Analysis Of Power Grid Cascading Failures Model Based On Complex Network Theory

The cross-regional power grid is the future trend of development. The large power grid solves the problem of cross-regional transmission of electrical energy, but it can also cause blackouts problems. The formation of large blackouts involving a number of reasons, and the cascading failure of high voltage power network is the main one of the rapid and large-scale collapse. On the one hand, relay protection system is directly involved in the process of cascading failures, rather than 35 k V high voltage power network is widely used as distance protection line main protection; on the other hand, relay protection system removes the fault elements which makes the power flow redistribution and may cause other lines overload or electric network oscillation, thus triggering a new round failure. The power flow transferring characteristics related to the topology of high voltage power network, the analysis is the hot issue in present research by using of complex network theory from the perspective of the whole system. For the relevant characteristics of cascading failures, the paper studied the following.First, the article summarizes the main reasons and the development of the previous typical blackouts, noting the background and significance of the research; introducing the current domestic and international three methods of the cascading failure problem research, and summarizes a variety of models and its characteristics.Then, the article proposed and established a cascading overload trip model based on distance protection, and analysises the action equation of impedance relay and the 3-zone distance protection. According to the trip due to overload, this paper propose a model of the process methods, specifically including: AC power flow calculation, ignoring the transient process, using directional impedance relay model, retaining only the third zone of the 3-zone distance protection and setting by overload, the trip order decided by the degree of overload. Through writing the MATLAB program to achieve this model, simulation gives the fault chains of the cascading overload trip process, and describes the effect of distance protection in the chain process. Model is more in line with the electrical characteristics of the real grid, the grid can be applied to the cascading failure analysis.Finally, the article improves the broadth first search so that it can adapt to the fully search in the weighted power network model, while summarizes the characteristics of the power network by comparing the telecommunications network, and proposes a weighted directed DC grid model and modeling method, specifically including: using an improved BFS method for fully searching the paths between generator-load nodes, considering the active power and the distribution according to kirchhoff law, setting the line weights by the reactance values, the path direction from generator to load as the positive direction of the paths. Simulation results show that the proposed model and the actual distribution of power in the trend is the same, which proves the rationality of the proposed model. Based on this model is proposed to measure the power flow reliability and topology change and simulating in the IEEE Power Grid of the small world and non-small-world characteristics, the results sorting the lines according to the importance, identifing vulnerable lines. So the parameters is effective and it can be used to identify key line in the power network.