JPH0727813A - Plotting method for accident point of power cable - Google Patents

Abstract

PURPOSE:To provide a method for plotting accident points of power cables by which the plotting distance error can be reduced. CONSTITUTION:In the method for plotting accident points of power cables by which the distance to an accident point is plotted by detecting a surge current generated when a ground accident occurs in a power cable buried underground with current sensors 7, 8, and 9 provided in insulation joint boxes and terminal joint box provided at multiple points and measuring the arriving time lags of the surge current at each sensor 7, 8, and 9 by utilizing a light emitting element and optical fibers 11, optical attenuators 13 are connected to the optical fibers 11 so as to adjust the optical losses of the fibers 11 to become equal to each other.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an accident point locating method for a ground fault of a power cable laid underground such as a long distance underground power transmission line.

[0002]

2. Description of the Related Art FIG. 2 is an explanatory diagram of an example of a conventional accident point locating method. In the drawings, 1 is a power cable such as a CVT cable, 2 is a branch cable, 3 is a switch, and 4
Is a terminal connection box, 5 is a branch connection box, and 6 is a customer-side power receiving facility. Current sensors 7, 8, 9, and 10 are installed in each terminal junction box 4 and branch junction box 5. The current sensors 7, 8, 9 and 10 are composed of a wire wound type CT and a light emitting element, detect a surge current at the time of a ground fault of the power cable 1, and convert it into an optical signal by the light emitting element. Transmitted to the master station 12 by the optical fiber 11 connected to the current sensor,
Here, the surge current arrival time difference between each current sensor is measured, and the orientation distance is calculated and displayed.

For example, if there is a ground fault accident A between the current sensor 7 and the current sensor 8, the master station 12 measures the time difference between the terminal (a) and the terminal (b) to perform distance localization. However, in this case, since the length of the optical fiber (l ₁ to l ₄ ) is different for each current sensor in the transmission time, the length is measured in advance and each time delay (= length / light Speed of light in the fiber)
It is necessary to obtain and subtract it from the measurement time difference. Although the cable is shown as a single wire in the figure, it is actually 3
Since there are many phases of power transmission lines, the current sensors may be attached at once for all three phases, or may be attached for each phase.

[0004]

In the conventional fault location method described above, when the ground fault occurs, the magnitudes of the optical signals reaching the master station 12 from the current sensors 7 and 8 are 7 and 8, respectively. If the current sensors have the same size, the distance l ₁ from the current sensor 7 to the master station 12 is short.
There is almost no optical loss inside, and a high-level optical signal is the master station.
Reach twelve. On the other hand, the distance between the switch 3 of the substation and the branch connection box 5 may be several kilometers, and in the case of a long distance, 10 kilometers, and the distance from the master station 12 to the current sensor of 8 is the maximum. It will be 10km. Its optical loss is 1 at a wavelength of 1.3 μm.
Since it is dB / km, it reaches about 10 dB, and the terminal of the master station 12 (b)
The magnitude of the optical signal reaching the
1/10 of the optical signal reaching the 12 terminals (a) (-
10 dB).

Therefore, when the time difference is measured, the operation time of the terminal (B) is delayed, resulting in an orientation error. This time delay will be described with reference to FIG. 4. The input signal at the terminal (b) of the current sensor 8 is detected with a delay of Δt ₂ . While 7
Since the input signal at the terminal (a) of the current sensor has a steep waveform, the time delay Δt ₁ is sufficiently smaller than Δt ₂ and the measurement time difference t ₁ becomes longer than the true time difference t ₀ by about Δt ₂ , There is a problem that an error occurs in the distance.

[0006]

SUMMARY OF THE INVENTION The present invention solves the above problems and provides a method for locating a fault point of a power cable in which the error in the locating distance is reduced. In the fault point locating method for power cables that measures the difference in the surge current arrival times to locate the distance to the fault point, insert an optical attenuator into the optical fiber connected to each current sensor to equalize the optical loss of each optical fiber. The second feature of the present invention is to insert an electrical attenuator into the optical / electrical conversion circuit, instead of optically inserting the attenuator as described above, and equivalently generate each current. It is to adjust the optical loss of the optical fiber connected to the sensor to be equal.

[0007]

As described above, according to the accident point locating method of the present invention, as shown in FIG.
According to the attenuation of the input signal of the 12 terminals (b), the terminal (a)
When the input signal of is attenuated, the delay time of both the input signals of the terminals (a) and (b) becomes Δt ₂ , the measurement time difference t ₂ becomes equal to the true propagation time difference t ₀ , and the error becomes small.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is an illustration of a concrete example of the accident point locating method of the present invention. In the drawing, the same reference numerals as those in FIG. 2 represent the same parts. As shown in the drawing, insert an optical attenuator 13 in the middle of the optical fiber 11 connecting the current sensors 7, 8, 9, 10 and the master station 12, and adjust so that the optical loss of each optical fiber 11 becomes equal. To do. As a result, the delay times of the input signals to the terminals (a), (b), (c), and (d) of the master station 12 become equal, and the measurement time difference becomes equal to the true propagation time difference.

As another means, although not shown,
Instead of inserting the optical attenuator as shown in FIG. 1, after converting the optical signal into an electric signal by the optical / electrical conversion circuit, the electric attenuator is inserted in the electric circuit and equivalently connected to each current sensor. The optical fibers may be adjusted to have the same optical loss so that the outputs of the electric signals are equalized.

[0010]

As described above, according to the power cable fault point locating method of the present invention, the error of the time difference measurement becomes small, and the error of the locating distance also becomes small. Therefore, the finding of the accident point can be shortened, which can contribute to the quick recovery of the accident, which in turn contributes to the improvement of the reliability of the power supply.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a specific example of an accident point locating method according to the present invention.

FIG. 2 is an explanatory diagram of an example of a conventional accident point locating method.

FIG. 3 is an explanatory diagram of a result of surge propagation time difference measurement by the method of the present invention.

FIG. 4 is an explanatory diagram of a result of surge propagation time difference measurement by a conventional method.

[Explanation of symbols]

 1 Main line CVT cable 2 Branch cable 3 Switch 4 Terminal box 5 Branch connection 6 Customer power receiving equipment 7, 8, 9, 10 Current sensor 11 Optical fiber 12 Master station 13 Optical attenuator

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Tatsuo Sasaki 1-3-1, Uchisaiwaicho, Chiyoda-ku, Tokyo Tokyo Electric Power Co., Inc. (72) Shunichi Iida 1-3-1, Uchisaiwai-cho, Chiyoda-ku, Tokyo Inside Kyoden Electric Co., Ltd.

Claims (2)

[Claims] 1. A surge current between the current sensors is detected by detecting a surge current in the case of a ground fault of a power cable laid in the ground with current sensors provided in an insulation connection box and a termination connection box installed at a plurality of locations. In the fault location method of the power cable that measures the time difference using the light emitting element and the optical fiber and locates the distance to the fault point, insert an optical attenuator into the optical fiber connected to each current sensor and A method for locating an accident point of a power cable, which is characterized by adjusting the light loss to be equal. 2. The surge current between the current sensors is detected by detecting the surge current of the power cable laid in the ground at the time of a ground fault accident with the current sensors provided in the insulation connection box and the termination connection box installed at a plurality of locations. In the fault point locating method of the power cable, which measures the time difference by using the light emitting element and the optical fiber, and locates the distance to the fault point, an electric attenuator is inserted into the optical / electrical conversion circuit to equivalently measure each current sensor. A fault location method for power cables, characterized in that the optical loss connected to the optical fiber is adjusted to be equal.