A method and system for calculating conductivity in single-phase tree-grounding faults

Abstract

The application discloses a kind of single-phase tree grounding fault conductivity calculation method and system, the method includes the following steps: constructing tree conductivity measurement system;Experimental stage, the temperature, weight and conductivity of current experimental sample are recorded continuously;After parameter acquisition ends, the absolute dry mass of experimental sample is measured, and the moisture content of experimental sample at corresponding time is calculated according to the absolute dry mass and the weight of experimental sample recorded in experimental stage;Replace experimental sample, repeat the execution experimental stage and calculate moisture content, save experimental data until reaching the set experimental number;Construct tree conductivity model, and the model parameters are fitted by least square method using the experimental data;The resistance of trees around distribution overhead line corridor is calculated in real time using the fitted tree conductivity model.The application has the advantages of high precision, real-time dynamic monitoring, simple structure and wide applicability.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of power distribution network fault analysis, and particularly relates to a conductivity calculation method and system in single-phase tree-contact grounding fault. BACKGROUND

[0002] China has high mountainous areas and forest coverage, especially in the southwest, northwest, and north China. According to statistical data, more than 20% of the power distribution lines are located in mountainous or forest-covered areas, and with the economic development, the power network construction gradually extends to these areas. The climate in different regions is obviously different. The climate in the north and central regions is cold and dry, while the climate in the south and southwest regions is humid and rainy. The climate in mountainous areas is unstable, and often appears strong wind, heavy rain, lightning and other severe weather, which directly affects the safe operation of overhead transmission lines and the probability of faults, and causes the problem of single-phase tree-contact grounding fault (TSF, Tree-contact Single-phase-to-ground Faults) caused by the contact between power distribution overhead lines and trees. Such faults not only affect the stable operation of the power system, but also may cause forest fires, causing serious environmental and economic losses. Therefore, how to effectively prevent and identify the occurrence of TSF has become a problem to be solved in the research and application of power systems.

[0003] The prior art accurately calculates the transition resistance by zero sequence current, voltage and other data, combined with the amplitude and phase angle correction of the residual current. The Chinese invention patent application with publication number CN118867985A discloses a method and system for calculating the conductivity of single-phase grounding fault, which includes the following steps: monitoring and obtaining the ground capacitance, rated voltage and arc suppression coil inductance value of the power distribution system, calculating the ground capacitance current and arc suppression coil current of the power distribution system when the ground is metallic; determining whether the bus zero sequence voltage is greater than the zero sequence voltage threshold, if not, executing the previous step; if yes, the power grid has a fault, and the next step is executed; obtaining the zero sequence current, arc suppression coil inductance current and zero sequence voltage of each outgoing line of the bus; calculating the ground residual current amplitude correction value and ground residual current phase angle correction value; and obtaining the ground conductivity by the ground conductivity calculation formula.

[0004] In addition, in the research of TSF fault model, TSF is classified as high impedance faults (HIF) of overhead line single-phase in the past. There is an arc-resistance series model at present, in which the arc has a long arc fault model in the air, simulating the nonlinearity of the fault, but the parameters of the arc model are measured by experiment. Subsequent scholars proposed a double nonlinear resistance series model, one resistance represents the fault arc in the form of Mayr model, and the other resistance represents the change of grounding resistance. Due to the use of empirical parameter correction method, the universality is poor, and the physical mechanism of TSF is different, so it is difficult to describe the slow change characteristic of the conductivity of the conductor touching the tree.

[0005] The above method is not suitable for TSF, and for TSF modeling, some scholars have proposed an equivalent model based on the actual physical process on the basis of TSF mechanism, but the resistivity correlation factor is not sufficient, and only the temperature rise stage is simulated, which affects the accuracy of the final calculation result. In addition, there are problems such as complex system structure design, inconvenience to build and maintain, etc., resulting in less flexible deployment. When the tree species need to be replaced or different environments need to be retested, a high deployment cost will be generated. SUMMARY

[0006] The present application provides a conductivity calculation method and system in single-phase tree grounding fault, aiming at solving the problems of insufficient correlation factors affecting accurate determination, complex system affecting deployment cost and other problems in the prior art.

[0007] To solve the above technical problems, the conductivity calculation method provided by the present application comprises the following steps:

[0008] A tree conductivity measurement system is constructed, which comprises a power supply module, an experimental circuit module and a parameter acquisition module. The experimental circuit module provides an electrical parameter acquisition interface to calculate the conductivity of the experimental sample. The parameter acquisition module acquires the temperature, weight and conductivity of the experimental sample during the experimental stage.

[0009] In the experimental stage, the experimental circuit module is connected to the power supply module, and the parameter acquisition module continuously records the temperature, weight and conductivity of the experimental sample at the set sampling frequency.

[0010] After the parameter acquisition is completed, the absolute dry mass of the experimental sample is measured, and the moisture content of the experimental sample at the corresponding time is calculated according to the absolute dry mass and the weight of the experimental sample recorded during the experimental stage.

[0011] Replace the experimental sample, repeat the experimental stage and calculate the moisture content, save the experimental data until the set number of experiments is reached.

[0012] A tree conductivity model is constructed, which is expressed as follows:

[0013] lnσ t (W,T)=AW+BT+CW·T+D

[0014] In the formula, σ t (W,T) represents the conductivity of the tree at time t, W is the water content of the tree at time t, T is the temperature of the tree at time t, A, B, C, and D are formula parameters, and the experimental data are fitted by the least square method;

[0015] The fitted tree conductivity model is used to calculate the resistance of the trees around the overhead distribution line corridor in real time, and the overhead line and tree contact fault are warned according to the real-time calculation result.

[0016] Preferably, the experimental circuit module comprises a first series circuit and a second series circuit connected in parallel across the power supply; the first series circuit comprises a voltage dividing resistor and a power supply voltage measuring resistor connected in series, and a first voltage collection point is led out between the voltage dividing resistor and the voltage measuring resistor; the second series circuit comprises an experimental sample and an experimental side measuring resistor connected in series, and a second voltage collection point is led out between the experimental sample and the experimental side measuring resistor, wherein the power supply voltage measuring resistor and the experimental side measuring resistor are grounded at the connection with the power supply.

[0017] Preferably, the conductivity calculation formula of the experimental sample is:

[0018]

[0019] In the formula, h is the height of the experimental sample, a and b are the length and width of the experimental sample respectively, R t is the resistance of the experimental sample;

[0020] The resistance R t of the experimental sample is expressed as follows:

[0021]

[0022] In the formula, R1 is the resistance value of the voltage dividing resistor, R2 is the resistance value of the power supply voltage measuring resistor, R3 is the resistance value of the experimental side measuring resistor, U1 is the voltage to ground of the first voltage collection point, and U2 is the voltage to ground of the second voltage collection point.

[0023] Preferably, the temperature sampling frequency of the experimental sample is 1Hz, the weight sampling frequency of the experimental sample is 1Hz, the voltage to ground sampling frequency of the first voltage collection point is 10kHz, and the voltage to ground sampling frequency of the second voltage collection point is 10kHz; the collected temperature, weight and voltage are recorded and saved after being aligned by time.

[0024] Preferably, the experimental sample is several groups of fresh pine beam blocks, each group containing at least 2 samples, each sample having a length, width and height of 3 cm; each group is soaked in water for different times, and at least one group is soaked for not less than one week.

[0025] Preferably, the experimental sample is coated with epoxy conductive silver glue on the contact surface between the wood block and the electrode.

[0026] Preferably, the experimental stage includes a wood block temperature rise stage, a moisture evaporation and recovery stage, and a flat evaporation heat dissipation stage, and the different stages are distinguished by the temperature of the experimental sample, wherein the wood block temperature rise stage and the moisture evaporation and recovery stage are separated by 98.1 DEG C, and the moisture evaporation and recovery stage and the flat evaporation heat dissipation stage are separated by 70 DEG C.

[0027] Preferably, the value ranges of the formula parameters A, B, C and D are [7, 8], [-0.7, 0.05], [-0.06, -0.03] and [-11, -8] respectively.

[0028] Preferably, the calculation method of the water content of the experimental sample is:

[0029] After the experiment, the wood block is placed in a drying oven, the drying temperature is set to 102 DEG C, and after running for 8 hours, the wood block is weighed and then placed back in the drying oven, and then weighed every 8 hours until the difference between the last two weights is not more than 0.2%, and the wood block is considered to have reached absolute dryness at this time, and the last weight is taken as the absolute dry mass of the wood block; the difference between the weight of the experimental sample collected during the experimental stage and the absolute dry mass and the absolute dry mass is the water content of the experimental sample.

[0030] Another aspect of the present application also provides a single-phase tree grounding fault conductivity calculation system, which is used to implement the above-mentioned calculation method, comprising:

[0031] A power supply module is used to provide stable power supply to the system;

[0032] An experimental circuit module is used to construct an experimental sample power loop and an electrical parameter measurement interface;

[0033] A parameter acquisition module further includes a temperature acquisition unit for acquiring the temperature of the experimental sample, a weight acquisition unit for acquiring the weight of the experimental sample, and a voltage acquisition unit for acquiring the voltage of the set voltage acquisition point to ground;

[0034] A model construction module is used to calculate the conductivity of the experimental sample according to the parameters of the experimental circuit module, and to calculate the water content of the experimental sample at the corresponding time through the weight and the absolute dry mass of the experimental sample during the experimental stage; and a tree conductivity model is fitted based on the experimental data through the least square method;

[0035] The monitoring and early warning module is used for calculating the resistance value of the trees around the overhead power distribution line corridor based on the fitted tree conductivity model and the real-time collected parameters, and early warning of the line and tree contact fault.

[0036] Compared with the prior art, the present application has the following technical effects:

[0037] 1. The conductivity calculation method provided by the present application captures the changes of tree conductivity under different temperature and humidity conditions through high-frequency data acquisition and multi-parameter synchronous monitoring, introduces the temperature and moisture content parameters of the trees into the conductivity calculation model, fits the binary model of the conductivity through a large amount of data, and ensures the output of high-precision conductivity results, which has high practical value in tree monitoring in the power line corridor.

[0038] 2. The conductivity calculation method system structure provided by the present application is simple and convenient to build and maintain, and can be quickly and flexibly deployed when different tree species need to be measured, or when the tree species need to be replaced or different environments need to be retested, and is suitable for various tree species and environments.

[0039] 3. The conductivity calculation method provided by the present application divides the experimental samples into groups, each group is soaked for different time to measure the temperature-resistivity data of different initial moisture contents, including at least one group soaked in water for one week to ensure that the wood absorbs enough water to reach a saturated state, and to simulate a wider moisture content range as much as possible, so that the collected data is more comprehensive, which helps to improve the accuracy of the final conductivity model fitting.

[0040] 4. The conductivity calculation method provided by the present application uses a voltage dividing resistor and a power supply voltage measuring resistor to accurately measure the output voltage of the power supply, and uses the accurate value to calculate the resistance of the experimental sample, which helps to improve the accuracy of the experimental sample resistance calculation.

[0041] 5. In the conductivity calculation method provided by the present application, the experimental wood block and the related installation, fixation, insulation, heating and conductive equipment. The insulating rubber pad not only provides stable support force, but also effectively isolates the external environment to prevent the influence of stray current on experimental data; the epoxy conductive silver paste is fully coated on the two sides of the wood block in the radial direction, which can enhance the physical and electrical contact between the copper foil electrode and the surface of the wood block, significantly reduce the contact resistance, and thus ensure uniform current distribution during the experiment; the wood block and the copper foil electrode are fixed by the clamp, which provides constant stress during the experiment to prevent the movement of the wood block during the experiment and ensure the stability of the current path; the above scheme ensures the accuracy of parameter acquisition in the experiment. BRIEF DESCRIPTION OF DRAWINGS

[0042] Figure 1 is a flowchart of the calculation method described in the present application;

[0043] Figure 2 is a schematic diagram of a tree conductivity measurement system according to an embodiment of the present application;

[0044] Figure 3 is a circuit schematic diagram of an experimental circuit module according to an embodiment of the present application;

[0045] Figure 4 is a wood block processing diagram according to an embodiment of the present application;

[0046] Figure 5 is a typical temperature-moisture content and conductivity relationship diagram according to an embodiment of the present application;

[0047] Figure 6 is a data and fitting plane diagram according to an embodiment of the present application. DETAILED DESCRIPTION

[0048] In order to make the purpose, technical solutions and advantages of the present application clearer, the technical solutions of the present application will be described clearly and completely below in combination with specific embodiments of the present application and with reference to the accompanying drawings.

[0049] Embodiment One

[0050] A single-phase tree grounding fault conductivity calculation method, as shown in Figure 1 , includes the following steps one to step six:

[0051] Step one, construct a tree conductivity measurement system, the tree conductivity measurement system includes a power supply module, an experimental circuit module and a parameter acquisition module, the experimental circuit module provides an electrical parameter acquisition interface to calculate the conductivity of the experimental sample, and the parameter acquisition module acquires the temperature, weight and conductivity of the experimental sample during the experimental stage.

[0052] The specific experimental system is shown in Figure 2 . The power supply module is responsible for providing stable AC power for the experiment. The AC current generator in the system outputs 220V, 50Hz current, and transmits the current to the experimental circuit through a dedicated power transmission line. The current is finally transmitted to the copper foil electrodes arranged at both ends of the wood block, ensuring that the current can effectively pass through the wood block to generate Joule heat for testing the change of conductivity with temperature and moisture content.

[0053] The core of the experimental circuit side is the experimental wood block and the related installation, insulation, heating and conducting equipment. Its detailed structure and process include electrode installation and insulation, wood block processing, clamp fixation.

[0054] Electrode installation and insulation: Copper foil electrodes are connected to both ends of the wood block. To ensure uniform stress on the wood block, insulating rubber pads are used to mount the electrodes. The copper plates on both sides are placed vertically on the rubber pads. The insulating rubber pads not only provide stable support but also effectively isolate the external environment, preventing the influence of stray current on experimental data.

[0055] Wood block treatment: During the experiment, the wood block needs to be treated in advance to ensure the stability of its moisture state. For this purpose, the wood block is soaked in water to ensure that it absorbs a certain amount of water. After soaking, the surface of the wood block is coated with epoxy conductive silver paste, which is fully coated on both sides of the wood block in the radial direction. This enhances the physical and electrical contact between the copper foil electrode and the wood block surface, significantly reducing the contact resistance and ensuring uniform current distribution during the experiment. To ensure sufficient data collection for fitting the plane, different soaking times can be used to allow the wood block to have different initial moisture contents for the experiment.

[0056] Clamp fixation: The wood block and copper foil electrode are fixed by a clamp, which provides a constant force during the experiment to prevent the wood block from moving during the experiment and ensure a stable current path. At the same time, this design also helps to reduce the influence of external vibrations and environmental factors on the accuracy of the experiment.

[0057] The parameter acquisition module is responsible for real-time acquisition of current, voltage, temperature and weight data, and transmits the data to the computer for processing. Specifically, the temperature measurement module is responsible for accurately monitoring the temperature change of the wood block, and is tightly attached to the heat film on the radial side wall of the wood block and connected to the thermocouple thermometer. The thermocouple thermometer can record the temperature of the wood block in real time at a high sensitivity measurement frequency (once per second) and transmit the temperature data to the data acquisition module; the weight measurement device uses a high-precision weighing balance to monitor the weight change of the wood block in the experimental circuit in real time, recording the weight change caused by water evaporation or absorption. The balance records weight data every second to ensure real-time monitoring of the moisture content of the wood block, and thus to measure the dynamic change of electrical conductivity with moisture content. The voltage and current acquisition module can accurately measure the voltage across the wood block and its change over time, and the acquisition module is designed with a sampling frequency of 10 kHz, which can capture subtle voltage changes. At the same time, the acquisition system records current and voltage data and transmits the measurement data to the computer for further analysis through high-speed data transmission.

[0058] As Figure 3As shown, the experimental circuit module includes a first series circuit and a second series circuit connected in parallel across the power supply; the first series circuit includes a voltage dividing resistor and a power supply voltage measuring resistor connected in series, and a first voltage collection point is led between the voltage dividing resistor and the voltage measuring resistor; the second series circuit includes an experimental sample and an experimental side measuring resistor connected in series, and a second voltage collection point is led between the experimental sample and the experimental side measuring resistor, wherein the power supply voltage measuring resistor and the experimental side measuring resistor are grounded at the connection with the power supply.

[0059] In Figure 3 , OUT1 and OUT2 are the first voltage collection point and the second voltage collection point respectively, R1 is the voltage dividing resistor, R2 is the power supply voltage measuring resistor, and Rt is the experimental sample. The power supply voltage accurate value can be measured by measuring the parameters of the R1 and R2 passage collection points.

[0060] Step two, experimental stage, connect the experimental circuit module to the power supply module, and the parameter collection module continuously records the temperature, weight and conductivity of the current experimental sample at the set sampling frequency.

[0061] Among them, the temperature of the wood block is recorded in real time by the thermocouple temperature measuring instrument at a high sensitivity measurement frequency, the weight change of the wood block in the experimental circuit is monitored in real time by using a high-precision weighing balance, and the voltage collection module can accurately measure the voltage of the first voltage collection point and the second voltage collection point to the ground and the change relationship thereof with time.

[0062] The following is the derivation process of the conductivity formula:

[0063] The power supply voltage accurate value is measured by R1 and R2, and the total power supply voltage expression is as follows:

[0064]

[0065] In the formula, U i is the accurate value of the actual power supply voltage, U1 is the voltage of the first voltage collection point to the ground, R1 is the resistance value of the voltage dividing resistor, and R2 is the resistance value of the power supply voltage measuring resistor.

[0066] The actual wood block voltage U t is measurable:

[0067] U t = U i -U2

[0068] In the formula, U2 is the voltage of the second voltage collection point to the ground.

[0069] The wood block current I t is measurable:

[0070]

[0071] wherein R3 is the resistance value of the measured resistance.

[0072] In the experiment, the resistance R between the positive and negative electrodes at both ends of the wood block exp may be expressed as:

[0073] R exp = 2·R c + R w

[0074] wherein R c is the contact resistance between the electrode and the wood block, and R w is the resistance of the wood block itself, since the contact surface between the wood block and the electrode is filled with epoxy conductive silver glue to level the surface of the wood block, as shown in Figure 4 The resistance of the epoxy conductive silver glue RC is extremely low and can be ignored, thereby enhancing the physical contact between the copper foil electrode and the wood block, ensuring the reliability of the electrical contact, effectively reducing the contact resistance, improving the overall conductive performance, and ensuring that the measured results of the experiment are approximately the resistance of the wood block itself.

[0075] Therefore, the expression of the resistance of the wood block R t is:

[0076]

[0077] By combining the above formulas, R t is expressed as follows:

[0078]

[0079] Further, the conductivity calculation formula of the experimental sample is:

[0080]

[0081] wherein h is the height of the experimental sample, a and b are the length and width of the experimental sample, respectively, and R t is the resistance of the experimental sample.

[0082] The experimental sample is a plurality of groups of fresh pine beam wood blocks, each group containing at least 2 samples, each sample having a length, width and height of 3 cm; each group is soaked in water for different times, and at least one group is soaked for not less than one week.

[0083] Since different initial moisture contents of wood blocks will result in different experimental curves, one embodiment of the present application divides several small wood blocks (e.g., 10) into a group, each group is soaked for different time to measure the temperature-resistivity data of different initial moisture contents. Until the last time of soaking in water for one week, which ensures that the wood absorbs enough water to reach the saturation state, the experiment is repeated to ensure that the most three-dimensional data distribution is collected on the plane to fit the plane.

[0084] During the experiment, the temperature sampling frequency of the experimental sample is 1 Hz, the weight sampling frequency of the experimental sample is 1 Hz, the ground voltage sampling frequency of the first voltage collection point is 10 kHz, and the ground voltage sampling frequency of the second voltage collection point is 10 kHz; the collected temperature, weight and voltage are recorded and saved after time alignment.

[0085] A group of classical curves are shown in Figure 5 The analysis of the conductivity waveform change divides the corresponding experimental process into three corresponding stages: wood block temperature rise stage, water evaporation and recovery stage, and evaporation heat dissipation flat stage. The distinguishing feature of different stages is the temperature of the experimental sample, wherein the wood block temperature rise stage and the water evaporation and recovery stage are separated by 98.1°C, and the water evaporation and recovery stage and the evaporation heat dissipation flat stage are separated by 70°C.

[0086] Specifically, the first stage is the wood block temperature rise stage, the initial temperature of the wood block before the experiment is 25.6°C, and the moisture content is 108.37%. In this stage, with the application of 220V alternating voltage on both sides of the wood block in the radial direction, the current is conducted through the water in the wood. As the main conductive medium, the water is affected by the Joule heating effect of the current, and the temperature rises rapidly. The rise in temperature causes part of the water in the wood to begin to evaporate, causing the moisture content of the wood to gradually decrease. At the same time, with the decrease of moisture content and the increase of wood temperature, the conductivity increases. With the further rise of temperature, the evaporation of water accelerates, and the moisture content continues to decrease. This stage is mainly characterized by the rapid change of temperature, and at the end of the stage, the temperature of the wood block rises to 98.1°C, and the moisture content decreases to 97.10%.

[0087] The second stage is the water evaporation and recovery stage. In the early stage of the second stage, the temperature of the experimental wood block rises from 98.1°C to about 100°C. At this time, the water in the wood evaporates and is quickly discharged, accompanied by a "buzz" sound. This phenomenon indicates that the free water in the wood evaporates and is quickly discharged. In the process of water evaporation, the temperature of the experimental wood block is maintained at about 100°C for a short time, because the evaporation of water absorbs a lot of heat, and at the same time the moisture content of the wood block decreases rapidly to 87.59%, which is a typical feature of water phase change.

[0088] In the middle and late stages of stage 2, as the moisture content gradually decreases, heat absorption weakens, and the temperature drops to 70°C. Simultaneously, the decrease in moisture causes conductivity to decrease as the moisture content and temperature drop. This stage lasts slightly longer than stage 1. The early stages of this stage are characterized by rapid changes in moisture content, while the middle and late stages show a simultaneous, uniform decline in both moisture content and temperature.

[0089] Stage three is the period of slow evaporative heat dissipation. During this stage, the wood enters a relatively stable state, with the temperature gradually decreasing from 70°C to 40°C, and the moisture content further decreasing from 80% to 46%. During this stage, the moisture in the wood primarily exists in the form of adsorbed water. As the temperature drops, the evaporation rate slows, resulting in a relatively stable rate of change in moisture content. Due to the decrease in moisture content and temperature within the wood, the electrical conductivity continues to decrease, reflecting a further weakening of the wood's conductive properties. This stage lasts longer because the evaporation of adsorbed water is slow, and the temperature drop relies primarily on heat dissipation to the air, which takes a long time to complete. Overall, Stage three can be viewed as the process of the electrical heating effect gradually weakening and the wood approaching a state of environmental equilibrium.

[0090] According to dielectric theory, the conductivity of high-loss dielectrics typically increases exponentially with increasing temperature and moisture content. Furthermore, the presence of highly polar water molecules effectively weakens the binding force between ions and wood attachment points, resulting in a near-linear relationship between the logarithm of conductivity and moisture content. Temperature and moisture content are also correlated; wood with higher moisture content contains more active ions, leading to a significant change in conductivity with temperature increases.

[0091] Step 3: After the parameter collection is completed, the absolute dry mass of the experimental sample is measured, and the moisture content of the experimental sample at the corresponding moment is calculated based on the absolute dry mass and the experimental sample weight recorded during the experimental stage.

[0092] Among them, the method for obtaining absolute dry mass data is as follows: after the experiment, the wood block is placed in a drying oven, the drying temperature is set to 102°C, and after running for 8 hours, the wood block is weighed and returned to the drying oven. It is then weighed every 8 hours until the difference between the last two weighings does not exceed 0.2%. The wood block is considered to have reached absolute dryness at this time, and the last weighing weight is taken as the absolute dry mass of the wood block; the ratio of the difference between the weight of the experimental sample collected during the experimental stage and the absolute dry mass to the absolute dry mass is the moisture content of the experimental sample.

[0093] Step 4: Replace the experimental sample, repeat the experimental phase and calculate the moisture content, and save the experimental data until the set number of experiments is reached.

[0094] Through a variety of Figure 5The shown classical water content Joule heating experiment data are fused together, considering the independence and correlation of temperature and conductivity expression and water content and conductivity expression, and a tree conductivity model considering water content and temperature is obtained by least square fitting of the data as shown in the following formula: Figure 6 As shown, the expression corresponding to step five is obtained.

[0095] Step five, a tree conductivity model is constructed, which is expressed as follows:

[0096] lnσ t (W,T)=AW+BT+CW·T+D

[0097] In the formula, σ t (W,T) represents the conductivity of the tree at time t, W represents the water content of the tree at time t, T represents the temperature of the tree at time t, A, B, C, and D are formula parameters, which are obtained by least square fitting using the experimental data.

[0098] In an embodiment of the present application, the experimental data of all groups are fitted to obtain the values of A, B, C, and D as 7.4580, 0.0569, -0.0495, and -10.7541, respectively, i.e., the fitted tree conductivity model is expressed as:

[0099] lnσ t (W,T)=7.4580W+0.0569T-0.0495W·T-10.7541

[0100] It is verified that the root mean square error of the model is 0.0125. This result can be substituted into the TSF model with actual physical meaning.

[0101] In some other embodiments of the present application, the tree conductivity model is fitted using the data of only one group of experimental samples, and the fitting of experimental data of all groups is completed, wherein the formula parameters fluctuate within a certain range. Specifically, the floating range of the obtained parameter A is between 7 and 8, the floating range of the parameter B is between -0.7 and 0.05, the floating range of the parameter C is between -0.06 and -0.03, and the floating range of the parameter D is between -11 and -8. Overall, the value range of the formula parameters A, B, C, and D is [7, 8], [-0.7, 0.05], [-0.06, -0.03], and [-11, -8], respectively.

[0102] Step six, the tree resistance around the overhead distribution line corridor is calculated in real time using the fitted tree conductivity model, and the overhead line and tree contact fault is warned according to the real-time calculation result.

[0103] Embodiment two

[0104] The embodiment is a single-phase contact tree grounding fault conductivity calculation system, which is used for implementing the calculation method in the embodiment one, and comprises:

[0105] A power supply module is configured to provide stable power supply for the system.

[0106] An experimental circuit module is configured to construct an experimental sample power-on circuit and an electrical parameter measurement interface.

[0107] A parameter acquisition module further comprises a temperature acquisition unit configured to acquire the temperature of the experimental sample, a weight acquisition unit configured to acquire the weight of the experimental sample, and a voltage acquisition unit configured to acquire the voltage of the set voltage acquisition point relative to the ground.

[0108] A model construction module is configured to calculate the conductivity of the experimental sample according to the parameters of the experimental circuit module, and calculate the moisture content of the experimental sample at the corresponding moment through the weight and the absolute dry mass of the experimental sample in the experimental stage; and fit the tree conductivity model through the least square method based on the experimental data.

[0109] A monitoring and early warning module is configured to calculate the resistance value of the trees around the power distribution overhead line corridor based on the fitted tree conductivity model and the real-time acquired parameters, and to perform early warning on the contact fault between the line and the trees.

[0110] 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 protection scope of the present application.

Claims

1. A method for calculating conductivity in a single-phase tree-to-ground fault, characterized in that: The following steps are involved: Constructing a tree conductivity measurement system, the tree conductivity measurement system includes a power supply module, an experimental circuit module, and a parameter acquisition module. The experimental circuit module provides an electrical parameter acquisition interface to calculate the conductivity of the experimental sample. The parameter acquisition module collects the temperature, weight, and conductivity of the experimental sample during the experimental phase. During the experimental phase, the experimental circuit module is connected to the power supply module, and the parameter acquisition module continuously records the temperature, weight, and conductivity of the current experimental sample at the set sampling frequency; After the parameter collection is completed, the absolute dry mass of the experimental sample is measured, and the moisture content of the experimental sample at the corresponding moment is calculated based on the absolute dry mass and the experimental sample weight recorded during the experimental stage; Replace the experimental sample, repeat the experimental phase and calculate the moisture content, and save the experimental data until the set number of experiments is reached; A tree electrical conductivity model is constructed, and the tree electrical conductivity model is expressed as follows: Where, express The electrical conductivity of the trees at each moment, for The moisture content of the tree at any moment, for The temperature of the trees at all times, are the formula parameters, which are obtained by least square fitting using the experimental data; The fitted tree conductivity model is used to calculate the resistance of trees around the distribution overhead line corridor in real time, and early warning of contact faults between overhead lines and trees is issued based on the real-time calculation results.

2. The method for calculating conductivity in a single-phase tree-to-ground fault according to claim 1, characterized in that: The experimental circuit module includes a first series circuit and a second series circuit connected in parallel at both ends of a power supply; the first series circuit includes a voltage divider resistor and a power supply voltage measuring resistor arranged in series, and a first voltage collection point is drawn between the voltage divider resistor and the power supply voltage measuring resistor; the second series circuit includes an experimental sample and an experimental side measuring resistor arranged in series, and a second voltage collection point is drawn between the experimental sample and the experimental side measuring resistor, wherein grounding is performed at the connection between the power supply voltage measuring resistor and the experimental side measuring resistor and the power supply.

3. The method for calculating conductivity in a single-phase tree-to-ground fault according to claim 2, characterized in that: The conductivity calculation formula of the experimental sample is: Where, is the height of the experimental sample, are the length and width of the experimental sample, is the resistance of the experimental sample; Resistance of the experimental sample The expression is as follows: Where, is the resistance of the voltage divider resistor, The resistance of the resistor is measured for the power supply voltage, is the resistance value of the resistor measured on the experimental side, is the ground voltage of the first voltage collection point, is the voltage to ground of the second voltage collection point.

4. The method for calculating conductivity in a single-phase tree-to-ground fault according to claim 3, characterized in that: The temperature sampling frequency of the experimental sample is 1 Hz, the weight sampling frequency of the experimental sample is 1 Hz, the voltage-to-ground sampling frequency of the first voltage collection point is 10 kHz, and the voltage-to-ground sampling frequency of the second voltage collection point is 10 kHz; the collected temperature, weight, and voltage are aligned in time and recorded and saved.

5. The method for calculating conductivity in a single-phase tree-to-ground fault according to claim 1, characterized in that: The experimental samples are several groups of fresh pine beams, each group contains at least 2 samples, and each sample is 3 cm in length, width and height; each group is soaked in water for different time periods, and at least one group is soaked for no less than one week.

6. The method for calculating conductivity in a single-phase tree-to-ground fault according to claim 5, characterized in that: The experimental sample is coated with epoxy conductive silver glue on the contact surface between the wood block and the electrode.

7. The method for calculating conductivity in a single-phase tree-to-ground fault according to claim 1, characterized in that: The experimental stages include a wood block temperature rise stage, a water evaporation and recovery stage, and a gentle evaporative heat dissipation stage. The distinguishing feature of the different stages is the experimental sample temperature. The wood block temperature rise stage and the water evaporation and recovery stage are separated by 98.1°C, and the water evaporation and recovery stage and the gentle evaporative heat dissipation stage are separated by 70°C.

8. The method for calculating conductivity in a single-phase tree-to-ground fault according to claim 1, characterized in that: The formula parameters The value ranges are [7,8], [-0.7,0.05], [-0.06,-0.03], and [-11,-8] respectively.

9. The method for calculating conductivity in a single-phase tree-to-ground fault according to claim 1, characterized in that: The calculation method of the moisture content of the experimental sample is: After the experiment, the experimental samples were placed in a drying oven and the drying temperature was set to 102°C. After running for 8 hours, the experimental samples were weighed and put back into the drying oven. Thereafter, they were weighed every 8 hours until the difference between the last two weighings did not exceed 0.2%. The experimental samples were considered to have reached absolute dryness at this time, and the last weighing weight was taken as the absolute dry mass of the experimental samples. The ratio of the difference between the experimental sample weight and the absolute dry mass collected during the experimental stage to the absolute dry mass was the moisture content of the experimental samples.

10. A conductivity calculation system for a single-phase tree-to-ground fault, characterized in that: The system is used to implement the calculation method according to any one of claims 1 to 9, comprising: Power supply module, used to provide stable power to the system; Experimental circuit module, used to build the experimental sample power circuit and electrical parameter measurement interface; The parameter acquisition module further includes a temperature acquisition unit for acquiring the temperature of the experimental sample, a weight acquisition unit for acquiring the weight of the experimental sample, and a voltage acquisition unit for acquiring the voltage between the set voltage acquisition point and the ground; The model building module is used to calculate the conductivity of the experimental sample based on the parameters of the experimental circuit module, and to calculate the moisture content of the experimental sample at the corresponding time through the experimental stage weight and absolute dry mass; and to fit the tree conductivity model based on the experimental data using the least squares method; The monitoring and early warning module is used to calculate the resistance value of trees around the distribution overhead line corridor based on the fitted tree conductivity model and real-time collected parameters, and to issue early warnings for line-tree contact faults.

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