Double-end optical lightning stroke positioning method and system applied to power aerial optical cable

Abstract

The invention provides a double-end optical lightning stroke positioning method and system applied to an electric power aerial optical cable, and relates to the technical field of optical fiber sensing. The basic principle of positioning is that single-end lightning stroke positioning is realized on the basis that the polarization state of an optical signal is obviously changed after the optical signal encounters lightning stroke, a single-end lightning stroke positioning point is detected by using oppositely transmitted pulse polarized light, and then a double-end positioning equation set is established to solve an actual lightning stroke positioning point, so that accurate lightning stroke positioning is realized; according to the invention, lightning stroke positioning is realized based on the polarized light time domain reflectometer by using the Faraday optical rotation effect of lightning stroke on the optical signal, and compared with the traditional lightning stroke positioning, the operation and maintenance cost is low, the precision is high, wide-area precise time synchronization is not needed, the system is simple, the installation is convenient, and the blind area of lightning stroke positioning is reduced.

Description

Technical Field

[0001] The present invention relates to the field of optical fiber sensing technology, and more specifically, to a double-ended optical lightning strike location method and system applied to an overhead power optical cable. Background Art

[0002] At present, there are three main methods for locating lightning strikes on power overhead optical cables: the single-ended loopback method, the double-ended method based on continuous light polarization state detection, and the single-ended polarized light time domain reflectometry method.

[0003] 1) The single-ended loopback method estimates the lightning strike location through the time difference between the polarization state changes of the continuous optical signal in the power overhead optical cable when it is struck twice. Its main advantage is that it does not require wide-area time synchronization and has a low deployment cost. Its main disadvantage is that there is a measurement blind spot. To shorten the measurement blind spot, a delayed optical fiber must be introduced at the loopback point, which shortens the measurement distance.

[0004] 2) The two-end method based on continuous light polarization state detection uses two independent optical fibers in the power overhead optical cable to synchronously transmit two continuous optical signals respectively. There are optical receivers and optical transmitters at both ends of the optical fiber. The time difference between the polarization state changes caused by lightning strikes during the two measurements is used to determine the lightning strike location. Its main advantage is that there is no measurement blind spot and the measurement distance is long; its main disadvantage is that it requires wide-area time synchronization, and the deployment cost is doubled compared to the single-ended loopback method.

[0005] 3) The single-ended polarized light time domain reflectometry method uses the light transmitting and receiving devices at the same end of the optical fiber to transmit pulsed polarized light and receive the Rayleigh scattered light reflected from various places of the optical fiber. By detecting the change in the polarization state of the Rayleigh scattered light at each point, the location where the polarization state changes suddenly due to the lightning strike is found, thereby realizing the location of the lightning strike. Its main advantage is that it does not require wide-area time synchronization and has low operating and maintenance costs; its main disadvantage is that the measurement distance is short.

[0006] Currently, there is no solution in the lightning strike location method based on power overhead optical cables that can achieve no measurement blind spots, long measurement distance and low operation and maintenance costs without the need for wide-area time synchronization. Summary of the invention

[0007] In view of the defects of the prior art, the purpose of the present invention is to provide a double-end lightning strike location method and system applied to power overhead optical cables, aiming to achieve lightning strike location applied to power overhead optical cables with no measurement blind spots, long measurement distance and low deployment cost without the need for wide-area time synchronization.

[0008] In order to solve the above technical problems, the technical solution of the present invention is as follows:

[0009] A double-ended optical lightning strike location method applied to an overhead power optical cable, wherein the overhead power optical cable comprises a plurality of optical fibers, comprising the following steps:

[0010] Inputting the first pulsed polarized light into the first optical fiber at one end of the power overhead optical cable for transmission;

[0011] After a certain period of time has passed since the first pulsed polarized light was emitted, the second pulsed polarized light is input into the second optical fiber at the other end of the power overhead optical cable for transmission;

[0012] A set of pulsed polarized light signals for double-end detection is formed by the first and second oppositely transmitted pulsed polarized light signals;

[0013] A strong magnetic field is formed around the overhead power optical cable struck by lightning, and the first and second pulsed polarized lights respectively undergo polarization state rotation due to the Faraday rotation effect when transmitting through the optical cable struck by lightning;

[0014] The polarization states of the Rayleigh scattered light corresponding to the first and second pulsed polarized light are detected at the transmitting ends of the first and second optical fibers respectively, and the time domain reflection curves of the first and second polarized light are constructed respectively, and the positions of the mutation points of the polarization states of the Rayleigh scattered light corresponding to the first and second pulsed polarized light are obtained respectively, so as to realize the single-end lightning strike point positioning respectively;

[0015] A double-end positioning equation group is established using the emission time of the first and second pulse polarized lights, the moment of sudden change in polarization state of Rayleigh scattered light, and the sudden change position. The double-end positioning equation group is solved to obtain the actual lightning strike positioning point, thereby achieving accurate lightning strike positioning.

[0016] Preferably, when the first pulsed polarized light reaches the end of the first optical fiber, the third pulsed polarized light is input into the third optical fiber at the other end of the power aerial optical cable for transmission;

[0017] When the second pulsed polarized light reaches the end of the second optical fiber, the fourth pulsed polarized light is input into the fourth optical fiber at one end of the power overhead optical cable for transmission;

[0018] The third and fourth counter-transmitted pulse polarized light signals constitute the next group of pulse polarized light signals for double-end detection, ensuring that pulse polarized light Rayleigh scattered light signals always exist everywhere in the power overhead optical cable, thereby achieving real-time and accurate lightning strike positioning and avoiding the occurrence of measurement blind spots.

[0019] Preferably, it is assumed that at time t0, the first pulsed polarized light enters the power overhead optical cable from the first optical fiber for transmission, and at time t, the Rayleigh scattered light signal is received at the transmitting end of the first optical fiber. Calculate the position of the Rayleigh scattering point corresponding to the Rayleigh scattering light signal, where L t is the distance between the Rayleigh scattering point corresponding to the received signal and the transmitting end of the pulse polarized light, and v is the speed of the pulse polarized light in the optical fiber;

[0020] Assume that the lightning strike occurs at a position L0 away from the first optical fiber transmitting end, and the total length of the optical fiber is L. At this time, the first pulse polarized light arrives at a position L1' away from the first optical fiber transmitting end. At time t1, the first optical fiber incident end receives the Rayleigh scattered light signal whose polarization state is affected by the magnetic field generated by the lightning strike. According to Calculate the position of the single-ended lightning strike point detected by the first pulse polarized light, where L1 is the distance between the single-ended detection lightning strike point of the first pulse polarized light and the first optical fiber transmitting end; at time t2, the second pulse polarized light enters the power overhead optical cable from the second optical fiber and transmits in the opposite direction to the first pulse polarized light. At this time, the second pulse polarized light arrives at a distance of L2' from the second optical fiber transmitting end. At time t3, the second optical fiber incident end receives the Rayleigh scattered light signal whose polarization state is affected by the magnetic field generated by the lightning strike. According to The position of the single-ended lightning strike point detected by the second pulse polarized light is calculated, where L2 is the distance between the single-ended detected lightning strike point of the second pulse polarized light and the second optical fiber emitting end.

[0021] Preferably, if the positions of the single-ended lightning strike points detected by the two oppositely transmitted pulse polarized lights coincide, the actual lightning strike location point L0 is L0=L1 or L0=L2;

[0022] If the positions of the single-end lightning strike points detected by the two oppositely transmitted pulse polarized lights do not overlap, the following double-end positioning equations are established:

[0023]

[0024] Wherein, Δt is the emission time difference between the first and second pulsed polarized light signals, Δt=t2-t0; c is the speed of light in vacuum, and n is the refractive index of the optical fiber core;

[0025] The double-terminal positioning equation group is solved to obtain the actual lightning strike positioning point L0, thereby achieving accurate lightning strike positioning.

[0026] Preferably, when L1+L2=L, the positions of the single-ended lightning strike points detected by the two oppositely transmitted pulse polarized lights coincide with each other;

[0027] When L1+L2>L, the positions of the single-ended lightning strike points detected by the two oppositely transmitted pulse polarized lights do not overlap.

[0028] The present invention also provides a double-ended optical lightning strike location system for power overhead optical cables, comprising:

[0029] The first to fourth pulse polarized light generating modules are used to generate first to fourth pulse polarized lights respectively and input the first to fourth optical fibers correspondingly;

[0030] The first to fourth polarization state detection modules are used to detect the polarization states of the first to fourth pulsed polarized light Rayleigh scattered light, respectively, and find the position of the polarization state mutation of the polarized light time domain reflection curve to realize the single-end lightning strike point positioning;

[0031] First to fourth circulators, each of the pulse polarized light generating modules is connected to the first end of the corresponding circulator, the second end of the circulator is connected to the corresponding optical fiber in the power overhead optical cable, and the third end of the circulator is connected to the corresponding polarization state detection module;

[0032] The first and second trigger modules are respectively used to generate a trigger signal when the current pulse polarized light is transmitted to the end of the optical fiber, so as to trigger the emission of the pulse polarized light transmitted in the opposite direction of the current pulse polarized light.

[0033] Preferably, each of the pulse polarized light modules comprises a pulse laser and a polarization controller, and the pulse light generated by the pulse laser is converted into pulse polarized light after passing through the polarization controller.

[0034] Preferably, each of the polarization state detection modules comprises a polarization state detection device, a Rayleigh scattering photoelectric detector and a signal processor connected in sequence, after the polarization state detection device detects the Rayleigh scattered light, it is converted into an electrical signal of the Rayleigh scattered light by the Rayleigh scattering photoelectric detector and transmitted to the signal processor, and the signal processor processes the electrical signal of the Rayleigh scattered light to obtain a POTDR curve;

[0035] The single-end lightning strike point is located by using the polarization state mutation point on the POTDR curve, and the precise lightning strike location is achieved by solving the double-end positioning equation using the polarization state mutation point detected by two pulse polarized lights transmitted in opposite directions.

[0036] Preferably, each of the trigger modules comprises a pulse polarization photodetector and a trigger circuit, wherein the pulse polarization photodetector is used to detect an electrical signal generated by pulse polarization light;

[0037] The electrical signal generated by the pulse polarized light is transmitted to the pulse polarized light generating module to be emitted pulse polarized light via the trigger circuit, and the pulse polarized light generating module is controlled by the trigger circuit to emit pulse polarized light.

[0038] Preferably, one detection cycle includes two pulsed polarized lights transmitted in opposite directions, and the detection cycle T is Wherein, L is the total length of the optical fiber, n is the refractive index of the optical fiber core, c is the speed of light in a vacuum, and Δt is the emission time difference between a set of oppositely transmitted pulsed polarized light signals;

[0039] The total length L of the optical fiber in the system satisfies Among them, τ is the relaxation time of the magnetic field formed by lightning strike.

[0040] In the invented system, when the first pulsed polarized light reaches the end of the first optical fiber, the first pulsed polarized light photodetector receives the first pulsed polarized light signal and transmits a first trigger signal to the third pulsed laser, and after receiving the first trigger signal, the third pulsed laser transmits a third pulsed polarized light in the same direction as the second pulsed polarized light to the third optical fiber;

[0041] When the second pulsed polarized light reaches the end of the second optical fiber, the second pulsed polarized light photodetector receives the second pulsed polarized light signal and transmits a second trigger signal to the fourth pulsed laser. After receiving the second trigger signal, the fourth pulsed laser transmits a fourth pulsed polarized light to the fourth optical fiber in the same direction as the first pulsed polarized light.

[0042] When the third and fourth pulsed polarized lights are transmitted to the third and fourth optical fiber ends respectively, the first and second pulsed lasers just enter the next detection cycle and re-emit the next set of first and second pulsed polarized lights respectively;

[0043] Four optical fibers and four sets of POTDR transceiver equipment are detected cyclically in the above manner, thereby ensuring that two oppositely transmitted pulsed polarized light signals exist simultaneously in the power overhead optical cable, and that all parts of the optical cable are covered by the Rayleigh scattered light of the detection light pulse, thereby achieving accurate lightning strike positioning of the power overhead optical cable.

[0044] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0045] The present invention provides a double-end optical lightning strike location method and system applied to power overhead optical cables. The basic principle of the double-end lightning strike location technology applied to power overhead optical cables in power systems provided by the present invention is to realize single-end lightning strike location based on the obvious change of polarization state of optical signals after being struck by lightning, and to detect single-end lightning strike location points by using oppositely transmitted pulsed polarized light to establish a double-end location equation group to solve the actual lightning strike location points, thereby realizing accurate lightning strike location.

[0046] The present invention has the following beneficial effects:

[0047] 1) Compared with the traditional single-ended loop-back lightning strike location method, the double-ended lightning strike location method and system of the present invention have no measurement blind spots and higher measurement accuracy; the reason why the single-ended loop-back lightning strike location method has a blind spot is that when the lightning strike point is close to the loop-back point, the time difference between the two polarization state changes may be too small, resulting in the two being almost overlapped in the time domain and unable to be distinguished. The double-ended lightning strike location method based on POTDR in the present invention realizes lightning strike location based on Rayleigh scattered light at various locations in the optical fiber, and its spatial resolution can reach one meter, which far exceeds the lightning strike location accuracy requirement, and there is no need to use the time difference between the two polarization state changes for lightning strike location, so the measurement accuracy is high and there is no measurement blind spot.

[0048] 2) Compared with the double-end lightning strike location method based on continuous light polarization state detection, the lightning strike location method and system of the present invention do not require wide-area time synchronization, and have low operation and maintenance costs; in the double-end lightning strike location method based on POTDR of the present invention, pulsed polarized light is emitted at a certain interval through a trigger circuit control, and the emission time interval of two pulsed polarized lights emitted from the opposite end depends on the response time of the trigger circuit, which is a fixed value. Therefore, it is not necessary to ensure time synchronization every time the two ends emit light signals as in the double-end method based on continuous light polarization state detection, so that the time difference of the polarization state change received at the two ends can be used to locate the lightning strike, and the operation and maintenance cost of ensuring that the two transmitting ends maintain time synchronization is very high. Therefore, from the perspective of not requiring wide-area time synchronization, the double-end POTDR lightning strike location method of the present invention has low operation and maintenance costs, and is convenient for large-scale promotion and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 This is a schematic diagram of OPGW composition.

[0050] Figure 2 This is a schematic diagram of the OPGW structure.

[0051] Figure 3 Schematic diagram of the Faraday rotation effect principle.

[0052] Figure 4 Schematic diagram of OTDR Rayleigh scattering principle.

[0053] Figure 5 Schematic diagram of the structure of a typical polarized light time domain reflection system.

[0054] Figure 6 The present invention is a schematic structural diagram of a double-ended optical lightning location system for use in an overhead power optical cable according to an embodiment of the present invention.

[0055] Figure 7 The present invention is a flowchart of a method for locating a lightning strike applied to an overhead power optical cable provided in one embodiment of the present invention.

[0056] Figure 8 To correct the lightning current waveform.

[0057] Fig. 9 The double-end lightning strike location situation where the polarization state mutation points obtained by detecting two oppositely transmitted pulse polarized lights coincide with each other.

[0058] Fig.10 The double-end lightning strike location situation where the polarization state mutation points obtained by detecting two oppositely transmitted pulse polarized lights do not overlap.

[0059] 111, 121, 131 and 141 - the first, second, third and fourth pulsed lasers; 112, 122, 132 and 142 - the first, second, third and fourth polarization controllers; 211, 221, 231 and 241 - the first, second, third and fourth polarization state detection devices; 212, 222, 232 and 242 - the first, second, third and fourth Rayleigh scattering photodetectors; 213, 223, 233 and 243 - the first, second, third and fourth signal processors; 31 to 34 - the first to fourth circulators; 411 and 421 - the first and second pulsed polarization photodetectors; 412 and 422 - the first and second trigger circuits; 51 to 54 - the first to fourth optical fibers. DETAILED DESCRIPTION

[0060] The drawings are for illustrative purposes only and should not be construed as limiting the present patent;

[0061] In order to better illustrate the present embodiment, some parts in the drawings may be omitted, enlarged or reduced, and do not represent the size of the actual product;

[0062] It is understandable to those skilled in the art that some well-known structures and their descriptions may be omitted in the drawings.

[0063] The technical solution of the present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0064] Taking the power overhead ground wire composite optical cable (OPGW) as an example, the structure and composition of the power overhead optical cable are introduced; Figure 1 As shown in Figure 1, the structure of OPGW is mainly composed of an optical unit and a ground line unit; Figure 2 As shown in the figure, the optical unit is composed of a stainless steel or aluminum protective tube and the optical fiber therein. The optical fiber generally has a surplus length (i.e., the optical fiber length is slightly longer than the protective tube) to prevent the protective tube from being gradually stretched mechanically during long-term operation, causing the optical fiber to be stressed and broken. Fiber paste is filled between the protective tube and the optical fiber to play a waterproof role. The ground wire unit is made of spirally twisted aluminum-clad steel wires, and grease is filled between the aluminum-clad steel wires. The main function of the aluminum-clad steel wire is to act as a conductor for grounding protection and attract lightning strikes to avoid direct lightning strikes on the transmission phase line.

[0065] Under the action of a magnetic field, a substance that does not have optical activity also develops optical activity, which can cause the light vector to rotate. That is, when light passes through a medium that does not have optical activity under the action of a magnetic field, the vibration plane of the light will rotate. This phenomenon is called the Faraday effect. Figure 3 As shown. The angle θ of the light vector rotation is related to the distance L that the light travels in the medium. B And it is proportional to the magnetic induction intensity B, and its calculation formula is as follows:

[0066] θ=VBL B(1)

[0067] Among them, V is called the Verdet constant, which is a characteristic constant of the material and determines the magneto-optical properties of the material. The positive or negative value of the Verdet constant depends on the type of material. When light passes through the material, if the Verdet constant is positive, the light vector will rotate clockwise; if the Verdet constant is negative, the light vector will rotate counterclockwise. For standard single-mode optical fiber, the Verdet constant at a wavelength of 1550nm at room temperature is about 0.53rad / (T·m).

[0068] The optical time domain reflection signal mainly obeys the Rayleigh scattering principle. Figure 4 As shown in the figure, the main cause of Rayleigh scattering is the non-uniformity of the optical fiber itself, which is an elastic scattering. The frequency of the scattered light of Rayleigh scattering is equal to the frequency of the incident signal light, and Rayleigh scattering itself will not cause a sudden change in the polarization state of the light. Positioning based on the relationship between the propagation time and distance of the scattered light is the most basic positioning principle of distributed optical fiber sensing based on optical time domain reflectometry technology.

[0069] If the light pulse propagates at a speed of v in the optical fiber, let the time of emitting the light pulse be 0. After a period of time t, the receiver just receives the Rayleigh scattered signal from point z (the distance between point z and the origin of the light pulse is z / 2). z can be represented by v and t as shown below:

[0070]

[0071] Where c is the speed of light in a vacuum and n is the refractive index of the fiber core.

[0072] Light will lose energy when propagating in an optical fiber. The total loss of the Rayleigh scattered signal from point z (compared to when the light pulse was just sent out) is:

[0073] P(z)=P0e -αz (3)

[0074] Where P0 is the initial optical power when the optical pulse is injected into the fiber, and α is the loss coefficient of the optical fiber. For a pulse light with a pulse width of T, the backscattered Rayleigh light power near point z is PB(z) as shown in the following formula:

[0075]

[0076] Among them, α R is the Rayleigh scattering coefficient of the optical fiber, β R is the backscatter coefficient.

[0077] The structural principle diagram of the polarization time domain reflectometer is as follows Figure 5As shown, the pulse laser emits a pulse light signal, which becomes polarized pulse light after passing through the polarizer. The polarized pulse light generates an optical time domain reflection signal while propagating along the optical fiber. The optical circulator collects the optical time domain reflection signal and sends it to the analyzer. The analyzer converts the change of the polarization state of the light into the change of the optical power. The detector completes the photoelectric conversion, and then completes the positioning of the change of the polarization state of the optical time domain reflection signal through signal processing.

[0078] In one embodiment of the present invention, see Figure 6 The system of the present invention is based on Figure 6 The system in the paper proposes a double-end lightning location method for power overhead optical cables, such as Figure 7 As shown; the method comprises the following steps:

[0079] Step 1: The first pulsed polarized light is emitted from the first optical fiber 51 at the left end of the power overhead optical cable, enters the first optical fiber 51 through the first circulator 31 and is transmitted from left to right;

[0080] The second pulsed polarized light is emitted from the second optical fiber 52 at the right end of the power overhead optical cable after a certain time interval, enters the second optical fiber 52 through the second circulator 32 and is transmitted from right to left.

[0081] Step 2: When the first pulse polarized light reaches the end of the first optical fiber 51, it is received by the first pulse polarization photodetector 411 and sends out a first trigger signal. When the second pulse polarized light reaches the end of the second optical fiber 52, it is received by the second pulse polarization photodetector 421 and sends out a second trigger signal.

[0082] Step 3: The first trigger signal triggers the third pulsed polarized light to be emitted from the third optical fiber 53 at the right end of the power overhead optical cable, and enters the third optical fiber 53 through the third circulator 33 and is transmitted from right to left;

[0083] The second trigger signal triggers the fourth pulsed polarized light to be emitted from the fourth optical fiber 54 at the left end of the power aerial optical cable, and enters the fourth optical fiber 54 through the fourth circulator 34 and is transmitted from left to right.

[0084] Step 4: After the third and fourth pulsed polarized lights reach the third and fourth optical fiber endpoints respectively, the next detection cycle is entered and steps 1 to 4 are executed again.

[0085] By repeating the above steps in a cycle, high-precision double-end lightning strike positioning can be achieved.

[0086] In the system of this embodiment, when the first pulsed polarized light reaches the end of the first optical fiber 51, the first pulsed polarized light photodetector 411 receives the first pulsed polarized light signal and transmits a first trigger signal to the third pulsed laser 131. After receiving the first trigger signal, the third pulsed laser 131 transmits a third pulsed polarized light in the same direction as the second pulsed polarized light to the third optical fiber 53.

[0087] When the second pulsed polarized light reaches the end of the second optical fiber 52, the second pulsed polarized light photodetector 421 receives the second pulsed polarized light signal and transmits a second trigger signal to the fourth pulsed laser 141. After receiving the second trigger signal, the fourth pulsed laser 141 transmits a fourth pulsed polarized light in the same direction as the first pulsed polarized light to the fourth optical fiber 54.

[0088] When the third and fourth pulsed polarized lights are transmitted to the ends of the third and fourth optical fibers 53 and 54, respectively, the first and second pulsed lasers 111 and 121 just enter the next detection cycle and re-emit the next set of first and second pulsed polarized lights, respectively;

[0089] Four optical fibers and four sets of POTDR transceiver equipment are detected cyclically in the above manner, thereby ensuring that two oppositely transmitted pulsed polarized light signals exist simultaneously in the power overhead optical cable, and that all parts of the optical cable are covered by the Rayleigh scattered light of the detection light pulse, thereby achieving accurate lightning strike positioning of the power overhead optical cable.

[0090] A lightning current passes through the ground wire of a section of overhead optical cable that has been struck by lightning. The lightning current forms a strong magnetic field around the section of optical cable. The strong magnetic field causes the polarization state of the detection pulse polarized light to rotate due to the Faraday rotation effect when it passes through the section of optical cable. The light signal output by the polarization state detection device is collected by the Rayleigh scattering photoelectric detector. According to Malus's law, the photoelectric detector detects the change in light intensity and calculates the polarization change of the light signal caused by the lightning strike. The polarization state mutation point caused by the Faraday effect of the lightning strike is found on the four POTDR curves obtained from the detection of the four pulse polarized light signals, and the positions of the polarization state mutation points L1 and L2 detected by the two adjacent oppositely transmitted pulse polarized lights and the total sensing distance L are determined.

[0091] If L1+L2>L, a double-end lightning strike location equation group is established to solve the actual lightning strike point to achieve accurate lightning strike location; if L1+L2=L, the position of the polarization state mutation point detected by the two oppositely transmitted pulse polarized lights is the actual lightning strike point.

[0092] The following is a detailed description of a double-end lightning strike location method for power overhead optical cables proposed by the present invention.

[0093] The present invention uses a double exponential function model of lightning current to illustrate the characteristics of lightning current waveform, and its expression is as follows:

[0094]

[0095] Where I0 represents the peak current, τ1 and τ2 represent the wave head and wave tail time constants respectively. represents the peak current correction factor. Under this model, It is the moment when the lightning current reaches its peak value, and its time domain waveform is as follows Figure 8 shown.

[0096] A section of overhead optical cable struck by lightning can be approximated by a powered solenoid model. The relationship between the magnetic field formed by the lightning current near the section of the cable and the lightning current is expressed as follows:

[0097] B=μNI (6)

[0098] Due to the Faraday rotation effect, the polarization rotation angle of the optical signal caused by lightning is obtained by equation (4).

[0099] In one embodiment of the present invention, after the optical signal is output by the polarization state detection device, it is collected by the photoelectric detector and transmitted to the signal acquisition card and the processor. The processor calculates the polarization state change according to Malus's law, and the expression is as follows:

[0100] I=I0cos 2 (θ F ) (7)

[0101] Where I0 is the intensity of the incident light signal, I is the intensity of the light detected by the photodetector, θ F is the polarization rotation angle caused by lightning strike.

[0102] When two adjacent oppositely transmitted pulse polarized light are detected, the POTDR curve is as follows: Fig. 9 As shown, when the pulse polarized light transmitted from right to left reaches point C, the lightning strike occurs at point B. At this time, the pulse polarized light transmitted from left to right reaches point A. The polarization state mutation points detected by the two oppositely transmitted pulse polarized light beams coincide with each other. The polarization state mutation point of the pulse polarized light emitted from the left end is L1 away from the transmitting end, and the polarization state mutation point of the pulse polarized light emitted from the right end is L2 away from the transmitting end. At this time, the two satisfy L1+L2=L, and this point is the actual location where the lightning strike event occurs.

[0103] When two adjacent oppositely transmitted pulse polarized light are detected, the POTDR curve is as follows: Fig.10 As shown, the pulsed polarized light transmitted from right to left is emitted at time t0 and transmitted to the right side of the transmitting end L D At point D, the lightning strike occurs at position A, which is L-L0 away from the right transmitting end. L is the total length of the optical fiber. At this time, at time t2, a pulse polarized light is transmitted from left to right and is transmitted to the left transmitting end L away. B Point B; at time t1, the right receiving end receives the Rayleigh scattered light signal whose polarization state is affected by the magnetic field generated by the lightning current, and at time t3, the left receiving end receives the Rayleigh scattered light signal whose polarization state is affected by the magnetic field generated by the lightning current; the polarization state mutation point C of the pulse polarized light emitted from the left end is at a distance from the transmitting end L1, and the polarization state mutation point E of the pulse polarized light emitted from the right end is at a distance from the transmitting end L2, L1 and L2 are respectively based on Since L1+L2>L, the polarization state mutation points obtained by detecting the two polarized pulses of opposite transmission do not overlap.

[0104]

[0105] In formula (8), L B , L D and L0 are unknown quantities, and the other parameters are all known quantities. Solving the above equations, we can obtain the actual lightning strike location point L0, thereby achieving accurate lightning strike location. Among them, Δt=t2-t0 is the emission time difference between two adjacent oppositely transmitted pulse polarized light signals, c is the speed of light in vacuum, and n is the refractive index of the optical fiber core.

[0106] In another embodiment of the present invention, one detection cycle of the system is composed of two groups of pulsed polarized light signals transmitted in opposite directions.

[0107]

[0108] Wherein, T is the system detection period, L is the total length of the optical fiber, n is the refractive index of the optical fiber core, c is the speed of light in a vacuum, τ is the relaxation time of the magnetic field formed by lightning strike, and Δt is the emission time difference between a set of oppositely transmitted pulsed polarized light signals; the total sensing distance of the system needs to satisfy:

[0109]

[0110] If the sensing distance is greater than the threshold value in the above formula, when a lightning strike occurs in an area near one end of the optical fiber, the pulsed polarized light transmitted from the other end of the optical fiber to that end area will not be able to reach the lightning strike point within the lightning relaxation time, resulting in the inability to establish a double-end positioning equation, causing a large lightning strike positioning error.

[0111] The same or similar reference numerals correspond to the same or similar components;

[0112] The terms used in the drawings to describe positional relationships are only used for illustrative purposes and should not be construed as limiting this patent;

[0113] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the embodiments here. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A double-ended optical lightning location method applied to an overhead power optical cable, wherein the overhead power optical cable comprises a plurality of optical fibers, characterized in that: The following steps are involved: Inputting the first pulsed polarized light into the first optical fiber at one end of the power overhead optical cable for transmission; After a certain period of time has passed since the first pulsed polarized light was emitted, the second pulsed polarized light is input into the second optical fiber at the other end of the power overhead optical cable for transmission; A set of pulsed polarized light signals for double-end detection is formed by the first and second oppositely transmitted pulsed polarized light signals; A strong magnetic field is formed around the overhead power optical cable struck by lightning, and the first and second pulsed polarized lights respectively undergo polarization state rotation due to the Faraday rotation effect when transmitting through the optical cable struck by lightning; The polarization states of the Rayleigh scattered light corresponding to the first and second pulsed polarized light are detected at the transmitting ends of the first and second optical fibers respectively, and the time domain reflection curves of the first and second polarized light are constructed respectively, and the positions of the mutation points of the polarization states of the Rayleigh scattered light corresponding to the first and second pulsed polarized light are obtained respectively, so as to realize the single-end lightning strike point positioning respectively; A double-end positioning equation group is established using the emission time of the first and second pulse polarized lights, the moment of sudden change in polarization state of Rayleigh scattered light, and the sudden change position. The double-end positioning equation group is solved to obtain the actual lightning strike positioning point, thereby achieving accurate lightning strike positioning.

2. A double-ended optical lightning strike location method for power overhead optical cables according to claim 1, characterized in that: When the first pulsed polarized light reaches the end of the first optical fiber, the third pulsed polarized light is input into the third optical fiber at the other end of the power overhead optical cable for transmission; When the second pulsed polarized light reaches the end of the second optical fiber, the fourth pulsed polarized light is input into the fourth optical fiber at the other end of the power overhead optical cable for transmission; The third and fourth counter-transmitted pulse polarized light signals constitute the next group of pulse polarized light signals for double-end detection, ensuring that Rayleigh scattered light signals of pulse polarized light always exist everywhere in the power overhead optical cable, thereby achieving real-time and accurate lightning strike positioning and avoiding the occurrence of measurement blind spots.

3. A double-ended optical lightning strike location method for power overhead optical cables according to claim 1 or 2, characterized in that: At time t0, the first pulsed polarized light enters the power overhead optical cable from the first optical fiber for transmission. At time t, the Rayleigh scattered light signal is received at the transmitting end of the first optical fiber. Calculate the position of the Rayleigh scattering point corresponding to the Rayleigh scattering light signal, where Lt is the distance between the Rayleigh scattering point corresponding to the received signal and the pulse polarized light transmitting end, and v is the light speed of the pulse polarized light in the optical fiber; Assume that the lightning strike occurs at a position L0 away from the first optical fiber transmitting end, and the total length of the optical fiber is L. At this time, the first pulse polarized light arrives at a position L1' away from the first optical fiber transmitting end. At time t1, the first optical fiber incident end receives the Rayleigh scattered light signal whose polarization state is affected by the magnetic field generated by the lightning strike. According to Calculate the position of the single-ended lightning strike point detected by the first pulse polarized light, where L1 is the distance between the single-ended detection lightning strike point of the first pulse polarized light and the first optical fiber transmitting end; at time t2, the second pulse polarized light enters the power overhead optical cable from the second optical fiber and transmits in the opposite direction to the first pulse polarized light. At this time, the second pulse polarized light arrives at a distance of L2' from the second optical fiber transmitting end. At time t3, the second optical fiber incident end receives the Rayleigh scattered light signal whose polarization state is affected by the magnetic field generated by the lightning strike. According to The position of the single-ended lightning strike point detected by the second pulse polarized light is calculated, where L2 is the distance between the single-ended detected lightning strike point of the second pulse polarized light and the second optical fiber emitting end; L1′ and L2′ are both unknown quantities.

4. A double-ended optical lightning strike location method for power overhead optical cables according to claim 3, characterized in that: If the single-ended lightning strike point detected by the two oppositely transmitted pulse polarized lights coincides with each other, the actual lightning strike location point L0 is L0 = L1 or L0 = L2; If the positions of the single-end lightning strike points detected by the two oppositely transmitted pulse polarized lights do not overlap, the following double-end positioning equations are established: Wherein, Δt is the emission time difference between the first and second pulsed polarized light signals, Δt=t2-t0; c is the speed of light in vacuum, and n is the refractive index of the optical fiber core; The double-terminal positioning equation group is solved to obtain the actual lightning strike positioning point L0, thereby achieving accurate lightning strike positioning.

5. A double-ended optical lightning strike location method for power overhead optical cables according to claim 4, characterized in that: When L1+L2=L, the positions of the single-ended lightning strike points detected by the two oppositely transmitted pulse polarized lights coincide; When L1+L2>L, the positions of the single-ended lightning strike points detected by the two oppositely transmitted pulse polarized lights do not overlap.

6. A double-ended optical lightning location system for power overhead optical cables, characterized in that: include: The first to fourth pulse polarized light generating modules are used to generate first to fourth pulse polarized lights respectively and input the first to fourth optical fibers correspondingly; The first to fourth polarization state detection modules are used to detect the polarization states of the first to fourth pulsed polarized light Rayleigh scattered light, respectively, and find the position of the polarization state mutation of the polarized light time domain reflection curve to realize the single-end lightning strike point positioning; First to fourth circulators, each of the pulse polarized light generating modules is connected to the first end of the corresponding circulator, the second end of the circulator is connected to the corresponding optical fiber in the power overhead optical cable, and the third end of the circulator is connected to the corresponding polarization state detection module; The first and second trigger modules are respectively used to generate a trigger signal when the current pulse polarized light is transmitted to the end of the optical fiber, so as to trigger the emission of the pulse polarized light transmitted in the opposite direction of the current pulse polarized light.

7. A double-ended optical lightning location system for power overhead optical cables according to claim 6, characterized in that: Each of the pulse polarized light modules comprises a pulse laser and a polarization controller. The pulse light generated by the pulse laser is converted into pulse polarized light after passing through the polarization controller.

8. A double-ended optical lightning location system for power overhead optical cables according to claim 6, characterized in that: Each of the polarization state detection modules comprises a polarization state detection device, a Rayleigh scattering photoelectric detector and a signal processor connected in sequence, wherein after the polarization state detection device detects the Rayleigh scattered light, the Rayleigh scattering photoelectric detector converts the Rayleigh scattered light into an electrical signal of the Rayleigh scattered light and transmits the signal to the signal processor, and the signal processor processes the electrical signal of the Rayleigh scattered light to obtain a POTDR curve; The single-end lightning strike point is located by using the polarization state mutation point on the POTDR curve, and the precise lightning strike location is achieved by solving the double-end positioning equation using the polarization state mutation point detected by two pulse polarized lights transmitted in opposite directions.

9. A double-ended optical lightning location system for power overhead optical cables according to claim 6, characterized in that: Each of the trigger modules includes a pulse polarization photodetector and a trigger circuit, wherein the pulse polarization photodetector is used to detect an electrical signal generated by pulse polarization light; The electrical signal generated by the pulse polarized light is transmitted to the pulse polarized light generating module to be emitted pulse polarized light via the trigger circuit, and the pulse polarized light generating module is controlled by the trigger circuit to emit pulse polarized light.

10. A double-ended optical lightning location system for power overhead optical cables according to any one of claims 6 to 9, characterized in that: One detection cycle includes two polarized pulses transmitted in opposite directions. The detection cycle T is Wherein, L is the total length of the optical fiber, n is the refractive index of the optical fiber core, c is the speed of light in a vacuum, and Δt is the emission time difference between a set of oppositely transmitted pulsed polarized light signals; The total length L of the optical fiber in the system satisfies Among them, τ is the relaxation time of the magnetic field formed by lightning strike.

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