Adaptive Quasi-Power Differential Protection Scheme for Active Distribution Networks

With the massive integration of distributed generations (DGs), distribution networks gradually become more active and flexible. Conventional overcurrent protection is difficult to adapt to such active distribution networks (ADNs). Current differential protection (CDP) is a good choice for solving this issue, but the multi-branch structure of ADNs especially the unmeasured T-connected load branch affects the protection's sensitivity. Therefore, the paper proposes a quasi-power differential protection (QDP) scheme based on Tellegen's theorem. First, the feasibility of applying Tellegen's theorem to ADNs was analyzed. On this basis, reasonable protection criteria were designed for different scenarios of ADNs. Then, an adaptive protection scheme was established, which can automatically adjust the criteria depending on the presence of T-connected branches within the protected section. Finally, extensive simulations were carried out in an ADN model using PSCAD/EMTDC software. The simulation results demonstrate that the proposed protection scheme has excellent adaptability to network topologies, fault types, fault resistances, and network structures of ADNs.