JPH0660861B2 - 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 provides an optical transmission path along an OF cable, and optically connects a plurality of oil leak detectors to the optical transmission path via an optical distributor, and directs light to the optical transmission path. The pulsed light incident through the coupler is distributed to each oil leak detector by the optical distributor, and the pulsed light passing through each oil leak detector is reflected by the light reflection part and passed through the oil leak detector again. After that, the reflected pulsed light returning to the optical transmission path is returned by the optical directional coupler, and the light intensity thereof is detected.

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 includes a plurality of optical distributors 2, and the optical distributors 2 are connected in series by an optical fiber 3. A plurality of oil leak detectors 4 are optically connected in parallel to each light distributor 2. Each oil leak detector 4 is composed of three liquid sensors 4a connected in cascade.

The liquid sensor 4a, as shown in FIG.
0 is bent in a U shape to form a bent portion 10A, and when light is incident on the optical fiber 10, the amount of light leakage depends on the refractive index of the substance adhering to the clad 10b of the bent portion 10A. Changes quantitatively. Therefore, the bent portion 1
When the oil leakage of the OF cable adheres to 0A, 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.

Optical fiber 10 forming these liquid sensors 4a
As shown in FIG. 1, a light-reflecting portion 6 formed by vacuum-depositing a metal such as aluminum is provided on the terminal surface of the.

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 OF oil is adhered to the sensor 4a and the radius of curvature thereof is reduced, the light loss sharply increases as compared with the case where the radius of curvature is reduced in air. Therefore, if the curvature radius of the sensor 4a (curved portion 10A) is set appropriately, the intrinsic loss (in air) of the sensor 4a can be suppressed low and the sensitivity of the sensor 4a (light loss when OF oil adheres) can be set high. it can. Therefore, as described above, even when three sensors 4a are connected in series, the total intrinsic loss can be reduced, so that the oil leak detector 4 described above can be used.
By using, it is possible to detect the oil leakage at the connection portion of the OF cable as described later.

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.

Next, the light emitting section 5 is optically connected to the incident end of the optical transmission line 1 via the optical directional coupler 7, and pulsed light is incident from the light emitting section 5 to the optical transmission line 1 through the optical directional coupler 7. . Therefore, the incident pulsed light is sequentially distributed to the respective oil leak detectors 4 via the light distributor 2, and enters the respective oil leak detectors 4 as distributed pulsed light. Therefore, each distributed pulsed light is reflected by the light reflector 6 after passing through each liquid sensor 4a, passes through each liquid sensor 4a again as reflected pulsed light, and is returned to the optical transmission line 1. Since the optical directional coupler 7 is arranged on the incident side of the optical transmission line 1, each reflected pulsed light returned into the optical transmission line 1 is extracted by the optical directional coupler 7.

As shown in FIG. 3, each reflected pulsed light is extracted from the optical directional coupler 7 with a predetermined time difference T. Therefore, it is possible to accurately determine which oil leak detector 4 each reflected pulsed light has passed through.

Now, when oil leakage does not occur in each connection portion of the OF cable, each reflected pulse light is reduced in light intensity by the oil leakage detector 4 by the amount of the round trip of its own loss, and the optical directional coupler 7 The light is separated from the pulsed light and is extracted. On the other hand, when an oil leak occurs at any of the OF cable connection parts and the OF oil adheres to the liquid sensor 4a of the corresponding oil leak detector 4, the reflection that passes through the oil leak detector 4 The attachment loss is added to the intrinsic loss of the pulsed light, and the light intensity is greatly reduced and the pulsed light is extracted. Therefore, by detecting the change (decrease) in the light intensity of the reflected pulsed light and the time difference T of the reflected pulsed light, it is possible to instantly know the occurrence and location of the oil leakage.

For example, when the liquid sensors 4a and 4a are arranged at positions 2.2 km and 2.7 km away from the optical directional coupler 7, respectively, the time difference T and the waveform of the reflected pulsed light when the pulsed light is incident on the optical transmission line 1 OTDR (Optical Time Domain Refl
ectometry) and examined, in a normal state, that is, in a state where no oil leak is attached to these liquid sensors 4a, 4a, as shown in FIG. Based on the pulsed light, the reflected pulsed light reflected at the 2.7 km position is only attenuated by about 10 dB.

Next, when OF oil was adhered to the liquid sensor 4a at the position of 2.2 km, as shown in FIG. 5, the reflected pulsed light reflected at the position of the sensor 4a was about 5 compared with the normal state.
dB attenuated.

Further, when OF oil was adhered to the liquid sensor 4a at the position of 2.7 km, the corresponding reflected pulsed light was attenuated by about 5 dB as compared with the normal state, as shown in FIG.

In the above embodiment, since the light reflecting portion 6 is provided on the end surface of the optical fiber 10 by vacuum evaporation of metal, the reflected pulsed light can be returned to the optical transmission line 1 with low loss. Therefore, the oil leak detector 4 can be composed of three or more liquid sensors 4a, and therefore the oil leak can be detected more efficiently.

The light reflecting portion 6 may be any light reflecting means having a mirror surface.

By the way, in the embodiment shown in FIG.
The received pulsed light to the oil leak detector 4 and the optical fiber 3
It is distributed to one. Therefore, since the intensity of the pulsed light is divided into two each time it passes through the light distributor 2, the reflected pulsed light extracted by the optical directional coupler 7 is gradually increased in light intensity as shown in FIG. Becomes smaller.

On the other hand, if an optical distributor that distributes pulsed light to the oil leak detector 4 and the optical fiber 3 at a distribution ratio of 1: 2 or more is used as the light distributor 2, the oil leak detector at the subsequent stage is used. Since the pulsed light can be distributed almost evenly to 4, the light intensity of the reflected pulsed light can be read even if the pulsed light is divided into a large number of distributed pulsed lights. Therefore, it is possible to further increase the number of connecting portions capable of detecting the oil leakage of the OF cable in proportion to the distribution number of the pulsed light.

(Effects of the Invention) According to the present invention, a plurality of oil leak detectors are optically connected in parallel to an optical transmission line arranged along an OF cable through an optical distributor, and an optical transmission line is connected to the optical transmission line. The pulsed light incident via the directional coupler is distributed to each oil leak detector and passed therethrough, and the distributed pulsed light is reflected by the reflecting section and returned to the optical transmission line as reflected pulsed light. Since the light is extracted by the optical directional coupler, the occurrence of the oil leak accident and the accident point can be accurately known automatically and instantly only by detecting the light intensity of each reflected pulsed light. 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, the pulsed light passing through the oil leak detector where the amount of passing light decreases due to the adhesion of oil leak is reflected by the light reflecting portion and passed through the oil leak detector again, so when oil leak occurs, The pulsed light is attenuated twice. As a result, the light intensity of the reflected pulsed light detected via the optical directional coupler is
Since there is a large difference between "normal time" and "at the time of oil leak", highly sensitive oil leak detection is possible.

Furthermore, since the pulsed light that has passed through the oil leak detector is reflected by the light reflector and transmitted, the amount of reflected light to be detected becomes greater than in the prior art. As a result, the difference between the signal (target light) and the noise (unnecessary reflected light, etc.) becomes large, so that the S / N is improved and it is possible to detect the oil leak that is hardly affected by the noise.

[Brief description of drawings]

FIG. 1 is a diagram showing a connection configuration of each oil leak detection device used in the method of the present invention, FIG. 2 is a front view of a liquid sensor, FIG. 3 is a diagram showing light intensity with respect to a time difference of reflected pulsed light, and FIG. 6 to 6 are loss characteristic diagrams of reflected pulsed light. 1 ... Optical transmission line, 2 ... Optical distributor, 3 ... Optical fiber, 4 ... Oil leak detector, 4a ... Liquid sensor, 6 ... Light reflecting part, 7 ... Optical directional coupler.

 ─────────────────────────────────────────────────── ─── 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 Within Showa Densen Denki Co., Ltd. (56) Reference JP-A-55-16550 (JP, A) JP 58-95243 (JP, A) JP 60-54612 (JP, B2)

Claims (2)

[Claims] 1. A plurality of oil-leakage detectors, which reduce the amount of light passing through due to the adherence of oil-leakage from the OF cable, are optically connected to an optical transmission path provided along the OF cable via an optical distributor.
After the pulsed light is incident on the optical transmission line via an optical directional coupler, the pulsed light is distributed to each of the oil leak detectors in the optical distributor and passed through the oil leak detector, After being reflected by the light reflecting portion, this reflected pulsed light is passed through the oil leak detector again, then returned to the optical transmission line via the optical distributor, and each reflected pulsed light returned to the optical transmission line is returned. O is characterized in that the presence or absence of oil leakage is detected by taking out by the light directional coupler and sequentially detecting the light intensity.
Oil leak detection method for F cable. 2. The optical distributor of the optical transmission line is set to have a large distribution ratio in a direction in which the transmission distance of the pulsed light increases. OF cable oil leak detection method.