OPGW optical cable lightning stroke positioning monitoring system and monitoring method based on distributed optical fiber sensing

Abstract

The invention discloses an OPGW optical cable lightning stroke positioning monitoring system and monitoring method based on distributed optical fiber sensing. Comprising a DFB laser, a first optical coupler, an acoustic optical modulator, a pulse signal generator, a scrambler, a first EDFA optical amplifier, a first optical isolator, an optical circulator, an FBG filter, an OPGW sensing optical cable, an electro-optical modulator, a microwave signal generator, a polarization regulator, a second EDFA optical amplifier, a second optical isolator, a second optical coupler and a variable optical attenuator which are connected in sequence. A third optical coupler, a balance detector, a low-frequency amplifier and a data processing module. The system can quickly and accurately position the lightning stroke position of the OPGW optical cable by measuring the Brillouin scattering frequency shift and the vibration state of the scattering signal.

Description

Technical Field

[0001] The invention relates to an OPGW optical cable lightning strike positioning monitoring system and a monitoring method based on distributed optical fiber sensing, and belongs to the technical field of optical fiber sensing and sensor network. Background Art

[0002] Optical Fiber Composite Overhead Ground Wire (OPGW) has the dual functions of communication and ground wire and is widely used in high-voltage overhead transmission lines above 220kV. Its operating status is related to the safety of high-voltage transmission lines and communication systems. In the process of power transmission, OPGW optical cables pass through various areas with complex terrain and harsh climate, which makes OPGW transmission lines susceptible to various damages such as line icing, overload, and lightning strike. Among them, lightning strike is the main cause of power transmission line failure in my country, and up to 60% of transmission line damage comes from lightning strike. When OPGW optical cable suffers from lightning strike failure, strong short-circuit current is generated in the transmission line in a short time, accompanied by a sharp rise in the temperature of the optical cable, causing the optical cable to soften, deform, or even carbonize, seriously affecting the physical and mechanical properties of the OPGW optical cable, and even causing power and data transmission service interruption. Therefore, adopting effective measures to monitor OPGW optical cable lightning strike failure in real time is of great significance to improving the reliability of the power grid and ensuring the safety of the power grid.

[0003] At present, electrical methods are widely used in power systems to locate lightning faults, such as the comprehensive lightning location method that combines the lightning strike position with the time difference for location, and the transmission line lightning location method based on the transmission line traveling wave theory. The former is greatly affected by climatic conditions and can only locate the lightning strike point when the circuit breaker trips; the latter's location accuracy is limited by factors such as line parameters, on-site operation mode, and uncertainty of traveling wave velocity, making it difficult to accurately locate. Therefore, both methods have great limitations in practical applications.

[0004] The optical detection method based on distributed fiber sensing (DOS) has the characteristics of long detection distance, high spatial resolution, rapid real-time response and anti-electromagnetic interference. More importantly, multiple redundant optical fibers have been pre-buried in the OPGW line, which provides convenient conditions for the implementation of distributed fiber sensing to detect lightning strikes on OPGW lines. Brillouin Optical Time-Domain Reflectometry (BOTDR) based on spontaneous Brillouin scattering can simultaneously provide long-distance, high-spatial-precision temperature and strain detection, and is widely used in real-time safety monitoring of large facilities such as power pipelines, mine bridges, etc. Brillouin scattering time-domain reflectometry technology senses the temperature and strain of the object being measured by measuring the frequency of the reflected signal (i.e., Brillouin frequency shift). When the OPGW line is struck by lightning, the temperature at the struck position rises sharply. Therefore, lightning monitoring and positioning can be performed by measuring the temperature at various positions on the OPGW line. However, the temperature change process at the lightning strike position is very fast, often shorter than the response cycle of the BOTDR system for temperature detection through frequency sweeping, resulting in fault omission. In addition, the BOTDR system has the problem of weak signal and low signal-to-noise ratio, which easily causes false alarms. Therefore, although there are schemes that try to locate lightning strikes on OPGW optical cables through BOTDR technology, how to improve the response speed of the system and reduce the missed alarm rate and false alarm rate is still a problem that needs to be solved urgently. Summary of the invention

[0005] In view of the problem that the existing spontaneous Brillouin scattering technology has slow response time and poor signal-to-noise ratio, and it is difficult to accurately and timely locate the lightning fault of the OPGW transmission line, the present invention proposes a technical solution based on the fusion of Brillouin scattering time domain analysis (BrillouinOptical Time-Domain Analysis, BOTDA) and polarization regulation, and simultaneously measures the polarization information generated by the temperature and vibration of the OPGW transmission line, and compares the two, thereby improving the response speed and spatial positioning accuracy of the system, and realizing the precise positioning of the lightning fault. On the one hand, the temperature change of the OPGW transmission line is sensed by measuring the Brillouin frequency shift. Since the BOTDA technology adopts stimulated Brillouin scattering, it has a higher signal-to-noise ratio and detection distance than the BOTDR technology, and is more suitable for detecting the instantaneous temperature change caused by lightning. On the other hand, the polarization state of the Brillouin scattering signal is measured. Since lightning strikes can cause local strain and violent vibration (generally more than 80Hz), its vibration frequency is much higher than the vibration frequency caused by breeze or temperature. The vibration of the OPGW optical fiber will change the change in the polarization of the Brillouin scattered light, so the lightning strike position can be located by detecting the high-frequency change of the optical power generated by the polarization change. In order to reduce the probability of missed reports and false alarms, the temperature information and vibration information are compared. If the two originate from the same position on the OPGW optical fiber, it means that the position has been struck by lightning. If the temperature signal does not change significantly due to the slow temperature response speed of the system, the lightning disaster can be preliminarily predicted by the vibration information, and further confirmed by the subsequent Brillouin frequency shift caused by the polarization mutation of the lightning strike point.

[0006] The present invention is achieved by adopting the following technical solutions:

[0007] An OPGW optical cable lightning strike location monitoring system based on distributed optical fiber sensing includes a DFB laser, a first optical coupler, an acousto-optic modulator, a pulse signal generator, a polarization scrambler, a first EDFA optical amplifier, a first optical isolator, an optical circulator, an FBG filter, an OPGW sensing optical cable, an electro-optic modulator, a microwave signal generator, a polarization regulator, a second EDFA optical amplifier, a second optical isolator, a second optical coupler, an adjustable optical attenuator, a third optical coupler, a balanced detector, a low-frequency amplifier and a data processing module.

[0008] The laser light generated by the DFB laser is divided into two transmission paths after passing through the first optical coupler.

[0009] The first output end of the first optical coupler is connected to the input end of the acousto-optic modulator, and the output waveform of the acousto-optic modulator is controlled by a pulse signal generator. The output end of the acousto-optic modulator is connected to the input end of the polarization scrambler. The output end of the polarization scrambler is connected to the input end of the first EDFA optical amplifier. The output end of the first EDFA optical amplifier is connected to the input end of the first optical isolator. The output end of the first optical isolator is connected to the first port of the optical circulator. The second port of the optical circulator is connected to the first port of the OPGW sensor optical cable.

[0010] The second output end of the first optical coupler is connected to the input end of the electro-optic modulator. The output of the electro-optic modulator is controlled by a microwave signal generator. The output end of the electro-optic modulator is connected to the input end of the polarization regulator. The output end of the polarization regulator is connected to the input end of the second EDFA optical amplifier. The output end of the second EDFA optical amplifier is connected to the input end of the second optical isolator. The output end of the second optical isolator is connected to the first port of the second optical coupler. The second port of the second optical coupler is connected to the second port of the OPGW sensor optical cable.

[0011] The third port of the optical circulator is connected to the input end of the FBG filter. The output end of the FBG filter is connected to the first input end of the third optical coupler.

[0012] The third port of the second optical coupler is connected to the input end of the adjustable optical attenuator. The output end of the adjustable optical attenuator is connected to the second input end of the third optical coupler.

[0013] The output end of the third optical coupler is connected to the input end of the balanced detector. The output end of the balanced detector is connected to the input end of the low-frequency amplifier. The output end of the low-frequency amplifier is connected to the data processing module.

[0014] Furthermore, the DFB laser emits continuous laser light with a central wavelength of 1550.12 nm and a line width ranging from 500 KHz to 1 MGHz.

[0015] Furthermore, the coupling ratio of the first optical coupler is 90%:10%.

[0016] Furthermore, the coupling ratio of the second optical coupler is 50%:50%.

[0017] Furthermore, the coupling ratio of the third optical coupler is 50%:50%.

[0018] Furthermore, the 3dB bandwidth of the FBG filter is 0.1nm, that is, 12GHz.

[0019] Furthermore, the frequency of the balanced detector is 300 MHz.

[0020] Furthermore, the polarization regulator can rotate the polarization state of the incident light by 90° under the control of the control signal of the data processing module, and the switching speed is 60ms.

[0021] The system obtains the distance from the suspected lightning strike location to the detection location through the transit time of the scattered signal. The frequency shift and optical power of the Brillouin scattering signal are measured respectively. The Brillouin frequency shift is obtained by beating the reference light with the stimulated Brillouin scattered light, and performing a frequency scan on the beat signal to obtain the power distribution at different frequencies, i.e., the Brillouin frequency shift spectrum. The temperature change of the suspected struck location on the optical cable is calculated by the Brillouin frequency shift spectrum. The polarization rotation angle of the polarization regulator is alternately set to 0° and 90°, and the power change of the scattered signal emitted from the suspected struck location on the OPGW optical cable over time is recorded, i.e., the optical power signal caused by the lightning vibration is measured, and the vibration frequency is obtained by fast Fourier transform. The temperature change and the vibration frequency are compared to determine whether the OPGW optical cable is struck by lightning. If there is a high probability of being struck by lightning, the system will issue an early warning.

[0022] Beneficial effects of the present invention:

[0023] (1) The Brillouin scattering measurement system disclosed in the present invention uses temperature measurement and vibration measurement to determine the lightning strike position of the OPGW optical cable, which improves the measurement accuracy of the system compared to monitoring the lightning strike status through the measurement of a single parameter.

[0024] (2) The measurement of both temperature and vibration parameters is based on scattered Brillouin signals, and the system structure is compact and simple. Common temperature and vibration measurements are based on Brillouin scattering and Rayleigh scattering, respectively. The two scattering systems have different working wavelengths, so it is necessary to integrate the two scattering systems together, which makes the system complex and increases the uncertainty of the measurement.

[0025] (3) The system uses BOTDA technology instead of the existing commonly used BOTDR technology for measurement, which greatly improves the detection signal-to-noise ratio and measurement distance. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a structural schematic diagram of an embodiment.

[0027] Figure 2 Schematic diagram of the polarization state and voltage control timing of the polarization modulator.

[0028] Markings in the figure: 1-DFB laser, 2-first optical coupler, 3-acousto-optic modulator, 4-pulse signal generator, 5-polarization scrambler, 6-first EDFA optical amplifier, 7-first optical isolator, 8-optical circulator, 9-FBG filter, 10-OPGW sensor cable, 11-electro-optic modulator, 12-microwave signal generator, 13-polarization regulator, 14-second EDFA optical amplifier, 15-second optical isolator, 16-second optical coupler, 17-adjustable optical attenuator, 18-third optical coupler, 19-balanced detector, 20-low-frequency amplifier, 21-data processing module. DETAILED DESCRIPTION

[0029] The present invention will be further described below in conjunction with the accompanying drawings.

[0030] An OPGW optical cable lightning strike location monitoring system based on distributed optical fiber sensing, such as Figure 1 As shown, the system includes a DFB laser 1, a first optical coupler 2, an acousto-optic modulator 3, a pulse signal generator 4, a polarization scrambler 5, a first EDFA optical amplifier 6, a first optical isolator 7, an optical circulator 8, a FBG filter 9, an OPGW sensor optical cable 10, an electro-optic modulator 11, a microwave signal generator 12, a polarization adjuster 13, a second EDFA optical amplifier 14, a second optical isolator 15, a second optical coupler 16, an adjustable optical attenuator 17, a third optical coupler 18, a balanced detector 19, a low-frequency amplifier 20 and a data processing module 21.

[0031] according to Figure 1 The monitoring system shown, the monitoring method and process of the present invention are as follows:

[0032] The DFB laser 1 generates a narrow linewidth continuous laser with a wavelength of 1550.12nm, which is divided into two paths through the first optical coupler 2. The first path of laser light is used as pump light to generate stimulated Brillouin scattering signals; the second path of laser light is used as reference light and detection light at the same time to detect stimulated Brillouin scattering signals. The power ratio of the two paths of laser light is 90%:10%.

[0033] The first laser beam is emitted from the first output end of the first optical coupler 2 and enters the acousto-optic modulator 3. The acousto-optic modulator 3 modulates the continuous laser beam into a pulse laser beam, and its pulse width and waveform are controlled by the pulse signal generator 4. The laser beam emitted from the laser acousto-optic modulator 3 enters the polarization scrambler 5 to suppress the depolarization noise, and then enters the first EDFA optical amplifier 6 for power amplification. The output end of the first EDFA optical amplifier 6 is connected to the first optical isolator 7 to eliminate the reflected laser beam in the optical path. The laser beam is emitted from the first optical isolator 7, passes through the optical circulator 8, and enters the first port of the OPGW sensor optical cable, thereby exciting and generating a Brillouin scattering signal in the OPGW optical fiber.

[0034] The second laser beam is emitted from the second output end of the first optical coupler 2 and enters the electro-optic modulator 11. Since the electro-optic modulator 11 is loaded with the microwave modulation signal emitted by the microwave signal generator 12, the laser beam emitted from the electro-optic modulator 11 undergoes sideband modulation, and its center frequency changes, and the frequency shift is equal to the Brillouin frequency shift loaded by the microwave signal generator. The modulated laser beam passes through the polarization adjuster 13 to tune the polarization state. The polarization modulation process is as follows: Figure 2 As shown: the polarization state of the outgoing light is changed by applying modulation voltages of different amplitudes to the polarization adjuster 13. When a high level is applied, the outgoing light passing through the polarization adjuster 13 has polarization in the direction of E1; when a low level is applied, the polarization direction of the outgoing light is deflected by 90° and has polarization in the direction of E2. The reference light E1 and the reference light E2, whose polarization directions are perpendicular to each other, have the following amplitudes respectively:

[0035]

[0036] Where P x is the normalized component of the E1 light amplitude in the x direction, P y is the normalized component of the E1 light amplitude in the y direction. The two satisfy Parameter A is the amplitude of the reference light, f loc is the local oscillator frequency of the reference light, is the phase of the reference light, t is the time variable, Represent the x and y direction vectors respectively. When the system performs measurement, high and low levels are applied alternately, so that the polarization state of the reference light changes alternately over time. The reference light laser after polarization modulation 13 enters the second EDFA optical amplifier 14, amplifies the optical power, and then enters the second optical coupler 16 through the second optical isolator 15. The laser is emitted from the second optical coupler 16 and is divided into two beams with a coupling ratio of 50%:50%. The first beam of light (to the right) enters the adjustable optical attenuator 17, and its light intensity is appropriately attenuated. The second beam of light is emitted from the second port of the second optical coupler 16 and enters the second port of the OPGW sensor optical cable as the detection light (upward). This light beam has the same frequency as the Brillouin scattered light generated by the first pump light in the OPGW optical cable, so interference superposition occurs to form stimulated Brillouin scattered light. Compared with the spontaneous Brillouin scattering of the BOTDR system, the stimulated Brillouin scattered light has a significantly increased signal intensity, thereby greatly improving the signal-to-noise ratio of the Brillouin scattered light.

[0037] The reversely transmitted Brillouin scattered light in the OPGW optical cable enters the second port of the optical circulator 8 and exits from the third port. The exiting light contains not only Brillouin scattered light, but also detection light, Rayleigh scattered light and noise of other frequencies. The FBG filter 9 filters out the unnecessary stray light and only allows the Brillouin scattered light to pass. The amplitude of the Brillouin scattered light is:

[0038]

[0039] Where P bx is the normalized amplitude of stimulated Brillouin scattered light along the x direction, P by is the normalized amplitude of the stimulated Brillouin scattered light along the y direction. The two satisfy Parameter B is the amplitude of the stimulated Brillouin scattered light, f b is the frequency of the Brillouin scattered light, is the phase of the Brillouin scattered light. The Brillouin scattered light is incident on the first input end of the third optical coupler 18 and is mixed with the reference light entering the second input end of the third optical coupler 18. By changing the light attenuation rate of the adjustable optical attenuator 17, the two beams of light entering the third optical coupler 18 have the same power. The power of the two beams of light after mixing is measured by the balanced detector 19, and the signal is amplified by the low-frequency amplifier 20 and then sent to the data processing module 21.

[0040] The measurement and processing process of the signal data by the data processing module 21 is as follows:

[0041] The first step is to set the polarization regulator 13 to work at a high level and the continuous sampling time is 1s. At this time, the reference light E1 and the Brillouin scattered light are mixed to obtain the light intensity I1 of the mixed signal:

[0042]

[0043] Step 2: Set the polarization regulator 13 to work at a low level, and the continuous sampling time is 1s. At this time, the reference light E2 is mixed with the Brillouin scattered light to obtain the light intensity I2 of the mixed signal:

[0044]

[0045] Step 3: Calculate and record I1, I2 and I b =I1+I2, where I b It is a polarization-independent Brillouin mixing signal, and its amplitude is proportional to the Brillouin scattering signal incident to the first input end of the third optical coupler 18.

[0046] I b =I1+I2=4AB

[0047] Step 4: Measure the next frequency point within the sweep range and repeat steps 1 to 3.

[0048] The frequency shift curve of the stimulated Brillouin signal is measured through the above-mentioned frequency sweep process, and the light intensity change signals I1 and I2 containing polarization information are obtained at the same time. When a certain part of the OPGW optical cable is struck by lightning, the temperature at that location undergoes a significant change, and the optical cable vibrates at a high frequency, causing the polarization of the scattered light to change periodically. The polarization change information induced by the vibration is encoded into the phase terms of I1 and I2. , thereby changing the light intensities I1 and I2.

[0049] The deflected damaged position is obtained by measuring the transit time (Δt) of the scattered signal, that is, L = Δt × c / (2n). In the formula, L is the distance between the damaged position and the detection position, c is the speed of light, and n is the refractive index of the optical fiber at the laser wavelength. The generated stimulated Brillouin signal simultaneously undergoes frequency shift and optical power (I b ) changes. The temperature (ΔT) change can be obtained through the Brillouin frequency shift (Δf) to obtain ΔT = Δf × C, where C is the temperature sensitivity coefficient of the OPGW optical cable. b The transient change of (t) is fast Fourier transformed to obtain the vibration frequency. Since the optical power measurement of the scattered signal is a time domain measurement of a fixed position, the time required is much faster than the frequency sweeping process of the Brillouin scattering spectrum, and the vibration state of the optical fiber can be monitored in real time. If the abnormal temperature position on the OPGW optical cable is consistent with the vibration position, and the temperature change and vibration frequency are drastic, there is a high probability that the position has been struck by lightning, and the system will issue a lightning strike warning.

[0050] The monitoring system of the embodiment of the present invention can be arranged at different positions of the optical cable according to actual needs to realize distributed, long-distance real-time monitoring.

[0051] The series of detailed descriptions listed above are only specific descriptions of feasible implementation methods of the present invention. They are not intended to limit the scope of protection of the present invention. All equivalent methods or changes that do not deviate from the technical creation of the present invention should be included in the scope of protection of the present invention.

Claims

1. An OPGW optical cable lightning strike location monitoring system based on distributed optical fiber sensing, characterized in that: The invention comprises a DFB laser (1), a first optical coupler (2), an acousto-optic modulator (3), a pulse signal generator (4), a polarization scrambler (5), a first EDFA optical amplifier (6), a first optical isolator (7), an optical circulator (8), an FBG filter (9), an OPGW sensor optical cable (10), an electro-optic modulator (11), a microwave signal generator (12), a polarization regulator (13), a second EDFA optical amplifier (14), a second optical isolator (15), a second optical coupler (16), an adjustable optical attenuator (17), a third optical coupler (18), a balanced detector (19), a low-frequency amplifier (20) and a data processing module (21); The laser light generated by the DFB laser (1) is divided into two transmission paths after passing through the first optical coupler (2); the specific two-path transmission paths are as follows: The first output end of the first optical coupler (2) is connected to the input end of the acousto-optic modulator (3), the output waveform of the acousto-optic modulator (3) is controlled by a pulse signal generator (4), the output end of the acousto-optic modulator (3) is connected to the input end of the polarization scrambler (5), the output end of the polarization scrambler (5) is connected to the input end of the first EDFA optical amplifier (6), the output end of the first EDFA optical amplifier (6) is connected to the input end of the first optical isolator (7), the output end of the first optical isolator (7) is connected to the first port of the optical circulator (8), and the second port of the optical circulator (8) is connected to the first port of the OPGW sensor optical cable (10); The second output end of the first optical coupler (2) is connected to the input end of the electro-optic modulator (11), the output of the electro-optic modulator (11) is controlled by a microwave signal generator, the output end of the electro-optic modulator (11) is connected to the input end of the polarization adjuster (13), the output end of the polarization adjuster (13) is connected to the input end of the second EDFA optical amplifier (14), the output end of the second EDFA optical amplifier (14) is connected to the input end of the second optical isolator (15), the output end of the second optical isolator (15) is connected to the first port of the second optical coupler (16), and the second port of the second optical coupler (16) is connected to the second port of the OPGW sensor optical cable (10); The third port of the optical circulator (8) is connected to the input end of the FBG filter (9), and the output end of the FBG filter (9) is connected to the first input end of the third optical coupler (18); The third port of the second optical coupler (16) is connected to the input end of the adjustable optical attenuator (17), and the output end of the adjustable optical attenuator (17) is connected to the second input end of the third optical coupler (18); The output end of the third optical coupler (18) is connected to the input end of the balanced detector (19), the output end of the balanced detector (19) is connected to the input end of the low-frequency amplifier (20), and the output end of the low-frequency amplifier (20) is connected to the data processing module (21); The data processing module (21) obtains the distance between the suspected lightning strike location and the monitoring location through the transit time of the scattered signal according to the received signal, and then respectively measures the frequency shift and optical power of the Brillouin scattering signal, wherein the Brillouin frequency shift is obtained by beating the reference light with the stimulated Brillouin scattered light, and performing frequency scanning on the beat signal to obtain the power distribution at different frequencies, that is, to obtain the Brillouin frequency shift spectrum, and then calculates the temperature change of the suspected lightning strike location on the optical cable through the Brillouin frequency shift spectrum; the polarization rotation angle of the polarization adjuster (3) is alternately set to 0° and 90°, and the power change of the scattered signal emitted from the suspected lightning strike location on the OPGW optical cable (10) over time is recorded, that is, the optical power signal caused by the lightning strike vibration is measured, and the vibration frequency is obtained by fast Fourier transforming the signal; the temperature change and the vibration frequency are compared to determine whether the OPGW optical cable is struck by lightning, and an early warning is issued.

2. The OPGW optical cable lightning strike location monitoring system based on distributed optical fiber sensing according to claim 1 is characterized in that: The DFB laser (1) emits continuous laser light with a central wavelength of 1550.12 nm and a line width ranging from 500 KHz to 1 MGHz.

3. The OPGW optical cable lightning strike location monitoring system based on distributed optical fiber sensing according to claim 1 is characterized in that: The coupling ratio of the first optical coupler (2) is 90%:10%, the coupling ratio of the second optical coupler (16) is 50%:50%, and the coupling ratio of the third optical coupler (18) is 50%:50%.

4. The OPGW optical cable lightning strike location monitoring system based on distributed optical fiber sensing according to claim 1 is characterized in that: The 3dB bandwidth of the FBG filter (9) is 0.1nm, i.e. 12GHz.

5. The OPGW optical cable lightning strike location monitoring system based on distributed optical fiber sensing according to claim 1 is characterized in that: The frequency of the balanced detector (19) is 300 MHz.

6. The OPGW optical cable lightning strike location monitoring system based on distributed optical fiber sensing according to claim 1 is characterized in that: The polarization regulator (13) can rotate the polarization state of the incident light by 90 degrees under the control of the control signal of the data processing module, and the switching speed is 60 ms.

7. The monitoring method of the OPGW optical cable lightning strike location monitoring system based on distributed optical fiber sensing according to claim 1 is characterized in that: The distance from the suspected lightning strike location to the monitoring system is obtained through the transit time of the scattered signal, and the frequency shift and optical power of the Brillouin scattering signal are measured respectively. The Brillouin frequency shift is obtained by beating the reference light with the stimulated Brillouin scattered light, and the power distribution at different frequencies is obtained by frequency scanning the beat signal, that is, the Brillouin frequency shift spectrum. The temperature change of the suspected lightning strike location on the optical cable is then calculated through the Brillouin frequency shift spectrum. The polarization rotation angle of the polarization regulator is alternately set to 0° and 90°, and the power change of the scattered signal emitted from the suspected struck location on the OPGW optical cable over time is recorded, that is, the optical power signal caused by the lightning vibration is measured, and the vibration frequency is obtained by fast Fourier transform. The temperature change and vibration frequency are compared to determine whether the OPGW optical cable is struck by lightning, and an early warning is issued.

8. The monitoring method according to claim 7, characterized in that: The specific monitoring process is as follows: S1, a narrow line width continuous laser with a wavelength of 1550.12 nm is generated by a DFB laser (1), and is divided into two paths after passing through a first optical coupler (2): the first path of laser light is used as pump light for generating stimulated Brillouin scattering signals; the second path of laser light is used as reference light and detection light for detecting stimulated Brillouin scattering signals, and the power ratio of the first path of laser light to the second path of laser light is 90%:10%; S2, a first path of laser light is emitted from a first output end of a first optical coupler (2) and enters an acousto-optic modulator (3). The acousto-optic modulator (3) modulates a continuous laser light into a pulsed laser light, and its pulse width and waveform are controlled by a pulse signal generator (4). The laser light emitted from the laser acousto-optic modulator (3) enters a polarization scrambler (5) to suppress depolarization noise, and then enters a first EDFA optical amplifier (6) for power amplification. The output end of the first EDFA optical amplifier (6) is connected to a first optical isolator (7) to eliminate reflected laser light in the optical path. The laser light is emitted from the first optical isolator (7), passes through an optical circulator (8), and enters a first port of an OPGW optical cable (10), thereby exciting and generating a Brillouin scattering signal in the OPGW optical fiber (10); S3, the second laser beam is emitted from the second output end of the first optical coupler (2) and enters the electro-optic modulator (11). The microwave modulation signal emitted by the microwave signal generator (12) loaded on the electro-optic modulator (11) causes the laser beam emitted from the electro-optic modulator (11) to undergo sideband modulation, and the center frequency thereof is changed. The frequency shift is equal to the Brillouin frequency shift loaded by the microwave signal generator. The modulated laser beam passes through the polarization regulator (13) to tune the polarization state. The polarization modulation process is as follows: the polarization state of the emitted light is changed by applying modulation voltages of different amplitudes to the polarization regulator (13). When a high level is applied, the emitted light passing through the polarization regulator 13 has polarization in the direction of E1; and when a low level is applied, the polarization direction of the emitted light is deflected by 90° and has polarization in the direction of E2. The directions E1 and E2 are two directions perpendicular to each other. The reference light E1 and the reference light E2, whose polarization directions are perpendicular to each other, respectively have the following amplitudes: Where P x is the normalized component of the E1 light amplitude in the x direction, P y is the normalized component of the E1 light amplitude in the y direction, and the two satisfy Parameter A is the amplitude of the reference light, f loc is the local oscillator frequency of the reference light, is the phase of the reference light, t is the time variable; High and low levels are alternately applied to the polarization modulator (13) so that the polarization state of the reference light changes alternately with time. The reference light laser after passing through the polarization modulator (13) enters the second EDFA optical amplifier (14) to amplify the optical power, and then enters the second optical coupler (16) through the second optical isolator (15). The laser is emitted from the second optical coupler (16) and is divided into two beams with a coupling ratio of 50%:50%. The first beam enters the adjustable optical attenuator (17) and its light intensity is attenuated. The second beam is emitted from the second port of the second optical coupler (16) and enters the second port of the OPGW optical cable (10) as detection light. The light beam has the same frequency as the Brillouin scattered light signal generated by the first pump light in the OPGW optical cable (10), and interference superposition occurs to form stimulated Brillouin scattered light. The reversely transmitted Brillouin scattered light in the OPGW optical cable (10) enters the second port of the optical circulator (8) and is emitted from the third port. The emitted light contains both Brillouin scattered light and detection light, Rayleigh scattered light and noise of other frequencies. The unnecessary stray light is filtered out by the FBG filter (9), and only the Brillouin scattered light is allowed to pass. At this time, the amplitude of the Brillouin scattered light is: Where P bx is the normalized amplitude of stimulated Brillouin scattered light along the x direction, P by is the normalized amplitude of stimulated Brillouin scattered light along the y direction, and the two satisfy Parameter B is the amplitude of the stimulated Brillouin scattered light, f b is the frequency of the Brillouin scattered light, is the phase of the Brillouin scattered light; The Brillouin scattered light is incident on the first input end of the third optical coupler (18) and is mixed with the reference light entering the second input end of the third optical coupler (18). By changing the light attenuation rate of the adjustable optical attenuator (17), the two beams of light entering the third optical coupler (18) have the same power. The power of the two beams of light after mixing is measured by a balanced detector (19), and the signal is amplified by a low-frequency amplifier (20) and then sent to a data processing module (21). The data processing module calculates the temperature change and the vibration change based on the input signal, and sends a warning signal when the temperature and vibration are abnormal.

9. The monitoring method according to claim 8, characterized in that: The working process of the data processing module (21) is as follows: The first step is to set the polarization regulator (13) to work at a high level, and the continuous sampling time is 1s. At this time, the reference light E1 and the Brillouin scattered light are mixed to obtain the light intensity I1 of the mixed signal: Step 2: Set the polarization regulator (13) to work at a low level, and keep sampling for 1 second. At this time, the reference light E2 is mixed with the Brillouin scattered light to obtain the intensity I2 of the mixed signal: Step 3: Calculate and record I1, I2 and I respectively b =I1+I2, where I b is the power of the polarization-independent Brillouin mixing signal, whose amplitude is proportional to the Brillouin scattering signal incident to the first input end of the third optical coupler 18; I b =I1+I2=4AB Step 4: Measure the next frequency point within the sweep range and repeat steps 1 to 3; Step 5: The frequency shift curve of the stimulated Brillouin signal is measured through the frequency sweep process, and the light intensity change signals I1 and I2 containing polarization information are obtained at the same time. When a certain part of the OPGW optical cable is struck by lightning, the temperature at that location undergoes a significant change, and the optical cable vibrates at high frequency, causing the polarization of the scattered light to change periodically. The polarization change information induced by the vibration is encoded into the phase terms of I1 and I2. In this way, the light intensities I1 and I2 are changed; The damaged position is obtained by measuring the transit time (Δt) of the scattered signal, i.e., L = Δt × c / (2n), where L is the distance between the damaged position and the detection position, c is the speed of light, and n is the refractive index of the optical fiber at the laser wavelength; According to the generated stimulated Brillouin signal, the frequency shift and optical power (I b ) changes, the temperature (ΔT) change can be obtained through the Brillouin frequency shift (Δf) to obtain ΔT = Δf × C, where C is the temperature sensitivity coefficient of the OPGW optical cable; for the optical power I b Perform fast Fourier transform on the transient changes to obtain the vibration frequency; If the abnormal temperature position on the OPGW optical cable is consistent with the vibration position, and the temperature change and vibration frequency are both severe, it is judged that there is a high probability that the position has been struck by lightning, and a lightning strike warning is issued at this time.

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