Study On Wide Area Current Differential Protection Algorithm In Power System

With the implementation of development stratagem about "transmit electricity from west to east, north supports power supply to south and vice versa, connect power grids nationwide" , the situation of large scale power grids and long transmission distances is a new challenge brought forward for relaying protection system and stability control system, which should not only protect electrical devices from being damaged by faults, but also avoid power system collapse by certain severe disturbances. Studies of the significant power system blackouts indicate that, in certain abnormal operation situations aroused by bigger disturbances, conventional protection relays based on the locally measured inputs is of easy misoperation. With the recent advances of communication technology, the wide area protection has been proposed as an approach not only to protect component, but also to imrpove system stability. Differently from conventional protection relays, with the acquisition of wide area information, wide area protection systems can more accurately detect components of fault and isolate faults in their smallest areas. In this dissertation, the background and research situation of the wide area protection are introduced, and various wide area protection systems proposed at present are summarized. The characteristics, the function making up and system structures are discussed, and a practical wide area protection system scheme is proposed in this dissertation.The analysis shows that the traditional criterion of current differential protection has the drawback and is not suit for wide area protection system. By improving the restraining characteristics, an improved current differential protection criterion is proposed in this dissertation. Theory analysis and simulation experiments show that: they are of the same security on external faults; furthermore, the improved has higher sensitivity and capability of detection on the faults with higher fault resistance.A wide area current differential protection arithmetic based on graph theory is proposed in this dissertation. The basic idea is that the topological structure of power system is described by graph nodes and edges; the most protection area of the IED can be obtained by the computation of adjacent matrices of the graph; and the relevant field of IED, i.e communication objects and exchanging data of the IED in each stage of fault, can be got with the computation of complete incidence matrices.Establishing one power system and its wide area protection system including power system communication in the EPOCHS platform, the wide area current differential protection arithmetic is implemented in Agents of EPOCHS. According to the simulation experiments on the faults, the results verify that the wide area current differential protection arithmetic based on graph theory is feasible and predominant.