Fault point location system

Details Fault point location system Fault point location system

1999-11-12

2003-07-22

Le, N. (Department: 2858)

Electricity: measuring and testing

Fault detecting in electric circuits and of electric components

For fault location

C324S522000

Reexamination Certificate

active

06597180

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a fault point location system. More particularly, the present invention relates to a fault point location system by which reference time is accurately determined. Furthermore, another present invention relates to a fault point location system by which accurate surge detection time is provided without increasing the frequency of erroneous detection. Still furthermore, another present invention relates to a fault point location system by which fault points can be accurately located.
Heretofore, when a fault occurs along the way of a power transmission line and distribution line (hereinafter designated “transmission and distribution line” or “TD line” for both lines), a method is known by which the fault point on the TD line is determined in accordance with a difference in surge detection time at two substations situated across the fault point (Japanese Patent Publication No. Sho 63 (1988)-51274, etc.). In the foregoing method, the accuracy of locating a fault point depends on the accuracy of determining the time at which a surge is detected (hereinafter designated the “surge detection time” or “SD time”) at the substations on both ends of the fault point.
The SD time is often determined by means of a reference clock provided in each substation in combination with GPS radio waves.
Many of these reference clocks employ the temperature compensated crystal oscillator or a crystal oscillator with a thermostat which presents a good clocking capability scarcely affected by variation in temperature. However, clock errors may be accumulated over a long period of time and thus become not negligible in surge detection (refer to FIG.
9
).
Accordingly, GPS radio waves are used for synchronizing the reference time between each substation. The GPS radio waves are transmitted by satellites of the GPS (Global Positioning System). The GPS is a system in which radio waves are received from a plurality of satellites for positioning on the basis of a difference in time for receiving the waves. For this purpose, the synchronization signal for which time is controlled with high accuracy is transmitted. This synchronization signal has an extremely small accumulation of errors over a long term depending on local areas.
However, as shown in
FIG. 8
, each synchronization signal lags or advances to a certain extent. For this reason, simple adjustment of the reference time with the synchronization signal may contrarily provide inaccurate time and result in an inadequate SD time.
Additionally, radio disturbance disabling the GPS radio waves to be received may result in a situation where time cannot be detected and thus fault points cannot be located.
On the other hand, in the detection of a surge, it is regarded to “have detected a surge” when a surge voltage or surge current exceeds a threshold value. The time at which a surge waveform rises can be more accurately captured (initially) with lower voltage or current threshold value, however, erroneous detection of a surge may frequently occur with exceedingly low threshold value due to current or voltage with noises occurring under normal conditions on a TD line. For this reason, the threshold value for recognizing the occurrence of a surge is set to a level higher to some extent so as not to detect a noise incorrectly. Therefore, “surge detection” is carried out after the expiration of a certain time in the rise of the surge waveform.
In addition, the surge received by the two substations across a fault point may take different waveforms due to propagation loss on the TD line. In such a case, as shown in
FIG. 12
, one of the substations with a more deformed surge waveform may have a longer rising time in the surge, thus delaying in “surge detection”. This disables accurate location of a fault point in accordance with a difference in SD time at substations across the fault point.
There is a method called the double potential method for compensating the lapse of time resulting from a threshold value set to a high level and obtaining more accurate “SD time”. As shown in
FIG. 13
, this method determines “SD time T” in a manner such that, on the graph with time on horizontal axis and voltage on the vertical axis, the two points (each of which exceeds reference level L
1
and L
2
that were set to a certain value respectively) on the graph of a surge waveform are connected with a straight line to make the intersection (time) of the line with the voltage of zero level, that is, the horizontal axis a “SD time T”.
That is, in the double potential method, when the voltage or current of a TD line exceeds a certain reference level and then increases further to exceed another reference level, an approximate line of the voltage curve is drawn by connecting the points of intersection of the two levels with the voltage curve, and the point of intersection of the approximate line with the voltage zero level is determined to be SD time T.
Various modified inventions and utility models have been applied for patent with this double potential method (Japanese Utility Model Publication No. Sho 58 (1983)-28219, Japanese Laid-Open Patent Publication No. Hei 8 (1996)-015362, etc.).
As mentioned above, however, the voltage and current of a TD line have noise. When a comparatively large noise occurs or a noise is imposed on a surge waveform, the voltage or current exceeds aforementioned first reference level L
1
on the TD line and then may decline. In such a case, as shown in
FIG. 14
, connecting “the point of intersection of another reference level L
2
with the voltage curve” to “the point of intersection of the first reference level L
1
with the voltage curve” with a straight line results in an inaccurate approximate line of the voltage curve and contrarily causes calculated SD time T to depart from the practically desirable time Tr.
SUMMARY OF THE INVENTION
The present invention solves these problems; the objects of the present invention are to provide a fault point location system by which accurate SD time is obtained to locate fault points, a fault point location system by which accurate SD time can be obtained without increasing the frequency of erroneous detection, and a fault point location system by which fault points can be accurately located.
A fault point location system of a first invention comprises substations (
1
) which are installed along a TD line to transmit information on the SD time to a master station (
2
), and the master station (
2
) which locates fault points on the basis of the information on said SD time; wherein
said substation (
1
) determines the difference between the standard time of the GPS has which is obtained from the GPS radio wave received, and the reference time of said substation (
1
) has at which said standard time has been obtained, accumulates said difference over a certain period of time, corrects the reference time by adding the average value of said difference stored to said reference time, determines the detection time of a surge voltage or surge current produced by a fault having occurred at a certain point on the TD line in accordance with said reference time, and then transmits the detection time to said master station (
2
) via a communication network.
And, said master station (
2
) determines, as shown in the fault location system of a second invention, in accordance with said SD time t
1
detected at one of a pair of substations across a fault point on said TD line network, said SD time t
2
detected at the other substation, surge propagation velocity v, and length L of the TD line between said substations, distance L
1
on the TD line from one of the substations to said fault point by equation L
1
=(L+(t
1
−t
2
)×v)/2.
Furthermore, said master station (
2
) determines, as shown in the fault point location system of a third invention, in accordance with said SD time t
1
detected by a substation nearest to the source-side end along said TD line network, said SD time t
2
detected by another substation at the distal end of the TD line net

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