Electricity: measuring and testing – Fault detecting in electric circuits and of electric components – For fault location
Reexamination Certificate
1998-12-08
2001-07-10
Metjahic, Safet (Department: 2858)
Electricity: measuring and testing
Fault detecting in electric circuits and of electric components
For fault location
C324S532000
Reexamination Certificate
active
06259255
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a surge locating system for locating a point where a surge occurs on a power transmission line, in particular, to a surge locating system which operates in combination with a wire wound grounding potential transformer (GPT).
A surge occurs on a power transmission line due to grounding, short circuit, back flashover, direct strike of lightning and the like. There has been known a surge locating system of power transmission line which locates a point where a surge occurs by receiving surges in adjacent master station and slave station and by evaluating levels of the surges received in respective stations.
In this type of surge locating system of power transmission line, a time difference between the times when a surge rising up to a certain level is received by adjacent master station and slave station respectively is measured, and then a distance L
1
from the master station to the point where the surge occurs is calculated based on the equation (1) as follows:
L
1
=(L−
c·&Dgr;t
)/2 (1)
where,
L: distance between a master station and a slave station placed each end respectively,
&Dgr;t: time difference between the times when the surge is received in two stations respectively,
c: surge propagation velocity.
Most of the surge locating systems of power transmission line used now widely are so-called B-type or micro B-type, in which the surge rising up to a certain level is received by a surge receiving station called master station and another station called slave station respectively, and the slave station transmits the event that the surge is received to the master station via a telecommunication network line of a ground system or a microwave telecommunication system, and the master station then calculates a time difference between own receiving time and a slave station's receiving time to locate the point where the surge occurs by applying it to the equation (1).
In the surge locating systems of power transmission line mentioned above, it is preferable that the same shape of waveform would be received at the master station and at the slave station. However, a waveform, a duration of wave front length, and a peak value are fluctuated or damped depending on a characteristics of instruments for receiving a surge from a power transmission line or a common bus in such electric facility as transforming station, loading conditions of the instruments, or an influence of other power transmission lines. Therefore, in this conventional surge locating system, the time difference between the surges received at a master station and a slave station must be compensated as if approximately same waveform are received at the master station and the slave station respectively. As for the surge compensating method, there has been known a two-potential method. In the two-potential method, based on the experimental principle that the leading edge of surge may be approximated to a straight line, an intersection point of a line which passes two points each corresponding to detection time of two different specific levels of surge and a line of zero surge level is assumed to be an initial arrival time of surge.
Japanese Utility Model Publication No. 28219 issued in 1983 discloses a surge locating system of power transmission line which uses this type of two-potential method. This surge locating system of power transmission line comprises plural surge detectors, which calculates the surge arrival time based on the intersection point of a line which passes two points each being detected by a surge detector of the highest detected level of surge and by another surge detector of the second highest detected level of surge respectively and a line of zero surge level.
This conventional surge locating device is configured based on the assumption that the surge is introduced through a capacitance potential device (PD).
In the capacitance potential device (PD), though a primary side voltage and a secondary side voltage are damped under predetermined ratios, a waveform introduced into the primary side is, basically without any modification, output to the secondary side. Then, the surge locating is implemented based on the damped surge waveform. The inventors of the present invention previously proposed a surge locating device which provides improved accuracy of surge locating by compensating the surge arrival time in respective electric facilities based on a gradient of received surge wave when the surge locating is implemented based on the surge wave detected through the capacitance potential device (PD).
In such conventional method as of disclosed in the above Japanese Utility Model Publication No. 28219 which determines the surge arrival time at respective stations based on the surge voltage waveform, the arrival time varies depending on the method for compensating or evaluating the surge waveform, so that the compensation or the evaluation directly gives an influence on the exactness of surge locating.
Namely, in the conventional method, the evaluation of the arrival waveforms at respective stations inevitably causes a factor of errors. As a result, it is difficult to accomplish an accurate surge locating.
In view of the above mentioned disadvantage of the conventional surge locating system which uses the conventional capacitance potential device (PD) and is associated with the compensation or the evaluation of the surge voltage waveform, the object of the present invention is to provide a surge locating system and a method thereof which will not necessitate an evaluation analysis of surge voltage waveform and is capable of surge locating with high accuracy by a simple configuration.
SUMMARY OF THE INVENTION
The above mentioned object of the present invention is accomplished by providing a surge locating system of a power transmission line for locating a point where a surge occurs by receiving in at least two stations independently said surge which occurs on the power transmission line, said surge locating system of a power transmission line comprising a surge detecting means for detecting a surge which occurs on the power transmission line, which is connected to a neutral point of a secondary side of a wire wound grounding potential transformer (GPT) connected to said power transmission line, the surge detecting means comprising a surge judging means which judges that a surge is detected when a voltage higher than predetermined level is detected, a time difference calculating means for calculating a time difference between surge detected times detected by the surge judging means in respective stations, and a locating means for locating a point where the surge occurs based on the time difference.
Preferably, the neutral point is a neutral point of a Y-connection three phase alternative current wiring.
In this case, it is also preferable that GPT is connected to the power transmission line via the capacitance potential device (PD).
It is also preferable that the surge detecting means is provided with a voltage limitation means for preventing a voltage higher than the predetermined level from being introduced.
On top of that, the surge detecting means is preferably provided with a high-pass filter which passes a voltage waveform having a frequency higher than a predetermined value.
A preferred embodiment of the invention is characterized in that the surge detecting means is connected to the high-pass filter and is equipped with a low-pass filter which only passes a voltage waveform having a frequency lower than a predetermined value.
In another preferred embodiment of the invention, the surge detecting means is equipped with a transforming means for transforming a surge voltage into other kind of physical quantity. In this case, the transforming means is a photo coupler.
According to another feature of the present invention is provided a surge locating method of a power transmission line for locating a point where a surge occurs by receiving in at least two stations independently the surge which occurs on a power transmission lin
Kojima Toshiaki
Ohira Sakari
Ozawa Masaaki
Frishauf, Holtz Goodman, Langer & Chick, P.C.
Metjahic Safet
Nguyen Vincent Q.
Tohoku Electric Power Co. Inc.
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