EXPERIENCE GAINED BY THE APPLICATION OF A REAL-TIME VOLTAGE SECURITY ASSESSMENT METHOD AT THE HELLENIC TRANSMISSION SYSTEM OPERATOR

Voltage instability is widely recognized as a significant threat of power system blackout. As far as real-time operation is concerned, there is a need for appropriate tools to identify dangerous contingencies and assess security margins. The Hellenic Interconnected System presents a structural geographical imbalance between the main generation site and the main load center. This imbalance leads to bulk power transfers over long distances leading to voltage stability problems in areas of the southern system during heavy load conditions. In order to improve the operational practices, a realtime Voltage Security Assessment (VSA) tool has been installed at the National Control Center of the Hellenic Transmission System Operator (HTSO). The scope of VSA is the analysis of the impact of significant contingencies and the determination of security margins in terms of power transfers or power consumption in load areas. The computations performed within the VSA tool are based on a Quasi-Steady-State simulation, a fast time-domain method well suited to the analysis of long-term voltage stability phenomena. VSA is performed on the current system state, provided by the Energy Management System (EMS) state estimator. The VSA application incorporates functions for filtering the contingencies, determining secure operation limits, and deriving post-contingency PV curves for the identified dangerous contingencies. This paper is a description of the experience and the added value gained by the application of the real-time VSA, in parallel with the existing EMS, at the control center of HTSO.