In recent years, power systems have become larger and more complicated. Deregulation of electric power industries has begun in some countries, and power system operations have become more difficult. However, the stability of the power supply is the most important consideration for customers. Therefore, power system operators should consider not only economic load dispatch but also on-line stability aspects. In this paper, we pay attention to one of the most important transient stability indices [critical clearing time (CCT)] and propose a new transient stability preventive control method using linear relationships between CCTs and generator rotor angles. At first, CCT calculations, as contingency screenings, are carried out to find contingencies that have smaller CCTs than predefined target values. The target values are taken as larger values than the actual circuit breaker operating times in the power system. A preventive control to achieve a more stable power system operating point is carried out by generator output rescheduling and generator terminal voltage control, which are determined using the relationships between CCTs and generator rotor angles. This proposed method is demonstrated using a Japanese standard power system called the IEE of Japan (IEEJ) EAST 10 machine system.
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