Method and apparatus for testing interline gap breakdown characteristics simulating a mountain-bridge condition

Abstract

This application relates to the field of breakdown voltage testing technology, specifically to a method and equipment for testing the breakdown characteristics of line gaps under simulated wildfire bridging conditions. The method includes: acquiring test parameters for each set of tests during a voltage boosting test; conducting a sag variation test on the conductor with stress and temperature, obtaining the sag through the conductor's physical characteristics and stress, determining the stress variation through temperature changes, and determining a fitting formula based on the sag variation; during the voltage boosting breakdown test, determining the sag variation through the fitting formula to obtain a corrected gap distance, and then obtaining the corrected bridging ratio and the true gap breakdown voltage gradient; collecting multiple sets of leakage current tests to obtain a correlation index; and correcting the leakage current by combining the difference between the gap distance and the corrected gap distance to obtain a corrected leakage current; and plotting a test curve using the corrected bridging ratio, corrected leakage current, and true gap breakdown voltage gradient to complete the test. This application improves the accuracy of gap breakdown characteristic analysis results.

Description

Technical Field

[0001] This application relates to the field of breakdown voltage testing technology, specifically to a test method and equipment for line gap breakdown characteristics under simulated wildfire bridging conditions. Background Technology

[0002] At present, the construction of power grids inevitably needs to pass through densely vegetated forest areas and mountainous areas. When wildfires occur under the transmission lines, the insulation strength of the line gaps will decrease significantly, which can easily cause the transmission lines to trip and stop. Therefore, it is necessary to conduct different types of gap breakdown tests on the lines under wildfire conditions, such as conductor-plate or rod-rod, to analyze the breakdown characteristics and provide data support and reliable opinions for the stable operation of the lines.

[0003] Existing experimental methods typically target a single variable, such as vegetation type, bridging height, or combustion intensity, and fit multiple sets of experimental results under certain proportions of the variable. The fitting results are then used to analyze the gap discharge characteristics and breakdown properties of the line. However, in current discharge tests, the gap distance is controlled according to a preset value. But during the voltage boost breakdown test, temperature changes alter the conductor stress through thermal expansion and contraction, and these stress changes directly affect the conductor sag. In other words, the gap distance is not fixed during the test. If a preset gap distance is directly used to analyze the gap discharge characteristics and breakdown properties, the analysis results will deviate from the gap breakdown characteristics under actual wildfire bridging conditions. Summary of the Invention

[0004] To address the technical problem of inaccurate gap breakdown characteristic analysis, this application provides a test method and equipment for line gap breakdown characteristics under simulated wildfire bridging conditions. The specific technical solution adopted is as follows: Firstly, this application proposes a test method for the breakdown characteristics of line gaps under simulated wildfire bridging conditions, the method comprising the following steps: In the pressure boosting test, the test parameters for each group of tests are obtained; For the conductor, a test is conducted to observe the change of sag with stress and temperature. An initial stress is preset and the initial sag is measured. After the temperature is increased, the temperature and stress are recorded. The physical characteristics and stress of the conductor are substituted into the parabolic approximation formula to obtain the sag. The stress change is determined by the thermal stress formula based on the temperature change before and after the temperature increase. The fitting relationship is determined by the stress change, temperature change and sag change after multiple temperature increases. In the voltage boosting breakdown test, the temperature change and stress change are substituted into the fitting relationship to calculate the sag change, and the difference between the sag change and the gap distance is used to obtain the corrected gap distance; the corrected gap distance is then compared with the difference between the flame height and the gap breakdown voltage to obtain the corrected bridging ratio and the true gap breakdown voltage gradient. In the boost breakdown test, leakage currents under different gap distances were collected, and the correlation index was obtained through a logarithmic function. The leakage current was then corrected by adjusting the correlation index based on the difference between the gap distance and the corrected gap distance to obtain the corrected leakage current. The test was completed by plotting the test curves after adjusting the bridging ratio, the leakage current, and the actual gap breakdown voltage gradient.

[0005] In the above scheme, this application obtains a fitting relationship between the gap distance between the conductor and the vegetation stack during the corrected voltage breakdown test by conducting a sag-temperature-tension fitting test on the conductor. Then, combining the real-time measured and recorded data from the voltage breakdown test, the gradient of the gap breakdown voltage is corrected, solving the problem of neglecting the influence of temperature rise on conductor sag in traditional gap breakdown characteristic analysis, thus improving the accuracy of the analysis results. Furthermore, this application obtains the continuous temporal distribution of the bridging ratio and the true gap breakdown voltage gradient through dynamic real-time correction, allowing for a more intuitive display of the gap breakdown characteristic analysis results. This application also fits the relationship between leakage current and gap distance based on Townshend theory, and corrects the collected original leakage current based on the fitting results and the corrected gap distance, further improving the accuracy of the gap breakdown characteristic analysis results.

[0006] In one embodiment, the test parameters include gap distance, breakdown voltage, leakage current, wire temperature, flame height, and breakdown time.

[0007] In one embodiment, the initial sag is the distance between the lowest point of the conductor after it sags and the original conductor.

[0008] In one embodiment, the method of substituting the physical characteristics and stress of the conductor into the parabola approximation formula to obtain the sag is as follows: , Represents gravitational acceleration. Indicates conductor density, Indicates the conductor span. Indicates conductor stress. It indicates a sag.

[0009] In one embodiment, the method for determining the fitting relationship by measuring the stress change, temperature change, and sag change after multiple temperature increases is as follows: , Indicates the amount of temperature change. Indicates the change in sag. Indicates the amount of stress change. , , Represents the fitting parameters; fitting parameters , , The units are respectively , , The change in sag is the difference between the sag calculated before and after the temperature increase.

[0010] In one embodiment, the corrected gap distance is the difference between the gap distance and the sag change at each moment.

[0011] In one embodiment, the corrected bridging ratio is the ratio of flame height to corrected gap distance; the true gap breakdown voltage gradient is the ratio of gap breakdown voltage to corrected gap distance.

[0012] In one embodiment, the method for collecting multiple sets of leakage currents at different gap distances and obtaining the correlation index using a logarithmic function is as follows: , Indicates the distance between the conductor and the grounding electrode. This represents a logarithmic function with the natural constant as its base. express Leakage current at any moment is a constant term, and n represents the correlation index.

[0013] In one embodiment, the method for obtaining the corrected leakage current by adjusting the leakage current through a correlation index based on the difference between the gap distance and the corrected gap distance is as follows: ,in, Indicates the gap distance. This represents the leakage current at time t. This represents the corrected gap distance at time t, where n represents the correlation index. This represents the corrected leakage current at time t.

[0014] On the other hand, a test device for simulating line gap breakdown characteristics under wildfire bridging conditions includes: The fixed suspension insulator is connected to the top beam via a circuit connection line, which is also connected to the conductor. The conductor is connected to the protective resistor, voltage divider, and power frequency test transformer. A vegetation stack is placed directly below the conductor, with a metal plate and refractory material placed under the vegetation stack. The vegetation stack and its components are placed on a lifting platform and connected to the non-inductive resistor and grounding resistor. The power frequency test transformer, signal acquisition system, and non-inductive resistor are connected via a data acquisition connection line. The leakage current and voltage are collected through the signal acquisition system, which consists of a computer and a signal acquisition card. In addition, relevant data are collected through a high-speed video recording device, displacement sensor, and high-definition infrared thermal imager.

[0015] The beneficial effects of this application are as follows: This application obtains a fitting formula for the gap distance between the conductor and the vegetation stack during the corrected voltage breakdown test by conducting a sag-temperature-tension fitting experiment on the conductor. Then, combining the real-time measurement and recording data from the voltage breakdown test, the gradient of the gap breakdown voltage is corrected, solving the problem of neglecting the influence of temperature rise on conductor sag in traditional gap breakdown characteristic analysis, thus improving the accuracy of the analysis results. Furthermore, this application obtains the continuous temporal distribution of the bridging ratio and the true gap breakdown voltage gradient through dynamic real-time correction, allowing for a more intuitive display of the gap breakdown characteristic analysis results. This application also fits the relationship between leakage current and gap distance based on Townshend theory, and corrects the collected original leakage current based on the fitting results and the corrected gap distance, further improving the accuracy of the gap breakdown characteristic analysis results. Attached Figure Description

[0016] To more clearly illustrate the technical solutions and advantages in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 A flowchart of a test method for simulating wildfire bridging conditions for line gap breakdown characteristics provided in one embodiment of this application; Figure 2 This is a flowchart of a test apparatus for simulating wildfire bridging conditions for line gap breakdown characteristics, provided in one embodiment of this application. Figure 3 This is a curve showing the change of gap breakdown voltage gradient with the modified bridging ratio under different vegetation stacks, gap distances, and modified gap distances, provided in one embodiment of this application. Figure 4 Leakage current and corrected leakage current as a function of number of tests were collected during the experiment on vegetation stacks made of shrubs; Figure 5 The leakage current and corrected leakage current curves as a function of number of tests were collected when testing vegetation stacks made of thatch.

[0018] Explanation of reference numerals in the attached figures: 101, Top beam; 102, Circuit connection wire; 103, Fixed suspension insulator; 104, Conductor; 105, High-speed video recording device; 106, Displacement sensor; 107, High-definition infrared thermal imager; 108, Non-inductive resistor; 109, Grounding resistor; 110, Vegetation stack; 111, Metal plate; 112, Refractory material; 113, Lifting platform; 114, Data acquisition connection; 115, Signal acquisition system; 116, Computer; 117, Signal acquisition card; 118, Voltage divider; 119, Power frequency test transformer; 120, Protective resistor. Detailed Implementation

[0019] The following, in conjunction with the accompanying drawings, details the specific scheme of the test method and equipment for simulating wildfire bridging conditions for line gap breakdown characteristics provided in this application.

[0020] Please see Figure 1 The document illustrates a flowchart of a test method for simulating wildfire bridging conditions to test line gap breakdown characteristics, provided in one embodiment of this application. The method includes the following steps: Step S001: In the pressure boosting test, obtain the test parameters for each group of tests.

[0021] The test platform for line gap breakdown characteristics simulating wildfire bridging conditions consists of a power frequency test transformer, protective resistor, voltage divider, conductor, insulator, ground electrode, signal acquisition system, and video recording equipment.

[0022] The equipment specifically includes: 101 represents the object of the fixed suspension insulator 103, which can be a top beam or a structural beam; 102 represents a circuit connection line; 104 represents a conductor; 105 represents a high-speed recording device; 106 represents a displacement sensor, such as a laser rangefinder or a high-precision level; 107 represents a high-definition infrared thermal imager; 108 represents a non-inductive resistor; 109 represents a grounding resistor; 110 represents a vegetation stack, artificially prepared in advance; 111 represents a metal plate; 112 represents refractory material; 113 represents a lifting platform; 114 represents a data acquisition connection; the signal acquisition system 115 acquires the leakage current and voltage during the test through the connection 114, and the signal acquisition system 115 consists of a computer 116 and a signal acquisition card 117; 118 represents a voltage divider; 119 represents a power frequency test transformer; 120 represents a protective resistor.

[0023] The specific experimental procedure is as follows: The voltage boosting test is conducted at a rate of 2-3 kV / s, and the output of the power frequency test transformer is controlled to adjust the conductor load. After each adjustment of the conductor load, the control platform adjusts the distance between the conductor and the vegetation stack to a preset value. There are multiple preset values; the preset value is the distance between the conductor and the vegetation stack.

[0024] Once any preset value is reached, use a spray bottle to evenly spray a fixed amount of alcohol onto the surface of the vegetation stack. Then, use a flame gun to continuously spray the center of the vegetation stack surface for 5-10 seconds to ignite the vegetation, thereby reducing the impact of vegetation heat release fluctuations on flame temperature, etc. When the alcohol flame disappears and the vegetation stack flame appears, the signal acquisition system and video recording equipment are activated to collect and record data. The leakage current is collected through a non-inductive resistor connected to the plate electrode, and the frequency of the signal acquisition system sampling leakage current and breakdown voltage is set to 1kHz. The laser displacement sensor measures the distance between the lowest point of the conductor and the vegetation stack in real time and records it as the gap distance. The high-definition infrared thermal imager collects the temperature of the conductor surface and the flame zone, and the average temperature of the area where the conductor is located in the infrared image is taken as the conductor temperature. The high-speed camera system records the flame height and the breakdown time. The gap distance, breakdown voltage, leakage current, conductor temperature, flame height, and breakdown time of each test are collectively referred to as the test parameters.

[0025] Multiple tests were conducted by adjusting the output of different power frequency test transformers and different vegetation stacks.

[0026] At this point, the experimental parameters for each group of experiments have been obtained.

[0027] Step S002: Conduct a sag test on the conductor as a function of stress and temperature. Obtain the sag by the physical characteristics of the conductor and the stress, determine the stress change by the temperature change, and determine the fitting relationship by combining the sag change.

[0028] Wildfire bridging refers to the phenomenon where flames or burning materials form a conductive path between high-voltage transmission lines during a wildfire, leading to electrical short circuits or tripping. In simulating wildfire bridging and analyzing gap breakdown characteristics, the ratio of the flame height at the moment of gap breakdown to the gap distance between the conductor and the vegetation stack is used as the bridging ratio, and the ratio of the gap breakdown voltage to the gap distance is used as the average breakdown voltage gradient. The line gap breakdown characteristics are analyzed using the bridging ratio and the average breakdown voltage gradient. For example, at different gap distances, the average breakdown voltage gradient decreases as the bridging ratio increases, mainly because the increased bridging ratio shortens the length of the non-flame zone.

[0029] During the voltage boosting test, temperature changes alter conductor stress through thermal expansion and contraction, directly affecting conductor sag. Furthermore, for different vegetation stacks, the temperature rise rate varies under the same test parameters, resulting in a non-fixed gap distance with temperature changes during the test. If only the preset height H reached by the lifting platform during the test is referenced, errors will occur in the bridging ratio and average breakdown voltage gradient, affecting the analysis of line gap breakdown characteristics. Therefore, this application considers first fitting a relationship between conductor sag and temperature and stress; using this relationship to correct the parameters in the voltage boosting breakdown test, and then performing breakdown characteristic analysis. The preset height is the height reached by the lifting platform.

[0030] First, data on the sag of the conductor under different temperatures and stress states are obtained, and the fitting relationship between sag and temperature and stress is obtained.

[0031] Specifically, two small insulating devices, such as insulating wire clamps, suspension insulators, or insulating clamps, are fixed as conductor supports. The initial value of the span is set to be consistent with the span of the conductor in the breakdown test mentioned above. The conductor span range is usually 1-10 meters. In this embodiment, the conductor span is 5m.

[0032] Furthermore, a displacement sensor is used to measure the height of the lowest point of the conductor from the horizontal ground; a high-definition infrared thermal imager is used to measure the conductor temperature non-contactly; and a stress testing instrument is used to test the conductor stress in real time.

[0033] At any ambient temperature, an initial stress L0 is applied to the conductor using a weight of known weight, and the initial sag h0 is measured. After the weight is added, the conductor will sag, and the gap distance will change from a preset value. The distance between the lowest point of the sag and the original conductor is taken as the initial sag.

[0034] The temperature is increased to the temperature at which the vegetation stack is fully burned in a fixed step size. After each temperature increase, the temperature is maintained for 2-5 minutes. After stabilization, the ambient temperature and conductor stress are recorded simultaneously. In this embodiment, the temperature increase step size is 10 degrees, and the stabilization time is set to 2 minutes.

[0035] Based on the above steps, different initial stresses were set, and different ambient temperatures and conductor stresses were measured.

[0036] Based on the parabolic approximation formula, the physical characteristics of the conductor and its thermal stress determine the sag, and its expression is: , Represents gravitational acceleration. Indicates conductor density, Indicates the conductor span. Indicates conductor stress. Indicates sag. Among them, This indicates the conductor load ratio.

[0037] The stress change caused by temperature change is obtained by using the basic formula for thermal stress. Therefore, the amount of temperature change is substituted into the basic formula for thermal stress to obtain the amount of stress change. In this embodiment, the amount of temperature change is 10 degrees.

[0038] Since temperature changes cause stress changes, which in turn cause sag changes, a polynomial regression fitting method is used to obtain the fitting formula for sag with temperature and stress: , Indicates the amount of temperature change. Indicates the change in sag. Indicates the amount of stress change. , , Represents the fitting parameters; fitting parameters , , The units are respectively , , Substitute the stress change from the above steps and the sag change after each temperature increase into the fitting equation to obtain the fitting parameters. The sag change is the difference between the sag calculated before and after the temperature increase.

[0039] For any vegetation stack, the temperature-stress-sag fitting data of each vegetation stack under a single line load (i.e., the output voltage of a fixed power frequency test transformer) are measured to obtain the fitting relationship.

[0040] Furthermore, following the above process, the output voltage of the power frequency test transformer is adjusted to achieve sag measurement under multiple loads and obtain the corresponding fitting relationship. In other embodiments, interpolation algorithms can also be used to interpolate between adjacent loads to further improve the coverage of various load values. For example, after adjusting the output voltage of the power frequency test transformer, the loads on the conductors may not be adjacent, such as 2, 5, and 7. In this case, an interpolation algorithm can be used to obtain fitting data for each load with a step size of 0.5, such as 3, 3.5, and 4, to achieve higher accuracy measurement.

[0041] Thus, the fitting formula for temperature-stress-sag was obtained.

[0042] In step S003, during the boost breakdown test, the sag change is determined by fitting the relationship to obtain the corrected gap distance, and then the corrected bridging ratio and the true gap breakdown voltage gradient are obtained.

[0043] Based on the distance between the conductor and the vegetation stack during the voltage breakdown test, and the actual sag of the conductor when the vegetation stack is burning and heating up, the true gap distance is obtained and recorded as the corrected gap distance. The breakdown judgment criteria are calculated using the corrected gap distance JH, eliminating the error caused by the fixed preset height H.

[0044] Specifically, at each preset height, the flame height fh recorded by the high-speed video recording device at different times is acquired, and the corrected bridging ratio is determined by combining this with the real-time corrected gap distance. The conductor sag increases in real-time with temperature, causing the actual gap distance to shorten; that is, the actual gap distance is less than the static gap distance before the vegetation stack ignition operation during the voltage boost breakdown test.

[0045] At this point, the gap distance between the lowest point of the conductor and the vegetation stack is obtained using a laser displacement sensor. Based on the temperature and stress changes at each moment, the sag change is calculated by substituting them into the fitting formula. The difference between the two is used as the correction gap distance. The specific expression is as follows: , Indicates the gap distance. This represents the change in sag at time t. This represents the corrected gap distance at time t.

[0046] The ratio of the flame height at time t to the corrected gap distance at that time is used as the corrected bridging ratio.

[0047] Furthermore, at each time step, the ratio of the gap breakdown voltage to the corrected gap distance is taken as the true gap breakdown voltage gradient at each time step, in kV / m.

[0048] For each vegetation stack, in the voltage breakdown test, by adjusting the position of the lifting platform, the distribution of the corrected bridging ratio over time is obtained under different gap distances H0, and then the true gap breakdown voltage gradient under different bridging ratios is obtained.

[0049] In this embodiment, the conductor span is 10m, the conductor specific load is 0.034N / (m·mm²), the conductor elastic modulus is 70GPa, and the conductor thermal expansion coefficient is... With a conductor-to-board gap distance of 1m, and shrubs and thatch prepared into 0.2m × 0.2m × 0.2m square vegetation stacks, and a conductor-to-plate gap distance of 0.8m, the actual gap breakdown voltage gradient under different bridging ratios is as follows: Figure 3 As shown.

[0050] Figure 3The comparison results of the actual gap breakdown voltage gradient and the gap breakdown voltage gradient calculated at a fixed gap distance under different bridging ratios are shown. The vertical axis represents the gap breakdown voltage gradient in kV / m, and the horizontal axis represents the bridging ratio as a percentage. y1 and y10 represent the distribution results of the gap breakdown voltage gradient of shrub-made vegetation stacks at the corrected gap distance JH and the fixed gap distance H, respectively; y2 and y20 represent the distribution results of the gap breakdown voltage gradient of thatch-made vegetation stacks at the corrected gap distance JH and the fixed gap distance H, respectively. Within the bridging ratio range of 55%-100%, during repeated burning of the vegetation stacks, the actual gap breakdown voltage gradient is generally greater than or equal to the gap breakdown voltage gradient at the specified gap distance.

[0051] At this point, the true gap breakdown voltage gradient was obtained.

[0052] Step S004: Collect multiple sets of leakage current tests to obtain the correlation index; and combine the difference between the gap distance and the corrected gap distance to correct the leakage current and obtain the corrected leakage current.

[0053] For leakage current measured during the voltage breakdown test, the leakage current directly reflects the degree of ionization and surface contamination within the gap. When the sag decreases, causing a change in the gap distance, the electric field multiplies under the same conductor load, and the amplitude and harmonic components of the leakage current in the conductor exhibit a nonlinear increase. At lower electric field strengths, the change in leakage current is mainly determined by the degree of surface contamination and is less sensitive to the gap distance; however, in the critical region where the electric field strength approaches the breakdown value, changes in the gap distance cause significant fluctuations in the leakage current.

[0054] Since the distance between the conductor and the plate electrode is much smaller than the length of the conductor, and the edge effect is negligible, the electric field on the surface of the conductor can be considered as a uniform electric field, and the electric field strength Q is equal to the potential difference between the conductor and the ground electrode (plate electrode). The ratio of the distance d1 between the conductor and the grounding electrode.

[0055] Half of the electric field strength calculated from the potential difference corresponding to the gap breakdown voltage is used as the threshold. If the electric field strength is greater than the threshold, it is considered that the field strength is in the critical region close to the breakdown value, and the leakage current is corrected according to the subsequent process. If the electric field strength is less than or equal to the threshold, no leakage current correction is performed.

[0056] The specific steps for correcting leakage current are as follows: Based on Townshend's theory, during the complete combustion of vegetation stacks, leakage currents are generated by localized ionization of the gas due to collisional ionization and electron avalanche effects within the gas. The leakage current typically increases exponentially with the electric field strength Q. The relationship between the electric field strength Q and the field strength Q is satisfied ,Will Substituting, we get .

[0057] The distance d1 between the conductor and the grounding electrode is determined by the gap distance. The distance d2 between the vegetation stack and the grounding electrode is composed of, i.e. Substitute In this process, leakage current can be obtained. The relationship between the gap distance and the formula: Since the dimensions of the vegetation stacks were artificially set before the experiment, the potential difference... Under the premise that d2 remains unchanged, the correlation index n can be solved by the data collected from the boost breakdown test.

[0058] Specifically, under the condition that the potential difference remains constant during the step-up breakdown test (i.e., the output of the power frequency test transformer is fixed), N sets of different preset gap distances H0 are collected. Leakage current at any time The logarithmic function is used for linear fitting to solve for n. N is greater than or equal to 10; in this embodiment, N is taken as 15. The solution formula is: , Indicates the distance between the conductor and the grounding electrode. This represents a logarithmic function with the natural constant as its base. express Leakage current at any moment is a constant term, and n represents the correlation index.

[0059] Furthermore, the real-time corrected gap distance will be... Substituting into the linear relationship, the leakage current is corrected to obtain the corrected leakage current, whose expression is: ,in, Indicates the gap distance. This represents the leakage current at time t. This represents the corrected gap distance at time t, where n represents the correlation index. This represents the corrected leakage current at time t.

[0060] The leakage current and corrected leakage current for different vegetation types in each experiment were plotted as follows: Figure 4 and Figure 5 , Figure 4 Curve 1 and Curve 2 in the figure represent the leakage current and corrected leakage current collected during the experiment using vegetation stacks made of shrubs, respectively. Figure 5 Curve 1 and Curve 2 in the figure represent the leakage current and corrected leakage current collected during the test of thatched vegetation stacks, respectively.

[0061] It should be noted that the horizontal axis represents the sequential value of the collected current, and the time interval between adjacent sequential values ​​is the sampling interval. Since no leakage current is generated in the initial stage of vegetation burning, correction is only necessary when the leakage current is not zero. Due to the burning properties of shrubs, correction is performed after 5-6 minutes of burning; thatch is more flammable than shrubs, so correction is performed after about 1 minute of burning. Figure 4 The time corresponding to 0 on the horizontal axis is not the initial time of the boost breakdown test. Similarly, Figure 5 The time corresponding to 0 on the horizontal axis is not the initial time of the boost breakdown test. In this embodiment, Figure 4 The horizontal axis value of 0 corresponds to the moment when the shrub vegetation stack has been burning for 6 minutes. Figure 5 The horizontal axis 0 corresponds to the moment when the thatched vegetation stack has been burning for 50 seconds. Due to the dynamic changes in the gap distance during combustion, as the temperature rises, the corrected gap distance JH is always less than the initial gap distance H. Therefore, the horizontal axis of the peak and valley values ​​of the leakage current after correction will shift to the left.

[0062] At this point, the corrected leakage current at each moment has been obtained.

[0063] Step S005: Plot the test curve by correcting the bridging ratio, the leakage current, and the actual gap breakdown voltage gradient to complete the test.

[0064] Based on the corrected leakage current and the actual gap breakdown voltage gradient, the first derivative of the leakage current and the gap breakdown voltage gradient at the breakdown time determined by the high-definition recording device is calculated and used as a warning threshold to evaluate the breakdown characteristics during the test. The first derivative at each moment in the test is compared with the warning threshold. If there is one that is greater than or equal to the warning threshold, the conductor has reached its limit.

[0065] The inflection point (maximum of the second derivative of the curve) in the bridging ratio versus time distribution curve is taken as the actual moment when the flame channel is completed. The horizontal axis of the bridging ratio versus time distribution curve represents time, and the vertical axis represents the corrected bridging ratio.

[0066] This completes the breakdown characteristic test.

[0067] Please see Figure 2 The diagram illustrates a flow chart of a test apparatus for simulating wildfire bridging conditions under test conditions, according to an embodiment of this application. The apparatus includes: The fixed suspension insulator 103 is connected to the top beam 101 via a circuit connection line 102. The circuit connection line is also connected to a conductor 104, which is connected to a protective resistor 120, a voltage divider 118, and a power frequency test transformer 119. A vegetation stack 110 is placed directly below the conductor, with a metal plate 111 and refractory material 112 pressing down on it. The vegetation stack and its components are placed on a lifting platform 113 and connected to a non-inductive resistor 108 and a grounding resistor 109. The power frequency test transformer 119, a signal acquisition system 115, and a non-inductive resistor 108 are connected via a data acquisition connection line 114. The leakage current and voltage are acquired through the signal acquisition system 115, which consists of a computer 116 and a signal acquisition card 117. In addition, relevant data are acquired through a high-speed video recording device 105, a displacement sensor 106, and a high-definition infrared thermal imager 107.

[0068] The various embodiments in this specification are described in a progressive manner. The same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on describing the differences from other embodiments.

Claims

1. A test method for line gap breakdown characteristics under simulated wildfire bridging conditions, characterized in that, The method includes the following steps: In the pressure boosting test, the test parameters for each group of tests are obtained; For the conductor, a test is conducted to observe the change of sag with stress and temperature. An initial stress is preset and the initial sag is measured. After the temperature is increased, the temperature and stress are recorded. The physical characteristics and stress of the conductor are substituted into the parabolic approximation formula to obtain the sag. The stress change is determined by the thermal stress formula based on the temperature change before and after the temperature increase. The fitting relationship is determined by the stress change, temperature change and sag change after multiple temperature increases. In the voltage boosting breakdown test, the temperature change and stress change are substituted into the fitting relationship to calculate the sag change, and the difference between the sag change and the gap distance is used to obtain the corrected gap distance; the corrected gap distance is then compared with the difference between the flame height and the gap breakdown voltage to obtain the corrected bridging ratio and the true gap breakdown voltage gradient. In the boost breakdown test, leakage currents under different gap distances were collected, and the correlation index was obtained through a logarithmic function. The leakage current was then corrected by adjusting the correlation index based on the difference between the gap distance and the corrected gap distance to obtain the corrected leakage current. The test was completed by plotting the test curves after adjusting the bridging ratio, the leakage current, and the actual gap breakdown voltage gradient.

2. The test method for line gap breakdown characteristics under simulated wildfire bridging conditions as described in claim 1, characterized in that, The test parameters include gap distance, breakdown voltage, leakage current, conductor temperature, flame height, and breakdown time.

3. The test method for line gap breakdown characteristics under simulated wildfire bridging conditions as described in claim 1, characterized in that, The initial sag is the distance between the lowest point of the conductor after it sags and the original conductor.

4. The test method for line gap breakdown characteristics under simulated wildfire bridging conditions as described in claim 1, characterized in that, The method for obtaining sag by substituting the physical characteristics and stress of the conductor into the parabola approximation formula is as follows: , Represents gravitational acceleration. Indicates conductor density, Indicates the conductor span. Indicates conductor stress. It indicates a sag.

5. The test method for line gap breakdown characteristics under simulated wildfire bridging conditions as described in claim 1, characterized in that, The method for determining the fitting relationship by measuring the stress change, temperature change, and sag change after multiple temperature increases is as follows: , Indicates the amount of temperature change. Indicates the change in sag. Indicates the amount of stress change. , , Represents the fitting parameters; fitting parameters , , The units are respectively , , The change in sag is the difference between the sag calculated before and after the temperature increase.

6. The test method for line gap breakdown characteristics under simulated wildfire bridging conditions as described in claim 1, characterized in that, The corrected gap distance is the difference between the gap distance and the change in sag at each moment.

7. The test method for line gap breakdown characteristics under simulated wildfire bridging conditions as described in claim 1, characterized in that, The corrected bridging ratio is the ratio of flame height to corrected gap distance; The true gap breakdown voltage gradient is the ratio of the gap breakdown voltage to the corrected gap distance.

8. The test method for line gap breakdown characteristics under simulated wildfire bridging conditions as described in claim 1, characterized in that, The method for collecting multiple sets of leakage currents at different gap distances and obtaining the correlation index using a logarithmic function is as follows: , Indicates the distance between the conductor and the grounding electrode. This represents a logarithmic function with the natural constant as its base. express Leakage current at any moment is a constant term, and n represents the correlation index.

9. The test method for line gap breakdown characteristics under simulated wildfire bridging conditions as described in claim 1, characterized in that, The method for obtaining the corrected leakage current by adjusting the difference between the gap distance and the corrected gap distance using a correlation index is as follows: ,in, Indicates the gap distance. This represents the leakage current at time t. This represents the corrected gap distance at time t, where n represents the correlation index. This represents the corrected leakage current at time t.

10. A test apparatus for simulating line gap breakdown characteristics under wildfire bridging conditions, characterized in that, include: The fixed suspension insulator (103) is connected to the top beam (101) via a circuit connection line (102). The circuit connection line is also connected to a conductor (104), which is connected to a protective resistor (120), a voltage divider (118), and a power frequency test transformer (119). A vegetation stack (110) is placed directly below the conductor, with a metal plate (111) and refractory material (112) placed under the vegetation stack. The vegetation stack and its components are placed on a lifting platform (113) and connected to a non-inductive resistor (108) and The grounding resistor (109) is connected; the power frequency test transformer (119), the signal acquisition system (115) and the non-inductive resistor (108) are connected through the data acquisition line (114). The leakage current and voltage are acquired through the signal acquisition system (115). The signal acquisition system consists of a computer (116) and a signal acquisition card (117). In addition, relevant data are acquired through a high-speed video recording device (105), a displacement sensor (106), and a high-definition infrared thermal imager (107).

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