Power cable, power line, power cable abnormal point detection system, and power cable abnormal point detection method

Abstract

A power cable according to the present disclosure comprises: a cable body that includes a conductor, an insulating layer, a semiconductive layer, and a sheath; a first optical fiber through which at least detection light and backscattered light of the detection light are transmitted; at least one excitation light transmission optical fiber through which at least one excitation light is transmitted; and at least one bidirectional optical amplification relay that amplifies the detection light using the excitation light transmitted by the first optical fiber or the excitation light transmission optical fiber, and amplifies the backscattered light using the excitation light transmitted by the excitation light transmission optical fiber.

Description

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

[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 Japanese Patent Application No. 2024-091484, filed on June 5, 2024. The entire contents of the Japanese patent application are incorporated herein by reference.

[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 disclosed 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 Optical Time Domain Analysis) method. The power cable core corresponds to the cable body of the power cable.

[0003] JP 2013-36876 A International Publication No. 2021 / 090644

[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 at least detection light and backscattered light of the detection light are transmitted; at least one excitation light transmitting optical fiber through which at least one excitation light is transmitted; and at least one bidirectional optical amplification repeater that amplifies the detection light by the excitation light transmitted by the first optical fiber or the excitation light transmitting optical fiber and amplifies the backscattered light by the excitation light transmitted by the excitation light transmitting optical fiber.

[0005] A power line according to the present disclosure includes a first power cable, a second power cable, and a connection section connecting the first and second power cables, wherein 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 at least detection light and backscattered light of the detection light are transmitted, and at least one excitation light transmitting optical fiber through which at least one excitation light is transmitted. The connection section includes a bidirectional optical amplification repeater that amplifies the detection light by the excitation light transmitted by the first optical fiber or the excitation light transmitting optical fiber, and amplifies the backscattered light by the excitation light transmitted by the excitation light transmitting optical fiber.

[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 at least detection light and backscattered light of the detection light are transmitted, and at least one excitation light transmitting optical fiber through which at least one excitation light is transmitted, a laser device that emits the detection light, at least one excitation device that emits at least one excitation light, a bidirectional optical amplification repeater that amplifies the detection light with the excitation light transmitted by the first optical fiber or the excitation light transmitting optical fiber and amplifies the backscattered light with the excitation light transmitted by the excitation light transmitting optical fiber, and a measurement device that detects anomalies in the power cable based on the backscattered light.

[0007] A power cable anomaly detection method according to the present disclosure detects an anomaly in a power cable having at least a cable main body including a conductor, an insulating layer, a semiconducting layer, and a sheath, and includes the steps of: at least one excitation device emitting at least one excitation light; a first laser device emitting detection light; a first optical fiber included in the power cable transmitting the detection light; the first optical fiber or at least one excitation light transmitting optical fiber included in the power cable transmitting the at least one excitation light; the first optical fiber transmitting backscattered light of the detection light; a bidirectional optical amplifier repeater amplifying the detection light with the excitation light transmitted by the first optical fiber or the excitation light transmitting optical fiber; the bidirectional optical amplifier repeater amplifying the backscattered light with the excitation light transmitted by the excitation light transmitted by the excitation light transmitting optical fiber; and a measurement device detecting an anomaly in the power cable using the backscattered light.

[0008] FIG. 1 is a cross-sectional view of a power cable 50 according to a first embodiment. FIG. 2 is a cross-sectional view of a detection line member 61 according to FIG. 1. FIG. 3 is a diagram illustrating a portion of the detection line member 61 according to the first embodiment in the longitudinal direction. FIG. 4 is a diagram illustrating the configuration of a power cable anomaly detection system 100 according to the first embodiment. FIG. 5 is a flowchart illustrating a procedure for detecting an anomaly in a power cable according to the first embodiment. FIG. 6 is a diagram illustrating a portion of the power line according to a second embodiment in the longitudinal direction. FIG. 7 is a cross-sectional view of a power cable 50A according to the second embodiment. FIG. 8 is a diagram illustrating the configuration of a connection unit 80 according to FIG. 6. FIG. 9 is a diagram illustrating the configuration of a bidirectional optical amplifier repeater 70 according to FIG. 8. FIG. 10 is a diagram illustrating a portion of the detection line member 61 according to a third embodiment in the longitudinal direction. FIG. 11 is a diagram illustrating the configuration of a power cable anomaly detection system 100A according to the third embodiment. Fig. 12 is a diagram showing a part of the longitudinal direction of the detection line member 61 in the fourth embodiment. Fig. 13 is a diagram showing the configuration of a power cable anomaly detection system 100B in the fourth embodiment. Fig. 14 is a flowchart showing the procedure for detecting an abnormal point in a power cable in the fifth embodiment.

[0009] [Problem to be Solved by the Present Disclosure] 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.

[0010] 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 an optical transmission line at predetermined intervals, and each optical amplifier repeater is supplied with power via a power feeder line within 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 line. When the optical amplifier repeater is equipped with a laser device, an optical fiber for transmitting pumping 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.

[0011] 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 that are suitable for long-distance power lines and that are capable of detecting anomalies using optical fibers and that are configured so that optical amplifier repeaters do not include laser devices.

[0012] 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 bidirectional optical amplifier 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.

[0013] [Outline of the embodiment] First, the embodiments of the present disclosure will be listed and described.

[0014] (1) A power cable (50) of the present disclosure 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 at least detection light and backscattered light of the detection light are transmitted; at least one excitation light transmitting optical fiber (7, 8, 75) through which at least one excitation light is transmitted; and at least one bidirectional optical amplifier repeater (10, 10A, 10B) that amplifies the detection light by the excitation light transmitted by the first optical fiber (6) or the excitation light transmitting optical fiber (7, 75) and amplifies the backscattered light by the excitation light transmitted by the excitation light transmitting optical fiber (8, 75).

[0015] The power cable (50) comprises a plurality of optical fibers (6, 7, 8, 75) 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 in a submarine power cable. 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) is not intended for communication purposes but for sensing purposes. That is, the first optical fiber (6) is used to detect damage or distortion in the cable body (60), the armor (59), or a connection portion (80) of a power line.

[0016] At least the optical fiber for transmitting excitation light may include an optical fiber for transmitting excitation light that amplifies the backscattered light. At least the optical fiber for transmitting excitation light may include an optical fiber (7) for transmitting excitation light that amplifies the detection light and an optical fiber (8) for transmitting excitation light that amplifies the backscattered light, separately. At least the optical fiber for transmitting excitation light may include an optical fiber (75) for transmitting excitation light that amplifies the detection light and the backscattered light. At least the optical fiber for transmitting excitation light may include an optical fiber (8) for transmitting excitation light that amplifies the backscattered light, and the optical fiber for transmitting excitation light that amplifies the detection light may be the first optical fiber (6).

[0017] The power cable (50) does not include a laser device for transmitting excitation light, nor does it include a power feeder for supplying power to the laser device. The power cable (50) can amplify detection light using excitation light transmitted through the first optical fiber (6) or the excitation light transmitting optical fiber (7, 75), and can amplify backscattered light using excitation light transmitted through the excitation light transmitting optical fiber (8, 75). Even when 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). Furthermore, the power cable (50) of the present disclosure can transmit both detection light and backscattered light using the first optical fiber (6). A power cable (50) with this configuration has a smaller number of optical fibers than a power cable in which the optical fiber transmitting detection light and the optical fiber transmitting backscattered light are separate optical fibers.

[0018] (2) In the power cable (50) of (1), the at least one excitation light includes a first excitation light for amplifying the detection light and a second excitation light for amplifying the backscattered light, the at least one excitation light transmitting optical fiber includes a first excitation light transmitting optical fiber (7) through which the first excitation light is transmitted and a second excitation light transmitting optical fiber (8) through which the second excitation light is transmitted, and the bidirectional optical amplifier repeater (10) amplifies the detection light by the first excitation light transmitted by the first excitation light transmitting optical fiber (7) and amplifies the backscattered light by the second excitation light transmitted by the second excitation light transmitting optical fiber (8). In this configuration, the optical fiber transmitting the first excitation light and the optical fiber transmitting the second excitation light are separate optical fibers. Compared to transmitting the two excitation light beams through a single optical fiber, this configuration makes it easier to reduce attenuation of the excitation light.

[0019] (3) In the power cable (50) of (1), the at least one excitation light includes a first excitation light for amplifying the detection light and a second excitation light for amplifying the backscattered light, the first excitation light is transmitted through the first optical fiber (6), the at least one excitation light transmitting optical fiber includes a first excitation light transmitting optical fiber (8) for transmitting the second excitation light, and the bidirectional optical amplifier repeater (10A) amplifies the detection light using the first excitation light transmitted through the first optical fiber (6) and amplifies the backscattered light using the second excitation light transmitted through the first excitation light transmitting optical fiber (8). In this configuration, the downstream detection light and the first excitation light can be transmitted through the same optical fiber. In this configuration, the number of optical fibers required is smaller than when the optical fiber transmitting the detection light and the optical fiber transmitting the first excitation light are separate optical fibers.

[0020] (4) In the power cable (50) of (1), at least one pumping light transmitting optical fiber (75) transmits pumping light for amplifying the detection light and the backscattered light, and the bidirectional optical amplifier repeater (10B) amplifies the detection light using the pumping light transmitted by the first pumping light transmitting optical fiber (75) and amplifies the backscattered light using the pumping light transmitted by the first pumping light transmitting optical fiber (75). In this configuration, the pumping light for amplifying the detection light and the backscattered light can be transmitted through a single optical fiber. This configuration requires fewer optical fibers than when the optical fibers transmitting the first pumping light and the second pumping light are each independent optical fibers. Furthermore, this configuration requires fewer devices for transmitting pumping light than the above case.

[0021] (5) In the power cable (50) of any one of (1) to (4) above, the cable main body (60) is disposed at the center of the power cable (50), and the power cable (50) includes a plurality of wires (58a, 58b) and at least one metal tube (63) outside the cable main body (60), and the metal tube (63) houses a first optical fiber (6), at least one optical fiber (7, 8, 75) for transmitting pumping light, and a bidirectional optical amplifier repeater (10, 10A, 10B). In this configuration, the first optical fiber (6), at least one optical fiber (7, 8, 75) for transmitting pumping light, and the bidirectional optical amplifier repeater (10, 10A, 10B) can be disposed in a position where abnormalities such as damage or distortion of the cable main body (60) or the armoring portion (59) can be easily detected due to abnormalities such as damage or distortion of the power cable (50).

[0022] (6) The power cable (50) of (5) further comprises an armored portion (59) provided on the outer periphery of the cable body (60), the armored portion (59) being composed of a plurality of wires (58a, 58b) and a detection wire member (61), and the detection wire member (61) houses a metal tube (63).

[0023] (7) The power line of the present disclosure includes a first power cable (50A-1), a second power cable (50A-2), and a connection portion (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) including a conductor (51), an insulating layer (53), semiconductive layers (52, 54), and a sheath (55), a first optical fiber (6) through which at least detection light and backscattered light of the detection light are transmitted, and at least one excitation light transmitting optical fiber (7, 8, 75) through which at least one excitation light is transmitted, and the connection section (80) includes a bidirectional optical amplification repeater (10, 10A, 10B) that amplifies the detection light by excitation light transmitted by the first optical fiber (6) or the excitation light transmitting optical fiber (7, 75) and amplifies the backscattered light by excitation light transmitted by the excitation light transmitting optical fiber (8, 75). Even in the case of a long-distance power line according to the present disclosure, the detection light can be amplified by the excitation light transmitted through the first optical fiber (6) or the excitation light transmitting optical fiber (7, 75), and the backscattered light can be amplified by the excitation light transmitted through the excitation light transmitting optical fiber (8, 75). With this configuration, even in the case of a long-distance power line, an abnormality in the power line can be detected by the first optical fiber (6).

[0024] (8) The power cable abnormality 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 at least detection light and backscattered light of the detection light are transmitted, and at least one excitation light transmitting optical fiber (7, 8, 75) through which at least one excitation light is transmitted, a laser device (21) that emits detection light, The power cable anomaly detection system (100) includes at least one excitation device (22, 22B, 24) that emits at least one excitation light, a bidirectional optical amplifier repeater (10, 10A, 10B) that amplifies detection light using the excitation light transmitted by a first optical fiber (6) or an excitation light transmission optical fiber (7, 75) and amplifies backscattered light using the excitation light transmitted by the excitation light transmission optical fiber (8, 75), and a measurement device (20) that detects anomalies in a power cable based on the backscattered light. The power cable anomaly detection system (100) is capable of amplifying the detection light and the backscattered light even when the power cable (50) forms a long-distance power line. Such a power cable anomaly detection system (100) can detect anomalies in a long-distance power line using the first optical fiber (6).

[0025] (9) The method for detecting an abnormal point in a power cable according to the present disclosure is a method for detecting an abnormal point in a power cable (50) having at least a cable main body (60) including a conductor (51), an insulating layer (53), a semiconductive layer (52, 54), and a sheath (55), and includes the steps of: at least one excitation device (22, 22B, 24) emitting at least one excitation light; a first laser device (21) emitting detection light; a first optical fiber (6) included in the power cable (50) transmitting the detection light; and a first optical fiber (6) or at least one optical fiber for transmitting excitation light included in the power cable (50) transmitting the detection light. a step of a bidirectional optical amplifier repeater (10, 10A, 10B) amplifying the detection light by the excitation light transmitted by the first optical fiber (6) or the excitation light transmitting optical fiber (7, 75); a step of the bidirectional optical amplifier repeater (10, 10A, 10B) amplifying the backscattered light by the excitation light transmitted by the excitation light transmitting optical fiber (8, 75); and a step of a measuring device (20) detecting an abnormality in the power cable using the backscattered light.

[0026] In this method, even when the power cable (50) constitutes a long-distance power line, the detection light can be amplified by the excitation light transmitted through the first optical fiber (6) or the excitation light transmitting optical fiber (7, 75), and the backscattered light can be amplified by the excitation light transmitted through the excitation light transmitting optical fiber (8, 75). 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).

[0027] [Details of the embodiment] Hereinafter, the embodiment will be described with reference to the drawings.

[0028] First Embodiment A power cable 50 will be described with reference to Figure 1. The power cable 50 is an optical-power composite cable. The power cable 50 includes a cable main body 60 for transmitting power, an armor portion 59, and a detection line member 61 for transmitting light. As will be described later, the detection line member 61 includes optical fibers 6, 7, and 8 that are used to detect abnormalities in the power cable or the like. Furthermore, the detection line member 61 of this example includes a plurality of bidirectional optical amplification repeaters 10, as will be described later.

[0029] 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 provided on 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.

[0030] The armor portion 59 has multiple 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 multiple wires 58a constituting the inner layer are tightly arranged along the outer surface of the cable main body 60. The multiple wires 58b constituting the outer layer are tightly arranged along the circumference of the outer surface formed by the multiple 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. Furthermore, 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.

[0031] In the armoring portion 59, a portion of the wire 58a constituting the inner layer of the two layers is replaced with a detection wire 61 to detect abnormalities such as damage or distortion in the cable main body 60 and the armoring portion 59. The detection wire 61 needs to be formed in at least one location in the armoring portion 59, but may be provided in multiple locations. While FIG. 1 illustrates a case where the armoring portion 59 has a multi-layer structure, a single-layer structure is also acceptable. Furthermore, a portion of the wire 58b constituting the outer layer of the armoring portion 59 may be replaced with the detection wire 61. The outer diameter of the detection wire 61 is equal to the outer diameter of the wires 58a and 58b adjacent to the detection wire 61. The outer diameters of all of the wires 58a, 58b, and the detection wire 61 may be equal.

[0032] The detection line member 61 will be described with reference to Figures 2 and 3. The detection line member 61 includes a metal tube 63 and a sheath 64 disposed 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, an optical fiber 7 for transmitting pumping light, an optical fiber 8 for transmitting pumping light, and a bidirectional 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.

[0033] The first optical fiber 6 transmits the detection light emitted from a laser device 21 (described later). The first optical fiber 6 also transmits backscattered light of the detection light. The excitation light transmitting optical fiber 7 is an optical fiber independent of the first optical fiber 6. The excitation light transmitting optical fiber 7 transmits first excitation light emitted from an excitation laser device 22 (described later). The excitation light transmitting optical fiber 8 is an optical fiber independent of the first optical fiber 6 and the excitation light transmitting optical fiber 7. The excitation light transmitting optical fiber 8 transmits second excitation light emitted from an excitation laser device 24 (described later). As in this example, when the excitation light transmitting optical fiber 7 is dedicated to the excitation light of the detection light and the excitation light transmitting optical fiber 8 is dedicated to the excitation light of the backscattered light, the detection light and the backscattered light can be effectively amplified. This makes it easy to minimize degradation of detection accuracy due to attenuation of the detection light and the backscattered light. Furthermore, by providing an optical fiber dedicated to excitation light, the intensity of the excitation light can be easily adjusted.

[0034] The detection line member 61 can be manufactured by connecting the first optical fiber 6, the optical fiber 7 for transmitting excitation light, and the optical fiber 8 for transmitting excitation light to the bidirectional optical amplifier repeater 10 and wrapping them with a metal tube 63, or by manufacturing a metal tube containing the first optical fiber 6, the optical fiber 7 for transmitting excitation light, and the optical fiber 8 for transmitting excitation light, and a metal tube containing the bidirectional optical amplifier repeater 10, and then welding, brazing, or joining these metal tubes with metal tape or the like.

[0035] The bidirectional optical amplifier repeater 10 provided in the detection line member 61 will be described with reference to Fig. 3. The bidirectional optical amplifier repeaters 10 are inserted at multiple locations along the first optical fiber 6, the pumping light transmitting optical fiber 7, and the pumping light transmitting optical fiber 8. Fig. 3 shows only one bidirectional optical amplifier repeater 10.

[0036] The housing 66 of the bidirectional optical amplifier repeater 10 accommodates the first circulator 18, the second circulator 19, the first erbium-doped fiber 1, the second erbium-doped fiber 4, and the optical directional couplers 5, 14, 15, and 16. Like the detection line 61, the housing 66 has a waterproof structure including a metal tube 63 and a sheath 64. While the outer diameter of the housing 66 is exaggerated in FIG. 3 to be larger than that of the detection line 61, the outer diameter of the housing 66 may be the same as that of the detection line 61. In other words, the detection line 61 may have a uniform outer diameter throughout its entire length, including the location where the bidirectional optical amplifier repeater 10 is provided. The metal tube 63 of the detection line 61 may also have a uniform outer diameter throughout its entire length, including the location where the bidirectional 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 along its entire length as described above and this outer diameter is the same as the outer diameter of the wire constituting the armored portion 59, the armored portion 59 is provided approximately concentrically on the cable main body 60 as shown in FIG. 1. The size of each component constituting the bidirectional optical amplifier repeater 10 may be adjusted so that it can be housed within the metal tube 63 having such an outer diameter. The bidirectional optical amplifier repeater 10 may further include an optical isolator (not shown).

[0037] Details of the configurations and operations of the first circulator 18, the second circulator 19, and the optical directional couplers 14, 15, and 16 will be explained in the next section on the power cable abnormality detection system 100.

[0038] The bidirectional optical amplifier repeater 10 amplifies the sensing light and the backscattered light by pumping light. Specifically, 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 in a direction away from the emission position of the laser device 21. The second pumping light excites erbium ions in the second erbium-doped fiber 4, thereby amplifying the backscattered light propagating through the first optical fiber 6 in a direction opposite to the traveling direction of the sensing light.

[0039] A power cable abnormality detection system 100 according to the first embodiment will be described with reference to FIG.

[0040] The power cable anomaly detection system 100 includes a power cable 50, a first optical fiber 6, an optical fiber 7 for transmitting pumping light, an optical fiber 8 for transmitting pumping light, a bidirectional optical amplifying repeater 10, and a control device 40. The control device 40 includes 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 a third circulator 17. 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, Figure 4 shows the first optical fiber 6, the optical fibers 7 and 8 for transmitting pumping light, and the bidirectional optical amplifying 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 a component independent of the power cable 50, and as will be described later, are connected to the first optical fiber 6, the excitation light transmitting optical fiber 7, or the excitation light transmitting optical fiber 8 at the end of the power cable 50 via optical isolators 25, 26, and 27 and a third circulator 17 as appropriate.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] 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 optical fibers 7 and 8 for transmitting pumping light.

[0045] The first optical fiber 6, the optical fiber 7 for transmitting pumping light, and the optical fiber 8 for transmitting pumping light are arranged close to each other (see also FIG. 2 ). The first optical fiber 6 has a first end EA and a second end EB. The optical fiber 7 for transmitting pumping light has a first end EC and a second end ED. The optical fiber 8 for transmitting pumping light has a first end EE and a second end EF. The directions from the first end EA to the second end EB, the first end EC to the second end ED, and the first end EE to the second end EF are directions in which light emitted from the laser device travels away from the emission position and may be referred to as the forward direction. The directions from the second end EB to the first end EA, the second end ED to the first end EC, and the second end EF to the first end EE are directions in which light approaches the emission position, opposite to the forward direction, and may be referred to as the reverse direction.

[0046] The detection light is transmitted through the first optical fiber 6 from the first end EA to the second end EB. The backscattered light of the detection light is transmitted through the first optical fiber 6 from the second end EB to the first end EA.

[0047] The first pumping light is transmitted through the pumping light-transmitting optical fiber 7 from the first end EC to the second end ED. The second pumping light is transmitted through the pumping light-transmitting optical fiber 8 from the first end EE to the second end EF.

[0048] The first optical fiber 6, the pumping light transmitting optical fiber 7, and the pumping light transmitting optical fiber 8 are preferably optical fibers with low transmission loss and large effective areas 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.

[0049] The bidirectional optical amplifier repeaters 10 are installed at each of a plurality of split locations along the first optical fiber 6, the optical fiber 7 for transmitting pumping light, and the optical fiber 8 for transmitting pumping light.

[0050] The bidirectional optical amplifying repeater 10 amplifies the sensing light with a first excitation light and amplifies the backscattered light with a second excitation light.

[0051] 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.

[0052] 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.

[0053] The optical isolator 27 is connected to the output port of the pumping laser device 24. The optical isolator 27 blocks the transmission of light to the pumping laser device 24.

[0054] For example, a commercially available three-port or four-port circulator can be used as the third circulator 17. In Fig. 4, the three-port circulator 17 is shown.

[0055] The third circulator 17 has a first port P1, a second port P2, and a third port P3. A signal input to the first port P1 is output from the second port P2. A signal input to the second port P2 is output from the third port P3. The first port P1 is connected to the optical isolator 25. The second port P2 is connected to the first end EA of the first optical fiber 6. The third port P3 is connected to the measuring device 20.

[0056] The third circulator 17 transmits the detection light sent from the pulse laser device 21 via the optical isolator 25 in the forward direction to the first optical fiber 6. The third circulator 17 sends the backscattered light that has been transmitted in the reverse direction through the first optical fiber 6 to the measuring device 20.

[0057] 3 and 4, the configuration and operation of the bidirectional optical amplifier repeater 10 will be described. The bidirectional optical amplifier repeater 10 includes a first circulator 18, a second circulator 19, a first erbium-doped fiber 1, optical directional couplers 5, 14, 15, and 16, and a second erbium-doped fiber 4.

[0058] The first circulator 18 may be, for example, a commercially available four-port circulator. The first circulator 18 has a first port P1, a second port P2, a third port P3, and a fourth port P4. A signal input to the first port P1 is output from the second port P2. A signal input to the fourth port P4 is output from the first port P1. In Figures 3 and 4, and Figures 10 to 13 described below, the third port P3 is an empty port and is not shown. The first port P1 is connected to the connection point ND1X of the first optical fiber 6. The second port P2 is connected to the optical directional coupler 15. The fourth port P4 is connected to the second erbium-doped fiber 4.

[0059] The optical directional coupler 14 is connected to the connection point ND2X of the optical fiber 7 for transmitting pumping light, the connection point ND2Y of the optical fiber 7 for transmitting pumping light, and the optical directional coupler 15 .

[0060] The optical directional coupler 15 is connected to the optical directional coupler 14 , the second port of the first circulator 18 and the first erbium-doped fiber 1 .

[0061] The second circulator 19 may be, for example, a commercially available four-port type. The second circulator 19 has a first port P1, a second port P2, a third port P3, and a fourth port P4. A signal input to the first port P1 is output from the second port P2. A signal input to the second port P2 is output from the third port P3. In Figures 3 and 4, the fourth port P4 is an empty port and is not shown. The first port P1 is connected to the first erbium-doped fiber 1. The second port P2 is connected to the connection point ND1Y of the first optical fiber 6. The third port P3 is connected to the optical directional coupler 5.

[0062] The optical directional coupler 16 is connected to the connection point ND3X of the optical fiber 8 for transmitting pumping light, the connection point ND3Y of the optical fiber 8 for transmitting pumping light, and the optical directional coupler 5 .

[0063] The optical directional coupler 5 is connected to the optical directional coupler 16 , the third port P 3 of the second circulator 19 , and the second erbium-doped fiber 4 .

[0064] The 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 connection point ND1Y of the first optical fiber 6. The connection point ND2X of the pumping light-transmitting optical fiber 7 is closer to the first end EC of the pumping light-transmitting optical fiber 7 and farther from the second end ED of the pumping light-transmitting optical fiber 7 than the connection point ND2Y of the pumping light-transmitting optical fiber 7. The connection point ND3X of the pumping light-transmitting optical fiber 8 is closer to the first end EE of the pumping light-transmitting optical fiber 8 and farther from the second end EF of the pumping light-transmitting optical fiber 8 than the connection point ND3Y of the pumping light-transmitting optical fiber 8.

[0065] The first circulator 18 sends the detection light that has been transmitted forward through the first optical fiber 6 to the optical directional coupler 15. The optical directional coupler 14 sends a portion of the first pumping light that has been transmitted forward through the pumping light-transmitting optical fiber 7 to the optical directional coupler 15, and transmits the remainder forward to the pumping light-transmitting optical fiber 7. The optical directional coupler 15 sends the detection light from the first circulator 18 and the first pumping light from the optical directional coupler 14 to the first erbium-doped fiber 1. The first erbium-doped fiber 1 amplifies the detection light from the optical directional coupler 15 by the first pumping light from the optical directional coupler 15. The second circulator 19 transmits the detection light from the first erbium-doped fiber 1 forward to the first optical fiber 6.

[0066] The second circulator 19 sends the backscattered light that has propagated in the backward direction through the first optical fiber 6 to the optical directional coupler 5. The backscattered light that has propagated in the backward direction through the first optical fiber 6 includes backscattered light that has been generated at a portion of the first optical fiber 6 connected to the second circulator 19 and propagated in the backward direction, and backscattered light that has been generated at a portion (not shown) of the first optical fiber 6 (closer to the second end EB) and sent via another bidirectional optical amplifier repeater 10. The optical directional coupler 16 sends a portion of the second pumping light that has propagated in the forward direction through the pumping light transmitting optical fiber 8 to the optical directional coupler 5, and transmits the remainder in the forward direction through the pumping light transmitting optical fiber 8. The optical directional coupler 5 sends the backscattered light from the second circulator 19 and the second pumping light from the optical directional coupler 16 to the second erbium-doped fiber 4. The second erbium-doped fiber 4 amplifies the backscattered light from the optical directional coupler 5 with the second pump light from the optical directional coupler 5 and sends the amplified light to the first circulator 18. The first circulator 18 transmits the backscattered light from the second erbium-doped fiber 4 back to the first optical fiber 6.

[0067] The first circulator 18 and the second erbium-doped fiber 4, and the second circulator 19 and the first erbium-doped fiber 1 may be directly connected as described above, or may be indirectly connected via a separate optical fiber.

[0068] The wavelength filter 28 is connected to the third circulator 17. The wavelength filter 28 passes backscattered light out of the light sent through the third circulator 17. 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.

[0069] 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.

[0070] 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 include a coherent-optical time-domain reflectometer (C-OTDR), which measures increased loss due to damage in the optical fiber, or a distributed acoustic sensor (DAS), which 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 subjected to damage, distortion, vibration, etc. caused by 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.

[0071] The procedure for detecting an abnormal point in a power cable in the first embodiment will be described with reference to Fig. 5. In step S101, the excitation laser device 22 starts emitting a first excitation light, and the excitation laser device 24 starts emitting a second excitation light. The start timing of the emission of the first excitation light and the start timing of the emission of the second excitation light may be simultaneous. The first excitation light is transmitted through the optical fiber 7 for transmitting excitation light. The second excitation light is transmitted through the optical fiber 8 for transmitting excitation light.

[0072] In step S102, the pulse laser device 21 emits detection light (pulsed light). The detection light is transmitted through the first optical fiber 6.

[0073] In step S103, the bidirectional 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 bidirectional optical amplifier repeater 10.

[0074] In step S104, the bidirectional optical amplifier repeater 10 amplifies the backscattered light with the second excitation light and sends it to the first optical fiber 6. The backscattered light is transmitted in the reverse direction through the first optical fiber 6, amplified by the second excitation light in the bidirectional optical amplifier repeater 10 along the way, and 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.

[0075] In step S105, the measuring device 20 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 third circulator 17, 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.

[0076] 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 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.

[0077] 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.

[0078] 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, a variance value of the physical quantity over a certain period may be used as a comparison target or threshold. This analysis process detects the presence or absence of an abnormality that may occur within a short period of time.

[0079] In step S108, the analyzer 12 adds up the physical quantities (intensity, phase difference, phase change, etc. of the backscattered light) of the signals sent through the optical receiver 23.

[0080] In step S109, the process proceeds to step S110 each time the addition process is completed a predetermined number of times, otherwise the process returns to step S102. The added value is stored and saved as needed.

[0081] 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 previous sum. For example, the analyzer 12 compares the difference between the average of the previous 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 previous 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 distortions 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.

[0082] As described above, according to this embodiment, by using the bidirectional optical amplifier repeater 10 that amplifies light transmitted through the first optical fiber 6, it is possible to accurately and quickly detect abnormalities such as ground faults, damage, or fatigue in a long-distance power cable 50, such as 300 km or more, 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 it will be possible to accurately and quickly detect abnormalities such as ground faults, damage, or fatigue in a long-distance power cable 50, such as 1,000 km or more. 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, a configuration is provided in which pump light is transmitted to the bidirectional optical amplifier repeater 10 via the pump light transmission optical fibers 7 and 8. Therefore, in this embodiment, there is no need to provide a pumping laser device that generates pumping light within the bidirectional optical amplifier repeater 10 and a power line for supplying a power supply voltage to the pumping laser device.

[0083] According to this embodiment, by providing a bidirectional optical amplifier repeater 10, one optical fiber can be used both to transmit the detection light and the backscattered light, thereby reducing the number of optical fibers.

[0084] Second Embodiment In the second and subsequent embodiments, differences from the first embodiment will be mainly described, and common points will not be described repeatedly.

[0085] A power line according to a second embodiment will be described with reference to Fig. 6. The power line includes a plurality of power cables 50A and a connection portion 80 that connects two adjacent power cables 50A. Fig. 6 shows a first power cable 50A-1 and a second power cable 50A-2.

[0086] A power cable 50A provided in a power line of the second embodiment will be described with reference to Fig. 7. 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 of the power cable 50A of the second embodiment is replaced with a detection wire member 61A.

[0087] Similar to the detection line member 61 of the first embodiment, the detection line member 61A includes a first optical fiber 6, an excitation light transmitting optical fiber 7, and an excitation light transmitting optical fiber 8. Unlike the detection line member 61 of the first embodiment, the detection line member 61A does not include a bidirectional optical amplifier repeater 10 along the way. The bidirectional optical amplifier repeater 10 is provided at the connection portion 80. In other words, the power cable 50A does not include the bidirectional optical amplifier repeater 10, but the connection portion 80, which is part of the power line, includes the bidirectional optical amplifier repeater 10.

[0088] 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, a third circulator 17, and a power supply (not shown), as shown in FIG. 4 . The power supply supplies power at a voltage corresponding to the devices 20, 21, and 24 to drive these devices.

[0089] Referring to FIG. 8 , a connection portion 80 provided in a power line according to the second embodiment will be described. 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 semiconductive portion 97 is formed around the insulating portion 98 so as to extend across the outer semiconductive 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 shielding 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.

[0090] Two adjacent detection line members 61A are connected to a bidirectional optical amplifying repeater 70. The bidirectional optical amplifying repeater 70 will be described with reference to FIG.

[0091] Similar to the bidirectional optical amplifier repeater 10 described in the first embodiment, the bidirectional optical amplifier repeater 70 includes a first circulator 18, a second circulator 19, a first erbium-doped fiber 1, optical directional couplers 5, 14, 15, and 16, and a second erbium-doped fiber 4, all housed in a waterproof housing 71. The connection relationships of the elements of the bidirectional optical amplifier repeater 70 are similar to those of the bidirectional optical amplifier repeater 10, and therefore will not be described repeatedly.

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

[0093] The second embodiment also provides the same effects as the first embodiment. Furthermore, in the second embodiment, since the detection line member 61A does not include the bidirectional optical amplifier repeater 10, 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 bidirectional optical amplifier repeater 70 can be adjusted within the available space within the connection portion 80.

[0094] As described above, the laser devices 21, 22, 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 21, 22, 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 21, 22, and 24 and the power source on land also simplifies control of laser conditions and maintenance of the laser devices. The laser devices 21, 22, and 24 and the power source may be disposed at only one end of the power line. The laser devices 21, 22, 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.

[0095] 10 and 11, a power cable anomaly detection system 100A according to a third embodiment will be described. The third embodiment differs from the first embodiment in that it does not include the optical fiber 7 for transmitting excitation light and the optical directional couplers 14 and 15.

[0096] The power cable anomaly detection system 100A includes a power cable 50, a first optical fiber 6, an optical fiber 8 for transmitting pumping light, a bidirectional optical amplifier repeater 10A, and a control device 40A. The control device 40A includes a pulsed laser device 21 (laser device), a pumping laser device 22, a measuring device 20, a pumping laser device 24, optical isolators 25, 26, and 27, an optical directional coupler 29, and a third circulator 17.

[0097] The pulse laser device 21 (laser device), pump laser device 22, measuring device 20, pump laser device 24, and optical isolators 25, 26, and 27 are the same as those in the first embodiment, and therefore description thereof will not be repeated. Figure 11 shows the first optical fiber 6, the pump light transmitting optical fiber 8, and the bidirectional optical amplifier repeater 10A, which are components of the power cable 50. The pulse laser device 21 (laser device), pump laser device 22, measuring device 20, and pump laser device 24 are each independent of the power cable 50, and are connected to the first optical fiber 6 or the pump light transmitting optical fiber 8 via the optical isolators 25, 26, and 27, the optical directional coupler 29, and the third circulator 17, as appropriate, at the end of the power cable 50.

[0098] The first port P1 of the third circulator 17 is connected to the optical directional coupler 29. The second port P2 is connected to the first end EA of the first optical fiber 6. The third port P3 is connected to the measuring device 20.

[0099] The optical directional coupler 29 outputs the detection light transmitted from the pulse laser device 21 via the optical isolator 25 to the first port P1 of the third circulator 17. The optical directional coupler 29 outputs the first excitation light transmitted from the excitation laser device 22 via the optical isolator 26 to the first port P1 of the third circulator 17.

[0100] The third circulator 17 transmits the detection light sent from the pulse laser device 21 via the optical isolator 25 and the optical directional coupler 29 forward to the first optical fiber 6. The third circulator 17 transmits the first excitation light sent from the excitation laser device 22 via the optical isolator 26 and the optical directional coupler 29 forward to the first optical fiber 6. The third circulator 17 sends the backscattered light that has transmitted in the reverse direction through the first optical fiber 6 to the measuring device 20.

[0101] The configuration and operation of the bidirectional optical amplifier repeater 10A will be described. The bidirectional optical amplifier repeater 10A includes a first circulator 18, a second circulator 19, a first erbium-doped fiber 1, optical directional couplers 5 and 16, and a second erbium-doped fiber 4. The basic configurations of the first circulator 18 and the second circulator 19, the operation of the second circulator 19, and the connection relationship of the optical directional couplers 5 and 16 are the same as those in the first embodiment, and therefore will not be described repeatedly.

[0102] In the first circulator 18, the first port P1 is connected to the connection point ND1X of the first optical fiber 6. The second port P2 is connected to the first erbium-doped fiber 1. The fourth port P4 is connected to the second erbium-doped fiber 4.

[0103] In the second circulator 19, the first port P1 is connected to the first erbium-doped fiber 1. The second port P2 is connected to the connection point ND1Y of the first optical fiber 6. The third port P3 is connected to the optical directional coupler 5.

[0104] The first circulator 18 sends the detection light and the first excitation light that have been transmitted forward through the first optical fiber 6 to the first erbium-doped fiber 1. The first erbium-doped fiber 1 amplifies the detection light from the first circulator 18 with the first excitation light from the first circulator 18 and sends the amplified detection light to the second circulator 19. The second circulator 19 transmits the detection light and the first excitation light from the first erbium-doped fiber 1 forward to the first optical fiber 6.

[0105] According to this embodiment, the first optical fiber 6 transmits the first excitation light in addition to the detection light and the backscattered light, so the number of optical fibers can be reduced compared to the first embodiment. The connection unit 80 described in the second embodiment may also include a bidirectional optical amplifying repeater 10A.

[0106] 12 and 13, a power cable anomaly detection system 100B according to a fourth embodiment will be described. The fourth embodiment differs from the first embodiment in that it includes an optical fiber 75 for transmitting excitation light instead of the optical fibers 7 and 8 for transmitting excitation light, and does not include the excitation laser device 24.

[0107] The power cable anomaly detection system 100B includes a power cable 50, a first optical fiber 6, an optical fiber 75 for transmitting excitation light, a bidirectional optical amplifier repeater 10B, and a control device 40B. The control device 40B includes a pulsed laser device 21 (laser device), an excitation laser device 22B, a measuring device 20, optical isolators 25 and 26B, and a third circulator 17.

[0108] The pulse laser device 21 (laser device), the measuring device 20, and the optical isolator 25 are the same as those in the first embodiment, and therefore description thereof will not be repeated. Figure 13 shows the first optical fiber 6, the pumping light transmitting optical fiber 75, and the bidirectional optical amplifying repeater 10B, which are components of the power cable 50. The pulse laser device 21 (laser device), the pumping laser device 22B, and the measuring device 20 are each independent of the power cable 50, and are connected to the first optical fiber 6 or the pumping light transmitting optical fiber 75 at the end of the power cable 50 via optical isolators 25, 26B and a third circulator 17, as appropriate.

[0109] The first optical fiber 6 and the pumping light-transmitting optical fiber 75 are arranged in close proximity. The pumping light-transmitting optical fiber 75 has a first end EG and a second end EH. The direction from the first end EG to the second end EH is sometimes referred to as the forward direction, and the direction from the second end EH to the first end EG is sometimes referred to as the reverse direction.

[0110] The excitation laser device 22B emits excitation light for exciting the detection light and the backscattered light. The excitation laser device 22B emits excitation light with a wavelength of, for example, 1480 nm.

[0111] The optical isolator 26B is connected to the output port of the pumping laser device 22B and blocks the transmission of light to the pumping laser device 22B.

[0112] The third circulator 17 transmits the detection light sent from the pulse laser device 21 via the optical isolator 25 in the forward direction to the first optical fiber 6. The third circulator 17 sends the backscattered light that has been transmitted in the reverse direction through the first optical fiber 6 to the measuring device 20.

[0113] The configuration and operation of the bidirectional optical amplifier repeater 10B will be described. The bidirectional optical amplifier repeater 10B includes a first circulator 18, a second circulator 19, a first erbium-doped fiber 1, optical directional couplers 5, 15, 145, and a second erbium-doped fiber 4. The basic configurations of the first circulator 18 and the second circulator 19 are the same as those of the first embodiment, and therefore will not be described repeatedly.

[0114] In the first circulator 18, the first port P1 is connected to the connection point ND1X of the first optical fiber 6. The second port P2 is connected to the optical directional coupler 15. The fourth port P4 is connected to the second erbium-doped fiber 4.

[0115] The optical directional coupler 145 is connected to the connection point ND4X of the optical fiber 75 for transmitting pumping light, the connection point ND4Y of the optical fiber 75 for transmitting pumping light, the optical directional coupler 15 and the optical directional coupler 5.

[0116] The optical directional coupler 15 is connected to the optical directional coupler 145 , the second port of the first circulator 18 and the first erbium-doped fiber 1 .

[0117] In the second circulator 19, the first port P1 is connected to the first erbium-doped fiber 1. The second port P2 is connected to the connection point ND1Y of the first optical fiber 6. The third port P3 is connected to the optical directional coupler 5.

[0118] The optical directional coupler 5 is connected to the optical directional coupler 145 , the third port P 3 of the second circulator 19 , and the second erbium-doped fiber 4 .

[0119] The connection point ND4X of the optical fiber 75 for transmitting pumping light is closer to the first end EG of the optical fiber 75 for transmitting pumping light and farther from the second end EH of the optical fiber 75 for transmitting pumping light than the connection point ND4Y of the optical fiber 75 for transmitting pumping light.

[0120] The optical directional coupler 145 sends a first proportion of the excitation light that has been transmitted forward through the optical fiber 75 for transmitting excitation light to the optical directional coupler 15, sends a second proportion to the optical directional coupler 5, and transmits the remainder forward to the optical fiber 75 for transmitting excitation light.

[0121] The optical directional coupler 145 has a configuration capable of adjusting the distribution ratio. Here, the optical directional coupler 145 distributes the pumping light transmitted forward through the pumping light-transmitting optical fiber 75 into a first ratio, a second ratio, and the remaining three ratios according to the adjusted distribution ratio.

[0122] As another example, an optical branching device (not shown) may be provided upstream of the optical directional coupler 145, and the optical branching device may transmit the pumping light divided according to the distribution ratio to the optical directional coupler 145.

[0123] The first circulator 18 sends the detection light that has been transmitted forward through the first optical fiber 6 to the optical directional coupler 15. The optical directional coupler 15 sends the detection light from the first circulator 18 and the pumping light from the optical directional coupler 145 to the first erbium-doped fiber 1. The first erbium-doped fiber 1 amplifies the detection light from the optical directional coupler 15 with the pumping light from the optical directional coupler 15 and sends the amplified light to the second circulator 19. The second circulator 19 transmits the detection light from the first erbium-doped fiber 1 forward to the first optical fiber 6.

[0124] The second circulator 19 sends the backscattered light that has propagated in the backward direction through the first optical fiber 6 to the optical directional coupler 5. The optical directional coupler 5 sends the backscattered light from the second circulator 19 and the pumping light from the optical directional coupler 145 to the second erbium-doped fiber 4. The second erbium-doped fiber 4 amplifies the backscattered light from the optical directional coupler 5 with the pumping light from the optical directional coupler 5 and sends the amplified light to the first circulator 18. The first circulator 18 transmits the backscattered light from the second erbium-doped fiber 4 in the backward direction to the first optical fiber 6.

[0125] According to this embodiment, by providing the optical fiber 75 for transmitting pumping light, the number of optical fibers can be reduced compared to the first embodiment, and the number of laser devices that emit pumping light can also be reduced. Furthermore, according to this embodiment, by providing an optical fiber dedicated to pumping light, the intensity of the pumping light can be easily adjusted. The connection unit 80 described in the second embodiment may also be provided with a bidirectional optical amplification repeater 10B.

[0126] Fifth Embodiment In the fifth embodiment, the pulsed laser device 21 can emit detection light having a constant wavelength and modulated at a plurality of frequencies. The pulsed laser device 21 emits detection light having a wavelength of 1560 nm, for example. The pulsed laser device 21 sequentially emits detection light modulated at a plurality of frequencies (f1 to fn) within one measurement period T (a predetermined time).

[0127] When a ground fault occurs, it is desirable to detect the fault point 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 during that time. To detect the fault point 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 the result. By adjusting the Δt interval of the pulse wave during one measurement period T and by 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 point detection.

[0128] The measuring device 20 includes a frequency filter that extracts multiple frequency components of the detection light emitted from the pulsed laser device 21 from the signal sent through the optical receiver 23. The frequency filter sequentially detects each of multiple frequency components fi (i = 1 to n) of the frequency components of the backscattered light at intervals of Δt within one measurement period T.

[0129] Referring to FIG. 14, a procedure for detecting an abnormal point in a power cable according to the fifth embodiment will be described.

[0130] The processes of steps S201, S203, and S204 are generally the same as the processes of steps S101, S103, and S104 in the first embodiment, respectively, and therefore will not be described again.

[0131] In step S202, the pulsed laser device 21 emits a plurality of frequency-modulated detection light beams (pulsed light beams). That is, the pulsed laser device 21 sequentially emits detection light beams modulated at frequencies fi (i = 1 to n) at intervals of Δt during one measurement period T (within a predetermined time). The detection light beams are transmitted through the first optical fiber 6.

[0132] In step S205, the measuring device 20 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 third circulator 17, 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. The frequency filter detects frequency components fi (i = 1 to n) from the frequency components of the backscattered light. The output of the frequency filter is sent to the analyzing device 12.

[0133] In step S206, if one measurement period T has elapsed since the previous transmission of the detection light (pulsed light) modulated at 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 at 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 at frequency fi. During the measurement period T, the measuring device 20 continues to receive the backscattered light. The measurement period T for the backscattered light of frequency fi begins from the time when the detection light modulated at 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, the provision of n frequency filters allows the detection of frequency components f1 to fn.

[0134] Alternatively, one measurement period T in step S206 may be set, unlike one measurement period T in step S202, to be equal to or greater than the difference between the time when the detection light modulated at the frequency f1 is emitted from the pulse 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.

[0135] In step S207, the analysis device 12 determines a physical quantity from the backscattered light sent through the output of the frequency filter. The analysis device 12 detects the presence or absence of an abnormality using the determined physical quantity (hereinafter referred to as the latest physical quantity). For a specific procedure for detecting the presence or absence of an abnormality, please refer to the description of step S107 in the first embodiment.

[0136] In step S208, the analyzer 12 sums the physical quantities (intensity, phase difference, phase change, etc. of the backscattered light) of the signals sent through the outputs of the frequency filters.

[0137] In step S209, the process proceeds to step S210 each time the addition process is completed a predetermined number of times, otherwise the process returns to step S202. The added value is stored and saved as needed.

[0138] In step S210, the analyzer 12 re-detects whether or not there is an abnormality by using an added value including the latest physical quantity (hereinafter referred to as the latest added value) and the past added value. For a specific procedure for re-detecting whether or not there is an abnormality, please refer to the description of step S110 in the first embodiment. After the re-detection, the added value is reset, and the process returns to step S202.

[0139] 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 abnormalities with high accuracy in a short time. In this embodiment, n times the number of measurements can be made in one round trip time (for example, 5 msec), making it easy to capture accident phenomena within 100 msec.

[0140] 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.

[0141] (Modifications) The present disclosure also includes the following modifications.

[0142] (1) Wavelength of 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 24 may adjust 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.

[0143] Even if the backscattered light is weak, it can be Raman amplified in the first optical fiber 6 by the second pumping light emitted from the pumping laser device 24. This makes it possible to increase the distance from the first end EA of the first optical fiber 6 to the bidirectional optical amplifying repeater 10.

[0144] (2) Pumping Light Transmitting Optical Fiber While the above embodiment illustrates the case where there is a single pumping light transmitting optical fiber 7, there may be multiple pumping light transmitting optical fibers 7. Connecting multiple pumping light transmitting optical fibers 7 to each optical amplifier repeater 10 reduces the attenuation of the pumping light in each pumping light transmitting optical fiber 7 and improves detection accuracy. For example, suppose the pumping light transmitting optical fiber 7 includes optical fibers a, b, and c, and bidirectional optical amplifier repeaters α, β, and γ are arranged in order of proximity to land. Optical fiber a may be connected only to bidirectional optical amplifier repeater α but not to bidirectional optical amplifier repeaters β and γ; optical fiber b may be connected only to bidirectional optical amplifier repeater β but not to bidirectional optical amplifier repeaters α and γ; and optical fiber c may be connected only to bidirectional optical amplifier repeater γ but not to bidirectional optical amplifier repeaters α and β. For example, optical fiber c is less likely to attenuate light because it does not pass through bidirectional optical amplifier repeaters α and β. The same applies to the other optical fibers a and b.

[0145] Similarly, there may be multiple optical fibers 8, 75 for transmitting pumping light. The number of pumping laser devices installed on land may correspond to the number of optical fibers transmitting pumping light, or a number of pumping laser devices less than the number of optical fibers may be installed. In the former case, the emission conditions according to the transmission distance of each optical fiber can be precisely adjusted. In the latter case, the number of pumping laser devices can be reduced. Multiple optical fibers are connected to one pumping laser device via an optical distributor. It is advisable to set the ratio of light distribution according to the transmission distance of each connected optical fiber.

[0146] (3) Filter As another example of combining the pump laser devices, a filter may be disposed in the optical amplifier. The filter is disposed in a position upstream of the first circulator 18 on the upstream side in the optical amplifier. The filter distributes the first pump light from the pump laser device 22B to the first circulator 18 on the upstream side. The filter distributes the second pump light from the pump laser device 22B to the optical directional coupler A. The second pump light input to the optical directional coupler A and the backscattered light that has passed through the second circulator 19 on the downstream side are combined by the optical directional coupler 5 and input to the second erbium-doped fiber 4.

[0147] When the wavelength of the first pumping light and the wavelength of the second pumping light are the same, the filter can distribute the pumping light to the upstream first circulator 18 and the optical directional coupler A according to a preset distribution ratio.

[0148] When the wavelength of the first pumping light is a first wavelength and the wavelength of the second pumping light is a second wavelength different from the first wavelength, the filter can direct the pumping light of the first wavelength to the upstream first circulator 18 and the pumping light of the second wavelength to the optical directional coupler A.

[0149] (4) Circulators The first circulator 18, the second circulator 19, and the third circulator 17 may each be an optical directional coupler.

[0150] 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.

[0151] 1 First erbium-doped fiber, 25, 26, 26B, 27 Optical isolator, 3, 5, 15, 16, 29, 145 Optical directional coupler, 4 Second erbium-doped fiber, 6 First optical fiber, 7, 8, 75 Optical fiber for transmitting pumping light, 10, 10A, 10B, 70 Optical amplifier repeater, 11 Pumping device, 12 Analysis device, 20 Measuring device, 21 Pulse laser device, 22, 22B, 24 Pumping laser device, 23 Optical receiver, 28 Wavelength filter, 50 Power cable, 51, 51A, 51B Conductor, 52 Inner semiconducting layer, 53, 53A, 53B Insulating layer, 54, 54A, 54B Outer semiconducting layer, 55, 64 Sheath, 57A, 57B Shielding layer, 58a, 58b Wire material, 59 Armor portion, 60 Cable main body, 61, 61A Detection line 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 Anomaly detection system, EA, EC, EG First end, EB, ED, EH Second end, ND1X, ND1Y, ND2X, ND2Y, ND3X, ND3Y, ND4X, ND4Y Connection point.

Claims

1. A power cable comprising: a cable body including a conductor, an insulating layer, a semiconducting layer, and a sheath; a first optical fiber through which at least detection light and backscattered light of the detection light are transmitted; at least one excitation light transmitting optical fiber through which at least one excitation light is transmitted; and at least one bidirectional optical amplification repeater that amplifies the detection light by the excitation light transmitted by the first optical fiber or the excitation light transmitting optical fiber, and amplifies the backscattered light by the excitation light transmitted by the excitation light transmitting optical fiber.

2. The power cable according to claim 1, wherein the at least one excitation light includes a first excitation light for amplifying the detection light and a second excitation light for amplifying the backscattered light, the at least one optical fiber for transmitting excitation light includes a first optical fiber for transmitting excitation light through which the first excitation light is transmitted and a second optical fiber for transmitting excitation light through which the second excitation light is transmitted, and the bidirectional optical amplifier repeater amplifies the detection light by the first excitation light transmitted by the first optical fiber for transmitting excitation light and amplifies the backscattered light by the second excitation light transmitted by the second optical fiber for transmitting excitation light.

3. The power cable according to claim 1, wherein the at least one excitation light includes a first excitation light for amplifying the detection light and a second excitation light for amplifying the backscattered light, the first optical fiber transmits the first excitation light, the at least one optical fiber for transmitting excitation light includes a first optical fiber for transmitting excitation light through which the second excitation light is transmitted, and the bidirectional optical amplifier repeater amplifies the detection light by the first excitation light transmitted by the first optical fiber and amplifies the backscattered light by the second excitation light transmitted by the first optical fiber for transmitting excitation light.

4. A power cable as claimed in claim 1, wherein the at least one optical fiber for transmitting excitation light includes a first optical fiber for transmitting excitation light through which excitation light for amplifying the detection light and the backscattered light is transmitted, and the bidirectional optical amplifier repeater amplifies the detection light by the excitation light transmitted by the first optical fiber for transmitting excitation light, and amplifies the backscattered light by the excitation light transmitted by the first optical fiber for transmitting excitation light.

5. A power cable according to any one of claims 1 to 4, wherein the cable body is arranged in the center of the power cable, the power cable comprises a plurality of wires and at least one metal tube on the outside of the cable body, and the first optical fiber, the at least one optical fiber for transmitting excitation light, and the bidirectional optical amplifier repeater are housed in the metal tube.

6. The power cable according to claim 5, further comprising an armored portion provided on the outer periphery of the cable body, the armored portion being composed of the plurality of wires and a detection wire member, and the detection wire member housing the metal tube.

7. A power line comprising a first power cable, a second power cable, and a connection section connecting the first power cable and the second power cable, wherein each of the first power cable and the second power cable comprises: a cable body including a conductor, an insulating layer, a semiconducting layer, and a sheath; a first optical fiber through which at least detection light and backscattered light of the detection light are transmitted; and at least one excitation light transmitting optical fiber through which at least one excitation light is transmitted; and the connection section comprises a bidirectional optical amplification repeater that amplifies the detection light by the excitation light transmitted by the first optical fiber or the excitation light transmitting optical fiber, and amplifies the backscattered light by the excitation light transmitted by the excitation light transmitting optical fiber.

8. A power cable anomaly detection system comprising: a cable main body including a conductor, an insulating layer, a semiconducting layer, and a sheath; a first optical fiber through which at least detection light and backscattered light of the detection light are transmitted; and at least one excitation light transmitting optical fiber through which at least one excitation light is transmitted; a laser device that emits the detection light; at least one excitation device that emits the at least one excitation light; a bidirectional optical amplification repeater that amplifies the detection light with the excitation light transmitted by the first optical fiber or the excitation light transmitting optical fiber and amplifies the backscattered light with the excitation light transmitted by the excitation light transmitting optical fiber; and a measuring device that detects anomalies in the power cable based on the backscattered light.

9. A method for detecting an abnormality in a power cable, the power cable comprising at least a cable main body including a conductor, an insulating layer, a semiconducting layer, and a sheath, the method comprising the steps of: at least one excitation device emitting at least one excitation light; a first laser device emitting detection light; a first optical fiber included in the power cable transmitting the detection light; a first optical fiber or at least one excitation light transmitting optical fiber included in the power cable transmitting at least one excitation light; a first optical fiber transmitting backscattered light of the detection light; a bidirectional optical amplifier repeater amplifying the detection light with the excitation light transmitted by the first optical fiber or the excitation light transmitting optical fiber; a bidirectional optical amplifier repeater amplifying the backscattered light with the excitation light transmitted by the excitation light transmitted by the excitation light transmitting optical fiber; and a measuring device detecting an abnormality in the power cable using the backscattered light.

Images