Prevention of Power System Blackouts Using Windowed-Prony Method

Zone-3 unit of conventional distance relay is vulnerable to voltage instability and load-encroachment which are known as system stress conditions. For such conditions, the impedance trajectory encroaches zone-3 reach. Based on the setting parameters of the relay, it is identified as a fault and relay may maloperate. However, the relay may maloperate for any three-phase fault during such stress events as the change in system parameters are identical for both the conditions. Zone-3 maloperation is the root cause behind 2012 Indian blackout. So, it is necessary to introduce a supporting algorithm to avoid relay maloperations and to curtail the occurrence of any blackout. This paper introduces windowed-Prony method to detect and discriminate fault from system stress conditions. This method will be activated when the impedance trajectory enters the setting zone-3 region. It is used to approximate the input signal and to estimate the error existing between actual and approximated signals. The squared error is considered as a fault detection index (FDI). The performance of this method is tested on IEEE 39 bus test system.