Research On Reliability Evaluation Models And Algorithms For High Voltage Directed Current Transmission System

With the development of High Voltage Directed Current (HVDC) transmission technologies, the increasing number of HVDC projects and the appearance of HVAC/HVDC hybrid transmission system, the reliability of HVDC system became a very important factor to the bulk power system's reliability. It's necessary to evaluate HVDC system's reliability and analyze the influence factors.The work of this thesis is supported by China Southern Power Gird company's project– YunNan - GangZhou Ultra High Voltage±800kV DC transmission system's reliability indices research, researches are implemented on HVDC system's reliability evaluation, components'reliability sensitivity analysis, UHVDC system's reliability analysis and reliability evaluation model for AC/DC hybrid system. Since HVDC system features in its numerous components and complex structure, under practical operation condition, the thesis studies on HVDC system's reliability evaluation methods and their application in practical engineering by combining fault tree analysis method with Markov theories. The main achievements are as follows:1. Based on HVDC system's typical connection manners and operation modes, Fault Tree Diagrams (FTD) are built by analyzing system's fault causation, HVDC and UHVDC subsystems'and system's Fault Tree Analysis (FTA) models are layer-established, and Frequency and Duration (FD) technique is combined for reservation analysis. Qualitative and quantitative methods with classical FTA theories are applied to DC system's indices calculation. Through 1x12-pulse and 2x12-pulse HVDC practical test systems, the methods are proved correct and efficient, based on the presented FTDs, system's failure causation and remediation can be quickly estimated.2. Evaluating UHVDC transmission system's reliability is evaluated using FD method. According to impacts of system functions with standby modes and operational conditions, DC system is divided into several subsystems. Based on Markov theories, the transit relationships and transit rates between subsystems are studied, and state transition diagrams are built accordingly. Combined with practical project, FTA method is applied for components'parameters preconditioning, and the calculation complexity is reduced significantly. The application of capacity merge in state transition studies makes the transition process much simpler. Finally, the reliability of system is evaluated using FD method. Through analysis of cases, the method is proved correct. 3. Sensitivity indices are proposed. The sensitivity analysis model of HVDC system's reliability indices is established by ombinging the FTA method and FD method. Probability sensitivity and key sensitivity indices are also defined. Effective solution is proposed for depicting the reliability impact of the components toward HVDC system.4. According to the theory and arithmetic analysis of FTA and FD methods, programs are developed for calculating the reliability of HVDC transmission system. Using the programs, the reliability of YunNan - GuangZhou±800kV 2x12-pulse UHVDC system is evaluated and the reliability results, including parameters'sensitivity, system's weakness link and standby modes are analyzed. At the same time, the impacts of different connection modes (1x12-pulse and 2x12-pulse) on reliability are discussed, several valuable conclusions are made. Finally, a series of reinforcement measures are presented.5. Based on the precondition that HVDC system's reliability is evaluated, using Monte Carlo simulation, researches on AC/DC hybrid transmission system's reliability evaluation are expanded. The reliability indices of IEEE-RTS 96 test system are calculated, and the results prove that the model is correct. At the same time, how to take into account of hybrid system's transient stabilization and voltage restriction to make the model more complete will be the subject in the future.