Data processing: measuring – calibrating – or testing – Measurement system in a specific environment – Earth science
Reexamination Certificate
2002-09-25
2004-07-27
Barlow, John (Department: 2863)
Data processing: measuring, calibrating, or testing
Measurement system in a specific environment
Earth science
C342S460000
Reexamination Certificate
active
06768946
ABSTRACT:
CROSS REFERENCES TO RELATED APPLICATIONS
This application is entitled to the benefit of and incorporates by reference essential subject matter disclosed in Japanese Patent Application No.2002-96237 filed Mar. 29, 2002.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a locating method, apparatus, system and program for locating the position of a lightning strike from the time difference of the arrival of lightning electromagnetic waves at several receiving stations, and more particularly relates to a lightning strike position locating method, apparatus, system and program in which there is no error caused by topography.
2. Description of the Related Art
Such lightning strike position locating system is called an “arrival time difference system. As disclosed in, for example, “
Rakurai Ichi Hyotei Sochi
(
LPATS
-
T
)—
Denryoku Setsubi no Unyo—Hoshu Taisaki Shien—[Lightning Position and Tracking System
(
LPATS
-
T
)—
Support for Operation and Maintenance of Power Equipment]—Toru Shioda, Denki Genba Gijutsu
1998, 7
, Special Collection
2
, Recent Technical Trends in Lightning Countermeasures
, p. 58”, an arrival time difference system is conceived by applying the principle that the track of points at which the difference between distance from two ground points (equivalent to the difference between arrival time of electromagnetic waves) is constant can be drawn as a hyperbolic curve. As is shown in
FIG. 13
of the present application, when there is a lightning strike at a certain ground point, electromagnetic waves generated in the vicinity of the ground surface by this lightning strike (hereafter referred to as “lightning electromagnetic waves”) are propagated to the receiving stations R
1
, R
2
and R
3
with the respective arrival times T
1
, T
2
and T
3
. In this case, if time measurement is synchronized among the respective receiving stations so that the instants in time at which the lightning electromagnetic waves arrive at the respective receiving stations can be measured, the arrival time difference among the respective receiving stations can be determined solely from the instants in time at which the lightning electromagnetic waves arrive. Accordingly, on the basis of the above-mentioned principle, hyperbolic curves L
12
and L
23
corresponding to, arrival time differences, determined by the difference between distance from two arbitrary points, can be determined. Consequently, if the lightning electromagnetic waves are received by receiving stations in at least three different locations, the intersection point X of the hyperbolic curves can be located as the point where the lightning electromagnetic waves are generated, i.e., as the lightning strike position.
FIG. 14
shows the construction of a conventional lightning strike position locating system. As is shown in this figure, a conventional lightning strike position locating system comprises receiving stations R
1
, R
2
and R
3
in at least three different locations which receive the lightning electromagnetic waves generated by the lightning strike, and a lightning strike position locating apparatus H′ which determines the difference between the arrival times of the electromagnetic waves that arrive at the respective receiving stations R
1
, R
2
and R
3
, uses the horizontal coordinates of the respective receiving station as a reference to calculate a ground point which has a difference in horizontal distance that would result in such arrival time difference, and takes this ground point as the lightning strike position. The lightning strike position locating apparatus H′ obtains the horizontal coordinates of the respective receiving stations R
1
, R
2
and R
3
from a receiving station coordinate memory
3
that stores the horizontal coordinates of the respective receiving stations R
1
, R
2
and R
3
, and locates the lightning strike position by the above-mentioned principle using these horizontal coordinates as a reference. The results of the location process are displayed by a display device
6
, or are stored in memory, printed and sent to a terminal.
Furthermore, in terms of the above-mentioned principle, it is sufficient if there are receiving stations in three different locations; however, it would also be possible to install receiving stations in four or more locations, and to select three appropriate stations for use in the location process. There is also an empirical rule that the position location process becomes more accurate as the positions of the receiving stations that are used are located at a greater distance from the lightning strike position. Accordingly, receiving stations are ordinarily installed at several locations over a broad area. For example, in Japan, the location of lightning strike positions throughout the entire Kanto, Chubu and Niigata regions has been realized by installing receiving stations at a total of six locations including Kashima, Fukushima, Kashiwazaki, Matsumoto and so on.
Furthermore, the horizontal distance between two points used in a conventional lightning strike position locating system is actually a distance that follows the curvature of the earth; for the sake of simplicity, however, this will be described as a distance connecting two points by a straight line in the present specification.
Errors have been confirmed in lightning strike positions located by such a conventional lightning strike position locating system. Using steel towers for which lightning strikes could be confirmed, the present applicant investigated the discrepancies between the actual positions of steel towers receiving lightning strikes and the positions of these steel towers located by means of a lightning strike position locating system in this case. As a result, it was demonstrated that a shift in the located position by a specified distance in a specified direction occurred when a specified combination of receiving stations was used for lightning strikes on steel towers in a specified region.
The present applicant judges that the cause of such discrepancies was topography. Specifically, lightning electromagnetic waves have the property of propagating along the ground surface. If there are depressions and elevations (also called “undulations”) in the ground surface, the propagation path as viewed from the lateral direction is not rectilinear, but includes indentations and projections. Since the time at which lightning electromagnetic waves arrive at a receiving station from the lightning strike position should depend on the creepage distance following depressions and elevations in the ground surface, the difference between arrival times should be evaluated using creepage distances. In conventional techniques, however, the above-mentioned arrival time difference system in which the ground surface is viewed as an ideal horizontal plane that has no depressions or elevations is employed; accordingly, the difference between arrival times is evaluated using horizontal distances. As a result, in the case of the location of lightning strike positions in the above-mentioned Kanto, Chubu and Niigata regions, there is a conspicuous discrepancy in the located positions of lightning strikes occurring in areas located on the other side of mountainous regions as seen from the receiving stations.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a lightning strike position locating method, apparatus, system and program which solve the above-mentioned problems, and which are free of topography-dependent error.
In order to achieve the above-mentioned object, the present invention provides a lightning strike position locating for locating the position of a lightning strike on the basis of a differences in the times at which lightning electromagnetic waves are received by a plurality of receiving stations, wherein the lightning strike position is located so that the distances from the lightning strike position to the receiving stations are creepage distances following depressions and elevations in the ground
Narita Tomomi
Okabe Shigemitsu
Taniguchi Sakae
Barlow John
McCormick Paulding & Huber LLP
Taylor Victor J.
The Tokyo Electric Power Company
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