A COHERENCY BASED RESCHEDULING METHOD FOR DYNAMIC SECURITY

For on-line dynamic security analysis (DSA), the preventive control or remedial action should be an integral part of the function if instabi lity for a contingency is detected. Research done so far in on-line re medial action has been in rescheduling generation and mast of the sugg ested methods for determining such preventive control use the sensitiv ities of the stability energy margin to the generator power injections . For any approach using the energy margin, computation time is a conc ern and a somewhat different approach was suggested that determines co ntrol action by maximizing coherency of the generators without the use of sensitivities. In this paper, a new coherency based sensitivity me thod is proposed for generation rescheduling. Different coherency indi ces have been defined and then compared by ranking the contingencies a ccording to these indices as well as the energy margin index. Since th e coherency indices are always functions of the rotor angles, the sens itivity trajectories of a coherency index, such as the most critical r otor angle, with respect to changes of generation can be calculated at every time step of the integration process. This paper suggests that these sensitivities calculated shortly after fault clearing be used fo r rescheduling the generation. The calculation of these sensitivities are obviously faster than the calculation of the energy margin sensiti vities. This paper also shows, with test results using several differe nt systems, that the rescheduling achieved by this method provides the necessary remedial action. It is also noted that this method is intui tively more direct as it uses the sensitivities of the worst affected generator angles for rescheduling.