JPH063403A - Detection of power cable grounding position - Google Patents

Abstract

PURPOSE:To easily detect the grounding position of a power cable by causing conduction and heating in accordance with the performance of an optical fiber thermal distribution measuring instrument used. CONSTITUTION:In detecting the grounding position of a power cable, when grounding takes place an a power-optical composite cable C containing an optical fiber, grounding point A is intendedly heated by making a current flow in the electric circuit consisting of a conductor 1 of the power cable and a shielding layer 3. By detecting the position where the temperature has risen using an optical fiber thermal distribution measuring instrument 11 connected to an end of a composite optical fiber 5, the grounding position A is found.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for detecting a ground fault position of a power cable of an electric power / optical composite cable which is combined by winding an optical fiber on the outer circumference of a built-in or outer coating.

[0002]

2. Description of the Related Art Generally, when a ground fault occurs in a power cable, a very large ground fault current flows between the conductor and the shielding layer in the vicinity of the ground fault. The temperature rises. An attempt has been made to detect the ground fault position by detecting this temperature rise by an optical fiber temperature distribution measuring device which is a sensor and an optical fiber built in the cable or laid along the outer circumference of the cable. (For example, refer to "Analysis of the 1st Annual Meeting of the Institute of Electrical Engineers of Japan," Possibility of locating the ground fault point using an optical fiber distributed temperature sensor ")

[0003] Here, when a ground fault occurs in a power cable, the power supply to the cable is instantaneously cut off for several tens of ms to protect the substation equipment connected to the cable, so that the temperature rises. Is limited to a very short period of time. Further, the temperature rises only in the very vicinity (for example, 1 m section) with the ground fault as the center (highest temperature). On the other hand, the optical fiber temperature distribution measuring device receives an optical pulse from one end of the optical fiber, temporally samples the backscattered light returning from the optical fiber to the incident end, and generates the temperature and time delay from its intensity. Position (distance from the incident end)
However, the temperature being measured is an average temperature in a fixed distance section of the optical fiber and a time average temperature within a fixed measurement time. Therefore, in order to detect the temperature rise in a limited distance section in an instant, it is necessary to make the average distance and the average time of temperature measurement as short as possible.

However, in general, this type of temperature distribution measuring device requires detection of very weak backscattered light generated from the optical fiber, and therefore the signal light (backscattered light) intensity as large as possible for measurement. For a long time to get
Alternatively, integration processing over a long distance, that is, averaging processing is required, and it may be difficult to detect the instantaneous temperature rise as described above.

[0005]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems, and can easily detect the ground fault position by energizing and generating heat according to the performance of the optical fiber temperature distribution measuring device used. A method for detecting the ground fault position of a power cable is provided, which is characterized by the power that combines optical fibers, and when a ground fault occurs in the optical composite cable, the electrical circuit that consists of the conductor and the shielding layer of the power cable. By intentionally heating the ground fault point by passing a current, by detecting the temperature rise position by the optical fiber temperature distribution measuring device connected to one end of the optical fiber which is the composite,
It is to detect the ground fault position.

[0006]

In the present invention, it is considered that the temperature rise is intentionally generated for a long time at the place where the ground fault occurs. A ground fault accident, that is, a cable in which the insulation between the conductor and the shield layer is broken and electrical continuity is generated by arc discharge, has a state in which current easily flows due to the trace at the ground fault point, as shown in Fig. 2. By connecting the current-carrying device 10 to one end of the cable and passing a current, an electric circuit connected from the conductor 1 through the ground fault point A to the shielding layer 3 can be formed. Here, since the electrical continuity of the ground fault point has a much higher electric resistance than that of the cable conductor, a larger amount of heat is generated than that of the conductor portion or the shielding layer portion. Since this heat generation can be controlled by the current flowing, the optical fiber temperature distribution measuring device can easily detect the heat generation point, that is, the ground fault point by supplying the current for a sufficient time to detect the temperature rise point. It is possible to

[0007]

EXAMPLE FIGS. 4A and 4B are cross-sectional views of a structural example of a power / optical composite cable which is the object of the present invention. In the drawings, 1 is a conductor, 2 is a cable insulator such as a cross-linked polyethylene insulator, 3 is a cable shielding layer, and 4 is an outer coating layer such as vinyl chloride or polyethylene. Reference numeral 5 denotes a composite optical fiber, and in FIG. 4A, the optical fiber 5 is wound around the cable insulator 2.
In (b), it is wrapped around the outer periphery of the outer coating layer 4.

FIG. 1 is an explanatory view of a concrete example of the ground fault position detecting method of the present invention. Electricity between the conductor 1 and the shielding layer 3 at one end of the optical composite cable C (either end may be formed or the end may be formed by cutting out the middle of the cable) resulting in a ground fault The device 10 is connected and a current of I (A) is passed. Here, when the electric resistance at the ground fault point A is R (Ω), the heat generation amount is obtained by I ² R (W). An optical fiber 5 is combined with this cable, and an optical fiber temperature distribution measuring device 11 is connected to one end of the optical fiber 5. Normally, when the cable is not intentionally heated, the temperature distribution along the cable is measured as shown in FIG. Here, energization is performed by the energization device 10,
When the ground fault generates heat, the measured temperature distribution is shown in Fig. 3 (b).
As a result, the temperature rise position indicates the ground fault position. Now, assuming that a temperature rise of 5 ° C. is obtained by energization, the current optical fiber temperature measuring device of this type requires an average temperature of, for example, 10 minutes to measure the temperature. Since the time can be continued arbitrarily, the temperature can be easily measured and the ground fault position can be detected.

[0009]

As described above, according to the ground fault position detecting method of the present invention, by controlling the energizing current and time of the energizing device, the energizing is performed according to the performance of the optical fiber temperature distribution measuring device used. It can generate heat and easily detect the ground fault position of the power cable.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a specific example of a ground fault position detection method of the present invention.

FIG. 2 is an explanatory diagram of the basic principle of the ground fault position detection method of the present invention.

3A and 3B are measurement diagrams of temperature distribution, and FIG. 3A shows the case where the cable is not intentionally heated.
(B) shows the case of intentional heating.

4A and 4B are cross-sectional views of a structural example of a power / optical composite cable.

[Explanation of symbols]

 C Power / optical composite cable A Ground fault 1 Conductor 2 Insulator 3 Shielding layer 4 Outer coating layer 5 Optical fiber 10 Current-carrying device 11 Optical fiber temperature distribution measuring device

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Masayuki Hirose 1-3-3 Shimaya, Konohana-ku, Osaka Sumitomo Electric Industries, Ltd. Osaka Works

Claims (1)

[Claims] 1. When a ground fault occurs in a power and optical composite cable that combines optical fibers, a ground fault is intentionally caused to generate heat by causing a current to flow in an electric circuit composed of a conductor and a shielding layer of the power cable, A ground fault position detecting method for a power cable, characterized in that the ground fault position is detected by detecting the temperature rise position by an optical fiber temperature distribution measuring device connected to one end of the composite optical fiber.