Sensor unit, power cable, and measurement system

Abstract

To easily measure the bend of a cable in the sea.SOLUTION: A sensor unit according to the present invention includes a base portion formed of a synthetic resin, a first tension member disposed along a longitudinal direction of the base portion inside the base portion, a second tension member disposed parallel to the first tension member inside the base portion, a first tape core wire disposed along the longitudinal direction of the base portion inside the base portion and disposed at a position away from a neutral plane of the base portion, and a first spacer disposed between the first tape core wire and the neutral plane.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a sensor unit, a power cable, and a measurement system. [Background technology]

[0002] Patent Documents 1 and 2 disclose examples of inventions for detecting cable bending. The curvature sensor disclosed in Patent Document 1 detects curvature variations and bending of a submarine power cable and is disposed between three twisted power cores. The curvature sensor includes an elastic elongated member and a plurality of fiber Bragg grating (FBG) fibers extending axially along the elongated member. The FBG fibers are disposed in a recess on the outer surface of the elongated member and are spliced ​​to an optical fiber that does not have a Bragg grating and that emits visible or ultraviolet electromagnetic waves from a monitoring system. The monitoring system detects the emitted electromagnetic waves reflected by the FBG fibers and determines the curvature of the submarine power cable based on the detected electromagnetic waves.

[0003] The composite cable disclosed in Patent Document 2 includes multiple power lines for transmitting power, a sensing cable, and multiple tension members. The sensing cable includes a slotted member, three sensing optical fibers, and a tension member. The slotted member has multiple grooves on its outer periphery for accommodating optical fibers, which are spaced circumferentially at predetermined intervals and extend spirally around the axis. A tension member is inserted longitudinally into the center of the cross section of the slotted member. When the composite cable is locally bent, the sensing cable also bends and distorts in response to the bending, and the shape and strain distribution of the sensing optical fiber in the longitudinal direction also change in response to changes in the shape of the composite cable in the longitudinal direction. The shape of the composite cable in the longitudinal direction can be detected by detecting the strain distribution in the longitudinal direction of the multiple sensing optical fibers. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2022-74010 [Patent Document 2] Japanese Patent Publication No. 2022-110605 Summary of the Invention [Problem to be solved by the invention]

[0005] In the curvature sensor disclosed in Patent Document 1, if the distance between the FBG fiber and the central axis of the elongated member that is the center of bending is short, the strain generated in the FBG fiber when bending occurs is small, so there is a limit to the sensitivity of bending measurement. When the sensing cable disclosed in Patent Document 2 is stored in a position away from the axis center in the composite cable, the sensing optical fiber extends spirally in the longitudinal direction relative to the center of the slot member, and the position of the sensing optical fiber fluctuates periodically in the longitudinal direction relative to the center of bending. In this case, the strain generated when the sensing optical fiber is bent becomes complex, so complex calculations are required to detect the shape of the composite cable.

[0006] The present invention has been made in view of the above, and has an object to make it possible to easily measure the bending of a cable underwater. [Means for solving the problem]

[0007] In order to solve the above-mentioned problems and achieve the object, the sensor unit of the present invention comprises: a base made of synthetic resin; a first tension member arranged inside the base along the longitudinal direction of the base; a second tension member arranged inside the base parallel to the first tension member; a first ribbon fiber arranged inside the base along the longitudinal direction of the base and at a position away from the neutral plane of the base; and a first spacer arranged between the first ribbon fiber and the neutral plane.

[0008] The sensor unit according to one aspect of the present invention may have a hollow tube, and the base portion may be disposed in the hollow portion of the tube so as to be rotatable relative to the tube.

[0009] In the sensor unit according to one aspect of the present invention, a second ribbon fiber may be disposed on the neutral plane.

[0010] In the sensor unit according to an aspect of the present invention, the number of optical fibers contained in the first ribbon may be smaller than the number of optical fibers contained in the second ribbon.

[0011] A sensor unit according to one aspect of the present invention may include a third optical fiber tape and a second spacer, wherein the third optical fiber tape is positioned symmetrically to the first optical fiber tape with the neutral plane as the center, and the second spacer is positioned between the second optical fiber tape and the third optical fiber tape.

[0012] In the sensor unit according to the aspect of the present invention, the first spacer may have a recess in which the first optical fiber ribbon is accommodated, and the first optical fiber ribbon may be accommodated in the recess.

[0013] A power cable according to one aspect of the present invention is a power cable for transmitting electric power, and includes any of the sensor units described above, with the base portion being rotatably arranged within a gap in the power cable.

[0014] A measurement system according to one aspect of the present invention includes a sensor unit as described above, a light source that outputs an optical pulse to be input to one of the optical fibers of the first ribbon fiber, a light receiving unit that receives scattered light generated in the first ribbon fiber by the optical pulse, and a processing unit that calculates the bending radius of a power cable having the sensor unit based on the measurement result of the scattered light received by the light receiving unit. [Effects of the Invention]

[0015] The present invention has the effect of easily measuring the bending of a cable underwater. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 is a schematic diagram of an offshore wind power generation system according to an embodiment. [Figure 2A] FIG. 2A is a cross-sectional view of a dynamic cable. [Figure 2B] FIG. 2B is a cross-sectional view of a dynamic cable. [Figure 3] FIG. 3 is a cross-sectional view of the sensor unit. [Figure 4] FIG. 4 is a diagram showing the dynamic cable in a bent state. [Figure 5A] FIG. 5A is a cross-sectional view taken along line AA in FIG. [Figure 5B] FIG. 5B is a cross-sectional view taken along line BB in FIG. [Figure 5C] FIG. 5C is a cross-sectional view taken along line CC in FIG. [Figure 5D] FIG. 5D is a cross-sectional view taken along line DD in FIG. [Figure 5E] FIG. 5E is a cross-sectional view taken along line EE in FIG. [Figure 5F] FIG. 5F is a cross-sectional view of the dynamic cable. [Figure 6] FIG. 6 is a diagram showing the configuration of the measurement system. [Figure 7] FIG. 7 is a diagram showing the measurement results of the amount of strain in the optical fiber. [Figure 8] FIG. 8 is a diagram showing the measurement results of the amount of strain in the optical fiber. [Figure 9] FIG. 9 is a cross-sectional view of a modified example of the sensor unit. [Figure 10] FIG. 10 is a cross-sectional view of a modified example of the sensor unit. [Figure 11] FIG. 11 is a cross-sectional view of a modified example of the sensor unit. [Figure 12] FIG. 12 is a cross-sectional view of a modified example of the sensor unit. [Figure 13]FIG. 13 is a cross-sectional view of a modified example of the sensor unit. [Figure 14] FIG. 14 is a cross-sectional view of a modified example of the sensor unit. [Figure 15] FIG. 15 is a cross-sectional view of a modified example of the sensor unit. [Figure 16] FIG. 16 is a diagram showing an example of the arrangement position of the sensor unit. [Figure 17] FIG. 17 is a cross-sectional view of a modified example of the sensor unit. [Figure 18] FIG. 18 is a diagram showing the relationship between the distance of the sensor unit from the neutral plane of the optical fiber and the optical loss. [Figure 19] FIG. 19 is a cross-sectional view of a modified example of the sensor unit. DETAILED DESCRIPTION OF THE INVENTION

[0017] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. Note that the present invention is not limited to the embodiments described below. In addition, in the description of the drawings, the same or corresponding elements are appropriately designated by the same reference numerals. Furthermore, it should be noted that the drawings are schematic, and the dimensional relationships between the elements may differ from the actual ones. There may also be parts in which the dimensional relationships and ratios between the elements differ from one another.

[0018] FIG. 1 is a schematic diagram of an offshore wind power generation system SYS1 according to an embodiment of the present invention. In the offshore wind power generation system SYS1, an offshore platform 5 is connected to an offshore substation 6 via a dynamic cable 1a. The offshore platform 5 is, for example, a tension-moored platform known as a TLP (Tension Leg Platform). The offshore platform 5 includes a float 51, a tower 52, a nacelle 53, a rotor 54, blades 54a, tendons 55, and a foundation 56. The offshore platform 5 is moored by connecting the semi-submerged float 51 and the foundation 56 installed on the seabed via the tendons 55, utilizing tension generated by buoyancy. A nacelle 53 is provided on top of the tower 52 attached to the float 51. The nacelle 53 supports a main shaft (not shown), to which a rotor 54 having blades 54a is attached. The nacelle 53 contains a generator that generates electricity by rotating the main shaft of the rotor 54, power equipment for supplying the power generated by the generator to the dynamic cable 1a, a wind direction and anemometer, and a computer device that communicates with a land-based monitoring device that monitors the offshore platform 5. The offshore platform 5 supplies power to the offshore substation 6 via the dynamic cable 1a at a voltage of, for example, 22 kV.

[0019] The offshore substation 6 is a facility that boosts the power transmitted at 22 kV from the offshore platform 5 to 66 kV. The power boosted to 66 kV by the offshore substation 6 is supplied to the onshore switchyard 7 via the dynamic cable 1b, the submarine joint 3, and the submarine cable 2.

[0020] A plurality of intermediate buoys 4 having buoyancy are attached to the dynamic cables 1a, 1b to ensure excess length between the floating body 51 and the seabed so that excessive tension is not generated in the dynamic cables 1a, 1b when the dynamic cables 1a, 1b vibrate underwater.

[0021] The submarine joint 3 is a joint that connects the dynamic cable 1b, which is connected to the offshore substation 6, with the submarine cable 2. The submarine cable 2 is installed on the seabed and connects the onshore switchyard 7 with the submarine joint 3, and transmits power transmitted via the submarine joint 3 to the onshore switchyard 7. The onshore switchyard 7 is a facility that opens and closes electric circuits with a switchgear (not shown). The switchgear installed in the onshore switchyard 7 is connected to an overhead power transmission line, and power supplied from the offshore substation 6 is transmitted via the overhead power transmission line.

[0022] 2A is a cross-sectional view perpendicular to the longitudinal direction of a dynamic cable 1a, which is an example of a power cable for transmitting electric power. The dynamic cable 1a mainly comprises a power line unit 100 and a covering 127 that surrounds the power line unit 100. The power line unit 100 is a three-core power cable formed by twisting together three power lines 103. The power line unit 100 may also have a single-core configuration consisting of a single power line 103. The power line 103 comprises, from the center, a conductor 107, an inner semiconductive layer 109 provided on the outer periphery of the conductor 107, an insulating layer 111 provided on the outer periphery of the inner semiconductive layer 109, an outer semiconductive layer 113 provided on the outer periphery of the insulating layer 111, a metal sheath 115 provided on the outer periphery of the outer semiconductive layer 113, and an inner sheath 117 provided on the outer periphery of the metal sheath 115.

[0023] The covering 127 includes a pressure tape 121, an iron wire armor 123 made of iron wire, and an outer sheath 125. The configurations of the power line 103 and the covering 127 are not limited to the example shown, and some of the components shown may be omitted, or other components may be added. For example, the power line 103 only needs to have at least the conductor 107 covered with an insulator (including the inner semiconductive layer 109, the insulating layer 111, and the outer semiconductive layer 113).

[0024] A spacer member 129 is disposed in the gap formed between the power line unit 100 and the covering 127. The spacer member 129 is formed, for example, by extrusion molding a resin, and is twisted around the power line unit 100. The spacer member 129 is flexible and easily bent and twisted. This allows it to be easily twisted together with the power lines 103 when manufacturing the dynamic cable 1a. Furthermore, while the manufactured dynamic cable 1a is flexible, the spacer member 129 can easily adapt to the flexibility of the dynamic cable 1a. The spacer member 129 fills the gap between the power lines 103 and the covering 127, maintaining the outer shape of the dynamic cable 1a. In this case, the spacer member 129 is resistant to external forces and is not easily crushed when lateral pressure is applied to the dynamic cable 1a. This prevents deformation of the dynamic cable 1a.

[0025] 2A, spacer member 129 may be disposed in one location, but is not limited to the example shown in FIG. 2A, and may be disposed in three locations, one in each gap between three power lines 103. In the gap formed between power line unit 100 and covering body 127, the portion where spacer member 129 is not disposed may be left empty without disposing any other member, and the gap may be filled with an intervening member made of, for example, a polypropylene string.

[0026] A sensor unit 10 having an optical fiber is disposed in a gap 130a provided in the spacer member 129. When the dynamic cable 1a includes a plurality of spacer members 129, the sensor unit 10 may be disposed in each gap 130a of the spacer members 129, or the sensor unit 10 may be disposed in at least one gap 130a. The sensor unit 10 may be housed in a gap 130b between the spacer member 129 and the power line unit 100, or in a gap 130c at the center of the three twisted power lines 103. Alternatively, the gap between the holding tape 121 and the power line unit 100 may be filled with a filler made of resin fibers such as polyethylene, and the sensor unit 10 may be housed in the filler to twist the power line unit 100 and the sensor unit 10 together. Details of the sensor unit 10 will be described later.

[0027] Dynamic cable 1b may have the same configuration as dynamic cable 1a. Dynamic cables 1a and 1b may be dynamic cable 1c shown in Fig. 2B, which is a cross-sectional view perpendicular to the longitudinal direction of dynamic cable 1c.

[0028] Dynamic cable 1c is made up of a power line unit 100 and a covering 127A that surrounds power line unit 100. Dynamic cable 1c does not include spacer member 129, but includes iron wire armor 123a, interposer 131, seat floor 132, and seat floor 133, and differs from dynamic cable 1a in that covering 127A includes pressure tape 121, seat floor 132, iron wire armor 123, seat floor 133, iron wire armor 123a, and outer sheath 125.

[0029] The filler 131 is made of, for example, a polypropylene string and fills the gap between the power line unit 100 and the pressure tape 121. In the dynamic cable 1c, the sensor unit 10 is disposed within the filler 131, and the sensor unit 10 is twisted to the power line unit 100. The seat 132 is made of, for example, a plastic string and covers the outer periphery of the pressure tape 121. An iron wire armor 123 is disposed on the outer periphery of the seat 132, and the seat 133 is provided on the outer periphery of the iron wire armor 123. The seat 133 is made of, for example, a plastic string. An iron wire armor 123a made of iron wire is disposed on the outer periphery of the seat 133. That is, in the dynamic cable 1c, the iron wire armor is doubled, with the seat 133 sandwiched between them. The outer periphery of the iron wire armor 123a is covered with an outer sheath 125.

[0030] The dynamic cable 1c may be configured to include a spacer member 129, similar to the dynamic cable 1a. When the dynamic cable 1c includes the spacer member 129, the sensor unit 10 is disposed in a gap 130a provided in the spacer member 129.

[0031] 3 is a cross-sectional view perpendicular to the longitudinal direction of the sensor unit 10. The sensor unit 10 is a unit used to measure the bending radius of the dynamic cables 1a and 1b. The sensor unit 10 includes a ribbon fiber 11A, a ribbon fiber 12, a spacer 13, tension members 14a and 14b, a base 15, and a tube 16. The ribbon fiber 11A, the ribbon fiber 12, the spacer 13, the tension members 14a and 14b, and the base 15 are integrated by extrusion molding, and the ribbon fiber 11A, the ribbon fiber 12, the spacer 13, and the tension members 14a and 14b are parallel to one another.

[0032] The metal tube 16 has a circular cross section and is hollow. A flexible base 15 containing the ribbon fiber 11A, ribbon fiber 12, spacer 13A, and tension members 14a and 14b is arranged inside the tube 16 along the longitudinal direction. The base 15 is formed of, for example, a synthetic resin and has a rectangular cross section. The base 15 may be made of, for example, polyethylene, but is not limited to polyethylene and may be made of other synthetic resins. The surface of the base 15 is preferably processed to reduce friction with the inner surface of the tube 16. When the base 15 is bent, the side toward the center of the bend contracts and the side opposite the center of the bend expands, with a non-stretchable surface existing at the boundary between the contracted and stretched regions. In the present invention, this non-stretchable surface is referred to as a neutral plane. In this embodiment, the neutral plane is located at a position that coincides with a line connecting the centers of the tension members 14a and 14b when viewed in a cross section perpendicular to the longitudinal direction of the sensor unit 10. Because base 15 has a rectangular cross-sectional shape, it bends easily in the short direction of the cross section, i.e., in the direction perpendicular to the neutral plane, and can easily bend in accordance with the bending of dynamic cable 1a. Because the long side of the cross section of base 15 is shorter than the inner diameter of tube 16, a gap is created between base 15 and the inner surface of tube 16, allowing base 15 to rotate freely inside tube 16.

[0033] Tension members 14a and 14b, which are metal wires, are located at the center of the short side of the rectangular cross section of base 15 and are arranged along the longitudinal direction of base 15. Tension members 14a and 14b are located at a distance from each other, and the distance from the center of the cross section of base 15 to tension member 14a is the same as the distance from the center of the cross section of base 15 to tension member 14b. One of tension members 14a and 14b is an example of a first tension member, and the other is an example of a second tension member.

[0034] The ribbon fiber 11A is formed by arranging a plurality of optical fibers 110 in parallel and collectively coating them with an ultraviolet-curable resin, while the ribbon fiber 12 is formed by arranging a plurality of optical fibers 120 in parallel and collectively coating them with an ultraviolet-curable resin. The ribbon fiber 11A is an example of a first ribbon fiber, and the ribbon fiber 12 is an example of a second ribbon fiber. The optical fibers 110, 120 are so-called glass optical fibers having a core and a cladding, and the optical fibers 110, 120 have a coating formed of, for example, a synthetic resin material that surrounds the cladding. In this embodiment, the ribbon fiber 11A has four optical fibers 110, but may have less than four optical fibers 110 or five or more optical fibers 110. Furthermore, the ribbon fiber 12 has four optical fibers 120, but may have less than four optical fibers 120 or five or more optical fibers 120.

[0035] The ribbon fiber 11A and the ribbon fiber 12 are arranged along the longitudinal direction of the base portion 15. The ribbon fiber 12 is located between the tension members 14a and 14b, and the optical fiber 120 is linear, connecting the centers of the tension members 14a and 14b, and is located on the neutral plane of the base portion 15. The ribbon fiber 11A is located a predetermined distance in the short direction of the cross section from the line connecting the centers of the tension members 14a and 14b. Therefore, the optical fiber 110 is located a predetermined distance in the direction perpendicular to the line connecting the centers of the tension members 14a and 14b. The optical fiber 110 is an example of a first optical fiber, and the optical fiber 120 is an example of a second optical fiber.

[0036] The spacer 13A is located between the optical fiber ribbon 11A and the optical fiber ribbon 12, and is arranged along the longitudinal direction of the base portion 15. The spacer 13A is an example of a first spacer. The material of the spacer 13A is a synthetic resin, such as polyolefin, polyethylene, polypropylene, or polyethylene terephthalate. The cross section of the spacer 13A perpendicular to the longitudinal direction is rectangular. The spacer 13A is preferably in contact with the optical fiber ribbon 11A and the optical fiber ribbon 12. The spacer 13A maintains a constant distance between the optical fiber ribbon 11A and the optical fiber ribbon 12.

[0037] Fig. 4 shows the dynamic cable 1a in a bent state. Fig. 5A is a cross-sectional view taken along line AA in Fig. 4, Fig. 5B is a cross-sectional view taken along line BB in Fig. 4, Fig. 5C is a cross-sectional view taken along line CC in Fig. 4, Fig. 5D is a cross-sectional view taken along line DD in Fig. 4, and Fig. 5E is a cross-sectional view taken along line EE in Fig. 4. When the bending center of the dynamic cable 1a is in the bending center direction shown in Fig. 4, a bending force acts on the tension members 14a and 14b and the base 15, causing the dynamic cable 1a to bend in an arc when viewed from a direction perpendicular to the longitudinal direction, as shown in Fig. 4.

[0038] As shown in Figure 4, when dynamic cable 1a bends, base 15 rotates so that the direction of the line connecting tension members 14a and 14b is perpendicular to the direction of the bending center. Therefore, base 15 does not bend in the direction of the line connecting tension members 14a and 14b. Instead, base 15 maintains the same orientation relative to the bending center at any longitudinal position, as shown in Figures 5A to 5E. For example, if the bending center is oriented in the direction shown in Figure 5F, base 15 rotates at the position of line AA in Figure 4, and the orientation of base 15 becomes the orientation shown in Figure 5F. At other longitudinal positions of dynamic cable 1a, base 15 maintains the same orientation as shown in Figure 5F. Because base 15 has a rectangular cross-sectional shape, it easily bends in a direction perpendicular to the neutral plane, allowing it to easily bend in accordance with the bending of dynamic cable 1a.

[0039] When a bending force is applied to the base 15, a tensile force acts on the side of the base 15 opposite the center of the bend, and a compressive force acts on the side of the base 15 toward the center of the bend. The center of the rectangular cross section of the base 15 in the transverse direction is the neutral plane, where neither tensile nor compressive forces act. Because neither tensile nor compressive forces act on the neutral plane, when the dynamic cable 1a is bent, the optical fiber 120 located at the neutral plane experiences only strain due to elongation of the optical fiber 120. Furthermore, because the optical fiber 110 is located away from the neutral plane in the transverse direction of the rectangular cross section of the base 15, both strain due to bending and strain due to elongation occur. In this embodiment, the bending radius of the dynamic cable 1a can be measured by measuring these strains.

[0040] Next, a measurement system SYS2 for measuring the bending radius of the dynamic cable 1a will be described. Fig. 6 shows the configuration of the measurement system SYS2. The measurement system SYS2 includes a measurement device 200 and optical circulators 210a and 210b. The measurement device 200 includes light sources 201a and 201b, light receiving units 202a and 202b, and a processing unit 203.

[0041] The light sources 201a and 201b output optical pulses. The optical pulse La1 output by the light source 201a is incident on one of the optical fibers 110 of the ribbon fiber 11A of the dynamic cable 1a via an optical circulator 210a connected to the measurement device 200, the submarine cable 2, the submarine joint 3, the dynamic cable 1b, and optical fibers (not shown) provided in the offshore substation 6. The optical pulse La2 output by the light source 201b is incident on one of the optical fibers 120 of the ribbon fiber 12 of the dynamic cable 1a via an optical circulator 210b connected to the measurement device 200, the submarine cable 2, the submarine joint 3, the dynamic cable 1b, and optical fibers (not shown) provided in the offshore substation 6. The optical fiber 110 in the ribbon fiber 11A onto which the optical pulse La1 does not enter, and the optical fiber 120 in the ribbon fiber 12 onto which the optical pulse La2 does not enter, are used, for example, for communication between the onshore switching station 7 and equipment in the nacelle 53.

[0042] In the optical fibers 110 and 120, scattered light is generated by the incident optical pulse. The scattered light generated in the optical fiber 110 is incident on the light receiving unit 202a via optical fibers (not shown) provided in the offshore substation 6, dynamic cable 1b, submarine joint 3, and submarine cable 2, and optical circulator 210a. The scattered light generated in the optical fiber 120 is incident on the light receiving unit 202b via optical fibers (not shown) provided in the offshore substation 6, dynamic cable 1b, submarine joint 3, and submarine cable 2, and optical circulator 210b.

[0043] Light receiving unit 202a includes a photodiode, receives scattered light generated in optical fiber 110 by the optical pulse, converts the received scattered light into an electrical signal, and outputs it to processing unit 203. Light receiving unit 202b includes a photodiode, receives scattered light generated in optical fiber 120 by the optical pulse, converts the received scattered light into an electrical signal, and outputs it to processing unit 203.

[0044] It is preferable that a reference optical fiber that is not housed in the dynamic cable is provided between the optical circulator 210a and the optical fiber 120, and the optical pulses La1 and La2 are incident on the optical fibers 110 and 120 via this reference optical fiber.

[0045] The processing unit 203 measures the distortion caused by bending in the optical fibers 110 and 120 using the electrical signal output from the light receiving unit 202. Methods for measuring this distortion include, for example, the well-known BOTDR (Brillouin Optical Time Domain Reflectometry) method, which uses Brillouin scattered light, or the well-known TW-COTDR (Tunable Wavelength Coherent Optical Time Domain Reflectometry) method, which uses Rayleigh scattered light. By using these methods, it is possible to measure the position where distortion occurs in the longitudinal direction of the optical fibers 110 and 120 and the amount of distortion.

[0046] The processing unit 203 converts the changes in the frequency and phase of the return scattered light detected by the light receiving units 202a and 202b into strain amounts and bending radius corresponding to the changes, and calculates R, which is the bending radius of the dynamic cable 1a. Incidentally, to calculate R, which is the bending radius of the dynamic cable 1a, the amount of strain in the optical fiber 120 due to tension alone is subtracted from the amount of strain in the optical fiber 110 due to bending and tension, to calculate ε, the amount of strain due to bending alone. If the distance from the neutral plane of the base 15 to the optical fiber 110 is d, when the base 15 is bent with a bending radius of R, ε is expressed by the relationship in equation (1).

[0047]

number

[0048] Since ε can be obtained by the above-mentioned BOTDR method or TW-COTDR method and d is predetermined, R can be calculated by equation (2).

[0049]

number

[0050] Because the sensor unit 10 is twisted with three power line units 100 by the dynamic cable 1a, the bending radius of the center of the dynamic cable 1a differs from the bending radius of the sensor unit 10. If the maximum bending radius of the sensor unit 10 resulting from twisting within the dynamic cable 1a, i.e., the maximum bending radius of the sensor unit 10 when the dynamic cable 1a is in a straight state, is Rmu, the bending radius of the dynamic cable 1a is Rc, and the maximum bending radius of the sensor unit 10 resulting from bending the dynamic cable 1a is Rmuc, then equation (3) approximately holds. Furthermore, equation (4) can be obtained by modifying equation (3).

[0051]

number

[0052]

number

[0053] FIG. 7 is a graph showing the measurement results of the amount of strain at a position where the dynamic cable 1a is not bent. By measuring scattered light using the BOTDR method or TW-COTDR method described above, it is possible to obtain the positions where strain occurs in the longitudinal direction of the optical fibers 110 and 120 and the amount of strain at the positions where strain occurs, as shown in FIG. 7. Even when the dynamic cable 1a is not bent, the sensor unit 10 detects that bending occurs due to the twisting within the dynamic cable 1a, and a strain amount ε1 occurs in accordance with the twist pitch. By measuring this ε1 and dividing the distance d to the optical fiber 110 by ε1 using equation (2), Ru can be calculated.

[0054] Fig. 8 is a graph showing the results of measuring the amount of strain at a position where a bend occurs in the dynamic cable 1a. The amount of strain ε2 that occurs at this time is measured, and Rmu can be calculated by dividing the distance d to the optical fiber 110 by ε2 using equation (2). Note that the graphs shown in Figs. 7 and 8 are just examples, and the results of measuring the amount of strain are not limited to those shown in Figs. 7 and 8.

[0055] The processing unit 203 uses the calculated Ru and Rmu to calculate Rc, which is the bending radius of the dynamic cable 1a, according to equation (4).

[0056] As described above, according to this embodiment, the base 15 is rotatably housed within the dynamic cable 1a. When the dynamic cable 1a is bent, the base 15 rotates and bends toward the bending center so that the neutral plane of the base 15 is perpendicular to the bending center direction. When the base 15 is bent in this manner, the optical fiber 110 is displaced from the neutral plane of the base 15, and strain corresponding to the bending occurs in the optical fiber 110. Therefore, the bending radius of the dynamic cable 1a can be measured by measuring the strain of the optical fiber 110. In this embodiment, the strain of the optical fibers 110 and 120 is measured using the BOTDR method or the TW-COTDR method. These methods can measure the strain in the longitudinal direction of the optical fibers 110 and 120 within a range of several tens of kilometers from one end of the optical fibers 110 and 120, making it easy to measure the bending radius of the dynamic cable 1a, even if the distance is long. Furthermore, in this embodiment, the spacer 13A is in contact with the ribbon fiber 11A and the ribbon fiber 12, and the distance between the optical fiber 110 and the optical fiber 120, i.e., d in equation (1), is kept constant. Therefore, compared to a configuration that does not include the spacer 13A, fluctuations in this d are suppressed, and the bending radius Rc of the dynamic cable 1a can be accurately measured.

[0057] [Variations] Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments and can be implemented in various other forms. For example, the above-described embodiments may be modified as follows to implement the present invention. The above-described embodiments and the following modifications may be combined with each other. The present invention also includes configurations in which the components of the above-described embodiments and modifications are appropriately combined. Furthermore, further effects and modifications can be easily derived by those skilled in the art. Therefore, the broader aspects of the present invention are not limited to the above-described embodiments and modifications, and various modifications are possible.

[0058] FIG. 9 is a cross-sectional view perpendicular to the longitudinal direction of a sensor unit 10A according to a modified example. The sensor unit 10A differs from the sensor unit 10 in that it further includes a ribbon fiber 11B and a spacer 13B. In the sensor unit 10A, the ribbon fiber 11A, 11B, and 12, the spacers 13A and 13B, and the tension members 14a and 14b are parallel to one another. The ribbon fiber 11B is an example of a third ribbon fiber, and the spacer 13B is an example of a second spacer. The ribbon fiber 11B is formed by arranging four optical fibers 110 in parallel and collectively covering them with an ultraviolet-curable resin. The ribbon fiber 11B is located a predetermined distance in the short direction of the cross section from a line connecting the centers of the tension members 14a and 14b, and is arranged along the longitudinal direction of the base 15 on the opposite side to the ribbon fiber 11A. The spacer 13B is made of the same material as the spacer 13A and is arranged along the longitudinal direction of the base 15. The spacer 13B is located between the optical fiber ribbon 11B and the optical fiber ribbon 12. The spacer 13B also has a rectangular cross section perpendicular to the longitudinal direction. The spacer 13B is preferably in contact with the optical fiber ribbon 11B and the optical fiber ribbon 12. In this modification, the optical pulse La1 may be incident on one of the optical fibers 110 contained in the optical fiber ribbon 11B.

[0059] FIG. 10 is a cross-sectional view perpendicular to the longitudinal direction of a sensor unit 10B according to a modified example. The sensor unit 10B differs from the sensor unit 10 in that it includes a ribbon fiber 11C instead of the ribbon fiber 11A. In the sensor unit 10B, the ribbon fiber 11C and 12, the spacer 13A, and the tension members 14a and 14b are parallel to one another. The ribbon fiber 11C is formed by arranging two optical fibers 110 in parallel and covering them together with an ultraviolet-curable resin. The ribbon fiber 11C contains fewer optical fibers than the ribbon fiber 12, and therefore has a lower Young's modulus and lower rigidity than the ribbon fiber 12. This makes the sensor unit 10B more flexible, making it easier to measure the bending radius of the dynamic cable 1a. Note that in the sensor unit 10B, the number of optical fibers 110 contained in the ribbon fiber 11C is not limited to two, as long as it is less than the number of optical fibers 120 contained in the ribbon fiber 12.

[0060] 11 is a cross-sectional view perpendicular to the longitudinal direction of a sensor unit 10C according to a modified example. The sensor unit 10C differs from the sensor unit 10 in that it does not include the spacer 13A and the ribbon fiber 11A and the ribbon fiber 12 are in contact with each other. In the sensor unit 10C, the ribbon fiber 11A, 12, and the tension members 14a, 14b are parallel to each other. In the sensor unit 10C, the ribbon fiber 11A and the ribbon fiber 12 are in contact with each other, and d in equation (1) is kept constant. This suppresses fluctuations in d, enabling accurate measurement of the bending radius Rc of the dynamic cable 1a.

[0061] FIG. 12 is a cross-sectional view perpendicular to the longitudinal direction of a sensor unit 10D according to a modified example. The sensor unit 10D differs from the sensor unit 10 in that it includes a ribbon fiber 11D instead of the spacer 13A. In the sensor unit 10D, the ribbon fiber 11A, 11D, and 12 and the tension members 14a and 14b are parallel to one another. The ribbon fiber 11D is formed by arranging multiple optical fibers 140 in parallel and collectively covering them with an ultraviolet-curable resin. The multiple optical fibers 140 are used, for example, for communications. The ribbon fiber 11D is in contact with the ribbon fiber 11A and the ribbon fiber 12. In the modified example shown in FIG. 12, the ribbon fiber 11D also functions as a spacer that maintains a constant distance between the ribbon fiber 11A and the ribbon fiber 12. In the sensor unit 10D, the ribbon fiber 11A and the ribbon fiber 11D are in contact with each other, and furthermore, the ribbon fiber 11D and the ribbon fiber 12 are in contact with each other, and since d in the equation (1) is kept constant, fluctuations in this d are suppressed, and the bending radius Rc of the dynamic cable 1a can be accurately measured.

[0062] FIG. 13 is a cross-sectional view perpendicular to the longitudinal direction of a sensor unit 10E according to a modified example. The sensor unit 10E differs from the sensor unit 10 in that it includes a spacer 13C instead of the spacer 13A. In the sensor unit 10E, the optical fiber ribbons 11A and 12, the spacer 13C, and the tension members 14a and 14b are parallel to one another. The spacer 13C has an H-shaped cross-section perpendicular to the longitudinal direction. The optical fiber ribbon 12 and the optical fiber ribbon 11A are accommodated in recesses in the spacer 13C and are in contact with the spacer 13C. In the sensor unit 10E, the optical fiber ribbon 11A and the optical fiber ribbon 11A are less likely to shift in the longitudinal and lateral directions of the cross section, allowing accurate measurement of the bending radius Rc of the dynamic cable 1a. The cross-sectional shape of the spacer 13c is not limited to that illustrated in FIG. 13 and may be any other shape as long as it has a recess and allows at least the optical fiber ribbon 11A to fit in the recess.

[0063] In the above-described embodiment, when the number of optical fibers 110 contained in the ribbon fiber 11A and the number of optical fibers 120 contained in the ribbon fiber 12 are odd numbers, the optical pulse La2 may be incident on the optical fiber 120 located at the center of the base 15, and the optical pulse La1 may be incident on the optical fiber 110 located from the center of the base 15 in the short direction of the cross section of the base 15. In this modified example, even if the sensor unit 10 does not rotate properly and the neutral plane is tilted from the line connecting the centers of the tension members 14a and 14b, the optical fiber 120 located at the center of the base 15 will not be strained by bending but will only be strained by elongation, thereby minimizing the effect on the measurement of the bending radius of the dynamic cable 1a.

[0064] In the above-described embodiment, the dynamic cable 1a may be configured without the tube 16. In this modification, the sensor unit 10 is disposed, for example, in the gap 130a, gap 130b, or gap 130c in the dynamic cable 1a, which is not filled with filler, and rotates in these gaps depending on the direction in which the dynamic cable 1a is bent. Even if the dynamic cable 1a is configured without the tube 16, the base 15 rotates depending on the direction in which the dynamic cable 1a is bent, so that the amount of strain due to bending can be measured, and the bending radius of the dynamic cable 1a can be measured. Furthermore, the dynamic cable 1c may also be configured without the tube 16.

[0065] In the above-described embodiment, the cross section of the base 15 perpendicular to the longitudinal direction is rectangular. However, the cross section of the base 15 is not limited to a rectangle and may have other shapes. FIG. 14 is a diagram showing a cross section perpendicular to the longitudinal direction of a sensor unit 10F according to a modified example. The sensor unit 10F shown in FIG. 14 has a base 15a instead of the base 15. In the sensor unit 10F, the ribbon fiber 11A, 12, the spacer 13A, and the tension members 14a, 14b are parallel to one another. The base 15a differs from the base 15 in that the cross section perpendicular to the longitudinal direction of the sensor unit 10F is convex. The tension members 14a, 14b are positioned a predetermined distance apart on the neutral plane of the base 15a and are arranged along the longitudinal direction of the base 15a.

[0066] The ribbon fiber 12 is located between the tension members 14a and 14b. The ribbon fiber 11A is located inside the protruding portion 15aa of the base portion 15a, a predetermined distance from the line connecting the centers of the tension members 14a and 14b in a direction perpendicular to the line. The spacer 13A is located between the ribbon fiber 11A and the ribbon fiber 12, and is in contact with the ribbon fiber 11A and the ribbon fiber 12. The base portion 15a has the protruding portion 15aa in a direction perpendicular to the neutral plane, and by placing the ribbon fiber 11A on this protruding portion 15aa, the amount of strain when bent can be increased.

[0067] FIG. 15 is a diagram showing a cross section perpendicular to the longitudinal direction of a sensor unit 10G according to a modified example. The sensor unit 10G shown in FIG. 15 has a base 15b instead of the base 15. In the sensor unit 10G, the ribbon fiber 11A, 12, the spacer 13A, and the tension members 14a, 14b are parallel to one another. The cross section perpendicular to the longitudinal direction of the base 15d is circular. The tension members 14a, 14b are located on a line passing through the center of the cross section of the base 15b and are arranged along the longitudinal direction of the base 15b. The distance from the center of the cross section of the base 15b to the tension member 14a is the same as the distance from the center of the cross section of the base 15b to the tension member 14b.

[0068] The ribbon fiber 11A and 12 are arranged along the longitudinal direction of the base 15b. The ribbon fiber 12 is located on a line (neutral plane) connecting the center of the tension member 14a and the center of the tension member 14b. The ribbon fiber 11A is also located at a predetermined distance from the line connecting the centers of the tension members 14a and 14b in a direction perpendicular to the line. The spacer 13A is located between the ribbon fiber 11A and the ribbon fiber 12 and is in contact with the ribbon fiber 11A and the ribbon fiber 12. The base 15b has a circular cross-sectional shape, so it can easily rotate inside the tube 16.

[0069] In the above-described embodiment, sensor unit 10 is disposed inside cover 127, but the position at which sensor unit 10 is disposed is not limited to the position in the embodiment. FIG. 16 is a diagram showing an example of the position at which sensor unit 10 is disposed. For example, as shown in FIG. 16, sensor unit 10 may be disposed on the outside of outer sheath 125. Alternatively, as shown in FIG. 16, sensor unit 10 may be disposed between the outer peripheral surface and inner peripheral surface of outer sheath 125. Alternatively, as shown in FIG. 16, sensor unit 10 may be disposed between presser tape 121 and outer sheath 125.

[0070] In the above-described embodiment, the sensor unit 10 includes the ribbon fiber 12. However, the sensor unit 10 may not include the ribbon fiber 12. FIG. 17 is a cross-sectional view perpendicular to the longitudinal direction of a sensor unit 10H that does not include the ribbon fiber 12. In this sensor unit 10H, the ribbon fiber 12 is not disposed at the neutral plane of the base 15, but the ribbon fiber 11A is disposed at a predetermined distance from the line connecting the centers of the tension members 14a and 14b in a direction perpendicular to the line. In the sensor unit 10H, the ribbon fiber 11A, the spacer 13A, and the tension members 14a and 14b are parallel to one another. Since strain occurs in the optical fiber 110 of the ribbon fiber 11A in response to bending of the dynamic cable 1a, the bending radius of the dynamic cable 1a can be measured by measuring this strain using the measurement system SYS2. Note that the sensor units 10A to 10G may also not include the ribbon fiber 12.

[0071] In the present invention, multiple sensor units 10 may be arranged on the dynamic cables 1a, 1b, and 1c. When the dynamic cables 1a, 1b, and 1c are equipped with multiple sensor units 10, the measurement system SYS2 receives scattered light from each sensor unit 10 and calculates the bending radius of the dynamic cable. By calculating the bending radius of the dynamic cable for each measurement result from the multiple sensor units 10, the bending radius can be determined with high accuracy.

[0072] Furthermore, in the present invention, when multiple sensor units 10 are arranged on a dynamic cable, the bending radius of the dynamic cable may be calculated for each measurement result from the multiple sensor units 10, and the direction of the bending center of the dynamic cable may be identified from the calculation results.

[0073] For example, when multiple sensor units 10 are twisted together in a power line unit 100 and arranged in a dynamic cable, the bending direction can be identified using the position of each sensor unit 10 in the cross section of the dynamic cable and information on the difference in strain (amount of change in strain). More specifically, for example, if the extraction position of the strain difference information is identified for each twist pitch and the difference in strain is extracted where each sensor unit 10 is on the same side of the dynamic cable, the bending direction can be identified more reliably by comparing them.

[0074] Furthermore, for example, by providing a means for identifying the absolute position coordinates of a specific point (e.g., the end) in the longitudinal direction of the dynamic cable, and correcting the results of the measurement of the bending direction distribution and the bending strain distribution using the absolute position coordinates, it is possible to calculate the absolute bending direction of any position on the dynamic cable.

[0075] FIG. 18 is a graph showing the relationship between the distance from the neutral plane of the base 15 of the sensor unit 10 to the center of the optical fiber 110 in the ribbon fiber 11A and the optical loss of the optical fiber 110. From the graph shown in FIG. 18, it is preferable that the distance from the neutral plane of the base 15 to the center of the optical fiber 110 be greater than 0 mm and equal to or less than 0.6 mm. By setting the distance from the neutral plane of the base 15 to the center of the optical fiber 110 within this range, when the optical fiber 110 is bent, the optical fiber 110 will experience strain due to bending and strain due to elongation. The bending radius of the dynamic cable 1a can be measured by measuring these strains with the measuring device 200. Furthermore, by setting the distance from the neutral plane of the base 15 to the center of the optical fiber 110 to be greater than 0 mm and equal to or less than 0.6 mm, the loss of light incident on the optical fiber 110 can be reduced. In the sensor unit 10C, when the diameter of the optical fibers 110 and 120 is 0.25 mm, the minimum distance from the neutral plane of the optical fiber 110 to the neutral plane is 0.25 mm. 18, when this distance is between 0.25 mm and 0.6 mm, the optical loss is small, but when this distance exceeds 0.6 mm, the optical loss in the optical fiber 110 increases. For this reason, in the sensor unit 10C, it is more preferable that the distance from the neutral plane of the base 15 to the center of the optical fiber 110 in the ribbon fiber 11A be greater than 0.25 mm and equal to or less than 0.6 mm.

[0076] FIG. 19 is a diagram showing a cross section perpendicular to the longitudinal direction of a sensor unit 10I according to a modified example. In sensor unit 10I, a covering portion 17 is provided on the outer peripheral surface of tube 16, and covering portion 17 is provided along the longitudinal direction of tube 16. The material of covering portion 17 is, for example, a polyolefin resin, and polyethylene is preferable. However, the material of covering portion 17 is not limited to polyethylene and may be other synthetic resins. The surface of covering portion 17 is preferably processed to reduce friction. [Explanation of symbols]

[0077] 1a~1c dynamic cable 2. Submarine Cables 3 Subsea Joint 4 intermediate buoys 5. Offshore Platform 6. Offshore Substation 7 Onshore Switchyard 10, 10A~10I sensor unit 11A, 11B, 11C, 11D, 12 ribbon fiber 110, 120, 140 optical fiber 13A, 13B spacers 14a, 14b tension members 15, 15a, 15b base 16 tubes 100 Power Line Unit SYS1 Offshore Wind Power Generation System SYS2 Measurement System

Claims

1. a base formed of a synthetic resin; a first tension member disposed inside the base along the longitudinal direction of the base; a second tension member disposed inside the base portion in parallel to the first tension member; a first ribbon optical fiber arranged inside the base along the longitudinal direction of the base and at a position away from the neutral plane of the base; a first spacer disposed between the first ribbon fiber and the neutral plane; A sensor unit comprising:

2. The base is rotatably disposed in the hollow portion of the tube. The sensor unit according to claim 1 .

3. A second optical fiber ribbon is disposed on the neutral plane. The sensor unit according to claim 1 .

4. The number of optical fibers contained in the first ribbon is smaller than the number of optical fibers contained in the second ribbon. The sensor unit according to claim 3 .

5. a third ribbon fiber and a second spacer; the third optical fiber ribbon is disposed at a position symmetrical to the first optical fiber ribbon with respect to the neutral plane; The second spacer is disposed between the second optical fiber ribbon and the third optical fiber ribbon. The sensor unit according to claim 3 .

6. the first spacer has a recess in which the first optical fiber ribbon is accommodated, The first optical fiber ribbon is housed in the recess. The sensor unit according to claim 1 .

7. A power cable for transmitting electric power, A sensor unit according to any one of claims 1 to 6, The base is rotatably disposed within the gap of the power cable. Power cable.

8. The sensor unit according to claim 1 ; a light source that outputs an optical pulse to be input to one of the optical fibers included in the first ribbon fiber; a light receiving unit that receives scattered light generated in the first ribbon fiber by the optical pulse; a processing unit that calculates a bending radius of the power cable having the sensor unit based on a measurement result of the scattered light received by the light receiving unit; A measurement system comprising:

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