The Algorithm Researches Of Novel Wide Area Backup Protection For Power Grid

With the enlargement and increasing complexity of power grids in China, traditional backup protection exposes many drawbacks and limitations such as protection failures and causing cascade trips. As new clean energy and distributed generation gradually connected into the power grid, as well as the rapid building of China's"Unified Strong Smart Grid", the power systems will operate in a much more complicated way. It brings a large amount of new problems and challenges to traditional backup relay protection.Generally speaking, methods of using wide-area information of the power grid to improve traditional backup protection which is not adaptive to the new situation under power grid's fast development can be divided into two kinds: firstly, using real-time wide-area information to form new power grid wide-area backup protection algorithm, i.e., fault location procedure which is based on the wide-area information can realize direct cooperation and action among protections instead of complex setting and cooperation among traditional backup relays; Secondly, by getting real-time power grid's operation information, online adaptive relay setting can be realize to overcome the shortcomings of traditional protections, especially of backup protections. The difficulties are large information transmitting and fast fault calculations and settings. Therefore, in view of the first method, this paper puts forward a sequence components based wide area backup protection algorithm for power grid. For a second thread, it puts forward a nodal impedance matrix parallel generating algorithm which can accelerate fault analysis and setting calculation speed.This paper presents a centralized wide area backup protection algorithm for power grids based on sequence component under the design philosophy that the algorithm should reasonably and effectively utilize communication resources and try to avoid communication congestion. Hence, the algorithm uses different wide area information in different fault locating steps. By using the uploaded information the Decision Center finally makes a protection decision. This novel protection scheme enjoys well rapidity. Besides, it has no such problems like complex settings and coordination among traditional standalone backup protections, mal-operation of backup relays during large flow transferring and so on. The feasibility and validity of the algorithm has been verified by the digital dynamic simulation.Fast generation and modification of nodal impedance matrix is the key to real-time computation of electric power systems, and the latter is the premise to realize the online relay settings. By tearing original bulk power networks into several independent small sub-networks which are connected through virtual circuit breakers, each sub-network's nodal Z-matrix can be obtained parallelly. Taking electromagnetic influence among sub-networks into consideration, these independent nodal Z-matrixes can be modified to form the original network's nodal Z-matrix exactly by using tools of decomposition-coordination method and Large Change Sensitivity Theory. The experiment results demonstrate the feasibility and validity of the proposed parallel algorithm.