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Abstract-This paper provides a methodology to restore transient stability. It relies on a well-behaved optimal power flow model with embedded transient stability constraints. The proposed methodology can be used for both dispatching and redispatching. In addition to power flow constraints and limits, the resulting optimal power flow model includes discrete time equations describing the time evolution of all machines in the system. Transient stability constraints are formulated by reducing the initial multi-machine model to a one-machine infinite-bus equivalent. This equivalent allows imposing angle bounds that ensure transient stability. The proposed optimal power flow model is tested and analyzed using an illustrative nine-bus system, the well-known New England 39-bus system, a ten-machine system, and a real-world 1228-bus system with 292 synchronous machines.

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This paper presents a security redispatching procedure that allows achieving an appropriate security level in terms of small-signal rotor angle stability. The proposed methodology is based on an OPF problem that explicitly considers security limits through stressed loading conditions. The solution of the proposed redispatching procedure yields the optimal preventive control actions to be implemented to ensure a given security level. The New England 39-bus, ten-machine and the IEEE 145-bus, 50-machine systems are used for illustrating, testing, and discussing the proposed technique.

An Optimal Power Flow (OPF)-based security-driven redispatching procedure to archive an appropriate security level is provided. The proposed procedure is particularly suited for security redispatching by an independent system operator. This procedure uses full ac equations and explicitly considers security limits through a stressed loading condition. Furthermore, a variety of FACTS devices can be incorporated in the redispatching problem to enhance system security. Several case studies based on the IEEE 24-bus system and on a real size model of the Italian system are analysed and discussed.