A submarine cable route detection apparatus and method and a cable fault location method

Abstract

The application discloses a submarine cable path detection device and method and a cable fault positioning method, and the detection device comprises a detection ship, a general control module, a rudder control module, a positioning and information transmission system, a cable path detection assembly, a fault detection assembly and a land centralized control center. The application applies low-frequency voltage to the fault of the submarine cable, so that an alternating magnetic field is generated in the sea area around the cable, and the trend of the submarine cable is detected and judged, the technical defects that the submarine cable is inconvenient to maintain when the actual line deviates from the original laid line are overcome, time is saved, and efficiency is improved. The cable fault positioning method of the application quickly positions the fault point, overcomes the problems that the previous determination of the submarine cable fault point is time-consuming and labor-consuming, and the positioning accuracy of the fault point is not high, and improves the positioning accuracy and efficiency of the fault point.

Description

TECHNICAL FIELD

[0001] The present application relates to a detection device in marine equipment, in particular to a submarine cable path detection device and method and a cable fault positioning method. BACKGROUND

[0002] In recent years, the development of ocean resources has been increasingly concerned, including the development and research of offshore wind power. Offshore wind power projects have broad prospects, and higher requirements for the maintenance of related equipment of offshore wind farms have also been put forward.

[0003] The submarine cable undertakes the transmission of electric power, so the maintenance of the submarine cable is also very important. Since the cable is laid on the seabed, and the seabed environment is very complex, after the submarine cable fails, how to detect and locate the fault is a difficult problem.

[0004] Liang Yuxiong, Wang Sheng (patent number: CN110794262A) and others put forward a submarine cable fault accurate positioning system, which includes a positioning module, a synchronous acoustic magnetic detection module, a magnetic field strength detection module, an automatic fault point analysis module and a data analysis module. The invention can quickly and accurately locate the fault point of long-distance submarine cable, and improve the fault point search efficiency. However, this invention detects along the original path of the submarine cable. Since the submarine cable has been serving in a complex seabed environment for a long time, it may deviate from the original laid path. At this time, the applicability of the system and method for submarine cable fault detection and positioning is insufficient. SUMMARY

[0005] The purpose of the present application is to overcome the shortcomings of the prior art, provide a submarine cable path detection device and method and a cable fault positioning method, and quickly locate the fault point of the submarine cable, avoiding the difficulty of maintenance caused by the deviation of the actual line of the submarine cable from the original laid line.

[0006] Technical scheme: The submarine cable path detection device of the present application comprises a detection ship, a general control module, a rudder control module, a positioning and information transmission system, a cable path detection assembly, a fault detection assembly and a land centralized control center.

[0007] The cable path detection assembly comprises a cable path detection module and a first magnetic field detection device; the first magnetic field detection device comprises a first induction coil, a second induction coil and a third induction coil; the central axis of the second induction coil is consistent with the forward direction of the detection ship; the first induction coil and the third induction coil are symmetrically arranged on the two sides of the second induction coil; the fault detection assembly comprises a fault positioning module and a second magnetic field detection device.

[0008] The fault positioning module comprises a fourth induction coil, and the central axis of the fourth induction coil is perpendicular to the bottom plate of the detection ship.

[0009] The submarine cable path detection method of the present invention includes the following steps:

[0010] (1) The main control module sends a command to the cable path detection module. The detection vessel departs from the cable entry point and adjusts its bow direction to both sides of the cable. During the adjustment process, the second induction coil detects the surrounding magnetic field. The cable path detection module stores the minimum induced electromotive force E detected by the second induction coil. 2min The instantaneous induced electromotive force measured by the second induction coil When the submarine cable runs parallel to the axis of the second induction coil, it indicates that the probe vessel and the cable run in the same direction.

[0011] (2) The cable path detection module measures the ratio of the induced potential E1 measured by the first induction coil to the induced potential E3 measured by the third induction coil. Feedback is sent to the rudder control module, which then controls the rudder blades to align the probe vessel with the cable.

[0012] (3) After the probe adjusts its course, repeat steps (1) to (2) to conduct the probe.

[0013] Instantaneous induced electromotive force in step (1)

[0014] in, Let S be the rate of change of magnetic induction intensity generated by alternating current in the submarine cable, and S be the effective area of ​​the second induction coil passing through the magnetic field lines.

[0015] In step (2), the ratio of the induced electromotive force E1 measured by the first induction coil to the induced electromotive force E3 measured by the third induction coil is... At that time, the probe vessel and the cable were aligned.

[0016] In step (2), if the rudder control module receives data from the cable path detection module... The rudder control module then controls the probe to deflect towards the first induction coil.

[0017] In step (2), if the rudder control module receives data from the cable path detection module... The rudder control module then controls the probe to deflect towards the third induction coil.

[0018] The submarine cable fault location method of the present invention includes the following steps:

[0019] (1) The main control module sends a command to the cable path detection module. The detection vessel departs from the cable entry point and adjusts its bow direction to both sides of the cable. During the adjustment process, the second induction coil detects the surrounding magnetic field. The cable path detection module stores the minimum induced electromotive force E detected by the second induction coil.2min When the instantaneous induced electromotive force E measured by the second induction coil i =E 2min When the submarine cable runs parallel to the axis of the second induction coil, it indicates that the probe vessel and the cable run in the same direction.

[0020] (2) The cable path detection module measures the ratio of the induced electromotive force E1 measured by the first induction coil to the third induced electromotive force E3 measured by the third induction coil. Feedback is sent to the rudder control module, which then controls the rudder blades to align the probe vessel with the cable.

[0021] (3) When the probe travels from the entry point to the direction of the submarine cable, it stores the induced potential E4 measured by the fourth induction coil of the fault location module as a threshold in the fault location module. After the probe detects the maximum distance between the fourth induction coil and the submarine cable, if the instantaneous induced potential E4 measured by the fourth induction coil is... i =0, then the fault in the submarine cable is determined to occur at the point where the probe enters the water; if the instantaneous induced electromotive force E i If the value is not equal to 0, the probe will continue probing until the instantaneous induced potential E is reached. i When = 0, the positioning and information transmission system transmits E i The coordinates P of the point = 0 1i The coordinates P of the previous instantaneous induced potential Ei equal to the threshold E4 2i Transmitted to the land-based control center, the P 2i To P 1i The interval between these points constitutes a fault range.

[0022] In step (3), the maximum distance between the fourth induction coil and the submarine cable

[0023] Where U0 is the permeability, B min I represents the minimum magnetic field strength detected by the fourth induction coil, and I represents the current intensity in the submarine cable.

[0024] In step (3), coordinate P 2i Let P be the coordinates 1i Previous distance P 1i The nearest point.

[0025] Working principle: Seawater has a strong shielding effect on high-frequency electromagnetic fields above MHz, resulting in short propagation distances and hindering detection. However, low-frequency or extremely low-frequency electromagnetic fields below 300 Hz propagate over long distances, with an effective range of hundreds of meters. This invention applies a low-frequency voltage to the faulty phase of a submarine cable, generating an alternating magnetic field in the surrounding sea area, thereby detecting and determining the cable's trajectory.

[0026] Beneficial effects: compared with the prior art, the present application has the following advantages:

[0027] (1) The present application overcomes the technical defects of inconvenient maintenance of the submarine cable when the actual line of the submarine cable deviates from the original laid line, saves time and improves efficiency by using the submarine cable detection device to detect and judge the specific direction of the submarine cable.

[0028] (2) The cable fault positioning method of the present application uses magnetic field detection device and data storage and analysis method to quickly detect the submarine cable and locate the fault point, overcomes the problem of time-consuming and labor-consuming and low accuracy of fault point positioning in the past, saves time and labor, and has high accuracy of fault point positioning. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 The principle diagram of the submarine cable detection device and fault positioning method of the present application;

[0030] Figure 2 The first magnetic field detection device and arrangement mode diagram in the cable path detection module of the present application;

[0031] Figure 3 The second magnetic field detection device arrangement mode diagram in the fault positioning module of the present application;

[0032] Figure 4 The flow chart of the cable path detection and fault positioning method of the present application;

[0033] Figure 5 The first detection state top view of the first magnetic field detection device 8 of the present application;

[0034] Figure 6 The second detection state top view of the first magnetic field detection device 8 of the present application;

[0035] Figure 7 The third detection state top view of the first magnetic field detection device 8 of the present application;

[0036] Figure 8 The specific arrangement mode top view of the induction coil of the first magnetic field detection device 8. DETAILED DESCRIPTION

[0037] As Figure 1 shown, the submarine cable detection device of the present application comprises a detection ship, a power module 1, a total control module 2, a cable path detection module 3, a rudder control module 4, a fault positioning module 5, a GPS positioning and information transmission system 6, a rudder blade 7, a first magnetic field detection device 8, a second magnetic field detection device 9 and a land centralized control center 10.

[0038] The power module 1 provides power for the whole submarine cable detection device, the total control module 2 is connected with the cable path detection module 3, the rudder control module 4, the fault positioning module 5, the GPS positioning and information transmission system 6 through the interface and the communication line to realize data communication. The cable path detection module 3 and the rudder control module 4 transmit data through the interface and the communication line to realize information interaction. The cable path detection module 3 is connected with the first magnetic field detection device 8 through a wire. The rudder control module 4 is connected with the rudder blade 7 through gear transmission or other mechanical structures. The fault positioning module 5 and the GPS positioning and information transmission system 6 realize data transmission communication through the interface and the communication line. The fault positioning module 5 is connected with the second magnetic field detection device 9 through a wire. The GPS positioning and information transmission system 6 and the land centralized control center 10 realize information transmission through remote information transmission.

[0039] Figure 2 For the specific structure of the first magnetic field detection device 8, the first magnetic field detection device 8 comprises a first induction coil 81, a second induction coil 82 and a third induction coil 83. As shown in the figure, the arrangement mode of the first induction coil 81, the second induction coil 82 and the third induction coil 83 is that the plane of the second induction coil 82 is perpendicular to the plane of the detection ship bottom plate, and the center axis direction of the coil is consistent with the forward direction of the detection ship. The first induction coil 81 and the third induction coil 83 are arranged on the two sides of the second induction coil 82. Figure 8

[0040] Referring to the figure, the plane where the first induction coil 81 and the third induction coil 83 are located and the plane where the second induction coil 82 is located form an angle of 45 degrees respectively. And the planes formed by the first induction coil 81, the second induction coil 82 and the third induction coil 83 are all perpendicular to the plane of the detection ship bottom plate. Figure 8

[0041] The first induction coil 81, the second induction coil 82 and the third induction coil 83 of the first magnetic field detection device 8 are connected with the cable path detection module 3 through a wire.

[0042] Figure 3 In the second magnetic field detection device 9, the fourth induction coil 91 is composed of the fourth induction coil 91. The arrangement mode of the fourth induction coil 91 is that the center axis of the fourth induction coil 91 is perpendicular to the plane of the detection ship bottom plate. The fourth induction coil 91 of the second magnetic field detection device 9 is connected with the fault positioning module 5 through a wire.

[0043] The size, dimension of the first induction coil 81, the second induction coil 82, the third induction coil 83 and the fourth induction coil 91 are all the same, all are made of copper wire with the same thickness, n turns, the outer diameter is D, the inner diameter is d, and the thickness is h. The specific size is appropriate to detect the magnetic field generated by the submarine cable. ​​

[0044] The maximum distance detected by the first induction coil 81, the second induction coil 82, the third induction coil 83 or the fourth induction coil 91 from the submarine cable is: wherein U0 is the magnetic permeability, B min is the minimum magnetic field intensity detected by the first induction coil 81, the second induction coil 82, the third induction coil 83 or the fourth induction coil 91, and I is the current intensity in the submarine cable.

[0045] In this embodiment, the detection ship starts from the sea surface at the point where the cable enters the water and uniformly moves forward along the cable path direction on one side of the submarine cable.

[0046] The working of the fault location module 5 and the cable path detection module 3 is independent of each other, and the total control module 2 simultaneously sends instructions to the fault location module 5 and the cable path detection module 3.

[0047] The working process of the cable path detection module 3 and the fault location module 5 is as shown in Figure 4 .

[0048] The detection process of the submarine cable detection device on the submarine cable direction includes the following steps:

[0049] (1) The total control module 2 sends instructions to the cable path detection module 3, and the cable path detection module 3 starts working. The working process of the cable path detection module 3 includes the following steps:

[0050] (1.1) As shown in Figure 8 , the initial direction of the detection ship after entering the water is adjusted 90° to the left, and then the direction of the detection ship head is adjusted back to the initial direction, and then adjusted 90° to the right, and then adjusted back to the initial direction. During the whole process of adjusting the direction of the detection ship head, the second induction coil 82 of the first magnetic field detection device 8 detects the surrounding magnetic field, and the cable path detection module 3 stores the maximum induced potential E 2max and the minimum induced potential E 2min detected during this process, and takes E 2max and E 2min as the threshold of the second induction coil 82.

[0051] The instantaneous induced potential when the first induction coil, the second induction coil or the third induction coil in the first magnetic field detection device 8 detects the surrounding magnetic field is: In formula ②, is the rate of change of the magnetic induction intensity generated by the alternating current in the submarine cable, and S is the effective area of the closed coil passing through the magnetic induction lines. When the instantaneous induced potential E i detected by the second induction coil 82 is E 2maxAt this time, the effective area of ​​the second induction coil 82 passing through the magnetic field lines is at its maximum, and the submarine cable route is perpendicular to the central axis of the second induction coil 82. When the second induction coil 82 measures the instantaneous induced electromotive force E... i =E 2min At this time, the effective area of ​​the second induction coil 82 passing through the magnetic field lines is the smallest, and the submarine cable route is parallel to the central axis of the second induction coil 82.

[0052] (1.2) Using the method in step (1.1), find the direction of travel of the probe vessel that is parallel to the direction of the submarine cable, with the central axis of the second induction coil 82 being parallel to the direction of the submarine cable. At this time, the direction of travel of the probe vessel is consistent with the direction of the submarine cable, and then continue to probe forward.

[0053] (1.3) such as Figure 5 As shown, the submarine cable detection device of the present invention continues to detect forward. At this time, the induced electromotive force E1 measured by the first induction coil 81 is equal to the induced electromotive force E3 measured by the third induction coil 83, E1=E3. At this time, the effective areas of the first induction coil 81 and the third induction coil 83 through the magnetic field lines are equal.

[0054] See Figure 6 When the submarine cable deviates to the left, i.e., towards the direction of the first induction coil 81, the effective area of ​​the first induction coil 81 passing through the magnetic field lines increases, while the effective area of ​​the third induction coil 83 passing through the magnetic field lines decreases. At this time, the ratio of the induced electromotive force E1 measured by the first induction coil 81 to the induced electromotive force E3 measured by the third induction coil 83 is...

[0055] like Figure 7 As shown, when the submarine cable deviates to the right, i.e., towards the direction of the third induction coil, the effective area of ​​the first induction coil 81 passing through the magnetic field lines decreases, while the effective area of ​​the third induction coil 83 passing through the magnetic field lines increases. At this time, the ratio of the induced electromotive force E1 measured by the first induction coil 81 to the induced electromotive force E3 measured by the third induction coil 83 is... The cable path detection module 3 determines the direction of the submarine cable by calculating the ratio of E1 to E3.

[0056] (1.4) After determining the direction of the submarine cable through the first magnetic field detection device 8, the cable path detection module 3 sets the ratio of the induced electromotive force E1 measured by the first induction coil 81 to the induced electromotive force E3 measured by the third induction coil 83. Feedback is sent to the rudder control module 4 via interface and communication line. The rudder control module 4 analyzes the data and then controls the rudder blades 7 via mechanical structure to adjust the probe's course. The specific analysis process of the rudder control module 4 is as follows:

[0057] (1.4.1) If the ratio of E1 / E3 received by the rudder control module 4 from the cable path detection module 3 is greater than 1, the rudder control module 4 will control the rudder blade 7 to make the detection ship deflect to the left, that is, deflect towards the direction of the first induction coil.

[0058] (1.4.2) If the ratio of E1 / E3 received by the rudder control module 4 from the cable path detection module 3 is less than 1, the rudder control module 4 will control the rudder blade 7 to make the detection ship deflect to the right, that is, deflect towards the direction of the third induction coil.

[0059] (1.5) After each course adjustment, the probe ship repeats steps (1.1) to (1.4) and continues to probe in this manner.

[0060] The fault location method of the submarine cable detection device of the present invention includes the following steps:

[0061] (1) The main control module 2 sends a command to the fault location module 5, and the fault location module 5 starts working. Through steps (1.1) and (1.2), the direction of travel of the probe vessel is found to be consistent with the direction of the submarine cable. In this embodiment, the probe vessel starts to travel from the near-shore position where it just enters the water until the direction of travel of the probe vessel is consistent with the direction of the submarine cable. At this time, the fourth induction coil 91 of the second magnetic field detection device 9 connected to the fault location module 5 starts to detect the surrounding magnetic field from this position, and stores the induced electromotive force E4 measured by the fourth induction coil 91 at this time into the fault location module 5. The fault location module 5 stores the measured induced electromotive force at any time. After the probe vessel continues to probe forward for a distance (this distance is the maximum distance that the fourth induction coil 91 can detect from the submarine cable, and this maximum distance is determined by formula ①), according to the instantaneous induced electromotive force measured at the position at the maximum distance, the following two methods of fault location of submarine cable are used:

[0062] (2.1) After the probe moves forward a certain distance from its initial entry point (this distance is the maximum distance between the probe and the submarine cable detected by the fourth induction coil 91, which is determined by equation ①), the instantaneous induced electromotive force E measured at this location is... i =0, then the fault location of the submarine cable is determined to be near the shore where the probe ship has just entered the water. At this time, the fault location is a fault point, that is, the probe ship detects from the position where it has just entered the water.

[0063] (2.2) After the probe moves forward a certain distance from its initial entry point (this distance is the maximum distance between the probe and the submarine cable detected by the fourth induction coil 91, which is determined by equation ①), the instantaneous induced electromotive force E measured at this location is... iIf the value is not equal to 0, it means that the fault location of the submarine cable does not occur at the near-shore position when the probe ship just enters the water. Therefore, the induced electromotive force E4 measured by the fourth induction coil 91 when the probe ship just enters the water is set as the threshold of the fault location module 5.

[0064] The second magnetic field detection device 9 continues to probe forward. The fault location module 5 sends a command to record position coordinate information through the interface and communication line of the GPS positioning and information transmission system 6. The GPS positioning and information transmission system 6 begins to record the instantaneous position coordinate information P of the probe at a set frequency. i And transmit the instantaneous position coordinate information P i The data is transmitted to the fault location module 5, which then transmits the instantaneous induced electromotive force E measured by the second magnetic field detection device 9. i The instantaneous location coordinate information P transmitted from the GPS positioning and information transmission system 6 i Corresponding storage.

[0065] When the instantaneous induced electromotive force E measured by the second magnetic field detection device 9 i When = 0, the fault location module 5 will output the location coordinate information P of this position. 1i and the position coordinates information P of the previous probe. 2i (Detector ship position coordinates P) 2i For position coordinate information P 1i The previous distance from P 1i The nearest point, and the second magnetic field detection device 9 is in the position coordinate information P 2i Instantaneous induction E measured at the location i The threshold E4) is fed back to the GPS positioning and information transmission system 6. The GPS positioning and information transmission system 6 transmits the location coordinate information P 1i and P 2i The information is transmitted remotely to the land-based control center 10. At this time, the located fault location is a fault range, namely P. 1i and P 2i The area between these locations represents the range in which submarine cable faults occur.

Claims

1. A method of submarine cable route surveying, characterised by: The submarine cable path detection device comprises a detection ship, a general control module (2), a rudder control module (4), a positioning and information transmission system (6), a cable path detection assembly, a fault detection assembly and a land centralized control center (10); The cable path detection assembly comprises a cable path detection module (3) and a first magnetic field detection device (8); the first magnetic field detection device (8) comprises a first induction coil (81), a second induction coil (82) and a third induction coil (83); the central axis of the second induction coil is consistent with the forward direction of the detection ship; the first induction coil and the third induction coil are symmetrically arranged on the two sides of the second induction coil; The fault detection assembly comprises a fault positioning module (5) and a second magnetic field detection device; The fault positioning module comprises a fourth induction coil (91), and the central axis of the fourth induction coil is perpendicular to the bottom plate of the detection ship; The detection method comprises the following steps: (1) The total control module (2) sends instructions to the cable path detection module (3), the detection ship sets off at the cable water inlet and adjusts the bow direction to both sides of the cable. In the process of adjustment, the second induction coil (82) detects the surrounding magnetic field, and the cable path detection module (3) stores the minimum induction potential E 2min detected by the second induction coil. When the instantaneous induction potential E i detected by the second induction coil is E 2min , it means that the submarine cable direction is parallel to the axis of the second induction coil, which indicates that the detection ship is consistent with the cable direction. (2) The cable path detection module (3) will compare the ratio of the induced voltage E1 measured by the first induction coil to the induced voltage E3 measured by the third induction coil The feedback to the rudder control module (4) and control the rudder (7) to adjust the detection boat and cable consistent with the direction; (3) After the detection ship adjusts the heading, steps (1) to (2) are repeated for detection.

2. A method of submarine cable route surveying according to claim 1, characterised in that: In step (1), the transient induced potential wherein is the rate of change of the magnetic induction produced by the alternating current in the submarine cable, S is the effective area of the second induction coil through the magnetic induction line.

3. A method of submarine cable route surveying according to claim 1, characterised in that: In step (2), when the ratio of the induced electromotive force E1 measured by the first induction coil to the induced electromotive force E3 measured by the third induction coil is the probe boat is aligned with the cable.

4. A method of submarine cable route surveying according to claim 1, characterised in that: In step (2), if the rudder control module (4) receives the data feedback from the cable path detection module (3) then the rudder control module (4) controls the detection ship to deflect towards the direction of the first induction coil.

5. A method of submarine cable route surveying according to claim 1, characterised in that: In step (2), if the rudder control module (4) receives the data feedback from the cable path detection module (3) then the rudder control module (4) controls the detection ship to deflect towards the third induction coil.

6. A method of subsea cable fault location, characterised by: The submarine cable path detection device comprises a detection ship, a general control module (2), a rudder control module (4), a positioning and information transmission system (6), a cable path detection assembly, a fault detection assembly and a land centralized control center (10); The cable path detection assembly comprises a cable path detection module (3) and a first magnetic field detection device (8); the first magnetic field detection device (8) comprises a first induction coil (81), a second induction coil (82) and a third induction coil (83); the central axis of the second induction coil is consistent with the forward direction of the detection ship; the first induction coil and the third induction coil are symmetrically arranged on the two sides of the second induction coil; The fault detection assembly comprises a fault positioning module (5) and a second magnetic field detection device; The fault positioning module comprises a fourth induction coil (91), and the central axis of the fourth induction coil is perpendicular to the bottom plate of the detection ship; The fault positioning method comprises the following steps: (1) The total control module sends an instruction to the cable path detection module, the detection ship sets off at the cable water inlet and adjusts the bow direction to both sides of the cable. In the process of adjustment, the second induction coil (82) detects the surrounding magnetic field, and the cable path detection module (3) stores the minimum induction potential E 2min detected by the second induction coil. When the instantaneous induction potential E i detected by the second induction coil is E 2min , it means that the submarine cable direction is parallel to the axis of the second induction coil, indicating that the detection ship is consistent with the cable direction. (2) The cable path detection module (3) will compare the ratio of the induced voltage E1 measured by the first induction coil to the third induced voltage E3 measured by the third induction coil The feedback to the rudder control module (4), and control the rudder (7) to adjust the detection ship and cable direction consistent; (3) When the detecting boat travels to the same direction as the submarine cable, the inductive potential E4 measured by the fourth inductive coil (91) of the fault location module is stored as a threshold value in the fault location module. After the detecting boat detects the maximum distance between the fourth inductive coil and the submarine cable, if the instantaneous inductive potential E4 measured by the fourth inductive coil is equal to 0, it is judged that the fault of the submarine cable occurs at the water entry point of the detecting boat; if the instantaneous inductive potential E4 is not equal to 0, the detecting boat continues to detect until the instantaneous inductive potential E4 is equal to 0. When the instantaneous inductive potential E4 is equal to 0, the positioning and information transmission system (6) transmits the coordinates P4 at which the instantaneous inductive potential E4 is equal to 0 and the coordinates P3 at which the last instantaneous inductive potential Ei is equal to the inductive potential E4 to the land control center. The coordinates P3 to P4 are a fault interval. i i i i 1i 2i 2i 1i ​​​​​​​​ 7. A method of submarine cable fault location according to claim 6, characterised in that: In step (3), the maximum distance of the fourth induction coil from the submarine cable wherein U0 is the magnetic permeability, B min is the minimum magnetic field strength detected by the fourth induction coil, and I is the current intensity in the submarine cable.

8. A method of submarine cable fault location according to claim 6, characterised in that: In step (3), the coordinates P 2i are the coordinates P 1i of the previous distance P 1i the nearest point.

Images