Applicability boundary calculation for directional current protection in distribution networks with accessed PV power sources

With rapid increase of the photovoltaic (PV) power sources accessed in distribution networks, the performance of current protection has been highly affected. It is universally acknowledged that the direction criterion can improve the performance of current protection, under the influence of PV sources, which however, still remains in qualitative cognition. In this paper, a method for quantitatively calculating the applicability boundary of directional current protection in distribution networks with accessed PV power sources, which is indexed by the PV capacity boundary, is proposed. Furthermore, a simplified assessment model is discussed to improve the computation speed, in the discussed case, the computation time of the simplified model is 11.576 h, which is only 64.26% of that of the initial model (18.014 h). On this basis, the applicability boundaries of current protection and directional current protection are discussed in a typical two-feeder distribution network. The case analysis shows that the increase of the applicability boundary of the current protection by introducing traditional power direction criterion is limited (36.7% in the discussed case). Differently, if the influence of PV sources on the direction criterion can be avoided, the applicability boundary can be further increased (by 142% in the discussed case). Finally, simulation cases based on PSCAD/EMTDC are carried out to fully demonstrate the correctness and accuracy of the proposed calculation method.