Study Of Wide-Area Backup Protection Critical Technologies For Smart Grid Based On Fault Element Identification

Protective relaying is the first defense line of electric power grid. When it operates fast and reliably, the safety of power grid can be guaranteed. Otherwise, grid instability and blackout event may occur. Traditional backup protection identifies faults based on local information. It has complex setting principle, poor adaptability to grid operation change and is inclined to misoperate under heavily loaded flow transfer. Consequently, it is meaningful to exploit novel protection technology and design new-style protection system which has excellent property and is adaptive to the grid operation change.Accompany with the development of wide-area measurement and communication technique, applying wide-area information to identify fault element and studying novel wide-area backup protection (WABP) based on fault element identification (FEI) becomes a hot spot in modern power system research. Supported by the National Natural Science Foundation of China (No.50837002), this dissertation researches the kernel problems of wide-area backup protection based on fault element identification in depth.How to partition a large scale power grid into several reasonable subsystems is one of the critical issues of WABP research. There are three indexes including communication reliability of substation, investment economy of protection system and communication balance among subsystems have been adopted to establish a integrated hierarchy so as to evaluate the property of partition result. Meanwhile, a two-layer clustering partition algorithm is proposed. Firstly, the protected grid is decomposed into multiple candidate subsystems according to the compactness among substations, and then the length of chromosome can be determined. During two-layer clustering process, the number of subsystems is optimized when genes within chromosomes are changed, and the candidate subsystems can be further merged. Simulation result demonstrates that the presented algorithm could partition practical large grid into several reasonable subsystems, and the application requirements and latency constraints are satisfied.A novel FEI algorithm and a fault area search algorithm based on fault component voltage comparison are proposed, respectively. The fault component voltage and current at one terminal of line are applied to calculate the fault component voltage at the other terminal. Afterwards, a comprehensive identification criterion based on the ratio between measured and calculated values is established to identify fault element. On the other hand, fault area search algorithm could decrease wide-area communication traffic through substation pickup detection, and then accelerate FEI through fault incident line search. Simulation test proves the validity of presented algorithms under various complex conditions.The distribution characteristic of fault component currents is illustrated, and corresponding FEI algorithm and fault area search algorithm are also proposed. The FEI algorithm comprises branch fault component current comparison criterion and two-terminal fault component current comparison criterion. Then, these two criteria are synthetically applied to identify various internal faults. The fault area search algorithm searches quasi suspected faulty lines through branch current magnitude comparison. After that, the suspected faulty lines are searched through incident matrix computation. Simulation result shows that the uploaded information of substations and the calculation quantity of central station can be dramatically reduced through fault area search. Moreover, the FEI algorithm could identify different types of faults and has good security.How to safeguard the reliability of protection decision result under information error and loss is a formidable challenge. An intelligent decision-making model and a decision-making algorithm based on multi-source information fusion are proposed, respectively. The Manhattan distance is applied to describe conflict degree, and a weighted evidence method is used to decrease the conflict degree among decision evidences. Finally, source evidence and traditional composition rule are all improved. Besides that, the operation information from WABP and local relays are chosen as decision evidences. The fault currents of branches are applied to calculate the trust degree of Zone-2 and-3 elements. Furthermore, the trust interval is partitioned into three parts so as to further improve the performance of decision-making algorithm. Simulation result shows that the proposed algorithm could make correct decision under multiple information error or loss.