A PROBABILISTIC APPROACH TO DYNAMIC POWER-SYSTEM SECURITY

In this paper, the problem of dynamic power system security is investigated. A probabilistic approach is chosen and an appropriate power system model is developed for analyzing the dynamic behavior of the different operational modes of the system. The model includes the transients induced by primary and secondary disturbance events. Pri mary events are defined to be state-independent disturbances such as line and unit faults and load changes and are modeled by random switches in the power system model. Secondary events are state-dependent variations in the structure such as forced line and unit outages and load shedding actions. They are modeled by switches in the model whose states depend on the instantaneous values of certain system variables. The power system model developed characterizes the interaction between the dynamic state of the system and the network topology as defined by the status of the various protective relays in the system. A dynamic security region is defined as a subset of state-structure space of the power system such that at any moment in time an operating point within the region satisfies all the constraints required for secure power system operation. Given an initial probability distribution of the system state and of the system structure, a fixed control policy, and a statistical characterization of the primary events, the probabilistic evolution of the state and structure is computed as the solution of a system of linear partial differential equations with matching conditions at the switching boundaries. A dynamic security measure is defined as the integral of the joint probability density of the state and structure of the system over the dynamic security region for all possible structural variations. This computation yields the probability that the power system remains secure for the range of primary events considered. Computer simulations for an example power system are presented to illustrate the utility of the approach developed. © 1990 IEEE