Concepts and characteristics of security margin based on dynamic security region

Region-based security analysis methods play an important role in power system analysis. To guide the safe operation of power systems, it is important to clarify the physical concepts and geometric characteristics of the security margin. On the basis of dynamic security region (DSR), this paper analyses the relationship between the security margin and stability margin in a one-machine infinite bus equivalent system. And then, the geometric characteristics of the security margin are further explained in multi-machine systems. The obtained characteristics provide a way for estimating the shape of DSR. Moreover, an approximate calculation of the normal vector of DSR boundaries is proposed. Even if the exact DSR boundary is unknown, the obtained normal vector allows us to select the key generators and adjust the output power to get a more safe operating point. Finally, the proposed characteristics are verified by simulations on different test systems.