Probabilistic Approach to Transient Stability Evaluation of Electrical Power Systems

A new probabilistic approach to transient stability evaluation of electrical power systems is proposed. The method is relevant to planning studies, where load level is a major source of uncertainty. The probabilistic nature of both the load demand and the circuit breaker operating time is taken into account for the purpose of obtaining an analytical evaluation of the instability probability. The approach is based upon the analytical computation of the probability distribution function of the critical clearing time for stability in terms of the load demand distribution. It allows the expression of the instability probability as an analytical function of all the relevant system parameters. The method is illustrated with reference to a simple (one machine - infinite bus) system, and the results are compared with those obtained by means of statistical (Monte Carlo) simulation. The time requirement of the two methods is comparable, but the proposed analytical approach offers a remarkable advantage over the Monte Carlo method for a sensitivity analysis with respect to the system parameters.