JPS63311148A - Power cable line having moisture absorption detecting function - Google Patents

Abstract

PURPOSE:To ensure the detection of a moisture absorbing state, by providing an optical fiber for transmission, which is arranged along the longitudinal direction of a cable, and providing an optical fiber type humidity sensor, which is arranged in a connecting box and connected with the optical fiber in series, and wherein a porous layer is formed at the outer surface part or a core. CONSTITUTION:An optical fiber 5 for transmission is led out of an end part 9 of a power cable 1 and connected to an optical pulse tester 10. A judging part 11 comprising a computer is connected to the tester 10. Light pulses are inputted into the optical fiber 5 for transmission from the tester 10. The time change in backward scattering light is measured. The elapsed time period from the time when the light pulse is inputted corresponds to the distance from the tester 10. When moisture is intruded into one of a plurality of connecting boxes 6, the porous layer of an optical fiber type humidity sensor 7 in the connecting box 6 adsorbs the moisture. The scattering amount of the light pulse at the interface between a core and the porous layer is changed in correspondence with the amount of the adsorbed moisture. A step is yielded in the level of the backward scattering light. Humidity is obtained based on the size of the step in the judging part 11 and compared with a threshold value. Thus, abnormality at the junction part and the like is judged.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a power cable line having a moisture absorption detection function, and more particularly to a power cable line equipped with an optical fiber type humidity sensor.

[Conventional technology] Generally, power cables are widely used and play an essential social function in modern life, but current power cables, which have become increasingly high-voltage, require a particularly high level of performance stability and reliability. requested. One of the causes of performance deterioration and failure of power cables that have such important functions is the infiltration of moisture into the cables. Normally, power cables are tightly coated to prevent moisture from entering, but in the unlikely event that moisture does infiltrate into the cable, it can be detected or performance deterioration due to long-term intrusion of minute moisture can be predicted. I couldn't do that.

By the way, as a so-called humidity sensor that detects moisture content and humidity, an electric resistance type sensor using ceramics or the like has been put into practical use. Therefore, there has been a proposal to arrange this sensor inside a power cable or a cable junction box to monitor the moisture absorption state of the power cable line.

[Problems to be solved by the invention] However, in order to incorporate an electric sensor into a power cable and detect its moisture absorption state, a metal lead wire for supplying power to the sensor and extracting a signal must be inserted into the cable. Therefore, it is susceptible to electromagnetic noise, making it difficult to perform stable detection. Furthermore, when applied to a long cable line, a large number of sensors and signal lead lines are required, which causes problems in terms of installation space and cost. Furthermore, since a voltage is induced in the ground system of a power cable, if a metal lead wire pulled out from the cable comes into contact with the cable by mistake, a circulating current may be generated and the entire power cable line may be destroyed.

Therefore, a moisture absorption detection method has been considered in which an optical fiber is installed inside the cable and the change in loss in a specific wavelength range due to moisture absorption in the optical fiber is used, but the phenomenon of increase in optical fiber absorption loss due to moisture absorption has an extremely long time constant. It is difficult to put it into practical use because it is large and a signal change cannot be detected until several years have passed even if moisture has entered.

SUMMARY OF THE INVENTION Thus, an object of the present invention is to solve the problems of the prior art described above and to provide a power cable line having a moisture absorption detection function that can safely and reliably detect a moisture absorption state.

[Means for Solving the Problems] In order to achieve the above object, the power cable line having a moisture absorption detection function according to the present invention is a power cable line in which the connecting portion of the cable is housed in a junction box. A transmission optical fiber provided along the longitudinal direction, and an optical fiber type humidity provided in the junction box, connected in series with the transmission optical fiber, and having a porous layer formed on the outer periphery of the core. It is equipped with a sensor.

[Function] Since the porous layer made of fine particles such as 5i02 has the effect of adsorbing moisture, an optical fiber type humidity sensor with a porous layer formed on the outer periphery of the core is installed inside the junction box. If the measurement light is propagated inside the junction box, the macroscopic refractive index of the porous layer will change when moisture enters the junction box. The amount changes. As a result, the intensity of the measurement light changes depending on the amount of moisture that has entered the junction box. That is, the state of moisture absorption in the junction box is detected by propagating measurement light into the core of the optical fiber type humidity sensor using a transmission optical fiber and measuring changes in its intensity.

Incidentally, the power cable main body generally has a covering structure such as a metal sheath, metal foil wrapped around it, vertically attached, or continuously extruded from plastic with relatively low water permeability, so that moisture infiltration is prevented. On the other hand, since the cable connection part is wrapped with tape at the site or during work or stored in the connection box, there is a gap between the tape, a gap in the connection box, or a gap between the cable sheathing and the connection box. There is a risk that moisture from outside may infiltrate through.

In fact, in many power cable systems, the location where the probability of failure such as insulation deterioration or breakdown is highest is at the cable connection.

Therefore, by arranging the humidity sensor within the junction box, it is possible to effectively detect moisture intrusion into the cable.

In addition, even if moisture absorption occurs in the cable body, the moisture tends to diffuse in the longitudinal direction of the cable and condense on the outer periphery of the cable inside the junction box, where the temperature is relatively low. Moisture absorption can be detected at the junction box before it becomes a dangerous situation.

[Example code] Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a sectional view showing a connecting portion of a power cable line having a moisture absorption detection function according to an embodiment of the present invention. A power cable 1 includes a conductor 2 and an insulator 3 provided on its outer periphery.
A metal sheath 4 is wrapped around the outer periphery of the insulator 3.
A transmission optical fiber 5 is provided along the longitudinal direction of the power cable 1 in the gap between the insulator 6 and the metal sheath 4. The connection portion of the power cable 1 as described above is housed in the connection box 6.

An optical fiber type humidity sensor 7 is provided in the junction box 6.
Both ends 8 are connected in series to the transmission optical fiber 5 by fusion splicing or the like.

This optical fiber type humidity sensor 7 has a structure in which a porous layer made of 5iOz fine particles is formed around the outer periphery of an optical fiber core.

Next, the operation of this embodiment will be described.

First, as shown in FIG.
DR device) 10 and a determination section 11 consisting of a computer is connected to the optical pulse tester 10.

Then, a light pulse was input into the transmission optical fiber 5 from the light pulse tester 10, and the temporal change in the backscattered light was measured. Here, it is assumed that the elapsed time after the input of the optical pulse corresponds to the distance from the optical pulse tester 10, and that moisture has now entered at least one location of the plurality of connection boxes 6. . Then, the porous layer of the optical fiber type humidity sensor 7 in the junction box 6 adsorbs moisture, and therefore the amount of scattering of the light pulse propagating in the core at the interface between the core and the porous layer becomes the amount of adsorbed moisture. It changes accordingly.

As a result, a step 12 as shown in FIG. 3 occurs in the level of backscattered light. The determination unit 11, which receives input of such temporal changes in the level of backscattered light, determines the humidity inside the junction box from the size of the step, compares this humidity with a preset threshold value, and determines the humidity of each cable. Determines cable deterioration or abnormality at the connection part.

In this way, a moisture absorption abnormality in the power cable can be quickly determined and an accident can be predicted.

[Effects of the Invention] As explained above, according to the present invention, the following excellent effects are exhibited.

(1) An optical fiber type humidity sensor is built into the connection box of the power cable connection part, and is connected in series to the transmission optical fiber along the length of the cable, so lead wires, etc. are connected from each sensor to the outside of the cable. There is no need to pull it out, which significantly improves safety and simplifies construction.

(2) Since it uses an optical fiber type humidity sensor consisting of a core and a porous layer, it has little deterioration over time and is less susceptible to disturbances, electromagnetic induction, etc., and can perform stable moisture absorption detection over a long period of time. .

(3) It is possible to detect the humidity distribution at the connection part of a long power cable at once, and moisture absorption can be detected quickly and with high sensitivity.

(4) Since the humidity sensor does not require any optical elements other than optical fibers and is small and easy to handle, no special structure is required for the power cable.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing a connecting part of a power cable line having a moisture absorption detection function according to an embodiment of the present invention, FIG. 2 is a configuration diagram of a measurement system for detecting moisture absorption using the embodiment, and FIG. FIG. 3 is a graph showing the measurement results according to the example. In the figure, 1 is a power cable, 5 is a transmission optical fiber, 6 is a connection box, and 7 is an optical fiber type humidity sensor. Patent applicant: Tokyo Electric Power Company, Hitachi Cable, Ltd.

Claims (3)

[Claims] (1) In a power cable line in which the connection part of the cable is housed in a junction box, there is a transmission optical fiber provided along the longitudinal direction of the cable, and a transmission optical fiber provided in the junction box and connected to the transmission optical fiber. A power cable line having a moisture absorption detection function, comprising: an optical fiber type humidity sensor connected in series and having a porous layer formed on the outer periphery of the core thereof. (2) The power cable line according to claim 1, wherein the porous layer is made of SiO_2 fine particles. (3) The moisture absorption state in the junction box is detected from the temporal change in backscattered light when pulsed light is incident on the transmission optical fiber. The power cable line described in item 2.