A partial discharge detection system and method for a three-core submarine cable

Abstract

The present application relates to partial discharge detection technical field, disclose a kind of three-core submarine cable partial discharge detection system and method, its system is emitted by light source pulse light, after enhancement by optical amplifier, first coupler divides into two ways, two pulse lights are respectively polarized and delayed, two light paths are output to circulator by second coupler, and input to the optical fiber of three-core submarine cable to be detected, the backscattering light in the optical fiber of three-core submarine cable is output by circulator, and is divided into two ways by third coupler, and the backscattering light is respectively polarized and delayed, and the backscattering light of two ways is coupled to photodetector by fourth coupler and is converted into electrical signal by photoelectric conversion, partial discharge detection is carried out to electrical signal by signal processing module, and partial discharge detection result is obtained, by the above light path design, while improving sensitivity, reduce signal interference and misjudgment, improve the accuracy of partial discharge detection to submarine cable.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of partial discharge detection, and in particular to a three-core submarine cable partial discharge detection system and method. BACKGROUND

[0002] Submarine cables are expensive and difficult to maintain because they are laid on the seabed. If partial discharge occurs in a submarine cable, it is difficult to use the detection methods for land cables because the electromagnetic waves of partial discharge attenuate severely when they propagate to both ends of the submarine cable, which is much longer than a land cable.

[0003] Because submarine cables are mostly optical fiber composite submarine cables, the current method for monitoring the state of submarine cables is mainly through optical fiber sensing technology. Partial discharge produces effects such as sound, electricity, and heat. The heat produced by partial discharge is relatively weak, and the monitoring accuracy is not high. The vibration information detection advantage is more obvious.

[0004] Because partial discharge produces multiple effects, a single technical principle has its own applicability. For example, Brillouin is more sensitive to vibration, and Raman is more suitable for temperature monitoring.

[0005] Currently, the related art using the Raman principle is used for temperature detection. However, the heat generated by partial discharge is very small, and the submarine water flow provides a good heat dissipation environment. It is difficult for this technology to reflect partial discharge through temperature, and the detection equipment is relatively complex and the cost is high.

[0006] There are also methods for vibration detection using Rayleigh scattering principle. Rayleigh scattering is the strongest signal among the three principles, but single Rayleigh scattering is not the most sensitive to vibration, resulting in insufficient sensitivity and low accuracy of partial discharge detection. SUMMARY

[0007] The present application provides a three-core submarine cable partial discharge detection system and method, which solves the problem of insufficient sensitivity and low accuracy of partial discharge detection for submarine cables.

[0008] Therefore, the first aspect of the present application provides a three-core submarine cable partial discharge detection system, comprising: a light source, an optical amplifier, a first coupler, a polarizer, a first delay optical fiber, a second coupler, a circulator, a third coupler, a polarization analyzer, a second delay optical fiber, a fourth coupler, a photodetector, and a signal processing module.

[0009] The light source is used to emit pulsed light.

[0010] The optical amplifier is connected with the light source and is used to amplify the pulsed light.

[0011] The input end of the first coupler is connected with the optical amplifier, the output end of the first coupler is connected with the polarizer and the first delay optical fiber respectively, and the pulsed light is split and input into the polarizer and the first delay optical fiber respectively;

[0012] The polarizer and the first delay optical fiber are connected with the input end of the second coupler, the output end of the second coupler is connected with the first end of the circulator, the polarizer is used for inputting the polarized pulsed light into the second coupler, the first delay optical fiber is used for inputting the delay-processed pulsed light into the second coupler, and the second coupler is used for coupling the polarized pulsed light and the delay-processed pulsed light into the circulator;

[0013] The second end of the circulator is connected with the three-core submarine cable to be detected, the third end of the circulator is connected with the input end of the third coupler, and the circulator is used for inputting the coupled pulsed light into the three-core submarine cable to be detected, receiving backscattered light returned by the three-core submarine cable to be detected, and inputting the backscattered light into the third coupler;

[0014] The output end of the third coupler is connected with the depolarizer and the second delay optical fiber respectively, the depolarizer and the second delay optical fiber are connected with the input end of the fourth coupler, the output end of the fourth coupler is connected with the photodetector, the third coupler is used for inputting the backscattered light into the depolarizer and the second delay optical fiber after splitting, the depolarizer is used for inputting the depolarized backscattered light into the fourth coupler, the second delay optical fiber is used for inputting the delay-processed backscattered light into the fourth coupler, and the fourth coupler is used for coupling the depolarized backscattered light and the delay-processed backscattered light into the photodetector;

[0015] The photodetector is connected with the signal processing module, the photodetector is used for converting the coupled backscattered light into an electric signal through photoelectric conversion, and the signal processing module is used for performing partial discharge detection on the electric signal to obtain a partial discharge detection result.

[0016] Optionally, the polarizer and the analyzer are integrated on a POL type manual optical fiber polarization platform, the POL type manual optical fiber polarization platform comprising a base, a first support frame, a second support frame, a polarizing optical fiber joint, an analyzing optical fiber joint, a first adjusting gear, a second adjusting gear, a rotating mechanism and a fixing piece; the first support frame and the second support frame are both mounted on the base, the first support frame and the second support frame are respectively provided with the first adjusting gear and the second adjusting gear, the polarizing optical fiber joint is arranged on the first adjusting gear, the analyzing optical fiber joint is arranged on the second adjusting gear, the rotating mechanism is fixedly connected with the base through the fixing piece, and the first adjusting gear and the second adjusting gear are respectively meshed with the rotating mechanism.

[0017] Optionally, the rotating mechanism comprises a single-chip microcomputer control circuit, a stepping motor, a rotating gear and a driving gear, the single-chip microcomputer control circuit is electrically connected with the stepping motor, an output shaft of the stepping motor is connected with the driving gear, the driving gear is meshed with the rotating gear, and the rotating gear is meshed with the first adjusting gear and the second adjusting gear.

[0018] Optionally, the signal processing module comprises a data acquisition module, a denoising module, a waveform identification module, a feature quantity extraction module and a partial discharge detection module.

[0019] The data acquisition module is configured to acquire the electrical signal.

[0020] The denoising module is configured to perform wavelet denoising processing on the electrical signal to obtain a smooth curve.

[0021] The waveform identification module is configured to perform smoothing processing on the smooth curve by a moving window least square polynomial, acquire a window in which a maximum value of curve data and a minimum value of curve data are located as a start point and an end point of the curve, and thus obtain a signal waveform.

[0022] The feature quantity extraction module is configured to calculate a feature quantity of the signal waveform of each window, the feature quantity comprising an average value, a deviation and a maximum slope of the waveform, and calculate a relative deviation of each feature quantity relative to other feature quantities, and if the relative deviation of two feature quantities is greater than 50%, the corresponding window is determined as a singular window.

[0023] The partial discharge detection module is configured to acquire a number of singular windows of the signal waveform within a preset window width, and if the number of singular windows of the signal waveform within the preset window width exceeds a preset window number threshold, it is determined that partial discharge occurs in a corresponding time period.

[0024] In a second aspect, the present application provides a method for detecting partial discharge of a three-core submarine cable, which applies the three-core submarine cable partial discharge detection system described above, and the method comprises the following steps:

[0025] emitting pulsed light through a light source;

[0026] amplifying the pulsed light;

[0027] splitting the pulsed light, polarizing one of the pulsed light, delaying the other pulsed light, and coupling the polarized pulsed light and the delayed pulsed light;

[0028] inputting the coupled pulsed light into the three-core submarine cable to be detected, and receiving backscattered light returned by the three-core submarine cable to be detected;

[0029] splitting the backscattered light, detecting the polarization of one of the backscattered light, delaying the other backscattered light, and coupling the detected backscattered light and the delayed backscattered light;

[0030] photoelectrically converting the coupled backscattered light into an electrical signal;

[0031] detecting the electrical signal to obtain a partial discharge detection result.

[0032] Optionally, the step of detecting the electrical signal to obtain a partial discharge detection result specifically comprises the following steps:

[0033] collecting the electrical signal;

[0034] performing wavelet denoising processing on the electrical signal to obtain a smooth curve;

[0035] performing smoothing processing on the smooth curve through a moving window least square polynomial, taking the window in which the maximum value of the curve data and the minimum value of the curve data are located as the start point and the end point of the curve, thereby obtaining a signal waveform;

[0036] calculating the characteristic quantity of each window signal waveform, the characteristic quantity including the average value, the deviation, and the maximum slope of the waveform, calculating the relative deviation of each characteristic quantity relative to other characteristic quantities, and identifying the corresponding window as a singular window if the relative deviation of two characteristic quantities is greater than 50%;

[0037] obtaining the number of singular windows of the signal waveform within a preset window width, and identifying that a partial discharge occurs within a corresponding time period if the number of singular windows of the signal waveform within the preset window width exceeds a preset window number threshold.

[0038] From the above technical solution can be seen, the present application has the following advantages:

[0039] The present application emits pulsed light from the light source, enhances it through the optical amplifier, and divides the pulsed light into two paths through the first coupler, and the two paths of pulsed light are subjected to polarization and delay respectively, and the two light paths are output to the circulator through the second coupler and input to the optical fiber of the three-core submarine cable to be detected, the backscattered light in the optical fiber of the three-core submarine cable is output through the circulator and divided into two paths through the third coupler, and the backscattered light is subjected to polarization and delay respectively, and the two paths of backscattered light are coupled to the photodetector through the fourth coupler to be converted into electrical signals through photoelectric conversion, and the electrical signals are subjected to partial discharge detection through the signal processing module to obtain the partial discharge detection result, and the combination of ODTR and PODTR technologies through the above light path design improves the sensitivity, reduces signal interference and misjudgment, improves the accuracy of partial discharge detection of submarine cables, and can be applied to distributed optical fiber monitoring and positioning of submarine cable partial discharge. BRIEF DESCRIPTION OF DRAWINGS

[0040] Figure 1 A structure schematic diagram of a three-core submarine cable partial discharge detection system provided by the embodiment of the present application is provided.

[0041] Figure 2 A structure schematic diagram of a POL type manual optical fiber polarization platform provided by the embodiment of the present application is provided.

[0042] Figure 3 An optical polarization state schematic diagram provided by the embodiment of the present application is provided.

[0043] Figure 4 A flowchart of a three-core submarine cable partial discharge detection method provided by the embodiment of the present application is provided. DETAILED DESCRIPTION

[0044] In order for the personnel in the technical field to better understand the present application scheme, the technical solutions in the embodiments of the present application will be described clearly and completely below in combination with the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by the personnel in the field without creative labor are within the protection scope of the present application.

[0045] For the convenience of understanding, please refer to Figure 1 The three-core submarine cable partial discharge detection system provided by the present application comprises a light source 11, an optical amplifier 12, a first coupler 13, a polarizer 14, a first delay optical fiber 15, a second coupler 16, a circulator 17, a third coupler 19, a depolarizer 20, a second delay optical fiber 21, a fourth coupler 22, a photodetector 23, and a signal processing module 24.

[0046] The light source 11 is used to emit pulsed light;

[0047] The light source 11 is a pulsed laser source, and the pulsed light has a central wavelength of 1550 nm.

[0048] The optical amplifier 12 is connected with the light source 11, and is used to amplify the pulsed light;

[0049] The input end of the first coupler 13 is connected with the optical amplifier 12, and the output end of the first coupler 13 is respectively connected with the polarizer 14 and the first delay optical fiber 15, which are used to split the pulsed light and input the pulsed light into the polarizer 14 and the first delay optical fiber 15 respectively.

[0050] The polarizer 14 and the first delay optical fiber 15 are both connected with the input end of the second coupler 16, and the output end of the second coupler 16 is connected with the first end of the circulator 17. The polarizer 14 is used to input the pulsed light after the polarized into the second coupler 16, the first delay optical fiber 15 is used to input the pulsed light after the delay into the second coupler 16, and the second coupler 16 is used to couple the pulsed light after the polarization and the pulsed light after the delay into the circulator 17.

[0051] The second end of the circulator 17 is connected with the three-core submarine cable to be detected, and the third end of the circulator 17 is connected with the input end of the third coupler 19. The circulator 17 is used to input the coupled pulsed light into the three-core submarine cable 18 to be detected, and receive the backscattered light returned by the three-core submarine cable 18 to be detected, and input the backscattered light into the third coupler 19.

[0052] In the detection process, the light is divided into incident light and scattered light. The incident light is generated by the light source 11 and enters the optical fiber of the three-core submarine cable. In the submarine cable optical fiber, due to Rayleigh scattering, backscattered light is generated and output from the optical fiber port. The pulsed light generated by the light source 11 after the optical amplifier 12 is divided into two signals, one of which becomes a polarized light after passing through the polarizer 14, and the other passes through the delay processing. In this way, the two signals have a time difference and can be coupled in the same optical path. In this way, one light source 11 can generate two kinds of incident light.

[0053] It should be noted that since there are two states of incident light, corresponding scattered light will be generated. If direct photoelectric conversion and data collection are performed, it cannot be distinguished which kind of incident light generates the scattered light. Therefore, the scattered light needs to be processed, and the method is consistent with the processing of the incident light. The difference lies in that the polarizing detector 20 is used to extract a specific polarized light signal. In this way, two signals will be generated, one before and one after. In an example, two groups of four signals are given. The four signals are all light intensity curves with time, and the time length of each signal is the time T of the light propagating back and forth in the submarine cable optical fiber.

[0054] The polarization state of the polarization detector 20 is set to be consistent with that of the polarizer 14. When the incident light is polarized, the scattered light generated has a small attenuation after passing through the polarization detector 20, and has a small difference with the delay signal. When the incident light is pulsed, the scattered light generated has a serious attenuation after passing through the polarization detector 20, and has a large difference with the delay signal. The type of scattered light can be determined by comparing the differences between the two groups of signals.

[0055] In order to effectively distinguish different signals and avoid the interference of signal mixing, the two groups of delay fibers need to be reasonably set. The purpose of the second delay fiber 21 is to output the two groups of scattered light to a signal processing terminal respectively, so the time delay T2 of the second delay fiber 21 is set to be slightly longer than the signal time length. The purpose of the first delay fiber 15 is to generate two groups of scattered light signals and output them to a signal processing terminal, so the time delay T1 of the first delay fiber 15 is set to be slightly longer than twice the signal time length. Considering the signal interference and the processing speed of the sampling device, the time delays of the first delay fiber 15 and the second delay fiber 21 are set as follows:

[0056] T1 = 2T + T / 2

[0057] T2 = T + T / 4

[0058] The output end of the third coupler 19 is connected with the polarization detector 20 and the second delay fiber 21 respectively, the polarization detector 20 and the second delay fiber 21 are connected with the input end of the fourth coupler 22, and the output end of the fourth coupler 22 is connected with the photodetector 23. The third coupler 19 is used for splitting the backscattered light and inputting it into the polarization detector 20 and the second delay fiber 21, the polarization detector 20 is used for detecting the polarization of the backscattered light and inputting it into the fourth coupler 22, the second delay fiber 21 is used for delaying the backscattered light and inputting it into the fourth coupler 22, and the fourth coupler 22 is used for coupling the backscattered light after polarization and the backscattered light after delay to the photodetector 23.

[0059] The photodetector 23 is connected with the signal processing module 24, and the photodetector 23 is used for converting the coupled backscattered light into an electric signal through photoelectric conversion, and the signal processing module 24 is used for detecting the electric signal to obtain a partial discharge detection result.

[0060] It should be noted that the three-core submarine cable partial discharge detection system provided in the embodiment, through the light source emitting pulse light, after enhancement by the optical amplifier, the first coupler divides the pulse light into two paths, the two paths of pulse light are respectively subjected to polarization and delay, the two paths of light pass through the second coupler and are output to the circulator, and are input to the optical fiber of the three-core submarine cable to be detected, the backscattered light in the optical fiber of the three-core submarine cable is output through the circulator, and is divided into two paths through the third coupler, the backscattered light is respectively subjected to polarization and delay, and the two paths of backscattered light are coupled to the photodetector through the fourth coupler to be converted into electrical signals through photoelectric conversion, the electrical signals are subjected to partial discharge detection through the signal processing module, and a partial discharge detection result is obtained, through the above light path design combined with the ODTR and PODTR technologies, the sensitivity is improved, the signal interference and misjudgment are reduced, the accuracy of the partial discharge detection of the submarine cable is improved, and the distributed optical fiber monitoring and positioning of the partial discharge of the submarine cable can be applied.

[0061] In one specific embodiment, the polarizer and the analyzer are integrated on a POL type manual optical fiber polarization platform, as shown in Figure 2 The POL type manual optical fiber polarization platform includes a base 30, a first support frame 32, a second support frame 33, a polarized optical fiber joint 34, an analyzed optical fiber joint 35, a first adjusting gear 36, a second adjusting gear 37, a rotating mechanism 28 and a fixing piece 31; the first support frame 32 and the second support frame 33 are both mounted on the base 30, the first support frame 32 and the second support frame 33 are respectively provided with the first adjusting gear 36 and the second adjusting gear 37, the polarized optical fiber joint 34 is arranged on the first adjusting gear 36, the analyzed optical fiber joint 35 is arranged on the second adjusting gear 37, the rotating mechanism 38 is fixedly connected with the base 30 through the fixing piece 31, and the first adjusting gear 36 and the second adjusting gear 37 are respectively meshed with the rotating mechanism 38.

[0062] The rotating mechanism includes a single-chip microcomputer control circuit, a stepping motor, a rotating gear and a driving gear, the single-chip microcomputer control circuit is electrically connected with the stepping motor, the output shaft of the stepping motor is connected with the driving gear, the driving gear is meshed with the rotating gear, and the rotating gear is meshed with the first adjusting gear and the second adjusting gear.

[0063] It should be noted that since the partial discharge position, the discharge amount and the like are random, the influence of stress generated thereby on the optical fiber is also random, and if the polarization state of the incident light is fixed, a large amount of information will be lost. Therefore, the polarization state of the polarized light needs to be adjusted to generate a plurality of polarized light signals. The polarizer and the analyzer are both integrated on the POL type manual optical fiber polarization platform, and the rotating adjusting gear can be rotated by 360° to generate a plurality of polarization states.

[0064] The polarization state of light can be set by rotating the polarizer, and the polarization state of light is fixed in three cases in the present application, as shown in Figure 3 The three states are 0°, 120°, and -120°, assuming that the initial position is 0°, controlled by the rotating mechanism, then rotated to 120°, then rotated back to 0°, and then to -120°. Such a design can avoid the entanglement of optical fibers, and each adjustment is separated by a time T1.

[0065] In one embodiment, the signal processing module includes a data acquisition module, a denoising module, a waveform recognition module, a feature extraction module, and a partial discharge detection module.

[0066] The data acquisition module is used to acquire the electrical signal.

[0067] The denoising module is used to perform wavelet denoising processing on the electrical signal to obtain a smooth curve.

[0068] The wavelet denoising is used to filter out interference signals and noise signals in the electrical signal, and finally obtain relatively smooth data, i.e., the curve of light intensity versus time.

[0069] The waveform recognition module is used to perform smoothing processing on the smooth curve by a moving window least square polynomial to obtain the maximum value of the curve data and the minimum value of the curve data as the starting point and the ending point of the curve, thereby obtaining a signal waveform.

[0070] The curve of light intensity versus time is a decaying curve with a high front end and a low tail. The moving window least square polynomial smoothing is used to smooth the waveform, calculate the average value of the data in the moving window, and identify the window where the maximum value and the minimum value are located as the starting point and the ending point of the curve, thereby completing the recognition of a signal waveform. The width of the moving window is 1s.

[0071] The feature extraction module is used to calculate the feature quantity of each window of the signal waveform, including the average value, the deviation, and the maximum slope of the waveform. It is also used to calculate the relative deviation of each feature quantity relative to other feature quantities. If the relative deviation of two feature quantities is greater than 50%, the corresponding window is identified as a singular window.

[0072] The feature extraction module is used to calculate the feature quantity of each window of the signal waveform, including the average value, the deviation, and the maximum slope of the waveform. It is also used to calculate the relative deviation of each feature quantity relative to other feature quantities. If the relative deviation of two feature quantities is greater than 50%, the corresponding window is identified as a singular window.

[0073] The partial discharge detection module is configured to acquire a number of singular windows of a signal waveform in a preset window width, and determine that partial discharge occurs in a corresponding time period if the number of singular windows of the signal waveform in the preset window width exceeds a preset threshold of the number of windows.

[0074] In one example, four groups of waveforms are compared in terms of singular windows in a 3s time period with a window width of 3s. If singular windows exist in three or more waveforms, it is determined that partial discharge occurs in the time period.

[0075] The above is a detailed description of an embodiment of the three-core submarine cable partial discharge detection system provided by the application, and the following is a detailed description of an embodiment of a three-core submarine cable partial discharge detection method provided by the application.

[0076] For ease of understanding, please refer to Figure 4 A three-core submarine cable partial discharge detection method using the three-core submarine cable partial discharge detection system described above, the method comprising:

[0077] S1, emitting pulsed light by a light source;

[0078] S2, amplifying the pulsed light;

[0079] S3, splitting the pulsed light, polarizing one of the pulsed light, delaying the other pulsed light, and coupling the polarized pulsed light and the delayed pulsed light;

[0080] S4, inputting the coupled pulsed light into the three-core submarine cable to be detected, and receiving backscattered light returned by the three-core submarine cable to be detected;

[0081] S5, splitting the backscattered light, detecting the polarization of one of the backscattered light, delaying the other backscattered light, and coupling the detected backscattered light and the delayed backscattered light;

[0082] S6, photoelectrically converting the coupled backscattered light into an electrical signal;

[0083] S7, detecting the electrical signal to obtain a partial discharge detection result.

[0084] In one specific embodiment, step S7 specifically comprises:

[0085] S701, collecting the electrical signal;

[0086] S702, performing wavelet denoising processing on the electrical signal to obtain a smooth curve;

[0087] S703, the maximum value of the curve data and the minimum value of the curve data are obtained as the starting point and the ending point of the curve by smoothing the smooth curve through the moving window least square polynomial, so as to obtain a signal waveform;

[0088] S704, the characteristic quantity of the signal waveform of each window is calculated, the characteristic quantity includes the average value, the deviation and the maximum slope of the waveform, the relative deviation of each characteristic quantity relative to other characteristic quantities is calculated, if the relative deviation of two characteristic quantities is greater than 50%, the corresponding window is determined as a singular window;

[0089] S705, the number of singular windows of the signal waveform in the preset window width is obtained, if the number of singular windows of the signal waveform in the preset window width exceeds the preset window number threshold, it is determined that the partial discharge occurs in the corresponding period.

[0090] Those skilled in the art can clearly understand that, for the convenience and brevity of description, the specific process of the above-described method can refer to the corresponding process in the foregoing system embodiments, which will not be repeated here.

[0091] In several embodiments provided by the present application, it should be understood that the disclosed device and method can be implemented by other means. For example, the device embodiments described above are only schematic, for example, the division of units is only a logical function division, and actual implementation can have another division manner, for example, a plurality of units or components can be combined or integrated into another system, or some features can be ignored or not executed. In addition, the coupling or direct coupling or communication connection between the units shown or discussed can be indirect coupling or communication connection through some interface, device or unit, which can be electrical, mechanical or other forms.

[0092] The units described as separate components can or can not be physically separate, and the components shown as units can or can not be physical units, that is, they can be located in one place, or they can be distributed on a plurality of network units. According to actual needs, part or all of the units can be selected to achieve the purpose of the embodiment.

[0093] In addition, each functional unit in each embodiment of the present application can be integrated in a processing unit, or each unit can exist physically, or two or more units can be integrated in one unit. The integrated unit can be realized in the form of hardware or in the form of software functional unit.

[0094] The above examples are only used to illustrate the technical solutions of the present application, and are not intended to limit the present application; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that the technical solutions recorded in the foregoing examples can be modified, or some technical features can be replaced by equivalent features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A partial discharge detection system for a three-core submarine cable, characterized in that, The application relates to a three-core submarine cable partial discharge detection device. The device comprises a light source, an optical amplifier, a first coupler, a polarizer, a first delay optical fiber, a second coupler, a circulator, a third coupler, a polarization analyzer, a second delay optical fiber, a fourth coupler, a photodetector and a signal processing module. The light source is used for emitting pulse light. The optical amplifier is connected with the light source and is used for amplifying the pulse light. The input end of the first coupler is connected with the optical amplifier, and the output end of the first coupler is connected with the polarizer and the first delay optical fiber respectively, so as to split the pulse light and input the pulse light into the polarizer and the first delay optical fiber respectively. The polarizer and the first delay optical fiber are both connected with the input end of the second coupler, and the output end of the second coupler is connected with the first end of the circulator. The polarizer is used for inputting the polarized pulse light into the second coupler, the first delay optical fiber is used for inputting the delay-processed pulse light into the second coupler, and the second coupler is used for coupling the polarized pulse light and the delay-processed pulse light into the circulator. The second end of the circulator is connected with a three-core submarine cable to be detected, the third end of the circulator is connected with the input end of the third coupler, and the circulator is used for inputting the coupled pulse light into the three-core submarine cable to be detected and receiving backscattered light returned by the three-core submarine cable to be detected, and then inputting the backscattered light into the third coupler. The output end of the third coupler is connected with the polarization analyzer and the second delay optical fiber respectively, and the polarization analyzer and the second delay optical fiber are both connected with the input end of the fourth coupler. The output end of the fourth coupler is connected with the photodetector, the third coupler is used for splitting the backscattered light and inputting the backscattered light into the polarization analyzer and the second delay optical fiber, the polarization analyzer is used for inputting the polarization-processed backscattered light into the fourth coupler, the second delay optical fiber is used for inputting the delay-processed backscattered light into the fourth coupler, and the fourth coupler is used for coupling the polarization-processed backscattered light and the delay-processed backscattered light into the photodetector. The photodetector is connected with the signal processing module, the photodetector is used for photoelectrically converting the coupled backscattered light into an electric signal, and the signal processing module is used for performing partial discharge detection on the electric signal to obtain a partial discharge detection result. The signal processing module comprises a data acquisition module, a denoising module, a waveform identification module, a feature extraction module and a partial discharge detection module. The data acquisition module is used for acquiring the electric signal. The denoising module is used for performing wavelet denoising processing on the electric signal to obtain a smooth curve. The waveform identification module is used for performing smoothing processing on the smooth curve through a moving window least square polynomial, obtaining a window in which a maximum value of curve data and a minimum value of curve data are located as a starting point and an ending point of the curve, and thus obtaining a signal waveform. The feature quantity extraction module is configured to calculate feature quantities of a signal waveform of each window, the feature quantities including an average value, a deviation, and a maximum slope of a waveform, and to calculate a relative deviation of each feature quantity relative to other feature quantities, and if the relative deviation of two feature quantities is greater than 50%, the corresponding window is determined as a singular window. The partial discharge detection module is configured to acquire a number of singular windows of a signal waveform within a preset window width, and if the number of singular windows of the signal waveform within the preset window width exceeds a preset window number threshold, it is determined that partial discharge occurs in a corresponding time period.

2. The three-core submarine cable partial discharge detection system of claim 1, wherein, The polarizer and the analyzer are integrated on a POL type manual optical fiber polarization platform, the POL type manual optical fiber polarization platform comprises a base, a first support frame, a second support frame, a polarizing optical fiber joint, an analyzing optical fiber joint, a first adjusting gear, a second adjusting gear, a rotating mechanism and a fixing piece, the first support frame and the second support frame are both installed on the base, the first support frame and the second support frame are respectively provided with the first adjusting gear and the second adjusting gear, the polarizing optical fiber joint is arranged on the first adjusting gear, the analyzing optical fiber joint is arranged on the second adjusting gear, the rotating mechanism is fixedly connected with the base through the fixing piece, and the first adjusting gear and the second adjusting gear are respectively meshed with the rotating mechanism.

3. The three-core submarine cable partial discharge detection system of claim 2, wherein, The rotating mechanism comprises a single-chip microcomputer control circuit, a stepping motor, a rotating gear and a driving gear, the single-chip microcomputer control circuit is electrically connected with the stepping motor, an output shaft of the stepping motor is connected with the driving gear, the driving gear is meshed with the rotating gear, and the rotating gear is meshed with the first adjusting gear and the second adjusting gear.

4. A method for detecting partial discharge of a three-core submarine cable, using the partial discharge detection system for a three-core submarine cable according to any one of claims 1 to 3, characterized by, The method comprises: emitting pulsed light through a light source; amplifying the pulsed light; splitting the pulsed light, polarizing one of the pulsed light and delaying the other pulsed light, coupling the polarized pulsed light and the delayed pulsed light; inputting the coupled pulsed light into the three-core submarine cable to be detected, and receiving backscattered light returned by the three-core submarine cable to be detected; splitting the backscattered light, analyzing one of the backscattered light and delaying the other backscattered light, and coupling the analyzed backscattered light and the delayed backscattered light; photoelectrically converting the coupled backscattered light into an electrical signal; performing partial discharge detection on the electrical signal to obtain a partial discharge detection result, comprising: collecting the electrical signal; performing wavelet denoising processing on the electrical signal to obtain a smooth curve; performing smoothing processing on the smooth curve through a moving window least square polynomial to obtain a maximum value of the curve data and a minimum value of the curve data as a starting point and an ending point of the curve, thereby obtaining a signal waveform; The characteristic quantity of the signal waveform of each window is calculated, the characteristic quantity including mean value, deviation and maximum slope of the waveform, the relative deviation of each characteristic quantity relative to other characteristic quantities is calculated, and if the relative deviation of two characteristic quantities is greater than 50%, the corresponding window is determined as a singular window; The number of singular windows of the signal waveform within a preset window width is obtained, and if the number of singular windows of the signal waveform within the preset window width exceeds a preset window number threshold, it is determined that local discharge occurs in the corresponding period.

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