An OPGW optical cable lightning stroke monitoring system based on dynamic BOTDR

Abstract

The application provides an OPGW optical cable lightning stroke monitoring system based on a dynamic BOTDR, which comprises a laser, a polarization maintaining fiber coupler, a first electro-optic modulator, a first doped fiber amplifier, a first circulator, a wavelength division multiplexer, a Raman amplifier, a to-be-measured optical fiber, an arbitrary waveform generator, a second electro-optic modulator, a second circulator, an optical filter, a cross-polarization crystal, an electric pulse generator, a second doped fiber amplifier, a second coupler, a balanced detector, a filtering and detecting module and a data acquisition card. The application can more accurately capture the temperature change of the optical cable when the optical cable is struck by lightning, monitor the temperature transient response of the optical cable during the lightning stroke process, and further accurately monitor the lightning stroke event of the OPGW optical cable and perform lightning fault positioning by using the technology based on optical frequency scanning to replace the traditional sweep frequency technology to obtain the Brillouin spectrum.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of power transmission line monitoring, in particular to an OPGW optical cable lightning monitoring system based on dynamic BOTDR. BACKGROUND

[0002] As a ground wire and communication transmission medium of power system, optical fiber composite overhead ground wire (OPGW) plays an important role. Due to its ground wire attribute, it is inevitably subjected to lightning damage, which seriously threatens the safe and stable operation of the power grid. Research on the causes of power grid line tripping in China shows that 60% of the safety problems of power transmission lines are caused by lightning. When OPGW optical cable has a short circuit or lightning fault, a strong short circuit current will flow, causing the temperature of the optical cable to rise sharply, resulting in softening or deformation of the optical cable, affecting the physical and mechanical properties of the OPGW optical cable, and increasing the hidden danger of the optical cable. Therefore, it is of great significance to monitor OPGW optical cable lightning faults with effective measures to improve the reliability of the power grid and ensure the safety of the power grid.

[0003] Distributed optical fiber sensing technology uses the spare fiber core in OPGW optical cable to monitor its temperature, strain, vibration and other states. There is no need for power supply in the line, which solves the problem that traditional photoelectric sensors cannot be widely applied due to power supply, communication, installation and other problems. Distributed optical fiber sensing technology uses optical fiber as a sensing and transmission medium, which is inherently safe, resistant to electromagnetic interference, has no electromagnetic radiation, long sensing distance, no blind area, high resolution, fast response, easy installation and operation, etc. It is particularly suitable for monitoring power cables. Monitoring lightning with distributed optical fiber sensing technology is an effective method.

[0004] Currently, some scholars have used distributed Brillouin optical time domain reflectometer (BOTDR) and distributed Brillouin optical time domain analyzer (BOTDA) for lightning monitoring. However, the traditional Brillouin spectrum measurement process is equal-interval sampling, which requires scanning multiple optical frequencies and takes tens of minutes to half an hour to measure once. The main discharge of lightning exists for a very short time, and the traditional Brillouin sensing equipment is difficult to capture the temperature change at the lightning moment. Therefore, there is an urgent need for a solution that can quickly and accurately monitor OPGW optical cable lightning events. SUMMARY

[0005] The present application aims to provide an OPGW optical cable lightning monitoring system based on dynamic BOTDR to solve the above technical problems, so as to accurately monitor OPGW optical cable lightning events for lightning fault positioning.

[0006] In order to solve the above technical problems, the application provides an OPGW optical cable lightning monitoring system based on a dynamic BOTDR, which comprises a laser, a polarization maintaining fiber coupler, a first electro-optic modulator, a first doped fiber amplifier, a first circulator, a wavelength division multiplexer, a Raman amplifier, a to-be-tested optical fiber, an arbitrary waveform generator, a second electro-optic modulator, a second circulator, an optical filter, a cross-polarization crystal, an electric pulse generator, a second doped fiber amplifier, a second coupler, a balanced detector, a filtering and detecting module and a data acquisition card.

[0007] An optical signal output end of the laser is connected with an input end of the polarization maintaining fiber coupler, a first output end of the polarization maintaining fiber coupler is connected with an input end of the first electro-optic modulator, an electric pulse driving signal of the first electro-optic modulator is provided by a first channel of the arbitrary waveform generator, an output end of the first electro-optic modulator is connected with a first optical signal port of the first circulator through the first doped fiber amplifier, a second optical signal port of the first circulator is connected with a first port of the wavelength division multiplexer, a third optical signal port of the first circulator is connected with an input end of the second doped fiber amplifier, an optical signal output end of the Raman amplifier is connected with a second port of the wavelength division multiplexer, and a third port of the wavelength division multiplexer is connected with the to-be-tested optical fiber.

[0008] A second output end of the polarization maintaining fiber coupler is connected with an input end of the second electro-optic modulator, an electric pulse driving signal of the second electro-optic modulator is provided by a second channel of the arbitrary waveform generator, an output end of the second electro-optic modulator is connected with a first optical signal port of the second circulator, a second optical signal port of the second circulator is connected with the optical filter, a third port of the second circulator is connected with an input end of the cross-polarization crystal, a driving signal of the cross-polarization crystal is provided by the electric pulse generator, the arbitrary waveform generator is triggered by the electric pulse generator, an output end of the cross-polarization crystal and an output end of the second doped fiber amplifier are simultaneously connected with an input end of the second coupler, an output end of the second coupler is connected with an input end of the balanced detector, and an output end of the balanced detector is connected with an electric signal input end of the data acquisition card through the filtering and detecting module.

[0009] The OPGW optical cable lightning monitoring system based on the dynamic BOTDR acquires data through the data acquisition card to obtain a Brillouin gain spectrum of the to-be-tested optical fiber, and identifies a lightning event of the to-be-tested optical fiber based on the Brillouin gain spectrum.

[0010] Further, the OPGW optical cable lightning monitoring system based on the dynamic BOTDR is specifically used for: acquiring the Brillouin frequency shift of each position point of the optical fiber to be measured based on the Brillouin gain spectrum, converting the Brillouin frequency shift into temperature change information based on a preset linear relationship, and then identifying the lightning event of the optical fiber to be measured based on the temperature change information.

[0011] Further, the second coupler is a four-port coupler, the output end of the orthogonally polarized crystal and the output end of the second doped fiber amplifier are connected with two input ends of the second coupler respectively, two output ends of the second coupler are connected with two input ends of the balanced detector, and the output end of the balanced detector is connected with the electric signal input end of the data acquisition card through the filter and detection module.

[0012] Further, the coupling ratio of the polarization maintaining fiber coupler and the second coupler is 50:50.

[0013] Further, the laser is a distributed feedback fiber laser.

[0014] Further, the frequency of the balanced detector is 350 MHz.

[0015] Further, the center frequency of the optical filter is 300 MHz, and the bandwidth is 100 MHz.

[0016] Compared with the prior art, the present application has the following beneficial effects:

[0017] The present application provides an OPGW optical cable lightning monitoring system based on dynamic BOTDR, comprising a laser, a polarization maintaining fiber coupler, a first electro-optic modulator, a first doped fiber amplifier, a first circulator, a wavelength division multiplexer, a Raman amplifier, an optical fiber to be measured, an arbitrary waveform generator, a second electro-optic modulator, a second circulator, an optical filter, an orthogonally polarized crystal, an electric pulse generator, a second doped fiber amplifier, a second coupler, a balanced detector, a filter and detection module, and a data acquisition card. The present application uses the technology based on optical frequency scanning to replace the traditional frequency sweeping technology to obtain the Brillouin spectrum, so as to more accurately capture the temperature change when the optical cable is struck by lightning, monitor the optical cable temperature transient response during the lightning occurrence process, and then accurately monitor the lightning event of the OPGW optical cable and locate the lightning fault. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 is a structural schematic diagram of the OPGW optical cable lightning monitoring system based on dynamic BOTDR provided by the present application;

[0019] Figure 2is the connection schematic diagram of the OPGW optical cable lightning monitoring system based on the dynamic BOTDR and the OPGW optical cable provided by the application;

[0020] Figure 3 is the synchronization relationship schematic diagram between the pulse signal, the agile frequency modulation signal and the polarization switching signal provided by the application;

[0021] In the figure, the reference signs are as follows:

[0022] 1, laser; 2, polarization maintaining fiber coupler; 3, first electro-optical modulator; 4, first doped fiber amplifier; 5, first circulator; 6, wavelength division multiplexer; 7, Raman amplifier; 8, optical fiber to be measured; 9, arbitrary waveform generator; 10, second electro-optical modulator; 11, second circulator; 12, optical filter; 13, orthogonally polarized crystal; 14, electric pulse generator; 15, second doped fiber amplifier; 16, second coupler; 17, balanced detector; 18, filtering and detection module; 19, data acquisition card. DETAILED DESCRIPTION

[0023] The technical solutions in the embodiments of the application will be clearly and completely described below with reference to the drawings in the embodiments of the application. Obviously, the described embodiments are only part of the embodiments of the application, rather than all the embodiments of the application. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the application.

[0024] Please refer to Figure 1 The embodiment of the application provides an OPGW optical cable lightning monitoring system based on dynamic BOTDR, which comprises a laser 1, a polarization maintaining fiber coupler 2, a first electro-optical modulator 3, a first doped fiber amplifier 4, a first circulator 5, a wavelength division multiplexer 6, a Raman amplifier 7, an optical fiber to be measured 8, an arbitrary waveform generator 9, a second electro-optical modulator 10, a second circulator 11, an optical filter 12, an orthogonally polarized crystal 13, an electric pulse generator 14, a second doped fiber amplifier 15, a second coupler 16, a balanced detector 17, a filtering and detection module 18 and a data acquisition card 19.

[0025] The light signal output end of the laser 1 is connected with the input end of the polarization maintaining fiber coupler 2, the first output end of the polarization maintaining fiber coupler 2 is connected with the input end of the first electro-optical modulator 3, the electric pulse driving signal of the first electro-optical modulator 3 is provided by the first channel of the arbitrary waveform generator 9, the output end of the first electro-optical modulator 3 is connected with the first optical signal port of the first circulator 5 through the first doped fiber amplifier 4, the second optical signal port of the first circulator 5 is connected with the first port of the wavelength division multiplexer 6, the third optical signal port of the first circulator 5 is connected with the input end of the second doped fiber amplifier 15, the light signal output end of the Raman amplifier 7 is connected with the second port of the wavelength division multiplexer 6, and the third port of the wavelength division multiplexer 6 is connected with the to-be-measured optical fiber 8.

[0026] The second output end of the polarization maintaining fiber coupler 2 is connected with the input end of the second electro-optical modulator 10, the electric pulse driving signal of the second electro-optical modulator 10 is provided by the second channel of the arbitrary waveform generator 9, the output end of the second electro-optical modulator 10 is connected with the first optical signal port of the second circulator 11, the second optical signal port of the second circulator 11 is connected with the optical filter 12, the third port of the second circulator 11 is connected with the input end of the orthogonally polarized crystal 13, the driving signal of the orthogonally polarized crystal 13 is provided by the electric pulse generator 14, the arbitrary waveform generator 9 is triggered by the electric pulse generator 14, the output end of the orthogonally polarized crystal 13 and the output end of the second doped fiber amplifier 15 are simultaneously connected with the input end of the second coupler 16, the output end of the second coupler 16 is connected with the input end of the balanced detector 17, and the output end of the balanced detector 17 is connected with the electric signal input end of the data acquisition card 19 through the filtering and detection module 18.

[0027] The OPGW optical cable lightning strike monitoring system based on the dynamic BOTDR acquires data through the data acquisition card 19 to obtain the Brillouin gain spectrum of the to-be-measured optical fiber 8, and identifies the lightning strike event of the to-be-measured optical fiber 8 based on the Brillouin gain spectrum.

[0028] In the embodiment of the application, further, the OPGW optical cable lightning strike monitoring system based on the dynamic BOTDR is specifically used for: obtaining the Brillouin frequency shift of each position point of the to-be-measured optical fiber 8 based on the Brillouin gain spectrum, converting the Brillouin frequency shift into temperature change information based on a preset linear relationship, and then identifying the lightning strike event of the to-be-measured optical fiber 8 based on the temperature change information.

[0029] In the embodiment of the application, further, the second coupler 16 is a four-port coupler, the output end of the orthogonally polarized crystal 13 and the output end of the second doped fiber amplifier 15 are respectively connected with two input ends of the second coupler 16, two output ends of the second coupler 16 are connected with two input ends of the balanced detector 17, and the output end of the balanced detector 17 is connected with the electric signal input end of the data acquisition card 19 through the filtering and detection module 18.

[0030] In the embodiment of the present application, further, the coupling ratios of the polarization maintaining fiber coupler 2 and the second coupler 16 are both 50:50.

[0031] In the embodiment of the present application, further, the laser 1 is a distributed feedback fiber laser.

[0032] In the embodiment of the present application, further, the frequency of the balanced detector 17 is 350MHz.

[0033] In the embodiment of the present application, further, the center frequency of the optical filter 12 is 300MHz and the bandwidth is 100MHz.

[0034] Based on the above scheme, in order to better understand the OPGW optical cable lightning monitoring system based on dynamic BOTDR provided by the embodiment of the present application, the following is described in detail:

[0035] Please refer to Figure 2 , the OPGW optical cable lightning monitoring system based on dynamic BOTDR connects one spare fiber core of the OPGW optical cable through the fiber distribution frame by the jumper.

[0036] Please continue to refer to Figure 1 , the OPGW optical cable lightning monitoring system based on dynamic BOTDR, comprising a laser 1, a polarization maintaining fiber coupler 2, a first electro-optic modulator 3, a first doped fiber amplifier 4, a first circulator 5, a wavelength division multiplexer 6, a Raman amplifier 7, a fiber to be measured 8, an arbitrary waveform generator 9 (AWG), a second electro-optic modulator 10, a second circulator 11, an optical filter 12, a crossed polarization crystal 13, an electric pulse generator 14, a second doped fiber amplifier 15, a second coupler 16, a balanced detector 17, a filtering and detection module 18, and a data acquisition card 19.

[0037] The optical signal output end of the laser 1 is in communication with the input end of the polarization maintaining fiber coupler 2, the first path output of the polarization maintaining fiber coupler 2 is in communication with the input end of the first electro-optic modulator 3, the electric pulse driving signal of the first electro-optic modulator 3 is provided by the first channel of the arbitrary waveform generator 9, the output end of the first electro-optic modulator 3 is in communication with the first doped fiber amplifier 4, the output end of the first doped fiber amplifier 4 is in communication with the first optical signal port of the first circulator 5, the second optical signal port of the first circulator 5 is in communication with the first port of the wavelength division multiplexer 6; the optical signal output end of the Raman amplifier 7 is in communication with the second port of the wavelength division multiplexer 6, and the third port of the wavelength division multiplexer 6 is in communication with the fiber to be measured 8.

[0038] The second path output of the polarization maintaining fiber coupler 2 is in communication with the input end of the second electro-optical modulator 10, the electrical pulse driving signal of the second electro-optical modulator 10 is provided by the second channel of the arbitrary waveform generator 9, the output end of the second electro-optical modulator 10 is in communication with the first optical signal port of the second circulator 11, the second optical signal port of the second circulator 11 is in communication with the optical filter 12, the third port of the second circulator 11 is in communication with the orthogonally polarized crystal 13, the driving signal of the orthogonally polarized crystal 13 is provided by the pulse generator, at the same time the pulse generator triggers the arbitrary waveform generator 9, the output end of the orthogonally polarized crystal 13 is in communication with the output end of the second doped fiber amplifier 15, at the same time in communication with the two input ends of the second coupler 16, the two output ends of the second coupler 16 are in communication with the two input ends of the balanced detector 17, the output end of the balanced detector 17 is in communication with the input end of the filtering and detection module 18 (filter and detector), the output end of the filtering and detection module 18 is in communication with the electrical signal input end of the data acquisition card 19.

[0039] As shown in Figure 1 The dynamic BOTDR system is divided into upper and lower paths, the upper path generates pump pulse light, and the lower path generates reference light with optical frequency scanning. The laser 1 is a distributed feedback fiber laser 1 with a wavelength near 1550 nm. The light output by the laser 1 is divided into upper and lower paths by the polarization maintaining fiber coupler 2, the upper path (50%) light enters the first electro-optical modulator 3 to be modulated into a pulse sequence. The electrical pulse signal is provided by the first channel of the arbitrary waveform generator 9, and 100 electrical pulses constitute a sequence, as shown in Figure 3 The pulse sequence repetition frequency is 1 Hz. The pulse width is 20 ns, and the time interval between adjacent pulses is 2 μs. The pulse power is amplified by the first doped fiber amplifier 4, and the pulse light is further combined with the optical signal output by the Raman fiber amplifier after passing through the wavelength division multiplexer 6, and then injected into the measured optical fiber 8 through the first circulator 5, and then communicated with the input end of the second doped fiber amplifier 15 through the three-port output of the first circulator 5.

[0040] The 50% light of the lower path enters the second electro-optical modulator 10 to generate reference light signals with optical frequency scanning, and the AWG channel 2 outputs a 10.4 to 10.796 GHz microwave chirp signal with an amplitude correction and loads it onto the second electro-optical modulator 10. The microwave signal step is 4 MHz, and similarly 100 microwave frequencies each with a duration of 2 μs, ensuring that the scattered signal of each pulse is frequency-mixed with the corresponding reference light, and the synchronization relationship is as shown in Figure 3The Stokes light component in the spontaneous Brillouin scattering signal is extracted by using the optical filter 12, and the power fluctuation caused by polarization is removed by using the orthogonal polarization crystal 13 because the optical fiber in the OPGW optical cable is a single-mode optical fiber. The electric pulse generator 14 provides a driving signal for the orthogonal polarization crystal 13 to realize the orthogonal polarization switching between adjacent microwave sequences. The beat frequency between the reference light and the spontaneous Brillouin scattering signal is realized by the second coupler 16, and is detected by the 350MHz balanced detector 17. The signal-to-noise ratio is enhanced by 3dB through the difference between two channels.

[0041] The center frequency of the optical filter 12 is 300MHz, and the bandwidth is 100MHz.

[0042] The dynamic BOTDR system acquires the Brillouin gain spectrum through the data acquisition card 19, and obtains the Brillouin frequency shift at each position point by using a fitting method. Because the Brillouin frequency shift changes linearly with temperature and strain, the Brillouin frequency shift is converted into temperature by using formula (1).

[0043] Delta v B =C v,T Delta T+C v,ε Delta epsilon (1)

[0044] In the formula, delta v B is the change amount of the Brillouin frequency shift, C v,T and C v,ε are the temperature coefficient and the strain coefficient of the change of the Brillouin frequency shift respectively, and for ordinary single-mode optical fibers, the values are usually C v,T =1.12MHz / ℃ and C v,ε =0.0492MHz / με, delta T and delta epsilon are the temperature change amount and the strain change amount respectively, because the temperature change is mainly reflected in the lightning moment, delta epsilon is 0, the change of the Brillouin frequency shift is only related to temperature, and the dynamic temperature change is obtained by formula (1).

[0045] Because the lightning is a process of a dramatic temperature change in an instant, the temperature change amount of the temperature rise rate and the spatial domain lightning point temperature relative to the ordinary area temperature is used as a temperature characteristic value for measuring lightning, the temperature response is used to identify the lightning event and positioning.

[0046] It should be noted that the measurement speed of the embodiment of the application is fast, reaches the order of seconds, can more accurately capture the temperature change of the optical cable when lightning strikes, and the optical cable temperature transient response during the lightning occurrence process can be monitored by using the embodiment of the application. The early intervention due to lightning abnormality can be quickly responded by using the embodiment of the application, and the probability of failure occurrence is reduced.

[0047] It should be noted that, for the above embodiments, for the sake of simple description, they are all expressed as a series of action combinations, but those skilled in the art should know that the embodiments of the present application are not limited by the action sequence described, because according to the embodiments of the present application, certain steps can be performed in other sequences or simultaneously. Secondly, those skilled in the art should know that the embodiments described in the specification are all optional embodiments, and the actions involved are not necessarily required by the embodiments of the present application.

[0048] The above is the preferred embodiment of the present application. It should be noted that, for those skilled in the art, without departing from the principles of the present application, a number of improvements and refinements can be made, which are also considered within the scope of protection of the present application.

Claims

1. A lightning strike monitoring system for OPGW optical cables based on dynamic BOTDR, characterized in that, It includes a laser, a polarization-maintaining fiber coupler, a first electro-optic modulator, a first erbium-doped fiber amplifier, a first circulator, a wavelength division multiplexer, a Raman amplifier, an optical fiber under test, an arbitrary waveform generator, a second electro-optic modulator, a second circulator, an optical filter, an orthogonal polarization crystal, an electrical pulse generator, a second erbium-doped fiber amplifier, a second coupler, a balanced detector, a filtering and detection module, and a data acquisition card. The optical signal output terminal of the laser is connected to the input terminal of the polarization-maintaining fiber coupler. The first output terminal of the polarization-maintaining fiber coupler is connected to the input terminal of the first electro-optic modulator. The electrical pulse drive signal of the first electro-optic modulator is provided by the first channel of the arbitrary waveform generator. The output terminal of the first electro-optic modulator is connected to the first optical signal port of the first circulator through the first erbium-doped fiber amplifier. The second optical signal port of the first circulator is connected to the first port of the wavelength division multiplexer. The third optical signal port of the first circulator is connected to the input terminal of the second erbium-doped fiber amplifier. The optical signal output terminal of the Raman amplifier is connected to the second port of the wavelength division multiplexer. The third port of the wavelength division multiplexer is connected to the fiber under test. The second output of the polarization-maintaining fiber coupler is connected to the input of the second electro-optic modulator. The electro-pulse drive signal of the second electro-optic modulator is provided by the second channel of the arbitrary waveform generator. The output of the second electro-optic modulator is connected to the first optical signal port of the second circulator. The second optical signal port of the second circulator is connected to the optical filter. The third port of the second circulator is connected to the input of the orthogonal polarization crystal. The drive signal of the orthogonal polarization crystal is provided by the electro-pulse generator. The arbitrary waveform generator is triggered by the electro-pulse generator. The output of the orthogonal polarization crystal and the output of the second erbium-doped fiber amplifier are simultaneously connected to the input of the second coupler. The output of the second coupler is connected to the input of the balanced detector. The output of the balanced detector is connected to the electrical signal input of the data acquisition card through the filtering and detection module. The OPGW optical cable lightning strike monitoring system based on dynamic BOTDR collects data through the data acquisition card to obtain the Brillouin gain spectrum of the optical fiber under test, and identifies lightning strike events on the optical fiber under test based on the Brillouin gain spectrum. The OPGW optical cable lightning strike monitoring system based on dynamic BOTDR is specifically used for: obtaining the Brillouin frequency shift at each location point of the optical fiber under test based on the Brillouin gain spectrum, converting the Brillouin frequency shift into temperature change information based on a preset linear relationship, and then identifying lightning strike events on the optical fiber under test based on the temperature change information.

2. The OPGW optical cable lightning strike monitoring system based on dynamic BOTDR according to claim 1, characterized in that, The second coupler is a four-port coupler. The output of the orthogonal polarization crystal and the output of the second erbium-doped fiber amplifier are respectively connected to the two inputs of the second coupler. The two outputs of the second coupler are connected to the two inputs of the balanced detector. The output of the balanced detector is connected to the electrical signal input of the data acquisition card through the filtering and detection module.

3. The OPGW optical cable lightning strike monitoring system based on dynamic BOTDR according to claim 1, characterized in that, The coupling ratio of the polarization-maintaining fiber coupler and the second coupler is 50:

50.

4. The OPGW optical cable lightning strike monitoring system based on dynamic BOTDR according to claim 1, characterized in that, The laser is a distributed feedback fiber laser.

5. The OPGW optical cable lightning strike monitoring system based on dynamic BOTDR according to claim 1, characterized in that, The frequency of the balanced detector is 350MHz.

6. The OPGW optical cable lightning strike monitoring system based on dynamic BOTDR according to claim 1, characterized in that, The optical filter has a center frequency of 300MHz and a bandwidth of 100MHz.

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