A power distribution line single-phase tree grounding fault risk assessment method and system

Abstract

The application discloses a power distribution line single-phase tree contact grounding fault risk assessment method and system, and the method comprises the following steps: a fractal tree network model is used to simplify and simulate the real shape of a tree to build a tree model; the initial moisture content of the tree model is obtained, and the temperature and transition resistance of the tree model are continuously monitored; a single-phase tree contact fault model is built, a conductor phase voltage is obtained, the current heat production, heat dissipation and heat absorption of the tree are continuously calculated, the water evaporation quality is calculated and obtained, and the moisture content of the tree is updated using the water evaporation quality; the binary relationship between the conductivity, moisture content and temperature of the tree model is fitted and obtained; the binary relationship is applied to the iterative calculation of the fault model to obtain the highest temperature of the tree in the whole process; and the risk level of the tree is assessed according to the highest temperature by taking a set temperature threshold value. The application can accurately realize the fire risk assessment of the size of the tree, and is helpful to the safe operation of the power grid and the protection of the ecological environment.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of tree fire assessment, and particularly relates to a method and system for evaluating the risk of single-phase grounding fault of distribution line. BACKGROUND

[0002] With the rapid development of modern power systems, distribution overhead lines have become an important way of power transmission, and the safety of their surrounding environment is directly related to the stable operation of the power grid and the reliability of power supply. The corridors of distribution overhead lines often pass through woodland, residential areas or farmland, and the trees around them play an important role in beautifying the environment and protecting the ecology, but at the same time they also bring potential risks of electric shock fire. Once the power transmission is caused by line fault or other factors to the nearby trees, it may cause temperature rise and lead to fire, which in turn poses a serious threat to the power grid and the surrounding environment.

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

[0004] Chinese patent application for invention with publication number CN106886841A discloses a line forest fire disaster assessment method and system without real-time collection of field information, which comprises the following steps: determining the type and height of vegetation; judging the type of fire behavior; obtaining alarm transmission line information; obtaining meteorological data at the location of forest fire occurrence; calculating the height of forest fire flame zone, ion zone and smoke zone; calculating the breakdown voltage of the flame zone; calculating the breakdown voltage of the ion zone; calculating the breakdown voltage of the smoke zone; calculating the trip probability of the transmission line; and evaluating the forest fire grade. The present application also provides a line forest fire disaster assessment system without real-time collection of field information.

[0005] In the above-mentioned scheme, the breakdown voltage of the flame zone, ion zone and smoke zone is calculated depending on static physical models, while the actual shape and parameters of these regions (such as non-uniform flame, complex airflow, etc.) may far exceed the assumed range of the model; therefore, the overly simplified model may not accurately reflect the complex fire behavior, resulting in a decrease in the accuracy of the forest fire grade evaluation result; and it highly depends on the accuracy and comprehensiveness of the input data (such as vegetation type, height, meteorological data, etc.), and if the data is inaccurate or missing, the reliability of the evaluation result will be significantly reduced.

[0006] In recent years, modeling methods based on physical processes have gradually become a new direction for studying fire risk. These methods can analyze the relationship between external environment and system parameters and fire occurrence conditions through simulation, providing more reliable data support for risk prediction. For example, by analyzing the geometric characteristics (height, radius, etc.), electrical conductivity, thermal physical 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.

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

[0008] The present application provides a power distribution line single-phase tree grounding fault risk assessment method and system, aiming to solve the problems of insufficient precision of existing technology in wildfire grade evaluation results, and high dependence on environmental data.

[0009] To solve the above technical problems, the risk assessment method provided by the present application comprises the following steps:

[0010] A fractal tree network model is used to simplify the real shape of the tree and construct a tree model;

[0011] The initial moisture content of the tree model is obtained, and the temperature and transition resistance of the tree model are continuously monitored;

[0012] A single-phase tree fault model is constructed, and in the simulation process of the single-phase tree fault model, the conductor phase voltage is obtained, the current heat, heat dissipation and heat absorption of the tree are continuously calculated, the water evaporation quality is further calculated and obtained, and the moisture content of the tree is updated using the water evaporation quality;

[0013] After aligning the updated moisture content of the tree, the monitored temperature and transition resistance of the tree model by time, the least square method is used for fitting to obtain the binary relationship between the electrical conductivity of the tree model and the moisture content and temperature;

[0014] The binary relationship is applied to the single-phase tree fault model for iterative calculation to obtain the temperature rise of the tree, and the temperature of the tree during the whole process is recorded according to the temperature rise of the tree;

[0015] According to the temperature of the tree during the whole process, the risk grade of the tree is evaluated according to the set temperature threshold.

[0016] Preferably, the construction method of the tree model is:

[0017] The fractal tree network model is used to simplify the real shape of the tree, and the structure size between two adjacent levels is set to be reduced in the same proportion;

[0018] In the tree model, the definitions of are the branch length ratio and the radius ratio of the network tree branch in the first and the second network, respectively, and are expressed as follows:

[0019]

[0020]

[0021] wherein, L1 and L2 are the branch length of the first and the second network, respectively, and R1 and R2 are the branch radius of the first and the second network, respectively.

[0022] Preferably, the water content of the tree is the absolute water content, which is obtained by experimental weighing, and the calculation formula is as follows:

[0023]

[0024] wherein, W is the fresh weight of the wood block obtained by experimental sampling, and M is the absolute dry weight of the wood block.

[0025] Preferably, the heat dissipation amount includes the convective heat dissipation amount and the radiative heat dissipation amount, the heat absorption amount includes the water evaporation heat absorption amount and the tree temperature rise heat absorption amount, and the relationship among the heat dissipation amount, the heat absorption amount and the current heat production amount is as follows:

[0026] Current heat production amount = convective heat dissipation amount + radiative heat dissipation amount + water evaporation heat absorption amount + tree temperature rise heat absorption amount.

[0027] Preferably, the calculation method of the water evaporation heat absorption amount is as follows:

[0028]

[0029]

[0030] wherein, Q is the water evaporation heat absorption amount, W is the current heat production amount, h is the convective heat dissipation amount, σ is the radiative heat dissipation amount, a is the evaporation absorption proportionality coefficient, and T is the temperature of the tree. ​​​​​​​​​​

[0031] Heat generated by electric current Convection heat dissipation Radiative heat dissipation The calculation methods are as follows:

[0032]

[0033]

[0034]

[0035] In the formula, The phase voltage of the overhead power distribution conductor. for Tree transition resistance at all times The heat dissipation coefficient of tree branches is the convective heat dissipation coefficient. The lateral surface area of ​​the branch. For the temperature of the trees, For ambient temperature, The heat transfer coefficient of the tree branch is radiative. is the Stefan-Boltzmann constant.

[0036] Preferably, in the single-phase tree-touch fault model, the tree path resistance... The calculation method is as follows:

[0037]

[0038] In the formula, The first Layer network branches and the first The ratio of tree lengths to the ratio of radii in a layered network. The total number of levels in the tree model. This refers to the basic branch length in the tree model, which is equivalent to the trunk height. The radius of the basic branches, i.e., the radius of the trunk. This represents the binary relationship between electrical conductivity, water content, and temperature in a tree model.

[0039] Preferably, the method for calculating the mass of water evaporated is as follows:

[0040]

[0041] In the formula, The mass of water evaporated. The evaporation of water absorbs heat. The temperature of the water;

[0042] The updated moisture content data is as follows ,in:

[0043]

[0044] is the absolute dry mass of the wood block.

[0045] Preferably, the calculation method of the tree temperature rise is as follows:

[0046]

[0047]

[0048] wherein, is the tree temperature rise, is the specific heat capacity of wood, is the specific heat capacity of water, is the fresh weight of the wood block obtained by experimental sampling, is the absolute dry mass of the wood block, is the heat absorption of the tree temperature rise, is the heat production of the electric current, is the heat dissipation by convection, is the heat dissipation by radiation, is the heat absorption of water evaporation;

[0049] The current tree temperature is the sum of the tree temperature of the previous iteration and the tree temperature rise of the current iteration.

[0050] Preferably, the temperature threshold is set to 100℃.

[0051] Another aspect of the present application also provides a power distribution line single-phase tree contact ground fault risk assessment system, which is used to implement the above-mentioned risk assessment method and comprises:

[0052] A tree modeling module is configured to simplify the real shape of a simulated tree based on a fractal tree network model to construct a tree model, wherein the structure size of adjacent two levels of the network decreases and the proportion is the same.

[0053] A parameter acquisition module comprises a water content acquisition unit configured to obtain the initial absolute water content of the tree model, a temperature acquisition unit configured to continuously monitor the temperature of the tree model, and a resistance acquisition unit configured to monitor the transition resistance of the tree model.

[0054] A single-phase tree contact fault simulation module comprises a voltage acquisition unit configured to obtain the phase voltage of the conductor in the single-phase tree contact fault model, and a heat calculation unit configured to calculate the water evaporation mass based on the relationship between the heat production of the tree electric current, the heat dissipation by convection, the heat dissipation by radiation, the heat absorption of water evaporation, and the heat absorption of the tree temperature rise, and update the real-time water content of the tree model.

[0055] A data processing module includes: an electrical conductivity fitting unit configured to align the updated tree moisture content, the monitored tree model temperature, and the transition resistance by time, and use a least square method fitting to obtain a binary relationship between the electrical conductivity of the tree model and the moisture content and the temperature; and a temperature rise calculation unit configured to perform iterative calculation in a single-phase tree fault model based on the fitted binary relationship, to obtain a temperature rise process of the tree model and record the temperature change in the whole process.

[0056] A risk assessment module is configured to analyze the recorded tree temperature in the whole process based on a set temperature threshold, and to assess the fire risk level of the tree.

[0057] Compared with the prior art, the present application has the following technical effects:

[0058] 1. The risk assessment method provided by the present application provides a scientific and quantitative method for risk assessment by simulating and analyzing the relationship between the height and radius of the tree and the temperature rise under different voltage levels (10 kV, 35 kV). This modeling analysis based on physical processes can quickly and accurately assess the fire risk of trees around the distribution overhead line corridor, filling the gap in the traditional risk assessment method based on experience and statistics.

[0059] 2. The risk assessment method provided by the present application obtains the temperature curve of the tree when a single-phase tree fault occurs by iteratively calculating variables such as electrical conductivity, resistance, and temperature. Through closed-loop calculation of the model, the dynamic changes of each parameter over time can be tracked in real time, eliminating the high dependence on external environmental data in the prior art, and making the assessment conclusion more reasonable.

[0060] 3. The risk assessment method provided by the present application is not only suitable for specific static conditions, but also can 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 application is more adaptable and can cover a wider range of actual scenarios.

[0061] 4. The risk assessment method provided by the present application models the single-phase tree fault of the distribution overhead line, obtains the conductor phase voltage data, and refines the electrical characteristic analysis of the fault environment. This effectively reduces the difficulty of complex calculation, preserves the key structural features, improves the applicability of the assessment model, and improves the accuracy of simulating the shape of the tree. Moreover, it is 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 DRAWINGS

[0062] Figure 1 is a flowchart of the risk assessment method described in the present application;

[0063] Figure 2 is a schematic diagram of the single-phase tree fault model and the tree model according to an embodiment of the present application;

[0064] Figure 3 is a schematic diagram of a tree 1-level catenary fire risk under a 10 kV level according to an embodiment of the present application;

[0065] Figure 4 is a schematic diagram of a tree 2-level catenary fire risk under a 10 kV level according to an embodiment of the present application;

[0066] Figure 5 is a schematic diagram of a tree 3-level catenary fire risk under a 10 kV level according to an embodiment of the present application;

[0067] Figure 6 is a schematic diagram of a tree 1-level catenary fire risk under a 35 kV level according to an embodiment of the present application;

[0068] Figure 7 is a schematic diagram of a tree 2-level catenary fire risk under a 35 kV level according to an embodiment of the present application;

[0069] Figure 8 is a schematic diagram of a tree 3-level catenary fire risk under a 35 kV level according to an embodiment of the present application. DETAILED DESCRIPTION

[0070] In order to make the objects, technical solutions and advantages of the present application clearer, the technical solutions of the present application will be described below in conjunction with specific embodiments of the present application and in reference to the accompanying drawings.

[0071] Embodiment One

[0072] The present embodiment is a method for evaluating the risk of single-phase tree contact grounding fault of a power distribution line, as shown in FIG. 1, comprising the following steps one to six: Figure 1

[0073] Step one, simplifying and simulating the real shape of a tree by using a fractal tree network model to construct a tree model.

[0074] When the conductor contacts the tree body, the current path from high to low is the conductor passing through each bifurcated branch and finally flowing into the ground through the trunk. Therefore, the equivalent circuit is a series connection of multiple tree branch bodies.

[0075] The tree is approximated as a cylinder with uniform electrical and thermal properties, and the transition part between branches is ignored, so as to simplify the model structure for calculation. The electrical 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 properties of the tree, accurate simulation of the TSF (Tree-contact Single-phase-to-ground Faults) current and its development process is achieved. ​

[0076] Trees, as typical natural fractal structures, exhibit similar geometric features in their overall shape from the trunk to the branches and twigs. A fractal tree network model can be used to simplify and simulate the real morphology of trees, such as... Figure 2 As shown, the structural dimensions between adjacent levels decrease and are proportional. 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 branching network has countless branch layers.

[0077] Specifically, the method for constructing the tree model is as follows:

[0078] A fractal tree network model is used to simplify the simulation of the real morphology of trees, and the structural size between adjacent levels is set to decrease while the proportion is the same.

[0079] In the tree model, define The first Layer network branches and the first The ratio of tree lengths to tree radii in a layered network is expressed as follows:

[0080]

[0081]

[0082] In the formula, They are the first Tree length and the first layer of the network The length of the branches in the layered network. They are the first The tree radius of the layer network and the first The tree radius of the layer network.

[0083] for and ,have:

[0084]

[0085]

[0086] In the formula, This refers to the basic branch length in the tree model, which is equivalent to the trunk height. This refers to the radius of the basic branches, which is the same as the radius of the trunk.

[0087] Step 2: Obtain the initial moisture content of the tree model and continuously monitor the temperature and transition resistance of the tree model.

[0088] The moisture content of the trees is the absolute moisture content, which is obtained through experimental weighing, and the calculation formula is as follows:

[0089]

[0090] wherein, is the fresh weight of the wood block obtained by sampling, is the absolute dry weight of the wood block.

[0091] The commonly used method for obtaining the temperature of the tree includes:

[0092] In the experimental scenario, thermocouple sensors can be arranged at different positions of the tree (such as the trunk and main branches), or an infrared temperature measuring instrument can be used to measure the surface temperature of the tree.

[0093] Based on the heat conduction characteristics of the tree and experimental data, the thermodynamic model is calibrated to estimate the internal temperature in real time.

[0094] The transition resistance can be calculated and obtained by the system voltage of the power distribution network and the monitored current passing through the tree.

[0095] Step three, constructing a single-phase contact tree fault model, in the simulation process of the single-phase contact tree 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 obtained, and the water content of the tree is updated using the water evaporation mass.

[0096] The heat dissipation includes convective heat dissipation and radiative heat dissipation, and 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:

[0097] Current heat generation = convective heat dissipation + radiative heat dissipation + water evaporation heat absorption + tree temperature rise heat absorption.

[0098] The calculation method of the water evaporation heat absorption is:

[0099]

[0100]

[0101] wherein, is the water evaporation heat absorption, is the current heat generation, is the convective heat dissipation, is the radiative heat dissipation, is the evaporation absorption proportionality coefficient, is the temperature of the tree.

[0102] Current heat generation , convective heat dissipation , radiative heat dissipation The calculation methods are respectively:

[0103]

[0104]

[0105]

[0106] wherein, is the phase voltage of the overhead power line, is is the tree transition resistance at time t, is the tree branch convective heat transfer coefficient, is the tree branch lateral area, is the tree temperature, is the ambient temperature, is the tree branch radiative heat transfer coefficient, is the Stefan-Boltzmann constant.

[0107] The phase voltage of the overhead power line is input as a known parameter for subsequent calculation of total heat generation, which can be obtained in the following ways:

[0108] Field measurement: In the fault simulation device, the phase voltage of the single-phase conductor is measured using a voltage sensor (such as a voltage transformer or a voltage divider);

[0109] Experimental setting: In experiments or simulations, the phase voltage value of the conductor is set according to the common voltage level of the power distribution system (such as 10 kV, 35 kV);

[0110] Real-time monitoring data: Real-time phase voltage data is obtained from the online monitoring equipment of the power distribution system for simulation model input.

[0111] The ambient temperature is usually considered as the external boundary condition, which can be determined by monitoring the ambient temperature of the fault site using a temperature and humidity sensor, or obtaining meteorological data of the fault occurrence area as input, etc.

[0112] The lateral area of the tree branch is an important geometric parameter of the tree model, which is used to calculate the heat dissipation. Its acquisition methods include calculation based on tree fractal structure and experimental measurement, etc. The calculation based on tree fractal structure assumes that the branches and trunks are approximately uniform cylinders, and according to the fractal geometric characteristics of the tree, the cross-sectional area and total length of each level of branches are calculated, and then the lateral area is determined according to the surface geometry; or use the fractal scaling factor to set the basic trunk area and the decreasing ratio , estimate the total lateral area of all levels by the formula Experimental measurement can use a laser scanner to model the tree shape in three dimensions, extract geometric data, and calculate the lateral area of the branches.

[0113] The calculation method of the water evaporation quality is:

[0114]

[0115] In the formula, For the mass of water evaporation. The evaporation of water absorbs heat. The temperature of the water;

[0116] The updated moisture content data is as follows ,in:

[0117]

[0118] The dry weight of the wood block.

[0119] Step four: After aligning the updated tree moisture content, monitored tree model temperature, and transition resistance by time, the least squares method is used for fitting to obtain the binary relationship between the tree model's conductivity and moisture content and temperature. The fitted relationship between conductivity and temperature and moisture content is expressed as follows:

[0120]

[0121] In the formula, for The conductivity calculated relative to temperature and moisture content at a given time. For the moisture content of trees, The temperature of the tree.

[0122] Step 5: Apply the binary relationship to the single-phase tree-contact fault model, perform iterative calculations to obtain the tree temperature rise, and record the tree temperature throughout the process based on the tree temperature rise.

[0123] The iterative calculation is based on the relationship between tree path resistance and moisture content and temperature. In the single-phase tree-touching fault model, the tree path resistance... The calculation method is as follows:

[0124]

[0125] In the formula, The first Layer network branches and the first The ratio of tree lengths to the ratio of radii in a layered network. This refers to the hierarchy of the lines in the tree model. This refers to the basic branch length in the tree model, which is equivalent to the trunk height. The radius of the basic branches, i.e., the radius of the trunk. This represents the binary relationship between electrical conductivity, water content, and temperature in a tree model.

[0126] The method for calculating the temperature rise of the trees is as follows:

[0127]

[0128]

[0129] wherein, is the tree temperature rise, is the specific heat capacity of wood, is the specific heat capacity of water, is the fresh weight of the wood block obtained by experimental sampling, is the oven-dry weight of the wood block, is the heat absorption of the tree temperature rise, is the heat production of the electric current, is the heat dissipation by convection, is the heat dissipation by radiation, is the heat absorption of water evaporation;

[0130] The current tree temperature is the sum of the tree temperature of the previous iteration and the tree temperature rise of the current iteration.

[0131] The iteration process is specifically as follows:

[0132] S1: At time t=0, the initial moisture content is obtained by calculating the fresh weight and oven-dry weight of the tree obtained by experimental weighing, and the initial tree temperature can be set as the current ambient temperature or the tree temperature collected by a temperature sensor; in the constructed single-phase tree fault model, are known, and the binary relationship is also known, so the initial tree path resistance can be calculated.

[0133] S2: At time t=0, the initial tree path resistance and the known voltage level are used to calculate the heat production of the electric current , the heat dissipation by convection , the heat dissipation by radiation , and the heat absorption of water evaporation , and then the water evaporation mass at the current time is calculated according to the heat absorption of water evaporation .

[0134] S3: At time t=0, after obtaining the water evaporation mass, the initial moisture content is updated to , wherein .

[0135] S4: At time t=0, the tree temperature rise is calculated according to the heat production of the electric current , the heat dissipation by convection , the heat dissipation by radiation , and the heat absorption of water evaporation , and the initial tree temperature is updated to wherein .

[0136] S5: at time t=1, repeat steps S1-S4 to replace the moisture content and temperature parameters used to calculate the tree trunk resistance with and , to obtain new moisture content and temperature .

[0137] S6: iterate the above steps until the set end condition is reached, and record the temperature sequence .

[0138] Step six, according to the temperature threshold set, evaluate the risk level of the tree according to the temperature of the tree throughout the process. That is, compare the above recorded temperature sequence with the set temperature threshold, and if any temperature reaches the set threshold, the tree is determined to be a high-risk tree.

[0139] The temperature threshold is set to 100℃, that is, if the temperature of the tree throughout the process reaches 100℃, the corresponding tree is marked as a high-risk tree. When the temperature reaches 100℃, the tree begins to lose water rapidly, and under the action of the joule heat generated by the current, it may cause current discharge or local overheating, increasing the risk of fire. Although 100℃ is lower than the ignition point of wood, this temperature condition has already provided favorable conditions for further combustion, which needs to be paid enough attention. Therefore, the tree that can reach 100℃ is defined as a high-risk tree in this embodiment.

[0140] In this embodiment, taking the voltage levels of 10kV and 35kV of the relatively common low-voltage distribution network in China as an example, Figures 3-8 the relationship between the size of the tree that can reach 100℃ and the level of the touch line under different voltage levels is shown, where the dark area is the size of the tree in the high-risk area, and the light area is the low-risk area. As Figure 3 shown, under the condition of the first level of the touch line of the tree with a voltage level of 10kV, only the tree with a trunk height less than 1.25m is a high-risk tree; under the condition of the voltage level of 35kV, the range of the high-risk tree expands to all trees with a trunk height less than 5.25m. Under the voltage level of 35kV, as the level of the touch line increases, the range of the high-risk tree also expands.

[0141] Through the above steps in this embodiment, the temperature curve of trees of different size specifications under different levels of touch tree can be obtained, and a complete risk assessment table of tree size and touch line level can be constructed.

[0142] Embodiment two

[0143] The embodiment is a power distribution line single-phase tree grounding fault risk assessment system, which is used to implement the risk assessment method as in embodiment one, comprising:

[0144] A tree modeling module is configured to simplify the real shape of a simulated tree based on a fractal tree network model to construct a tree model, wherein the structure size of adjacent two levels of the network decreases and the proportion is the same.

[0145] A parameter acquisition module comprises a water content acquisition unit configured to obtain the initial absolute water content of the tree model, a temperature acquisition unit configured to continuously monitor the temperature of the tree model, and a resistance acquisition unit configured to monitor the transition resistance of the tree model.

[0146] A single-phase tree fault simulation module comprises a voltage acquisition unit configured to obtain the conductor phase voltage in the single-phase tree fault model, and a heat calculation unit configured to calculate the water evaporation mass based on the relationship between the tree current heat generation, the convective heat dissipation, the radiative heat dissipation, the water evaporation heat absorption, and the tree temperature rise heat absorption, and update the real-time water content of the tree model.

[0147] A data processing module comprises a conductivity fitting unit configured to align the updated tree water content, the monitored tree model temperature, and the transition resistance by time, and use the least square method to fit to obtain the binary relationship between the conductivity of the tree model and the water content and the temperature, and a temperature rise calculation unit configured to perform iterative calculation in the single-phase tree fault model based on the fitted binary relationship to obtain the temperature rise process of the tree model and record the whole process temperature change.

[0148] A risk assessment module is configured to analyze the recorded tree temperature based on the set temperature threshold to evaluate the fire risk level of the tree.

[0149] The above only describes the preferred embodiments of the present application, and it should be noted that for those skilled in the art, without departing from the inventive concept, several modifications and improvements can be made, which are all within the scope of protection of the present application.

Claims

1. A method for risk assessment of single-phase tree-contact grounding faults in power distribution lines, characterized in that, Includes the following steps: A tree model is constructed by simplifying the simulation of the real morphology of trees using a fractal tree network model. The initial moisture content of the tree model was obtained, and the temperature and transition resistance of the tree model were continuously monitored. A single-phase tree-contact fault model is constructed. During the simulation of the single-phase tree-contact fault model, the phase voltage of the conductor is obtained, and the heat generated by the current, heat dissipation and heat absorption of the tree are continuously calculated. The water evaporation mass is further calculated and the water evaporation mass is used to update the water content of the tree. After aligning the updated tree moisture content, monitored tree model temperature, and transition resistance by time, the least squares method was used for fitting to obtain the binary relationship between the tree model conductivity and moisture content and temperature. The binary relationship is applied to the single-phase tree-contact fault model, iterative calculations are performed to obtain the tree temperature rise, and the tree temperature is recorded throughout the process based on the tree temperature rise. The risk level of trees is assessed based on the temperature of the trees throughout the entire process, using a set temperature threshold.

2. The method for risk assessment of single-phase tree-contact grounding faults in power distribution lines according to claim 1, characterized in that, The method for constructing the tree model is as follows: A fractal tree network model is used to simplify the simulation of the real morphology of trees, and the structural size between adjacent levels is set to decrease while the proportion is the same. In the tree model, define The first Layer network branches and the first The ratio of tree lengths to tree radii in a layered network is expressed as follows: In the formula, They are the first Tree length and the first layer of the network The length of the branches in the layered network. They are the first The tree radius of the layer network and the first The tree radius of the layer network.

3. The method for risk assessment of single-phase tree-contact grounding faults in power distribution lines according to claim 1, characterized in that, The moisture content of the trees is the absolute moisture content, obtained through experimental weighing, and the calculation formula is: In the formula, The fresh weight of the wood blocks obtained from the experimental sampling. The dry weight of the wood block.

4. The method for risk assessment of single-phase tree-contact grounding faults in power distribution lines according to claim 1, characterized in that, The heat dissipation includes convective heat dissipation and radiative heat dissipation, and the heat absorption includes heat absorption due to water evaporation and heat absorption due to tree temperature rise. The relationship between heat dissipation, heat absorption, and heat generated by electric current is as follows: Heat generated by electric current = heat dissipation by convection + heat dissipation by radiation + heat absorbed by water evaporation + heat absorbed by tree temperature rise.

5. The method for risk assessment of single-phase tree-contact grounding faults in power distribution lines according to claim 4, characterized in that, The method for calculating the heat absorbed by water evaporation is as follows: In the formula, The evaporation of water absorbs heat. To generate heat from electric current, For convective heat dissipation, For radiative heat dissipation, This is the evaporation absorption ratio coefficient. For tree temperature; Heat generated by electric current Convection heat dissipation Radiative heat dissipation The calculation methods are as follows: In the formula, The phase voltage of the overhead power distribution conductor. for Tree transition resistance at all times The heat dissipation coefficient of tree branches is the convective heat dissipation coefficient. The lateral surface area of ​​the branch. For the temperature of the trees, For ambient temperature, The heat transfer coefficient of the tree branch is radiative. is the Stefan-Boltzmann constant.

6. The method for risk assessment of single-phase tree-contact grounding faults in power distribution lines according to claim 1, characterized in that, In the single-phase tree-contact fault model, the tree path resistance... The calculation method is as follows: In the formula, The first Layer network branches and the first The ratio of tree lengths to the ratio of radii in a layered network. The total number of levels in the tree model. This refers to the basic branch length in the tree model, which is equivalent to the trunk height. The radius of the basic branches, i.e., the radius of the trunk. This represents the binary relationship between electrical conductivity, water content, and temperature in a tree model.

7. The method for risk assessment of single-phase tree-contact grounding faults in power distribution lines according to claim 1, characterized in that, The method for calculating the mass of water evaporated is as follows: In the formula, The mass of water evaporated. The evaporation of water absorbs heat. The temperature of the water; The updated moisture content data is as follows ,in: The dry weight of the wood block.

8. The method for risk assessment of single-phase tree-contact grounding faults in power distribution lines according to claim 1, characterized in that, The method for calculating the temperature rise of the trees is as follows: In the formula, For the trees to warm up, For the specific heat capacity of wood, The specific heat capacity of water, The fresh weight of the wood blocks obtained from the experimental sampling. The dry weight of the wood block. To absorb heat for the trees to warm up, To generate heat from electric current, For convective heat dissipation, For radiative heat dissipation, The evaporation of water absorbs heat; The current tree temperature is the sum of the tree temperature in the previous iteration and the tree temperature rise in the current iteration.

9. The method for risk assessment of single-phase tree-contact grounding faults in power distribution lines according to claim 1, characterized in that, The temperature threshold is set to 100℃.

10. A risk assessment system for single-phase tree-contact grounding faults in power distribution lines, characterized in that, The system is used to implement the risk assessment method as described in any one of claims 1-9, including: The tree modeling module is used to simplify and simulate the real morphology of trees based on a fractal tree network model, and to construct a tree model in which the structural size of adjacent network levels decreases 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-contact fault simulation module includes: a voltage acquisition unit, used to acquire the conductor phase voltage in the single-phase tree-contact fault model; and a heat calculation unit, used to calculate the water evaporation mass based on the relationship between the heat generated by tree current, convective heat dissipation, radiative heat dissipation, water evaporation heat absorption, and tree temperature rise heat absorption, and update the real-time moisture content of the tree model. The data processing module includes: a conductivity fitting unit, which aligns the updated tree moisture content, monitored tree model temperature, and transition resistance by time, and uses the least squares method to fit the binary relationship between the conductivity, moisture content, and temperature of the tree model; and a temperature rise calculation unit, which performs iterative calculations in the single-phase tree-contact fault model based on the fitted binary relationship, obtains the temperature rise process of the tree model, and records the temperature changes throughout the process. The risk assessment module is used to analyze the tree temperatures recorded throughout the process based on a set temperature threshold to assess the fire risk level of the trees.

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