Power distribution overhead line corridor surrounding tree fire risk assessment method and system

Abstract

The invention discloses a fire risk assessment method and system for trees around a power distribution overhead line corridor, and the method comprises the following steps: simplifying and simulating the real form of a tree through a fractal tree network model, and constructing a tree model; obtaining the initial moisture content of the tree model, and continuously monitoring the temperature and transition resistance of the tree model; the method comprises the following steps: constructing a single-phase tree touch fault model, obtaining a conductor phase voltage, continuously calculating current heat production, heat dissipation and heat absorption of a tree, calculating to obtain moisture evaporation mass, and updating the moisture content of the tree by using the moisture evaporation mass; fitting to obtain a binary relationship among the conductivity, the moisture content and the temperature of the tree model; applying the binary relation to the fault model for iterative calculation, and obtaining the highest temperature of the tree in the whole process; and evaluating the risk level of the tree according to the highest temperature by using a set temperature threshold value. According to the method, the fire risk assessment of the tree size can be accurately realized, the safe operation of a power grid is ensured, and the ecological environment is protected.

Description

Technical Field

[0001] The invention belongs to the technical field of tree fire assessment, and in particular relates to a method and system for assessing tree fire risks around a distribution overhead line corridor. Background Art

[0002] With the rapid development of modern power systems, overhead distribution lines have become an important way of power transmission. The safety of the surrounding environment is directly related to the stable operation of the power grid and the reliability of power supply. The corridors of overhead distribution lines usually pass through woodlands, residential areas or farmlands. The surrounding trees play an important role in beautifying the environment and protecting the ecology, but they also bring potential risks of electric shock and fire. Once a line fault or other factors cause power to be transmitted to nearby trees, it may cause temperature rise and cause fire, which will pose a serious threat to the power grid and the surrounding environment.

[0003] Traditional methods for assessing the fire risk of distribution lines usually rely on experience and statistical analysis. These methods predict fire risks by summarizing historical data and expert experience, but lack quantitative analysis of physical processes and are difficult to accurately assess for different voltage levels, tree species, sizes, and surrounding environmental conditions. In addition, with the increasing complexity of the power grid, empirical methods have shown limitations in dealing with diverse scenarios and emergencies, and a scientific and systematic assessment method is urgently needed to make up for the shortcomings.

[0004] The Chinese invention patent application with publication number CN106886841A discloses a line wildfire disaster assessment method and system without real-time collection of on-site information, the method comprising the following steps: determining vegetation type and vegetation height; judging the fire behavior type of the fire scene; obtaining alarm transmission line information; obtaining meteorological data at the location of the wildfire; calculating the height of the wildfire flame area, ion area and smoke area; calculating the breakdown voltage of the flame area; calculating the breakdown voltage of the ion area; calculating the breakdown voltage of the smoke area; calculating the probability of transmission line tripping; and evaluating the wildfire level. The present invention also provides a line wildfire disaster assessment system without real-time collection of on-site information.

[0005] The calculation of breakdown voltage in the flame zone, ion zone and smoke zone in the above scheme relies on a static physical model, while the actual morphology and parameters of these areas (such as non-uniform flames, complex airflow, etc.) may far exceed the model's assumed range; therefore, an overly simplified model may not accurately reflect complex fire behaviors, resulting in a decrease in the accuracy of wildfire level assessment results; and it is highly dependent on the accuracy and comprehensiveness of input data (such as vegetation type, height, meteorological data, etc.). If the data is inaccurate or missing, the reliability of the assessment results will be significantly reduced.

[0006] In recent years, modeling methods based on physical processes have gradually become a new direction for studying fire risks. These methods can provide more reliable data support for risk prediction by simulating and analyzing the relationship between external environment and system parameters and fire conditions. For example, by analyzing the geometric characteristics (height, radius, etc.), conductivity, thermophysical parameters of trees and their interaction with line voltage, the temperature rise process caused by electric shock and its contribution to fire can be quantified more accurately. However, the current research on the fire risk of trees around distribution overhead lines is still in its early stages, and the existing analysis is mostly focused on theoretical discussions, and a set of evaluation methods with practical operational value has not yet been formed.

[0007] Therefore, a tree fire risk assessment method around distribution overhead line corridors based on simulation analysis is developed, which can provide a scientific and quantitative assessment basis for the risk of tree electric shock fire by combining the relationship between different voltage levels, tree size and temperature rise, which is of great significance for the safe operation of the power grid and the protection of the ecological environment. Summary of the invention

[0008] The present invention provides a method and system for assessing tree fire risks around a distribution overhead line corridor, aiming to solve the problems of insufficient accuracy of forest fire grade assessment results in the prior art and high dependence on environmental data.

[0009] In order to solve the above technical problems, the fire risk assessment method proposed in the present invention comprises the following steps:

[0010] The fractal tree network model is used to simplify and simulate the real form of trees and construct a tree model;

[0011] Obtaining the initial moisture content of the tree model, and continuously monitoring the temperature and transition resistance of the tree model;

[0012] A single-phase tree-touch fault model is constructed. During the simulation of the single-phase tree-touch fault model, the conductor phase voltage is obtained, the current heat generation, heat dissipation and heat absorption of the tree are continuously calculated, the water evaporation mass is further calculated, and the water content of the tree is updated using the water evaporation mass;

[0013] After aligning the updated tree moisture content, monitored tree model temperature and transition resistance in time, the least squares method was used for fitting to obtain the binary relationship between the tree model conductivity and moisture content and temperature;

[0014] Applying the binary relationship to a single-phase tree-touch fault model, performing iterative calculations, obtaining the tree temperature rise, and recording the temperature of the tree during the entire process based on the tree temperature rise;

[0015] The risk level of the trees is assessed based on the temperature of the trees throughout the process with a set temperature threshold.

[0016] Preferably, the tree model is constructed by:

[0017] The fractal tree network model is used to simplify the real form of simulated trees, and the structural size between two adjacent levels is set to decrease and the proportion is the same;

[0018] In the tree model, α and β are defined as the length ratio and radius ratio of the branches of the k+1th layer network and the kth layer network, respectively, as follows:

[0019]

[0020] In the formula, l k , l k+1 are the branch lengths of the k-th layer network and the k+1-th layer network, r k 、r k+1 They are the branch radius of the k-th layer network and the branch radius of the k+1-th layer network respectively.

[0021] Preferably, the tree moisture content is an absolute moisture content, which is obtained by experimental weighing and is calculated using the following formula:

[0022]

[0023] In the formula, m s is the fresh weight of the wood block obtained from the experimental sampling, and m0 is the absolute dry mass of the wood block.

[0024] Preferably, the heat dissipation includes convection heat dissipation and radiation heat dissipation, the heat absorption includes water evaporation heat absorption and tree temperature rise heat absorption, and the relationship between the heat dissipation, heat absorption and current heat generation is:

[0025] Heat generated by electric current = heat dissipated by convection + heat dissipated by radiation + heat absorbed by water evaporation + heat absorbed by tree temperature rise. Preferably, the heat absorbed by water evaporation is calculated as follows:

[0026] Q w =(Q s -Q c -Q r )·k f

[0027] k f =(1+e 98-T ) -1

[0028] In the formula, Q w The heat absorbed by water evaporation, Q s Q is the heat generated by the current. c is the convective heat dissipation, Q r is the radiation heat dissipation, k f is the evaporation absorption proportional coefficient, T is the tree temperature;

[0029] Current heat generation Q s , Convection heat dissipation Q c , radiant heat dissipation Q r The calculation methods are:

[0030]

[0031] Q c =∫k c S c (TT e )dt

[0032]

[0033] Where U is the phase voltage of the overhead distribution line, R t is the tree transition resistance at time t, k c is the branch convection heat dissipation coefficient, S c is the lateral area of ​​the branch, T is the tree temperature, T e is the ambient temperature, k r is the branch radiation heat transfer coefficient, and δ0 is the Stefan-Boltzmann constant.

[0034] Preferably, in the single-phase tree-touching fault model, the tree path resistance R t The calculation method is:

[0035]

[0036] Where α and β are the length ratio and radius ratio of the branches of the k+1th layer network and the kth layer network, respectively; n is the total number of tree models; l0 is the basic branch length in the tree model, i.e., the trunk height; r0 is the basic branch radius, i.e., the trunk radius; σ t (W,T) is the binary relationship between the conductivity of the tree model and its moisture content and temperature.

[0037] Preferably, the calculation method of the water evaporation mass is:

[0038]

[0039] In the formula, Δm is the mass of water evaporated, Q w The heat absorbed by water evaporation, T w is the water temperature;

[0040] The updated moisture content data is W-ΔW, where:

[0041]

[0042] m0 is the absolute dry mass of the wood block.

[0043] Preferably, the calculation method of the tree temperature rise is:

[0044]

[0045] Q t =Q s -Q c -Q r -Q w

[0046] Where ΔT is the temperature rise of the tree, c t is the specific heat capacity of wood, c w is the specific heat capacity of water, m s is the fresh weight of the wood block obtained by experimental sampling, m0 is the absolute dry weight of the wood block, Q t The heat absorbed by the tree due to temperature rise, Q s Q is the heat generated by the current. c is the convective heat dissipation, Q r is the radiation heat dissipation, Q w Absorbs heat for water evaporation;

[0047] The current tree temperature is the sum of the tree temperature in the previous iteration and the tree temperature rise in this iteration.

[0048] Preferably, the temperature threshold is set to 100°C.

[0049] Another aspect of the present invention further provides a system for assessing tree fire risks around distribution overhead line corridors, the system being used to implement the above-mentioned risk assessment method, comprising:

[0050] The tree modeling module is used to simplify the real morphology of simulated trees based on the fractal tree network model and construct a tree model, in which the structural sizes of two adjacent levels of networks decrease and the proportions are the same;

[0051] The parameter acquisition module includes: a moisture content acquisition unit for acquiring the initial absolute moisture content of the tree model; a temperature acquisition unit for continuously monitoring the temperature of the tree model; and a resistance acquisition unit for monitoring the transition resistance of the tree model.

[0052] The single-phase tree-touch fault simulation module includes: a voltage acquisition unit for obtaining the conductor phase voltage in the single-phase tree-touch fault model; a heat calculation unit for calculating the water evaporation mass based on the relationship between the tree current heat generation, convection heat dissipation, radiation heat dissipation, water evaporation heat absorption and tree temperature rise heat absorption, and updating the real-time moisture content of the tree model;

[0053] The data processing module includes: a conductivity fitting unit, which is used to align the updated tree moisture content, the monitored tree model temperature and the transition resistance in time, and use the least square method to fit the binary relationship between the conductivity and the moisture content and the temperature of the tree model; a temperature rise calculation unit, which is used to perform iterative calculations in the single-phase tree contact fault model based on the fitted binary relationship, obtain the temperature rise process of the tree model and record the temperature changes of the whole process;

[0054] The risk assessment module is used to analyze the tree temperatures recorded throughout the entire process based on the set temperature threshold and assess the fire risk level of the trees.

[0055] Compared with the prior art, the present invention has the following technical effects:

[0056] 1. The risk assessment method proposed in this invention provides a scientific and quantitative method for risk assessment by simulating and analyzing the relationship between the height and radius of trees and temperature rise under different voltage levels (10kV, 35kV). This modeling and analysis based on physical processes can quickly and accurately assess the fire risk of trees around the distribution overhead line corridor, filling the gap of traditional risk assessment methods based on experience and statistics.

[0057] 2. The risk assessment method proposed in the present invention iteratively calculates variables such as conductivity, resistance, and temperature to obtain the temperature curve of the tree when a single-phase tree-touching fault occurs. Through the closed-loop calculation of the model, the dynamic changes of various parameters over time can be tracked in real time, thus getting rid of the existing technology's high dependence on external environmental data, making the assessment conclusion more reasonable.

[0058] 3. The risk assessment method model proposed in the present invention is not only applicable to specific static conditions, but can also dynamically simulate the electrical and thermal characteristics of trees under different external environments (such as different humidity, temperature, and heat dissipation conditions). Compared with static physical models, the present invention is more adaptable and can cover a wider range of practical scenarios.

[0059] 4. The risk assessment method proposed in the present invention models the single-phase tree-touching fault of the distribution overhead line, obtains the conductor phase voltage data, and refines the electrical characteristics analysis of the fault environment. It effectively reduces the difficulty of complex calculations, retains key structural features, improves the applicability of the assessment model and the accuracy of simulating tree morphology. It is also highly targeted and can more accurately simulate the fire risk of trees around the distribution line corridor, providing precise support for the protection and fault handling of the power system. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] Figure 1 is a schematic diagram of the risk assessment method of the present invention;

[0061] Figure 2 It is a schematic diagram of a single-phase tree-touching fault model and a tree model according to an embodiment of the present invention;

[0062] Figure 3 This is a schematic diagram of the risk of a level 1 fire caused by touching a wire when the voltage is 10 kV according to an embodiment of the present invention;

[0063] Figure 4 This is a schematic diagram of a level 2 tree contact fire risk at 10kV level according to an embodiment of the present invention;

[0064] Figure 5 This is a schematic diagram of a level 3 fire risk of a tree touching a wire at 10 kV level according to an embodiment of the present invention;

[0065] Figure 6 This is a schematic diagram of a level 1 tree contact fire risk at 35kV level according to an embodiment of the present invention;

[0066] Figure 7 This is a schematic diagram of a level 2 tree contact fire risk at 35kV level according to an embodiment of the present invention;

[0067] Figure 8 This is a schematic diagram of the risk of a level 3 tree-contact fire at 35 kV level described in an embodiment of the present invention. DETAILED DESCRIPTION

[0068] In order to make the objectives, technical solutions and advantages of the present invention more clear, the technical solutions of the present invention will be clearly and completely described below in combination with specific embodiments of the present application and with reference to the accompanying drawings.

[0069] Embodiment 1

[0070] This embodiment is a method for assessing the fire risk of trees around distribution overhead line corridors. Figure 1 As shown, the steps include steps one to six:

[0071] Step 1: Use the fractal tree network model to simplify and simulate the real shape of the tree and construct a tree model.

[0072] When constructing a tree model, when the wire touches the tree, the current path from high to low is that the wire passes through one of each branch and finally flows into the ground through the trunk. Therefore, the equivalent circuit is a series connection of multiple branches.

[0073] The tree is approximated as a cylinder with uniform electrical and thermal characteristics, and the transition part between branches is ignored. The model structure is simplified to facilitate calculation. The conductivity of the tree is affected by temperature and moisture content, so the main parameters in the model include temperature, moisture content and tree size. By modeling the electrical and thermal characteristics of the tree, the TSF (Tree-contact Single-phase-to-ground Faults) current and its development process can be accurately simulated.

[0074] As a typical natural fractal structure, trees have similar geometric features in their overall shape from trunks to branches to small twigs. The fractal tree network model is used to simplify and simulate the real shape of trees, such as Figure 2 As shown, the structural sizes between two adjacent levels decrease and the proportions are the same. Since the TSF pathway consists of only one tree and trunk at each level, the specific number of branches is not discussed. The tree-like branch network has countless branch layers.

[0075] Specifically, the method for constructing the tree model is:

[0076] The fractal tree network model is used to simplify the real form of simulated trees, and the structural size between two adjacent levels is set to decrease and the proportion is the same;

[0077] In the tree model, α and β are defined as the length ratio and radius ratio of the branches of the k+1th layer network and the kth layer network, respectively, as follows:

[0078]

[0079] In the formula, l k , l k+1 are the branch lengths of the k-th layer network and the k+1-th layer network, r k 、r k+1 They are the branch radius of the k-th layer network and the branch radius of the k+1-th layer network respectively.

[0080] For l k and r k ,have:

[0081] l k =l0α k

[0082] r k =r0α ｋ

[0083] Where l0 is the basic branch length in the tree model, that is, the trunk height, and r0 is the basic branch radius, that is, the trunk radius.

[0084] Step 2: obtaining the initial moisture content of the tree model and continuously monitoring the temperature and transition resistance of the tree model.

[0085] The water content of the tree is the absolute water content, which is obtained by experimental weighing and the calculation formula is:

[0086]

[0087] In the formula, m s is the fresh weight of the wood block obtained from the experimental sampling, and m0 is the absolute dry mass of the wood block.

[0088] Commonly used methods for obtaining tree temperature include:

[0089] In the experimental scenario, thermocouple sensors can be arranged at different locations of the tree (such as the trunk and main branches), or infrared thermometers can be used to measure the surface temperature of the tree;

[0090] Based on the thermal conductivity of trees and experimental data, the thermodynamic model is calibrated to estimate the internal temperature in real time.

[0091] The transition resistance can be calculated from the system voltage of the distribution network and the current passing through the trees.

[0092] Step three, construct a single-phase tree-touch fault model. During the simulation of the single-phase tree-touch fault model, obtain the conductor phase voltage, continuously calculate the current heat generation, heat dissipation and heat absorption of the tree, further calculate the water evaporation mass, and use the water evaporation mass to update the tree moisture content.

[0093] The heat dissipation includes convection heat dissipation and radiation heat dissipation, and the heat absorption includes water evaporation heat absorption and tree temperature rise heat absorption. The relationship between heat dissipation, heat absorption and current heat generation is:

[0094] Heat generated by electric current = heat dissipation by convection + heat dissipation by radiation + heat absorption by water evaporation + heat absorption by temperature rise of trees. The calculation method of heat absorption by water evaporation is:

[0095] Q w =(Q s -Q c -Q r )·k f

[0096] k f =(1+e 98-T ) -1

[0097] In the formula, Q w The heat absorbed by water evaporation, Q s Q is the heat generated by the current. c is the convective heat dissipation, Q r is the radiation heat dissipation, k f is the evaporation absorption proportional coefficient, T is the tree temperature;

[0098] Current heat generation Q s , Convection heat dissipation Q c , radiant heat dissipation Q r The calculation methods are:

[0099]

[0100] Qc =∫k c S c (TT e )dt

[0101]

[0102] Where U is the phase voltage of the overhead distribution line, R t is the tree transition resistance at time t, k c is the branch convection heat dissipation coefficient, S c is the lateral area of ​​the branch, T is the tree temperature, T e is the ambient temperature, k r is the branch radiation heat transfer coefficient, and δ0 is the Stefan-Boltzmann constant.

[0103] Among them, the phase voltage of the distribution overhead conductor is used as a known input parameter for the subsequent calculation of the total heat generation, which can be obtained in the following way:

[0104] On-site measurement, in the fault simulation device, use a voltage sensor (such as a voltage transformer or a voltage divider) to measure the phase voltage of a single-phase conductor;

[0105] Experimental setting, in the experiment or simulation, the phase voltage value of the conductor is set according to the common distribution system voltage level (such as 10kV, 35kV);

[0106] Real-time monitoring data,real-time phase voltage data is obtained from the online monitoring equipment of the distribution system,which is used as the input of the simulation model.

[0107] The ambient temperature is usually regarded as the external boundary condition, which can be determined by using temperature and humidity sensors to monitor the ambient temperature at the fault site, or obtaining meteorological data of the fault area as input.

[0108] The lateral area of ​​branches is an important geometric parameter of the tree model, which is used to calculate the heat dissipation. The methods to obtain it include calculation based on the fractal structure of trees and experimental measurement. The calculation based on the fractal structure of trees assumes that branches and trunks are approximately uniform cylinders. According to the fractal geometric characteristics of trees, the cross-sectional area and total length of each level of branches are calculated, and then the lateral area is determined according to its surface geometry. Alternatively, the fractal scale factor is used to set the basic trunk area A. n and decreasing ratio r, through formula A n =A0·r n Estimate the sum of the lateral areas of all levels. Experimental measurements can use laser scanners to model the morphology of trees in three dimensions, extract geometric data, and calculate the lateral area of ​​branches.

[0109] The calculation method of the water evaporation mass is:

[0110]

[0111] In the formula, Δm is the mass of water evaporated, Q w The heat absorbed by water evaporation, T w is the water temperature;

[0112] The updated moisture content data is W-ΔW, where:

[0113]

[0114] m0 is the absolute dry mass of the wood block.

[0115] Step 4: After aligning the updated tree moisture content, the monitored tree model temperature and the transition resistance by time, the least squares method is used for fitting to obtain the binary relationship between the tree model conductivity, moisture content and temperature. The relationship between conductivity, temperature and moisture content after fitting is expressed as follows:

[0116] lnσ t (W,T)=7.458W+0.057T-0.050W·T-10.754

[0117] In the formula, σ t (W,T) is the conductivity calculated relative to temperature and moisture content at time t, W is the moisture content of the tree, and T is the temperature of the tree.

[0118] Step five, applying the binary relationship to the single-phase tree-touch fault model, performing iterative calculations, obtaining the tree temperature rise, and recording the tree temperature during the entire process based on the tree temperature rise.

[0119] The basis of iterative calculation is the relationship between tree path resistance, moisture content and temperature. In the single-phase tree contact fault model, the tree path resistance R t The calculation method is:

[0120]

[0121] Where α and β are the length ratio and radius ratio of the branches of the k+1th layer network and the kth layer network, respectively; n is the level of the touch line in the tree model; l0 is the basic branch length in the tree model, i.e., the trunk height; r0 is the basic branch radius, i.e., the trunk radius; σ t (W,T) is the binary relationship between the conductivity of the tree model and its moisture content and temperature.

[0122] The calculation method of the tree temperature rise is:

[0123]

[0124] Q t =Q s -Q c -Qr -Q w

[0125] Where ΔT is the temperature rise of the tree, c t is the specific heat capacity of wood, c w is the specific heat capacity of water, m s is the fresh weight of the wood block obtained by experimental sampling, m0 is the absolute dry weight of the wood block, Q t The heat absorbed by the tree due to temperature rise, Q s Q is the heat generated by the current. c is the convective heat dissipation, Q r is the radiation heat dissipation, Q w Absorbs heat for water evaporation;

[0126] The current tree temperature is the sum of the tree temperature in the previous iteration and the tree temperature rise in this iteration.

[0127] The specific iterative process is:

[0128] S1: At t = 0, the initial moisture content W is calculated by the fresh weight and absolute dry mass of the tree obtained by experimental weighing. The initial tree temperature T can be set to the current ambient temperature or the tree temperature can be collected by a temperature sensor. In the constructed single-phase tree contact fault model, α, β, l0, and r0 are all known, and the binary relationship is also known, so the initial tree path resistance R can be calculated. t .

[0129] S2: At t = 0, use the initial tree path resistance R t And the known voltage level, calculate the current heat generation Q according to the above formula s , Convection heat dissipation Q c , radiant heat dissipation Q r , water evaporation heat absorption Q w , and then according to the water evaporation heat absorption Q w Calculate the water evaporation mass at the current moment.

[0130] S3: At t=0, after obtaining the water evaporation mass, the initial water content W is updated to W1, where W1=W-ΔW.

[0131] S4: At t = 0, the heat generated by the current is Q s , Convection heat dissipation Q c , radiant heat dissipation Q r , water evaporation heat absorption Q w Calculate the tree temperature rise ΔT and update the initial tree temperature T to T1, where T1 = T + ΔT.

[0132] S5: At time t=1, repeat steps S1-S4 to replace the moisture content and temperature parameters used to calculate the tree path resistance with W1 and T1 to obtain a new moisture content W2 and temperature T2.

[0133] S6: Iterate the above steps until the set end condition is reached, and record the temperature sequence T, T1, …, T during the iteration process. n .

[0134] Step 6: Using the set temperature threshold, evaluate the risk level of the tree according to the temperature of the tree during the whole process. n The tree is compared with the set temperature threshold. If any temperature reaches the set threshold, the tree is judged to be a high-risk tree.

[0135] The temperature threshold is set to 100°C, that is, if the temperature of the tree reaches 100°C during the whole process, the corresponding tree will be marked as a high-risk tree. When the temperature reaches 100°C, the tree begins to lose water rapidly. Under the action of Joule heat generated by the electric current, it may cause current discharge or local overheating, increasing the risk of fire. Although 100°C is lower than the auto-ignition point of wood, this temperature condition has provided favorable conditions for further combustion and requires sufficient attention. Therefore, this embodiment defines trees that can reach 100°C as high-risk trees.

[0136] In this embodiment, the voltage levels of 10kV and 35kV of the medium and low voltage distribution networks which are more common in China are taken as examples. Figure 3-8 The relationship between the tree sizes of pine trees with heights ranging from 1m to 10m and radii ranging from 5cm to 1m at different voltage levels and at different levels where the wire may reach 100°C is shown. The dark areas are the tree sizes related to the high-risk areas, and the light areas are the low-risk areas. Figure 3 As shown in the figure, when the voltage level is 10KV and the wire touches the first level of trees, only trees with a trunk height of less than 1.25m are high-risk trees; if the voltage level is 35kV, the range of high-risk trees is expanded to all trees with a trunk height of less than 5.25m. At the voltage level of 35kV, as the level of wire contact increases, the range of high-risk trees is also expanding.

[0137] By obtaining the temperature curves of trees of different sizes at different levels of contact with trees through the above steps of this embodiment, a complete risk assessment table of tree sizes and contact levels can be constructed. Line patrol personnel can focus on high-risk tree sizes according to the risk assessment table as required, such as pruning in advance to prevent fires.

[0138] Embodiment 2

[0139] This embodiment is a system for assessing tree fire risks around distribution overhead line corridors. The system is used to implement the risk assessment method described in the first embodiment, including:

[0140] The tree modeling module is used to simplify the real morphology of simulated trees based on the fractal tree network model and construct a tree model, in which the structural sizes of two adjacent levels of networks decrease and the proportions are the same;

[0141] The parameter acquisition module includes: a moisture content acquisition unit for acquiring the initial absolute moisture content of the tree model; a temperature acquisition unit for continuously monitoring the temperature of the tree model; and a resistance acquisition unit for monitoring the transition resistance of the tree model.

[0142] The single-phase tree-touch fault simulation module includes: a voltage acquisition unit for obtaining the conductor phase voltage in the single-phase tree-touch fault model; a heat calculation unit for calculating the water evaporation mass based on the relationship between the tree current heat generation, convection heat dissipation, radiation heat dissipation, water evaporation heat absorption and tree temperature rise heat absorption, and updating the real-time moisture content of the tree model;

[0143] The data processing module includes: a conductivity fitting unit, which is used to align the updated tree moisture content, the monitored tree model temperature and the transition resistance in time, and use the least square method to fit the binary relationship between the conductivity and the moisture content and the temperature of the tree model; a temperature rise calculation unit, which is used to perform iterative calculations in the single-phase tree contact fault model based on the fitted binary relationship, obtain the temperature rise process of the tree model and record the temperature changes of the whole process;

[0144] The risk assessment module is used to analyze the tree temperatures recorded throughout the entire process based on the set temperature threshold and assess the fire risk level of the trees.

[0145] The above is only a preferred embodiment of the present invention. It should be pointed out that a person skilled in the art can make several modifications and improvements without departing from the inventive concept of the present invention, which all belong to the protection scope of the present invention.

Claims

1. A method for assessing tree fire risk around a distribution overhead line corridor, characterized in that: The following steps are involved: The fractal tree network model is used to simplify and simulate the real form of trees and construct a tree model; Obtaining the initial moisture content of the tree model, and continuously monitoring the temperature and transition resistance of the tree model; A single-phase tree-touch fault model is constructed. During the simulation of the single-phase tree-touch fault model, the conductor phase voltage is obtained, the current heat generation, heat dissipation and heat absorption of the tree are continuously calculated, the water evaporation mass is further calculated, and the water content of the tree is updated using the water evaporation mass; After aligning the updated tree moisture content, monitored tree model temperature and transition resistance in time, the least squares method was used for fitting to obtain the binary relationship between the tree model conductivity and moisture content and temperature; Applying the binary relationship to a single-phase tree-touch fault model, performing iterative calculations, obtaining the tree temperature rise, and recording the temperature of the tree during the entire process based on the tree temperature rise; The risk level of the trees is assessed based on the temperature of the trees throughout the process with a set temperature threshold.

2. A method for assessing tree fire risk around a distribution overhead line corridor according to claim 1, characterized in that: The tree model is constructed as follows: The fractal tree network model is used to simplify the real form of simulated trees, and the structural size between two adjacent levels is set to decrease and the proportion is the same; In the tree model, α and β are defined as the length ratio and radius ratio of the branches of the k+1th layer network and the kth layer network, respectively, as follows: In the formula, l k , l k+1 are the branch lengths of the k-th layer network and the k+1-th layer network, r k 、r k+1 They are the branch radius of the k-th layer network and the branch radius of the k+1-th layer network respectively.

3. A method for assessing tree fire risk around a distribution overhead line corridor according to claim 1, characterized in that: The water content of the tree is the absolute water content, which is obtained by experimental weighing and the calculation formula is: In the formula, m s is the fresh weight of the wood block obtained from the experimental sampling, and m0 is the absolute dry mass of the wood block.

4. A method for assessing tree fire risk around a distribution overhead line corridor according to claim 1, characterized in that: The heat dissipation includes convection heat dissipation and radiation heat dissipation, and the heat absorption includes water evaporation heat absorption and tree temperature rise heat absorption. The relationship between heat dissipation, heat absorption and current heat generation is: Heat generated by electric current = heat dissipation by convection + heat dissipation by radiation + heat absorption by water evaporation + heat absorption by temperature rise of trees.

5. A method for assessing tree fire risk around a distribution overhead line corridor according to claim 4, characterized in that: The calculation method of the heat absorption of water evaporation is: Q w =(Q s -Q c -Q r )·k f k f =(1+e 98-T ) -1 In the formula, Q w The heat absorbed by water evaporation, Q s Q is the heat generated by the current. c is the convective heat dissipation, Q r is the radiation heat dissipation, k f is the evaporation absorption proportional coefficient, T is the tree temperature; Current heat generation Q s , Convection heat dissipation Q c , radiant heat dissipation Q r The calculation methods are: Q c =∫k c S c (T-T e )dt Where U is the phase voltage of the overhead distribution line, R t is the tree transition resistance at time t, k c is the branch convection heat dissipation coefficient, S c is the lateral area of ​​the branch, T is the tree temperature, T e is the ambient temperature, k r is the branch radiation heat transfer coefficient, and δ0 is the Stefan-Boltzmann constant.

6. A method for assessing tree fire risk around a distribution overhead line corridor according to claim 1, characterized in that: In the single-phase tree-touching fault model, the tree path resistance R t The calculation method is: Where α and β are the length ratio and radius ratio of the branches of the k+1th layer network and the kth layer network, respectively; n is the total number of tree models; l0 is the basic branch length in the tree model, i.e., the trunk height; r0 is the basic branch radius, i.e., the trunk radius; σ t (W,T) is the binary relationship between the conductivity of the tree model and its moisture content and temperature.

7. A method for assessing tree fire risk around a distribution overhead line corridor according to claim 1, characterized in that: The calculation method of the water evaporation mass is: In the formula, Δm is the mass of water evaporated, Q w The heat absorbed by water evaporation, T w is the water temperature; The updated moisture content data is W-ΔW, where: m0 is the absolute dry mass of the wood block.

8. A method for assessing tree fire risk around a distribution overhead line corridor according to claim 1, characterized in that: The calculation method of the tree temperature rise is: Q t =Q s -Q c -Q r -Q w Where ΔT is the temperature rise of the tree, c t is the specific heat capacity of wood, c w is the specific heat capacity of water, m s is the fresh weight of the wood block obtained by experimental sampling, m0 is the absolute dry weight of the wood block, Q t The heat absorbed by the tree due to temperature rise, Q s Q is the heat generated by the current. c is the convective heat dissipation, Q r is the radiation heat dissipation, Q w Absorbs heat for water evaporation; The current tree temperature is the sum of the tree temperature in the previous iteration and the tree temperature rise in this iteration.

9. A method for assessing tree fire risk around a distribution overhead line corridor according to claim 1, characterized in that: The temperature threshold is set to 100°C.

10. A system for assessing tree fire risk around distribution overhead line corridors, characterized in that: The system is used to implement the risk assessment method according to any one of claims 1 to 9, comprising: The tree modeling module is used to simplify the real morphology of simulated trees based on the fractal tree network model and construct a tree model, in which the structural sizes of two adjacent levels of networks decrease and the proportions are the same; The parameter acquisition module includes: a moisture content acquisition unit for acquiring the initial absolute moisture content of the tree model; a temperature acquisition unit for continuously monitoring the temperature of the tree model; and a resistance acquisition unit for monitoring the transition resistance of the tree model. The single-phase tree-touch fault simulation module includes: a voltage acquisition unit for obtaining the conductor phase voltage in the single-phase tree-touch fault model; a heat calculation unit for calculating the water evaporation mass based on the relationship between the tree current heat generation, convection heat dissipation, radiation heat dissipation, water evaporation heat absorption and tree temperature rise heat absorption, and updating the real-time moisture content of the tree model; The data processing module includes: a conductivity fitting unit, which is used to align the updated tree moisture content, the monitored tree model temperature and the transition resistance in time, and use the least square method to fit the binary relationship between the conductivity and the moisture content and the temperature of the tree model; a temperature rise calculation unit, which is used to perform iterative calculations in the single-phase tree contact fault model based on the fitted binary relationship, obtain the temperature rise process of the tree model and record the temperature changes of the whole process; The risk assessment module is used to analyze the tree temperature recorded throughout the entire process based on the set temperature threshold and assess the fire risk level of the trees.

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