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Study On Construction Mode And Key Technologies Of Smart Grid Hierarchical Protection

Posted on:2014-02-16Degree:DoctorType:Dissertation
Country:ChinaCandidate:Z X LiFull Text:PDF
GTID:1222330398987139Subject:Power system and its automation
Abstract/Summary:PDF Full Text Request
The power grid is the critical infrastructure whose safe operation is of great significance to the national economic development and social stability. Large scale blackouts which happen frequently domestic and overseas recently sound the alarm about the security defense of power grid. As the first defense line to ensure the safety of power grid, relay protection is of great importance for isolating fault element quickly and preventing the fault development effectively. However, under the background of modern complicated power grid, more and more problems of traditional relay protections have been exposed, such as setting cooperation of back-up protections is very difficult, fail-to-trip or malopeartion of protections may happen if the structure or operation status of power grid changes unintentionally, cascading trips and large scale blackout may occur under condition of heavy load transfer and so on. In recent years, with the development of information sharing technology in smart substation and fiber communication technology, the information resources which can be used by relay protection system have changed significantly. Meanwhile, it provides a chance for fundamentally improving the performance of traditional relay protection. As a part of the project "Limited Wide Area Intelligent Protection against the Catastrophe of Power Grid"(50877031) which is supported by the Natural Science Foundation of China, this dissertation conducts an in-depth and systematic study on the construction mode and cooperation scheme of novel hierarchical relay protection system based on information sharing, partition of limited wide area protection, fault element identication algorithm based on multi-information and so on. The study can deepen the research contents and technical requirements of hierarchical relay protection system, improve the performance of traditional relay protection. It is of important therotical and practical significance for the construction of reliable first defense line and safety of power grid.The novel substation under background of smart grid has the advantages of information sharing and information integration. Based on it, in order to meet the requirements of smart grid, revew the construction mode of traditional relay protection and propose novel construction mode have been one of the research focuses of relay protection. Based on the information sharing technology, a novel hierarchical relay protection system which consists of bay-level protection, substation-level protection and wide-area-level protection is proposed. The bay-level protection realizes the primary protection function and simplified back up protection function of conventional single bay. The substation-level protection which is also called "substation protection" realizes the relay protection function of the whole substation integratedly by taking full advantages of substation information. The wide-area-level protection which is also called "wide-area protection" realizes the back up protection function of the power grid with redundant information of the regional power grid. Based on the hierarchical structure, the direct sampling/networked sampling mode of information measurement in the substation and communication mode between substations are discussed. Meanwhile, according to different sampling modes and communication modes, construction modes of relay protection are proposed with respect of different voltage levels. The advantages and disadvantages of different construction modes are analyzed.Generally speaking, the researches of different level protections are independent with each other. In order to better realize the functions of the hierarchical relay protection system of smart grid, the protection configurations of different level protections and the coordination principles are studied. According to the functions of different level protections, the information interaction process and tripping coordination among the bay-level protection, substation-level protection and wide-area-level protection are studied. Based on the analysis of information flow of the hierarchical relay protection system, the information organization and interaction of the information flow are proposed. Meanwhile, the setting calculation principles of the bay-level distance protection and zero-sequence overcurrent protection, as well as the faulted area identification method of the wide-area-level protection are proposed. According to the requirements of the cooperation between the substation-level protection and wide-area-level protection, the auxiliary criteria for the downward decisions of the wide-area-level protection and the tripping strategy under condition of complicated decision-making are studied further. Moreover, specified to the phenomenon that maloperation of distance protection may occur under condition of heavy load transfer, a self-adptive distance protection scheme is proposed to improve the performance of the bay-level protection. In order to prevent the transimission line operating beyond the limit under condition of heavy load transfer, an over-load protection based on the constraint of thermal stability is proposed.Due to the large and complicated structure of modern power grid, it is difficult to protect the whole power grid with single hierarchical relay protection system. How to divide the wide-area power grid into several reasonable protection partitions and realize the relay protection functions in accordance with different partitions are the key issues which needs to be solved by the hierarchical relay protection. Based on the concept of limited wide-area protection, the basic principles of protection partition of power grid which include protection partition according to different voltage levels, choice of central station, division of protection scope, the overlap and interaction of different protection partitions and so on are proposed. The performance evaluation system of protection partition is built with the balance index of communication amount between different protection partitions and calculation amount index of decision-making center. The number of protection partitions, the information exchange between different protection partitions and function coordination are taken as constraint conditions for the performance evaluation system. An implementation method of protection partition based on graph theory is put forward. The adjacent matrix is built based on the topological structure of power grid. Then the reachable matrix which can determine the scope of protection partitions can be obtained with calculation of adjacent matrix. Finally, various partition results can be got based on the search of reachable matrix. With the optimization of partitions, the optimal protection partition of power grid can be obtained.The basic task of relay protection is identifying and isolating the fault element quickly. Hence, the fault element identification is always the research focus of relay protection. By taking full advantages of redundant measurement information within the substation scope and wide-area scope, the comprehensive criteria of fault element identification with fusion of action information of multi-protection are studied. In order to solve the problem that the setting cooperations of traditional distance protection and zero-sequenceo over current protection are very complicated, novel distance protection scheme and zero-sequenceo over current protection scheme based on multi information sources are proposed. With respect to the information mistake and information loss which may occur during the measurement, judgement and transfer of wide-area information, an information fault tolerant algorithm based on the measurement of fault information is proposed. The fault information measurement of different elements within the wide-area scope can be obtained with the calculation of fitness function. Based on it, the fault element can be identified with high reliability and fault tolerance.Currently, the digital simulation is taken to validate the performance of wide-area protection. However, the electromechanical dymanic characteristics and measurement error of digital simulation can not accurately reflect the physical characteristics of actual power grid. On the other hand, the physical concepts of dynamic simulation experiment are clear and intuitive. Meanwhile, it can accurately reflect the characteristics of actual power grid. Hence, the wide-area protection dynamic simulation experiment is of great significance for promoting the wide-area protection into engineering application. Relying on the power systems dynamic simulation laboratory of CEEE, HUST, a model of the power grid with3-generator and6-node is built. With the dynamic simulation model, the performance of the fault element identification algorithm of the proposed wide-area protection is validated by simulating various conventional faults and complex faults and collecting the fault information within the wide-area scope. The results show that the fault element identification algorithm can correctly identify the fault element under various fault conditions and it has high information fault tolerance.In the end, the dissertation gives systematical summary and points out the further work.
Keywords/Search Tags:smart grid, wide-area protection, substation protection, bay-level protection, hierarchical protection, information sharing, fault element identification
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