A reliable accelerated protection scheme for converter-dominated power networks

Rising penetration of converter-based sources with different control operations is introducing severe non-homogeneity in the power systems, especially during faults. Such non-homogeneity leads the decision derived by available distance and directional relays to be unreliable. Performances of the available communication-assisted tripping schemes being dependent on these two relay decisions at both ends become a concern for the protection of converter-dominated power networks. This work demonstrates the impact of converter-based sources on both distance and directional relays and the possible maloperation of the accelerated protection schemes. A new transfer trip scheme has been proposed mitigating the issue. Considering the homogeneity present in the negative and zero sequence networks in high voltage transmission system even with converter-based sources, two indices are derived using local voltage and current data to identify the fault direction at each end of a protected line. The decisions are transferred to the alternative ends through low-bandwidth communication channels to ensure the protection decision derived for the line to be
dependable as well as secured. The scheme is tested for a 9-bus and a 39-bus system, even with 100% converter-based sources using PSCAD/ EMTDC simulation platform and found to be reliable for different faults and system conditions. Comparative assessment with a few advanced techniques demonstrates the superiority of the proposed method.