JPS62270902A - Power cable failure detecting sensor - Google Patents

Abstract

PURPOSE:To detect an abnormality which has been generated in a power cable, with high sensitivity, with a high accuracy, and also, at low cost, by providing an optical fiber in which a thin wall clad optical fiber part and a thick wall clad optical fiber part having a specific thickness have been formed alternately, on the power cable. CONSTITUTION:An optical fiber in which a thin wall clad optical fiber part 8 whose clad thickness is about 1/10-1/20 of a core diameter and a thick wall clad optical fiber part 11 whose clad thickness is about 1/1-1/8 of the core diameter and which is usually used for communication have been formed alternately is provided on a power cable. The thin wall clad optical fiber part 8 and the thick wall clad optical fiber part 11 are formed by a welding connection of these optical fibers and a chemical treatment of the clad. When an external damage or a dielectric breakdown is generated in the power cable, a lateral pressure works on the thin wall clad optical fiber part 8 and a local bend occurs, and a microbend loss is generated. By this microbend loss, a level of backscattering light drops, by which a power cable accident and an accident point can be detected.

Description

[Detailed Description of the Invention] 3. Detailed Description of the Invention [Field of Industrial Application] The present invention is a lightning cable vehicle accident system using an optical fiber as a sensor for detecting accidents such as trauma and insulation breakdown of power cables. Yuru Sen + Jita 1 Oru.

[Prior art] Power cables installed in tunnels or conduits deteriorate in performance due to external damage or deterioration of the insulation, eventually leading to insulation breakdown, and depending on operating conditions, ground faults can occur that can cause major damage. It turns out. However, in these accidents, the current situation is that the occurrence of the accident is only known after insulation breakdown occurs and an abnormality occurs in the 10 operational control devices at the electrical station, and the accident point is usually carried out with the system stopped. Murray loop method and pulse radar method are used. However, these orientation methods have problems such as poor positioning accuracy and time-consuming installation, and are highly dependent on human patrols.

As a measure to solve such problems, recently, as shown in FIG. The fiber 4 is installed to prevent damage or breakage of the optical fiber 4 that occurs when the cable is damaged.
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It has been considered that the backscattered light level can be determined from changes in the level of backscattered light as shown in FIG.

In this method, if there is no abnormality in the optical fiber 4, the trajectory 5
However, when the optical fiber 4 is broken or damaged, reflected light from the optical fiber breakage point appears and forms a trajectory 6 shown by a broken line, so that the breakage point can be located.

[Problems to be Solved by the Invention] However, with this method, it is difficult to determine if the optical fiber 4 has not been damaged to the extent that it will break. As for the dielectric breakdown at , the influence does not extend to the optical fiber 4 shown in FIG. 1, and no abnormality can be detected.

Furthermore, when installing the optical fiber 4 in a cable as shown in FIG. 6, a protective MFFt is required to protect the optical fiber 4 from the thermal and mechanical forces of the cable. It can be said that it is difficult to convey changes due to accidents, etc., and the probability of misorientation is high.

The object of the present invention is to eliminate the drawbacks of the prior art described above,
An object of the present invention is to provide a novel power cable accident detection sensor that can detect abnormalities occurring in power cables with high sensitivity, high precision, and at low cost.

Means for Solving Problems] The present invention has a cladding thickness of approximately 1/10 to 1/1/1 of the core diameter.
A thin clad optical fiber section with a thickness of 20 mm and a thick clad optical fiber section with a cladding thickness of about 1/1 to 1/8 of the core diameter, which is usually used for communication, are formed alternately. It is attached to the cable. The thin clad optical fiber section and the thick clad optical fiber section are formed by fusion splicing these optical fibers or chemically treating the cladding. Optical fibers are installed in the anti-corrosion layer of power cables or around the cable periphery.

[Function] When trauma or dielectric breakdown occurs in a power cable, lateral pressure acts on the thin clad optical fiber, causing local bending.
Microbend loss occurs. Since the level of backscattered light decreases due to this microbend loss, power cable faults and fault points can be detected. Further, since the entire length of the optical fiber is a thin clad optical fiber, and the optical fiber structure is such that thin clad optical fibers and thick optical IJ fibers are alternately formed, a reduction in the SN ratio due to external noise can be avoided.

[Examples] Examples of the present invention will be described in detail below with reference to the drawings.

FIG. 1 shows the structure of an optical fiber 7 which is the main element of the power cable accident detection sensor of the present invention. In the same figure, 8
The thickness of the cladding 9 is 1/10 to 1/2 of the diameter of the core 10.
0 is a thin clad optical fiber portion having a thin cladding layer, and 11 is a thick clad optical fiber used as a normal communication optical fiber in which the thickness of the cladding 12 is about 1/1 to 1/8 of the core diameter 13. Department. The thin clad optical fiber section 8 and the thick clad optical fiber section 11 are linearly integrated by alternating R connections.

The optical fiber 7 constructed in this manner is reinforced with a protective coating and placed on the shielding layer '14 and anticorrosion layer 15 of the power cable, as shown in FIG. In addition, 1 is a conductor, 2
is an insulator. Further, the power cable shown in FIG. 2 has an optical fiber 7 pulled out at its terminal end, and the pulled out optical fiber 7 is 0TDRSi! 1ffi (not shown).

The pulsed light incident on the optical fiber 7 from the light source of the OT D R device propagates through the optical fiber 7.
Backscattered light, which is a reflected light component, returns to the light source side due to Rayleigh scattering that occurs inside the light source. By measuring the backscattered light intensity and the delay time between the backscattered light and the incident pulsed light, a locus 16 shown by the solid line in FIG. 3 is obtained as data 17.

In this embodiment, the thin clad optical fiber part 8 and the thick clad optical fiber part 11 shown in FIG. A step occurs at the connection portion of the optical fiber section 8.11. In FIG. 3, 17 is a portion where the level of backscattered light is reduced by the thin clad optical fiber portion 8, and 18 is a portion where the level of backscattered light is reduced by the thick cladding optical fiber portion 11. Therefore, the configuration is such that the position of the thin clad optical fiber section 8 can be clearly located.

In the power cable accident detection sensor of the present embodiment having such a configuration, when a trauma or an insulation breakdown accident occurs in the power cable, lateral pressure or local bending occurs in the thin clad optical fiber section 8, resulting in a so-called high sensitivity sensor. Microbend loss occurs, and the backscattered light level distribution is trace 19 shown by the broken line in Figure 3.
As a result, the backscattered light level in the vicinity of the accident point 20 is reduced, and the accident and the accident point can be easily determined. Incidentally, microphone [1] bend loss is a well-known development, but it can be said that optical fibers with a normal structure have low sensitivity because they are covered with a reinforcing layer or the like. On the other hand, in this embodiment, by providing a thin clad optical fiber portion 8, leakage of higher-order modes is actively promoted, resulting in extremely high sensitivity. Furthermore, if the entire length of the optical fiber 7 is made of thin-clad optical fiber, it is easily affected by external noise, which leads to a decrease in the S/N ratio. This problem can be avoided by adopting a multi-point purchasing method.

In addition, as for the structure of the linear integrated optical fiber having a thin clad optical fiber part, instead of the 81-connection method in the above embodiment, the cladding part is locally melted by chemical treatment, etc., as shown in Fig. 4. You can also create it by The distribution of the backscattered light level according to this embodiment is shown by a solid line 21 (normal time) and a broken line 22 (at an accident time) in FIG.

[Effects of the Invention] In summary, the present invention provides the following excellent effects.

(1) A thin clad optical fiber section is installed in the optical fiber used as an accident detection sensor, and highly sensitive changes in the thin clad optical fiber section are utilized, so damage only occurs due to high energy such as power cable ground faults. However, it is also possible to detect minute accidental damages such as microscopic damage and external injuries.

(2) As a sensor for detecting accidents, no elements or jigs other than optical fibers are required, and there is no need to measure at a specific wavelength. Therefore, the measurement system can be simplified, handling is easy, and costs can be reduced.

(3) Since the accident detection sensor unit can be configured to be integrated with the power cable, the status of the power cable can be constantly monitored v1 even before an accident occurs, and the presence or absence of an accident and the location of the accident point can be determined in a short time.

[Brief explanation of drawings]

FIG. 1 is a vertical cross-sectional view showing an embodiment of an optical fiber used in a power cable accident detection sensor according to the present invention, FIG. 2 is a cross-sectional view of the same optical fiber attached to a power cable, and FIG. The figure is a characteristic diagram showing the change in the level of backscattered light when accident location is carried out using the same type cable; FIG. 4 is a vertical cross-sectional view of an optical fiber according to another embodiment of the present invention;
The figure is a characteristic diagram showing changes in the level of backscattered light when power cable accident location is performed using the same optical fiber, Figure 6 is a cross-sectional view of a power cable equipped with a conventional accident detection sensor, and Figure 7 is a cross-sectional view of a power cable equipped with a conventional accident detection sensor. The figure is a characteristic diagram showing changes in the level of backscattered light when accident location is performed using the same type of cable. In the figure, 1 is a conductor, 2 is an insulator, 3 is a fr layer, 4 is an optical fiber, 7 is an optical fiber, 8 is a thin clad optical fiber section, 9.12 is a cladding, 10° 13 is a core, and 11 is a In the thick clad optical fiber section, 14 is a shielding layer, and 15 is an anticorrosion layer. Agent Patent Attorney RI311

Claims (2)

[Claims] (1) The thickness of the cladding is approximately 1/10 to 1/20 of the core diameter.
A power cable is provided with an optical fiber in which thin-walled optical fiber sections with a cladding thickness of about 1/1 to 1/8 of the core diameter are alternately formed and thick-walled optical fiber sections with a cladding thickness of about 1/1 to 1/8 of the core diameter. Characteristic power cable accident detection sensor. (2) The power cable accident detection sensor according to claim 1, wherein the optical fiber is provided within the anti-corrosion layer of the power cable and on the outer periphery of the cable.