Cable insulation defect detection equipment and detection method based on optical fiber

Abstract

The invention relates to an optical fiber-based cable insulation defect detection device and detection method, the detection device comprises a photoelectric collector and a sensing detection unit, the sensing detection unit comprises a first sensing optical fiber ring and a second sensing optical fiber ring which are wound on a large-current current-carrying cable and are spaced, the first sensing optical fiber is arranged at the starting end of the large-current current-carrying cable in a surrounding mode, the first sensing optical fiber ring and the second sensing optical fiber ring are both in communication connection with the photoelectric collector, and the photoelectric collector is used for obtaining induction currents in the first sensing optical fiber ring and the second sensing optical fiber ring. And whether the high-current current-carrying cable has an insulation defect or not is judged according to a difference value between the induction current of the first sensing optical fiber ring and the induction current of the second sensing optical fiber ring.

Description

Technical Field

[0001] The present application relates to the technical field of power monitoring, and in particular to an optical fiber-based cable insulation defect detection device and an insulation defect detection method. Background Art

[0002] High-current carrying cables are used in many fields, such as submarine cables, and are also widely used in fields such as electrolytic smelting and controlled nuclear fusion. Due to their large volume, heavy weight, or being placed underwater, the insulation detection and positioning of high-current carrying cables are crucial. Currently, there is no relatively mature method for detecting the insulation performance of high-current carrying cables. Summary of the Invention

[0003] The present application provides an optical fiber-based cable insulation defect detection device and a detection method, which can solve the technical problem of potential safety hazards easily caused by existing insulation defects of high-current carrying cables.

[0004] An optical fiber-based cable insulation defect detection device includes: An optoelectronic collector; and A sensing detection unit, where the sensing detection unit includes a first sensing optical fiber loop and a second sensing optical fiber loop that are wound around the high-current carrying cable at intervals. The first sensing optical fiber loop is wound around the starting end of the high-current carrying cable. Both the first sensing optical fiber loop and the second sensing optical fiber loop are communicatively connected to the optoelectronic collector. The optoelectronic collector is configured to respectively obtain the induced currents in the first sensing optical fiber loop and the second sensing optical fiber loop, and determine whether there is an insulation defect in the high-current carrying cable based on the difference between the induced currents of the first sensing optical fiber loop and the second sensing optical fiber loop.

[0005] In one of the solutions, the magnetic circuit loops where the first sensing optical fiber loop and the second sensing optical fiber loop are located respectively further include a quarter-wave plate and a reflector.

[0006] In one of the solutions, the optoelectronic collector includes a light source, a photodetector, a coupler, an optical fiber polarizer, a phase modulator, a polarization-maintaining fiber delay loop, and a signal processing circuit. The light source, the coupler, the optical fiber polarizer, and the phase modulator are sequentially connected by optical fibers. Opposite ends of the signal processing circuit are respectively connected to the photodetector and the phase modulator. Opposite ends of the photodetector are respectively connected to the coupler and the signal processing circuit. Opposite ends of the polarization-maintaining fiber delay loop are respectively connected to the phase modulator, the first sensing optical fiber loop, and the second sensing optical fiber loop.

[0007] In one of the solutions, the second sensing optical fiber loop is arranged at the tail end of the high-current carrying cable.

[0008] In one of the solutions, a third sensing optical fiber loop is further arranged between the first sensing optical fiber loop and the second sensing optical fiber loop. The third sensing optical fiber loop is evenly wound around the large-current carrying cable, and the third sensing optical fiber loop is configured to cooperate with an optoelectronic collector to detect the average induced current of the large-current carrying cable.

[0009] In one of the solutions, controllable single-pole multi-throw optical switches are respectively arranged between the first sensing optical fiber loop, the second sensing optical fiber loop, and the third sensing optical fiber loop and the optoelectronic collector. The controllable single-pole multi-throw optical switch is used to control one of the first sensing optical fiber loop, the second sensing optical fiber loop, and the third sensing optical fiber loop to be connected to the optoelectronic collector.

[0010] In one of the solutions, the induced current at the start end of the large-current carrying cable sensed by the first sensing optical fiber loop is I1, the induced current at the end of the large-current carrying cable sensed by the second sensing optical fiber loop is I2, the average induced current of the large-current carrying cable sensed by the third sensing optical fiber loop is I3, and ΔI 1,2 = I1 - I2, ΔI 1,3 = I1 - I3. Let K = ΔI 1,3 / ΔI 1,2 , where L is the length of the large-current carrying cable, and D = K * L, where D is the distance from the failure point to the second sensing optical fiber loop.

[0011] In one of the solutions, a linear moving component is further included. The linear moving component can carry the second sensing optical fiber loop to move uniformly at a preset position on the large-current carrying cable.

[0012] An optical fiber detection method for cable insulation defect detection includes: Providing the above-mentioned optical fiber-based cable insulation defect detection device; Obtaining the induced currents in the first sensing optical fiber loop and the second sensing optical fiber loop in real time; Judging whether the difference between the induced currents at two positions is 0. When the difference is not 0, determining the insulation failure position.

[0013] In one of the solutions, when the difference is not 0, the average induced current of the large-current carrying cable is further obtained. Let the induced current at the start end be I1, the induced current at the end be I2, and the average induced current be I3, and ΔI 1,2 = I1 - I2, ΔI 1,3 = I1 - I3. Let K = ΔI 1,3 / ΔI 1,2 , where L is the length of the large-current carrying cable, and the optoelectronic collector also obtains the insulation failure position according to the formula D = K * L, where D is the distance from the failure point to the second sensing optical fiber loop.

[0014] A fiber - based cable insulation defect detection device and its detection method provided by this application can achieve the following technical effects: 1. For the fiber - based cable insulation defect detection device provided by this application, when current flows through a large - current - carrying cable, a magnetic field will be generated. This magnetic field will affect the optical signals of the compensation sensing fiber loop and the measurement sensing fiber loop in the first sensing fiber loop. The second sensing fiber loop can be set at the end of the large - current - carrying cable during detection. If there is an insulation failure in the transmission path of the large - current - carrying cable, the induced current at the starting end will be inconsistent with the induced current at the end, and it can be determined that there is a defect in the insulation of the large - current - carrying cable.

[0015] 2. The third fiber loop is evenly and spirally wound between the starting end and the end of the large - current - carrying cable. Controllable single - pole multi - throw optical switches are respectively arranged between the first sensing fiber loop, the second sensing fiber loop, and the third sensing fiber loop and the optoelectronic collector. The controllable single - pole multi - throw optical switch is used to control one of the first sensing fiber loop, the second sensing fiber loop, and the third sensing fiber loop to be connected to the optoelectronic collector; the optoelectronic collector can obtain the average induced current of the large - current - carrying cable through the third fiber loop, and then obtain the distance from the failure point to the second sensing fiber loop. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 FIG. is a schematic structural diagram of a fiber - based cable insulation defect detection device provided by the first embodiment of this application.

[0017] Figure 2 FIG. is a schematic structural diagram of a fiber - based cable insulation defect detection device provided by the second embodiment of this application.

[0018] Description of the reference numerals: 100, fiber - based cable insulation defect detection device; 10, light source; 14, detector; 11, coupler; 12, polarizer; 13, phase modulator; 15, signal processing circuit; 16, polarization - maintaining fiber delay loop; 101, large - current - carrying cable; 3, controllable single - pole multi - throw optical switch; 1, optoelectronic collector; 20, first sensing fiber loop; 22, second sensing fiber loop; 30, quarter - wave plate; 32, mirror; 2, sensing detection unit; 202, starting end; 203, end; 24, third sensing fiber loop. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0019] The following further elaborates in detail on the fiber - based cable insulation defect detection device and its detection method provided by this application in conjunction with the attached Figure 1-2 drawings.

[0020] Embodiment 1 Please refer to Figure 1, for a large - current carrying cable 101 with a power supply distance of dozens of meters or even longer, multiple insulation supports are required. Usually, a tower is used to support the large - current carrying cable 101. If there is an insulation defect in the large - current carrying cable 101, the current will shunt along the tower, posing a safety hazard. Therefore, a fiber - based cable insulation defect detection device 100 is needed to monitor the insulation condition of the large - current carrying cable 101 in real - time. A fiber - based cable insulation defect detection device 100 provided in this application monitors the current in the large - current carrying cable in real - time to determine the insulation state of the large - current carrying cable 101.

[0021] Specifically, a fiber - based cable insulation defect detection device 100 includes an optoelectronic collector 1 and a sensing and detection unit 2.

[0022] In this embodiment, the optoelectronic collector 1 is a fiber optic current sensor. More specifically, the optoelectronic collector 1 includes a light source 10, a photodetector 14, a coupler 11, a fiber optic polarizer 12, a phase modulator 13, a signal processing circuit 15, and a polarization - maintaining fiber delay loop 16.

[0023] The light source 10, the coupler 11, the fiber optic polarizer 12, and the phase modulator 13 are connected in sequence through optical fibers. The two opposite ends of the signal processing circuit 15 are respectively connected to the photodetector 14 and the phase modulator 13. The two opposite ends of the photodetector 14 are respectively connected to the coupler 11 and the signal processing circuit 15. The two opposite ends of the polarization - maintaining fiber delay loop 16 are respectively connected to the phase modulator 13 and a controllable single - pole multi - throw optical switch 3. The phase modulator 13 performs phase modulation on the polarized optical signal so that the magnetic field change can be detected by measuring the phase change subsequently.

[0024] The photodetector 14 is responsible for converting the received optical signal into an electrical signal. The phase - modulated optical signal will generate current or voltage changes in the detector 14, and these changes are related to the intensity and direction of the external magnetic field, thus reflecting the current situation in the large - current carrying cable 101.

[0025] The polarization - maintaining fiber delay loop 16 ensures that the optical signal maintains consistent polarization characteristics during the transmission process in the optical fiber and delays the signal to a certain extent, enabling the system to process and analyze the phase change.

[0026] The signal processing circuit 15 receives the electrical signal converted by the photodetector 14 and performs further processing to decode the relevant information of the current change. By analyzing the signal, it can be determined whether there is an insulation defect in the large - current carrying cable 101. The signal processing circuit 15 can extract useful data from the photodetector 14 for fault diagnosis.

[0027] Specifically, the light source 10 is a superluminescent diode light source 10 (SLD). The light source 10 emits a laser beam, which is coupled into the fiber polarizer 12 through the coupler 11. After polarization by the fiber polarizer 12, it becomes linearly polarized light. The pigtail of the fiber polarizer 12 is fusion-spliced with the pigtail of the phase modulator 13 at 45°. The linearly polarized light is injected into the polarization-maintaining fiber delay loop 16 at 45°, and is transmitted along the X-axis and Y-axis of the polarization-maintaining fiber delay loop 16 respectively. These two orthogonally polarized modes of linearly polarized light become left-handed and right-handed circularly polarized light respectively after passing through the quarter-wave plate, and enter the sensing and detecting unit 2 for propagation.

[0028] The sensing and detecting unit 2 is communicatively connected to the photoelectric collector 1. The sensing and detecting unit 2 mainly includes a current-carrying wire and a sensing fiber loop through which the current-carrying wire passes. The current transmitted in the current-carrying wire generates a magnetic field, which generates the Faraday magneto-optical effect in the sensing fiber loop, causing a phase difference between the left-handed circularly polarized light and the right-handed circularly polarized light in the sensing fiber loop. After reflection at the end face of the mirror, the polarization modes of the two circularly polarized lights are interchanged (i.e., the left-handed light becomes right-handed light, and the right-handed light becomes left-handed light), and then pass through the sensing fiber loop again, and the Faraday magneto-optical effect causes the phase difference generated by the two lights to double. After these two lights pass through the quarter-wave plate again, they are restored to linearly polarized light and return, and interference occurs at the fiber polarizer 12.

[0029] Finally, the light carrying the non-reciprocal phase difference information generated by the Faraday magneto-optical effect enters the photodetector 14 through the coupler 11 and is converted into an electrical signal.

[0030] Therefore, according to the Faraday magneto-optical effect and Ampere's circuital law, the magnitude of the current transmitted in the current-carrying wire is proportional to the phase difference. Therefore, the value of the current to be measured can be calculated by detecting the optical phase difference signal.

[0031] Specifically, in this embodiment, the sensing and detecting unit 2 includes a first sensing fiber loop 20 and a second sensing fiber loop 22 that are wound around the large-current carrying cable 101 at intervals and have the same number of turns. The first sensing fiber loop 20 is wound around the starting end 202 of the large-current carrying cable 101. Both the first sensing fiber loop 20 and the second sensing fiber loop 22 are communicatively connected to the photoelectric collector 1. The photoelectric collector 1 is used to respectively obtain the induced currents in the first sensing fiber loop 20 and the second sensing fiber loop 22, and determine whether there is an insulation defect in the large-current carrying cable 101 according to the difference between the induced currents in the first sensing fiber loop 20 and the second sensing fiber loop 22.

[0032] The magnetic circuit loops where the first sensing optical fiber loop 20 and the second sensing optical fiber loop 22 are located respectively further include a quarter-wave plate 30 and a mirror 32. The quarter-wave plate 30 converts linearly polarized light into circularly polarized light, so as to utilize the Faraday magneto-optical effect to generate a certain phase difference between the two circularly polarized lights, and then indirectly measure the value of the current to be measured that generates the magnetic field by detecting the phase difference.

[0033] In this embodiment, the second sensing optical fiber loop 22 is arranged at the tail end 203 of the large-current carrying cable 101.

[0034] The working principle of the optical fiber detection device is as follows: The pigtail of the optical fiber polarizer 12 is fused with the pigtail of the phase modulator 13 at 45°. The linearly polarized light is injected into the polarization-maintaining optical fiber delay loop 16 at 45°, and is transmitted along the X-axis and Y-axis of the polarization-maintaining optical fiber delay loop 16 respectively. When the controllable single-pole multi-throw optical switch 3 is connected to the first sensing optical fiber loop 20 through an optical fiber, these two orthogonally polarized lights are respectively converted into left-handed elliptical / circularly polarized light and right-handed elliptical / circularly polarized light under the action of the quarter-wave plate 30. Due to the magnetic field around the large-current carrying cable 101 causing the Faraday effect, these two elliptical / circularly polarized lights are transmitted at different speeds. After passing through the mirror 32 at the tail end of the first sensing optical fiber loop 20, the polarization modes of the two elliptical / circularly polarized lights are interchanged (i.e., the left-handed elliptical / circularly polarized light becomes the right-handed elliptical / circularly polarized light, and the right-handed elliptical / circularly polarized light becomes the left-handed elliptical / circularly polarized light), and then pass through the first sensing optical fiber loop 20 again, and interact with the magnetic field generated by the large-current carrying cable 101 again, doubling the generated Faraday phase. Then the quarter-wave plate 30 realizes the conversion of elliptical / circularly polarized light into linearly polarized light. When the two optical waves meet at the optical fiber polarizer 12 of the transmission optical cable, interference occurs, and the interference signal returns to the photodetector 14 through the optical fiber coupler 11. Since the two interfering optical waves respectively pass through the left-handed and right-handed modes of the X-axis and Y-axis of the polarization-maintaining optical fiber delay loop 16 during the transmission process of the optical path, only with a slight difference in time, the light returning to the detector only carries the non-reciprocal phase difference generated by the Faraday effect. The phase difference Φ generated by the Faraday effect is Φ = 4VNI, where V is the Verdet constant of the optical fiber; N is the number of sensing optical fiber loops; I is the current passing through the current-carrying wire. Therefore, measuring the phase difference between these two optical waves can accurately measure the magnitude of the current passing through the large-current carrying cable 101. If the large current-carrying cable 101 has no insulation defect, the difference between the induced currents of the first sensing optical fiber loop 20 and the second sensing optical fiber loop 22 is 0; if the large current-carrying cable 101 has an insulation defect, the current will shunt along the metal tower, and there will be a difference in the induced currents in the first sensing optical fiber loop 20 and the second sensing optical fiber loop 22, that is to say, the difference between the induced currents of the first sensing optical fiber loop 20 and the second sensing optical fiber loop 22 is not 0. Therefore, it can be judged whether the large current-carrying cable 101 has an insulation defect according to the real-time current situation obtained by the optoelectronic collector 1.

[0035] Embodiment 2 Please refer to Figure 2 , Embodiment 2 is basically the same as Embodiment 1, the difference is that in this embodiment, a third sensing optical fiber loop 24 is further arranged between the first sensing optical fiber loop 20 and the second sensing optical fiber loop 22. The third sensing optical fiber loop 24 is wound evenly in a single turn in a spiral shape on the large current-carrying cable 101, and the third sensing optical fiber loop 24 is configured to cooperate with the optoelectronic collector 1 to detect the average induced current of the large current-carrying cable 101.

[0036] Controllable single-pole multi-throw optical switches 3 are respectively arranged between the first sensing optical fiber loop 20, the second sensing optical fiber loop 22, and the third sensing optical fiber loop 24 and the optoelectronic collector 1. The controllable single-pole multi-throw optical switch 3 can be selectively connected to one of the first sensing optical fiber loop 20, the second sensing optical fiber loop 22, and the third sensing optical fiber loop 24.

[0037] Let the induced current at the starting end 202 of the large current-carrying cable 101 be I1, the induced current at the tail end 203 of the large current-carrying cable 101 be I2, the average induced current I3, and ΔI 1,2 = I1 - I2, ΔI 1,3 = I1 - I3, let K = ΔI 1,3 / ΔI 1,2 , L is the length of the large current-carrying cable 101, and the optoelectronic collector 1 obtains the insulation failure position according to the formula D = K * L, where D is the distance from the failure point to the second sensing optical fiber loop 22.

[0038] It should be noted that Figure 2 in, the magnetic circuit loop where the third sensing optical fiber loop 24 is located also includes a quarter-wave plate 30 and a mirror 32. For the sake of clear drawing display, in Figure 2 the quarter-wave plate 30 and the mirror 32 are omitted in the magnetic circuit loops of the first sensing optical fiber loop 20 and the second sensing optical fiber loop 22. In fact, they need to actually exist.

[0039] Embodiment 3 Embodiment 3 is basically the same as Embodiment 1, except that in this embodiment, the fiber - based cable insulation defect detection device 100 further includes a linear movement component (not shown in the figure), and the linear movement component can carry the second sensing fiber loop 22 to move linearly. The initial position of the second sensing fiber loop 22 is at the tail end 203 of the large - current - carrying cable 101. When the difference between the induced currents of the first sensing fiber loop 20 and the second sensing fiber loop 22 is not 0, the linear movement component carries the second sensing fiber loop 22 to move uniformly on the surface of the large - current - carrying cable 101 from the tail end 203 until the position where the difference between the induced currents of the first sensing fiber loop 20 and the second sensing fiber loop 22 is 0 is detected. The position between this position and the adjacent non - zero position is the position where the insulation defect of the large - current - carrying cable 101 exists.

[0040] The present invention also relates to an optical fiber detection method for cable insulation defect detection, including: S1: Provide a fiber - based cable insulation defect detection device 100; S2: Real - time obtain the induced currents in the first sensing fiber loop 20 and the second sensing fiber loop 22 wound on the large - current - carrying cable 101, and judge whether the difference between the induced currents of the first sensing fiber loop 20 and the second sensing fiber loop 22 is 0; S3: When the difference is not 0, determine the insulation failure position.

[0041] In this embodiment, when the difference is not 0, the average induced current of the large - current - carrying cable 101 is also obtained. Let the induced current at the start end 202 be I1, the induced current at the tail end 203 be I2, the average induced current be I3, ΔI 1,2 = I1 - I2, ΔI 1,3 =I1 - I3, let K = ΔI 1,3 / ΔI 1,2 , L is the length of the large - current - carrying cable 101, and the optoelectronic collector 1 obtains the insulation failure position according to the formula D = K * L, where D is the distance from the failure point to the second sensing fiber loop 22.

[0042] In summary, the fiber - based cable insulation defect detection device 100 and the magnetic insulation defect detection method provided by the present invention can obtain the induced current according to the magnetic ring circuit to judge in real - time whether there is an insulation defect in the large - current - carrying cable 101. If there is an insulation defect, the defect position is determined on the large - current - carrying cable 101, and a warning message is sent to the terminal to ensure the electrical safety of the large - current - carrying cable 101 in the fields of large - capacity transformers and controlled nuclear fusion.

[0043] The above are all preferred embodiments of the present application, and the protection scope of the present application is not limited thereby. Therefore, all equivalent changes made according to the structure, shape, and principle of the present application shall be covered within the protection scope of the present application.

Claims

1. An optical fiber-based cable insulation defect detection device, characterized in that, Comprising: An optoelectronic collector (1); And A sensing and detecting unit (2), the sensing and detecting unit (2) includes a first sensing optical fiber loop (20) and a second sensing optical fiber loop (22) which are wound around a large-current carrying cable (101) with the same number of turns at intervals. The first sensing optical fiber loop (20) is wound around the starting end (202) of the large-current carrying cable (101). Both the first sensing optical fiber loop (20) and the second sensing optical fiber loop (22) are communicatively connected to the optoelectronic collector (1). The optoelectronic collector (1) is configured to respectively obtain the induced currents in the first sensing optical fiber loop (20) and the second sensing optical fiber loop (22), and determine whether there is an insulation defect in the large-current carrying cable (101) according to the difference between the induced currents of the first sensing optical fiber loop (20) and the second sensing optical fiber loop (22).

2. The fiber-optic cable insulation defect detection device according to claim 1, wherein: The optoelectronic collector (1) includes a light source (10), a photodetector (14), a coupler (11), an optical fiber polarizer (12), a phase modulator (13), a polarization-maintaining optical fiber delay loop (16), and a signal processing circuit (15). The light source (10), the coupler (11), the optical fiber polarizer (12), and the phase modulator (13) are sequentially connected by optical fibers. Opposite ends of the signal processing circuit (15) are respectively connected to the photodetector (14) and the phase modulator (13). Opposite ends of the photodetector (14) are respectively connected to the coupler (11) and the signal processing circuit (15). Opposite ends of the polarization-maintaining optical fiber delay loop (16) are respectively connected to the phase modulator (13), the first sensing optical fiber loop (20), and the second sensing optical fiber loop (22).

3. The cable insulation defect detection device based on optical fiber according to claim 2, characterized in that: The second sensing optical fiber loop (22) is arranged at the tail end (203) of the large-current carrying cable (101).

4. The fiber-based cable insulation defect detection device according to claim 3, characterized in that: A third sensing optical fiber loop (24) is further arranged between the first sensing optical fiber loop (20) and the second sensing optical fiber loop (22). The third sensing optical fiber loop (24) is wound around the large-current carrying cable (101) in a spiral and evenly. The third sensing optical fiber loop (24) is configured to cooperate with the optoelectronic collector (1) to detect the average induced current of the large-current carrying cable (101).

5. The cable insulation defect detection device based on optical fiber according to claim 4, characterized in that: The magnetic circuit loops where the first sensing optical fiber loop (20), the second sensing optical fiber loop (22), and the third sensing optical fiber loop (24) are located respectively further include a quarter-wave plate (30) and a mirror (32).

6. The fiber - based cable insulation defect detection device according to claim 4, wherein: Controllable single-pole multi-throw optical switches (3) are respectively arranged between the first sensing optical fiber loop (20), the second sensing optical fiber loop (22), the third sensing optical fiber loop (24) and the optoelectronic collector (1).

7. An optical fiber-based cable insulation defect detection device according to claim 4, characterized in that: The induced current at the starting end (202) of the large current-carrying cable (101) sensed by the first sensing optical fiber loop (20) is I1, and the induced current at the ending end (203) of the large current-carrying cable (101) sensed by the second sensing optical fiber loop (22) is I2. The average induced current of the large current-carrying cable (101) sensed by the third sensing optical fiber loop (24) is I3, ΔI 1,2 = I1 - I2, ΔI 1,3 = I1 - I3. Let K = ΔI 1,3 / ΔI 1,2 , L is the length of the large current-carrying cable (101), D = K * L, where D is the distance from the failure point to the second sensing optical fiber loop (22).

8. An optical fiber-based cable insulation defect detection device according to claim 1, characterized in that: It further includes a linear moving component, and the linear moving component can carry the second sensing optical fiber loop (22) to move uniformly at a preset position on the large-current carrying cable (101).

9. A fiber - based cable insulation defect detection method, characterized in that, Comprising: Providing the fiber-based cable insulation defect detection device (100) according to any one of claims 1-8; Real-time obtaining the induced currents in the first sensing optical fiber loop (20) and the second sensing optical fiber loop (22); Determine whether the difference between the induced currents at two positions is 0. When the difference is not 0, determine the insulation failure position.

10. A method for detecting cable insulation defects based on optical fiber according to claim 9, characterized in that: When the difference is not zero, the average induced current of the large current-carrying cable (101) is also obtained. Let the induced current at the starting end (202) be I1, the induced current at the tail end (203) be I2, and the average induced current be I3, ΔI 1,2 = I1 - I2, ΔI 1,3 = I1 - I3, let K = ΔI 1,3 / ΔI 1,2 , L is the length of the large current-carrying cable (101), and the photoelectric collector (1) also obtains the insulation failure position according to the formula D = K * L, where D is the distance from the failure point to the second sensing optical fiber ring (22).

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