CN118070489A - Same-grade uneven icing thickness calculation method based on ultra-weak optical fibers - Google Patents
Same-grade uneven icing thickness calculation method based on ultra-weak optical fibers Download PDFInfo
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Abstract
The invention provides a method for calculating the same-grade uneven icing thickness based on ultra-weak optical fibers, which comprises the following steps: 1. selecting one of tower line segments in the ice-covered area, and acquiring basic data of the overhead transmission line in the selected tower line segment; 2. installing an ultra-weak optical fiber data acquisition device beside the selected tower line segment, and establishing a relation between the tension of the insulator and the acquired data; 3. based on the acquired basic data and the tension measurement value of the insulator, establishing the relation between the icing thickness and the basic data as well as the tension and deflection angle of the insulator; 4. establishing tower line simulation models under different terrains, verifying the effectiveness of a calculation method under different icing conditions, and improving the icing thickness calculation method according to simulation results; 5. judging ice coating working conditions through axial tension of the suspension points and selecting an ice coating thickness calculation formula; the calculation method provided by the invention effectively improves the accuracy of the calculation of the ice coating thickness when the same grade of uneven ice coating is performed.
Description
Technical Field
The invention relates to the technical field of power catastrophe protection of overhead transmission lines, in particular to a method for calculating the same-grade uneven icing thickness based on ultra-weak optical fibers.
Background
The transmission line in the power system is an essential important component, and is used for carrying and distributing electric energy, so that the stable operation of the transmission line is one of important conditions for maintaining good social and economic development. However, most of the transmission lines are in the field environment, no special protection measures exist, various natural factors can damage the transmission lines, and line icing is one of the transmission lines. In recent years, icing disaster accidents occur in various places throughout the country, and losses brought to power grid companies and national economy are immeasurable. Aiming at serious icing disaster accidents, the method is an effective defense means for carrying out the detailed division guiding differentiated anti-icing reconstruction work of the ice region of the power transmission line and carrying out the deicing work. However, the fine division of the ice area needs to be based on long-term, large-scale and accurate ice-viewing data; similarly, the effective development of ice melting and deicing work is not separated from an early warning mechanism based on accurate ice viewing data. Therefore, the accurate acquisition of the icing data of the power transmission line has important significance for ice disaster prevention work.
The existing method for measuring the thickness of the ice coating mainly comprises the following steps: an icing thickness monitoring method, an image monitoring method, a meteorological method, a weighing method and the like based on tension and inclination sensors. The ice coating thickness monitoring method based on the tension and the inclination angle is to obtain corresponding data through an online monitoring device, but the problem of power reliability of the online monitoring device is not solved at present, and the method can not meet the reliability requirement; the image monitoring method belongs to an online monitoring device, the image detection method acquires real-time images of the power transmission line, and adopts an image processing technology to acquire information such as equivalent icing thickness of a power transmission line wire. The meteorological monitoring method is an indirect monitoring method, and the accuracy of the method is relatively low by monitoring factors such as temperature, wind speed, wind direction, air humidity and the like and then predicting the thickness of the ice coating through the ice coating prediction model. The weighing method utilizes the tensile force, the inclination angle and the like of the insulator string as input quantities, provides an equivalent icing thickness mechanical model based on a single wire and a split wire according to a mechanical balance equation, combines the characteristics of the insulator string, establishes an icing thickness mechanical model under the ice wind load, and rapidly obtains the icing thickness through the mechanical models. The weighing method is simple in principle, and the tension and the offset of the insulator measured by the ultra-weak optical fiber can be used as an important control factor for safe operation of the power transmission line.
The prior art also discloses a method and a system for calculating ice coating thickness of a tangent tower wire based on a weighing method, for example, CN104182611a discloses a method and a system for calculating ice coating thickness of a tangent tower wire based on a weighing method, wherein the method comprises the following steps: firstly, calculating the horizontal stress of the wire without icing, then sequentially obtaining the initial horizontal calculation stress of the wire under the icing condition and the horizontal recalculation stress of the wire under the icing condition, and finally obtaining the equivalent icing thickness according to the specific load of the recalculation icing. The invention makes up the defect of the linear tower wire icing thickness calculation model in engineering application, has the advantages of less input monitoring parameters, low requirement on monitoring equipment, high calculation accuracy and the like, has good effect in actual engineering application, and has good popularization and application prospect. According to the method, complicated calculation steps are reduced, parameters required by calculation are reduced, the calculation convenience is greatly improved, in actual engineering application, the overhead transmission line is usually erected in a mountain area with complex environment, the terrain environment of the mountain area is complex, and the method does not verify the calculation effectiveness under the complex terrain and has a certain limit.
For example, CN107704844a discloses a method for identifying the thickness of ice coating on a power transmission line based on binocular parallax images of an unmanned aerial vehicle, and belongs to the technical field of picture processing. The method comprises the steps of related information acquisition, ice coating image acquisition, parallax image preprocessing, image binarization, contour extraction, ice coating thickness calculation and the like. According to the invention, the ice coating outline is extracted by processing the parallax image, and the foreground and the background are separated by utilizing the distance information, so that the separation effect is good. And preprocessing the parallax image according to the characteristic that the gray values of adjacent intervals of the parallax image are similar, so that the gray level distribution of the image is more uniform. The binarization threshold value calculation method is provided, the binarization threshold value is automatically determined, and the method is high in adaptability. The ice coating thickness is calculated by calculating the ratio of the number of pixels contained in the ice coating wire outline to the number of pixels contained in the non-ice coating wire outline in the range of the fixed row interval, so that the possibility of generating larger measurement errors due to the change of the ice coating shape is reduced, and the method is high in adaptability and accuracy. According to the invention, the unmanned aerial vehicle is used for acquiring the icing image so as to calculate the icing thickness, so that workers do not need to observe the icing condition in person in a mountain area, the safety of the workers is improved, but in winter, severe weather conditions such as raining, snowing and hazing are often accompanied, the icing thickness of the overhead transmission wire cannot be accurately captured by the unmanned aerial vehicle lens, and the reliability of the icing monitoring system is reduced.
For example, "analysis and improvement research of the effectiveness of a power transmission line equivalent icing thickness calculation model under special topography" in the power grid technology is disclosed, in order to analyze the effectiveness of a tangent tower power transmission line equivalent icing thickness calculation model under a common power transmission line longitudinal section model in online monitoring of power transmission line icing, a finite element method is adopted to establish a power transmission line mechanical simulation model, the accuracy of power transmission line equivalent icing thickness calculation results under a power transmission line valley passing model, a mountain turning model and a continuous mountain-up (down) model is researched, and a tangent tower power transmission line equivalent icing thickness calculation model considering equivalent length change is provided. The result shows that under the condition of uniform icing, when the absolute value of the tower height difference coefficient does not exceed 0.2 for the transmission line trough model, the relative error between the equivalent icing thickness calculation result and the assumed value is within 16%; however, when the tower height difference coefficient is larger, if the tower height difference coefficient is-0.3, the relative error between the calculated result of the equivalent icing thickness and the assumed value is larger than 40%. After the equivalent icing thickness calculation model is improved, the relative error between the equivalent icing thickness calculation result and the assumed value is reduced, and the larger the icing thickness is, the smaller the relative error is. And for the power transmission line mountain-turning model and the continuous mountain-up (down) model, the relative error of the thickness result calculated by the equivalent icing thickness is not more than 5%. The paper effectively improves the accuracy of the ice coating thickness calculation method when the ice is uniformly coated, the overhead transmission line is built in a mountain area with complex environment, the overhead transmission line has long span, the situations of uneven ice coating of adjacent files and uneven ice coating of the same file are very easy to occur, and the paper does not analyze the effectiveness of the ice coating thickness calculation method when the working conditions occur, so that certain limitations exist.
Disclosure of Invention
The invention aims to solve the technical problem of providing a method for calculating the same-grade uneven icing thickness based on ultra-weak optical fibers, which solves the problem of lower calculation precision of a traditional icing thickness calculation model when the same-grade uneven icing occurs.
In order to solve the technical problems, the technical scheme adopted by the invention is that the method for calculating the same-grade nonuniform icing thickness based on the ultra-weak optical fiber comprises the following steps:
step1: selecting one of tower line segments in the ice-covered area, and acquiring basic data of the overhead transmission line in the selected tower line segment;
step2: installing an ultra-weak optical fiber data acquisition device beside the selected tower line segment, and establishing a relation between the tension of the insulator and the acquired data;
step3: based on the acquired basic data and the tension measurement value of the insulator, establishing the relation between the icing thickness and the basic data as well as the tension and deflection angle of the insulator;
step4: establishing tower line simulation models under different terrains, verifying the effectiveness of a calculation method under different icing conditions, and improving the icing thickness calculation method according to simulation results;
step5: and judging the icing working condition through the axial tension of the suspension point and selecting an icing thickness calculation formula.
In a preferred embodiment, the ultra-weak fiber data in step2 includes a center wavelength, a temperature, an effective elastance coefficient, a thermal expansion coefficient of the optical fiber, a thermal optical effect coefficient of the ultra-weak optical fiber, and a young's modulus of the optical fiber of the ultra-weak optical fiber grating.
In a preferred embodiment, the relational expression between the tensile force of the insulator and the data of the ultra-weak optical fiber established in step2 is:
（1）
wherein F is the axial tension of the insulator; e is Young's modulus of the ultra-weak optical fiber; epsilon is the strain of the ultra-weak fiber.
In a preferred embodiment, the base data in step3 includes an outside diameter of the overhead transmission line, a cross-sectional area of the overhead transmission line, a span of the overhead transmission line, a height difference angle between the overhead transmission lines, a temperature expansion coefficient of the overhead transmission line, and an elastic coefficient of the overhead transmission line.
In a preferred scheme, the expression of the relation between the ice coating thickness and the basic data and the tension of the insulator in step3 is as follows:
（2）
Wherein G is the sum of dead weights of the lead, the insulator chain and the hardware fitting; θ is the insulator deflection angle; q ice is the unit icing load of the wire; s a、Sb respectively represents the vertical span line length from the tangent tower to the large side and the small side;
Wherein, the wire unit icing load q ice can be expressed as:
（3）
Considering the icing shape as cylindrical, the wire icing thickness can be expressed as:
（4）
wherein ρ is ice coating density, and D is the outer diameter of the wire.
In a preferred scheme, the unit icing load q ice is expressed by an axial tension force F of the insulator as follows:
（5）
In the preferred scheme, different terrains in step4 are respectively a large-span large-altitude-difference working condition, a large-span working condition, a large-altitude-difference working condition and a non-large-span large-altitude-difference working condition, the model of the adopted simulation wire is JLB20A-100 aluminum-clad steel stranded wire, and the icing working condition is that vertical span icing is larger than non-vertical span icing and vertical span icing is smaller than non-vertical span icing.
In the preferred scheme, a tower height difference coefficient and a gear ratio are utilized to judge whether the transmission tower is in a working condition of large height difference and large gear, and the tower height difference coefficient and the gear ratio have the following expression:
（6）
Wherein α is a tower height difference coefficient, phi is a gear ratio, h 1 is a tangent tower to large side height difference, h 2 is a tangent tower to small side height difference, l 1 is a tangent tower to large side gear, and l 2 is a tangent tower to small side gear.
In general, when the tower height difference coefficient α is greater than 0.2, the line is considered to be in a large height difference condition, and when the gear ratio Φ is greater than 2, the line is considered to be in a large gear condition.
In the preferred scheme, the method for judging the icing condition by the axial tension at the suspension point in step5 is that if the axial tension at the suspension point at the side of the tangent tower is greater than the axial tension at the suspension point at the large and small sides, the icing condition is that the icing with the vertical span is greater than the icing with the non-vertical span, and if the axial tension at the suspension point at the side of the tangent tower is less than the axial tension at the suspension point at the large and small sides, the icing condition is that the icing with the vertical span is less than the icing with the non-vertical span.
In a preferred scheme, the expression of the ice coating thickness calculation formula after the improvement of the simulation result is as follows:
（7）
in the formula, S 'a and S' b respectively represent the lengths of non-vertical span wires from the tangent tower to the large-size side and the small-size side.
The same-grade uneven icing thickness calculating method based on the ultra-weak optical fiber has the following beneficial effects:
1. Compared with the traditional method, the method reduces the interference of electromagnetic environment around the overhead transmission line on information transmission, so that the obtained information is more reliable, the energy consumption for transmitting the ultra-weak optical fiber is less than that for the traditional optical fiber, the problem of difficult power supply in the traditional method is solved, and the reliability of a monitoring system is increased;
2. The invention analyzes the effectiveness of the calculation method under the terrains of large span and large height difference, non-large span and large height difference, and uniformly icing, non-uniformly icing and same-span non-uniformly icing, and fully selects various working conditions and terrains, so that the result is more comprehensive and accurate;
3. According to the invention, the icing condition is judged by the axial tension of the suspension point of the insulator, and compared with the icing condition obtained by the horizontal tension of the transmission wire in the traditional method, the tension of the suspension point of the insulator is easier to obtain, and the horizontal tension of the transmission wire is difficult to measure, so that the accuracy of the icing condition judgment can be greatly improved;
4. According to the invention, the traditional ice coating thickness calculation formula is improved, and when the vertical ice coating thickness is lower than the non-vertical ice coating thickness, the traditional ice coating thickness calculation method is poor in accuracy, and the calculation accuracy is greatly improved after the formula is improved.
Drawings
The invention is further described below with reference to the accompanying drawings and examples of implementation:
FIG. 1 is a schematic flow chart of the present invention;
FIG. 2 is a schematic diagram of a system according to the present invention;
FIG. 3 is a graph of the vertical plane of the tangent tower of the present invention;
FIG. 4 is a schematic diagram of different working conditions of the present invention;
FIG. 5 is a schematic diagram of different ice coating conditions according to the present invention.
Detailed Description
Embodiments of the present invention will be further described with reference to the accompanying drawings.
Example 1:
as shown in fig. 1 to 5, a method for calculating the same-grade uneven icing thickness based on ultra-weak optical fibers comprises the following steps:
step1: selecting one of tower line segments in the ice-covered area, and acquiring basic data of the overhead transmission line in the selected tower line segment;
step2: installing an ultra-weak optical fiber data acquisition device beside the selected tower line segment, and establishing a relation between the tension of the insulator and the acquired data;
step3: based on the acquired basic data and the tension measurement value of the insulator, establishing the relation between the icing thickness and the basic data as well as the tension and deflection angle of the insulator;
step4: establishing tower line simulation models under different terrains, verifying the effectiveness of a calculation method under different icing conditions, and improving the icing thickness calculation method according to simulation results;
step5: and judging the icing working condition through the axial tension of the suspension point and selecting an icing thickness calculation formula.
In this embodiment, the ultra-weak fiber data in step2 includes a center wavelength, a temperature, an effective elastance coefficient, a thermal expansion coefficient of the optical fiber, a thermal optical effect coefficient of the ultra-weak optical fiber, and a young's modulus of the optical fiber of the ultra-weak optical fiber grating.
The relational expression of the tension of the insulator and the ultra-weak fiber data established in step2 is as follows:
（1）
Wherein F is the axial tension of the insulator; e is Young's modulus of the ultra-weak optical fiber; epsilon is the strain of the ultra-weak fiber.
The basic data in step3 comprises the outer diameter of the transmission line, the cross section area of the overhead transmission line, the span of the overhead transmission line, the altitude difference angle between the overhead transmission lines, the temperature expansion coefficient of the overhead transmission line and the elasticity coefficient of the overhead transmission line.
In a preferred scheme, the expression of the relation between the ice coating thickness and the basic data and the tension of the insulator in step3 is as follows:
（2）
Wherein G is the sum of dead weights of the lead, the insulator chain and the hardware fitting; θ is the insulator deflection angle; q ice is the unit icing load of the wire; s a、Sb respectively represents the vertical span line length from the tangent tower to the large side and the small side;
Wherein, the wire unit icing load q ice can be expressed as:
（3）
Considering the icing shape as cylindrical, the wire icing thickness can be expressed as:
（4）
wherein ρ is ice coating density, and D is the outer diameter of the wire.
The unit icing load q ice is expressed by the axial tension F of the insulator as follows:
（5）
Different terrains in step4 are respectively a large-span large-altitude-difference working condition, a large-span working condition, a large-altitude-difference working condition and a non-large-span large-altitude-difference working condition, the model of the adopted simulation wire is JLB20A-100 aluminum-clad steel strand, the icing working condition is that vertical span icing is larger than non-vertical span icing, and vertical span icing is smaller than non-vertical span icing.
Judging whether the transmission tower is in a working condition with large height difference and large span by utilizing a tower height difference coefficient and a span ratio, wherein the tower height difference coefficient and the span ratio are expressed as follows:
（6）
Wherein α is a tower height difference coefficient, phi is a gear ratio, h 1 is a tangent tower to large side height difference, h 2 is a tangent tower to small side height difference, l 1 is a tangent tower to large side gear, and l 2 is a tangent tower to small side gear.
In general, when the tower height difference coefficient α is greater than 0.2, the line is considered to be in a large height difference condition, and when the gear ratio Φ is greater than 2, the line is considered to be in a large gear condition.
The method for judging the icing condition by the axial tension at the hanging point in step5 is that if the axial tension of the hanging point at the side of the tangent tower is larger than that of the hanging point at the large and small sides, the icing condition is that the icing with the vertical span is larger than that of the icing with the non-vertical span, and if the axial tension of the hanging point at the side of the tangent tower is smaller than that of the hanging point at the large and small sides, the icing condition is that the icing with the vertical span is smaller than that of the icing with the non-vertical span.
In a preferred scheme, the expression of the ice coating thickness calculation formula after the improvement of the simulation result is as follows:
（7）
in the formula, S 'a and S' b respectively represent the lengths of non-vertical span wires from the tangent tower to the large-size side and the small-size side.
Example 2:
In another preferred embodiment, referring to the flow chart of fig. 1 based on the above embodiment 1, a specific implementation step of the method for calculating the same-grade non-uniform icing thickness based on the ultra-weak optical fiber is as follows:
step1: selecting one of tower line segments in the ice-covered area, and acquiring basic data of the overhead transmission line in the selected tower line segment;
step2: installing an ultra-weak optical fiber data acquisition device beside the selected tower line segment, and establishing a relation between the tension of the insulator and the acquired data;
step3: based on the acquired basic data and the tension measurement value of the insulator, establishing the relation between the icing thickness and the basic data as well as the tension and deflection angle of the insulator;
step4: establishing tower line simulation models under different terrains, verifying the effectiveness of a calculation method under different icing conditions, and improving the icing thickness calculation method according to simulation results;
step5: and judging the icing working condition through the axial tension of the suspension point and selecting an icing thickness calculation formula.
In this implementation, the base data in step1 includes the outside diameter of the overhead transmission line, the cross-sectional area of the overhead transmission line, the span of the overhead transmission line, the altitude difference angle between the overhead transmission lines, the temperature expansion coefficient of the overhead transmission line, and the elastic coefficient of the overhead transmission line.
The ultra-weak fiber data in step2 comprises the center wavelength, the temperature, the effective elastance coefficient, the thermal expansion coefficient of the optical fiber, the thermal-optical effect coefficient of the ultra-weak optical fiber and the Young modulus of the optical fiber of the ultra-weak optical fiber grating.
When a relation between the ultra-weak optical fiber and the tension of the insulator is established, the outside temperature and the strain change can cause the shift of the center wavelength of uwFBG (ultra-weak optical fiber grating), and the relation between the wavelength change, the temperature change and the strain change is established firstly, wherein the expression is as follows:
（8）
Wherein Δλ B is the wavelength variation, Δε is the strain variation, ΔT is the temperature variation, λ B is the center wavelength of the ultra-weak fiber grating, pe is the effective elasto-optical coefficient, a 0 is the thermal expansion coefficient of the fiber, and ζ is the thermo-optical effect coefficient of the fiber.
After the formula (8) is simplified, the relation can be obtained:
（9）
Wherein Deltalambda B1 is the wavelength drift amount of the strain fiber grating, K ε1 is the strain sensitivity of the strain fiber grating, K T1 is the temperature sensitivity of the strain fiber grating, deltalambda B2 is the wavelength drift amount of the temperature compensation fiber grating, and K T2 is the temperature sensitivity of the temperature compensation fiber grating.
Considering that the internal temperature of the buried optical cable is basically consistent, wavelength drift caused by temperature change can be effectively eliminated by adopting a difference method, so that strain change of one unit is obtained, and the axial strain of the weak optical fiber can be described as follows:
（10）
the axial tension of the insulator is calculated by strain as follows:
（1）
wherein F is the axial tension of the insulator, E is the Young's modulus of the ultra-weak fiber grating, and epsilon is the strain of the ultra-weak fiber grating.
When the relation between the tension of the insulator and the thickness of the ice coating is established in Step3, the relation between the horizontal stress of the power transmission line and the line length, the span, the altitude difference angle and the wire self-weight specific load in the span is established according to the vertical plane stress schematic diagram of the power transmission line shown in fig. 3, and the relation is shown in the following formula:
（11）
Wherein sigma 0 is horizontal stress, gamma is wire self-weight specific load, l is span, beta is height difference angle, and S t span inner line length.
Defining a middle tower A as a main rod tower, a left tower B as a large side and a right tower C as a small side, respectively calculating horizontal stress of wires on the large side and the small side according to a formula (11), wherein the relation between the horizontal stress and the bottom-most point span from the main rod tower A to the small side of the large side is as follows:
（12）
Wherein l a is the main tower to large side lowest point horizontal span, l b is the main tower to small side lowest point horizontal span, l 1 is the main tower large side horizontal span, l 2 is the main tower small side horizontal span, h 1 is the height difference between the main tower and the large side, h 2 is the height difference between the main tower and the small side, sigma 10 is the large side wire horizontal stress, sigma 20 is the small side wire horizontal stress, beta 1 is the height difference angle between the main tower and the large side, and beta 2 is the height difference angle between the main tower and the small side.
The relation between the line length and the horizontal span, the wire self-weight specific load, the horizontal stress and the altitude difference angle is as follows:
（13）
In the formula, S a is the lowest point line length from the main pole tower to the large-size side wire, and S b is the lowest point line length from the main pole tower to the small-size side wire.
From the mechanical equilibrium equation:
（2）
Wherein G is the sum of dead weights of the wire, the insulator string and the hardware fitting, theta is the deflection angle of the insulator, and q ice is the unit icing load of the wire.
Considering ice coating as uniform cylindrical ice coating, the wire ice coating thickness can be expressed as:
（4）
wherein ρ is ice coating density, and D is the outer diameter of the wire.
And (3) expressing the icing load q ice in the formula (4) by using the tension of the insulator, wherein the icing thickness calculation formula is as follows:
（5）
The tower line model for establishing different working conditions in Step4 comprises working conditions of large span, large altitude, non-large span and large altitude, different working conditions are shown in fig. 4, a tower altitude coefficient and a span ratio are generally utilized to judge whether the transmission tower is in the working conditions of large altitude and large span, and the expression of the tower altitude coefficient and the span ratio is as follows:
（6）
Wherein α is a tower height difference coefficient, phi is a gear ratio, h 1 is a tangent tower to large side height difference, h 2 is a tangent tower to small side height difference, l 1 is a tangent tower to large side gear, and l 2 is a tangent tower to small side gear.
The simulated condition data are shown in table 1:
Table 1 tower line simulation conditions
The wire and insulator data shown in Step4 are: the wire adopts a JLB20A-100 aluminum-clad steel strand, the diameter is 13.73mm, the mass is 674.1kg/km, the elastic modulus is 147.2GPa, the tension is 14.524kN, the mass of the I-type insulator string is 3kg, and the string length is 0.5m.
The different ice coating conditions shown in Step4 are respectively that the vertical gear ice coating is smaller than the non-vertical gear ice coating (the first ice coating condition) and the vertical gear ice coating is larger than the non-vertical gear ice coating (the second ice coating condition), and the schematic ice coating conditions are shown in fig. 5.
The verification of the effectiveness of the calculation method of the ice coating thickness shown in Step4 means that the simulated insulator pulling force F is brought into formula (5), the calculated ice coating thickness is compared with the average equivalent ice coating thickness, the average equivalent ice coating thickness is an error for facilitating the analysis of the calculation method, and the calculation method of the average equivalent ice coating thickness is not practical, and comprises the following steps:
（14）
Wherein b ave is the average equivalent ice coating thickness, b 1 is the vertical ice coating thickness, b 2 is the non-vertical ice coating thickness, l 'a is the large-side non-vertical span length, and l' b is the small-side non-vertical span length.
The error analysis expression is shown as follows:
（15）
Where e is the absolute error of the ice coating thickness, e r is the relative error of the ice coating thickness, and b 0 is the calculated ice coating thickness.
The simulation results of different tower line working conditions under the first ice coating working condition are shown in table 2:
TABLE 2 simulation results of icing conditions of the first class
The simulation results of different tower line working conditions under the second type of icing working conditions are shown in table 3:
TABLE 3 simulation results of icing conditions of the second class
The improved icing thickness calculation method according to the simulation result shown in Step4 refers to that the calculation model error is smaller when the first type of icing occurs on the power transmission wire, and the error is larger when the second type of icing occurs, and the calculation formula needs to be improved according to the second type of icing working condition, and according to the simulation results obtained in table 2 and table 3, it is found that in actual situations, the tangent tower insulator also bears the vertical downward force of the non-vertical gear in the large-size side and the small-size side, and the formula (5) only considers the vertical downward force of the large-size side and the small-size side, and does not consider the vertical downward force of the non-vertical gear, so the formula can be improved after considering the vertical downward force of the non-vertical gear:
（7）
in the formula, S 'a and S' b respectively represent the lengths of non-vertical span wires from the tangent tower to the large-size side and the small-size side.
When the second ice coating working condition occurs, the calculation result of the formula (7) is shown in the table 4, and the relation between the absolute error and the relative error after improvement is shown in the following formula:
（16）
Where b * is the modified equivalent icing thickness value, e * is the modified absolute error, and e×r is the relative error.
Table 4 improved calculation results
After the second type of icing working condition of the power transmission line is improved, the accuracy of the calculated result is obviously improved, and the working efficiency of operation and maintenance personnel can be effectively improved.
The Step5 is used for judging the icing condition through the axial tension of the hanging point, namely, if the axial tension of the hanging point of the main rod tower is smaller than the axial tension of the hanging point of the large side or the small side, the icing condition is judged to be the first type of icing condition, and if the axial tension of the hanging point of the main rod tower is larger than the axial tension of the hanging point of the large side or the small side, the icing condition is judged to be the second type of icing condition.
In summary, the invention provides a method for calculating the same-grade uneven icing thickness based on ultra-weak optical fibers, which comprises the steps of selecting one tower line segment in an icing area, collecting basic data of an overhead transmission line in the selected tower line segment, establishing the relation between icing thickness and basic data, tension and deflection angle of an insulator based on the collected basic data and tension measurement value of the insulator, establishing tower line simulation models under different terrains, verifying the effectiveness of the calculation method under different icing working conditions, improving the icing thickness calculation method according to the simulation result, judging the icing working condition through axial tension of a hanging point, and selecting an icing thickness calculation formula. According to simulation results, the improved calculation method can effectively reduce errors of working conditions that the vertical gear icing thickness is larger than the non-vertical gear icing thickness.
Claims (10)
1. The method for calculating the same-grade uneven icing thickness based on the ultra-weak optical fiber is characterized by comprising the following steps of:
step1: selecting one of tower line segments in the ice-covered area, and acquiring basic data of the overhead transmission line in the selected tower line segment;
step2: installing an ultra-weak optical fiber data acquisition device beside the selected tower line segment, and establishing a relation between the tension of the insulator and the acquired data;
step3: based on the acquired basic data and the tension measurement value of the insulator, establishing the relation between the icing thickness and the basic data as well as the tension and deflection angle of the insulator;
step4: establishing tower line simulation models under different terrains, verifying the effectiveness of a calculation method under different icing conditions, and improving the icing thickness calculation method according to simulation results;
step5: and judging the icing working condition through the axial tension of the suspension point and selecting an icing thickness calculation formula.
2. The method for calculating the same-grade uneven icing thickness based on the ultra-weak optical fiber according to claim 1, wherein the ultra-weak optical fiber data in step2 comprises the center wavelength, the temperature, the effective elastance coefficient, the thermal expansion coefficient, the thermal optical effect coefficient and the Young modulus of the ultra-weak optical fiber.
3. The method for calculating the same-grade uneven icing thickness based on the ultra-weak optical fiber according to claim 2, wherein the relational expression of the tension of the insulator and the ultra-weak optical fiber data established in step2 is as follows:
（1）
Wherein F is the axial tension of the insulator; e is Young's modulus of the ultra-weak optical fiber; epsilon is the strain of the ultra-weak fiber.
4. The method for calculating the same-grade uneven icing thickness based on ultra-weak optical fibers according to claim 1, wherein the basic data in step3 comprises an outer diameter of a transmission line, a cross-sectional area of the overhead transmission line, a grade distance of the overhead transmission line, a height difference angle between the overhead transmission lines, a temperature expansion coefficient of the overhead transmission line and an elastic coefficient of the overhead transmission line.
5. The method for calculating the same-grade uneven icing thickness based on the ultra-weak optical fiber according to claim 1, wherein the expression of the relation between the icing thickness and the basic data and the tension of the insulator in step3 is as follows:
（2）
Wherein G is the sum of dead weights of the lead, the insulator chain and the hardware fitting; θ is the insulator deflection angle; q ice is the unit icing load of the wire; s a、Sb respectively represents the vertical span line length from the tangent tower to the large side and the small side;
Wherein, the wire unit icing load q ice can be expressed as:
（3）
Considering the icing shape as cylindrical, the wire icing thickness can be expressed as:
（4）
wherein ρ is ice coating density, and D is the outer diameter of the wire.
6. The method for calculating the same-grade uneven icing thickness based on the ultra-weak optical fiber according to claim 5, wherein the unit icing load q ice is expressed by an axial tension F of an insulator as follows:
（5）。
7. The method for calculating the same-grade uneven icing thickness based on the ultra-weak optical fibers according to claim 1, wherein different terrains in step4 are respectively a large-grade large-height difference working condition, a large-grade working condition, a large-height difference working condition and a non-large-grade large-height difference working condition, the model of the adopted simulation wire is JLB20A-100 aluminum-clad steel strand, the icing working condition is that vertical grade icing is larger than non-vertical grade icing, and the vertical grade icing is smaller than non-vertical grade icing.
8. The method for calculating the same-grade uneven icing thickness based on the ultra-weak optical fibers according to claim 7, wherein whether the transmission tower is in a working condition with a large height difference and a large grade distance is judged by utilizing a tower height difference coefficient and a grade distance ratio, and the expression of the tower height difference coefficient and the grade distance ratio is as follows:
（6）
Wherein alpha is a tower height difference coefficient, phi is a gear ratio, h 1 is a straight line tower to large side height difference, h 2 is a straight line tower to small side height difference, l 1 is a straight line tower to large side gear, and l 2 is a straight line tower to small side gear;
in general, when the tower height difference coefficient α is greater than 0.2, the line is considered to be in a large height difference condition, and when the gear ratio Φ is greater than 2, the line is considered to be in a large gear condition.
9. The method for calculating the same-gear uneven icing thickness based on the ultra-weak optical fiber according to claim 8, wherein the step5 is characterized in that the method for judging the icing condition through the axial tension at the suspension point is that if the axial tension of the suspension point at the side of the tangent tower is larger than the axial tension of the suspension point at the large and small numbers, the icing condition is that the vertical gear icing is larger than the non-vertical gear icing, and if the axial tension of the suspension point at the side of the tangent tower is smaller than the axial tension of the suspension point at the large and small numbers, the icing condition is that the vertical gear icing is smaller than the non-vertical gear icing.
10. The method for calculating the same-grade uneven icing thickness based on the ultra-weak optical fiber according to claim 9, wherein the expression of the icing thickness calculation formula after the improvement by the simulation result is:
（7）
in the formula, S 'a and S' b respectively represent the lengths of non-vertical span wires from the tangent tower to the large-size side and the small-size side.
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