LOCAL AND GLOBAL CONTROL OF EXCITATION FOR TRANSIENT STATE POWER SYSTEM EMERGENCIES.

Two alternative feedback control strategies for transient stability enhancement of a power system through forcing of excitation of synchronous machines in the system are presented. The first scheme derives the control as a function of rotor angle position, frequency and acceleration of each generator in the system relative to those of a reference machine. This has been termed as the global control strategy. The second, called the local strategy, depends on data local to each generator. Algorithms developed with the two control strategies are tested for a number of fault conditions in the system. While the global scheme is superior in terms of overall transient performance, the frequency variation and terminal voltage characteristics of the individual generators are better with the local control. The local scheme is preferred from implementation viewpoint because it is relatively simple and inexpensive.