Skip to Main Content
Over the last ten years, we have heard so often in conferences, seminars, and workshops that the power system will soon be operated very near to its limits that this statement has become a cliché. Unfortunately, it is no longer possible to comply with the classical preventive N-1 security standards during all of the hours in a year. The system is indeed no longer able to survive all single faults without postfault actions. More and more corrective (i.e., postfault) actions are defined and prepared by operators, and the cliché is now a reality, as a matter of fact. To be more precise, it is no longer possible to maintain the N-1 security of the system at all moments by using only preventive actions, and the number of hours during which the system requires corrective actions to be secure is increasing. More and more, new sp<?Pub Caret?>ecial protection schemes (SPSs) are deployed to implement some of these corrective actions automatically. Devices such as phase-shifting transformers (PSTs) and static var compensators (SVCs) are added in the system to increase its controllability. As a result, the system becomes more and more complex.