Diagnostic method, diagnostic program, and diagnostic device

Abstract

To provide a diagnostic method, a diagnostic program, and a diagnostic device that can improve the accuracy of diagnosis of cable conditions.SOLUTION: The diagnostic method for diagnosing a condition of a cable 40 includes obtaining a measured value of the temperature of each of a part of the cable 40 to be diagnosed and a part of the cable 40 other than the part to be diagnosed and determining that the condition of the part of the cable 40 to be diagnosed is abnormal when the amount of change in the temperature of each of the part of the cable 40 to be diagnosed and the part other than the part to be diagnosed satisfies diagnostic conditions applicable to a diagnosis based on a change over time in the temperature of each of the part of the cable 40 to be diagnosed and the part other than the part to be diagnosed and the temperature of the part to be diagnosed satisfies the diagnostic conditions applicable to a diagnosis based on the temperature of the part of the cable 40 to be diagnosed.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present disclosure relates to a method, a program, and an apparatus for diagnosing the condition of a submarine cable. [Background technology]

[0002] Conventionally, a method for monitoring submarine cables is known in which the thermal resistance of the ground surrounding the submarine cable is calculated from the time-dependent changes in the temperature and current of the submarine cable, and the height of the cable covering is estimated from the thermal resistance of the ground (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2016-201989 Summary of the Invention [Problem to be solved by the invention]

[0004] The condition of a cable is determined not only by the height of the earth and sand covering the cable when it is buried in the seabed, but also by various other factors such as damage to the outer covering of the cable or cable breakage, etc. In diagnosing the condition of a cable, various factors need to be taken into consideration.

[0005] The present disclosure has been made in view of the above points, and aims to provide a diagnostic method, a diagnostic program, and a diagnostic device that can improve the accuracy of diagnosing the condition of a cable. [Means for solving the problem]

[0006] (1) A diagnostic method according to some embodiments diagnoses the condition of a cable including a diagnostic target portion and a portion other than the diagnostic target portion. The diagnostic target portion corresponds to a portion of the cable where the temperature of the cable is to be measured. The portion other than the diagnostic target portion corresponds to a portion different from the portion corresponding to the diagnostic target portion. The diagnostic method includes: acquiring a temperature measurement value at the diagnostic target portion of the cable corresponding to the diagnostic target portion as the temperature of the diagnostic target portion of the cable; acquiring a temperature measurement value at the diagnostic target portion of the cable corresponding to the diagnostic target portion as the temperature of the portion other than the diagnostic target portion of the cable; and determining that the diagnostic target portion is in an abnormal state if the amount of change in temperature of the diagnostic target portion and the portion other than the diagnostic target portion of the cable satisfies a diagnostic condition applicable to a diagnosis based on changes over time in the temperature of the diagnostic target portion and the portion other than the diagnostic target portion of the cable, and if the temperature of the diagnostic target portion satisfies a diagnostic condition applicable to a diagnosis based on the temperature of the diagnostic target portion of the cable. In this manner, the condition of each portion of the cable is continuously diagnosed. Furthermore, the influence of environmental changes on the diagnosis of the condition of each portion of the cable is reduced. As a result, the accuracy of diagnosing the condition of each part of the cable is improved.

[0007] (2) In one embodiment, the diagnostic method according to (1) may include determining whether the temperature of the diagnostic target portion satisfies a diagnostic condition applied to a diagnosis based on the temperature of the diagnostic target portion of the cable after determining that the amount of change in temperature between the diagnostic target portion and a portion other than the diagnostic target portion satisfies a diagnostic condition applied to a diagnosis based on the temperature of the diagnostic target portion of the cable. This allows the condition of each portion of the cable to be continuously diagnosed. Furthermore, the influence of environmental changes on the diagnosis of the condition of each portion of the cable is reduced. As a result, the accuracy of diagnosing the condition of each portion of the cable is improved.

[0008] (3) In one embodiment, the diagnostic method according to (2) above may include changing the portion other than the diagnostic target portion to a different portion of the cable so that the amount of change in temperature between the diagnostic target portion and the portion other than the diagnostic target portion satisfies a diagnostic condition applied to a diagnosis based on the change in temperature over time of the diagnostic target portion and the portion other than the diagnostic target portion of the cable. By doing so, the condition of the cable 40 is diagnosed assuming different geological conditions even without geological data. As a result, the accuracy of diagnosing the condition of the cable 40 is improved.

[0009] (4) In one embodiment, in any one of (1) to (3) above, the diagnostic conditions applied to the diagnosis based on the temperature changes over time of the diagnosis target portion and the portion other than the diagnosis target portion of the cable may include a condition based on a value representing the state of the diagnosis target portion, taking into account the state of the portion other than the diagnosis target portion of the cable, the value being calculated based on the amount of change in the temperature of the diagnosis target portion and the temperature of the portion other than the diagnosis target portion. The diagnostic conditions applied to the diagnosis based on the temperature of the diagnosis target portion of the cable may include a condition based only on the change in the temperature of the diagnosis target portion over time. In this way, the influence of environmental changes on the diagnosis of the state of each portion of the cable is reduced. As a result, the accuracy of diagnosing the state of each portion of the cable is improved.

[0010] (5) In one embodiment, in the above (4), the condition based solely on the change over time in the temperature of the portion to be diagnosed may include the temperature of the portion to be diagnosed of the cable falling outside a determination range. The determination range may be set based on the magnitude of the current flowing through the cable and the environment surrounding the portion to be diagnosed of the cable. This reduces the influence of environmental changes on the diagnosis of the condition of each portion of the cable. As a result, the accuracy of the diagnosis of the condition of each portion of the cable is improved.

[0011] (6) In one embodiment, in (4) or (5) above, the value representing the state of the diagnosis target portion of the cable taking into account the state of the portion other than the diagnosis target portion may be calculated as the absolute value of the difference between a value obtained by multiplying a temperature change in the diagnosis target portion by a coefficient corresponding to the diagnosis target portion of the cable and a value obtained by multiplying a temperature change in the portion other than the diagnosis target portion of the cable by a coefficient corresponding to the portion other than the diagnosis target portion of the cable. The coefficient corresponding to the diagnosis target portion of the cable may be set based on the environment surrounding the diagnosis target portion of the cable. The coefficient corresponding to the portion other than the diagnosis target portion of the cable may be set based on the environment surrounding the portion other than the diagnosis target portion of the cable. The condition based on the value representing the state of the diagnosis target portion taking into account the state of the portion other than the diagnosis target portion of the cable may include that the value representing the state of the diagnosis target portion taking into account the state of the portion other than the diagnosis target portion of the cable is equal to or greater than a judgment value. The judgment value may be set based on the coefficient corresponding to the diagnosis target portion of the cable and the coefficient corresponding to the portion other than the diagnosis target portion of the cable. In this way, the influence of environmental changes on the diagnosis of the state of each portion of the cable is reduced. As a result, the accuracy of diagnosing the state of each portion of the cable is improved.

[0012] (7) As an embodiment, in any one of (4) to (6) above, the value representing the state of the cable's diagnostic target portion, taking into account the state of the portion of the cable other than the diagnostic target portion, may be corrected based on the difference between the time when the temperature of the cable's diagnostic target portion starts to change and the time when the temperature of the portion of the cable other than the diagnostic target portion starts to change. In this way, the state of each portion of the cable is diagnosed taking into account heat generation in the cable 40. As a result, the accuracy of diagnosing the cable's state is improved.

[0013] (8) A diagnostic program according to some embodiments causes a computer to execute any one of the diagnostic methods described above in (1) to (7). By doing so, the condition of each part of the cable is continuously diagnosed. Furthermore, the influence of environmental changes on the diagnosis of the condition of each part of the cable is reduced. As a result, the accuracy of diagnosing the condition of each part of the cable is improved.

[0014] (9) A diagnostic device according to some embodiments includes a control unit that executes any one of the diagnostic methods described above in (1) to (7). This allows the condition of each part of the cable to be continuously diagnosed. Furthermore, the influence of environmental changes on the diagnosis of the condition of each part of the cable is reduced. As a result, the accuracy of diagnosing the condition of each part of the cable is improved. [Effects of the Invention]

[0015] According to the diagnostic method, diagnostic program, and diagnostic device disclosed herein, the accuracy of diagnosing the condition of a cable is improved. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 is a schematic diagram illustrating an example of the configuration of a diagnostic system according to an embodiment. [Figure 2] 1 is a block diagram illustrating an example of the configuration of a diagnostic system according to an embodiment. [Figure 3] FIG. 2 is a schematic diagram showing an example of the configuration of a cable. [Figure 4A] 1 is a cross-sectional view showing an example of a cable buried underground. [Figure 4B] FIG. 1 is a cross-sectional view showing an example of a cable that is nearly exposed on the seabed. [Figure 5] 1 is a flowchart illustrating an example of a procedure of a diagnostic method according to an embodiment. [Figure 6] FIG. 1 is a schematic diagram showing an example of the configuration of a cable passing through multiple different geological formations. [Figure 7] FIG. 10 is a diagram illustrating an example of the relationship between the buried state of a cable and temperature distribution. [Figure 8A] 10 is a graph showing an example of a change over time in the heat generation temperature of a cable. [Figure 8B] 10 is a graph showing an example of the change over time in temperature at point X of a cable. [Figure 8C] 10 is a graph showing an example of the change over time in temperature at point Y of a cable. DETAILED DESCRIPTION OF THE INVENTION

[0017] A diagnostic system 1 (see FIG. 1) according to an embodiment of the present disclosure diagnoses the condition of a submarine cable connected to an offshore wind power generation device, etc. Hereinafter, an embodiment of the diagnostic system 1 will be described in comparison with a comparative example.

[0018] (Comparative Example) A comparative example is a method of diagnosing a submarine cable by visual inspection by a diver or by inspection using devices such as sonar or an ROV (remotely operated vehicle). The diagnostic method according to the comparative example is not a method that can be performed continuously, but is performed only once a year or once every few years, for example. The condition of a submarine cable can suddenly change due to natural phenomena such as scouring caused by ocean currents or typhoons, or sedimentation caused by earthquakes, or human activity such as contact with anchors or fishing gear. The diagnostic method according to the comparative example cannot immediately detect sudden changes in the condition of a submarine cable. The inability to immediately detect changes in the condition of a submarine cable makes it difficult to identify the cause of the change. Furthermore, if a submarine cable begins to generate heat due to bending or other reasons, the amount of power that can be transmitted may be limited or the submarine cable itself may deteriorate if the change in condition is not discovered. Furthermore, the heat generation increases power loss.

[0019] Other problems with the diagnostic methods according to the comparative examples include the cost and time required to perform the diagnosis. Furthermore, the diagnostic method according to the comparative example cannot be performed when the ocean is in rough conditions due to bad weather, etc. Furthermore, in the diagnostic method according to the first comparative example, the accuracy of visual diagnosis is reduced due to the adhesion of sediments or marine organisms to the portion where the submarine cable is buried.

[0020] Therefore, the present disclosure describes a diagnostic system 1 (see FIG. 1) that can continuously, easily, or without the need for visual inspection diagnose various conditions of a submarine cable, such as the height of earth and sand covering the submarine cable when the cable is buried in the seabed, or damage to the outer coating of the submarine cable or a break in the submarine cable.

[0021] (Embodiments of the present disclosure) 1, a diagnostic system 1 according to one embodiment includes a diagnostic device 10, a temperature measuring device 20, and a display device 30. The diagnostic system 1 diagnoses the condition of a cable 40.

[0022] In this embodiment, the cable 40 is assumed to be a submarine cable that is buried underground 80 so as to pass through the seabed 81 in order to transport electricity generated by the offshore wind power generation equipment 70 to land 82, or for communication between the offshore wind power generation equipment 70 and equipment such as the diagnostic device 10 on land 82, or for various other purposes. The destination to which the cable 40 transports electricity or the destination to which the cable 40 is connected for communication is not limited to equipment on land 82, but may also be equipment on or under the sea.

[0023] Cable 40 includes a portion that is buried in the ground 80 due to the unevenness of the seabed 81, and a portion that is exposed from the ground 80 to the underwater 84 due to the seabed 81 being excavated. The portions that are buried in the ground 80 are exemplified as buried portion 51 and buried portion 53. The portion that is exposed from the ground 80 to the underwater 84 is exemplified as exposed portion 52. Cable 40 includes a portion that is not exposed to the underwater 84 but is buried shallowly in the ground 80. The portion that is buried shallowly in the ground 80 is exemplified as shallow buried portion 54.

[0024] The exposed portion 52 or the shallowly buried portion 54 may be formed when the shape of the seabed 81 becomes concave due to a phenomenon called scouring, in which the seabed 81 is eroded by ocean currents. The exposed portion 52 or the shallowly buried portion 54 may also be formed when the cable 40 is lifted up due to movement of the seabed 81 caused by an earthquake or the like.

[0025] The cable 40 includes a portion that is pulled out from underground 80 into the sea 84 to connect to the offshore wind power generation device 70. The portion that is pulled out from underground 80 into the sea 84 is exemplified as an interface portion 55.

[0026] The submarine cable is prone to bending or breakage due to collision of fishing gear, anchors, etc. with the exposed portion 52 or shallowly buried portion 54. The diagnostic system 1 may diagnose whether the submarine cable is exposed to the seawater 84 or is close to being exposed.

[0027] The temperature of a submarine cable differs depending on whether it is buried underground 80 or exposed to or almost exposed to the sea 84. Therefore, in the diagnostic system 1 according to this embodiment, the temperature measurement device 20 measures the temperature of at least a part of the cable 40. The diagnostic device 10 diagnoses, as the state of the cable 40, whether the cable 40 is buried underground 80 or exposed to the sea 84, based on the temperature of at least a part of the cable 40. The diagnostic device 10 may diagnose not only the buried state of the cable 40, but also the heat generation state of the cable 40. The display device 30 displays the diagnostic results of the state of the cable 40.

[0028] (Example of configuration of diagnostic system 1) An example of the configuration of the diagnostic system 1 illustrated in FIG. 2 will be described below.

[0029] <Diagnostic device 10> As will be described later, the diagnostic device 10 diagnoses the condition of the cable 40 based on the temperature of each part of the cable 40 measured by the temperature measuring device 20, and displays the diagnostic results on the display device 30. As will be described later, the measurement of the temperature of each part of the cable 40 relies on a fiber (sensor) connected to the cable 40. When measuring the temperature of each part of the cable 40 along the longitudinal direction of the cable 40, the fiber connected to the temperature measuring device 20 and running along the cable 40 functions as a sensor. When the cable 40 is a submarine cable, a vacant fiber among the fibers present inside the cable 40 may be used as a sensor, as will be described later.

[0030] The diagnostic device 10 includes a control unit 12 , a storage unit 14 , and an interface 16 .

[0031] The control unit 12 controls each component of the diagnostic device 10. The control unit 12 may be configured to include a processor such as a CPU (Central Processing Unit). The control unit 12 may realize predetermined functions by causing the processor to execute predetermined programs.

[0032] The storage unit 14 may store various types of information used in the operation of the control unit 12, or programs for realizing the functions of the control unit 12. The storage unit 14 may function as a work memory for the control unit 12. The storage unit 14 may be configured, for example, as a semiconductor memory. The storage unit 14 may be configured to include a volatile memory or a non-volatile memory. The storage unit 14 may be configured as a non-transitory computer-readable storage medium. The storage unit 14 may be included in the control unit 12.

[0033] The memory unit 14 may store information about the cable 40 when it is buried. The information about the cable 40 when it is buried may include the buried position or buried depth of the cable 40 when it is properly buried. The information about the cable 40 when it is buried may include measured values ​​of the temperature of each part of the cable 40 when no current is flowing through the cable 40, immediately after the cable 40 is properly buried or immediately after maintenance of the cable 40 is properly performed. The information about the cable 40 when it is buried may include information about the geology of the location where the cable 40 is buried. The information about the geology may include the type of soil or the thermal conductivity of the soil. The memory unit 14 may store information about the cable 40 after it is buried. The information about the cable 40 after it is buried may include measured values ​​of the temperature of each part of the cable 40 when a current is flowing through the cable 40. The information about the cable 40 after it is buried may include data correlating the magnitude of the current flowing through the cable 40, the magnitude of the voltage applied to the cable 40, and the temperature of each part of the cable 40. The memory 14 may contain characteristics of the temperature measurements in the cable 40 .

[0034] The interface 16 includes a communication device that communicatively connects the diagnostic apparatus 10 to the temperature measuring apparatus 20, the display apparatus 30, or the like. The communication device may be configured to be capable of communication based on a mobile communication standard such as 4G (4th Generation), LTE (Long Term Evolution), or 5G (5th Generation). The communication device may be configured to be capable of communication based on a LAN (Local Area Network) communication standard. The communication device may be configured to be capable of wired or wireless communication.

[0035] The interface 16 may be configured to include a display device. The display device may include various displays such as a liquid crystal display. The interface 16 may be configured to include an audio output device such as a speaker. The interface 16 is not limited to these, and may be configured to include various other output devices.

[0036] The interface 16 may be configured to include an input device that accepts input from a user. The input device may include, for example, a keyboard or physical keys, or may include a touch panel or touch sensor, or a pointing device such as a mouse. The interface 16 may be configured to include another computer or the diagnostic device 10. The input device is not limited to these examples and may be configured to include various other devices. The input device may be configured to allow input of parameters, etc. for diagnosing the condition of the cable 40 in the diagnostic device 10.

[0037] The diagnostic device 10 may be configured as a PC (Personal Computer) or as at least one server device. The diagnostic device 10 may also be realized in a cloud computing system.

[0038] <Temperature measurement device 20> The temperature measuring device 20 measures the temperature of at least a portion of the cable 40. The portion of the cable 40 whose temperature is measured by the temperature measuring device 20 is also referred to as the measurement target portion. In order for the diagnostic system 1 to diagnose the entire buried condition or disconnection status of a long cable 40, it is necessary to measure the temperatures of hundreds or even thousands of points in the cable 40. The measurement target portions may be set at predetermined intervals, such as 1-m intervals, along the longitudinal direction of the cable 40, or may be set at irregular intervals. In this embodiment, as illustrated in FIG. 3 , the cable 40 includes a power line 41, an optical fiber 42, and a coating 43. The power line 41 and the optical fiber 42 are protected inside the coating 43. In this embodiment, the temperature measuring device 20 uses the optical fiber 42 to measure the temperature of each portion of the cable 40 along the longitudinal direction. The optical fiber 42 used for temperature measurement is also referred to as a DTS (Distributed Temperature Sensor).

[0039] Specifically, the temperature measuring device 20 transmits pulsed light to the optical fiber 42. The pulsed light incident on the optical fiber 42 is scattered by Raman scattering at various positions in the optical fiber 42. Light scattered by Raman scattering is also referred to as Raman scattered light. At least a portion of the Raman scattered light returns to the incident side of the optical fiber 42. The temperature measuring device 20 acquires a signal based on the Raman scattered light that returns to the incident side of the fiber.

[0040] The Raman scattered light includes Stokes light, which is shifted to a longer wavelength than the wavelength of the incident pulsed light, and anti-Stokes light, which is shifted to a shorter wavelength than the wavelength of the incident pulsed light. The intensity of each component of the Raman scattered light depends on the temperature of the optical fiber 42 at the position where Raman scattering occurs. By analyzing the Raman scattered light that is reflected back, the temperature measuring device 20 can calculate the temperature of the optical fiber 42 at the position where the optical signal is scattered. The temperature measuring device 20 can also calculate the position where the received optical signal is reflected based on the time from when the optical signal is transmitted until the optical signal is reflected back. Therefore, the temperature measuring device 20 can calculate the temperature of the optical fiber 42 at each position on the optical fiber 42.

[0041] The temperature of each part of the optical fiber 42 is considered to be approximately the same as the temperature of each part of the cable 40 corresponding to each part of the optical fiber 42. The temperature measurement device 20 can measure the temperature of each part of the cable 40 by measuring the temperature of each part of the optical fiber 42. In this embodiment, it is assumed that the temperature of each part of the cable 40 is measured at intervals of 1 m. The intervals at which the temperature is measured are not limited to 1 m and may be set to various lengths.

[0042] The temperature measurement device 20 may be configured to measure the temperature of the measurement target portion of the cable 40 by a temperature sensor separate from the optical fiber 42 installed in the temperature measurement target portion of the cable 40. The temperature sensor may be attached to the outside of the sheath 43 of the cable 40 or may be embedded inside the sheath 43. The temperature sensor may also be attached to a connection portion of the cable 40.

[0043] The temperature measurement device 20 is not limited to a measurement method using an optical fiber 42 or a measurement method using a temperature sensor, and may be configured to measure the temperature of the measurement target portion of the cable 40 using various other methods.

[0044] <Display device 30> The display device 30 displays the diagnosis results of the condition of the cable 40 by the diagnostic device 10. The display device 30 may display various data including the temperature measurement results of at least a portion of the cable 40 or the time variation of the temperature measurement results. The display device 30 may include various displays, such as a liquid crystal display. The display device 30 may be included in the diagnostic device 10 as a display device of the interface 16 of the diagnostic device 10. The diagnostic device 10, the temperature measuring device 20, and the display device 30 may be configured integrally. A partial combination of the diagnostic device 10, the temperature measuring device 20, and the display device 30 may be configured integrally. The diagnostic device 10, the temperature measuring device 20, and the display device 30 may each be configured as separate entities.

[0045] The diagnostic system 1 may include a speaker that outputs the diagnostic result of the condition of the cable 40 by voice, or may include various other output devices. The diagnostic system 1 may include another output device in addition to the display device 30 as a device that outputs the diagnostic result of the condition of the cable 40, or may include another output device instead of the display device 30.

[0046] (Example of operation of diagnostic system 1) As described above, in the diagnostic system 1 according to this embodiment, the diagnostic device 10 can diagnose the condition of the diagnostic target portion of the cable 40 based on the measured temperature value of the measurement target portion of the cable 40.

[0047] For example, as shown in FIGS. 4A and 4B , the amount of heat transferred from the cable 40 to the underwater 84 varies depending on the burial depth of the cable 40 in the ground 80. As illustrated in FIG. 4A , when the cable 40 is buried deep in the ground 80, the amount of heat removed from the cable 40 by the ocean current 85 in the underwater 84 is small. On the other hand, as illustrated in FIG. 4B , when the cable 40 is about to be exposed from the ground 80 to the underwater 84 or when the cable 40 is exposed to the underwater 84, the amount of heat removed from the cable 40 by a portion of the ocean current 85 in the underwater 84 that is close to the cable 40, 86, increases. When the cable 40 is buried abnormally, the amount of sediment on the cable 40 decreases, causing the cable 40 to come closer to seawater or come into contact with seawater. When the cable 40 comes closer to seawater or comes into contact with seawater, the cable 40 loses heat to the seawater. Because cable 40 loses heat to seawater, the temperature of the portions of cable 40 that are close to or in contact with seawater becomes relatively lower than the temperature of the portions of cable 40 that are normally buried. Therefore, the portions of cable 40 that are at a lower temperature in the portion to be diagnosed are losing heat to seawater, and it is determined that the amount of sediment on cable 40 has decreased, indicating an abnormal burial state. Comparing Figures 4A and 4B, the closer the buried location of the portion to be diagnosed of cable 40 is to the seawater 84, the lower the temperature of the portion to be diagnosed of cable 40. Therefore, diagnostic device 10 can diagnose the buried location of each portion of cable 40 based on the temperature of each portion of cable 40.

[0048] Furthermore, if the cable 40 is bent or damaged, the resistance value of the power line 41 of the cable 40 may increase. The increase in the resistance value of the power line 41 increases the amount of heat generated at the bent or damaged portion. The temperature of the portion of the cable 40 where the amount of heat generated has increased increases. The diagnostic device 10 can diagnose abnormalities such as bending or damage occurring in each portion of the cable 40 based on the temperature of each portion of the cable 40.

[0049] The diagnostic device 10 is not limited to diagnosing abnormalities in the buried position of the cable 40 or abnormalities such as bending or breakage of the cable 40, but can also diagnose various other conditions of the cable 40. An example of the operation of the diagnostic system 1 will now be described.

[0050] <Diagnosis based on temperature of the diagnosis target portion of the cable 40> The control unit 12 of the diagnostic device 10 acquires a measured value of the temperature of the portion of the cable 40 to be diagnosed from the temperature measuring device 20. The portion to be diagnosed is also referred to as the diagnostic target portion.

[0051] The control unit 12 determines that the condition of the diagnosis target portion of the cable 40 is normal when the temperature of the diagnosis target portion of the cable 40 is within a predetermined temperature range. The control unit 12 determines that the condition of the diagnosis target portion of the cable 40 is abnormal when the temperature of the diagnosis target portion of the cable 40 is not within the predetermined temperature range. The predetermined temperature range to be compared with the temperature of the diagnosis target portion of the cable 40 is also referred to as the judgment range. If the temperature of the cable 40 decreases as the buried position of the cable 40 becomes shallower, the control unit 12 may set only the lower limit of the judgment range and not the upper limit of the judgment range. Conversely, if the temperature of the cable 40 increases as the buried position of the cable 40 becomes shallower, the control unit 12 may set only the upper limit of the judgment range and not the lower limit of the judgment range.

[0052] The control unit 12 may set the determination range based on the magnitude of the current flowing through the cable 40. For example, the control unit 12 may set the determination range so that the median value of the determination range increases as the current flowing through the cable 40 increases.

[0053] The control unit 12 may set the judgment range based on the environmental conditions of the underground 80 at the location where the diagnostic target portion of the cable 40 is buried or the environment of the undersea 84 near the location where the diagnostic target portion of the cable 40 is buried. For example, the control unit 12 may set the judgment range based on the geology of the location where the diagnostic target portion of the cable 40 is buried. The control unit 12 may set the judgment range so that the median value of the judgment range decreases as the thermal conductivity of the geology where the diagnostic target portion of the cable 40 is buried increases. For example, the control unit 12 may set the judgment range based on the seawater temperature near the location where the diagnostic target portion of the cable 40 is buried. The control unit 12 may set the judgment range so that the median value of the judgment range decreases as the seawater temperature decreases. For example, the control unit 12 may set the judgment range based on the depth at which the diagnostic target portion of the cable 40 is buried. The control unit 12 may set the determination range so that the deeper the buried position of the diagnostic target portion of the cable 40 is, the narrower the temperature width of the determination range, assuming that the temperature of the diagnostic target portion of the cable 40 is less likely to change. In other words, the control unit 12 may set the determination range based on the magnitude of the current flowing through the cable 40 and the environment surrounding the diagnostic target portion of the cable 40.

[0054] The control unit 12 may set the determination range based on the measured temperature of the diagnostic portion of the cable 40 when the diagnostic portion of the cable 40 was first buried. The control unit 12 may set the determination range based on the measured temperature of the diagnostic portion of the cable 40 when it was most recently confirmed that the condition of the diagnostic portion of the cable 40 was normal. The control unit 12 may set the determination range based on the measured temperature of the boundary portion 55 where the cable 40 is pulled out from the ground 80 to the sea 84. The control unit 12 may set the determination range based on a statistical value, such as the average value of values ​​measured over a predetermined period of time for the temperature of the diagnostic portion of the cable 40. The determination range is not limited to these examples and may be set based on various other information.

[0055] Based on the temperature of the diagnosis target portion of the cable 40, the control unit 12 may calculate a value representing the state of the diagnosis target portion of the cable 40, such as whether an abnormality has occurred in the burial status of the cable 40 in the diagnosis target portion of the cable 40. A burial abnormality may cause a portion of the cable 40 exposed from the seabed to get caught on an anchor or the like and be damaged, which could result in an accident or a dangerous event occurring during the operation of the facility or activities around the facility. Therefore, the value representing the state of the diagnosis target portion of the cable 40 is also referred to as a risk level. The control unit 12 calculates a higher risk level value the closer the state of the diagnosis target portion of the cable 40 is to an abnormality. The control unit 12 calculates a lower risk level value the closer the state of the diagnosis target portion of the cable 40 is to normal. The control unit 12 may diagnose the state of the diagnosis target portion of the cable 40 as abnormal if the risk level is equal to or greater than a predetermined threshold. The predetermined threshold used to determine the risk level is also referred to as a risk threshold.

[0056] The risk level value may be calculated as a normalized value in the range of 0 or more and 1 or less. The control unit 12 may calculate the risk level value representing the state of the diagnostic portion of the cable 40 as 1 when the diagnostic portion of the cable 40 is buried sufficiently deep underground 80 and in a normal state, and may calculate the risk level so that the risk level becomes a value greater than 1 as the diagnostic portion of the cable 40 is buried shallower. The expression of the risk level value is not limited to these examples. As long as the degree of risk of the state of the cable 40 can be grasped, the risk level value may be expressed freely, including as a percentage, etc. In the following description, the risk level value is expressed as a normalized value in the range of 0 or more and 1 or less, and is closer to 0 as the state of the diagnostic portion of the cable 40 is closer to normal, and closer to 1 as the state of the diagnostic portion of the cable 40 is closer to abnormal.

[0057] For example, if the risk level is 0.5 or higher, the control unit 12 may output a warning indicating that the diagnostic target portion of the cable 40 is still buried but is now buried shallower and is approaching exposure to the seawater 84. For example, if the risk level is 0.95 or higher, the control unit 12 may determine that the diagnostic target portion of the cable 40 is exposed to the seawater 84 and output information indicating that the state of the diagnostic target portion of the cable 40 has become abnormal. For example, the control unit 12 may calculate the risk level so that the risk level becomes 0.5 when the diagnostic target portion of the cable 40 is buried approximately 50 cm deep. The control unit 12 may set risk level thresholds corresponding to multiple levels so that the state of the diagnostic target portion of the cable 40 can be diagnosed at multiple levels according to the abnormality level. The values, such as 0.5 or 0.95, calculated by the control unit 12 as the risk level value corresponding to the state of the cable 40, such as an abnormality, are not limited to these values. The control unit 12 may appropriately set the risk level value according to the state of the cable 40, such as an abnormality.

[0058] In order to diagnose the conditions of multiple portions of the cable 40, the control unit 12 may set multiple diagnosis target portions of the cable 40 and diagnose the conditions of each of the multiple diagnosis target portions of the cable 40. The control unit 12 may set different judgment ranges for at least some of the diagnosis target portions of the cable 40. The control unit 12 may also set the same judgment range for at least some of the diagnosis target portions of the cable 40.

[0059] As described above, the condition of the diagnosis target portion of the cable 40 is diagnosed based on the measured value of the temperature of the diagnosis target portion of the cable 40. In this way, the condition of each portion of the cable 40 is continuously diagnosed.

[0060] The control unit 12 may separately set a determination range or danger threshold for diagnosing a state in which the cable 40 is exposed to the sea 84, and a determination range or danger threshold for diagnosing a state in which the cable 40 is bent or broken. In this way, the control unit 12 can separately diagnose whether the state of the cable 40 is an abnormality in which the cable 40 is exposed to the sea 84, or an abnormality such as bending or breakage.

[0061] <Diagnosis Based on Changes in Temperature Over Time in Multiple Portions of Cable 40> In the diagnostic system 1 according to this embodiment, the diagnostic device 10 may perform a diagnosis based on the change over time in temperature of multiple portions of the cable 40. Immediately after the cable 40 is laid, the entire cable 40 is considered to be buried. Even if a temperature determined to be an abnormal value is measured in this state, the state of the cable 40 may be diagnosed as if that temperature were a correct value.

[0062] The control unit 12 of the diagnostic device 10 acquires temperature measurement values ​​of multiple portions of the cable 40 from the temperature measurement device 20. The control unit 12 acquires, as the temperatures of the multiple portions of the cable 40, temperature measurement values ​​of a diagnosis target portion whose condition is to be diagnosed and temperature measurement values ​​of portions other than the diagnosis target portion. The diagnosis target portion of the cable 40 corresponds to a portion of the temperature measurement target portion of the cable 40. The portion other than the diagnosis target portion of the cable 40 corresponds to a measurement target portion different from the measurement target portion of the cable 40 corresponding to the diagnosis target portion. The control unit 12 acquires the temperature measurement value of the measurement target portion of the cable 40 corresponding to the diagnosis target portion of the cable 40 as the temperature of the portion other than the diagnosis target portion of the cable 40. The portion other than the diagnosis target portion of the cable 40 may be a portion separated by a predetermined distance along the cable 40 from the diagnosis target portion of the cable 40. A portion of cable 40 that was not the diagnostic target portion at one time may become the diagnostic target portion of cable 40 at another time. A portion of cable 40 that was the diagnostic target portion at one time may become a portion of cable 40 other than the diagnostic target portion at another time. If the environment in which cable 40 is buried changes as a whole, it is expected that the temperature of each of multiple portions of cable 40 will change due to the influence of the environmental change. Control unit 12 can diagnose the condition of the diagnostic target portion of cable 40 by comparing the amount of change in temperature of the diagnostic target portion of cable 40 with the amount of change in temperature of portions of cable 40 other than the diagnostic target portion.

[0063] For example, the control unit 12 may diagnose that the condition of the diagnosis target portion of the cable 40 has changed if the temperature of portions other than the diagnosis target portion of the cable 40 does not change but the temperature of the diagnosis target portion of the cable 40 changes. For example, the control unit 12 may diagnose that the condition of the diagnosis target portion of the cable 40 has changed if the amount of change in temperature of the diagnosis target portion of the cable 40 is greater than the amount of change in temperature of portions other than the diagnosis target portion of the cable 40 before and after the passage of a predetermined time. The control unit 12 may diagnose that the condition of the diagnosis target portion of the cable 40 has become abnormal if the amount of change in temperature of the diagnosis target portion of the cable 40 is equal to or greater than a predetermined threshold. The predetermined threshold compared with the amount of change in temperature of the diagnosis target portion of the cable 40 is also referred to as a change amount threshold.

[0064] The control unit 12 may calculate a value representing the state of the diagnosis target portion of the cable 40 taking into account the state of the portion other than the diagnosis target portion, for example, based on the amount of change in the temperature of the diagnosis target portion of the cable 40 and the temperature of the portion other than the diagnosis target portion. The value representing the state of the diagnosis target portion of the cable 40 taking into account the state of the portion other than the diagnosis target portion is a value that takes into account the relationship between the measured temperature of the portion other than the diagnosis target portion and the reference value when determining the risk level based on the relationship between the measured temperature of the diagnosis target portion and the reference value. The control unit 12 may diagnose whether the state of the diagnosis target portion of the cable 40 has become abnormal based on the value representing the state of the diagnosis target portion of the cable 40 taking into account the state of the portion other than the diagnosis target portion of the cable 40. The control unit 12 may diagnose that the state of the diagnosis target portion of the cable 40 has become abnormal, for example, when the value representing the state of the diagnosis target portion of the cable 40 taking into account the state of the portion other than the diagnosis target portion of the cable 40 is equal to or greater than a judgment value.

[0065] The control unit 12 may calculate a value representing the state of the diagnosis target portion of the cable 40, taking into account the state of the portion of the cable 40 other than the diagnosis target portion, based on, for example, weighted values ​​for the amount of change in temperature of the diagnosis target portion and the amount of change in temperature of the portion of the cable 40 other than the diagnosis target portion. The control unit 12 may weight the amount of change in temperature of the diagnosis target portion by multiplying the amount of change in temperature of the diagnosis target portion by a coefficient corresponding to the diagnosis target portion. The control unit 12 may set the coefficient corresponding to the diagnosis target portion based on the surrounding environment of the position where the diagnosis target portion of the cable 40 is buried. The control unit 12 may weight the amount of change in temperature of the portion of the cable 40 other than the diagnosis target portion by a coefficient corresponding to the portion of the cable 40 other than the diagnosis target portion. The control unit 12 may set the coefficient corresponding to the portion of the cable 40 other than the diagnosis target portion based on the surrounding environment of the position where the diagnosis target portion of the cable 40 is buried. That is, the control unit 12 may calculate a value representing the state of the diagnosis target portion of the cable 40, taking into account the state of the portions of the cable 40 other than the diagnosis target portion, as the absolute value of the difference between a value obtained by multiplying the amount of change in temperature of the diagnosis target portion by a coefficient corresponding to the diagnosis target portion and a value obtained by multiplying the amount of change in temperature of the portions other than the diagnosis target portion by a coefficient corresponding to the portions other than the diagnosis target portion. The control unit 12 may set a judgment value for the value representing the state of the diagnosis target portion of the cable 40, taking into account the state of the portions of the cable 40 other than the diagnosis target portion, based on the coefficient corresponding to the diagnosis target portion and the coefficient corresponding to the portions other than the diagnosis target portion.

[0066] As described above, the control unit 12 can diagnose the condition of the diagnosis target portion of the cable 40 based on the change over time in temperature of the diagnosis target portion and portions other than the diagnosis target portion of the cable 40. In this way, the influence of environmental changes on the diagnosis of the condition of each portion of the cable 40 is reduced.

[0067] The control unit 12 may separately set a change amount threshold for diagnosing a state in which the cable 40 is exposed to the sea 84 or a judgment value for a value representing the state of the portion of the cable 40 to be diagnosed taking into account the state of the portion of the cable 40 other than the portion to be diagnosed, and a change amount threshold for diagnosing a state in which the cable 40 is bent or broken or a judgment value for a value representing the state of the portion of the cable 40 to be diagnosed taking into account the state of the portion of the cable 40 other than the portion to be diagnosed. In this way, the control unit 12 can separately diagnose whether the state of the cable 40 is an abnormality in which the cable 40 is exposed to the sea 84 or an abnormality such as bending or breakage.

[0068] The number of parts other than the diagnosis target part with which the control unit 12 compares the change in temperature over time of the diagnosis target part is not limited to 1. The control unit 12 may diagnose the condition of the diagnosis target part of the cable 40 by comparing the change in temperature over time of two or more parts other than the diagnosis target part with the change in temperature over time of one diagnosis target part.

[0069] <Combination of diagnostic methods> The control unit 12 may diagnose that the state of the diagnosis target portion of the cable 40 is likely to be abnormal based on a diagnosis based on the temperature changes over time of the diagnosis target portion and portions other than the diagnosis target portion of the cable 40. After diagnosing that the state of the diagnosis target portion of the cable 40 is likely to be abnormal, the control unit 12 may diagnose whether the state of the diagnosis target portion of the cable 40 is abnormal based only on the temperature changes over time of the diagnosis target portion of the cable 40.

[0070] The control unit 12 may diagnose that the state of the diagnosis target portion of the cable 40 may be abnormal based only on the change over time in temperature of the diagnosis target portion of the cable 40. After diagnosing that the state of the diagnosis target portion of the cable 40 may be abnormal, the control unit 12 may diagnose whether the state of the diagnosis target portion of the cable 40 is abnormal by diagnosing based on the change over time in temperature of each of the diagnosis target portion of the cable 40 and portions other than the diagnosis target portion.

[0071] As a comparative example, assume that the control unit 12 monitors only the change over time in the measured temperature of one diagnostic portion of the cable 40, and determines that there may be an abnormality in that diagnostic portion if the temperature of that diagnostic portion increases. However, a mere increase in the temperature of one diagnostic portion of the cable 40 may not be enough to determine that there is an abnormality in that diagnostic portion. For example, if the temperature of the entire cable 40 is increasing due to power transmission through the cable 40, even if the temperature of one diagnostic portion of the cable 40 increases, the temperatures of the adjacent diagnostic portion or other diagnostic portions will also increase. If the temperature of the entire cable 40 is increasing, the control unit 12 will not determine that there is an abnormality in that diagnostic portion based on the increase in temperature in that diagnostic portion.

[0072] Therefore, in the diagnostic system 1 according to the present disclosure, even if the temperature of a certain diagnostic target portion of the cable 40 is elevated, the control unit 12 does not immediately determine that the diagnostic target portion is abnormal, but instead checks the temperatures of portions other than the diagnostic target portion. For example, the control unit 12 may check the temperature of a measurement target portion adjacent to the measurement target portion corresponding to the diagnostic target portion, or the temperature of another measurement target portion located within a predetermined distance from the diagnostic target portion, as the temperature of the portion other than the diagnostic target portion. If the temperature of the diagnostic target portion rises but the temperature of portions other than the diagnostic target portion does not, the control unit 12 may determine that the temperature has changed only in the diagnostic target portion and that the diagnostic target portion is abnormal. If the temperature of portions other than the diagnostic target portion rises when the temperature of the diagnostic target portion rises, the control unit 12 checks the range of the temperature increase, similar to that of the diagnostic target portion. If the control unit 12 can identify the range of the temperature increase, similar to that of the diagnostic target portion, it may determine that the cable 40 is abnormal within that range.

[0073] As described above, by checking not only the temperature of the diagnosis target portion of cable 40 but also the temperature of portions other than the diagnosis target portion, control unit 12 is less likely to erroneously diagnose an abnormality in the diagnosis target portion of cable 40 compared to checking only the temperature of the diagnosis target portion of cable 40. In other words, the accuracy of diagnosing an abnormality in the diagnosis target portion of cable 40 is improved.

[0074] The control unit 12 may diagnose whether the condition of the diagnosis target portion of the cable 40 is abnormal by first performing a diagnosis based on the temperature change over time of each of the diagnosis target portion and portions other than the diagnosis target portion of the cable 40, and then performing a diagnosis based only on the temperature change over time of the diagnosis target portion of the cable 40. The control unit 12 may diagnose whether the condition of the diagnosis target portion of the cable 40 is abnormal by performing a diagnosis based only on the temperature change over time of the diagnosis target portion of the cable 40 and portions other than the diagnosis target portion of the cable 40, and then performing a diagnosis based on the temperature change over time of each of the diagnosis target portion of the cable 40. In other words, the control unit 12 may diagnose whether the condition of the diagnosis target portion of the cable 40 is abnormal by performing a diagnosis that combines the diagnosis based on the temperature change over time of each of the diagnosis target portion of the cable 40 and portions other than the diagnosis target portion of the cable 40 and the diagnosis based only on the temperature change over time of the diagnosis target portion of the cable 40. In this way, the accuracy of diagnosing the condition of each portion of the cable 40 is improved.

[0075] In a diagnosis based on the change over time in the temperature of the diagnosis target portion and the portion other than the diagnosis target portion of the cable 40, the control unit 12 may determine whether the change over time in the temperature of the diagnosis target portion and the portion other than the diagnosis target portion satisfies a diagnostic condition applied to the diagnosis based on the change over time in the temperature of the diagnosis target portion and the portion other than the diagnosis target portion of the cable 40. The diagnostic condition applied to the diagnosis based on the change over time in the temperature of the diagnosis target portion and the portion other than the diagnosis target portion of the cable 40 may include a condition based on a value representing the state of the diagnosis target portion in consideration of the state of the portion other than the diagnosis target portion of the cable 40, which is calculated based on the amount of change in the temperature of the diagnosis target portion of the cable 40 and the amount of change in the temperature of the portion other than the diagnosis target portion of the cable 40. The diagnostic condition applied to the diagnosis based on the change over time in the temperature of the diagnosis target portion and the portion other than the diagnosis target portion of the cable 40 may include a condition in which the temperature of the portion other than the diagnosis target portion of the cable 40 does not change, but the temperature of the diagnosis target portion of the cable 40 changes. The diagnostic conditions applied to the diagnosis based on the change over time in the temperature of the diagnosis target portion of the cable 40 and the portion other than the diagnosis target portion may include the amount of change in the temperature of the diagnosis target portion of the cable 40 being greater than the amount of change in the temperature of the portion other than the diagnosis target portion of the cable 40 before and after the passage of a predetermined time. The diagnostic conditions applied to the diagnosis based on the change over time in the temperature of the diagnosis target portion of the cable 40 and the portion other than the diagnosis target portion may include the amount of change in the temperature of the diagnosis target portion of the cable 40 being equal to or greater than a change amount threshold. The diagnostic conditions applied to the diagnosis based on the change over time in the temperature of the diagnosis target portion of the cable 40 and the portion other than the diagnosis target portion may include the value representing the state of the diagnosis target portion of the cable 40 being equal to or greater than a judgment value, taking into account the state of the portion other than the diagnosis target portion of the cable 40.

[0076] In a diagnosis based solely on the change over time in the temperature of the diagnosis target portion of cable 40, control unit 12 may determine whether the temperature of the diagnosis target portion satisfies diagnostic conditions that are applied to a diagnosis based solely on the change over time in the temperature of the diagnosis target portion of cable 40. The diagnostic conditions that are applied to a diagnosis based solely on the change over time in the temperature of the diagnosis target portion of cable 40 may include a condition based on the temperature of the diagnosis target portion of cable 40. The diagnostic conditions that are applied to a diagnosis based solely on the change over time in the temperature of the diagnosis target portion of cable 40 may include the temperature of the diagnosis target portion of cable 40 falling outside a determination range. The diagnostic conditions that are applied to a diagnosis based solely on the temperature of the diagnosis target portion of cable 40 may include the risk level calculated based on the temperature of the diagnosis target portion of cable 40 being equal to or greater than a risk level threshold.

[0077] <Diagnosis result output> The control unit 12 may display the diagnosis result on the display device 30. The control unit 12 may output the diagnosis result in other ways, such as by voice. The control unit 12 may output the diagnosis result to notify the user of the abnormality when it diagnoses that the condition of a part of the cable 40 is abnormal. The control unit 12 may output the diagnosis result even when it diagnoses that the condition of the cable 40 is normal.

[0078] The control unit 12 may display on the display device 30 the measured values ​​of the temperature of each part of the cable 40 used in the diagnosis. The control unit 12 may also display on the display device 30 the change over time in the temperature of each part of the cable 40. The control unit 12 may display on the display device 30 a value or the like representing the state of the diagnosed part of the cable 40, taking into account the risk calculated in the diagnosis or the state of parts of the cable 40 other than the diagnosed part. The control unit 12 may display the measured values ​​of the temperature of each part of the cable 40 in association with the diagnosis results. By having a person such as a worker managing the cable 40, a monitor, or an operator of the diagnosis device 10 check the measured values ​​of the temperature of each part of the cable 40 together with the diagnosis results, the person's diagnostic skills or knowledge can be improved.

[0079] <Example of diagnostic procedure> The control unit 12 of the diagnostic device 10 may execute a diagnostic method including the steps of the flowchart illustrated in Fig. 5 in order to diagnose the condition of the cable 40. The diagnostic method may be realized as a diagnostic program executed by a processor or computer constituting the control unit 12. The diagnostic program may be stored in a non-transitory computer-readable medium.

[0080] The control unit 12 acquires, from the temperature measurement device 20, the measured temperatures of the diagnosis target portion of the cable 40 and the portion other than the diagnosis target portion (step S1).

[0081] The control unit 12 determines (step S2) whether the temperature changes over time of the diagnosis target portion of the cable 40 and the portions other than the diagnosis target portion satisfy the diagnostic conditions applied to the diagnosis based on the temperature changes over time of the diagnosis target portion of the cable 40 and the portions other than the diagnosis target portion. If the temperature changes over time of the diagnosis target portion of the cable 40 and the portions other than the diagnosis target portion do not satisfy the diagnostic conditions (step S2: NO), the control unit 12 diagnoses that the condition of the diagnosis target portion of the cable 40 is not abnormal, and ends the execution of the procedure of the flowchart in FIG.

[0082] If the temperature changes over time of the diagnosis target portion of cable 40 and the portions other than the diagnosis target portion satisfy the diagnostic conditions applied to a diagnosis based on the temperature changes over time of the diagnosis target portion of cable 40 and the portions other than the diagnosis target portion (step S2: YES), control unit 12 determines whether the temperature of the diagnosis target portion of cable 40 satisfies the diagnostic conditions applied to a diagnosis based on the temperature of the diagnosis target portion of cable 40 in a diagnosis based on the temperature of the diagnosis target portion of cable 40 (step S3). If the temperature of the diagnosis target portion of cable 40 does not satisfy the diagnostic conditions (step S3: NO), control unit 12 diagnoses that the condition of the diagnosis target portion of cable 40 is not abnormal, and ends the execution of the procedure of the flowchart in FIG.

[0083] If the temperature of the diagnostic target portion of cable 40 satisfies the diagnostic condition (step S3: YES), control unit 12 determines that the state of the diagnostic target portion of cable 40 is abnormal, and notifies the abnormality of the diagnostic target portion of cable 40 (step S4). After executing the procedure of step S4, control unit 12 ends execution of the procedure of the flowchart in FIG.

[0084] 5, the control unit 12 performs a diagnosis based on the temperature change over time of the diagnosis target portion of the cable 40 and portions other than the diagnosis target portion before performing a diagnosis based on the temperature of the diagnosis target portion of the cable 40. The control unit 12 may perform a diagnosis based on the temperature of the diagnosis target portion of the cable 40 before performing a diagnosis based on the temperature change over time of the diagnosis target portion of the cable 40 and portions other than the diagnosis target portion. The control unit 12 may perform only one of the diagnosis based on the temperature change over time of the diagnosis target portion of the cable 40 and portions other than the diagnosis target portion of the cable 40 or the diagnosis based on the temperature of the diagnosis target portion of the cable 40.

[0085] <Summary> As described above, in the diagnostic system 1 according to this embodiment, the diagnostic device 10 can diagnose the condition of each part of the cable 40 based on the temperature of each part of the cable 40. In this way, the condition of each part of the cable 40 is continuously diagnosed. Furthermore, the diagnostic device 10 can diagnose the condition of each part of the cable 40 based on the change over time in the temperature of multiple parts of the cable 40. In this way, the influence of environmental changes on the diagnosis of the condition of each part of the cable 40 is reduced. As a result, the accuracy of diagnosing the condition of each part of the cable 40 is improved.

[0086] Furthermore, the diagnostic device 10 can diagnose the condition of the cable 40 separately, determining whether the condition is an abnormality due to exposure to the seawater 84 or an abnormality such as bending or breakage. In this way, various conditions can be diagnosed separately from one another. As a result, the accuracy of diagnosing various conditions of the cable 40 is improved.

[0087] The diagnostic system 1 diagnoses the condition of the cable 40 even when an entity managing the cable 40 (e.g., a human such as a worker, a monitor, or an operator of the diagnostic device 10) is not present on-site. As a result, the frequency and cost of human visits to the site where the cable 40 is buried are reduced. Furthermore, the reliability of the cable 40 is improved by realizing continuous diagnosis.

[0088] The diagnostic system 1 clarifies the diagnostic criteria for the condition of each part of the cable 40. As a result, the reliability of the cable 40 is improved.

[0089] The diagnostic system 1 monitors the condition of each section of the cable 40, which extends for hundreds or thousands of meters, by setting temperature measurement sections at intervals of, for example, one meter to minimize oversights. Measuring the temperature throughout the entire cable 40 requires a sensor the same length as the cable 40. However, since the optical fiber 42 functions as a sensor, this can be easily achieved by installing it along the cable 40. Furthermore, multiple optical fibers 42 are inherently embedded in the submarine cable. Among the multiple optical fibers 42, unused fibers not used for other functions are directly utilized as temperature sensors. The diagnostic system 1 monitors whether there are any sections with elevated temperatures among the hundreds, thousands, or tens of thousands of measurement sections along the cable 40. When the diagnostic system 1 finds a measurement section with elevated temperatures, it checks the temperatures of measurement sections adjacent to or located nearby the measurement section, thereby improving diagnostic accuracy.

[0090] In the diagnostic system 1 according to the embodiment described above, the control unit 12 of the diagnostic device 10 diagnosed whether the diagnostic target portion of the cable 40 is abnormal based on the temperature change over time of the diagnostic target portion of the cable 40. Assuming there are no changes in the overall environment, such as changes in seawater temperature, if the diagnostic target portion of the cable 40 is normal, the measured temperature of the diagnostic target portion of the cable 40 should not have changed from a reference value (the temperature measured when the diagnostic target portion of the cable 40 is properly buried and the cable 40 itself is normal). The temperature change over time of the diagnostic target portion of the cable 40 (the difference between the temperature at a certain time and the temperature a predetermined time prior to that time) represents the degree to which the current measured temperature deviates from the reference value of the temperature measured under normal conditions. Therefore, the control unit 12 may diagnose whether the diagnostic target portion of the cable 40 is abnormal by comparing the temperature of the diagnostic target portion of the cable 40 with the reference value.

[0091] (Other embodiments) Other embodiments are described below.

[0092] <Diagnosis based on geological conditions> The geological features of the seabed 81 in which the cable 40 is buried may not be uniform. For example, the geological features in which the portion of the cable 40 to be diagnosed is buried may differ from the geological features in which the other portions of the cable 40 are buried. The control unit 12 of the diagnostic device 10 may diagnose the condition of each portion of the cable 40, assuming that the geological features in which a certain portion of the cable 40 (e.g., the portion to be diagnosed) is buried are different from the geological features in which other portions of the cable 40 (e.g., the portions other than the portion to be diagnosed) are buried.

[0093] The current flowing through cable 40 may cause the temperature of the entire cable 40 to rise. However, the extent of the temperature rise may vary from part to part of cable 40. The extent of the temperature rise in the diagnostic target portion of cable 40 may be determined by the environment in which the diagnostic target portion of cable 40 is buried, or the quality of the soil and sand that make up the ground 80 in which the diagnostic target portion of cable 40 is buried. For example, the measured temperature of the diagnostic target portion of cable 40 may differ depending on the type of soil and sand that make up the ground 80 in which the diagnostic target portion of cable 40 is buried.

[0094] The temperature change over time may be expressed as the amount of temperature change per minute, such as if the temperature measured at a certain time was 27°C and the temperature measured one minute earlier was 25°C, and the temperature rose by 2°C in one minute. When the temperature measurement value of a temperature measurement portion (N) corresponding to a certain diagnostic portion rises by 2°C in one minute, the control unit 12 does not immediately determine that the diagnostic portion is abnormal, but instead checks the temperature of a portion other than the diagnostic portion, such as the temperature of a measurement portion (N+1) adjacent to the temperature measurement portion (N) corresponding to the diagnostic portion, or the temperature of the further adjacent measurement portion (N+2). If the temperatures of the measurement portions (N), (N+1), and (N+2) all rise, but the temperatures of the further adjacent measurement portion (N+3) and the measurement portion (N-1) adjacent in the opposite direction do not rise, the control unit 12 may determine that the cable 40 is abnormal at the temperature measurement portions (N), (N+1), and (N+2) of the cable 40.

[0095] Here, the criteria for determining whether a change in temperature over time indicates an abnormality in cable 40 differ depending on the environment in which cable 40 is buried or the quality of the soil and sand that constitutes underground 80 in which the portion of cable 40 to be diagnosed is buried. In other words, when determining whether the temperature has increased in each measurement target portion, control unit 12 may assume that the environment in which cable 40 is buried or the quality of the soil and sand that constitutes underground 80 in which the portion of cable 40 to be diagnosed is buried will differ.

[0096] The control unit 12 may estimate changes in the geology by comparing the temperature changes over time at two adjacent points in the temperature measurement target portion of the cable 40. For example, if the amount of temperature change at a certain point differs from the amount of temperature change at an adjacent point, the control unit 12 may estimate that the two points are included in different geologies.

[0097] For example, assume that the measured temperature at the temperature measurement target portion (N) of the cable 40 that is normally buried is 25°C, the measured temperatures at the adjacent measurement target portions (N+1) to (N+5) are 25°C, and the measured temperature at the further adjacent measurement target portion (N+6) is 27°C. In this case, the control unit 12 may infer that the geological features in which the cable 40 is buried have changed between the measurement target portions (N+5) and (N+6). The control unit 12 is not limited to inferring that the geological features have changed, and may infer that other environmental changes have occurred.

[0098] For example, suppose the reference temperature value for measurement portions (N) to (N+5) is 25°C. The measured temperature values ​​for measurement portions (N) to (N+5) are 27°C. In this case, the temperature has risen by 2°C in measurement portions (N) to (N+5). On the other hand, suppose the reference and measured temperature values ​​for measurement portions (N+6) to (N+100) are both 27°C. In this case, the temperature has not risen in measurement portions (N+6) to (N+100). Based on these temperature measurement results, control unit 12 may determine that an abnormality has occurred in measurement portions (N) to (N+5).

[0099] Geological data is difficult to obtain because it is vast and located deep below the surface. As described above, the control unit 12 can determine the condition of the diagnosis target portion of the cable 40 by assuming the geology without using the geological data itself or being explicitly aware of the geology. If the control unit 12 can obtain geological data, it may determine whether the temperature change over time in each diagnosis target portion of the cable 40 corresponds to an abnormality based on the geological data. The control unit 12 may measure the temperature of each measurement target portion of the cable 40 via fiber, and when a certain measurement target portion is designated as the diagnosis target portion, it may compare the temperature of the diagnosis target portion with the temperatures of the surrounding measurement target portions other than the diagnosis target portion, and based on the relationship, estimate the change point in the environment (geology) and make a determination taking into account the temperature difference conditions in each area.

[0100] Even when geological data is only partially acquired, when there are concerns about the accuracy of the geological data, or when no geological data can be acquired at all, the control unit 12 sets the reference temperature for each measurement target portion as a diagnosis target portion based on the temperature of each measurement target portion of the cable 40 when the cable 40 is properly buried (before operation begins or immediately after installation, etc.). The control unit 12 may estimate that a range including measurement target portions where the measured temperature is the same when the cable 40 is properly buried is a range with consistent environmental conditions or the same geology. In the above example, the range including measurement target portions (N) to (N+5) is estimated to be a certain geology for which the reference temperature value is set to 25°C. The range including measurement target portions (N+6) to (N+100) is another geology for which the reference temperature value is set to 27°C. When the operation of the cable 40 begins, and time has passed since the cable 40 was normally buried, and changes may occur in the buried state of the cable 40 or in the state of the cable 40 itself, the control unit 12 determines whether each measurement target part is a diagnosis target part or whether the diagnosis target part is abnormal based on the reference temperature value set for each measurement target part.

[0101] If there is a measurement object part whose measured temperature value is 27°C within a range including a measurement object part whose reference temperature value is 25°C, the control unit 12 determines that the temperature of the diagnosis object part has risen when that measurement object part is used as the diagnosis object part, and determines that the diagnosis object part is abnormal. On the other hand, if there is a measurement object part whose measured temperature value is 27°C within a range including a measurement object part whose reference temperature value is 27°C, the control unit 12 determines that the temperature of the diagnosis object part has not changed when that measurement object part is used as the diagnosis object part, and determines that the diagnosis object part is not abnormal.

[0102] When comparing the temperature measurements of multiple measurement target portions (for example, comparing the temperature of a diagnosis target portion with the temperature of a portion other than the diagnosis target portion), the control unit 12 may compare the temperature measurements of adjacent measurement target portions, taking into account the high possibility that adjacent measurement target portions have the same geology and environment. On the other hand, the control unit 12 may record the addresses (N+x) of measurement target portions whose normal temperature measurements were 25°C, even if they are not necessarily adjacent, and compare the temperature measurements of measurement target portions whose normal temperature measurements were the same. In other words, the control unit 12 may identify measurement target portions whose temperature measurements deviate from the normal temperature measurements of measurement target portions whose normal temperature measurements should be 25°C as abnormal portions.

[0103] As illustrated in FIG. 6 , the cable 40 is assumed to be buried so as to pass through a portion of geology α, a portion of geology β, and a portion of geology γ. The control unit 12 does not need to know data on the differences in the geology in which the cable 40 is buried. The normal temperature of the cable 40 buried in geology α is assumed to be 25°C. The normal temperature of the cable 40 buried in geology β is assumed to be 27°C. The normal temperature of the cable 40 buried in geology γ is assumed to be 23°C. The control unit 12 may acquire the normal temperatures of each portion of the cable 40 as measured values ​​of the initial temperature when the cable 40 was buried. The control unit 12 may consider the differences in the normal temperatures of each portion of the cable 40 to be due to differences in the geology in which the cable 40 is buried, or may consider them to be due to differences in the environment other than the geology, or may not associate them with any factor.

[0104] Assume that the control unit 12 estimates that A1, A2, and A3 are included in geology β. The control unit 12 may acquire the temperatures of each of the portions of A1, A2, and A3 estimated to be included in geology β. Assume that the temperature at A2 is 25°C, which is lower than the normal temperature of 27°C for geology β. Assume that the temperatures at A1 and A3 are the normal temperature of 27°C. In this case, the control unit 12 may diagnose that the condition of the portion of cable 40 corresponding to A2 is abnormal. If the temperature at A1 is 26°C, which is lower than the normal temperature, the control unit 12 may compare the temperature of a portion farther from A1 than A2 with the normal temperature, thereby diagnosing whether the abnormal condition of the portion of cable 40 corresponding to A2 extends only to the portion corresponding to A1 or extends to a portion farther from A2.

[0105] Assume that the control unit 12 estimates that C, C-1, and C-2 are included in geology γ. Assume that the control unit 12 estimates that C+1 and C+2 are included in geology α. The control unit 12 may acquire the temperature of each of the portions of C, C-1, and C-2 estimated to be included in geology γ. The control unit 12 may also acquire the temperature of each of the portions of C+1 and C+2 estimated to be included in geology α adjacent to geology γ. Assume that the temperature at C is 20°C, lower than the normal temperature of 23°C for geology γ. Assume that the temperatures at C-1 and C-2 are the normal temperature of 23°C. Assume that the temperatures at C+1 and C+2 are the normal temperature of 25°C for geology α. In this case, the control unit 12 may diagnose that the condition of the portion of the cable 40 corresponding to C is abnormal. The control unit 12 may diagnose that the condition of the portion of the cable 40 corresponding to C-1 is normal based on the fact that the temperature at C-1 and the temperature at C-2 are the same. Furthermore, the control unit 12 may diagnose that the condition of the portion of the cable 40 corresponding to C+1 is normal based on the fact that the temperature at C+1 is the same as the temperature at C+2. In other words, with regard to the diagnosis of C, the control unit 12 may change the portion other than the diagnosis target portion to a different portion of the cable 40 so that the amount of change in temperature of the diagnosis target portion and the portion other than the diagnosis target portion satisfies the diagnosis conditions applied to a diagnosis based on the change over time in temperature of the diagnosis target portion and the portion other than the diagnosis target portion of the cable 40. In this way, the condition of the cable 40 is diagnosed taking into account the geology. As a result, the accuracy of diagnosing the condition of the cable 40 is improved.

[0106] The control unit 12 may acquire the temperature of portion D that is estimated to be included in the geology α. The temperature of portion D is assumed to be the normal temperature of 25°C for the geology α. In this case, the control unit 12 may diagnose that the condition of the portion of the cable 40 corresponding to D is normal. The control unit 12 may acquire the temperature of portion B that is included in the geology γ. The temperature of portion B is assumed to be the normal temperature of 23°C for the geology γ. In this case, the control unit 12 may diagnose that the condition of the portion of the cable 40 corresponding to B is normal.

[0107] The control unit 12 may acquire the temperatures of the portions E1, E2, and E3 that are estimated to be included in the geology α and that are close to the portion where the cable 40 is raised onto land 82. The temperature at E1, which is the starting point of burial, is close to the temperature of seawater. The temperatures at E2 and E3 are assumed to be 25°C, the normal temperature for the geology α. In this case, the control unit 12 may diagnose that the portions of the cable 40 corresponding to E2 and E3 are in a normal state. Furthermore, the portion where the cable 40 is raised onto land 82 is less susceptible to influence from fishing gear, anchors, or the like. The control unit 12 may diagnose changes in the environment of the area where the cable 40 is buried based on changes over time in the temperature of at least one portion of E2 or E3. The control unit 12 may diagnose changes in the current flowing through the cable 40 based on changes over time in the temperature of at least one portion of E1, E2, or E3.

[0108] <Diagnosis taking into account heat generation in cable 40> As illustrated in FIG. 7 , when the overall temperature of the cable 40 increases due to the flow of current through the cable 40, the surface temperature of the cable 40 is determined according to the amount of heat loss at each portion of the cable 40. In the graph of FIG. 7 , the horizontal axis represents the longitudinal position of the cable 40. The vertical axis represents temperature. The cable heat generation temperature graph represents the temperature of the diagnosed portion of the cable 40 when there is no heat loss. The cable surface temperature graph represents the temperature drop due to heat loss, and changes around the exposure start portion 45, where the cable 40 begins to be exposed to the seawater 84. In the portion of the graph buried in the ground 80 to the left of the exposure start portion 45, the cable surface temperature is lowered by the amount of heat conduction loss, which is determined according to the depth to which the cable 40 is buried. In the portion of the graph exposed to the seawater 84 to the right of the exposure start portion 45, the cable surface temperature is lowered by the amount of convection heat loss, which is determined according to the area of ​​the surface of the cable 40 exposed to the seawater 84.

[0109] The control unit 12 may identify the exposure start portion 45 of the cable 40 based on the temperature change in the longitudinal direction of the cable 40. The control unit 12 may calculate the depth to which the cable 40 is buried based on the temperature change in the longitudinal direction of the cable 40. The control unit 12 may also calculate the percentage of the area of ​​the surface of the cable 40 that is exposed to the seawater 84 based on the temperature change in the longitudinal direction of the cable 40.

[0110] The cable 40 may be laid exposed to the seabed 81 and underwater 84, rather than being buried in the ground 80, and protected by wave-dissipating blocks, gravel, or the like placed on top of the cable 40. In this case, the cable 40 may be cooled by convection heat loss caused by seawater seeping in through gaps in the wave-dissipating blocks, gravel, or the like. The control unit 12 may diagnose the condition of the cable 40 by taking into account changes in heat generation due to changes in the current flowing through the cable 40.

[0111] As illustrated in Fig. 8A, the control unit 12 calculates the heat generation temperature of the cable 40 in the absence of heat loss based on the change over time in the current in the cable 40. In the graph of Fig. 8A, the horizontal axis represents time, and the vertical axis represents temperature. Assume that the current flowing through the cable 40 starts to decrease from time T11, causing the heat generation temperature to start decreasing. Assume that the current flowing through the cable 40 starts to increase from time T12, causing the heat generation temperature to start increasing.

[0112] The control unit 12 acquires the change over time in the measured temperature at point X of the cable 40, as illustrated in FIG. 8B. The control unit 12 also acquires the change over time in the measured temperature at point Y of the cable 40, as illustrated in FIG. 8C. In the graphs of FIGS. 8B and 8C, the horizontal axis represents time, and the vertical axis represents temperature. The temperature at point X of the cable 40 begins to decrease from time T21 and begins to increase from time T22. The temperature at point Y of the cable 40 begins to decrease from time T31 and begins to increase from time T32. It is assumed that times T31 and T32 are later than times T21 and T22.

[0113] The difference in the timing of the temperature change at point X and point Y is due to differences in the heat dissipation characteristics, such as the amount of heat dissipation or the heat capacity of the soil, at each point. The control unit 12 may calculate the geothermal conductivity at each point based on the differences in the heat dissipation characteristics at each point. The geothermal conductivity is determined based on the properties of the materials that make up the soil, or the structure or density of the soil. The control unit 12 may correct values, such as a value representing the condition of the portion of the cable 40 to be diagnosed, based on the geothermal conductivity, taking into account the risk level of each portion of the cable 40 or the condition of portions of the cable 40 other than the portion to be diagnosed. The control unit 12 may acquire, as the timing of the temperature change, the time when the temperature change begins or the time when the temperature change rate reaches its maximum value (the time when the slope of the temperature change graph is steepest). For example, when point X is set as the part to be diagnosed and point Y is set as a part other than the part to be diagnosed, control unit 12 may correct the value representing the state of the part to be diagnosed of cable 40, taking into account the state of the part of cable 40 other than the part to be diagnosed, based on the difference between the timing at which the temperature of point X as the part to be diagnosed changes and the timing at which the temperature of point Y as the part other than the part to be diagnosed.

[0114] As described above, by taking into consideration the heat generated by the cable 40, the accuracy of diagnosing the condition of the cable 40 is improved.

[0115] <Diagnosis when no current flows through cable 40> As described above, the control unit 12 can correct values, etc., that represent the state of the diagnostic target portion of the cable 40 by taking into account the heat generation in the cable 40 and by taking into account the degree of danger or the state of portions of the cable 40 other than the diagnostic target portion. When no current flows through the cable 40, the cable 40 does not heat up. Even when the cable 40 does not heat up, the control unit 12 can correct values, etc., that represent the state of the diagnostic target portion of the cable 40 by taking into account other information and by taking into account the degree of danger or the state of portions of the cable 40 other than the diagnostic target portion.

[0116] The temperature of seawater changes in a daily cycle. The control unit 12 may correct values, etc., representing the state of the portion of cable 40 to be diagnosed, taking into account the degree of risk of each portion of cable 40 or the state of portions of cable 40 other than the portion to be diagnosed, based on the difference between the change in seawater temperature and the change in temperature of each portion of cable 40. The control unit 12 may correct values, etc., representing the state of the portion of cable 40 to be diagnosed, taking into account the degree of risk of each portion of cable 40 or the state of portions of cable 40 other than the portion to be diagnosed, based on not only daily data but also long-term data when electricity does not flow for a long period of time, such as during construction.

[0117] When the cable 40 is buried deep underground 80, the temperature of each portion of the cable 40 is less susceptible to diurnal changes in seawater temperature. However, the temperature of seawater may also change over an annual cycle due to, for example, the changing of seasons or the meandering of ocean currents. The control unit 12 may correct a value representing the condition of the portion of the cable 40 to be diagnosed, taking into account the risk of each portion of the cable 40 or the condition of portions of the cable 40 other than the portion to be diagnosed, based on the difference between the moving average of the seawater temperature and the moving average of the temperature of each portion of the cable 40. Specifically, the control unit 12 may calculate the difference between the timing at which the slope of the moving average of the seawater temperature reverses and the timing at which the slope of the moving average of the temperature of each portion of the cable 40 reverses. The control unit 12 may use the difference in timing at which the slope of the moving average of the temperature of each part of the cable 40 reverses as a parameter that is inversely proportional to the thermal conductivity of the earth, and may correct values ​​such as values ​​representing the condition of the part of the cable 40 being diagnosed, taking into account the risk of each part of the cable 40 or the condition of parts of the cable 40 other than the part being diagnosed.

[0118] <Example of correction using geothermal conductivity> The control unit 12 may correct parameters, such as values ​​representing the state of the cable 40's diagnostic target portion, based on the geothermal conductivity of the buried portion of the cable 40, taking into account the risk level used in diagnosing each portion of the cable 40 or the state of portions of the cable 40 other than the diagnostic target portion. The control unit 12 may set geothermal conductivity parameters for each cell obtained by dividing the cable 40 into small regions. A group of parameters is also referred to as a profile. The control unit 12 may associate, as characteristic data, burial information, such as the buried depth of the cable 40, and time, with the location information of the cable 40 (e.g., the distance from the temperature measuring device 20). The control unit 12 may associate, as historical data, time, the temperature at that position of the cable 40, the voltage applied to the cable 40, and the current flowing through the cable 40, with the location information of the cable 40. The control unit 12 may associate, as historical data, the type of underground and the geothermal conductivity with the location information of the cable 40. The control unit 12 may associate the estimated buried depth, long-term change rate, short-term change rate, and abnormality level as historical data with the position information of the cable 40.

[0119] The temperature measurement device 20 outputs the measured temperature value and the distance to the point where the measured value was obtained. Here, the voltage, current, and heat generation amount of the cable 40 are the same for each cell of the cable 40, if the voltage drop is considered an error. Therefore, the measured heat dissipation amount and temperature of each cell of the cable 40 with the same or similar profile are the same. The same or similar profile is specified by the same or similar depth and the same or similar thermal conductivity. Even if the power transmitted by the cable 40 changes, the heat generation amount and heat dissipation amount of the cable 40 will follow, so that cells with the same or similar profile will have the same or similar heat generation pattern.

[0120] On the other hand, in the initial stage of burial when the burial depth of the cable 40 does not change much, differences in temperature change due to current tracking may occur. When the cable is buried at a certain depth, the difference in temperature change is due to the thermal conductivity of the earth. In this case, the thermal conductivity of each cell is corrected by back-calculating from the difference in temperature change. When the burial depth is sufficiently deep, heat convection does not need to be taken into account. The correction value for the thermal conductivity of the earth may be calculated as ratio data or as a bias. The correction value for the thermal conductivity of the earth may be stored for each type of underground.

[0121] <Determining exposed parts> A submarine cable has a section that is systematically exposed from the ground 80 to the seabed 81. The amount of heat dissipation inside the ground 80 is determined mainly by the thermal conductivity of the ground 80. However, there is a point where the amount of heat dissipation increases sharply as one approaches the section exposed to the seabed 81. This point is located near the exposed section 52. One way to determine the exposed section of the cable 40 is to check the location of the exposed section on the seabed 81 against location information from information on the installation work, etc., and compare the temperature change at that location.

[0122] The exposed portion may also be identified by calculation. In a shallowly buried location, thermal conduction, radiation, and convection-based thermal radiation are dominant. On the other hand, in an exposed location, the amount of heat radiation increases rapidly due to the disappearance of thermally conductive areas with low heat radiation. Utilizing this, the temperature of a cell buried shallower than a certain depth gradually decreases compared to the temperature of a cell buried deeper and with the same or similar profile. Furthermore, when convection becomes dominant instead of conduction, for example, due to exposure to the seabed 81, the temperature further decreases. Therefore, the portion where the temperature decreases may be determined to be the exposed portion.

[0123] <Other examples of diagnostic subjects> The diagnostic system 1 may be applied to diagnose the condition of various other cables 40, not limited to the submarine cable of the offshore wind power generation device 70 described above. The diagnostic system 1 may be applied to diagnose the condition of, for example, a submarine cable for providing power or communications to a remote island or the like. The diagnostic system 1 may also be applied to diagnose the condition of a cable 40 laid on land. For example, the diagnostic system 1 may be applied to diagnose the condition of a cable 40 that is buried in the ground even on land, or a cable 40 that is laid in an area where human access is difficult, such as a mountainous region. The diagnostic system 1 may also be applied to diagnose the deterioration condition of the cable 40. The diagnostic system 1 may also be applied to diagnose the water ingress condition of the cable 40.

[0124] Although the embodiments of the present disclosure have been described based on the drawings and examples, it should be noted that those skilled in the art can make various modifications or alterations based on the present disclosure. Therefore, it should be noted that these modifications or alterations are included in the scope of the present disclosure. For example, the functions included in each component can be rearranged so as not to cause logical inconsistencies, and multiple components can be combined or divided into one. [Explanation of symbols]

[0125] 1 Diagnostic System 10 diagnostic device (12: control unit, 14: memory unit, 16: interface) 20 Temperature measuring device 30 Display device 40 Cable (41: power line, 42: optical fiber, 43: coating, 51: buried portion, 52: exposed portion, 53: buried portion, 54: shallow buried portion, 55: boundary portion) 70 Offshore wind power generation equipment 80 underground 81 Undersea 84 Undersea

Claims

1. A diagnostic method for diagnosing a condition of a cable including a diagnostic target portion and a portion other than the diagnostic target portion, comprising: the diagnosis target portion corresponds to a part of the cable temperature measurement target portion, the portion other than the diagnostic target portion corresponds to a measurement target portion different from a measurement target portion corresponding to the diagnostic target portion, acquiring a measured value of a temperature at a measurement target portion corresponding to the diagnosis target portion of the cable as a temperature of the diagnosis target portion of the cable; acquiring a measured value of a temperature at a measurement target portion corresponding to a portion other than the diagnosis target portion of the cable as a temperature of the portion other than the diagnosis target portion of the cable; determining that the state of the diagnosis target portion of the cable is abnormal when the amount of change in temperature of the diagnosis target portion and the portion other than the diagnosis target portion of the cable satisfies a diagnosis condition applied to a diagnosis based on a change over time in temperature of the diagnosis target portion and the portion other than the diagnosis target portion of the cable, and when the temperature of the diagnosis target portion of the cable satisfies a diagnosis condition applied to a diagnosis based on the temperature of the diagnosis target portion of the cable; A diagnostic method comprising:

2. 2. The diagnostic method according to claim 1, further comprising: determining whether the temperature of the diagnostic portion of the cable satisfies a diagnostic condition applied to a diagnosis based on a change over time in the temperature of the diagnostic portion of the cable and a portion other than the diagnostic portion after determining that the amount of change in the temperature of the diagnostic portion of the cable and a portion other than the diagnostic portion satisfies a diagnostic condition applied to a diagnosis based on a change over time in the temperature of the diagnostic portion of the cable.

3. 3. The diagnostic method according to claim 2, further comprising changing the portion other than the diagnostic target portion of the cable to a different portion of the cable so that an amount of change in temperature of the diagnostic target portion of the cable and the portion other than the diagnostic target portion satisfies a diagnostic condition applied to a diagnosis based on a change over time in temperature of the diagnostic target portion of the cable and the portion other than the diagnostic target portion.

4. a diagnostic condition applied to the diagnosis based on the change over time in temperature of the diagnostic target portion of the cable and the portion other than the diagnostic target portion includes a condition based on a value representing the state of the diagnostic target portion in consideration of the state of the portion other than the diagnostic target portion of the cable, the value being calculated based on the amount of change in temperature of the diagnostic target portion of the cable and the amount of change in temperature of the portion other than the diagnostic target portion of the cable; The diagnostic conditions applied to the diagnosis based on the temperature of the diagnostic target portion of the cable include a condition based only on a change in the temperature of the diagnostic target portion over time. The diagnostic method according to claim 1.

5. the condition based only on the change over time in the temperature of the diagnosis target portion includes the temperature of the diagnosis target portion of the cable being outside a determination range; The diagnostic method according to claim 4 , wherein the determination range is set based on the magnitude of the current flowing through the cable and the surrounding environment of the diagnostic target portion of the cable.

6. A value representing the state of the diagnostic part taking into account the state of the part of the cable other than the diagnostic part is calculated as the absolute value of the difference between the value obtained by multiplying the amount of change in temperature of the diagnostic part of the cable by a coefficient corresponding to the diagnostic part of the cable, and the value obtained by multiplying the amount of change in temperature of the part of the cable other than the diagnostic part by a coefficient corresponding to the part of the cable other than the diagnostic part, a coefficient corresponding to the diagnostic target portion of the cable is set based on a surrounding environment of the diagnostic target portion of the cable; a coefficient corresponding to a portion of the cable other than the diagnostic target portion is set based on a surrounding environment of the portion of the cable other than the diagnostic target portion; the condition based on the value representing the state of the diagnostic target portion in consideration of the state of the portion other than the diagnostic target portion of the cable includes that the value representing the state of the diagnostic target portion in consideration of the state of the portion other than the diagnostic target portion of the cable is equal to or greater than a determination value; the determination value is set based on a coefficient corresponding to a diagnostic target portion of the cable and a coefficient corresponding to a portion of the cable other than the diagnostic target portion. The diagnostic method according to claim 4.

7. 5. The diagnostic method according to claim 4, wherein the value representing the state of the diagnostic target portion taking into account the state of the portion of the cable other than the diagnostic target portion is corrected based on the difference between the time when the temperature of the diagnostic target portion of the cable starts to change and the time when the temperature of the portion of the cable other than the diagnostic target portion starts to change.

8. A diagnostic program that causes a computer to execute the diagnostic method according to any one of claims 1 to 7.

9. A diagnostic device comprising a control unit that executes the diagnostic method according to any one of claims 1 to 7.

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