OPGW optical cable sag calculation method based on catenary equation and Brillouin distributed optical fiber sensing

Abstract

The invention discloses an OPGW optical cable sag calculation method based on a catenary equation and Brillouin distributed optical fiber sensing. The OPGW optical cable sag calculation method comprises the following steps of obtaining coordinates of towers at two ends of a span, tower heights, a span horizontal length Lh and a span height difference h; measuring the length Sf of the optical fiber in the span by adopting a Brillouin distributed optical fiber sensing technology, and converting the actual suspension length Sc of the optical cable according to the preset excess length ratio eta of the optical fiber to the optical cable structure; establishing a catenary equation with height difference correction; the sag f is defined as the vertical difference between the highest point and the lowest point of the optical cable, and a sag value is output and compared with a preset safety threshold value; and inputting a calculation result into a monitoring platform to realize real-time display and storage. Long-distance, high-precision and continuous on-line monitoring is realized, and the system is suitable for operation state evaluation and safety early warning of OPGW optical cables of ultra-high voltage transmission lines, mountainous areas or plateau lines.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of OPGW optical cable sag calculation, and particularly to an OPGW optical cable sag calculation method based on catenary equation and Brillouin distributed optical fiber sensing. BACKGROUND

[0002] In the operation process of overhead transmission line, the conductor or optical cable presents a curve shape similar to catenary under the action of self weight, and the vertical distance between the lowest point and the support point is the sag. The size of the sag is directly related to the safety clearance of the line and the ground, buildings and vegetation, and is also closely related to the mechanical stress level, thermal expansion state and long-term operation stability of the line. Excessive sag may lead to insufficient safety distance, discharge flashover or line trip, and also make the optical fiber in a long-term large strain state, thereby shortening the service life. On the other hand, too small sag means that the line tension is too large, which increases the risk of mechanical damage such as broken strands and broken wires. Therefore, accurately obtaining the sag and realizing real-time monitoring are the core needs of the operation and maintenance of the transmission line.

[0003] At present, the sag measurement of the transmission line mainly relies on laser ranging method, image measurement method and manual measurement method. The laser ranging method directly measures the curve shape of the conductor by arranging laser ranging devices on the tower or the ground, and then calculates the sag. This method needs to erect devices at multiple observation points, and the arrangement period is long. In addition, the ranging accuracy significantly decreases in rainy, snowy and foggy weather. The image measurement method obtains the conductor image by means of high-resolution camera or unmanned aerial vehicle aerial photography, and calculates the sag by using image recognition and geometric fitting. This method has a decreased accuracy in insufficient light, cluttered background or conductor shaking, and relies on manual or unmanned aerial vehicle regular inspection, so it is difficult to realize continuous online monitoring. The manual measurement method uses manual methods such as measuring tools and markers for visual or contact measurement. This method is greatly limited by terrain and weather conditions, has low work efficiency, and has great safety risks.

[0004] The above methods need to install special devices on the tower or erect measurement base stations, and have a long construction period. The measurement accuracy is easily disturbed by external factors such as environmental light, wind speed and temperature. In addition, these methods are mainly for periodic or temporary measurement, and cannot realize 24-hour continuous online monitoring. On the other hand, optical fiber composite overhead ground wire (OPGW) has been widely used in modern transmission lines, and contains a communication optical fiber unit inside. The length change of the optical fiber can reflect the deformation of the line under the influence of factors such as temperature change, mechanical tension and wind load. Therefore, the sag calculation based on optical fiber length measurement has natural real-time and long-distance coverage capabilities.

[0005] The existing monitoring technology based on the length of the optical fiber can only accurately obtain the accurate length change of the optical fiber between the splicing points by means of optical time domain reflection (OTDR), Brillouin distributed optical fiber sensing (BOTDR / BOTDA) and the like, and cannot obtain the distance between two towers, and there are still two major deficiencies in actual application, one is that an accurate mathematical inversion model is not established, and the existing method is based on linear assumption or empirical coefficient to estimate the cable sag, and the inversion is not strictly combined with the catenary mathematical equation, so that the precision is limited. Two is that the complex span conditions are not fully considered: for mountainous and plateau lines, there is a significant height difference between towers, and the existing simple model cannot accurately process the influence of the height difference on the sag. SUMMARY

[0006] In order to overcome the above-mentioned shortcomings of the prior art, the purpose of the present application is to provide an OPGW cable sag calculation method based on catenary equation and Brillouin distributed optical fiber sensing, which realizes long-distance, high-precision and continuous online monitoring, and is suitable for UHV transmission line, mountainous or plateau line OPGW cable operation state evaluation and safety warning.

[0007] The technical scheme adopted by the present application to solve its technical problems is: an OPGW cable sag calculation method based on catenary equation and Brillouin distributed optical fiber sensing, comprising the following steps:

[0008] Step one: obtaining the coordinates of the towers at both ends of the span, the tower height, and the span horizontal length Lh and the span height difference Ah;

[0009] Step two: measuring the optical fiber length Sf in the span by using the Brillouin distributed optical fiber sensing technology, and converting the actual suspension length S of the optical cable according to the preset excess length ratio η of the optical fiber and the optical cable structure c ; Step three: establishing a catenary equation with height difference correction;

[0010] Step four: the sag f is defined as the vertical difference between the highest point and the lowest point of the optical cable, and the sag value is output and compared with the preset safety threshold.

[0011] As a further improvement of the present application: the span height difference Ah in step one is the right end tower top height minus the left end tower top height, and the tower top height includes the terrain height and the tower height.

[0012] As a further improvement of the present application: the step two includes: the optical fiber length S f According to the strain pattern measured by the Brillouin distributed optical fiber sensing technology;

[0013] According to the shape of the catenary of each span, the length S c of the two end points of the catenary is obtained.

[0014] As a further improvement of the present application: the actual suspension length calculation formula of the optical cable in step two is as follows:

[0015]

[0016] wherein: S c : actual hanging length of the optical cable; S f : length of the optical fiber within the span; η: preset length ratio of the optical fiber and the optical cable structure.

[0017] As a further improvement of the present application: the catenary equation with height difference correction in step three is as follows:

[0018]

[0019] wherein: a: catenary parameter; C: constant term.

[0020] As a further improvement of the present application: the simultaneous conditions of the catenary equation with height difference correction include:

[0021] The constraint on the length of the optical cable is:

[0022]

[0023] wherein: L h is the tower height and the horizontal length of the span.

[0024] As a further improvement of the present application: the simultaneous conditions of the catenary equation with height difference correction include:

[0025] The constraint on the height difference is:

[0026] y(L h )-y0=Δh

[0027] wherein Δh is the height difference of the span.

[0028] As a further improvement of the present application: the definition of the sag f in step four is the vertical difference between the highest point and the lowest point of the optical cable, and the calculation formula is as follows:

[0029]

[0030] wherein L h is the tower height and the horizontal length of the span.

[0031] The output sag value is compared with a preset safety threshold.

[0032] As a further improvement of the present application: it further includes step five: inputting the calculation result into a monitoring platform to realize real-time display and storage.

[0033] As a further improvement of the present application: in step five, when the sag exceeds the safety threshold, an alarm is triggered, and historical data are recorded for operation and maintenance analysis.

[0034] Compared with the prior art, the present application has the advantages that: the BOTDR optical fiber measurement precision and the catenary mathematical model are combined, the sag calculation is accurate, and different span and height difference conditions are adapted; without manual inspection or additional equipment, the optical fiber length measurement and sag calculation can realize real-time online monitoring; the line with significant height difference in mountainous areas, plateaus and other spans can be supported, and temperature and wind load data can be corrected; linkage with the operation and maintenance platform can be realized, and out-of-limit sag automatic alarm can be realized to improve the line safety; without additional measurement equipment, the existing OPGW optical fiber can be used to complete the whole line monitoring, and the operation and maintenance cost is reduced. BRIEF DESCRIPTION OF DRAWINGS

[0035] In order to more clearly illustrate the technical solutions, the following will briefly introduce the drawings needed to be used in the embodiments. Obviously, the drawings in the following description only represent some embodiments of the present application, and all other drawings obtained by those of ordinary skill in the art without creative labor based on these drawings also belong to the protection scope of the present application.

[0036] Figure 1 The method flowchart of the present application.

[0037] Figure 2 The catenary form schematic diagram in the present application.

[0038] Figure 3 The system composition block schematic diagram of the OPGW optical cable sag calculation method application based on the catenary equation and the Brillouin distributed optical fiber sensing of the present application.

[0039] Figure 4 The catenary test result diagram of the plurality of continuous towers in the tension section measured by the BOTDR of the specific embodiment of the present application. DETAILED DESCRIPTION

[0040] In order to make the purpose, technical solutions and advantages of the present application more clear, the following will combine the specific embodiments of the present application and the corresponding drawings to clearly and completely describe the technical solutions of the present application. Obviously, the described embodiments only represent 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 of ordinary skill in the art without creative labor also belong to the protection scope of the present application.

[0041] It should be noted that the terms "include" and "have" and any variations thereof in the specification and claims of the present application and the above-mentioned drawings are intended to cover the non-exclusive inclusion, for example, the process, method, system, product or equipment including a series of steps or units does not have to be limited to the clearly listed steps or units, but can include other steps or units that are not clearly listed or inherent to these processes, methods, products or equipment.

[0042] The conductor or optical cable of overhead transmission line approximately assumes a catenary shape under the action of self-weight, and the vertical distance of the lowest point relative to the supporting point is called sag. The sag is directly related to the safety clearance of the line from the ground, buildings and vegetation, and reflects the mechanical stress, thermal expansion state and long-term operation stability of the line. Optical fiber composite overhead ground wire (OPGW) has been widely used in transmission lines. The communication optical fiber contained therein can obtain the length variation, strain and temperature distribution along the line through Brillouin distributed optical fiber sensing (such as BOTDR / BOTDA), and has the potential of long-distance coverage and real-time monitoring. Existing estimation methods based on optical fiber length or strain mostly use linear approximation or empirical coefficients, and do not take the catenary mathematical equation (considering self-weight, tension, span geometry, etc.) as the basis for inversion, resulting in limited accuracy of the inverse calculation from the optical fiber measurement to the sag value. There is a significant difference in the height of the tower in mountainous and plateau lines, and the traditional plane or simplified model cannot accurately describe the influence of the height difference on the spatial curve of the conductor / optical cable and the length of the optical fiber. Brillouin distributed sensing provides length variation, strain and / or temperature data along the optical fiber, but the real spatial projection length between towers, the accurate position of the supporting point and other geometric boundary conditions are not directly available, making the unique inverse calculation from the optical fiber length to the spatial sag uncertain. Brillouin measurement is sensitive to both temperature and strain, and it is difficult to distinguish the length variation caused by thermal expansion and mechanical tension under a single measurement channel, which affects the accuracy of the sag inversion. BOTDR / BOTDA has physical limits in spatial resolution, signal-to-noise ratio and absolute measurement accuracy, which limits the detection capability of small sag changes or local deformation. The laying method of the optical fiber in the OPGW, the end fixation and the coupling of the optical fiber and the metal components, etc. will produce local length deviation or non-equivalent strain, and if not modeled and corrected, it will introduce systematic errors. Wind load, ice and snow, day and night temperature difference and line vibration will cause time-varying length / strain signals, and the inversion algorithm is required to be accurate and robust to noise and dynamic disturbance under real-time online conditions. Therefore, developing a method for accurately measuring the length of the optical fiber using Brillouin distributed optical fiber sensing technology and inversely calculating the sag of the OPGW optical cable combined with the catenary equation (including height difference correction) can realize long-distance, high-precision and real-time sag calculation without adding any additional sensors. This can not only significantly improve the automation level of transmission line operation and maintenance, but also reduce the cost of inspection, and improve the safety and reliability of line operation.

[0043] The present application will be further described in conjunction with the accompanying drawings and examples: as Figures 1 to 4The method for calculating the sag of OPGW optical cables based on the catenary equation and Brillouin distributed fiber sensing includes the following steps: obtaining the coordinates, tower heights, horizontal span length Lh, and span height difference Δh of the towers at both ends of the span; measuring the fiber length Sf within the span using Brillouin distributed fiber sensing technology; and calculating the actual suspension length S of the optical cable based on the preset excess length ratio η between the fiber and the cable structure. c A catenary equation with elevation correction is established; the sag f is defined as the vertical difference between the highest and lowest points of the optical cable, the sag value is output and compared with a preset safety threshold; the calculation results are input into the monitoring platform for real-time display and storage. This enables long-distance, high-precision, continuous online monitoring, suitable for OPGW optical cable operation status assessment and safety early warning in UHV transmission lines, mountainous or plateau lines.

[0044] As a specific embodiment of the present invention, a method for calculating the sag of OPGW optical cables based on the catenary equation and Brillouin distributed optical fiber sensing includes the following steps:

[0045] Step 1: Parameter Acquisition

[0046] (1) Obtain the coordinates, tower height, and horizontal span length Lh of the towers at both ends of the span;

[0047] (2) Obtain the span height difference Δh, where Δh is the difference between the height of the right tower top and the height of the left tower top.

[0048] The height of the tower top includes both the elevation of the terrain and the height of the tower itself.

[0049] Step 2: Fiber optic length measurement;

[0050] The Brillouin distributed fiber optic sensing technology (BOTDR / BOTDA) is used to measure the fiber length S within the span. f Its length is determined based on the strain pattern measured by Brillouin distributed optical fiber sensing technology. The length of the optical fiber is calculated by determining the length of the two ends of the catenary based on the catenary shape of each section, thus realizing fully distributed online measurement.

[0051] The actual suspension length S of the optical cable is calculated based on the preset excess length ratio η of the optical fiber and cable structure. c :

[0052]

[0053] In the formula: S c Actual suspension length of the optical cable; S f : Length of optical fiber within the span; η: Preset ratio of the excess length of the optical fiber to the optical cable structure.

[0054] Specifically, such as Figure 4 As shown, the optical cable length S measured by BOTDR f =916.03,

[0055] Step three: catenary parameter calculation:

[0056] Assuming that the optical cable is in the form of catenary under the action of its own weight, the catenary equation with height difference correction is established:

[0057]

[0058] Simultaneous conditions:

[0059] (1) Optical cable length constraint:

[0060]

[0061] (2) Height difference constraint:

[0062] y(L h )-y0=Δh

[0063] In the formula: L h : tower height and horizontal length of span; △h: height difference of span.

[0064] The catenary parameters a and constant term C are solved by numerical iteration to obtain the accurate curve shape of the optical cable.

[0065] Step four: sag calculation

[0066] The sag f is defined as the vertical difference between the highest point and the lowest point of the optical cable:

[0067]

[0068] The sag value is output and compared with the preset safety threshold.

[0069] Specifically, when the horizontal span L h = 906m, the height difference is 1m, and the calculated sag is 3.65m.

[0070] Step five: real-time monitoring and alarm:

[0071] The calculation results are input into the monitoring platform to realize real-time display and storage;

[0072] When the sag exceeds the safety threshold, an alarm is triggered, and historical data are recorded for operation and maintenance analysis.

[0073] The present application couples the full-length / strain information of the optical fiber measured by Brillouin distributed optical fiber sensing (BOTDR / BOTDA) with a catenary mathematical model containing height difference correction, calculates the spatial curve of the cable and the sag by numerical iteration, and introduces the real length constraint measured by the optical fiber into the inversion process based on the catenary equation as the physical reference, avoiding the system deviation caused by simple linear or empirical estimation, thereby significantly improving the inversion accuracy from the optical fiber length to the sag value. The introduction of the height difference constraint term in the catenary model can accurately restore the three-dimensional curve shape of the wire / cable in mountainous / plateau spans with significant terrain drop, overcoming the lack of applicability of traditional plane or simplified models. Directly using the OPGW optical fiber that has been laid and Brillouin distributed sensing, continuous online measurement of multiple spans and long distances is realized, without the need for additional installation of laser, camera and other measurement equipment on the tower, eliminating the blind area and weather restrictions of artificial regular inspection. The method framework can incorporate temperature compensation and environmental (wind, ice) correction strategies to eliminate the influence of thermal expansion and other non-mechanical tension factors on length changes, ensuring that the sag estimation better reflects the mechanical tension and structural deformation nature. Without additional sensors or high-frequency manual inspection, 24 / 7 sag monitoring and threshold alarm can be realized, which is convenient for early detection of over-limit sag and linkage of operation and maintenance decisions, thereby reducing inspection costs and reducing line operation risks. By introducing parameters such as cable preset length ratio, laying characteristics, and endpoint fixation method in the model, the systematic deviation caused by laying methods can be modeled and corrected, improving the engineering practicability and result reliability. Numerical iteration solution combined with filtering / robustness processing can meet the online calculation efficiency requirements while ensuring accuracy, making the system available for real-time monitoring and historical data storage analysis. The results can be directly output to the operation and maintenance monitoring platform to realize real-time visualization, historical backtracking and alarm strategy configuration; at the same time, the method can be integrated with other state monitoring (such as tension meters, weather stations) to improve the judgment reliability.

[0074] The main function of the present application: the present application couples the full-distributed optical fiber length / strain / temperature information measured by Brillouin distributed optical fiber sensing (BOTDR / BOTDA) with the catenary mathematical model containing height difference correction, and inversely calculates the three-dimensional curve of the optical cable and calculates the sag through numerical iteration, which has significant engineering benefits: first, the inversion is based on the physical catenary equation, which avoids the system deviation caused by linear or empirical estimation, greatly improves the sag inversion accuracy; second, the model explicitly introduces the tower height difference constraint, which can accurately process the span in mountainous areas, plateaus and other areas with significant terrain drop; third, the existing OPGW optical fiber is directly used to realize long-distance, all-weather and online monitoring, without the need to increase laser or camera measuring equipment on the tower, thereby reducing the construction and operation cost; fourth, the method supports temperature-strain decoupling and laying length ratio correction measures, which can eliminate the systematic errors introduced by thermal expansion and installation methods, and improve the result reliability; fifth, combined with filtering and robust processing, it can resist dynamic disturbances such as wind load, ice and snow and vibration, and meet the real-time online calculation and alarm requirements; finally, the sag result can be linked with the operation and maintenance platform to realize visualization, historical backtracking and over-limit automatic alarm, and improve the operation safety and operation automation level of the transmission line.

[0075] The functions described herein can be implemented in hardware, software executed by a processor, firmware, or any combination thereof. If implemented in software executed by a processor, the functions can be stored on or transferred over as one or more instructions or code on a computer-readable medium. Other examples and implementations are within the scope and spirit of the disclosure and appended claims. For example, due to the nature of software, functions described above can be implemented using software executed by a processor, hardware, firmware, hardwiring, or combinations of any of these. Also, each of the functions can be implemented as a separate process or combined as a single process. Further, the functions can be implemented at least in part outside an operating system routine.

[0076] In several embodiments provided in the present application, it should be understood that the disclosed technical content can be implemented by other ways. Among them, the above-mentioned device embodiments are only schematic, for example, the division of the units can be a logical function division, and actual implementation can have another division way, for example, a plurality of units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point, the coupling or direct coupling or communication connection between the units or modules shown or discussed can be indirect coupling or communication connection through some interfaces, units or modules, which can be electrical or other forms.

[0077] The units described as separate components may or may not be physically separate, and the components of the control device may or may not be physical units, i.e. may be located in one place or distributed over a plurality of units. Some or all of the units can be selected as appropriate to achieve the purpose of the embodiment.

[0078] In summary, those skilled in the art can make other various corresponding transformation schemes according to the technical solutions and technical concepts of the present application without creative mental labor after reading the present application file, which all belong to the protection scope of the present application.

Claims

1. An OPGW cable sag calculation method based on catenary equation and Brillouin distributed fiber sensing, characterized in that, The method comprises the following steps: Step one: Obtain the coordinates of the towers at both ends of the span, the tower height, and the span horizontal length L h , the span height difference Δh; Step two: measure the fiber length S in the span by using Brillouin distributed fiber sensing technology f ; and c convert the actual cable suspension length S according to the preset length ratio η of the fiber and the cable structure Step three: establishing a catenary equation with height difference correction; Step four: defining sag f as the vertical difference between the highest point and the lowest point of the optical cable, outputting the sag value, and comparing it with the preset safety threshold. 2.The OPGW cable sag calculation method based on catenary equation and Brillouin distributed fiber sensing according to claim 1, wherein, The span height difference △h in step one is the height of the right end tower top minus the height of the left end tower top, and the tower top height includes the terrain height and the tower height. 3.The OPGW cable sag calculation method based on catenary equation and Brillouin distributed fiber sensing according to claim 1, wherein, The step two includes: the optical fiber length S in the span f Strain pattern measured according to Brillouin distributed fiber sensing technology; According to the catenary shape of each file, the length S of the two end points of the catenary is calculated c . 4.The OPGW cable sag calculation method based on catenary equation and Brillouin distributed fiber sensing according to claim 1, wherein, The actual optical cable suspension length calculation formula in step two is as follows: In the formula: S c : actual suspended length of the optical cable; S f : length of the optical fiber within the span; η: the preset excess length ratio of optical fiber and optical cable structure.

5. The catenary equation and Brillouin distributed fiber sensing based OPGW cable sag calculation method according to claim 1, characterized in that, The catenary equation with height difference correction in step three is as follows: In the formula, a is the catenary parameter; and C is the constant term.

6. The catenary equation and Brillouin distributed fiber sensing based OPGW cable sag calculation method according to claim 5, characterized in that, The simultaneous conditions of the catenary equation with height difference correction include: The optical cable length constraint is: In the formula: L h Tower height and span length at level.

7. The catenary equation and Brillouin distributed fiber sensing based OPGW cable sag calculation method according to claim 6, characterized in that, The simultaneous conditions of the catenary equation with height difference correction also include: The height difference constraint is: y(L h -y0 = Ah In the formula, △h is the span height difference. 8.The OPGW cable sag calculation method based on catenary equation and Brillouin distributed fiber sensing according to claim 1, wherein, The sag f in step four is defined as the vertical difference between the highest point and the lowest point of the optical cable, and the calculation formula is as follows: wherein L h is the tower height and the horizontal length of the span; The output sag value is compared with the preset safety threshold. 9.The OPGW cable sag calculation method based on catenary equation and Brillouin distributed fiber sensing according to claim 1, wherein, Step five: inputting the calculation result into a monitoring platform to realize real-time display and storage. 10.The OPGW cable sag calculation method based on the catenary equation and the Brillouin distributed fiber sensing of claim 9, wherein, In step five, when the sag exceeds the safety threshold, an alarm is triggered, and historical data is recorded for operation and maintenance analysis.

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