JPH0670435A - Measurement of burial depth of subaqueous power cable - Google Patents

Abstract

PURPOSE:To make it possible to monitor the underground depth over the full length by a method wherein light is cast on an optical fiber and then a temperature distribution in the longitudinal direction of a power cable is detected due to Raman scattering light of the light cast on the optical fiber. CONSTITUTION:An optical combined subaqueous power cable 1 wherein optical fibers 2 are combined is buried in the water bottom soil 4 at the depth of L. The optical fibers 2 in the buried optical combined subaqueous power cable 1 are used as a licensor. Light from a laser light source or an LED light source is cast on the optical fibers 2 and then the intensity of Raman scattering light contained in back scattering light of the light cast on the optical fibers 2 is detected. By this, data about a temperature distribution in the longitudinal direction of the optical compound subaqueous power cable 1 can be attained. By this method, a change in the underground depth L of the cable 1 can be known accurately and the underground depth L can be monitored over the full length of the cable 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring a buried depth of a submarine power cable which is a composite of optical fibers buried under the water.

[0002]

2. Description of the Related Art Most of the accidents of submarine power cables are caused by damages to the cables due to anchors, fishing gears, etc., and preventing them is the key to improving the reliability of submarine power cables. . Therefore, when laying a submarine cable, a method of burying the cable at a depth of, for example, 1 to 6 m below the sea bottom is adopted from the viewpoint of preventing external damage. However, the seafloor topography is not uniform in some places, and there are many undulations. Also, the tidal current direction at each location is not constant, and the tidal current is extremely fast. Since it changes every moment, it is important to always monitor the burial depth checked by divers immediately after installation and take measures when it becomes shallow.

However, it is very difficult to measure the burial depth. Conventionally, (a) a method of directly diving by diving a diver at a necessary time. (B) A method in which the electromagnetic field generated by the cable is measured in spots while moving the search coil at a right angle to the cable, and this is repeated. Was taken. However, none of the above-mentioned methods is very difficult to work and is not always monitored.

[0004]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned problems and makes it possible to constantly monitor the burial depth of an optical composite submarine power cable that has been laid underground, over the entire length. The present invention provides a depth measurement method, which is characterized in that the optical fiber of the optical fiber composite submarine power cable embedded in the water bottom is used as a line sensor, and light is incident from one end or both ends of the optical fiber, The temperature distribution in the length direction of the power cable is detected from the Raman scattered light included in the side scattered light, and the buried depth is monitored over the entire length from this.

[0005]

FIG. 2 is a schematic cross-sectional view of an example of an optical fiber composite submarine power cable. In the drawing, 11 is a cable conductor having a hollow oil passage 11a formed therein, 12 is a cable insulating layer formed by winding oil-impregnated insulating paper, 13 is a lead cover, 14 is an inclusion such as a plastic string, and 15 is For example, in an optical fiber unit in which an optical fiber is housed in a stainless pipe, the inclusions 14 and the optical fiber units 15 are alternately arranged, and wound around the lead cover 13 with an anticorrosion layer or the like interposed. An armoring iron wire 17 is twisted on it via a seat 16 and an outer yarn 18 is further provided on it.

In addition to this, as shown in FIG. 3, a hollow wire 17a may be used as the glazed iron wire 17, and the hollow fiber 17a may be housed in the hollow portion 17a. In the case of a core, an optical fiber unit in which an optical fiber is housed in, for example, a stainless pipe may be interposed in the twist gap.

FIG. 1 is a schematic explanatory view of a specific example of the method for measuring the buried depth of a submarine power cable of the present invention. In the drawing,
Reference numeral 1 denotes a water bottom power cable in which an optical fiber 2 is combined, and this water bottom power cable 1 is buried in a water bottom soil 4 at a depth L. In this way, one or a plurality of the optical fibers 2 in the buried optical composite underwater power cable 1 is used as a line sensor, and the DTS 3 (Di
stributed Tempera-ture Sensor) is installed, light is incident on the optical fiber 2 from a laser light source or an LED light source, and the intensity of Raman scattered light included in the backscattered light is detected to determine the length direction of the submarine power cable. It is possible to obtain data of temperature distribution of.

According to the result of actual measurement by the present inventor, for example, D
Assuming that the thermal resistance of the seabed soil (confirmed by actual measurement) is 70 ℃ ・ cm / W when the maximum current of 2800A is applied to the C500KV, 1 × 3000mm ² iron-insulated submarine OF cable, as shown in Fig. 2. Even when an optical fiber is compounded on the outside of the lead cover of the cable, for example, when the burial depth decreases from 3 m to 1 m, the lead cover temperature decreases from 62.6 ° C to 54.5 ° C by 8 ° C, and when exposed further, 33 ° C (20 ° C). It has been confirmed that the difference will decrease.

Therefore, the burial depth should be measured separately with a diver after installation, and the temperature distribution in the cable length direction at this time should be compared with the temperature distribution in the cable length direction measured by the method of the present invention. As a result, it is possible to accurately detect changes in the burial depth and constantly monitor the burial depth over the entire length of the cable. And when it becomes shallow, measures can be taken immediately. If the same cable is laid under multiple lines, by comparing them under the same conditions of use, we can understand the tendency to become relatively shallow or, on the contrary, too deeply buried. You can also do it.

[0010]

As described above, according to the buried depth measuring method for a submarine power cable of the present invention, it is possible to constantly monitor the buried depth over the entire length of the cable without requiring labor unlike the conventional method. This is possible and extremely effective in improving the reliability of submarine power cables.

[Brief description of drawings]

FIG. 1 is a schematic explanatory view of a specific example of a method for measuring a buried depth of a submarine power cable of the present invention.

FIG. 2 is a schematic cross-sectional view of an example of an optical fiber composite submarine power cable.

FIG. 3 is a cross-sectional view of an example in which an optical fiber unit is housed in an armouring iron wire.

[Explanation of symbols]

 1 Optical composite underwater power cable 2 Optical fiber 3 DTS 4 Soil

Claims (1)

[Claims] 1. The Raman scattering included in the backscattered light, wherein the optical fiber of the optical fiber composite underwater power cable buried and laid at the bottom of the water is used as a line sensor and light is incident from one end or both ends of the optical fiber. A method for measuring the burial depth of a submarine power cable, which comprises detecting a temperature distribution in the lengthwise direction of the power cable from light and monitoring the burial depth over the entire length.