Directional element based on the magnitude of positive-sequence superimposed impedance for active distribution networks

The complex phase characteristics of inverter-interfaced distributed generators (IIDGs) during faults limit the effectiveness of traditional fault-component-based directional elements. In distribution networks with high-penetration, multi-point-connected IIDGs, the applicability challenge of traditional directional elements becomes more severe. This paper investigates the behavior of positive-sequence superimposed impedance magnitudes of IIDGs during low-voltage ride-through (LVRT) under AC faults, considering various voltage sag levels. The variation boundaries of positive-sequence superimposed impedance magnitudes of IIDGs are quantitatively analyzed, forming the basis for a novel directional element that determines fault direction by comparing forward and reverse positive-sequence superimposed impedance magnitudes. To analyze applicability of the proposed directional element, the grid code of voltage deviation for IIDG integration is incorporated to define safe and risk regions for the proposed directional element. Extensive simulations verify its reliable performance under diverse fault types, locations, transition resistances, IIDG outputs, and control strategies. The proposed method ensures high applicability in complex distribution scenarios with high-penetration, multi-point-connected IIDGs.