JPS6255570A - Location of fault point for cable line - Google Patents

Abstract

PURPOSE:To enable accurate location of a fault point without being affected by a reflected wave even for a cross-bond line, by measuring a discharge pulse generated at the fault point at both ends of a cable line. CONSTITUTION:When a high DC voltage is applied to a final end (A) of a cable line suffering an insulation breakdown, a discharge pulse generates at a fault point (X) and travels to both final ends (A) and (B) thereof. A first wave of the travelling wave is observed by a synchroscope or the like at both the ends (A) and (B) to measure the time at which the travelling waves peak. The peak time is expressed at the final end (A) by the formula 1 (wherein sigma: constant determined by surge impedance and cable structure, b: 1.386 (Th)<1/2>, provided that Th is half pulse height time) and at the final end (B), it is done by the formula II (wherein L: overall length of cable line). The constant (b) is cancelled from both the formulas to calculate the distance (x) to the fault point X. The measurements at both the ends can be made either by synchronism or by moving them.

Description

[Detailed description of the invention] [Technical field of invention] The present invention relates to a method for locating accident points on cable lines.

In particular, it relates to a method for locating fault points on cable lines, which allows fault points to be accurately located even on cross-bond lines.

[Technical background of the invention and its problems] Conventionally, as a fault point locating method for cable lines, a DC voltage is applied to a cable line where an accident has occurred, and a discharge pulse generated at the fault point is transferred to the terminal end of the cable line. The accident point has been located by detecting the accident point and determining the distance from the end of the cable line to the accident point.

This method is based on the following principle. That is, by applying a DC voltage to the cable line where the fault occurred, the discharge pulse generated at the fault point becomes a rectangular crest exponential wave tail traveling wave and travels toward both ends.

As shown in FIG. 2, the wave front of this traveling wave changes and distorts as the propagation distance increases, and the time tn+a at which the peak occurs becomes delayed. According to traveling wave theory, the time t ma when this peak occurs
x is given by equation (1).

2/y σX However, σ: Constant determined from surge impedance and cable structure b: 1.3g67 time (Th: half-wave height time) X: Distance from the end of the cable line to the accident point By determining the time t wax at which the pulse reaches its peak when it reaches the terminal end, tl, the distance from the cable line terminal end to the accident point
This is what we are trying to find. However, although the constant σ in the equation can be easily determined, it is often difficult to determine b by measurement, especially in cross-bond lines, due to the influence of reflected waves.

[Purpose of the invention] The present invention was made in view of the above-mentioned conventional difficulties.

We propose a method for locating accident points on cable lines that can accurately locate accident points without being affected by reflected waves even on cross-bond lines.

[Summary of the Invention] In order to achieve the above object, according to the cable line fault location method of the present invention, a discharge pulse generated at the fault point is detected by applying a DC voltage to the cable line where the fault has occurred. Measure at both ends of the cable line, and determine the times t and t when the discharge pulses reached at both ends of the cable line reach their peaks, respectively.
From both equations (1) and (2).

2σ However, σ: constant b determined from surge impedance and cable structure: 1.386V” (Th: half-wave height time) T, full length of two cable lines Calculate the distance Hx from one end of the cable line to the fault point. By doing so, the accident point on the cable line can be located.

[Embodiments of the invention] An embodiment of the present invention will be described below with reference to FIG.

When a high-voltage DC voltage is applied to the terminal end A of the cable line where the insulation has broken down, a discharge pulse is generated at the fault point X, and the discharge pulse advances to both terminal ends A and r3.

The first wave of this traveling wave is observed at both terminal portions A and B using a synchronizer or the like, and the time at which the traveling wave reaches its peak is measured. The time at which this peak occurs is expressed by equation (1) for the end portion.

2σ σX However, σ: Constant determined from surge impedance and cable structure b: 1.386f (Th: Half-wave height time)
At the terminal end B, it is expressed by equation (2).

By eliminating the constant S from both of these equations, the distance to the accident point
Calculate.

Note that the measurements at both ends may be performed at the same time or may be performed while moving.

[Effects of the Invention] As explained above, in the present invention, the discharge pulse generated at the fault point is measured at both ends of the cable line, so even if there is reflection, such as on a cross-bond line, the influence of reflection can be ignored. It becomes possible to accurately locate the accident point without receiving any damage.

[Brief explanation of drawings]

FIG. 1 is a diagram of a line system system related to the cable line fault location method according to the present invention, and FIG. 2 is a waveform diagram of a discharge pulse propagation signal based on traveling wave theory.

Claims (1)

[Claims] By applying a DC voltage to the cable line where the accident occurred, the discharge pulses generated at the fault point are measured at both ends of the cable line, and the discharge pulses that have reached both ends of the cable line are determined. Calculate the peak times t_m_a_x and t'_m_a_x, respectively, and from both formulas (1) and (2), t_m_a_x/b^2={[(2σ/b)x+1]}
/{4log{1.53[1+(b/σx)]}}...
...(1) t'_m_a_x/b^2=[(2σ/b
)(L-x)+1]/{4log{1.53{1+[b
/σ(L-x)]}}}...(2) However, σ:
Constant b determined from surge impedance and cable structure: 1.386√Th (Th: half-wave height time) L: Full length of cable line Distance x from one end of the cable line to the accident point is calculated. Cable line accident point location method.