JP2003222565A - Water invasion detecting method for cable - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve problems in a conventional water invasion detecting method for a cable that a water-absorptive expanding agent or an oil-absorptive expanding agent has to be included in the cable, that the outer diameter of the cable is necessarily thickened since space has to be secured therein for including the water-absorptive expanding agent or the oil-absorptive expanding agent, and that cost is increased by the amount of the expanding agents. <P>SOLUTION: A light pulse is launched into optical fiber in a cable of every kind such as an optical cable or a power cable. Based on the ratio of stroke side intensity to anti-stroke side intensity of resultantly generated Raman scattered light, whether the cable is invaded by water or not and/or what part is invaded by water are/is detected. <P>COPYRIGHT: (C)2003,JPO

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for detecting inundation of various cables such as an optical cable and a power cable. 2. Description of the Related Art As a method for detecting inundation of a power cable, there is a method disclosed in Japanese Patent Application Laid-Open No. Hei 7-280695. According to this method, a detection optical fiber and an oil-absorbing and expanding material or a water-absorbing and expanding material are incorporated in the outer periphery of an insulating layer of a power cable or in a protective tube accommodated in each coating layer, and leakage of insulating oil is detected from the strain distribution of the detecting optical fiber. And to detect inundation into the cable. Specifically, an optical pulse is transmitted to the optical fiber for detection, and the frequency difference between the optical pulse and the Brillouin scattered light is measured. At this time, when the leaked insulating oil or intruded water comes into contact with the oil-absorbing or expanding material, the expanded optical fiber presses the detection optical fiber against the inner wall of the protective tube, causing the fiber to bend. Since the distortion of the optical fiber for detection increases at the place where the bend occurs, oil leakage or water infiltration can be detected by observing the distortion. [0003] In the above-mentioned conventional method for detecting water infiltration, an oil-absorbing and expanding material or a water-absorbing and expanding material must be disposed in advance in a protective tube. Therefore, the outer diameter of the protection tube increases, and the outer diameter of the cable housing the protection tube also increases. Further, the manufacturing cost is increased by the amount of the oil-absorbing expanding material or the water-absorbing expanding material. [0004] A method for detecting the inundation of a cable according to the present invention comprises applying an optical pulse to an optical fiber in various cables such as an optical cable and a power cable, and setting a stroke side and a non-stroke side of the Raman scattered light. In this case, the presence or absence of water intrusion of the cable and / or the location of inundation of the cable are detected based on the intensity ratio. (Embodiment 1) An embodiment of a method for detecting inundation of a cable according to the present invention will be described below.
First, the principle of the cable immersion detection method of the present invention will be described. When light is incident on the optical fiber, Raman scattered light is generated on the stroke side where the intensity is low in sensitivity to temperature and on the anti-stroke side where the intensity is high. Therefore, it is known that the temperature of the optical fiber can be calculated from the intensity ratio of the Raman scattered light on the stroke side and the anti-stroke side. On the other hand, if there is a submerged portion and a non-submerged portion in the cable, the temperature fluctuation of the submerged portion is delayed as compared with the non-submerged portion due to a specific heat difference between water and air. The cable inundation detection method of the present invention detects inundation of a cable using these two principles. Specifically, the inundation of the cable is detected as follows. An optical pulse is continuously or intermittently incident on an unused optical fiber (hereinafter referred to as an "empty core wire for detection") in an optical cable or a power cable (a composite cable in which an optical fiber is housed together with a power line). The temperature of the free core wire for detection is measured by a thermometer for detecting scattered light. This temperature measuring device is a measuring device utilizing the above principle, and calculates the temperature of the free core wire for detection based on the intensity ratio between the Raman scattered light on the stroke side and the Raman scattered light on the anti-stroke. In the above state, when the cable is flooded and a flooded portion and a non-flooded portion occur in the cable,
A temperature difference occurs between the flooded part and the unflooded part. For example, if the temperature of the flooded water is higher than the cable temperature before the flooding,
The temperature of the submerged part is temporarily higher than that of the non-submerged part.
On the other hand, if the temperature of the flooded water is lower than the temperature of the cable before the flooding, the non-flooded portion temporarily becomes lower in temperature than the flooded portion. However, when the temperature is varied, the temperature of the inundated portion decreases or increases due to the influence of the environmental temperature, and the temperature difference from the non-immersed portion is eliminated. Thereafter, when the environmental temperature changes, a temperature change occurs in both the flooded portion and the non-flooded portion. For example, the flooded part and the non-flooded part which became the same temperature at night,
During the day, the temperature rises as it is warmed by sunlight and other effects. At this time, since the temperature fluctuation of the submerged portion is delayed as compared with the non-submerged portion, a temperature difference occurs between the submerged portion and the non-submerged portion. The intensity ratios are different, and the difference between the intensity ratios is detected as a temperature difference by a thermometer. Therefore, if a temperature difference of a predetermined value or more is detected at any point in the longitudinal direction of the detection free core wire by the temperature measuring device, it can be determined that water is present. Further, by calculating at which point in the longitudinal direction of the detection free core wire a temperature difference equal to or greater than a predetermined value occurs, it is possible to identify a location where water is generated. Hereinafter, an experiment conducted to confirm the effect of the method for detecting inundation of a cable according to the present invention will be described. In this experiment, as shown in FIG. 1, two 24-core aluminum tube optical cables for an optical fiber overhead ground wire (OPGW) were prepared and placed in the thermostat 1. Of these, one optical cable 2 is not flooded, and the other optical cable 3 is flooded in advance over its entire length. Further, an optical fiber is arranged in each of the optical cables 2 and 3, and one end of each of the optical fibers is fusion-spliced (unified) outside the thermostat.
A fiber core corresponding to the free core for detection is configured. Further, the temperature measuring device 5 is connected to one end of the integrated optical fiber 4. In the above experimental system, the temperature in the thermostat 1 was increased from 20 ° C. to 60 ° C. at a temperature gradient of 40 ° C./hour. Then, immediately after the temperature reaches 60 ° C., the portion of the optical fiber 4 disposed in the submerged cable 3 is approximately 15 times smaller than the portion disposed in the non-submerged optical cable 2.
A temperature delay of ° C. was measured. Thereafter, when the thermostat was left for 3 hours, the temperature of the optical fiber 4 became almost the same over the entire length (FIG. 2). From the above experimental results, when the cable has a flooded portion and a non-flooded portion, the temperature variation of the flooded portion is delayed with respect to the non-flooded portion, and a temperature difference occurs between the two portions. It was confirmed that the temperature can be measured by a thermometer that measures the temperature of the optical fiber based on the intensity ratio between the Raman scattered light on the stroke side and the Raman scattered light on the anti-stroke. Therefore, it is possible to make an optical pulse incident on an arbitrary empty core wire in various cables, and to determine whether or not the cable is flooded and / or where the cable is flooded based on the intensity ratio of the stroke side and the anti-stroke side of the Raman scattered light. It is possible. In the above-described embodiment, a temperature difference which occurs again due to a temperature fluctuation difference between the two parts after the temperature difference is eliminated is detected instead of a temperature difference generated between the water-immersed part and the non-water-immersed part at the time of occurrence of waterlogging. To determine the presence or absence of flooding. However, the presence or absence of flooding may be determined by detecting the temperature difference between the flooded portion and the unflooded portion when flooding occurs. According to the method for detecting inundation of a cable according to the present invention, an optical pulse is incident on an optical fiber in a cable, and the intensity of Raman scattered light generated as a result on the stroke side and the non-stroke side is determined. Detects the presence or absence of flooding. Therefore, the following effects are obtained. (1) It is possible to reliably and easily detect the presence or absence of water intrusion in various cables such as an optical cable and a power cable. (2) Arbitrary optical fiber in various cables (empty core wire)
Therefore, there is no need to lay a new detection optical fiber. (3) Since no oil-absorptive material or water-absorptive material is required to detect inundation, there is no inconvenience such as an increase in cable outer diameter, and the manufacturing cost is reduced. (4) Since it is not necessary to house the protection tube in the cable and arrange the detection optical fiber therein, it is possible to detect inundation without changing the structure of the existing cable.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an explanatory view schematically showing an experimental system used for confirming the effects of the present invention. FIG. 2 is a diagram showing the results of an experiment using the experimental system shown in FIG. [Description of Signs] 1 constant temperature bath 2 non-flooded optical cable (non-flooded cable) 3 flooded optical cable (flooded cable) 4 optical fiber 5 temperature measuring instrument

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Claims (1)

Claims 1. An optical pulse in an optical fiber in various cables such as an optical cable and a power cable, and the presence or absence of water in the cable based on the intensity ratio of the Raman scattered light between the stroke side and the non-stroke side. And / or a water infiltration point.