A method for monitoring the sag of an optical line based on Rayleigh-Brillouin scattering light

Abstract

The application provides a line sag monitoring method based on Rayleigh-Brillouin scattering light, and relates to the technical field of power transmission line operation and maintenance. The method comprises the following steps: according to the spatial geometric characteristic relationship of the overhead transmission line, a spatial shape state equation under initial condition constraint is established; a function mapping relationship between the stable state phase drift of the optical fiber and the slowly varying sag of the line is constructed based on the stable state reference value of the optical fiber interference phase under the initial condition in the spatial shape state equation; and the spatial state constraint is constructed according to the function mapping relationship based on the response characteristic of the Brillouin scattering spectrum to the temperature change, and the line load ratio influence in the sag change is identified according to the spatial state constraint. The method constructs a monitoring system of phase stable state drift-line length-sag mapping, solves the horizontal stress and identifies the ice load ratio according to the temperature constraint provided by the Brillouin frequency shift, and improves the precision and stability of the sag monitoring.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of power transmission line operation and maintenance, in particular to a line sag monitoring method based on Rayleigh-Brillouin scattering light. BACKGROUND

[0002] With the rapid growth of ultra / extra-high voltage transmission line scale, the accidents caused by excessive sag of overhead lines are increasing, and the size of conductor sag directly affects the safety distance and icing risk assessment. However, the existing technology mostly uses video, laser ranging, tension meter and other methods for sag monitoring, which is easy to be disturbed by weather in long distance and complex terrain, and the sag inversion based on empirical formula is unstable and difficult to be checked online under different terrain and climate conditions.

[0003] Among the existing line sag monitoring methods using distributed optical fiber sensing technology, the method of measuring line sag by temperature cannot identify the sag change caused by line icing. And this method of directly measuring line stress by Brillouin optical time domain reflection technology and then solving the line sag cannot be demodulated alone because the Brillouin scattering spectrum is affected by both temperature and strain, and it is also impossible to distinguish whether the change of Brillouin scattering spectrum is caused by temperature or strain. Although the temperature can be measured by a meteorological sensor for correction, the cable temperature lags behind the ambient temperature to some extent, especially after the line icing, because the ice layer will seriously affect the heat exchange process between the line and the external environment, which will cause a large error in the measurement result. Therefore, it is necessary to design a line sag monitoring method based on Rayleigh-Brillouin scattering light. SUMMARY

[0004] The purpose of the present application is to provide a line sag monitoring method based on Rayleigh-Brillouin scattering light, which constructs a monitoring system of phase steady-state drift-line length-sag mapping, solves the horizontal stress according to the temperature constraint provided by the Brillouin frequency shift and identifies the icing specific load, so as to improve the accuracy and stability of the sag monitoring.

[0005] To achieve the above purpose, the present application provides the following scheme:

[0006] A line sag monitoring method based on Rayleigh-Brillouin scattering light, comprising the following steps:

[0007] According to the spatial geometric characteristic relationship of overhead transmission line, a spatial configuration state equation under the initial condition constraint is established;

[0008] Based on the steady-state reference value of optical fiber interference phase in the spatial configuration state equation under the initial condition, a functional mapping relationship between the optical fiber steady-state phase drift and the line slow-varying sag is constructed;

[0009] Based on the response characteristics of Brillouin scattering spectrum to temperature change, the spatial state constraint is constructed according to the function mapping relationship, and the line load ratio influence in sag change is identified according to the spatial state constraint.

[0010] Optionally, according to the spatial geometric feature relationship of the overhead transmission line, the spatial shape state equation under the initial condition constraint is established, including:

[0011] The length of the overhead line is determined according to the span length and the height difference angle of the overhead transmission line.

[0012] The overhead line state equation is constructed according to the length of the overhead line.

[0013] The spatial shape state equation is obtained by converting the overhead line state equation through the oblique parabolic catenary equation.

[0014] Optionally, according to the spatial geometric feature relationship of the overhead transmission line, the spatial shape state equation under the initial condition constraint is established, and further including:

[0015] The sag size is determined according to the spatial shape state equation.

[0016] The maximum sag and the position of the maximum sag are obtained by deriving the spatial shape state equation.

[0017] Optionally, based on the steady-state reference value of the fiber interference phase under the initial condition in the spatial shape state equation, a function mapping relationship between the fiber steady-state phase drift and the slowly changing sag of the line is constructed, including:

[0018] Based on the initial state of the overhead transmission line, the change amount of the steady-state reference value is determined.

[0019] The fiber infinitesimal length is calculated according to the change amount of the steady-state reference value and the fiber interference phase.

[0020] The cable length change amount is obtained by accumulating the change amount of the fiber infinitesimal length.

[0021] The horizontal stress and the sag size are calculated according to the cable length change amount.

[0022] The function mapping relationship is obtained according to the horizontal stress, the sag size and the cable length change amount.

[0023] Optionally, based on the initial state of the overhead transmission line, the change amount of the steady-state reference value is determined, including:

[0024] The spatial difference phase change amount is obtained by integrating the time difference phase of the initial state.

[0025] The change amount of the steady-state reference value is obtained by summing the spatial difference phase change amount.

[0026] Optionally, based on the response characteristics of Brillouin scattering spectrum to temperature change, a spatial state constraint is constructed according to a function mapping relationship, and a line load ratio influence in sag change is identified according to the spatial state constraint, comprising:

[0027] Determine the overhead line temperature according to the Brillouin scattering spectrum;

[0028] Construct a first variant equation according to the overhead line state equation;

[0029] Determine whether the overhead line temperature satisfies the constraint condition represented by the first variant equation, and if not, determine that the line load ratio has changed;

[0030] Construct a second variant equation according to the horizontal stress;

[0031] Determine the horizontal stress after the line load ratio changes according to the second variant equation;

[0032] Determine the line load ratio influence based on the horizontal stress through the overhead line state equation.

[0033] The application discloses the following technical effects: the line sag monitoring method based on Rayleigh-Brillouin scattering light provided by the application, the method comprises the following steps: according to the spatial geometric characteristic relationship of the overhead transmission line, a spatial shape state equation under initial condition constraint is established; a function mapping relationship between the stable state phase drift of the optical fiber and the slowly changing sag of the line is constructed based on the stable state reference value of the optical fiber interference phase under the initial condition in the spatial shape state equation; based on the response characteristics of Brillouin scattering spectrum to temperature change, a spatial state constraint is constructed according to the function mapping relationship, and a line load ratio influence in sag change is identified according to the spatial state constraint. The method constructs a monitoring system of phase stable drift-line length-sag mapping, solves the horizontal stress according to the temperature constraint provided by the Brillouin frequency shift and identifies the ice load ratio, and the precision and stability of the sag monitoring are improved. BRIEF DESCRIPTION OF DRAWINGS

[0034] In order to more clearly illustrate the technical solutions of the embodiments of the application or the prior art, the following will briefly introduce the drawings needed in the embodiments. Obviously, the drawings in the following description are only some embodiments of the application, and for those skilled in the art, other drawings can also be obtained without creative labor.

[0035] Figure 1 The line sag monitoring method flow chart of the application;

[0036] Figure 2 The overhead line mechanical structure schematic diagram of the embodiment of the application;

[0037] Figure 3 The BOTDR measurement result graph of the embodiment of the application;

[0038] Figure 4 A line space configuration reconstruction result map of the embodiment of the present application;

[0039] Figure 5 A line measured map of the embodiment of the present application;

[0040] Figure 6 A line sag measurement result map when not covered with ice of the embodiment of the present application;

[0041] Figure 7 A line sag measurement error map when not covered with ice of the embodiment of the present application;

[0042] Figure 8 A line sag measurement result map when covered with ice of the embodiment of the present application;

[0043] Figure 9 A line sag measurement error map when covered with ice of the embodiment of the present application. DETAILED DESCRIPTION

[0044] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the present application.

[0045] The above purposes, features and advantages of the present application can be more obvious and easy to understand. The present application will be described in further detail below with reference to the drawings and specific embodiments.

[0046] As shown in Figure 1 The present application provides a line sag monitoring method based on Rayleigh-Brillouin scattering light, comprising the following steps:

[0047] Step 100: establishing a space configuration state equation under initial condition constraints according to the spatial geometric feature relationship of the overhead transmission line;

[0048] Step 200: constructing a function mapping relationship between the fiber steady-state phase drift and the line slow-varying sag based on the steady-state reference value of the fiber interference phase in the space configuration state equation under the initial condition;

[0049] Step 300: constructing a space state constraint according to the function mapping relationship based on the response characteristics of the Brillouin scattering spectrum to temperature changes, and identifying the line specific load influence in the sag change according to the space state constraint.

[0050] Preferably, the specific process of step 100 comprises:

[0051] Determine the length of the overhead line according to the span length and the height difference angle of the overhead transmission line;

[0052] Construct the state equation of the overhead line according to the length of the overhead line;

[0053] Convert the state equation of the overhead line through the oblique parabolic catenary equation to obtain the spatial configuration state equation.

[0054] Specifically, for the actual operation of the overhead transmission line, since the cable diameter is much smaller than the span of the line, it can be regarded as an ideal flexible line model, so as to ignore the influence of the rigidity of the cable itself, and the load of the overhead line is uniformly distributed under normal circumstances, so the overhead line can be simplified and modeled, and combined with the parameters such as elastic modulus and thermal expansion coefficient, the spatial form change of the line under different operating conditions can be calculated according to the initial spatial configuration of the actual overhead transmission line, so as to describe the sag of each point along the line. The overhead transmission line to be measured in the embodiment is composed of n continuous spans, each suspension insulator string is parallel to the plumb line when it is completed, and the span lengths of the spans are represented as L 01 , L 02 , …, L 0n When the weather conditions or the cable state of the overhead transmission line change, the change in the embodiment is that ice is generated, the sag of the overhead line will change due to the change of the horizontal stress, assuming that the temperature of the overhead transmission line at t1 is T t1 , the specific load of the kth span is , and the expression (1) of the length of the overhead line at the kth span at t1 is:

[0055] ;

[0056] Wherein, S t1k is the length of the overhead line at the kth span at t1, L 0k is the span length of the overhead line at the kth span when the line is completed, is the height difference angle of the overhead line at the kth span when the line is completed, is the specific load of the overhead line at the kth span at t1, is the horizontal stress of the overhead line at t1. The expression (2) of the length of the overhead line at the kth span at t2 is:

[0057] ;

[0058] Wherein, S t2k is the length of the overhead line at the kth span at t2, is the specific load of the overhead line at the kth span at t2, is the horizontal stress of the overhead line at t2.

[0059] Thus, the expression (3) of the state equation of the overhead line at the kth span is:

[0060] ;

[0061] wherein E is the cable elastic modulus, a is the cable thermal expansion coefficient, T t2 is the temperature of the overhead transmission line at time t2.

[0062] Further, in an actual overhead transmission line, there is a certain height difference between the suspension points at both ends of the overhead line, and the expression (4) of the spatial configuration equation of the kth span of the overhead transmission line at time t is obtained based on the oblique parabolic catenary equation in the embodiment:

[0063] ;

[0064] and the sag at any point in the span can be further calculated according to the expression (5) wherein H 0k is the height difference between the suspension points at both ends of the kth span of the overhead line. Then, the derivative of the expression (5) is taken to obtain the position where the maximum sag occurs, which is at x=L 0k / 2 in the embodiment, i.e., at the center of the span, and the maximum sag coincides with the sag at the center of the span. The expression (6) of the maximum sag is: ; and when the height difference between the suspension points at both ends of the overhead line is small and much smaller than the span, the expression (5) is simplified to the expression (7) for solving the isohypse overhead line.

[0065] It should be noted that in an actual overhead transmission line, the horizontal stress of the line is difficult to directly measure, and when the temperature, specific load and horizontal stress of the line at time t1 are known, and the temperature and specific load of the line at time t2 are measured, the horizontal stress of the overhead line at time t2 can be measured, and the sag at any point of the overhead line can be further calculated according to the expression (5).

[0066] Preferably, the specific steps of the step 200 include:

[0067] determining the variation of the steady-state reference value based on the initial state of the overhead transmission line;

[0068] calculating the fiber element length according to the variation of the steady-state reference value and the optical fiber interference phase;

[0069] performing accumulation operation on the variation of the fiber element length to obtain the cable length variation;

[0070] calculating the horizontal stress and the sag size according to the cable length variation;

[0071] obtaining the function mapping relationship according to the horizontal stress, the sag size and the cable length variation.

[0072] The initial strain of the overhead transmission line in a sunny and windless environment is recorded as 0, and the change of the line sag will be caused by the change of temperature or specific load. Based on the mechanical structure of the fiber optic ground wire, when the cable length changes, the length of the internal optical fiber will also change, thereby causing the change of the optical signal interference phase inside the optical fiber. Taking the optical fiber microelement in any span as the target object, the phase change amount caused by the spatial interference is expressed as formula (8): fiber_i

[0073]

[0074] wherein k is the kth span, i is the ith sensing point, and n is the refractive index of the optical fiber, is the change amount of the phase steady-state reference value of the kth span of the optical fiber, and is the photoelastic coefficient of the sensing optical fiber. Then, the spatial resolution of the phase optical time domain sensitive optical time domain reflection system is defined as fiber_x, and the length change amount of the internal optical fiber of the kth span is obtained by accumulating the length change amounts of each sensing optical fiber microelement, and formula (9) is:

[0075]

[0076] When the spatial resolution fiber_x of the phase optical time domain sensitive optical time domain reflection system is small enough, that is, the number of microelements of the overhead line is sufficient, according to the actual measurement results, the change of the optical fiber length is approximately equal to the change of the cable length S.

[0077] Further, in actual measurement, the true value of the steady-state reference value of the interference light phase inside the optical fiber cannot be directly measured, and the steady-state reference value is restored by the time differential phase, and the spatial differential phase change amount of the steady-state reference value is represented by the integral of the time differential phase, and formula (10) is:

[0078]

[0079] is the spatial differential phase change amount of the optical fiber of the kth span and the ith sensing point, is the change amount of the interference phase of the optical fiber of the kth span and the ith sensing point with time. The true value of the steady-state reference value in the embodiment does not affect the measurement result of the sag , so the initial reference value is recorded as 0, and the change amount of the phase steady-state reference value in one span is obtained by summing the spatial differential phase change amounts of each sensing point , and formula (11) is: ​​​​​​

[0080] ;

[0081] The expression (12) for finally determining the cable length change amount is: .

[0082] Further, in actual operation, the specific load of the overhead transmission line does not change most of the time, so after the cable length change is obtained, the expression (1) and the expression (2) are combined into an expression (13): , so as to calculate the horizontal stress s of the overhead line at the time t2. t2 After that, the overhead line spatial configuration is reconstructed through the expression (4), and then the sag of any point along the line in the span is obtained. In some embodiments, without considering the change of the line specific load, the expression (13) and the expression (12) are combined into an expression (14): .

[0083] It should be noted that by using the phase-sensitive optical time domain reflection technology in the distributed optical fiber sensing technology, the change amount of the optical fiber phase stable reference value is introduced according to the line length change caused by the change of the line sag, so as to realize the online monitoring of the horizontal stress of the overhead line only through the optical fiber, solve the problem that the traditional method is difficult to directly solve the line sag through the reliable line mechanical state equation and line sag formula, improve the monitoring accuracy of the line sag, and greatly reduce the operation and maintenance cost.

[0084] Preferably, the specific steps of the step 300 include:

[0085] determining the temperature of the overhead line according to the Brillouin scattering spectrum;

[0086] constructing a first variational equation according to the state equation of the overhead line;

[0087] determining whether the temperature of the overhead line meets the constraint condition represented by the first variational equation, and if not, determining that the line specific load changes;

[0088] constructing a second variational equation according to the horizontal stress;

[0089] determining the horizontal stress after the change of the line specific load according to the second variational equation;

[0090] determining the influence of the line specific load based on the horizontal stress through the state equation of the overhead line.

[0091] Specifically, in the actual operation of overhead transmission line, the main reason for the change of sag is the change of temperature and specific load. When the specific load of overhead transmission line changes due to icing in winter, the change of line sag obtained according to step 200 will not conform to the actual value, so the state equation of overhead line is modified according to the measured temperature in step 300.

[0092] In the embodiment, when the temperature of overhead line changes, the change of Brillouin spectrum in the backscattered light of the internal optical fiber of the overhead line will be caused synchronously, and the expression (15) of the relationship between the change and the temperature is: v B

[0093] ;

[0094] Wherein, C vt is the Brillouin temperature response coefficient. The temperature of overhead line at t2 is obtained by measuring the Brillouin spectrum of the optical fiber of overhead line and the initial value of temperature at t1. Then, the expression (3) is rewritten as expression (16):

[0095] ;

[0096] The horizontal stress of overhead line at t2 and the temperature of overhead line calculated according to expression (14) are substituted into expression (16) together. If the spatial state constraint of overhead transmission line represented by the expression is not satisfied, it means that the specific load of line at t1 and t2 is different, that is, it is determined that the specific load of line changes, and the change of sag caused by icing load of line needs to be calculated. Then, expression (13) is rewritten as expression (17):

[0097] ;

[0098] Thus, the horizontal stress of overhead line at t2 after the change of specific load is calculated, and expression (18) is:

[0099] ;

[0100] After the horizontal stress of overhead line at t2 is obtained by expression (18), the specific load of line at the current time is calculated by expression (3) or expression (13), and then substituted into expression (5) to obtain the sag of any point along the overhead line at t2.

[0101] ​It should be noted that the method directly measures the temperature of the cable body through the internal optical fiber of the cable by using the Brillouin optical time domain reflection technology. The internal optical fiber of the fiber optic ground wire uses loose tube optical fiber. When the icing is not serious (icing thickness < 20 mm), the influence of strain on Brillouin scattering spectrum can be basically ignored, so the Brillouin optical time domain reflection technology can be used for temperature measurement. In addition, the general icing thickness > 20 mm is serious icing, and the operation and maintenance personnel will immediately take ice removal measures, so in actual application, the application scenario of icing thickness > 20 mm does not need to be considered. The embodiment combines the change law of the optical fiber interference phase, rewrites the expression (3) of the traditional line mechanics equation as expression (18), realizes the solution of the line horizontal stress under the comprehensive action of temperature and icing by introducing the change amount of the optical fiber interference phase steady-state reference value, and considers the influence of various factors such as overhead line type, erection height difference angle, span, etc. can maximize the coverage of various actual operating conditions, and finally realizes the accurate monitoring of the line sag, and can only rely on the optical fiber sensing to provide the specific reasons for the change of the overhead line sag under most working conditions.

[0102] It can be understood that the traditional line mechanics equation before rewriting focuses on establishing the direct relationship between the temperature, horizontal stress and specific load of the overhead line at any two moments, and the applicable object includes all overhead lines, not limited to a special line structure. The method uses the optical fiber in the overhead line as a sensing unit and a communication unit, realizes the integration of transmission and communication, and uses the structural characteristics that the optical fiber and the line length change synchronously, introduces the line length change amount through expression (13) and expression (17) to eliminate the ratio of the specific load and the horizontal stress at t2 moment. The change amount of the optical fiber interference phase steady-state reference value is also introduced to obtain expression (18), which realizes the solution of the line horizontal stress under the comprehensive action of temperature and icing. Finally, expression (5) is used to realize the accurate monitoring of the line sag.

[0103] The embodiment takes an overhead transmission line in a city as an example, and the specific implementation process of the example is as follows:

[0104] 1. On-site survey is conducted at the target line belonging to the substation and the adjacent tower to obtain the span length, overhead line type and cross-sectional area, overhead line specific load, overhead line hanging point height difference angle and other spatial geometric parameters and cable material parameters such as elastic modulus and thermal expansion coefficient at t1 moment, as shown in Figure 2

[0105] ​2. In the substation communication cabinet, select the idle optical fiber overhead ground wire internal optical fiber core two-core to connect the phase-sensitive optical time domain reflectometry (Φ-OTDR) and Brillouin optical time domain reflectometry (BOTDR) respectively, carry out fiber core connectivity test, and divide the full optical path according to the line span according to the field survey results, and establish the overhead line maximum sag calculation formula of each span according to expression (6);

[0106] 3. In the initial working condition of clear and windless, collect the steady-state reference value of the optical fiber interference phase as 0, and collect the initial value v B0 of the Brillouin scattering spectrum as a zero-point reference for subsequent calculation;

[0107] 4. During the operation of the line, the time difference phase of the interference phase obtained by Φ-OTDR is time-integrated by using expression (10), and the integrated phase signals of each point in a span are accumulated according to expression (11) to obtain the steady-state value change of the interference phase of the whole span;

[0108] 5. The horizontal stress of the overhead line at t2 is calculated by using expression (14);

[0109] 6. During the operation of the line, the Brillouin spectrum obtained by BOTDR is analyzed, and the difference between the initial value v B0 is obtained to obtain the temperature of each sensing point of the overhead line according to expression (15); considering that the temperature of the overhead line in a span is approximately equal, the average value of the temperature measured by each sensing point is selected as the temperature T t2 of the overhead line at t2 in the span;

[0110] 7. The temperature T t2 of the overhead line at t2 is substituted into expression (3) to calculate the horizontal stress at t2, if the difference between the horizontal stress calculated according to expression (14) exceeds 10%, it is indicated that the change of the sag of the line is not completely caused by the temperature, and the correction calculation is needed by expression (18);

[0111] 8. After obtaining the horizontal stress that passes the verification, the sag f of each point along the line is calculated according to expression (5), and the maximum sag value f m of the span is calculated according to expression (6);

[0112] 9. The final output is the sag distribution result of the span level and the reason for the change of the sag, so as to provide decision support for the operation and maintenance unit, thereby avoiding the safety risk caused by icing or excessive sag.

[0113] It should be noted that, for example,Figure 3 The BOTDR measurement result shown is the measurement result of the Brillouin frequency shift of the overhead transmission line with a full length of 50 km at different times after the idle core of the optical fiber overhead ground wire in the transformer substation communication cabinet is connected to the Brillouin optical time domain reflectometer (BOTDR), and the complete span distribution and the optical fiber transmission path of the measured line are covered. The black line represents the Brillouin frequency spectrum along the line measured at 6:00, the red line represents the Brillouin frequency spectrum along the line measured at 12:00, and the blue line represents the Brillouin frequency spectrum along the line measured at 18:00. It can be seen that the frequency (10.82-10.88 GHz) of the optical signal distributed along the line distance (0-50000 m) presents regular differences with the monitoring time: the external environment temperature corresponding to different monitoring times is different, and the temperature change will directly cause the Brillouin scattering spectrum of the optical fiber inside the overhead line to change correspondingly, and the Brillouin frequency shift change of the optical fiber is linearly related to the temperature change, so that the real-time temperature of the line can be inversely deduced by measuring the frequency shift change; and the spatial distribution trend of the frequency shift curve at different times is almost the same, indicating that the temperature changes of each section of the line have synchronicity, and there is no local temperature abnormal interference, further verifying the stability of the temperature measurement. In addition, the figure also shows the ability of the Brillouin optical time domain reflectometer (BOTDR) to monitor the temperature change of the long-distance overhead transmission line, which can effectively perceive the state change of the overhead line caused by temperature at different times, providing accurate temperature parameter support for the subsequent line horizontal stress verification and the inverse deduction of the sag size through temperature verification of the line, and ensuring the accuracy of the sag monitoring result.

[0114] As shown in the line space configuration reconstruction result shown in Figure 4 The line space configuration reconstruction result shown is a comparison diagram drawn based on the single-span mechanical characteristics of the target overhead transmission line, wherein the "measured value" is the measured sag value of different points along the line obtained by the unmanned aerial vehicle laser ranging, and the "theoretical value" is calculated based on the traditional overhead line mechanical model, showing the theoretical distribution of the sag of any point along the line under ideal working conditions.

[0115] As shown in the line measured graph shown in Figure 5 The line measured graph shown is the phase monitoring result along the line obtained by continuously collecting a certain 50-kilometer overhead transmission line for 10 minutes after connecting the idle core in the optical fiber composite overhead ground wire to the phase-sensitive optical time domain reflectometer (Φ-OTDR). It can be seen that along with the change of the line distance (0-50 km), the phase signal presents obvious vertical bar characteristics, which is due to the fact that different spans of the line are affected by their own geometric space characteristics and the external environment, resulting in significant differences in the vibration response of each span. The figure also shows the ability of the phase-sensitive optical time domain reflectometer (Φ-OTDR) to monitor the dynamic change of the phase of the long-distance overhead transmission line, which can effectively perceive the state difference of the line at different times and different spans within the 10-minute collection period, providing accurate raw data support for the inverse deduction of the phase signal segmentation and line length change in the line sag monitoring.

[0116] Figure 6 and Figure 7 is the result chart of the comparison of the maximum sag of the overhead transmission line 1-6 span and the measurement error. Among them Figure 6 The "field measurement result" is the real value of the maximum sag of each span obtained by traditional manual field survey, the "optical fiber measurement result" is the maximum sag value calculated by connecting the idle core in the optical fiber composite overhead ground wire to the phase-sensitive optical time domain reflectometer and Brillouin optical time domain reflectometer, and the maximum sag value is calculated by integrating the phase signal and the horizontal stress back propagation, and the "temperature estimation result" is the maximum sag value back propagated only according to the temperature change by measuring the ambient temperature through the temperature sensor without considering the influence of different spans on the horizontal stress of the line. From Figure 6 It can be known that in all spans 1-6, the sag value deviation of the optical fiber measurement and the field measurement is always controlled within 0.1m, and the real level of the maximum sag of each span can be accurately fitted as a whole, and the deviation of the temperature estimation result and the real value is more significant. Figure 7 Then the difference is further quantified, and from the overall data distribution, the relative error of the optical fiber measurement result is lower than that of the temperature estimation result, which shows the high accuracy and significant superiority of the method.

[0117] Figure 8 and Figure 9 is the result chart of the comparison and analysis of the maximum sag and measurement error of the same span of the overhead transmission line under different ice thickness conditions. From Figure 8 It can be known that as the ice thickness increases from 4.12mm to 18.54mm, the sag value deviation of "optical fiber measurement" and "field measurement" is always controlled within 0.2m, and the overall change trend of the real value can be accurately followed; and the deviation of the "temperature estimation result" and the real value is significant, and the deviation of some ice thickness conditions exceeds 0.5m, and the influence of the increase of the ice thickness on the sag cannot be reflected. Figure 9 The errors of the two types of measurement methods are quantified and compared, and the relative error of the optical fiber measurement result is controlled within 5%, and the relative error of the temperature estimation result is generally higher than that of the optical fiber measurement result, and the relative error of some working conditions has exceeded 20%. The result shows that the method has high accuracy and anti-interference, and successfully solves the technical pain point that the traditional temperature estimation method ignores the influence of the ice thickness on the horizontal stress of the line, and the error of the sag measurement value is too large.

[0118] The beneficial effects of the present application are as follows:

[0119] 1) Through the phase-sensitive optical time domain reflectometry (Φ-OTDR), micron-level line length change detection is realized, combined with Brillouin optical time domain reflectometry (BOTDR) for accurate temperature measurement, so that the sag measurement error is controlled within 0.1m when not covered with ice, and within 0.2m when covered with ice, the relative error is less than 5%, which greatly improves the monitoring accuracy;

[0120] 2) By fusing phase and Brillouin frequency shift data, temperature change and ice-induced specific load change are distinguished, false judgments caused by environmental factors are avoided, and the inversion stability and anti-interference ability are significantly improved;

[0121] 3) By inversely solving the line length change through the optical fiber phase change, the stress is indirectly solved, which breaks through the bottleneck of the mechanical state equation in practical application, effectively reduces the frequency of manual inspection and field calibration, and reduces the transformation and operation cost;

[0122] 4) The distributed optical fiber sensing technology is used to continuously collect optical fiber phase and temperature data, realize real-time online monitoring of sag, and timely find line state changes, improve line safety margin and operation decision efficiency.

[0123] The various embodiments in the specification are described in a progressive manner, and each embodiment focuses on the difference from other embodiments. The same or similar parts between the various embodiments can be mutually referred to.

[0124] In the present application, specific examples are used to illustrate the principles and implementation methods of the present application. The above description of the embodiments is only used to help understand the method and core idea of the present application. Meanwhile, for those skilled in the art, according to the idea of the present application, the specific implementation method and application range will be changed. In summary, the content of the specification should not be understood as a limitation of the present application.

Claims

1. A method for monitoring line sag based on Rayleigh-Brillouin scattering light, characterized in that, Includes the following steps: Based on the spatial geometric characteristics of overhead transmission lines, a spatial configuration state equation under initial condition constraints is established. Based on the steady-state reference value of the fiber interference phase under the initial conditions in the aforementioned spatial configuration state equation, a functional mapping relationship between the steady-state phase drift of the fiber and the gradually varying sag of the line is constructed, specifically as follows: Based on the initial state of the overhead transmission line, the change in the steady-state reference value is determined; The length of the fiber element is calculated based on the steady-state reference value and the change in the fiber interference phase. The change in the length of the optical fiber element is accumulated to obtain the change in cable length. The horizontal stress and the sag are calculated based on the change in cable length. The function mapping relationship is obtained based on the horizontal stress, the sag size, and the change in cable length. Based on the response characteristics of Brillouin scattering spectrum to temperature changes, spatial state constraints are constructed according to the function mapping relationship, and the influence of line load ratio on sag variation is identified according to the spatial state constraints.

2. The line sag monitoring method based on Rayleigh-Brillouin scattering light according to claim 1, characterized in that, Based on the spatial geometric characteristics of overhead transmission lines, spatial configuration state equations under initial condition constraints are established, including: The length of the overhead transmission line is determined based on the span length and elevation difference angle of the overhead transmission line. Construct the overhead line state equation based on the overhead line length; The state equation of the overhead line is transformed by the equation of the oblique parabola catenary to obtain the state equation of the spatial configuration.

3. The line sag monitoring method based on Rayleigh-Brillouin scattering light according to claim 2, characterized in that, Based on the spatial geometric characteristics of overhead transmission lines, a spatial configuration state equation under initial condition constraints is established, which also includes: The sag size is determined based on the spatial configuration state equation; Differentiating the spatial configuration state equation yields the maximum sag and the position of the maximum sag.

4. The line sag monitoring method based on Rayleigh-Brillouin scattering light according to claim 3, characterized in that, Based on the initial state of the overhead transmission line, the change in the steady-state reference value is determined, including: Integrating the time difference phase of the initial state yields the spatial difference phase change. The change in the spatial differential phase is summed to obtain the change in the steady-state reference value.

5. The line sag monitoring method based on Rayleigh-Brillouin scattering light according to claim 4, characterized in that, Based on the response characteristics of Brillouin scattering spectrum to temperature changes, spatial state constraints are constructed according to the aforementioned function mapping relationship. The influence of line load ratio on sag variation is then identified based on these spatial state constraints, including: The overhead line temperature was determined based on the Brillouin scattering spectrum. The first variant equation is constructed based on the overhead line state equation; Determine whether the temperature of the overhead line meets the constraint conditions represented by the first variant equation; if not, determine that the line load ratio has changed. A second variant equation is constructed based on the horizontal stress; The horizontal stress after the change in line load is determined according to the second variant equation; Based on the horizontal stress, the specific load effect of the line is determined by the overhead line state equation.

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