Supervising Zone 3 Operation for Inverter Integrated Networks

Distance relays are commonly used for identification of faults in high voltage transmission lines. Zone 3 corresponds to an overreaching backup region of a distance relay. In this work, the performance of distance relay zone 3 operation is investigated in the presence of an inverter-based resource (IBR). The inverters operate in the grid following (GFL) or grid forming (GFM) mode. Effect of change in control parameters of an inverter on apparent impedance observed by the distance relays is examined. Further, a wide area measurement-based supervision algorithm to support zone 3 operations is developed. The proposed algorithm can identify fault conditions in the network in presence of IBRs and thus make distance relay zone 3 operations more dependable and secure. Impedance calculated using voltage and current measurements obtained from synchrophasor devices placed at strategic locations are used to develop indices which can detect a fault condition in the network. The method is tested on the modified New-England 39 bus system with IBR connected at different locations in the network. The results are obtained using PSCAD simulations and validated in real time using RTDS. The proposed method's accuracy in fault identification and its advantages over existing methods are highlighted using various test cases discussed in this paper.