Power cable, power line, power cable abnormality detection system, and power cable abnormality detection method

Abstract

This power cable includes: a cable body including a conductor, an insulating layer, a semiconductive layer, and a sheath; a first optical fiber through which detection light is transmitted; a second optical fiber through which backscattered light of the detection light is transmitted; an optical fiber through which first excitation light for amplifying the detection light is transmitted; an optical fiber through which second excitation light for amplifying the backscattered light is transmitted; and at least one optical amplification repeater for amplifying the detection light by means of the first excitation light and amplifying the backscattered light by means of the second excitation light.

Description

[Technical Field]

[0001] The present disclosure relates to a power cable, a power line, a power cable anomaly detection system, and a power cable anomaly detection method. This application claims priority to international application PCT / JP2023 / 016834 filed on April 28, 2023, the entire contents of which are incorporated herein by reference. [Background technology]

[0002] Systems for detecting abnormalities such as ground faults, external damage, or fatigue in power cables have been known for some time. For example, the undersea cable in Patent Document 1 is composed of a power cable core, a two-layer armor, and a line sensor with optical fiber. Using the optical fiber, strain changes are measured over the entire length of the undersea cable by the PPP-BOTDA (Pulse Prepump Brillouin Time Domain Analysis) method. The power cable core corresponds to the cable body of the power cable. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-36876 [Patent Document 2] International Publication No. 2021 / 090644 Summary of the Invention

[0004] The power cable of the present disclosure comprises a cable body including a conductor, an insulating layer, a semiconducting layer, and a sheath, a first optical fiber through which detection light is transmitted, a second optical fiber through which backscattered light of the detection light is transmitted, an optical fiber through which first excitation light for amplifying the detection light is transmitted, an optical fiber through which second excitation light for amplifying the backscattered light is transmitted, and at least one optical amplification repeater that amplifies the detection light with the first excitation light and amplifies the backscattered light with the second excitation light.

[0005] The power line of the present disclosure includes a first power cable, a second power cable, and a connection section connecting the first and second power cables. Each of the first and second power cables includes a cable main body including a conductor, an insulating layer, a semiconducting layer, and a sheath, a first optical fiber through which detection light is transmitted, a second optical fiber through which backscattered light of the detection light is transmitted, an optical fiber through which first excitation light for amplifying the detection light is transmitted, and an optical fiber through which second excitation light for amplifying the backscattered light is transmitted. The connection section includes an optical amplifier repeater that amplifies the detection light with the first excitation light and amplifies the backscattered light with the second excitation light.

[0006] The power cable anomaly detection system of the present disclosure includes a power cable including a cable main body including a conductor, an insulating layer, a semiconducting layer, and a sheath, a first optical fiber through which detection light is transmitted, a second optical fiber through which backscattered light of the detection light is transmitted, an optical fiber through which first excitation light for amplifying the detection light is transmitted, and an optical fiber through which second excitation light for amplifying the backscattered light is transmitted, a laser device that emits the detection light, an excitation device that emits the first excitation light and the second excitation light, an optical amplification repeater that amplifies the detection light with the first excitation light and amplifies the backscattered light with the second excitation light, and a measurement device that detects anomalies in the power cable based on the backscattered light.

[0007] The disclosed method for detecting an abnormality in a power cable detects an abnormality in a power cable including a cable main body including a conductor, an insulating layer, a semiconducting layer, and a sheath, a first optical fiber through which detection light is transmitted, and a second optical fiber through which backscattered light of the detection light is transmitted. The power cable includes an optical fiber through which first excitation light for amplifying the detection light is transmitted, and an optical fiber through which second excitation light for amplifying the backscattered light is transmitted. The method for detecting an abnormality in a power cable includes the steps of: an excitation device emitting the first excitation light and the second excitation light; a first laser device emitting the detection light; an optical amplifier repeater amplifying the detection light with the first excitation light; an optical amplifier repeater amplifying the backscattered light with the second excitation light; and a measurement device detecting an abnormality in the power cable using the backscattered light. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a cross-sectional view of a power cable 50 according to a first embodiment. [Figure 2] FIG. 2 is a cross-sectional view of the detecting wire member 61 of FIG. [Figure 3] FIG. 3 is a diagram showing a part of the detection line member 61 in FIG. 1 in the longitudinal direction. [Figure 4] FIG. 4 is a diagram showing the configuration of the power cable abnormal point detection system 100 of the first embodiment. [Figure 5] FIG. 5 is a flowchart showing the procedure for detecting an abnormal point in a power cable in the first embodiment. [Figure 6] FIG. 6 is a diagram showing a portion of the power line in the longitudinal direction according to the second embodiment. [Figure 7] FIG. 7 is a cross-sectional view of a power cable 50A according to the second embodiment. [Figure 8] FIG. 8 is a diagram showing the configuration of the connection section 80 in FIG. [Figure 9] FIG. 9 is a diagram showing the configuration of the optical amplifying repeater 70 of FIG. [Figure 10]FIG. 10 is a diagram showing the configuration of a power cable abnormal point detection system 100A according to the third embodiment. [Figure 11] FIG. 11 is a diagram showing the configuration of a power cable abnormal point detection system 100B according to the fourth embodiment. [Figure 12] FIG. 12 is a diagram showing the configuration of a power cable abnormal point detection system 100C according to the fifth embodiment. [Figure 13] FIG. 13 is a diagram showing the configuration of a power cable abnormal point detection system 100E according to the sixth embodiment. [Figure 14] FIG. 14 is a diagram for explaining the detection light emitted from the pulse laser device 21E of FIG. [Figure 15] FIG. 15 is a flowchart showing the procedure for detecting an abnormal point in a power cable in the sixth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] [Problem to be solved by this disclosure]

[0010] In Patent Document 1, the measurement pulse light emitted from one end of the optical fiber and the backscattered light are attenuated as they propagate through the optical fiber. As a result, the accuracy with which the optical fiber detects damage or distortion in the power line core, armor, etc., which correspond to the cable body of the power cable, decreases. In Patent Document 1, the length of the power cable in which the optical fiber can measure damage or distortion is limited to a range in which the signal-to-noise ratio (SNR) can be ensured in the measurement system even if the measurement pulse light and backscattered light are attenuated.

[0011] Patent Document 2 discloses an optical cable and an optical transmission line for communication applications, but does not disclose a power cable. As described in paragraph

[0003] of Patent Document 2, optical amplifier repeaters are inserted into the optical transmission line at predetermined intervals, and each optical amplifier repeater is supplied with power via a power feeder in the optical cable. Each optical amplifier repeater is equipped with a laser device, and power is supplied to the laser device via the power feeder. When the optical amplifier repeater is equipped with a laser device, an optical fiber for transmitting pump light is not required. However, when the optical amplifier repeater is equipped with a laser device, laser devices corresponding to the number of optical amplifier repeaters are required, as well as power feeders and power supplies for the laser devices.

[0012] Therefore, an object of the present disclosure is to provide a power cable, a power line, a power cable anomaly detection system, and a power cable anomaly detection method, which are suitable for long-distance power lines and in which abnormal points can be detected using optical fiber and in which the optical amplifier repeater is configured not to include a laser device. [Effects of this disclosure]

[0013] According to the present disclosure, it is possible to provide a power cable that is capable of detecting abnormal points using optical fiber and is suitable for long-distance power lines even though the optical amplification repeater is configured not to include a laser device, a power line, a power cable abnormal point detection system, and a power cable abnormal point detection method. [Outline of the embodiment] First, embodiments of the present disclosure will be listed and described.

[0014] (1) A power cable (50) of the present disclosure includes a cable body (60) including a conductor (51), an insulating layer (53), semiconductive layers (52, 54), and a sheath (55), a first optical fiber (6) through which detection light is transmitted, a second optical fiber (7) through which backscattered light of the detection light is transmitted, an optical fiber (A) through which first excitation light for amplifying the detection light is transmitted, an optical fiber (B) through which second excitation light for amplifying the backscattered light is transmitted, and at least one optical amplifier repeater (10) that amplifies the detection light with the first excitation light and amplifies the backscattered light with the second excitation light.

[0015] The power cable (50) comprises a plurality of optical fibers (6, 7, A, B) and a cable body (60). The power cable (50) may further comprise an armor (59). A power cable (50) having an armor is typically used for submarine power cables. The cable body (60) is the main body of the power cable. The semiconductive layers (52, 54) provided in the cable body (60) are one or both of an inner semiconductive layer (52) and an outer semiconductive layer (54). The first optical fiber (6) and the second optical fiber (7) are not intended for communication purposes but for sensing purposes. That is, the first optical fiber (6) and the second optical fiber (7) are used to detect damage or distortion in the cable body (60), the armor (59), or a connection portion (80) of a power line. The optical fiber (A) may also serve as the first optical fiber (6) through which detection light is transmitted, or may be dedicated to excitation light. The optical fiber (B) may also be used as the second optical fiber (7) through which the backscattered light is transmitted, or may be dedicated to the excitation light. The power cable (50) does not have a laser device for transmitting the excitation light and does not have a power feeder line for supplying power to the laser device. The power cable (50) can amplify the detection light by the excitation light transmitted through the optical fiber (A) and can amplify the backscattered light by the excitation light transmitted through the optical fiber (B). Even if a long-distance power line is constructed, such a power cable (50) can detect abnormalities in the long-distance power cable using the first optical fiber (6) and the second optical fiber (7).

[0016] (2) In the power cable (50) of (1) above, the optical fiber (A) through which the first excitation light is transmitted is the first optical fiber (6). In this configuration, the first optical fiber (6) can transmit the detection light and the first excitation light.

[0017] (3) In the power cable (50) of (1) or (2) above, the optical fiber (B) through which the second excitation light is transmitted is the second optical fiber (7). In this configuration, the second optical fiber (7) can transmit the backscattered light of the detection light and the second excitation light.

[0018] (4) In the power cable (50) of (1) to (3) above, the optical amplifier repeater (10) includes a branching structure (38) that guides backscattered light generated in the first optical fiber (6) to the second optical fiber (7). The branching structure (38) guides the backscattered light to the second optical fiber (7) and allows the backscattered light to be transmitted by the second optical fiber (7).

[0019] (5) In the power cable (50) described above in (1) to (4), the cable body (60) is disposed at the center of the power cable (50), and includes a plurality of wires (58a, 58b) and at least one metal tube (63) on the outside of the cable body (60), and the first optical fiber (6), the second optical fiber (7), and the optical amplifier repeater (10) are housed in the metal tube (63). In this configuration, the first optical fiber (6), the second optical fiber (7), and the optical amplifier repeater (10) can be disposed in positions where abnormalities such as damage or distortion of the cable body (60) or the armoring part (59) can be easily detected due to abnormalities such as damage or distortion of the power cable (50).

[0020] (6) The power cable (50) of (5) further comprises an armored portion (59) provided on the outer periphery of the cable main body (60), the armored portion (59) being composed of a plurality of wires (58a, 58b) and a detection wire member (61), the detection wire member (61) accommodating a metal tube (63), and the outer diameter of the detection wire member (61) being equal to the outer diameter of the wire member adjacent to the detection wire member (61) among the plurality of wires (58a, 58b).

[0021] (7) In the power cable (50) of (1) to (6) above, the detection light is transmitted in the direction from the first end (EA) to the second end (EB) of the first optical fiber (6), and the backscattered light is transmitted in the direction from the second end (ED) to the first end (EC) of the second optical fiber (7). The optical amplifier repeater (10) comprises a first erbium-doped fiber (1) that amplifies the detection light transmitted from the direction of the first end (EA) of the first optical fiber (6) using first excitation light, a branching optical fiber (39), a first optical directional coupler (3) that sends the detection light amplified by the first erbium-doped fiber (1) toward the second end (EB) of the first optical fiber (6) and sends the backscattered light transmitted from the direction of the second end (EB) of the first optical fiber (6) to the branching optical fiber (39), a second erbium-doped fiber (4), and a second optical directional coupler (5) that sends the backscattered light that has transmitted through the branching optical fiber (39) and the backscattered light that has transmitted from the direction of the second end (ED) of the second optical fiber (7) to the second erbium-doped fiber (4). The second erbium-doped fiber (4) amplifies the backscattered light sent through the second optical directional coupler (5) with the second excitation light and sends it toward the first end (EC) of the second optical fiber (7). In this configuration, the first erbium-doped fiber (1) amplifies the detection light, and the second erbium-doped fiber (4) amplifies the backscattered light.

[0022] (8) The power cable (50) of (1) to (7) above further includes one or more third optical fibers (8) that are optical fibers independent of the first optical fiber (6) and through which the first excitation light is transmitted. In this configuration, the first excitation light and the detection light can be transmitted through separate optical fibers.

[0023] (9) The power cable (50) of (1) to (8) above further includes one or more fourth optical fibers (9) that are optical fibers independent of the second optical fiber (7) and through which the second excitation light is transmitted. In this configuration, the second excitation light and the backscattered light can be transmitted through separate optical fibers.

[0024] (10) The power cable (50) of (7) further includes one or more third optical fibers (8) that are optical fibers independent of the first optical fiber (6) and through which the first excitation light is transmitted. The first excitation light is transmitted in a direction from the first end (EE) to the second end (EF) of the third optical fiber (8). The optical amplifying repeater (10B) further includes a third optical directional coupler (120) that sends a portion of the first excitation light transmitted from the first end (EE) of the third optical fiber (8) to the first erbium-doped fiber (1) and sends the remainder of the first excitation light toward the second end (EF) of the third optical fiber (8). In this configuration, the amplification degree of the detection light can be adjusted by adjusting the branching ratio of the light in the third optical directional coupler (120).

[0025] (11) The power cable (50) of (7) or (10) further includes one or more fourth optical fibers (9) that are optical fibers independent of the second optical fiber (7) and through which second pumping light is transmitted. The second pumping light is transmitted in a direction from the first end (EG) to the second end (EH) of the fourth optical fiber (9). The optical amplifying repeater (10C) further includes a fourth optical directional coupler (121) that sends a portion of the second pumping light transmitted from the first end (EG) of the fourth optical fiber (9) to the second erbium-doped fiber (4) and sends the remainder of the second pumping light in a direction toward the second end (EH) of the fourth optical fiber (9). In this configuration, the amplification degree of the backscattered light can be adjusted by adjusting the branching ratio of the light in the fourth optical directional coupler (121).

[0026] (12) A power line according to the present disclosure includes a first power cable (50A-1), a second power cable (50A-2), and a connection section (80) that connects the first power cable (50A-1) and the second power cable (50A-2). Each of the first power cable (50A-1) and the second power cable (50A-2) includes a cable main body (60) that includes a conductor (51), an insulating layer (53), semiconductive layers (52, 54), and a sheath (55), a first optical fiber (6) through which detection light is transmitted, a second optical fiber (7) through which backscattered light of the detection light is transmitted, an optical fiber (A) through which first excitation light for amplifying the detection light is transmitted, and an optical fiber (B) through which second excitation light for amplifying the backscattered light is transmitted. The connection unit (80) includes an optical amplifier repeater (10) that amplifies the detection light with a first excitation light and amplifies the backscattered light with a second excitation light. Even in a long-distance power line according to the present disclosure, the detection light and the backscattered light can be amplified by the excitation light transmitted through the optical fibers (A) and (B). With this configuration, even in a long-distance power line, an abnormality in the power line can be detected by the first optical fiber (6) and the second optical fiber (7).

[0027] (13) The power cable anomaly detection system (100) of the present disclosure includes a power cable (50) including a cable main body (60) including a conductor (51), an insulating layer (53), semiconductive layers (52, 54), and a sheath (55), a first optical fiber (6) through which detection light is transmitted, a second optical fiber (7) through which backscattered light of the detection light is transmitted, an optical fiber (A) through which first excitation light for amplifying the detection light is transmitted, and an optical fiber (B) through which second excitation light for amplifying the backscattered light is transmitted, a laser device (21) that emits the detection light, an excitation device (11) that emits the first excitation light and the second excitation light, an optical amplifier repeater (10) that amplifies the detection light with the first excitation light and amplifies the backscattered light with the second excitation light, and a measurement device (20) that detects anomalies in the power cable based on the backscattered light. The power cable anomaly detection system (100) can amplify the detection light and backscattered light by the excitation light transmitted through the optical fibers (A) and (B), even when the power cable (50) forms a long-distance power line. Such a power cable anomaly detection system (100) can detect anomalies in the long-distance power line using the first optical fiber (6) and the second optical fiber (7).

[0028] (14) In the power cable anomaly detection system (100A) described above in (13), the second excitation light is transmitted through the second optical fiber (7), and the excitation device (11A) emits the second excitation light having a wavelength shorter than that of the detection light. In this configuration, the backscattered light can be Raman amplified in the second optical fiber (7).

[0029] (15) In the power cable anomaly detection system (100E) described above in (13) or (14), the laser device (21E) sequentially emits a plurality of frequency-modulated detection lights within a predetermined time, and the measurement device (20E) includes a frequency filter (41) that detects each of a plurality of frequency components of the backscattered light. With this configuration, a plurality of pieces of backscattered light data can be acquired in one measurement period.

[0030] (16) In the power cable anomaly detection system (100) described above in (13) to (15), the measurement device (20) includes a wavelength filter (28) that cuts off the first excitation light and the second excitation light in order to detect the wavelength of the detection light emitted by the laser device (21). In this configuration, it is possible to extract backscattered light of the same wavelength as the wavelength of the detection light emitted by the laser device (21), and in some cases, backscattered light of a Raman-amplified wavelength.

[0031] (17) The method for detecting an abnormality in a power cable (50) of the present disclosure detects an abnormality in the power cable (50) that includes a cable main body (60) including a conductor (51), an insulating layer (53), semiconductive layers (52, 54), and a sheath (55), a first optical fiber (6) through which detection light is transmitted, and a second optical fiber (7) through which backscattered light of the detection light is transmitted. The power cable (50) includes an optical fiber (A) through which first excitation light for amplifying the detection light is transmitted, and an optical fiber (B) through which second excitation light for amplifying the backscattered light is transmitted. The method for detecting an abnormality in a power cable (50) includes the steps of: an excitation device (11) emitting first excitation light and second excitation light; a first laser device (21) emitting detection light; an optical amplifier repeater (10) amplifying the detection light with the first excitation light; the optical amplifier repeater (10) amplifying backscattered light with the second excitation light; and a measuring device (20) detecting an abnormality in the power cable (50) using the backscattered light. With this method, even if the power cable (50) forms a long-distance power line, the detection light and the backscattered light can be amplified by the excitation light transmitted through the optical fibers (A) and (B), respectively. This method for detecting an abnormality in a power cable (50) can detect an abnormality in a long-distance power line using the first optical fiber (6) and the second optical fiber (7). [Details of the embodiment] Hereinafter, embodiments will be described with reference to the drawings. First Embodiment

[0032] First, a power cable 50 will be described with reference to Figure 1. The power cable 50 is an optical-electrical composite cable. The power cable 50 comprises a cable main body 60 for transmitting electric power, an armor portion 59, and a detection line member 61 for transmitting light. As will be described later, the detection line member 61 comprises optical fibers 6 and 7 used to detect abnormal points in the power cable or the like. Furthermore, the detection line member 61 in this example comprises a plurality of optical amplification repeaters 10, as will be described later.

[0033] The cable body 60 is the main body of the power cable 50. The cable body 60 is composed of a conductor 51, an inner semiconductive layer 52, an insulating layer 53, an outer semiconductive layer 54, and a sheath 55. The conductor 51, inner semiconductive layer 52, insulating layer 53, outer semiconductive layer 54, and sheath 55 are arranged in this order from the center of the cable body 60. The insulating layer 53 is an electrical insulator made of, for example, cross-linked polyethylene. The semiconductive layers 52 and 54 are made of a semiconductive material. The sheath 55 is, for example, a lead sheath. The cable body 60 may also be provided with a shielding layer, a water-blocking layer, a corrosion-resistant layer, and the like. The shielding layer is made of a conductive material. The water-blocking layer is, for example, made of a laminate of a metal layer and a resin layer. An armor portion 59 is arranged around the outer periphery of the cable body 60. The armor portion 59 protects the cable body 60 from external damage and supports the load of the power cable.

[0034] The armor portion 59 has a plurality of wires 58a, 58b. In this example, the armor portion 59 has a multi-layer structure consisting of an inner layer and an outer layer. The plurality of wires 58a constituting the inner layer are arranged without gaps along the outer peripheral surface of the cable main body 60. The plurality of wires 58b constituting the outer layer are arranged without gaps along the circumference of the outer peripheral surface formed by the plurality of wires 58a. The wires 58a, 58b are made of, for example, metal or fiber-reinforced plastic. The metal is, for example, a magnetic material such as iron. When the wires 58a, 58b are made of metal, they have excellent strength. When the wires 58a, 58b are made of a non-magnetic material such as resin, they are lightweight. A resin layer (not shown) may be provided between the inner layer and the outer layer. Also, a resin layer (not shown) formed to cover the armor portion 59 may be provided. These resin layers are formed by winding a string-like body made of resin such as polypropylene.

[0035] In the armored portion 59, a portion of the wire 58a constituting the inner layer of the two layers is replaced with a detection wire member 61 to detect abnormalities such as damage or distortion in the cable main body 60 and the armored portion 59. The detection wire member 61 needs to be formed in at least one location in the armored portion 59, but may be provided in multiple locations. FIG. 3 illustrates a case where the armored portion 59 has a multi-layer structure, but it may also have a single-layer structure. Also, a portion of the wire 58b constituting the outer layer in the armored portion 59 may be replaced with the detection wire member 61. The outer diameter of the detection wire member 61 is equal to the outer diameter of the wire member adjacent to the detection wire member 61 among the multiple wire members 58a and the multiple wire members 58b. The outer diameters of all the wire members 58a, all the wire members 58b, and the detection wire member 61 may be equal. The detection line member 61 will be described with reference to FIGS.

[0036] The detection line member 61 comprises a metal tube 63 and a sheath 64 provided around the metal tube 63. The metal tube 63 is made of a metal such as stainless steel. The metal tube 63 houses a first optical fiber 6, a second optical fiber 7, and an optical amplifier repeater 10. A jelly compound 62 is embedded in the gaps in the metal tube 63. The sheath 64 is made of a resin such as polyethylene, and constitutes the outermost layer of the detection line member 61. The metal tube 63 and the sheath 64 function as waterproof and anti-corrosion layers.

[0037] The first optical fiber 6(A) transmits the detection light emitted from a laser device 21, which will be described later. In this example, the first optical fiber 6(A) also transmits the first excitation light emitted from an excitation laser device 22, which will be described later. The second optical fiber 7(B) is an optical fiber independent of the first optical fiber 6(A). The second optical fiber 7(B) transmits backscattered light of the detection light. In this example, the second optical fiber 7(B) also transmits the second excitation light emitted from an excitation laser device 24, which will be described later. The optical fiber A may be used as the first optical fiber 6, which transmits the detection light, as in this example, or may be dedicated to the excitation light. The optical fiber B may be used as the second optical fiber 7, which transmits the backscattered light, as in this example, or may be dedicated to the excitation light.

[0038] The detection line member 61 can be manufactured by connecting the first optical fiber 6 and the second optical fiber 7 to the optical amplifier repeater 10 and wrapping them with a metal tube 63, or by preparing a metal tube containing the first optical fiber 6 and the second optical fiber 7 and a metal tube containing the optical amplifier repeater, and then welding, brazing, or joining these metal tubes with metal tape or the like. The optical amplifier repeater 10 provided in the detection line member 61 will be described with reference to FIG.

[0039] Optical amplification repeaters 10 are inserted at multiple locations along the first optical fiber 6 and the second optical fiber 7. In Fig. 3, only one optical amplification repeater 10 is shown.

[0040] The first erbium-doped fiber 1, the second erbium-doped fiber 4, the optical directional couplers 3 and 5, and the branching optical fiber 39 are housed within a housing 66 of the optical amplifier repeater 10. The housing 66, like the detection line member 61, has a waterproof structure including a metal tube 63 and a sheath 64. In FIG. 3, the outer diameter of the housing 66 is exaggerated to be larger than that of the detection line member 61, but the outer diameter of the housing 66 may be the same as that of the detection line member 61. In other words, the detection line member 61 may have a uniform outer diameter throughout its entire length, including the portion where the optical amplifier repeater 10 is provided. The metal tube 63 provided in the detection line member 61 may also have a uniform outer diameter throughout its entire length, including the portion where the optical amplifier repeater 10 is provided. Furthermore, the outer diameter of the detection line member 61 or the metal tube 63 may be the same as the outer diameter of the wires 58a, 58b constituting the armored portion 59 that are adjacent to the detection line member 61 in the circumferential direction of the cable main body 60 (wire 58a in FIG. 1). If the outer diameter of the detection line member 61 or the metal tube 63 has a uniform outer diameter over its entire length as described above and is the same as the outer diameter of the wires constituting the armored portion 59, the armored portion 59 is provided approximately concentrically with the cable main body 60 as shown in FIG. 1. The size of each component constituting the optical amplifier repeater 10 may be adjusted so that it can be housed within the metal tube 63 having such an outer diameter. Note that while FIG. 3 shows the first erbium-doped fiber 1, the second erbium-doped fiber 4, the optical directional couplers 3 and 5, and the branching optical fiber 39, the optical amplifier repeater 10 may further include an optical isolator.

[0041] The first pumping light excites erbium ions in the first erbium-doped fiber 1, thereby amplifying the sensing light propagating through the first optical fiber 6. The second pumping light excites erbium ions in the second erbium-doped fiber 4, thereby amplifying the backscattered light propagating through the second optical fiber 7.

[0042] The branching optical fiber 39, the optical directional coupler 3, and the optical directional coupler 5 form a branching structure 38 that guides the backscattered light generated in the first optical fiber 6 to the second optical fiber 7. Instead of providing the branching structure 38, a configuration in which a portion of the backscattered light leaks from the first optical fiber 6 to the second optical fiber 7 may be used. Referring to FIG. 4, a power cable abnormality detection system 100 will be described.

[0043] The power cable anomaly detection system 100 includes a power cable 50, a first optical fiber 6, a second optical fiber 7, an optical amplifier repeater 10, a pulsed laser device 21 (laser device), an excitation laser device 22, a measurement device 20, an excitation laser device 24, optical isolators 25, 26, and 27, and optical directional couplers 29, 30, 31, and 32. The measurement device 20 includes a wavelength filter 28, an optical receiver 23, and an analysis device 12. Of the components of the power cable 50, Fig. 4 shows the first optical fiber 6, the second optical fiber 7, and the optical amplifier repeater 10. The pulse laser device 21 (laser device), the excitation laser device 22, the measuring device 20, and the excitation laser device 24 are each components independent of the power cable 50, and are connected to the first optical fiber 6 or the second optical fiber 7 at the end of the power cable 50 via optical isolators 25, 26, and 27 and optical directional couplers 29, 30, 31, and 32 as appropriate, as described below.

[0044] The pulsed laser device 21 emits detection light in the form of a pulse wave. The detection light may be light in a wavelength band known as the C-band or L-band. The C-band is a wavelength band with a wavelength of 1525 nm or more and 1563 nm or less. The L-band is a wavelength band with a wavelength of 1560 nm or more and 1610 nm or less. The pulsed laser device 21 emits detection light with a wavelength of 1560 nm, for example. Light with a wavelength of 1560 nm is known to have low transmission loss in optical fiber. Furthermore, light with a long wavelength such as 1560 nm is known to have high transmission loss due to distortion caused by bending, etc., and is therefore suitable for detecting abnormalities in power cables and the like using optical fiber.

[0045] The excitation laser device 22 emits first excitation light for exciting the detection light. The excitation laser device 22 emits the first excitation light having a wavelength of, for example, 1480 nm.

[0046] The excitation laser device 24 emits second excitation light for exciting the backscattered light. The excitation laser device 24 emits the second excitation laser light having a wavelength of, for example, 1480 nm.

[0047] The pumping laser device 22 and the pumping laser device 24 constitute the pumping device 11. The pumping device 11 may not use two pumping laser devices, but may branch the output of one pumping laser device into two and output the two to the first optical fiber 6 and the second optical fiber 7.

[0048] The first optical fiber 6 and the second optical fiber 7 are arranged in close proximity (see also FIG. 2). The first optical fiber 6 has a first end EA and a second end EB. The direction from the first end EA to the second end EB is sometimes referred to as the forward direction, and the direction from the second end EB to the first end EA is sometimes referred to as the reverse direction. The second optical fiber 7 has a first end EC and a second end ED. The direction from the first end EC to the second end ED is sometimes referred to as the forward direction, and the direction from the second end ED to the first end EC is sometimes referred to as the reverse direction.

[0049] The first optical fiber 6 transmits the detection light and the first excitation light from the first end EA to the second end EB.

[0050] The second excitation light is transmitted through the second optical fiber 7 from the first end EC to the second end ED. The backscattered light of the detection light is transmitted through the second optical fiber 7 toward the first end EC.

[0051] The first optical fiber 6 and the second optical fiber 7 preferably have low transmission loss and a large effective area so that high-power light can be transmitted over long distances. An optical fiber with a large effective area is, for example, an optical fiber with a core diameter of 110 μm or more. The core diameter of the optical fiber may be 125 μm or more, or even 135 μm or more.

[0052] The optical amplifier repeaters 10 are installed at each of a plurality of split points along the first optical fiber 6 and the second optical fiber 7.

[0053] The optical amplifying repeater 10 amplifies the sensing light with a first excitation light and amplifies the backscattered light with a second excitation light.

[0054] The optical isolator 25 is connected to the output port of the pulse laser device 21. The optical isolator 25 blocks the transmission of light to the pulse laser device 21.

[0055] The optical isolator 26 is connected to the output port of the pump laser device 22. The optical isolator 26 blocks the transmission of light to the pump laser device 22.

[0056] The optical isolator 27 is connected to the output port of the pump laser device 24. The optical isolator 27 blocks the transmission of light to the pump laser device 24.

[0057] The optical directional coupler 29 is connected to the optical directional coupler 30, the optical isolator 25, and the optical isolator 26. The optical directional coupler 29 sends the detection light emitted from the pulsed laser device 21 and the first excitation light sent through the optical isolator 26 to the optical directional coupler 30.

[0058] The optical directional coupler 30 is connected to the first end EA of the first optical fiber 6, the optical directional coupler 29, and the optical directional coupler 31. The optical directional coupler 30 transmits the detection light and the first excitation light sent through the optical directional coupler 29 in the forward direction to the first optical fiber 6. The optical directional coupler 30 sends backscattered light that is generated at the portion 6a of the first optical fiber 6 and transmitted in the reverse direction through the portion 6a to the optical directional coupler 31. Note that an optical circulator may be provided instead of the optical directional couplers 30 and 31.

[0059] The optical directional coupler 32 is connected to the first end EC of the second optical fiber 7, the optical isolator 31, and the optical isolator 27. The optical directional coupler 32 transmits the second pumping light emitted from the pumping laser device 24 in the forward direction to the second optical fiber 7. The optical directional coupler 32 sends the backscattered light that has transmitted in the reverse direction through the second optical fiber 7 to the optical directional coupler 31.

[0060] The optical directional coupler 31 is connected to the optical directional coupler 32, the measuring device 20, and the optical directional coupler 30. The optical directional coupler 31 sends the backscattered light that has propagated in the reverse direction through the portion 6a of the first optical fiber 6 and sent through the optical directional coupler 30 to the measuring device 20. The optical directional coupler 31 sends the backscattered light that has propagated in the reverse direction through the second optical fiber 7 and sent through the optical directional coupler 32 to the measuring device 20. The configuration and operation of the optical amplifying repeater 10 will be described with reference to FIGS.

[0061] The optical amplifying repeater 10 comprises a first erbium-doped fiber 1 , an optical directional coupler 3 , an optical directional coupler 5 , a second erbium-doped fiber 4 , and a branching optical fiber 39 .

[0062] The first erbium-doped fiber 1 is connected to a first connection point ND1X of the first optical fiber 6 and the optical directional coupler 3. The first erbium-doped fiber 1 amplifies the detection light transmitted forward through the first optical fiber 6 by the first excitation light transmitted forward through the first optical fiber 6.

[0063] The optical directional coupler 3 is connected to the branching optical fiber 39, the first erbium-doped fiber 1, and the second connection point ND1Y of the first optical fiber 6. The optical directional coupler 3 sends the amplified sensing light and the first excitation light to the first optical fiber 6. The optical directional coupler 3 sends, to the branching optical fiber 39, backscattered light that is generated at the portion 6b of the first optical fiber 6 and propagates through the portion 6b in the reverse direction.

[0064] The first connection point ND1X of the first optical fiber 6 is closer to the first end EA of the first optical fiber 6 and farther from the second end EB of the first optical fiber 6 than the second connection point ND1Y of the first optical fiber 6.

[0065] The optical directional coupler 5 is connected to the branching optical fiber 39, the second connection point ND2Y of the second optical fiber 7, and the second erbium-doped fiber 4. The optical directional coupler 5 sends to the second erbium-doped fiber 4 backscattered light that has propagated through the branching optical fiber 39 (i.e., backscattered light that is generated at the portion 6b of the first optical fiber 6 and propagates in the opposite direction through the portion 6b) and backscattered light that has propagated in the opposite direction through the second optical fiber 7 (i.e., backscattered light that is generated at a portion (not shown) of the first optical fiber 6 (the side closer to the second end EB) and sent to the second optical fiber 7 via the optical amplifier repeater 10 (not shown)).

[0066] The second erbium-doped fiber 4 is connected to the optical directional coupler 5 and the first connection point ND2X of the second optical fiber 7.

[0067] The second erbium-doped fiber 4 amplifies the backscattered light sent through the optical directional coupler 5 using the second excitation light that has been transmitted forward through the second optical fiber 7, and outputs it toward the first end EC of the second optical fiber 7.

[0068] The first connection point ND2X of the second optical fiber 7 is closer to the first end EC of the second optical fiber 7 and farther from the second end ED of the second optical fiber 7 than the second connection point ND2Y of the second optical fiber 7.

[0069] The optical directional couplers 3 and 5 may be provided with auxiliary fibers that function as optical fibers 6 and 7. For example, when the optical directional coupler 3 includes first and second auxiliary fibers, the first erbium-doped fiber 1 is connected to a first end of the first auxiliary fiber, and the optical directional coupler 3 is connected to a second end of the first auxiliary fiber. The optical directional coupler 3 is connected to a first end of the second auxiliary fiber, and the second connection point ND1Y of the first optical fiber 6 is connected to a second end of the second auxiliary fiber.

[0070] The wavelength filter 28 is connected to the optical directional coupler 31. The wavelength filter 28 passes backscattered light out of the light sent through the optical directional coupler 31. The wavelength filter 28 does not pass the first excitation light and the second excitation light. The wavelength of the backscattered light that passes through the wavelength filter 28 is, for example, the same as the wavelength of the detection light. The output of the wavelength filter 28 is sent to the optical receiver 23.

[0071] The optical receiver 23 has a semiconductor light-receiving element and converts the light transmitted through the wavelength filter 28 into an electrical signal. Here, detection is performed by utilizing the coherence of the optical signal, thereby improving detection sensitivity.

[0072] The analysis device 12 uses multiple signals sent through the optical receiver 23 to detect whether an abnormality has occurred in the cable main body 60 or the armored portion 59, and if an abnormality has occurred, detects the abnormal point. The analysis device 12 can basically detect the location of an abnormal point in the power cable 50 based on the time difference between the transmission time of the detection signal and the reception time of the backscattered light. For example, detection methods can use a coherent-optical time-domain reflectometer (C-OTDR) that measures increased loss due to damage in the optical fiber, or a distributed acoustic sensor (DAS) that detects distortion or vibration in the power cable. When an abnormality occurs in the cable main body 60 or the armored portion 59, the optical fiber is damaged, distorted, vibrated, or the like due to the abnormality. Using this damage to the optical fiber, an abnormal point in the cable main body 60 or the armored portion 59 can be detected. Referring to FIG. 5, the procedure for detecting an abnormal point in a power cable in the first embodiment will be described.

[0073] In step S101, the pumping laser device 22 starts emitting the first pumping light, and the pumping laser device 24 starts emitting the second pumping light. The start timing of the emission of the first pumping light and the start timing of the emission of the second pumping light may be simultaneous. The first pumping light is transmitted through the first optical fiber 6. The second pumping light is transmitted through the second optical fiber 7.

[0074] In step S102, the pulse laser device 21 emits detection light (pulsed light). The detection light is transmitted through the first optical fiber 6.

[0075] In step S103, the optical amplifier repeater 10 amplifies the sensing light with the first excitation light. The backscattered light propagates in the reverse direction through the first optical fiber 6 and enters the optical amplifier repeater 10.

[0076] In step S104, the optical amplifier repeater 10 amplifies the backscattered light with the second excitation light and sends it to the second optical fiber 7. The backscattered light is transmitted in the reverse direction through the second optical fiber 7, is amplified by the second excitation light in the optical amplifier repeater 10 along the way, and is input to the measuring device 20. If an abnormality occurs in the power cable 50, such as the cable main body 60 or the armored portion 59, the physical quantity (intensity, phase, etc.) of the backscattered light will fluctuate (or attenuate if it is intensity), and the measuring device 20 can determine whether or not there is a fluctuation in the physical quantity, thereby determining the occurrence and location of the abnormality.

[0077] In step S105, the measuring device 20 performs a receiving process for the backscattered light. That is, the wavelength filter 28 sends the backscattered light, which is part of the light sent through the optical directional coupler 31, to the optical receiver 23. The optical receiver 23 converts the light sent through the wavelength filter 28 into an electrical signal and sends it to the analyzing device 12.

[0078] In step S106, if one measurement period T has elapsed since the previous emission of the detection light (pulsed light), the process proceeds to step S107. One measurement period T may be set to be equal to or greater than the difference between the time when the detection light is emitted from the pulsed laser device 21 and the time when the backscattered light generated at the second end EB of the first optical fiber 6 is received by the optical receiver 23. If one measurement period T is equal to the above-mentioned time difference, the accuracy of anomaly detection is improved. The above-mentioned time depends on the length of the optical fiber and the transmission speed of light in the optical fiber. Therefore, if the length of the first optical fiber 6 and the second optical fiber 7 is, for example, 500 km, one measurement period T is approximately 5 msec. During one measurement period T, the measuring device 20 continues to receive the backscattered light.

[0079] In step S107, the analysis device 12 obtains a physical quantity from the backscattered light sent through the optical receiver 23. The analysis device 12 uses the obtained physical quantity (hereinafter referred to as the latest physical quantity) to detect the presence or absence of an abnormality.

[0080] The presence or absence of an abnormality may be detected, for example, by comparing the latest physical quantity with one or more thresholds. The one or more thresholds are values ​​corresponding to each position on the power cable 50, and are set, for example, according to the physical quantity of backscattered light calculated according to the transmission distance when there is no abnormality in the power cable 50. The physical quantity calculated for each measurement period T may be accumulated, and this accumulated information may be used. The accumulated information indicates past trends, and using the accumulated information tends to reduce the influence of noise. For example, the analysis device 12 may compare the difference between the latest physical quantity and the immediately preceding physical quantity with a preset threshold. Instead of the immediately preceding physical quantity, an average value of the physical quantity over a certain period going back in time may be used. Instead of the average value, the variance value of the physical quantity over a certain period may be used as the comparison target or threshold. This analysis process detects the presence or absence of an abnormality that may occur within a short period.

[0081] In step S108, the analyzer 12 adds up the physical quantities of the signals sent through the optical receiver 23 (intensity of the backscattered light, phase difference, phase change, etc.).

[0082] In step S109, the process proceeds to step S110 each time the addition process is completed a specified number of times, otherwise the process returns to step S102. The added value is stored and saved as needed.

[0083] In step S110, the analyzer 12 redetects the presence or absence of an abnormality using a sum including the latest physical quantity (hereinafter referred to as the latest sum) and the past sum. For example, the analyzer 12 compares the difference between the average of the past sums and the average of the latest sum with a preset threshold. The average of the sums is calculated, for example, by dividing the sum by a specified number of times. Instead of the average, the variance of the sum may be used as the comparison target or threshold. The variance indicates signal variation due to noise. Using accumulated information such as the average of the past sums tends to further reduce the influence of noise. This analysis process detects the presence or absence of an abnormality that may occur over a long period of time (such as minute distortion or phase changes that persist over a long period of time). In other words, external damage to the power cable 50 or the occurrence of permanent damage such as fatigue can also be detected. The sum is then reset, and the process returns to step S102.

[0084] As described above, according to this embodiment, by using the optical fibers 6 and 7 and the optical amplifier repeater 10 that amplifies the light transmitted through the optical fibers 6 and 7, it is possible to accurately and quickly detect abnormalities such as ground faults, damage, or fatigue in the power cable 50 over a long distance of 300 km or even 500 km or more. Furthermore, according to this embodiment, by emitting detection light from both ends of the power cable 50, it is expected that abnormalities such as ground faults, damage, or fatigue in the power cable 50 over a long distance of 1,000 km or more can be accurately and quickly detected. In particular, when the power cable 50 is laid on the seabed, it is possible to eliminate the need to pull the power cable 50 onto a ship for inspection. Furthermore, according to this embodiment, it is possible to detect the fault point in the power cable 50 immediately after the occurrence of a ground fault. Furthermore, according to this embodiment, by transmitting pumping light to the optical amplifier repeater 10 via the optical fibers 6 and 7, it is not necessary to provide a pumping laser device that generates pumping light in the optical amplifier repeater 10 and a power line for supplying power voltage to the pumping laser device. <Second embodiment>

[0085] In the second and subsequent embodiments, differences from the first embodiment will be mainly described, and common points will not be described repeatedly. A power line according to the second embodiment will be described with reference to FIG.

[0086] The power line includes a plurality of power cables 50A and a connection portion 80 that connects two adjacent power cables 50A. In Fig. 6, a first power cable 50A-1 and a second power cable 50A-2 are shown. A power cable 50A provided in a power line according to the second embodiment will be described with reference to FIG.

[0087] The power cable 50A of the second embodiment differs from the power cable 50 of the first embodiment in that a part of the wire 58b is replaced with a detection wire member 61A.

[0088] The detection line member 61A includes a first optical fiber 6 and a second optical fiber 7, similar to the detection line member 61 of the first embodiment. Unlike the detection line member 61 of the first embodiment, the detection line member 61A does not include an optical amplifier repeater 10 along the way. The optical amplifier repeater 10 is provided at the connection section 80. In other words, the power cable 50A does not include the optical amplifier repeater 10, but the connection section 80, which is part of the power line, includes the optical amplifier repeater 10.

[0089] Next, a power line according to a second embodiment will be described. Typically, both ends of the power line are located on land. The majority of the power line, excluding both ends, i.e., the middle portion of the power line including the connection section 80, is laid on the seabed. When detection light is emitted from each end of the power line, a control device is provided at each end of the power line. When detection light is emitted from only one end of the power line, a control device is provided at one end of the power line. The control device includes a pulsed laser device 21, a pumping laser device 22, a measuring device 20, a pumping laser device 24, optical isolators 25, 26, and 27, optical directional couplers 29, 30, 31, and 32, as shown in FIG. 4, and a power supply (not shown). The power supply supplies power at a voltage corresponding to the devices 20, 21, and 24 to drive these devices. Referring to FIG. 8, a connection portion 80 provided on the power line of the second embodiment will be described.

[0090] The conductor 51A of the cable main body 60 of the power cable 50A-1 and the conductor 51B of the cable main body 60 of the power cable 50A-2 are connected by a sleeve 99. An insulating portion 98 made of insulating tape or the like is formed around the conductors 51A, 51B and the sleeve 99. The insulating portion 98 is provided across the insulating layers 53A, 53B of each of the cable main bodies 60. A semiconducting portion 97 is formed around the insulating portion 98 so as to extend across the outer semiconducting layers 54A, 54B of each of the cable main bodies 60. These are surrounded and protected by a metal tube 94. The metal tube 94 is filled with a waterproof compound (not shown). The metal tube 94 also functions as a member for electrically connecting the shield layers 57A, 57B of each of the cable main bodies 60. A protective layer 92 made of protective tape or the like is formed on the outer surface of the metal tube 94. Two adjacent detection line members 61A are connected to an optical amplifier repeater 70. The optical amplifier repeater 70 will be described with reference to FIG.

[0091] Like the optical amplifying repeater 10 described in the first embodiment, the optical amplifying repeater 70 includes a first erbium-doped fiber 1, a second erbium-doped fiber 4, optical directional couplers 3 and 5, and a branching optical fiber 39 housed in a waterproof housing 71. Like the optical amplifying repeater 10 of the first embodiment, the optical amplifying repeater 70 may further include an optical isolator.

[0092] The first pumping light excites erbium ions in the first erbium-doped fiber 1, thereby amplifying the sensing light propagating through the first optical fiber 6. The second pumping light excites erbium ions in the second erbium-doped fiber 4, thereby amplifying the backscattered light propagating through the second optical fiber 7.

[0093] The branching optical fiber 39 , the optical directional coupler 3 and the optical directional coupler 5 form a branching structure 38 that guides backscattered light generated in the first optical fiber 6 to the second optical fiber 7 .

[0094] The second embodiment also provides the same effects as the first embodiment. Furthermore, in the second embodiment, the detection line member 61A does not include the optical amplifier repeater 10, so the outer diameter of the detection line member 61A can be easily adjusted to a uniform outer diameter along its entire length. The size of the optical amplifier repeater 70 can be adjusted within the available space within the connection section 80.

[0095] As described above, the laser devices 20, 21, and 24 and the power source are disposed at the end of the power line that is installed on land. By disposing the laser devices 20, 21, and 24 at both ends of the power line, detection light and excitation light can be transmitted from each end, allowing the detection range of one laser device to be half the length of the power line. Because the detection range is short, the attenuation of light transmitted through the optical fiber is reduced, enabling abnormalities to be detected with high accuracy and in a short time. Disposing the laser devices 20, 21, and 24 and the power source on land also simplifies control of laser conditions and maintenance of the laser devices. The laser devices 20, 21, and 24 and the power source may be disposed at only one end of the power line. The laser devices 20, 21, and 24 and the power source are not provided on the power cable 50 and the connection portion 80 that are installed on the seabed. <Third embodiment>

[0096] A power cable abnormal point detection system 100A according to the third embodiment will be described with reference to FIG.

[0097] The abnormal point detection system 100A of the third embodiment differs from the abnormal point detection system 100 of the first embodiment in that the abnormal point detection system 100A of the third embodiment includes an excitation device 11A instead of the excitation device 11. The excitation device 11A includes an excitation laser device 24A instead of the excitation laser device 24.

[0098] The excitation laser device 24A emits second excitation light. The wavelength of the second excitation light can be set to a value shorter than the wavelength of the detection light. For example, the wavelength of the second excitation light may be set so that the difference between the wavelength of the second excitation light and the wavelength of the detection light is in the range of 70 nm to 120 nm. For example, if the wavelength of the detection light is 1560 nm, the wavelength of the second excitation light may be 1450 nm to 1480 nm. The excitation laser device 24A adjusts the wavelength of the second excitation light so that the wavelength of the second excitation light is shorter than the wavelength of the detection light, in this case, in the range of 70 nm to 120 nm.

[0099] Even if the backscattered light is weak, the second pumping light emitted from the pumping laser device 24A causes the backscattered light to be Raman amplified at the portion 7a of the second optical fiber 7. This allows the distance from the first end EC of the second optical fiber 7 to the optical amplifying repeater 10 to be increased. <Fourth embodiment>

[0100] A power cable anomaly detection system 100B according to a fourth embodiment will be described with reference to Fig. 11. The anomaly detection system 100B according to the fourth embodiment differs from the anomaly detection system 100 according to the first embodiment in that the anomaly detection system 100B includes a third optical fiber 8, does not include an optical directional coupler 29, and includes an optical amplifying repeater 10B instead of the optical amplifying repeater 10.

[0101] The optical amplifier repeater 10B and the third optical fiber 8 are constructed in the detection line member 61, similar to the optical amplifier repeater 10, the first optical fiber 6, and the second optical fiber 7 described in the first embodiment.

[0102] The third optical fiber 8 has a first end EE and a second end EF. The direction from the first end EE to the second end EF is sometimes referred to as the forward direction, and the direction from the second end EF to the first end EE is sometimes referred to as the reverse direction.

[0103] It is desirable to use an optical fiber with low transmission loss and a large effective area for the third optical fiber 8 so that high-power light can be transmitted over long distances. For examples of optical fibers with a large effective area, please refer to the description of the first embodiment.

[0104] The detection light is transmitted through the first optical fiber 6. The first excitation light emitted from the excitation laser device 22 is transmitted through the third optical fiber 8.

[0105] The optical directional coupler 30 is connected to the first end EA of the first optical fiber 6, the optical isolator 25, and the optical directional coupler 31. The optical directional coupler 30 transmits the detection light sent through the optical isolator 25 in the forward direction to the first optical fiber 6. The optical directional coupler 30 sends to the optical directional coupler 31 the backscattered light that is generated at the portion 6a of the first optical fiber 6 and has transmitted through the portion 6a in the backward direction.

[0106] The optical amplifying repeater 10B includes an optical directional coupler 120 and an optical fiber 122 in addition to the configuration of the optical amplifying repeater 10 described in the first embodiment.

[0107] The optical directional coupler 120 sends a portion of the first pumping light transmitted forward from the first end EE of the third optical fiber 8 to the first erbium-doped fiber 1 via the optical fiber 122, and sends the remainder of the first pumping light toward the second end EF of the third optical fiber 8. The amplification degree of the detection light can be adjusted by adjusting the branching ratio of the light in the optical directional couplers 120 in the plurality of optical amplifier repeaters 10B. For example, the optical directional coupler 120 in the optical amplifier repeater 10B closer to the first end EE of the third optical fiber 8 may send a small proportion of the input first pumping light to the first erbium-doped fiber 1, and the optical directional coupler 120 in the optical amplifier repeater 10B closer to the second end EF of the third optical fiber 8 may send a large proportion of the input first pumping light to the first erbium-doped fiber 1.

[0108] Although FIG. 11 illustrates an example in which there is a single third optical fiber 8, there may be multiple third optical fibers 8. Connecting multiple third optical fibers 8 to each amplifier repeater 10B reduces the attenuation of the pumping light in each third optical fiber 8, resulting in high detection accuracy. For example, assume that the third optical fiber 8 includes optical fibers a, b, and c, and optical amplifier repeaters α, β, and γ are arranged in descending order of proximity to land. Optical fiber a may be connected only to optical amplifier repeater α and not to optical amplifier repeaters β and γ; optical fiber b may be connected only to optical amplifier repeater β and not to optical amplifier repeaters α and γ; and optical fiber c may be connected only to optical amplifier repeater γ and not to amplifier repeaters α and β. For example, optical fiber c is less likely to attenuate light because it does not pass through optical amplifier repeaters α and β. The same applies to the other optical fibers a and b. <Fifth embodiment>

[0109] A power cable anomaly detection system 100C according to a fifth embodiment will be described with reference to Fig. 12. The anomaly detection system 100C according to the fifth embodiment differs from the anomaly detection system 100B according to the fourth embodiment in that it includes a fourth optical fiber 9, does not include an optical directional coupler 32, and includes an optical amplifying repeater 10C instead of the optical amplifying repeater 10B.

[0110] The optical amplifier repeater 10C, the third optical fiber 8 and the fourth optical fiber 9 are constructed in the detection line member 61, similar to the optical amplifier repeater 10, the first optical fiber 6 and the second optical fiber 7 described in the first embodiment.

[0111] The fourth optical fiber 9 has a first end EG and a second end EH. The direction from the first end EG to the second end EH may be referred to as the forward direction, and the direction from the second end EH to the first end EG may be referred to as the reverse direction.

[0112] It is desirable to use an optical fiber with low transmission loss and a large effective area for the fourth optical fiber 9 so that high-power light can be transmitted over long distances. For examples of optical fibers with a large effective area, please refer to the description of the first embodiment.

[0113] The backscattered light is transmitted to the second optical fiber 7. The second excitation light emitted from the excitation laser device 24 is transmitted to the fourth optical fiber 9.

[0114] The optical directional coupler 31 is connected to the first end EC of the second optical fiber 7, the wavelength filter 28, and the optical directional coupler 30. The optical directional coupler 31 sends the backscattered light transmitted in the reverse direction through the second optical fiber 7 to the wavelength filter 28. The optical directional coupler 31 sends to the wavelength filter 28 the backscattered light that is generated at the portion 6a of the first optical fiber 6 and transmitted in the reverse direction through the portion 6a, which is transmitted through the optical directional coupler 30.

[0115] The optical amplifying repeater 10C includes an optical directional coupler 121 and an optical fiber 123 in addition to the configuration of the optical amplifying repeater 10B described in the fourth embodiment.

[0116] The optical directional coupler 121 sends a portion of the second pumping light transmitted forward from the first end E of the fourth optical fiber 9 to the second erbium-doped fiber 4 via the optical fiber 123, and sends the remainder of the second pumping light toward the second end EH of the fourth optical fiber 9. The amplification degree of the backscattered light can be adjusted by adjusting the branching ratio of the light in the optical directional couplers 121 in the plurality of optical amplifier repeaters 10C. For example, the optical directional coupler 121 in the optical amplifier repeater 10C closer to the first end E of the fourth optical fiber 9 may send a small proportion of the input second pumping light to the second erbium-doped fiber 4, and the optical directional coupler 121 in the optical amplifier repeater 10C closer to the second end EH of the fourth optical fiber 9 may send a large proportion of the input second pumping light to the second erbium-doped fiber 4.

[0117] 12 illustrates an example in which there is a single fourth optical fiber 9, but there may be multiple fourth optical fibers 9, just like the third optical fiber 8. If multiple fourth optical fibers 9 are connected to each amplifying repeater 10C, the attenuation of the pump light in each fourth optical fiber 9 is small, and detection accuracy is high. For details, please refer to the explanation for the case in which there are multiple third optical fibers 8. Sixth Embodiment

[0118] A power cable anomaly detection system 100E according to the sixth embodiment will be described with reference to Fig. 13. The anomaly detection system 100E according to the sixth embodiment differs from the anomaly detection system 100 according to the first embodiment in that the pulse laser device 21 is replaced with a pulse laser device 21E, and the measuring device 20 is replaced with a measuring device 20E.

[0119] The pulsed laser device 21E can emit detection light of a fixed wavelength that is modulated at a plurality of frequencies. The pulsed laser device 21E emits detection light of, for example, a wavelength of 1560 nm. As shown in FIG. 14, the pulsed laser device 21E sequentially emits detection light modulated at a plurality of frequencies (f1 to fn) within one measurement period T (a predetermined time).

[0120] In the event of a ground fault, it is desirable to detect the fault location using optical fiber within approximately 100 msec after the fault occurs. For example, if one measurement period T is 5 msec, 20 measurements (100 msec) are performed over the above time. To detect the fault location with an accuracy of 100 m, assuming the speed of light is approximately 2 × 10 m / sec, the Δt interval of the pulse wave should be approximately 1.0 μsec (microsecond). The Δt interval can be calculated by dividing the required length (here, 100 m) by the speed of light and then doubling it. By adjusting the Δt interval of the pulse wave during one measurement period T and using multiple frequencies for the modulation frequency of the pulse wave during one measurement period T rather than a single frequency, i.e., frequency multiplexing, the signal S / N ratio can be improved, thereby further increasing the accuracy of fault location detection.

[0121] The measurement device 20E includes a frequency filter 41 in addition to the configuration of the measurement device 20 described in the first embodiment.

[0122] The frequency filter 41 extracts a plurality of frequency components of the detection light emitted from the pulsed laser device 21E from the signal sent through the optical receiver 23. During one measurement period T, the frequency filter 41 sequentially detects each component of a plurality of frequencies fi (i = 1 to n) from among the frequency components of the backscattered light at intervals of Δt.

[0123] With reference to FIG. 15, a procedure for detecting an abnormal point in a power cable in the sixth embodiment will be described.

[0124] In step S201, the pumping laser device 22 starts emitting the first pumping light, and the pumping laser device 24 starts emitting the second pumping light. The start timing of the emission of the first pumping light and the start timing of the emission of the second pumping light may be simultaneous. The first pumping light is transmitted through the first optical fiber 6. The second pumping light is transmitted through the second optical fiber 7.

[0125] In step S202, the pulsed laser device 21E emits a plurality of frequency-modulated detection lights (pulsed lights). That is, the pulsed laser device 21E sequentially emits detection lights modulated at frequencies fi (i = 1 to n) at intervals of Δt during one measurement period T (within a predetermined time). The detection lights are transmitted through the first optical fiber 6.

[0126] In step S203, the optical amplifier repeater 10 amplifies the sensing light with the first excitation light. The backscattered light propagates in the reverse direction through the first optical fiber 6 and enters the optical amplifier repeater 10.

[0127] In step S204, the optical amplifier repeater 10 amplifies the backscattered light with the second excitation light and sends it to the second optical fiber 7. The backscattered light is transmitted in the reverse direction through the second optical fiber 7, is amplified by the second excitation light in the optical amplifier repeater 10 along the way, and is input to the measuring device 20E. If an abnormality occurs in the power cable 50, the physical quantities (intensity, phase, etc.) of the backscattered light will fluctuate (or attenuate if it is intensity), and therefore the measuring device 20E can determine whether or not there is a fluctuation in the physical quantities, thereby determining the occurrence and location of the abnormality.

[0128] In step S205, the measuring device 20E executes a receiving process for the backscattered light. That is, the wavelength filter 28 sends the backscattered light, which is part of the light sent through the optical directional coupler 31, to the optical receiver 23. The optical receiver 23 converts the light sent through the wavelength filter 28 into an electrical signal and sends it to the frequency filter 41. The frequency filter 41 detects the frequency components fi (i = 1 to n) from the frequency components of the backscattered light. The output of the frequency filter 41 is sent to the analyzing device 12.

[0129] In step S206, if one measurement period T has elapsed since the previous transmission of the detection light (pulsed light) modulated with frequency fi, the process proceeds to step S207. As in the first embodiment, one measurement period T may be set to be equal to or greater than the difference between the time when the detection light modulated with frequency fi is transmitted from the pulsed laser device 21 and the time when the optical receiver 23 receives the backscattered light generated at the second end EB of the first optical fiber 6 by the detection light modulated with frequency fi. During the measurement period T, the measurement device 20 continues to receive the backscattered light. The measurement period T for the backscattered light of frequency fi starts from the time when the detection light modulated with frequency fi is transmitted. When the measurement period T for fn ends, the process proceeds to step S207. Although the measurement periods for multiple frequencies overlap with each other, the provision of n frequency filters 41 enables the detection of frequency components f1 to fn.

[0130] Alternatively, one measurement period T in step S206 may be set to be different from one measurement period T in step S202 and equal to or greater than the difference between the time when the detection light modulated at the frequency f1 is emitted from the pulsed laser device 21 and the time when the optical receiver 23 receives the backscattered light generated at the second end EB of the first optical fiber 6 by the detection light modulated at the frequency fn.

[0131] In step S207, the analysis device 12 determines a physical quantity from the backscattered light sent through the output of the frequency filter 41. The analysis device 12 uses the determined physical quantity (hereinafter referred to as the latest physical quantity) to detect the presence or absence of an abnormality.

[0132] The presence or absence of an abnormality may be detected, for example, by comparing the latest physical quantity with one or more thresholds. The one or more thresholds are values ​​corresponding to each position on the power cable 50, and are set, for example, according to the physical quantity of backscattered light calculated according to the transmission distance when there is no abnormality in the power cable 50. The physical quantity calculated for each measurement period T may be accumulated, and this accumulated information may be used. The accumulated information indicates past trends, and using the accumulated information tends to reduce the influence of noise. For example, the analysis device 12 may compare the difference between the latest physical quantity and the immediately preceding physical quantity with a preset threshold. Instead of the immediately preceding physical quantity, an average value of the physical quantity over a certain period going back in time may be used. Instead of the average value, the variance value of the physical quantity over a certain period may be used as the comparison target or threshold. This analysis process detects the presence or absence of an abnormality that may occur within a short period.

[0133] In step S208, the analyzer 12 adds up the physical quantities (intensity, phase difference, phase change, etc. of the backscattered light) of the signals sent through the output of the frequency filter 41.

[0134] In step S209, each time the addition process is completed a predetermined number of times, the process proceeds to step S210, otherwise the process returns to step S202. The added value is stored and saved as needed.

[0135] In step S210, the analyzer 12 redetects the presence or absence of an abnormality using a sum including the latest physical quantity (hereinafter referred to as the latest sum) and the past sum. For example, the analyzer 12 compares the difference between the average of the past sums and the average of the latest sum with a preset threshold. The average of the sums is calculated, for example, by dividing the sum by a specified number of times. Instead of the average, the variance of the sum may be used as the comparison target or threshold. The variance indicates signal variation due to noise. Using accumulated information such as the average of the past sums tends to further reduce the influence of noise. This analysis process detects the presence or absence of an abnormality that may occur over a long period of time (such as minute distortion or phase changes that persist over a long period of time). In other words, external damage to the power cable 50 or the occurrence of permanent damage such as fatigue can also be detected. The sum is then reset, and the process returns to step S202.

[0136] In this embodiment, by multiplexing the frequencies of the detection light (f1 to fn), it is possible to increase the number of pieces of data obtained in one measurement period to n. By averaging many pieces of data, it is possible to detect abnormal points with high accuracy in a short time. In this embodiment, n times of measurements can be made in one round trip time (for example, 5 msec), making it easy to capture accident phenomena within 100 msec.

[0137] It is also possible to synchronize the time of the accident based on the trip information and analyze the measurement data before and after the accident at short time intervals. This allows the signal change point to be detected with high accuracy in a short time, improving the accuracy of detecting the accident point.

[0138] The embodiments disclosed herein are illustrative in all respects and should not be considered limiting. The scope of the present invention is defined by the claims, not by the above-described embodiments, and is intended to include meanings equivalent to the claims and all modifications within the scope thereof. [Explanation of symbols]

[0139] 1 first erbium-doped fiber, 25, 26, 27 optical isolator, 3, 5, 29, 30, 31, 31D, 32, 32D, 120, 121 optical directional coupler, 4 second erbium-doped fiber, 6 first optical fiber, 6a, 6b first optical fiber section, 7 second optical fiber, 7a second optical fiber section, 8 third optical fiber, 9 fourth optical fiber, 10, 10B, 10C, 70 optical amplifier repeater, 11, 11A excitation device, 12 analysis device, 20, 20E measurement device, 21, 21E pulse laser device, 22, 24, 24A excitation laser device, 23 optical receiver, 28 wavelength filter, 38 branching structure, 39 branching optical fiber, 41 frequency filter, 50, 50A power cable, 51, 51A, 51B conductor, 52 Inner semiconductive layer, 53, 53A, 53B Insulating layer, 54, 54A, 54B Outer semiconductive layer, 55, 64 Sheath, 57A, 57B Shielding layer, 58a, 58b Wire material, 59 Armoring portion, 60 Cable body, 61, 61A Detection wire member, 62 Jelly compound, 63, 94 Metal tube, 66 Housing, 80 Connection portion, 92 Protective layer, 97 Semiconductive portion, 98 Insulating portion, 99 Sleeve, 100, 100A, 100B, 100C, 100D, 100E Anomaly detection system, 122, 123 Optical fiber, EA, EC, EE, EG First end, EB, ED, EF, EH Second end, ND1X, ND1Y, ND2X, ND2Y Connection point.

Claims

1. a cable body including a conductor, an insulating layer, a semiconductive layer, and a sheath; a first optical fiber through which the sensing light is transmitted; a second optical fiber through which backscattered light of the detection light is transmitted; an optical fiber through which a first excitation light for amplifying the detection light is transmitted; an optical fiber through which second excitation light for amplifying the backscattered light is transmitted; and at least one optical amplifying repeater that amplifies the sensing light with the first excitation light and amplifies the backscattered light with the second excitation light.

2. The power cable according to claim 1 , wherein the optical fiber through which the first excitation light is transmitted is the first optical fiber.

3. The power cable according to claim 1 , wherein the optical fiber through which the second excitation light is transmitted is the second optical fiber.

4. The power cable according to claim 1 , wherein the optical amplifying repeater comprises a branching structure that guides the backscattered light generated in the first optical fiber to the second optical fiber.

5. The cable body is disposed at the center of the power cable, The power cable is A plurality of wires and at least one metal tube are provided on the outside of the cable body, The power cable according to claim 1 , wherein the first optical fiber, the second optical fiber, and the optical amplifier repeater are housed in the metal tube.

6. Further, an armor portion is provided on the outer periphery of the cable main body, The armoring portion is composed of the plurality of wires and a detection wire member, the detection wire member accommodates the metal tube; The power cable according to claim 5 , wherein an outer diameter of the detection line member is equal to an outer diameter of a wire member adjacent to the detection line member among the plurality of wire members.

7. the sensing light is transmitted in a direction from a first end to a second end of the first optical fiber, and the backscattered light is transmitted in a direction from the second end to the first end of the second optical fiber; The optical amplifier repeater comprises: a first erbium-doped fiber that amplifies the sensing light transmitted from the first end of the first optical fiber by the first excitation light; a branching optical fiber; a first optical directional coupler that sends the sensing light amplified by the first erbium-doped fiber toward the second end of the first optical fiber and sends the backscattered light transmitted from the second end of the first optical fiber to the branching optical fiber; a second erbium-doped fiber; and a second optical directional coupler that sends the backscattered light that has been transmitted through the branching optical fiber and the backscattered light that has been transmitted from the direction of the second end of the second optical fiber to the second erbium-doped fiber, 2. The power cable according to claim 1, wherein the second erbium-doped fiber amplifies the backscattered light sent through the second optical directional coupler with the second excitation light and sends the backscattered light toward the first end of the second optical fiber.

8. The power cable according to claim 1 , further comprising one or more third optical fibers that are independent of the first optical fiber and through which the first excitation light is transmitted.

9. 9. The power cable according to claim 1, further comprising one or more fourth optical fibers that are independent of the second optical fiber and through which the second excitation light is transmitted.

10. further comprising one or more third optical fibers that are independent of the first optical fiber and through which the first excitation light is transmitted; the first excitation light is transmitted in a direction from a first end to a second end of the third optical fiber; 8. The power cable according to claim 7, wherein the optical amplifier repeater further includes a third optical directional coupler that sends a portion of the first pumping light transmitted from the first end of the third optical fiber to the first erbium-doped fiber and sends the remainder of the first pumping light toward the second end of the third optical fiber.

11. further comprising one or more fourth optical fibers that are independent of the second optical fiber and through which the second excitation light is transmitted; the second excitation light is transmitted in a direction from a first end to a second end of the fourth optical fiber; 11. The power cable according to claim 7 or 10, wherein the optical amplifier repeater further includes a fourth optical directional coupler that sends a portion of the second pumping light transmitted from the first end of the fourth optical fiber to the second erbium-doped fiber and sends the remainder of the second pumping light toward the second end of the fourth optical fiber.

12. A power line including a first power cable, a second power cable, and a connection portion that connects the first power cable and the second power cable, Each of the first power cable and the second power cable comprises: a cable body including a conductor, an insulating layer, a semiconductive layer, and a sheath; a first optical fiber through which the sensing light is transmitted; a second optical fiber through which backscattered light of the detection light is transmitted; an optical fiber through which a first excitation light for amplifying the detection light is transmitted; an optical fiber through which second excitation light for amplifying the backscattered light is transmitted; The power line, wherein the connection section includes an optical amplifying repeater that amplifies the sensing light by the first excitation light and amplifies the backscattered light by the second excitation light.

13. a power cable including: a cable main body including a conductor, an insulating layer, a semiconductive layer, and a sheath; a first optical fiber through which detection light is transmitted; a second optical fiber through which backscattered light of the detection light is transmitted; an optical fiber through which first excitation light for amplifying the detection light is transmitted; and an optical fiber through which second excitation light for amplifying the backscattered light is transmitted; a laser device that emits the detection light; an excitation device that emits the first excitation light and the second excitation light; an optical amplifying repeater that amplifies the sensing light by the first excitation light and amplifies the backscattered light by the second excitation light; and a measuring device that detects an abnormal point in the power cable based on the backscattered light.

14. the second excitation light is transmitted through the second optical fiber; The power cable anomaly detection system according to claim 13 , wherein the excitation device emits the second excitation light having a wavelength shorter than a wavelength of the detection light.

15. the laser device sequentially emits a plurality of frequency-modulated detection lights within a predetermined time period; The power cable anomaly detection system according to claim 13 , wherein the measurement device includes a frequency filter that detects each of the plurality of frequency components of the backscattered light.

16. 16. The power cable anomaly detection system according to claim 13, wherein the measurement device includes a wavelength filter that cuts out the first excitation light and the second excitation light in order to detect a wavelength of the detection light emitted by the laser device.

17. A method for detecting an abnormality in a power cable including a cable main body including a conductor, an insulating layer, a semiconductive layer, and a sheath, a first optical fiber through which detection light is transmitted, and a second optical fiber through which backscattered light of the detection light is transmitted, the method comprising: the power cable includes an optical fiber through which a first excitation light for amplifying the detection light is transmitted, and an optical fiber through which a second excitation light for amplifying the backscattered light is transmitted, an excitation device transmitting the first excitation light and the second excitation light; a first laser device emitting the detection light; an optical amplifier repeater amplifying the detection light by the first excitation light; the optical amplifying repeater amplifying the backscattered light by the second pumping light; a step of detecting an abnormal point in the power cable using the backscattered light by a measuring device.

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