Synergistic Method for Machine-Learning-Based Diagnosis and Gradient-Based Optimization of Lightning Damage Mechanisms

Summary form only given. Lightning induce voltages have been seriously reconsidered by power utilities and researchers due to the increasing demand of good quality by customers in power supply. The contribution reviews the standard procedures to evaluate the flashover rate vs basic insulation level (BIL) curves (IEEE 1410 Guide-Distribution Lightning Performance) and describes another methodology used to estimate such curves by means of a statistical program based on the Monte Carlo method for the evaluation of the lightning performances of distribution lines. The program provides the number of lightning events that exceed, for a certain ground flash density, a given value which, in turn, allows estimation of the frequency distribution of lightning-induced voltages for a given line, as well as the flashover rate vs. BIL curves. The computation of the induced voltages is performed using the LIOV code (lightning induced over-voltage), developed within the framework of an international research collaboration involving the University of Bologna Department of Electrical Engineering, the Swiss Federal Institute of Technology (Power Systems Laboratory) and the University of Rome La Sapienza (Department of Electrical Engineering). The influence of the main parameters of interest is examined (ground resistivity, lightning current peak amplitude and rise time, return-stroke velocity) along with the influence of the various critical distance expressions used in the analysis.

Ground flash density is the basic parameter of various lightning protection projects. Obtaining a more accurate ground flash density can improve the precision of differential lightning protection for transmission lines. In this paper, the software Google Earth was used to select a grid area in the mountainous area of Guangdong Province, China. The software ArcGIS was used to make a statistical analysis of 10 years lightning localization system data in this selected area to obtain the 10 years average ground flash density distribution map of this area. The results show that there is a significant difference in ground flash density of mountainous areas. When calculating the lightning shielding failure trip-out rate of transmission lines, ignoring this difference will cause great errors. In order to further study this difference, this paper puts forward the concept of mesoscopic terrain and gives the definition of mesoscopic terrain.

As overhead distribution lines and their associated equipments are most prone to insulation failure due to lightning and very much affected in terms of reliability, a study was intended to determine the line lightning performance and to analyze available mitigation options focusing on medium voltage overhead distribution line. This paper describes the simulation studies in determining the lightning performance of the chosen line using commercially available software. A Monte Carlo statistical method is applied for the simulation of lightning activity, while a three-dimensional Electro-geometric model is adopted for the determination of stroke termination. Shielding from the nearby objects is also taken into account. Linear and non-linear tower footing resistance representation, counterpoises, leader propagation flashover model are among standard features used in the simulations. Simulations are carried out to study the effects of critical flashover voltage, tower footing resistance and ground flash density on the line lightning performance. In addition, several mitigation steps to improve the lightning performance are also recommended.

By use of ATP-EMTP software, built the simulation of 220kV double-circuit transmission line. Then discussed the factors that affect the lightning performance of each tower, such as the height of tower, grounding resistance, insulation configurations, grounding wires and so on. The simulation results show that the tower height has a great impact on the lightning performance of double-circuit, so we should minimize tower height considering the actual condition; reduce the ground resistance can improve the lightning impulse withstand level effectively, especially in the low resistance. For tension tower, using an unbalanced insulation is the most effective way to reducing double tripping. For straight-line tower, increasing the piece of glass insulator is also an effective way to reducing double tripping rate. If the conditions allow, a coupling grounding wire can reduce the double-line trip obviously by use of its shunt and coupling function.

Various approaches for generating woodgrain patterns using computer graphics have been proposed so far. However, the generation of various woodgrain patterns with conventional methods is difficult due to the need for the adjustment of numerous parameters to express a real woodgrain pattern. In this paper, a new mathematical approach for generating woodgrain patterns is proposed. Virtual trees are generated by simulating tree growing based on past actual weather information obtained from public organizations, and woodgrain patterns are then acquired by cutting the trunks of the virtual trees. In order to simulate tree growing, growth models of tree are constructed in consideration of dendrological characteristics and environmental conditions. Growth of tree is influenced by various environmental factors, such as sunlight, temperature, carbon dioxide concentration, wind, precipitation, soil nutrient, inclination of ground, survival amongst surrounding trees, etc. With this system, the growth model of trees is constructed based on precipitation, temperature, sunlight, and inclination of ground, which especially have strong effects on tree growth. With this approach, various types of virtual trees can be obtained by changing growth conditions such as period and location of growth without the need to reset complicated parameters of tree species, and then the virtual trees can be cut at arbitrary areas, thus allowing a variety of woodgrain patterns to be easily generated by one parameter setup.

Lightning has been a major concern to the power system researchers as it may cause damage to the transmission line. One of the event that will cause lightning overvoltage and most likely to occur is backflashover. A study has been carried out to investigate the effects of line parameters such as ground resistance, soil resistivity, tower surge impedance, tower height and number of shield wires to the values of tower top voltage, backflashover rate (BFR) and probability of transformer damage at substation. A sample of worst performance of transmission line in Peninsular Malaysia i.e. 132 kV Kuala Krai-Gua Musang transmission line data was obtained from Tenaga Nasional Berhad (TNB) for the purpose of backflashover analysis. Power System Computer Aided Design (PSCAD) software was used to model integral part of transmission line components such as insulator gap, tower and footing resistance followed by doing the backflashover simulation and analysis. Findings from the analysis imply that the values of BFR and probability of transformer damage are strongly influenced by the values of line parameters. Right selection of line parameters may reduce BFR and probability of transformer damage, thus improve the transmission line performance. Findings of this research can be useful guideline towards high voltage transmission line design and planning in Malaysia.

The three-circuit flexible DC transmission line in the same tower has great advantages in saving transmission corridors, but its lightning protection design is obviously different from single-circuit or double-return overhead lines. Especially in the case of forming a DC grid, the striking flashover rate should be strictly controlled. For this reason, the lightning withstand performance of ±500kV three-circuit flexible DC transmission lines arranged on the same tower is analyzed by using electrical geometric model and traveling wave method. With such method and model the effect of polar line arrangement, grounding resistance, tower height on the lightning protection are analyzed. The computational results prove that when the lightning protection angle of overhead ground wire is designed to be -14° and the recommended E layout scheme is adopted for the pole conductor, the striking flashover rate can be controlled to be less than 0.1 times/(100km·a). The research results lay the foundation for the lightning protection design of the ±500kV three-circuit flexible DC lines arranged on the same tower.

Composite cross-arms have a broad application in the transmission line project, however, research on the lightning performance of composite cross-arm towers in ultra-high voltage (UHV) transmission lines is rare in the literatures. This paper constructs a model of composite cross-arm using EMTP software. Considering the characteristics of composite cross-arm tower, Lightning back-strike performance in 500kV double-circuit transmission lines under different grounding resistance, tower height and voltage phase angle is investigated. The result shows that the model is valid, which provides a basis for the application of composite cross-arm towers in UHV line design.

Adopting plusmn500 kV HVDC double circuit transmission lines to transmit power can both economize line corridor and add unit corridor aera transmission capacity, so plusmn500 kV HVDC double circuit transmission lines are more and more adopted. Because the length of double circuit transmission lines is high, it is more likely to be attacked by lightning stroke, so lightning performance for double circuit transmission lines is studied in this paper. Applying ATP can calculate backflashover withstand level when the datas like tower height, polarity configuration modes, soil resistivity and grounding resistance are changed. In the calculation, the insulators' behavior is judged by comparing the insulators' volt-time curves to the overvoltage, the system voltage and the induced voltage's influence on lightning withstanding level is considered.

In order to improve the utilization efficiency of the existing transmission corridor, it is necessary to erect two circuits on the same tower. Transmission lines are widespread and easy to be stroke by lightning. Therefore, great attention has been paid to the research of lightning protection for the transmission lines. When two ±800kV transmission line are erected on the same tower, the height of the tower is further increased, and they may be more easily stroke by the lighting. To look for better lightning protection measures, we carried out the research on the influence factors of lightning performance of ±800kV UHVDC double-circuit transmission lines. The conductor type and the spacing between upper and lower line have little influence on the lightning performance, and the influences can be ignored; shielding angle, tower height and ground resistance are the main factors affecting the lightning performance. The research results can provide reference for lightning protection of ± 800kV double-circuit UHVDC line erected on the same tower.

Tower grounding of transmission line is one of the most important measure to maintain the normal operation of power system and to guarantee the security of personnel. There is no need to lay artificial grounding when the natural grounding follows the regulators. In some northwest district of China whose number of thunder is few, ground flash density and lightning trip-out rate is low and therefore the counter trip-out rate is less, especially for high pressure transmission line. If the current standard is adopted in these areas, the term is too harsh to implement with economic benefit. So, it is significant to propose a new grounding standard to be applied in northwest district of China. In this paper, we modeled the tower and its grounding body of transmission line by the electromagnetic method. Then we calculated the counter trip-out rate under the condition of natural grounding and proposed the standard of natural grounding for 750kV transmission line in less thunder region.

Objective To study the practicality and repeatability of B-mode ultrasonography on diagnosis and score of carotid atherosclerosis. Methods Ninety-nine B-mode ultrasonography pictures of carotid atherosclerosis were obtained from field investigation. According to the established standard（normal scored as 0, other scored as 1 - 7 by the severity）, the 99 pictures were diagnosed and scored once together by three trained inexperienced members of the research team. Ten days later, these pictures were diagnosed and scored respectively, by the three members.The diagnostic results were analyzed with statistical methods to test the feasibility and repeatability of this set of diagnostic and scoring system. Results The joint diagnostic results by the three group members were regard as standard with scores 0 in 27 cases, 1 in 27 cases, 2 in 10 cases, 3 in 4 cases, 4 in 13 cases, 5 in 8 cases, 6 in 6 cases, and 7 in 4 cases. Independent diagnostic results by member A was 0 in 29 cases, 1 in 24 cases, 2 in 11 cases, 3 in 2 cases, 4 in 12 cases, 5 in 11 cases, 6 in 6 cases, and 7 in 4 cases. Independent diagnostic results by member B was 0 in 29 cases, 1 in 22 cases, 2 in 14 cases, 3 in 4 cases, 4 in 13 cases, 5 in 5 cases, 6 in 8 cases, and 7 in 4 cases. Independent diagnostic results by member C was 0 in 28 cases, 1 in 25 cases, 2 in 8 cases, 3 in 5 cases, 4 in 14 cases, 5 in 10 cases, 6 in 4 cases, and 7 in 5 cases. Comparison of the 4 diagnostic scores, the difference was not statistically significant（F = 0.019, P 〉 0.05）. Joint diagnostic results of the three members were compared with the standard and correlation coefficient were 0.977,0.987,0.932, respectively（all P 〈 0.01 ）. The correlation coefficient of diagnostic results of each member were 0.969,0.935,0.928, respectively （all P 〈0.01 ）. Diagnostic results of each member were consistent with the standard and the compliance rate were 88.9% （88/99） ,90.9%（90/99） and 86.9%（86/99）, respectively. Conclusions B-mode ultrasonography is a non-injure method for diagnosis of carotid atherosclerosis in epidemiology investigation. The method is easy to grasp and has a good repeatability. Key words: Athemsclerosis; Uhrasonography, Doppler, color; Feasibility studies

In order to improve the lightning withstand level of transmission lines, to reduce line lightning trip-out rate and the accident rate, to improve power supply reliability, grounding resistance in grounding grid of transmission line tower should be effectively ameliorated. As to the transmission line tower grounding grid in the plateau mountainous with thin soil, dry soil and complex geological conditions, the grounding electrode landfill layer is shallow and grounding resistance is significantly higher. Improvement of grounding grid and application of special resistance reducing material can reduce the the grounding resistance effectively. This technology has been applied to an actual construction reformation of transmission line tower grounding grid. The comparison of the test results verifies that grounding resistance can be effectively reduced by using a combination of above methods in complex geological environment.

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Optimal route selection of a transmission line is significantly beneficial to reduce its lightning trip-out rate. This paper proposes a method, considering the minimal annual flash number to transmission lines, to select the optimal route from the initial point to the destination based on the lightning location system. First, the ground flash density and distribution of lightning peak current maps are drawn via the improved grid method. The flash grid and flash node are proposed based on these maps. The objective function is expressed as the summation of the grid distance of the flash node, and solved via the Dijkstra algorithm. The conditional minimum transit cost is also provided to find the optimal corridor. Five 500-kV transmission lines are used to validate the effectiveness of the proposed method. The results indicate that the annual expected flash numbers of all lines are markedly reduced.