Research On The Key Technology Of Application Of Space-time Lightning Monitoring And Protection In EHV Power Grid

The EHV transmission lines with a large transmission capacity and wide distributions often play as a branch line of local electrical network, so their safety and reliability are especially important to realize the electric power development strategy of"West-to-East Power Transmission, North-to-South Power Exchange and Nationwide Interconnection". The research indicated that, at present, the lightning stroke is still the primary factor that threatens the transmission line's normal operation, especially for the EHV transmission lines. The trip-out rate caused by lightning stroke has been at the top of each kind of trip-out rate during a normal year. Although the domestic and foreign scholars have conducted a lot of researches on the lightning protection of EHV transmission lines, the lightning accidents still stay at a high level.In this paper, aiming at the present problem of serious lightning accidents and using various equipments of lightning monitoring system, Doppler weather radar and on-line monitoring system of power system overvoltage, the key problem of lightning protection in the construction and operation process of EHV transmission lines has been investigated applying some mathematical method such as optimization and artificial neutral network, on the basis of the analysis of parameters and discipline of lightning activities, combining the regulation methods in lightning performance calculation of back-flashover and shielding failure, and a more full time-space monitoring and protection system has been set up, which has taken lightning protection estimation, design, early-warning operation and recognition after stroke into consideration.In the aspect for the parameter statistics of lightning activities, taking Chongqing as an example, using data of Lighting Location System, which based on classic grid statistical methods, analyzing the main parameter statistics of lightning activity which closely related to the power transmission lines such as lightning day, ground flash density, cumulative probability distribution of lightning current amplitude. In the aspect for the research of lightning law, using coefficient of variation and Allan factor to investigate the relevance of ground flash occurrence .The differences of parameter region of lightning activity are more significant in Chongqing, ground flash appears more significant feature of relevance.Lightning parameter after gridding has improved correlation calculation method of lightning withstand performance estimation of the transmission lines in traditional regulations, which make it more adapted to the estimation demand adopting realistic lightning location data. An estimation model about lightning withstand performance of EHV transmission line has been established using lightning location data, which is demonstrated here that the calculation method in both this model and regulations keep a high degree of consistent.Applying Dijkstra optimization theory in optimization technique and graph theory, an optimal design algorithm of EHV transmission line corridor selection has been proposed. This algorithm has taken minimizing line's trip-out numbers into consideration, which is able to find the shortest path fast and accurately from origin to terminal point of transmission lines. For example, an EHV transmission line in Chongqing, has demonstrated the feasibility of this model in transmission line's optimal selection and the advantages of traditional artificial line's selection.Applying Doppler weather radar, the linear extrapolated method in SCIT algorithm to predict thunderclouds'motion has been improved using BP neutral network, on the basis of researches on various thundercloud's recognition, tracing and advantages and disadvantages of prediction algorithm, aiming at the thunderclouds'possible nonlinear motion, which makes it more adapted to nonlinear motion of thunderclouds, a lightning early-warning model of EHV transmission line has been established using lightning withstand performance estimation model of EHV transmission line for reference, and combining the statistical parameters of lightning activities, which obtains a better result in the simulation experiments of one EHV transmission line.On the basis of analysis and researches on different kind of lightning overvoltage, six overvoltage recognition characteristic quantities have been proposed using Hilbert-Huang Transform (HHT) as the signal analysis and calculation method, and present lightning overvoltage HHT-SVM recognition method to distinguish overvoltage using these characteristic quantities based on Support Vector Machine (SVM) method. This model can reach accuracy degree of 92.8% after amounts of instance data verification, and has a high value of application.Besides, due to the general applicability of space-time lightning monitoring system and models, it is convenient to apply such system and models into the running safeguard system in different power grids.