Voltage stability monitoring and control studies in the Hellenic interconnected system

A critical contingency identified by the on-line VSA tool running at the Control Center of the Independent Power Transmission Operator of the Hellenic Interconnected System, is analyzed. The contingency leads to a voltage collapse through a succession of undervoltage generator trips, the first of which occurs before the onset of voltage instability. In order to improve the security margins of the system, dispersed and centralized static compensation schemes are investigated. Preliminary simulated results showing the performance of an Autonomous Protection System against voltage collapse for this contingency are also presented.