JPH0660862B2 - Oil leak detection method for OF cable - Google Patents

Description

TECHNICAL FIELD OF THE INVENTION The present invention relates to an oil leak detection method for an OF cable, which detects an oil leak occurring in the OF cable by using an optical transmission line and an oil leak detector.

(Technical background of the invention) In an OF cable, an oil passage provided inside the cable is filled with low-viscosity oil, and an oil pressure higher than atmospheric pressure is applied to the oil passage by an external hydraulic adjustment tank. Generation of voids due to temperature changes is suppressed, and cable deterioration is prevented.

In such OF cables, oil leakage often occurs mainly at the cable connection portion. Therefore, conventionally, maintenance and inspection of the vicinity of the connection portion as a center and electrical leakage detection have been performed. I am using a vessel.

(Problems of background art) However, when oil leakage occurs at the connection portion of the OF cable due to a sudden accident such as an earthquake, it is necessary to immediately detect this oil leakage and take countermeasures. . Further, the electric oil leak detector cannot detect the oil leak accurately due to the electromagnetic induction from the OF cable. Therefore, the emergence of a method that always operates automatically and accurately detects oil leakage is desired.

(Object of the Invention) An object of the present invention is to provide an oil leak detection method for an OF cable, which is capable of detecting oil leak in an OF cable automatically and with high accuracy.

(Summary of the Invention) The present invention includes a bending portion formed by bending an optical fiber,
A plurality of oil-leakage detectors, in which the amount of light passing through is reduced by the oil-leakage from the F-cable adhering to the curved portion, are arranged in series in the optical transmission path provided along the OF-cable while keeping a certain distance. Then, pulsed light is incident on the optical transmission line via an optical directional coupler, the pulsed light is sequentially passed through the plurality of oil leak detectors, and the backscattered light reflected by the optical transmission line is transmitted. The leaking oil is detected based on the light intensity of the backscattered light taken out by the light directional coupler.

Embodiments of the Invention Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 shows an optical transmission line 1 used in the method of the present invention. The optical transmission line 1 is composed of a plurality of optical fibers 2, and a plurality of oil leak detectors 4 are arranged in series between the optical fibers 2. Each oil leak detector 4 is composed of three liquid sensors 4a connected in cascade.

The liquid sensor 4a, as shown in FIG.
It is composed of a bent portion 10A formed by bending 0 into a U shape, and when light passes through the optical fiber 10, the light passing therethrough depends on the refractive index of the substance adhered to the clad 10b of the bent portion 10A. Leaks. Therefore, the bent portion 10A is O
When the oil leakage from the F cable is attached, a large amount of light leaks from the curved portion 10A, so that the occurrence of the oil leakage can be known. Incidentally, 10a is a core.

By the way, when the radius of curvature of the liquid sensor 4a (curved portion 10A) is decreased, the bending loss (specific loss) of light in the air of the sensor 4a gradually increases. Further, when insulating oil used for the OF cable is attached to the sensor 4a and the radius of curvature thereof is reduced, the optical loss increases sharply as compared with the case where the radius of curvature in air is reduced. Therefore, the sensor 4
If the radius of curvature of a (curved portion 10A) is set appropriately,
The intrinsic loss of the sensor 4a (in the air) can be suppressed low, and the sensitivity of the sensor 4a (light loss when insulating oil adheres) can be set high. Therefore, as described above, even if three sensors 4a are connected in series, the total intrinsic loss can be reduced. Therefore, by using the oil leak detector 4, the oil leak at the connection portion of the OF cable will be described later. Can be detected.

Next, the oil leakage detection method of the present invention will be described.

That is, the optical transmission line 1 is arranged along an OF cable (not shown). In this case, each liquid sensor 4a of each oil leak detector 4 is positioned so as to be located below the connection portion of the OF cable.

Then, the light emitting section 5 is optically connected to the incident end of the optical transmission line 1 through the optical directional coupler 3, and pulsed light is incident on the optical transmission line 1 from the light emitting section 5 through the optical directional coupler 3. , The optical fiber 2 and the oil leak detector 4 sequentially pass the pulsed light. Therefore, the backscattered light is generated in the optical transmission line 1 by the propagation of this pulsed light to each optical fiber 2 and the oil leak detector 4.

Then, in the method of the present invention, this backscattered light is extracted by the light directional coupler 3 and the light intensity thereof is detected.

Now, when oil leakage does not occur in each connection portion of the OF cable, the backscattered light is reduced in light intensity stepwise by each oil leakage detector 4 by its own loss (loss in air). , Is separated from the pulsed light by the optical directional coupler 3 and is extracted. On the other hand, when an oil leak occurs at one of the OF cable connection portions and the OF oil adheres to the liquid balancer 4a of the corresponding oil leak detector 4, when the oil passes through the oil leak detector 4. In the backscattered light, the oil loss adhesion loss is added to the intrinsic loss,
The light intensity is greatly reduced and the light is extracted. Therefore, by detecting the change (decrease) in the intensity of the backscattered light, it is possible to instantly know the occurrence and location of the oil leakage.

By the way, 500 m and 700 m from the optical directional coupler 3
The liquid sensors 4a and 4a are arranged at distant positions, respectively, and the time difference and the waveform of the backscattered light when the pulsed light is incident on the optical transmission path 1 are shown in OTDR (Optical Time Domain Reflectom).
(Etry) and analyzed, the normal state, that is,
As shown in FIG. 3, the backscattered light has a distance of 500 when the liquid sensors 4a and 4a are not leaked.
The optical loss characteristics of 5.9 dB and 5.1 dB were shown at the positions corresponding to m and 700 m, respectively. These light losses are attenuations due to the intrinsic loss of the liquid sensors 4a, 4a.

Next, when OF oil was attached to the liquid sensor 4a at a position of 500 m, the backscattered light was 500 as shown in FIG.
An optical loss characteristic of 30 dB was shown at a position corresponding to m. This optical loss is the attenuation due to the addition of the attachment loss to the intrinsic loss.

Further, when OF oil was adhered to the liquid sensor 4a at the position of 700 m, as shown in FIG.
An optical loss characteristic of about 35 dB was exhibited at a position corresponding to m.
Similarly, this optical loss is attenuation due to the addition of the attachment loss to the intrinsic loss.

From the above, it is clear that the occurrence and location of oil leakage can be instantly known by examining the intensity of the backscattered light.

Next, when water was attached to the liquid sensor 4a at the position of 500 m, the backscattered light showed an optical loss characteristic of 8.6 dB at the position corresponding to 500 m as shown in FIG.
When water was attached to the liquid sensor 4a at the 0 m position, the backscattered light showed a light loss characteristic of 7.9 dB at the position corresponding to 700 m as shown in FIG. Therefore, when water adheres to the liquid sensor 4a, the light loss of the backscattered light is smaller than that at the time of oil leakage, so that the occurrence of oil leakage accident and the adhesion of water can be clearly discriminated. Therefore, it is possible to effectively prevent the alarm device or the like from malfunctioning on the monitoring side.

(Effects of the Invention) According to the present invention, a plurality of oil leak detectors are arranged in series at a fixed distance in an optical transmission line arranged along an OF cable, and an optical directivity is provided in the optical transmission line. The light intensity of this backscattered light is detected by injecting an optical pulse through the coupler and separating the backscattered light reflected by the optical transmission line from the pulsed light by the optical directional coupler. Just by doing so, it is possible to know the occurrence of the oil leak accident and the point of the accident automatically and instantly. Further, it is not necessary to use a separate optical transmission line for each oil leak detector, and oil leak can be detected at low cost.

Further, in the present invention, since the sensitivity of oil leak detection can be set by appropriately setting the radius of curvature of the curved portion of the optical fiber, it is possible to distinguish between the occurrence of oil leak and the adhesion of water. It is possible to effectively prevent the alarm device or the like from malfunctioning on the monitoring side.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram showing the arrangement of each oil leak detection device used in the method of the present invention, FIG. 2 is a front view of a liquid sensor, and FIGS. 3 to 5 are normal states and when oil leak is attached to the liquid sensor. FIG. 6 is a loss characteristic diagram of backscattered light in FIG. 6, and FIGS. 6 and 7 are loss characteristic diagrams of backscattered light when moisture adheres to the liquid sensor. 1 ... Optical transmission line, 2, 10 ... Optical fiber, 3 ... Optical directional coupler, 4 ... Oil leak detector, 4a ... Liquid sensor, 5 ... Light emitting part.

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Akitoshi Ikeda 1-8-2 Marunouchi, Chiyoda-ku, Tokyo Electric Power Development Co., Ltd. (72) Inventor Kiyohiro Shigemitsu 1-2-8 Marunouchi, Chiyoda-ku, Tokyo Within Gengen Development Co., Ltd. (72) Inventor Shigenori Matsuoka 1-6-5 Shinjuku, Shinjuku-ku, Tokyo Within Development Electronics Technology Co., Ltd. (72) Inventor Keiichi Sakamoto 2-1-1 Oda Ei, Kawasaki-ku, Kawasaki-shi, Kanagawa No. 1 Showa Densen Denki Co., Ltd. (72) Inventor Haruyoshi Furukawa 2-1-1 Oda Sakae, Kawasaki-ku, Kawasaki-shi, Kanagawa Showa Densen Denki Co., Ltd. (56) Reference JP-A-56-82428 (JP, A) JP 58-95243 (JP, A) JP 60-54612 (JP, B2)

Claims (1)

[Claims] 1. A curved portion formed by bending an optical fiber,
An oil leak detector capable of setting the sensitivity of oil leak detection by decreasing the amount of light passing through by the oil leak from the OF cable adhering to the curved portion and changing the radius of curvature of the curved portion, A plurality of optical transmission lines provided along the OF cable are arranged in series while maintaining a certain distance, and pulsed light is made incident on the optical transmission line via an optical directional coupler. After passing through a plurality of oil leak detectors sequentially, the backscattered light reflected by the optical transmission line is taken out by the optical directional coupler, and the change in the intensity of the backscattered light is detected to detect the oil leak. O characterized by detecting presence or absence
Oil leak detection method for F cable.