Theoretical explanation of hyper-plane boundary of dynamic security region

The dynamic security region (DSR) of an electrical power system has received more and more attention in recent years for providing plenty of security information and good prospect in online application. This paper tries to explain in theory that why hyper-planes (HPs) can approximate well the critical boundary of DSR determined by transient stability in real power systems. Such explanation is based on the instability separation mode and corresponding system reduction. An example on a two-generator-infinite-bus system at last helps to illustrate the relation of the instability separation mode and HP property of DSR boundary.