A comprehensive approach to transient stability control part II: open loop emergency control

Summary form only given. The transient stability-constrained dispatch of an electric power system is a problematic task for the system operator who, under economic pressure, may be reluctant to take expensive preventive actions against very harmful contingencies. The open-loop emergency control (OLEC) technique proposed in this paper aims to relieve such preventive actions by complementing them with emergency ones. This is achieved by combining generation rescheduling, assessed and taken preventively, with generation tripping, assessed preventively but triggered only if the anticipated harmful contingency actually occurs. The relative size of preventive vs emergency control may be modulated so as to furnish panoply of solutions. Besides, the technique may stabilize simultaneously many contingencies. Simulations conducted on the EPRI 88-machine system illustrate various possibilities of the OLEC technique and compare it with the purely preventive one. Tradeoffs between preventive control and OLEC are also discussed, especially in the context of liberalized electricity markets. It is shown that OLEC is indeed able to provide a good compromise between economics and security, and to realize important savings.