 118 of determining the arcing source position. First, in the step 100, the operator measures the magnetic fields while moving the detector along the electrical wiring or the outer wall in which the electrical wiring is installed. Regardless that the detector is in a moving path or in a stationary state, the coil-type sensor 10 continuously senses the change of the magnetic field and transforms the change into the electrical signal (step 102). The preamplifier preamplifies the electrical signal from the coil-type sensor 10, and the notch filter 14 and the band pass filter 16 filters the arcing frequency component while suppressing the power line frequency. The filtered signal is amplified again by the main amplifier 18 (step 104). The amplified signal is output in audible sound through the speaker 22 (step

106). The passband of the band pass filter 16 includes or approximately corresponds to the audible frequency band of human being. Thus, the operator can easily hear the sound provided by the speaker 22 even though the amplified signal from the main amplifier 18 is not manipulated any further. In particular, the sound fluctuates continuously according to the unstable nature of the arcing, and thus the operator can easily recognize the presence of arcing. On the other hand, the peak level detector 24 generates, from the amplified signal, the peak detection signal which is always nonnegative (step 108). Subsequently, the level of the peak detection signal is displayed on the LED bar of the first display 26 (step 110). In the steps 112 through 116, the operator determines the presence of arcing based on the visual and audible alarm provided through the first display 22 and the speaker 26, respectively. First, in the step 112, it is determined whether multiple lamps of the 10 LED lamps in the LED bar are highlighted. If no lamp is turned on or just a few lamps are turned on, it is regarded that there is no arcing source near the measuring point and the process proceeds to the step 100 to detect arcing at another position. On the other hand, multiple lamps in the LED bar are highlighted in the step 112, it is determined whether the audio sound is highest (step 1 14). In the case that the audio sound is not so high in spite of the highlighting of multiple LED lamps, it is determined that the position is not near the arcing source but the LED lamps are turned on because of electromagnetic noise having frequencies near the human audible band. Thus, the process proceeds to the step 100 to detect arcing at another position.

If it is determined in the step 114 that the audio sound is high enough, it is determined whether the highlighting state of the LED bar and the audible alarm fluctuates with time (step 116). Generally, because the arcing does not break out continuously but repeats intermittently, the fact that the audio alarm through the speaker or the earphone and the visual alarm through the LED bar simultaneously reach respective maximum states cannot result in a hasty conclusion that the arcing source is near the position. Thus, if it is determined in the step 116 that the highlighting state and the audible alarm do not fluctuate with time, the operator may determine that the alarms stem from another kind of noise source and direct the process to the step 100 to detect arcing at another position.

If it is determined in the step 116 that the highlighting state of the LED bar and the audible alarm fluctuates with time, the operator may temporarily conclude that the arcing source is near the position (step 118). After the arcing source is located approximately in the step 118, the steps 100 through 118 can be repetitively carried out while the measuring position is changed slightly in order to precisely determine the arcing source position. In such a case, the position at which the highlighting state of the LED bar and the audible alarm fluctuate intermittently and repetitively between their maximum and minimum is preferably determined to be the arcing source. Meanwhile, whenever the presence of arcing is identified sequentially at plural positions adjacent to one another, the microprocessor 30 compares the current peak level with the maximum level stored in the RAM 34 to display the comparison result through the second display 36 etc., so that the operator exactly points out the arcing source.

On the other hand, when the arcing source is roughly found, the position scanning for finding the precise arcing source need not have to be carried out for an extensive range but is enough to perform for a small range in the vicinity. It is because the electromagnetic field generated by the change of the current attenuates with the cubic of the distance from the source and thus the signal sensed by the coil- type sensor drastically changes with the distance between the sensor and the arcing source. Similarly, when the operator moves the coil-type sensor in the step 110, it is sufficient to move the sensor only along the electrical wiring or the outer wall in which the electrical wiring is installed.

Although the present invention has been described in detail above, it should be understood that the foregoing description is illustrative and not restrictive. Those of ordinary skill in the art will appreciate that many obvious modifications can be made to the invention without departing from its spirit or essential characteristics. Thus, it should be apparent that the invention can be modified in arrangement and detail without departing from such principles. We claim all modifications and variation coming within the spirit and scope of the following claims.

Industrial Applicability

As described above, the present invention enables a dweller at home, a worker in a building, or an operator who maintains the electrical wiring to detect an electrical fire indication due to electrical arcing and determine the arcing source position accurately. Since the detector provides audible alarms highly correlated with the high frequency noise signal due to the arcing, the user can intuitively and easily determine the presence of the arcing. Accordingly, when the arcing which may cause an electrical fire breaks out in the electrical wiring at home or in an office building, the operator or a maintenance person can accurately locate the arcing source position to rapidly repair or change the wiring. Furthermore, the arcing source position detector according to the present invention has a simple configuration, so that it can be manufactured at low cost and configured in a portable form. Accordingly, lots of consumers can easily obtain to use regardless of their location.

Claims

What is claimed is:

1. An arcing source position detector comprising: a magnetic field sensor for sensing high frequency magnetic field generated by high frequency noise due to arcing occurring in an electrical wiring to output a detection signal; a preamplifier for preamplifying the detection signal to output a preamplified signal; means for filtering the preamplified signal to selectively pass frequency components in a predetermined frequency band and output a filtered signal; means for converting the filtered signal into sound; and means for displaying the level of the filtered signal.

2. The arcing source position detector as claimed in claim 1, wherein said filtering means comprises: a notch filter for suppressing a frequency of electrical power distributed through the electrical wiring.

3. The arcing source position detector as claimed in claim 1, further comprising: a main amplifier, coupled to said filtering means, for amplifying the filtered signal.

4. The arcing source position detector as claimed in claim 3, further comprising: a peak level detector for receiving an amplified signal from the main amplifier and detect peak levels of the amplified signal to output a peak detection signal comprising the peak levels.

5. The arcing source position detector as claimed in claim 4, wherein said peak level detector comprises: a rectifier for rectifying the amplified signal.

6. The arcing source position detector as claimed in claim 4, further comprising: displaying means for receiving the peak detection signal to display the peak levels.

7. The arcing source position detector as claimed in claim 6, further comprising: a memory; and comparing means for receiving the peak levels to store in said memory and comparing an instantaneous peak level with a maximum value among the peak levels stored in said memory to display a comparison result on said displaying means.

8. The arcing source position detector as claimed in claim 7, wherein said displaying means comprises; a first display for displaying the peak levels; and a second display for displaying the comparison result.

9. A method for detecting an arcing source position, comprising: moving positions and measuring a high frequency magnetic field signal at each position; transforming the magnetic field signal into an electrical signal, amplifying and filtering the electrical signal to selectively pass frequency components of a predetermined band, transforming the filtered signal into sound, and displaying a level of the filtered signal on a display device; and determining one of the positions as a position closest to the arcing source based on the sound and displayed level for the positions.

10. The method as claimed in claim 9, wherein the predetermined band includes a band of 2 KHz - 20 KHz.