Adaptive relaying to balance protection dependability with power system security

The 28 September 2003 blackout in Italy raised doubts about the ability of distance relays in distinguishing voltage collapse and remote short-circuits. The combined presence of reduced voltages and high power flows may trigger distance relays, with the consequent tripping of healthy lines, reducing the system survivability. The paper addresses an analysis of the behavior of distance protections during the sequence of events that led to the separation of the Italian network from the UCTE (Union for the Coordination of Transmission of Electricity, nowadays updated to European Network of Transmission System Operator for Electricity - ENTSOE-E) power system. Preliminary studies aimed to develop an approach based on adapting relaying for mitigating the effects of cascading events, is presented. The under studying methodology allows to balance protection system dependability versus overall power system functional security. Preliminary test results are obtained by implementing this approach on a test case based on the Italian power system configuration.