分布式光伏配电网无压方向元件新判据OA

Three-stage overcurrent protection in distribution networks with distributed photovoltaic(PV)generation requires directional elements.However,traditional power directional elements are prone to maloperation and failure to operate under the influence of PV low voltage ride-through and negative-sequence current suppression strategies,and they also require voltage transformers.To address these issue,this paper proposes a novel criterion for current-only directional element suitable for distribution networks with distributed PV generation.First,in situations where the topology of the system behind the protection device and information on multiple PV units are unavailable,this paper proposes an equivalent method to simplify the distribution network with multiple distributed PV units into an equivalent single PV network.Based on this equivalent model,a composite sequence network is established,and the phase relationships among sequence currents under forward and reverse faults are analyzed.Subsequently,a novel current-only directional criterion is proposed based on the phase difference between the negative-sequence current flowing through the protected line and the positive-sequence current of a passive branch connected to the same bus.The analysis reveals that this directional element offers significant advantages,including applicability to scenarios with high PV penetration,eliminating the need for voltage transformers,and immune to transient resistances.Finally,PSCAD-based simulations verify the performance advantages of the proposed directional element and the accuracy of this simplified equivalent method.