A double-end optical lightning stroke positioning method and system applied to power overhead optical cable

Abstract

The application provides a double-end optical lightning stroke positioning method and system applied to power overhead optical cables, and relates to the technical field of optical fiber sensing; the basic principle of positioning is to realize single-end lightning stroke positioning based on the obvious change of the polarization state of optical signals after the optical signals encounter lightning strokes; the application first uses counter-transmitted pulse polarized light to detect a single-end lightning stroke positioning point, then establishes a double-end positioning equation set to solve an actual lightning stroke positioning point, so that accurate lightning stroke positioning is realized; the application uses the Faraday optical rotation effect of lightning strokes on optical signals to realize lightning stroke positioning based on a polarized light time domain reflectometer; compared with traditional lightning stroke positioning, the application has low operation and maintenance cost, high precision, does not need wide-area accurate time synchronization, has a simple system, is convenient to install, and reduces the blind area of lightning stroke positioning.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of optical fiber sensing, more particularly, to a double-end optical lightning positioning method and system applied to power overhead optical cable. BACKGROUND

[0002] Currently, the lightning positioning methods applied to power overhead optical cable mainly include single-end loopback method, double-end method based on continuous optical polarization state detection and single-end polarization optical time domain reflection method.

[0003] 1) The single-end loopback method calculates the lightning position by the time difference of the continuous optical signal encountering lightning polarization state change in the power overhead optical cable for two times, the main advantage of which is that it does not need wide-area time synchronization and has lower deployment cost, and the main disadvantage of which is that there is a measurement blind area, and in order to shorten the measurement blind area, a delay optical fiber needs to be transmitted at the loopback point, which will shorten the measurement distance.

[0004] 2) The double-end method based on continuous optical polarization state detection utilizes two independent optical fibers in the power overhead optical cable to synchronously transmit two continuous optical signals, and there are optical receivers and optical transmitters at both ends of the optical fibers, and the lightning position is determined by the time difference of the lightning-induced polarization state change in the two measurement processes, the main advantage of which is that there is no measurement blind area and the measurement distance is longer, and the main disadvantage of which is that it needs wide-area time synchronization and the deployment cost is doubled compared with the single-end loopback method.

[0005] 3) The single-end polarization optical time domain reflection method utilizes the light transmission and reception devices at the same end of the optical fiber to transmit pulsed polarization light and receive Rayleigh scattering light reflected from each point of the optical fiber, and the lightning position is determined by detecting the polarization state change of the Rayleigh scattering light at each point, so as to realize lightning positioning, the main advantage of which is that it does not need wide-area time synchronization and has lower operation and maintenance cost, and the main disadvantage of which is that the measurement distance is shorter.

[0006] Currently, there is no scheme in the lightning positioning methods based on power overhead optical cable that can realize no measurement blind area, longer measurement distance and lower operation and maintenance cost without wide-area time synchronization. SUMMARY

[0007] In view of the defects of the prior art, the purpose of the present application is to provide a double-end lightning positioning method and system applied to power overhead optical cable, which aims to realize lightning positioning applied to power overhead optical cable without measurement blind area, longer measurement distance and lower deployment cost without wide-area time synchronization.

[0008] To solve the above technical problems, the technical scheme of the present application is as follows:

[0009] A double-end optical lightning positioning method applied to power overhead optical cable, the power overhead optical cable comprising a plurality of optical fibers, comprising the following steps:

[0010] transmitting the first pulsed polarized light into a first optical fiber at one end of the power overhead optical cable;

[0011] transmitting the second pulsed polarized light into a second optical fiber at the other end of the power overhead optical cable after a certain time interval from the first pulsed polarized light emission;

[0012] composing a set of pulsed polarized light signals for double-end detection by the first and second counter-transmitted pulsed polarized light signals;

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

[0014] detecting the polarization state of the Rayleigh scattered light corresponding to the first and second pulsed polarized light at the emission end of the first and second optical fiber respectively, constructing the first and second polarized light time domain reflection curves respectively, obtaining the mutation point position of the polarization state of the Rayleigh scattered light corresponding to the first and second pulsed polarized light respectively, and realizing single-end lightning point positioning respectively;

[0015] establishing a double-end positioning equation set by using the emission time of the first and second pulsed polarized light, the mutation time and position of the polarization state of the Rayleigh scattered light, and solving the double-end positioning equation set to obtain the actual lightning positioning point, thereby realizing accurate lightning positioning.

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

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

[0018] composing a next set of pulsed polarized light signals for double-end detection by the third and fourth counter-transmitted pulsed polarized light signals, ensuring that there is always a pulsed polarized light Rayleigh scattered light signal in each part of the power overhead optical cable, thereby realizing real-time accurate lightning positioning and avoiding the emergence of a measurement blind area.

[0019] Preferably, t0 is the time when the first pulsed polarized light enters the power overhead optical cable from the first optical fiber for transmission, and t is the time when the Rayleigh scattered light signal is received at the emission end of the first optical fiber, and the position of the Rayleigh scattering point corresponding to the Rayleigh scattered light signal is calculated according to wherein L t is the distance from the pulsed polarized light emission end to the Rayleigh scattering point corresponding to the received signal, and v is the speed of the pulsed polarized light in the optical fiber;

[0020] Suppose that the lightning stroke occurs at a position with a distance L0 from the first optical fiber transmitting end, the total length of the optical fiber is L, at this time the first pulse polarized light reaches a position with a distance L1' from the first optical fiber transmitting end, at a time t1 the Rayleigh scattering light signal with the polarization state affected by the magnetic field generated by the lightning stroke is received at the first optical fiber incident end, according to the single-end lightning stroke point position detected by the first pulse polarized light is calculated, wherein L1 is the distance from the single-end lightning stroke point of the first pulse polarized light to the first optical fiber transmitting end; at a time t2 the second pulse polarized light is transmitted in the power overhead optical cable by the second optical fiber in a direction opposite to the first pulse polarized light, at this time the second pulse polarized light reaches a position with a distance L2' from the second optical fiber transmitting end, at a time t3 the Rayleigh scattering light signal with the polarization state affected by the magnetic field generated by the lightning stroke is received at the second optical fiber incident end, according to the single-end lightning stroke point position detected by the second pulse polarized light is calculated, wherein L2 is the distance from the single-end lightning stroke point of the second pulse polarized light to the second optical fiber transmitting end.

[0021] Preferably, if the single-end lightning stroke point positions detected by the two pulse polarized lights transmitted in opposite directions coincide, the actual lightning stroke positioning point L0 is L0=L1 or L0=L2;

[0022] If the single-end lightning stroke point positions detected by the two pulse polarized lights transmitted in opposite directions do not coincide, the following double-end positioning equation set is established:

[0023]

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

[0025] The actual lightning stroke positioning point L0 is obtained by solving the double-end positioning equation set, so that the precise lightning stroke positioning is realized.

[0026] Preferably, when L1+L2=L, the single-end lightning stroke point positions detected by the two pulse polarized lights transmitted in opposite directions coincide.

[0027] When L1+L2>L, the single-end lightning stroke point positions detected by the two pulse polarized lights transmitted in opposite directions do not coincide.

[0028] The application further provides a double-end optical lightning stroke positioning system applied to a power overhead optical cable, comprising:

[0029] First to fourth pulse polarized light generating modules for generating first to fourth pulse polarized lights respectively, corresponding to input first to fourth optical fibers;

[0030] The first to fourth polarization state detection modules are respectively used for detecting the polarization states of the first to fourth pulse polarized light Rayleigh scattering lights, and finding the polarization state mutation positions of the polarization time domain reflection curves to realize single-end lightning point positioning.

[0031] The first to fourth circulators are respectively connected with the first ends of the corresponding circulators, the second ends of the circulators are connected with the corresponding optical fibers in the power overhead optical cable, and the third ends of the circulators are connected with the corresponding polarization state detection modules.

[0032] The first and second trigger modules are respectively used for generating a trigger signal when the current pulse polarized light is transmitted to the end of the optical fiber, and triggering the emission of the pulse polarized light transmitted to 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 through the polarization controller.

[0034] Preferably, each of the polarization state detection modules comprises polarization state detection devices, Rayleigh scattering photoelectric detectors and signal processors connected in sequence, the polarization state detection devices detect Rayleigh scattering light, the Rayleigh scattering light is converted into an electrical signal of Rayleigh scattering light through the Rayleigh scattering photoelectric detectors and is transmitted to the signal processors, the signal processors process the electrical signal of Rayleigh scattering light to obtain a POTDR curve.

[0035] The single-end lightning point positioning is completed by using the polarization state mutation points on the POTDR curve, and the accurate lightning positioning is realized by solving the double-end positioning equation through the polarization state mutation points detected by the two pulse polarized lights transmitted to the opposite directions.

[0036] Preferably, each of the trigger modules comprises a pulse polarized light photoelectric detector and a trigger circuit, and the pulse polarized light photoelectric detector is used for detecting the electrical signal generated by the pulse polarized light.

[0037] The electrical signal generated by the pulse polarized light is transmitted to the pulse polarized light generation module of the pulse polarized light to be emitted through the trigger circuit, and the pulse polarized light generation module emits the pulse polarized light under the control of the trigger circuit.

[0038] Preferably, two pulse polarized lights transmitted to the opposite directions are included in one detection period, and the detection period 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 vacuum, and Δt is the emission time difference between a group of pulse polarized light signals transmitted to the opposite directions.

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

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

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

[0042] When the third and fourth pulsed polarized light respectively reach the third and fourth optical fiber ends, the first and second pulsed lasers reemit the next set of first and second pulsed polarized light respectively at this time when the first and second pulsed lasers are just entering the next detection cycle;

[0043] The four optical fibers and the four sets of POTDR transceiver equipment are cyclically detected in the above manner, thereby ensuring that two oppositely transmitted pulsed polarized light signals exist in the power overhead optical cable at the same time, and each part of the optical cable is covered by the Rayleigh scattering light of the detection light pulse, thereby realizing accurate lightning positioning of the power overhead optical cable.

[0044] Compared with the prior art, the technical scheme of the application has the beneficial effects that:

[0045] The application provides a double-end optical lightning positioning method and system applied to a power overhead optical cable, and the basic principle of the double-end lightning positioning technology applied to the power overhead optical cable in the power system provided by the application is to realize single-end lightning positioning based on the obvious change of the polarization state of the optical signal after the optical signal encounters lightning and to realize accurate lightning positioning by establishing a double-end positioning equation group to solve the actual lightning positioning point by using oppositely transmitted pulsed polarized light to detect the single-end lightning positioning point;

[0046] The application has the following beneficial effects:

[0047] 1) Compared with the traditional single-end loopback lightning positioning method, the double-end lightning positioning method and system of the application have no measurement blind area and higher measurement accuracy; the reason why the single-end loopback lightning positioning method has a blind area is that when the lightning point is close to the loopback point, the time difference of the two polarization state changes may be too small to distinguish the two in the time domain, and the double-end lightning positioning method based on POTDR in the application realizes lightning positioning according to the Rayleigh scattering light at each part of the optical fiber, and the spatial resolution can reach one meter, which is far higher than the lightning positioning accuracy requirement, and the time difference of the two polarization state changes is not needed for lightning positioning, so the measurement accuracy is high and there is no measurement blind area.

[0048] 2) Compared with the double-end lightning stroke positioning method based on continuous light polarization state detection, the lightning stroke positioning method and system of the application do not need wide-area time synchronization, and the operation and maintenance cost is low; in the double-end lightning stroke positioning method based on POTDR in the application, the pulsed polarized light is transmitted at intervals controlled by a trigger circuit, the transmission time interval of the two pulsed polarized light transmitted from the opposite ends depends on the response time of the trigger circuit, and is a fixed value, so it is not necessary to ensure time synchronization every time the light signal is transmitted at the two ends as in the double-end method based on continuous light polarization state detection, so as to use the time difference of the polarization state change received at the two ends to position the lightning stroke, and the operation and maintenance cost of ensuring that the two transmission ends keep time synchronization is very high, so from the perspective of not needing wide-area time synchronization, the operation and maintenance cost of the double-end POTDR lightning stroke positioning method in the application is relatively low, and it is convenient for large-scale popularization and application. BRIEF DESCRIPTION OF DRAWINGS

[0049] Figure 1 It is an OPGW composition schematic diagram.

[0050] Figure 2 It is an OPGW structure schematic diagram.

[0051] Figure 3 It is a Faraday optical rotation effect principle schematic diagram.

[0052] Figure 4 It is an OTDR Rayleigh scattering principle schematic diagram.

[0053] Figure 5 It is a typical polarized light time domain reflection system structure schematic diagram.

[0054] Figure 6 It is a double-end optical lightning stroke positioning system structure schematic diagram applied to power overhead optical cable provided in an embodiment of the application.

[0055] Figure 7 It is a lightning stroke positioning method flowchart applied to power overhead optical cable provided in an embodiment of the application.

[0056] Figure 8 It is a lightning current waveform correction diagram.

[0057] Figure 9 It is a double-end lightning stroke positioning situation in which the polarization state mutation points detected by two opposite transmitted pulsed polarized lights coincide.

[0058] Figure 10 It is a double-end lightning stroke positioning situation in which the polarization state mutation points detected by two opposite transmitted pulsed polarized lights do not coincide.

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

[0060] The accompanying drawings are only intended to illustrate, and cannot be understood as a limitation to the patent;

[0061] In order to better illustrate the embodiments, some components in the drawings can be omitted, enlarged or reduced, and do not represent the actual size of the product;

[0062] It can be understood by those skilled in the art that some well-known structures in the drawings and their descriptions can be omitted.

[0063] The technical solutions of the present application will be further described below in combination with the drawings and embodiments.

[0064] The structure and composition of the power overhead optical cable (OPGW) are introduced as an example. As shown in Figure 1 , the structure of the OPGW mainly consists of an optical unit and a ground wire unit. As shown in Figure 2 , the optical unit consists of a stainless steel or aluminum protective tube and an optical fiber therein. The optical fiber generally has excess length (i.e. the length of the optical fiber is slightly longer than the protective tube) to avoid the optical fiber from being broken due to stress caused by the gradual mechanical stretching of the protective tube during long-term operation. Fiber paste is filled between the protective tube and the optical fiber to play a role of waterproofing, etc. The ground wire unit is formed by helical twisting of aluminum-clad steel wires, and oil paste is filled between the aluminum-clad steel wires. The main role of the aluminum-clad steel wire is to serve as a conductor for grounding protection and to attract lightning to avoid direct lightning strikes on the power phase line.

[0065] Under the action of a magnetic field, a substance originally without optical rotation also produces optical rotation, which can cause the rotation of the optical vector, i.e. when light passes through a medium without optical rotation under the action of a magnetic field, the vibration plane of the light will rotate, which phenomenon is called Faraday effect, as shown in Figure 3 The angle of rotation of the optical vector θ is proportional to the distance L B of the light passing through the medium and the magnetic induction intensity B, and the calculation formula is as follows:

[0066] θ = VBL B(1)

[0067] where V is called Verdet constant, which is a material constant and determines the magneto-optical properties of the material. The sign 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 a standard single-mode optical fiber, the Verdet constant at 1550 nm wavelength at room temperature is about 0.53 rad / (T·m).

[0068] The optical time domain reflection signal is mainly subject to Rayleigh scattering principle. As shown in Figure 4 , the main cause of Rayleigh scattering is the non-uniformity of the optical fiber itself, which is an elastic scattering. The scattered light of Rayleigh scattering has the same frequency as the incident signal light, and Rayleigh scattering itself does not cause the polarization state of light to change abruptly. The positioning based on the relationship between the propagation time of scattered light and the distance is the most basic positioning principle of distributed optical fiber sensing based on optical time domain reflection technology.

[0069] If the optical pulse propagates in the optical fiber at a speed of v, and the time when the optical pulse is sent out is set as 0, after t time, the receiver just receives the Rayleigh scattering signal from the z point (the distance from the z point to the sending end of the optical pulse is z / 2). v and t can be used to express z as follows:

[0070]

[0071] where c is the speed of light in vacuum, and n is the refractive index of the optical fiber core.

[0072] The total loss of the Rayleigh scattering signal from the z point (compared to the time when the optical pulse is just sent out) is as follows:

[0073] P(z)=P0e -αz (3)

[0074] where P0 is the initial optical power of the optical pulse when it is sent into the fiber, and a is the loss coefficient of the optical fiber. For a pulse light with a pulse width of T, the backscattered Rayleigh scattering light power near the z point is PB(z) as follows:

[0075]

[0076] where a R is the Rayleigh scattering coefficient of the optical fiber, and b R is the backscattering coefficient.

[0077] The structure principle diagram of the polarization optical time domain reflectometer is as shown in Figure 5As shown, the pulse laser emits a pulse light signal, which becomes a 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 polarization analyzer. The polarization analyzer converts the change in optical polarization state into a change in optical power. The detector completes photoelectric conversion and, after signal processing, locates the change in polarization state of the optical time domain reflection signal.

[0078] In one embodiment of the present application, referring to the system in Figure 6 , the present application proposes a double-end lightning positioning method applied to power overhead optical cable based on the system in Figure 6 , as shown in Figure 7 ; the method comprises the following steps:

[0079] Step one: a first pulse 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 via the first optical circulator 31, and transmits from left to right.

[0080] A second pulse 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 via the second optical circulator 32, and transmits from right to left.

[0081] Step two: the first pulse polarized light is received by the first pulse polarized photodetector 411 when it reaches the end of the first optical fiber 51, and a first trigger signal is emitted; the second pulse polarized light is received by the second pulse polarized photodetector 421 when it reaches the end of the second optical fiber 52, and a second trigger signal is emitted.

[0082] Step three: the first trigger signal triggers the emission of a third pulse polarized light from the third optical fiber 53 at the right end of the power overhead optical cable, which enters the third optical fiber 53 via the third optical circulator 33 and transmits from right to left.

[0083] The second trigger signal triggers the emission of a fourth pulse polarized light from the fourth optical fiber 54 at the left end of the power overhead optical cable, which enters the fourth optical fiber 54 via the fourth optical circulator 34 and transmits from left to right.

[0084] Step four: after the third and fourth pulse polarized lights reach the ends of the third and fourth optical fibers respectively, the next detection cycle is entered, and steps one to four are re-executed.

[0085] The above steps are repeated in a loop, thereby achieving high-precision double-end lightning positioning.

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

[0087] When the second pulse polarized light reaches the end of the second optical fiber 52, the second pulse polarized light detector 421 receives the second pulse polarized light signal and emits a second trigger signal to the fourth pulse laser 141, and the fourth pulse laser 141 emits a fourth pulse polarized light which is transmitted in the same direction as the first pulse polarized light to the fourth optical fiber 54 after receiving the second trigger signal.

[0088] When the third and fourth pulse polarized light respectively reaches the end of the third and fourth optical fiber 53 and 54, the first and second pulse lasers 111 and 121 are just entering the next detection cycle, and re-emits the next set of first and second pulse polarized light respectively.

[0089] The four optical fibers and the four sets of POTDR transceiver equipment are detected in the above-mentioned manner, so as to ensure that there are two opposite transmission pulse polarized light signals in the power overhead optical cable at the same time, and the Rayleigh scattering light of the detection pulse covers each part of the optical cable, so as to realize the accurate lightning positioning of the power overhead optical cable.

[0090] The ground wire of the power overhead optical cable which is struck by lightning has lightning current passing through it, and the lightning current forms a strong magnetic field around the optical cable, which causes the polarization state to rotate due to the Faraday rotation effect when the detection pulse polarized light passes through the optical cable. The light signal output by the polarization state detection device is collected by the Rayleigh scattering photodetector, and the polarization change caused by lightning is calculated according to Malus law by detecting the light intensity change of the photodetector. The polarization state mutation points caused by the Faraday effect of lightning are found on the four POTDR curves detected by the four pulse polarized light signals, and the positions L1 and L2 of the polarization state mutation points detected by the adjacent two opposite transmission pulse polarized light and the total sensing distance L are determined.

[0091] If L1+L2>L, then the double-end lightning positioning equation set is established to solve the actual lightning point and realize accurate lightning positioning; if L1+L2=L, then the positions of the polarization state mutation points detected by the two opposite transmission pulse polarized light are the actual lightning points.

[0092] The following will be described in detail a double-end lightning positioning method applied to a power overhead optical cable.

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

[0094]

[0095] In the formula, I0 represents the peak current, τ1 and τ2 represent the wave head and tail time constants respectively, The peak current correction factor is represented by I0, and under this model, is the time when the lightning current reaches the peak, and its time-domain waveform is shown in Figure 8 .

[0096] The power overhead cable section that encounters lightning can be approximated by a current-carrying solenoid model, and the relationship between the magnetic field formed by the lightning current near the cable section and the lightning current is expressed as follows:

[0097] B = μNI (6)

[0098] According to the Faraday optical rotation effect, the rotation angle of the polarization state of the optical signal caused by lightning is obtained from formula (4).

[0099] In an embodiment of the present application, the optical signal is collected by a photodetector after being output by the polarization state detection device and transmitted to a signal acquisition card and a processor, and the processor calculates the polarization state change size according to Malus' law, and the expression is as follows:

[0100] I = I0cos 2 (θ F ) (7)

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

[0102] When the POTDR curves detected by the adjacent two oppositely transmitted pulsed polarized lights are as shown in Figure 9 , the lightning occurs at point B when the right-to-left transmitted pulsed polarized light reaches point C, at this time, the left-to-right transmitted pulsed polarized light reaches point A, the polarization state mutation points of the two oppositely transmitted pulsed polarized lights coincide, the polarization state mutation point of the left-end transmitted pulsed polarized light is L1 away from the emission end, the polarization state mutation point of the right-end transmitted pulsed polarized light is L2 away from the emission end, at this time, they satisfy L1+L2=L, and this point is the actual lightning event occurrence position.

[0103] When the POTDR curves detected by the adjacent two oppositely transmitted pulsed polarized lights are as shown in Figure 10 , the right-to-left transmitted pulsed polarized light is emitted at time t0, and when it is transmitted to point D away from the right-end emission end L D , the lightning occurs at position A away from the right-end emission end L-L0, L is the total length of the optical fiber, at this time, the left-to-right transmitted pulsed polarized light is transmitted to point B away from the left-end emission end L B at time t2; the Rayleigh scattering light signal with the polarization state affected by the magnetic field generated by the lightning current is received at the right-end receiving end at time t1, and the Rayleigh scattering light signal with the polarization state affected by the magnetic field generated by the lightning current is received at the left-end receiving end at time t3; the polarization state mutation point C of the left-end transmitted pulsed polarized light is away from the emission end L1, and the polarization state mutation point E of the right-end transmitted pulsed polarized light is away from the emission end L2, L1 and L2 are respectively calculated according to The calculation is obtained. Since L1+L2>L, the polarization state mutation points obtained by detecting the two oppositely transmitted pulse polarized lights are not coincident, and according to

[0104]

[0105] In formula (8), L B , L D and L0 are unknown quantities, and other parameters are known quantities, the actual lightning location point L0 is obtained by solving the equation group, so that the accurate lightning location is realized, wherein Δt=t2-t0 is the transmission time difference between the two adjacent oppositely transmitted pulse polarized light signals, c is the light speed in vacuum, and n is the optical fiber core refractive index.

[0106] In another embodiment of the present application, one detection cycle of the system is composed of two groups of oppositely transmitted pulse polarized light signals, and is

[0107]

[0108] Wherein, T is the system detection cycle, L is the total length of the optical fiber, n is the optical fiber core refractive index, c is the light speed in vacuum, τ is the relaxation time of the magnetic field formed by lightning, and Δt is the transmission time difference between the two groups of oppositely transmitted pulse 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 lightning occurs in a region close to one end of the optical fiber, the pulse polarized light transmitted from the other end of the optical fiber to the region will not be able to reach the lightning point within the lightning relaxation time, so that the double-end location equation cannot be established, and a larger lightning location error is caused.

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

[0112] The terms describing the positional relationship in the drawings are only used for exemplary illustration, and cannot be understood as a limitation on the patent;

[0113] Obviously, the above embodiments of the present application are only examples for clearly illustrating the present application, and are not a limitation on the embodiments of the present application. For those skilled in the art, other different forms of changes or variations can be made on the basis of the above description. Here, all the embodiments need not and cannot be exhausted. Any modification, equivalent replacement and improvement made within the spirit and principle of the present application should be included in the protection scope of the claims of the present application.

Claims

1. A double-ended optical lightning-strike location method applied to a power overhead optical cable, said power overhead optical cable comprising a number of optical fibers, characterized in that, The method comprises the following steps: transmitting the first pulse polarized light into the first optical fiber at one end of the power overhead optical cable; transmitting the second pulse polarized light into the second optical fiber at the other end of the power overhead optical cable after a certain time interval from the first pulse polarized light emission; forming a set of pulse polarized light signals for double-end detection by the first and second counter-transmitted pulse polarized light signals; a strong magnetic field is formed around the power overhead optical cable struck by lightning, and the first and second pulse polarized light respectively undergoes polarization state rotation due to the Faraday rotation effect when transmitting through the optical cable struck by lightning; detecting the polarization state of the Rayleigh scattering light corresponding to the first and second pulse polarized light at the emission end of the first and second optical fibers respectively, constructing the first and second polarization light time domain reflection curves respectively, obtaining the mutation point position of the polarization state of the Rayleigh scattering light corresponding to the first and second pulse polarized light respectively, and realizing single-end lightning point positioning respectively; establishing a double-end positioning equation set by using the transmission time of the first and second pulse polarized light, the mutation time and position of the polarization state of the Rayleigh scattering light, and solving the double-end positioning equation set to obtain the actual lightning positioning point, thereby realizing accurate lightning positioning; Set The first moment of the first pulse polarized light from the first optical fiber into the power overhead optical cable transmission, t The first moment of the first fiber emission end receiving Rayleigh scattering light signal, according to The calculation of the Rayleigh scattering point corresponding to the Rayleigh scattering light signal position, wherein, The distance between the receiving signal corresponding to the Rayleigh scattering point and the pulse polarized light emission end, v The speed of light in the optical fiber of the pulse polarized light; Let the lightning strike occur at a position away from the first optical fiber launch end , the total length of the optical fiber is , at this time the first pulse polarized light reaches the position away from the first optical fiber launch end , , at the moment the Rayleigh scattering light signal with the polarization state affected by the lightning generated magnetic field is received at the first optical fiber incident end, according to the single-end lightning strike point position detected by the first pulse polarized light is calculated, wherein is the distance from the single-end lightning strike point detected by the first pulse polarized light to the first optical fiber launch end; at the moment the second pulse polarized light is transmitted in the power overhead optical cable by the second optical fiber in the opposite direction to the first pulse polarized light, at this time the second pulse polarized light reaches the position away from the second optical fiber launch end , , at the moment the Rayleigh scattering light signal with the polarization state affected by the lightning generated magnetic field is received at the second optical fiber incident end, according to the single-end lightning strike point position detected by the second pulse polarized light is calculated, wherein is the distance from the single-end lightning strike point detected by the second pulse polarized light to the second optical fiber launch end; and are unknown quantities; If the single-end lightning strike point positions detected by the two polarized light pulses of the transmission coincide, the actual lightning strike positioning point is or ; if the single-end lightning point positions detected by the two counter-transmitted pulse polarized light do not coincide, the following double-end positioning equation set is established: wherein, is the time difference of transmission between the first and second pulsed polarized light signals, ; c is the speed of light in vacuum, n is the fiber core refractive index; Solving the double-end positioning equation set obtains an actual lightning stroke positioning point Thus, accurate lightning stroke positioning is realized.

2. The method of claim 1, wherein the method is applied to a double ended optical lightning strike location method for overhead power cables. transmitting the third pulse polarized light into the third optical fiber at the other end of the power overhead optical cable when the first pulse polarized light reaches the end of the first optical fiber; transmitting the fourth pulse polarized light into the fourth optical fiber at the other end of the power overhead optical cable when the second pulse polarized light reaches the end of the second optical fiber; forming the next set of pulse polarized light signals for double-end detection by the third and fourth counter-transmitted pulse polarized light signals, ensuring that there is always Rayleigh scattering light signal of the pulse polarized light in the power overhead optical cable, thereby realizing real-time accurate lightning positioning and avoiding the emergence of a measurement blind area.

3. The dual-ended optical lightning-strike location method applied to power overhead optical cables according to claim 1, characterized in that, When the two pulses of polarized light transmitted towards the point of the lightning strike are detected by the single-ended probe, the positions of the two pulses coincide. When the single end lightning strike point positions detected by the two polarized light pulses of the opposite transmission do not coincide.

4. A two-ended optical lightning-strike location system applied to a power overhead optical cable, characterized in that, The method comprises the following steps: first to fourth pulse polarized light generation modules for generating first to fourth pulse polarized light respectively and inputting into first to fourth optical fibers respectively; first to fourth polarization state detection modules for detecting the polarization state of the Rayleigh scattering light of the first to fourth pulse polarized light respectively and finding the polarization state mutation position of the polarization light time domain reflection curve to realize single-end lightning point positioning; first to fourth circulators, each of the pulse polarized light generation modules is connected with the first end of the corresponding circulator, the second end of the circulator is connected with the corresponding optical fiber in the power overhead optical cable, and the third end of the circulator is connected with the corresponding polarization state detection module; first and second trigger modules for generating a trigger signal when the current pulse polarized light transmits to the end of the optical fiber, triggering the emission of the counter-transmitted pulse polarized light of the current pulse polarized light; each of the polarization state detection modules comprises a polarization state detection device, a Rayleigh scattering light photoelectric detector and a signal processor connected in sequence, the polarization state detection device detects the Rayleigh scattering light, converts it into an electrical signal of the Rayleigh scattering light through the Rayleigh scattering light photoelectric detector and transmits it to the signal processor, and the signal processor processes the electrical signal of the Rayleigh scattering light to obtain a POTDR curve; The single-end lightning stroke point is positioned by using the polarization state mutation point on the POTDR curve, and the accurate lightning stroke is positioned by solving the double-end positioning equation group through the polarization state mutation points detected by the two opposite transmission pulse polarized lights; Set at the moment the first pulse polarized light from the first optical fiber into the power overhead optical cable transmission, t at the moment the first optical fiber emission end receiving Rayleigh scattering light signal, according to the calculation of the Rayleigh scattering light signal corresponding to the position of the Rayleigh scattering point, wherein, for the receiving signal corresponding to the distance of the Rayleigh scattering point from the pulse polarized light emission end, v for the pulse polarized light in the optical fiber speed; Let the lightning strike occur at a position that is a distance from the first optical fiber launch end, and the total length of the optical fiber be At time , the Rayleigh scattered light signal with the polarization state affected by the magnetic field generated by the lightning strike is received at the first optical fiber incident end. According to , the single-end lightning strike point position detected by the first pulsed polarized light is calculated, where is the distance from the first pulsed polarized light single-end lightning strike point to the first optical fiber launch end; At time , the second pulsed polarized light is transmitted in the power overhead optical cable by the second optical fiber in the opposite direction of the first pulsed polarized light. At this time, the second pulsed polarized light reaches a position that is a distance from the second optical fiber launch end, At time , the Rayleigh scattered light signal with the polarization state affected by the magnetic field generated by the lightning strike is received at the second optical fiber incident end. According to , the single-end lightning strike point position detected by the second pulsed polarized light is calculated, where is the distance from the second pulsed polarized light single-end lightning strike point to the second optical fiber launch end; and are both unknown quantities; If the single-end lightning strike point positions detected by the two polarized light pulses of the transmission coincide, the actual lightning strike positioning point is or ; If the single-end lightning stroke point positions detected by the two opposite transmission pulse polarized lights do not coincide, the following double-end positioning equation group is established: wherein, is the difference in transmission time between the first and second polarized optical signals, ; c is the speed of light in a vacuum, n is the fiber core refractive index; Solving the double-end positioning equation set obtains an actual lightning stroke positioning point Thus, accurate lightning stroke positioning is realized.

5. A two-ended optical lightning-stroke location system for use with an electric power overhead optical cable according to claim 4, characterized in that, Each pulse polarized light generation module 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.

6. A two-ended optical lightning-stroke location system for use with an electric power overhead optical cable according to claim 4, wherein Each trigger module comprises a pulse polarized light photoelectric detector and a trigger circuit, and the pulse polarized light photoelectric detector is used for detecting the electric signal generated by the pulse polarized light. The electric signal generated by the pulse polarized light is transmitted to the pulse polarized light generation module to be emitted via the trigger circuit, and the pulse polarized light generation module is controlled by the trigger circuit to emit the pulse polarized light.

7. A two-terminal optical lightning-stroke location system for use with an overhead power cable as claimed in any one of claims 4 to 6, wherein, two counter-propagating pulses of polarized light are included in one probe cycle is wherein is the total fiber length, n is the fiber core refractive index, c is the speed of light in vacuum, is the emission time difference between a set of counter-propagating pulse polarized light signals; Total length of optical fibers in the system satisfies wherein, is the relaxation time of the magnetic field formed by the lightning strike.

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