Method and system for calculating conductivity in single-phase contact tree grounding fault

Abstract

The invention discloses a conductivity calculation method and system in a single-phase tree-touching grounding fault. The method comprises the following steps: constructing a tree conductivity measurement system; in an experiment stage, continuously recording the temperature, the weight and the conductivity of the current experiment sample; after parameter acquisition is finished, measuring the absolute dry mass of the experimental sample, and calculating the moisture content of the experimental sample at the corresponding moment according to the absolute dry mass and the weight of the experimental sample recorded in the experimental stage; replacing the experiment sample, repeatedly executing the experiment stage, calculating the water content, and storing experiment data until the set experiment frequency is reached; constructing a tree conductivity model, and fitting parameters of the model by using the experimental data through a least square method; and calculating the resistance of the trees around the power distribution overhead line corridor in real time by using the fitted tree conductivity model. The device has the advantages of high precision, real-time dynamic monitoring, simple structure and wide applicability.

Description

Technical Field

[0001] The invention belongs to the technical field of distribution network fault analysis, and in particular relates to a conductivity calculation method and system in a single-phase tree-to-ground fault. Background Art

[0002] China has a high mountainous area and forest coverage rate, especially in the southwest, northwest, and north China. According to statistics, more than 20% of distribution lines are located in mountainous areas or forested areas, and with economic development, power network construction has gradually extended 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 south and southwest regions are humid and rainy. The climate in mountainous areas is unstable, and severe weather such as strong winds, heavy rains, and lightning often occur. These climatic conditions directly affect the operating safety and fault probability of overhead transmission lines, and the problem of single-phase tree-contact grounding faults (TSF, Tree-contact Single-phase-to-ground Faults) caused by the contact between distribution overhead lines and trees is also becoming increasingly serious. Such faults not only affect the stable operation of the power system, but may also cause forest fires, resulting in serious environmental and economic losses. Therefore, how to effectively prevent and identify the occurrence of TSF has become an urgent problem to be solved in the research and application of power systems.

[0003] The prior art uses zero-sequence current, voltage and other data combined with the amplitude and phase angle correction of the grounding residual current to accurately calculate the transition resistance. The Chinese invention patent application with publication number CN118867985A discloses a method and system for calculating the conductivity of a single-phase grounding fault, which includes the following steps: monitoring and obtaining the ground capacitance, rated voltage, and arc suppression coil inductance of the distribution system, and calculating the ground capacitance current and arc suppression coil current of the distribution system when metallic grounding occurs; judging 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 fails, and executing the next step; obtaining the zero-sequence current, arc suppression coil inductance current, and zero-sequence voltage of each outgoing line of the bus; calculating the grounding residual current amplitude correction value and the grounding residual current phase angle correction value; and obtaining the grounding conductivity through the grounding conductivity calculation formula.

[0004] In addition, in the study of TSF fault models, TSF was previously classified as a single-phase high-impedance grounding fault (HIF) on overhead lines. Currently, there is an arc-resistance series model, in which the arc has a long arc fault model in the air, which simulates the nonlinearity of the fault, but the arc model parameters are measured experimentally. Subsequent scholars proposed a dual nonlinear resistor series model, in which one resistor represents the fault arc in the form of a Mayr model, and the other resistor represents the change in grounding resistance. Due to the use of empirical parameter correction methods, the versatility is poor, and they are all different from the physical mechanism of TSF, making it difficult to describe the slow-changing conductivity characteristics of the wire-contact tree fault.

[0005] The above method is not very applicable to TSF. For TSF modeling, some scholars have proposed an equivalent model based on the actual physical process based on the TSF mechanism, but the resistivity correlation factor is not fully considered, and only the temperature rise stage is simulated, which affects the accuracy of the final calculation results. In addition, there are problems such as complex system structure design, inconvenient construction and maintenance, resulting in inflexible deployment. When it is necessary to change the tree species or encounter different environments and need to re-experiment, it will incur high deployment costs. Summary of the invention

[0006] The present invention provides a method and system for calculating conductivity in a single-phase tree-to-ground fault, aiming to solve the problems in the prior art that correlation factors are not sufficient to affect accurate determination and system complexity affects deployment costs.

[0007] In order to solve the above technical problems, the conductivity calculation method proposed in the present invention comprises the following steps:

[0008] Constructing a tree conductivity measurement system, the tree conductivity measurement system comprising a power supply module, an experimental circuit module and a parameter acquisition module, the experimental circuit module providing an electrical parameter acquisition interface to calculate the conductivity of the experimental sample, the parameter acquisition module acquiring the temperature, weight and conductivity of the experimental sample during the experimental stage;

[0009] 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;

[0010] 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 time is calculated based on the absolute dry mass and the experimental sample weight recorded during the experimental stage;

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

[0012] A tree conductivity model is constructed, and the tree conductivity model 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, which are obtained by least squares fitting using the experimental data;

[0015] The fitted tree conductivity model is used to calculate the resistance of trees around the distribution overhead line corridor in real time, and an early warning of contact faults between overhead lines and trees is issued based on the real-time calculation results.

[0016] Preferably, 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-dividing resistor and a power supply voltage measuring resistor arranged in series, and a first voltage collection point is drawn between the voltage-dividing resistor and the 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 point between the power supply voltage measuring resistor and the experimental side measuring resistor and 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, and R t is the resistance of the experimental sample;

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

[0021]

[0022] Wherein, R1 is the resistance of the voltage divider resistor, R2 is the resistance of the power supply voltage measuring resistor, R3 is the resistance 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 1 Hz, the weight sampling frequency of the experimental sample is 1 Hz, the voltage sampling frequency to ground of the first voltage collection point is 10 kHz, and the voltage sampling frequency to ground of the second voltage collection point is 10 kHz; the collected temperature, weight and voltage are aligned in time and recorded and saved.

[0024] Preferably, 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 a different time, and at least one group is soaked for no 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 stages include a wood block temperature rise stage, a water evaporation and recovery stage, and a gentle evaporative heat dissipation stage, and the distinguishing feature of different stages is the experimental sample temperature, 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 gentle evaporative heat dissipation stage are separated by 70°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 moisture content of the experimental sample is:

[0029] After the experiment, the wood block was placed in a drying box and the drying temperature was set to 102°C. After running for 8 hours, the wood block was weighed and put back into the drying box. It was then weighed every 8 hours until the difference between the last two weighings did not exceed 0.2%. The wood block was considered to have reached absolute dryness at this time, and the last weighing weight was 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 was the moisture content of the experimental sample.

[0030] In another aspect of the present invention, a conductivity calculation system for a single-phase tree-to-ground fault is provided. The system is used to implement the above calculation method, including:

[0031] Power supply module, used to provide stable power to the system;

[0032] Experimental circuit module, used to construct the experimental sample power circuit and electrical parameter measurement interface;

[0033] 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 of the set voltage acquisition point to the ground;

[0034] The model building module is used to calculate the conductivity of the experimental sample according to the parameters of the experimental circuit module, and to calculate the moisture content of the experimental sample at the corresponding moment through the experimental stage weight and the absolute dry mass; and to fit the tree conductivity model based on the experimental data by the least square method;

[0035] 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 the parameters collected in real time, and to issue early warnings for line-tree contact faults.

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

[0037] 1. The conductivity calculation method proposed in the present invention captures the changes in 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 tree into the conductivity calculation model, and fits the binary model of conductivity through a large amount of data to ensure high-precision conductivity result output, which has high practical value in tree monitoring in power line corridors.

[0038] 2. The conductivity calculation method proposed in the present invention has a simple system structure design and is easy to build and maintain. When it is necessary to measure the conductivity of different tree species, when it is necessary to change the tree species or when encountering different environments and need to re-experiment, it can be quickly and flexibly deployed and is suitable for a variety of tree species and environments.

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

[0040] 4. The conductivity calculation method proposed in the present invention uses a voltage divider resistor and a power supply voltage measuring resistor to accurately measure the power supply output voltage, and uses the precise value to calculate the resistance of the experimental sample, which helps to improve the accuracy of the calculation of the resistance of the experimental sample.

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

[0042] Figure 1 is a schematic flow chart of the calculation method of the present invention;

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

[0044] Figure 3 is a circuit schematic diagram of the experimental circuit module described in an embodiment of the present invention;

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

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

[0047] Figure 6 It is a schematic diagram of the data and fitting plane described in the embodiment of the present invention. DETAILED DESCRIPTION

[0048] 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.

[0049] Embodiment 1

[0050] A method for calculating the conductivity in a single-phase tree-to-ground fault. Figure 1 As shown, the steps include steps one to six:

[0051] Step 1: construct a tree conductivity measurement system, which 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 as follows Figure 2 As shown. The power supply module is responsible for providing a stable AC power supply for the experiment. The AC power generator in the system outputs 220V, 50Hz current and transmits the current to the experimental circuit through a dedicated transmission line. The current is finally transmitted to the copper foil electrodes set at both ends of the wood block to ensure 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 is the experimental wooden block and its related installation, fixing, insulation, heating and conductive equipment. Its detailed structure and process include electrode installation and insulation, wooden block processing, and fixture fixing.

[0054] Electrode installation and insulation: Copper foil electrodes are connected to both ends of the wooden block. In order to ensure that the wooden block is evenly stressed, insulating rubber pads are used to install the electrodes, and 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 and prevent stray current from affecting the 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. To this end, the wood block is soaked in water to ensure that the wood block absorbs a certain amount of moisture. After soaking, the surface of the wood block will be coated with epoxy conductive silver glue, which is fully coated on both radial sides of the wood block, 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. In order to ensure that enough data is collected to fit the plane, different soaking times can be used to give the wood block different initial moisture contents for experiments.

[0056] Fixture fixation: The wooden block and copper foil electrode are fixed by the fixture, which provides a constant force during the experiment to prevent the wooden block from moving during the experiment and ensure the stability of the current path. At the same time, this design also helps to reduce the impact of external vibration and environmental factors on the experimental accuracy.

[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, it includes a temperature measurement module, which is responsible for accurately monitoring the temperature change of the wood block. The heat transfer plate is attached to the radial side wall of the wood block and connected to a thermocouple thermometer. The thermocouple thermometer can record the temperature of the wood block in real time with 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, and record the weight change caused by water evaporation or absorption. The balance records the weight data once a second to ensure real-time monitoring of the moisture content of the wood block, and then realizes the dynamic change measurement of conductivity with moisture content. The voltage and current acquisition module can accurately measure the voltage at both ends of the wood block and its change over time. The acquisition module is designed with a sampling frequency of 10kHz, which can capture subtle voltage changes. At the same time, the acquisition system records current and voltage data, and imports the measurement data into the computer for further analysis through high-speed data transmission.

[0058] like Figure 3As shown, 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-dividing resistor and a power supply voltage measuring resistor arranged in series, and a first voltage collection point is drawn between the voltage-dividing resistor and the 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 point between the power supply voltage measuring resistor and the experimental side measuring resistor and the power supply.

[0059] exist Figure 3 In the figure, 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 measurement resistor, and Rt is the experimental sample. The precise value of the power supply voltage can be measured by measuring the parameters of the R1 and R2 channel collection points.

[0060] Step 2: 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.

[0061] Among them, the temperature of the wood block is recorded in real time by a thermocouple thermometer with a high-sensitivity measurement frequency, and the weight change of the wood block in the experimental circuit is monitored in real time by a high-precision weighing balance. The voltage acquisition module can accurately measure the voltage to ground of the first voltage collection point and the second voltage collection point, as well as their changing relationship over time.

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

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

[0064]

[0065] Where U i is the precise value of the actual voltage of the power supply, U1 is the voltage to ground of the first voltage acquisition point, R1 is the resistance of the voltage divider resistor, and R2 is the resistance of the power supply voltage measurement resistor.

[0066] Can measure the actual wood block voltage U t for:

[0067] U t =U i -U2

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

[0069] Wood block current I t for:

[0070]

[0071] Where R3 is the resistance of the test side measurement resistor.

[0072] During the experiment, the resistance R between the positive and negative poles of the wooden block exp It can be expressed as:

[0073] R exp =2·R c +R w

[0074] In the formula, R c is the contact resistance between the electrode and the wood block, 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 fill the surface of the wood block, Figure 4 As shown in the figure, the resistance RC of epoxy conductive silver glue 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 experimental results are close to the resistance of the wood block itself.

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

[0076]

[0077] Combining the above formulas, R t The statement is as follows:

[0078]

[0079] Then, the conductivity calculation formula of the experimental sample is obtained as follows:

[0080]

[0081] In the formula, 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 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 a different time, and at least one group is soaked for no less than one week.

[0083] Since wood blocks with different initial moisture contents will obtain different experimental curves, one embodiment of the present invention divides several (e.g., 10) small wood blocks into a group, and each group is immersed for different time periods to conduct experiments to measure temperature-resistivity data with different initial moisture contents. The last time the wood blocks are immersed in water for a week is to ensure that the wood absorbs enough water to reach a saturated state, and the experiment is repeated to ensure that enough three-dimensional data are collected and distributed on the plane to fit the plane.

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

[0085] A set of classic curves such as Figure 5 As shown in the figure, the conductivity waveform change is analyzed and the corresponding experimental process is divided into three corresponding stages: wood block temperature rise stage, water evaporation and recovery stage, and evaporation and heat dissipation slow stage. The distinguishing feature of different stages is the experimental sample temperature, among which the wood block temperature rise stage and water evaporation and recovery stage are separated by 98.1℃, and the water evaporation and recovery stage and evaporation and heat dissipation slow stage are separated by 70℃.

[0086] Specifically, stage one is the temperature rise stage of the wood block. The initial temperature of the wood block before the experiment is 25.6℃ and the moisture content is 108.37%. During this stage, with the application of 220V AC voltage to both sides of the wood block in the radial direction, the current is conducted through the moisture in the wood. As the main conductive medium, the moisture is affected by the Joule heat effect of the current and the temperature rises rapidly. The increase in temperature causes part of the moisture in the wood to evaporate, causing the moisture content of the wood to gradually decrease. At the same time, with the decrease in moisture content and the increase in the temperature of the wood block, the conductivity increases. As the temperature rises further, the evaporation of moisture accelerates, causing the moisture content to continue to decrease. This stage is mainly characterized by rapid changes in temperature. At the end of the stage, the temperature of the wood block rises to 98.1℃ and the moisture content drops to 97.10%.

[0087] Stage 2 is the period of water evaporation and recovery. In the early stage of stage 2, the temperature of the experimental wood block increased from 98.1°C to around 100°C. At this time, the water inside the wood is close to the boiling point at high temperature, resulting in a large number of bubbles on the surface and radial area of ​​the wood block, accompanied by a "hissing" buzzing sound. This phenomenon indicates that the free water in the wood evaporates and is quickly discharged due to heat. During the process of large-scale evaporation of water, the temperature of the experimental wood block will briefly remain at around 100°C, because the evaporation of water absorbs a large amount of heat, and the moisture content of the wood block quickly decreases to 87.59%, which is a typical feature of water phase change.

[0088] In the middle and late stages of stage 2, as the water content gradually decreases, the heat absorption weakens and the temperature drops to 70°C. At the same time, due to the decrease in water content, the conductivity decreases with the decrease in water content and temperature. This stage is slightly longer than stage 1. In the early stage of this stage, the water content changes rapidly, and in the middle and late stages, the water content and temperature decrease at a uniform rate at the same time.

[0089] Stage three is the period of slow evaporation and heat dissipation. In stage three, the wood block enters a relatively stable state, the temperature gradually drops from 70°C to 40°C, and the moisture content further decreases from 80% to 46%. In this stage, the moisture in the wood mainly exists in the form of adsorbed water. As the temperature decreases, the evaporation rate slows down, so the rate of change of the moisture content is relatively stable. Due to the reduction of moisture inside the wood and the drop in temperature, the conductivity continues to decrease, reflecting the further weakening of the wood's electrical conductivity. This stage lasts for a long time, because the evaporation process of adsorbed water is relatively slow, and the temperature reduction mostly relies on heat dissipation to the air, which takes a long time to complete. Stage three as a whole can be regarded as a process in which the electric heating effect gradually weakens and the wood approaches an environmental equilibrium state.

[0090] According to dielectric theory, the conductivity of high-loss dielectrics usually shows an exponential growth trend with the increase of temperature and moisture content. In addition, the presence of highly polar water molecules effectively weakens the binding force between ions and wood attachment points, making the logarithm of conductivity and moisture content show an approximate linear function relationship. At the same time, temperature and moisture content are correlated. The wood blocks with higher moisture content have more active ions in them, and the conductivity changes significantly after the temperature rises.

[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 time 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 box, and the drying temperature is set to 102°C. After running for 8 hours, the wood block is weighed and put back into the drying box, and 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 stage and calculate the moisture content, and save the experimental data until the set number of experiments is reached.

[0094] Through a lot of different Figure 5The Joule heating experimental data of the classic moisture content shown in the figure are integrated together, and the independence and correlation of the expressions of temperature and conductivity and moisture content and conductivity are considered. The tree conductivity model taking into account moisture content and temperature is obtained by fitting the data using the least squares method. Figure 6 As shown, the expression corresponding to step five is obtained.

[0095] Step 5: construct a tree conductivity model, 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 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, which are obtained by least squares fitting using the experimental data.

[0098] In one embodiment of the present invention, the experimental data of all groups are fitted, and the values ​​of A, B, C, and D are 7.4580, 0.0569, -0.0495, and -10.7541, respectively. That is, 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 invention, a set of experimental sample data is used alone to fit the tree conductivity model, and the experimental data fitting of all groups is completed, wherein the formula parameters fluctuate within a certain range. Specifically, the obtained floating range of parameter A is between 7 and 8, the floating range of parameter B is between -0.7 and 0.05, the floating range of parameter C is between -0.06 and -0.03, and the floating range of parameter D is between -11 and -8. In general, 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.

[0102] Step six, use the fitted tree conductivity model to calculate the resistance of trees around the distribution overhead line corridor in real time, and issue an early warning of overhead line-tree contact faults based on the real-time calculation results.

[0103] Embodiment 2

[0104] This embodiment is a conductivity calculation system for a single-phase tree-to-ground fault, and the system is used to implement the calculation method as described in the first embodiment, including:

[0105] Power supply module, used to provide stable power to the system;

[0106] Experimental circuit module, used to construct the experimental sample power circuit and electrical parameter measurement interface;

[0107] 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 of the set voltage acquisition point to the ground;

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

[0109] 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 the parameters collected in real time, and to issue early warnings for line-tree contact faults.

[0110] 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 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 comprising a power supply module, an experimental circuit module and a parameter acquisition module, the experimental circuit module providing an electrical parameter acquisition interface to calculate the conductivity of the experimental sample, the parameter acquisition module acquiring the temperature, weight and conductivity of the experimental sample during the experimental stage; 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 time 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 stage and calculate the moisture content, and save the experimental data until the set number of experiments is reached; A tree conductivity model is constructed, and the tree conductivity model is expressed as follows: lnσ t (W,T)=AW+BY+CW·T+D 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, which are obtained by least squares 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 an 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-dividing resistor and a power supply voltage measuring resistor arranged in series, and a first voltage collection point is drawn between the voltage-dividing resistor and the 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 point 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: In the formula, 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; The resistance R of the experimental sample t The statement is as follows: Wherein, R1 is the resistance of the voltage divider resistor, R2 is the resistance of the power supply voltage measuring resistor, R3 is the resistance 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.

4. The method for calculating conductivity in a single-phase tree-to-ground fault according to claim 3 is 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 sampling frequency to ground of the first voltage collection point is 10 kHz, and the voltage sampling frequency to ground 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 a different time, 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 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.

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 wood block was placed in a drying box and the drying temperature was set to 102°C. After running for 8 hours, the wood block was weighed and put back into the drying box. It was then weighed every 8 hours until the difference between the last two weighings did not exceed 0.2%. The wood block was considered to have reached absolute dryness at this time, and the last weighing weight was 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 was the moisture content of the experimental sample.

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 construct 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 of the set voltage acquisition point to the ground; The model building module is used to calculate the conductivity of the experimental sample according to the parameters of the experimental circuit module, and to calculate the moisture content of the experimental sample at the corresponding moment through the experimental stage weight and the absolute dry mass; and to fit the tree conductivity model based on the experimental data by the least square 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 the parameters collected in real time, and to issue early warnings for line-tree contact faults.

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