Development of a Directional Element for Solar Inverter-Rich Distribution Networks

The high penetration of electronic-coupled distributed energy sources, especially photovoltaic systems into distribution networks has created new challenges for traditional non-directional protection systems. Fault currents can now come from multiple sources, making protection location and direction detection difficult. Although conventional negative-sequence directional elements have been proposed as alternative solutions for detecting unbalanced fault direction, the unusual waveforms of current and voltage contributed by photovoltaic systems can adversely affect their performance. This paper proposes a new directional approach that utilizes prefault voltage and during-fault negative-sequence current component to determine the direction of unbalanced faults in photovoltaic system-dominated distribution networks while considering the dynamic voltage support of photovoltaic systems as imposed by new grid code requirement. The proposed method is validated through numerical analysis and EMT simulations in the software environment PowerFactory/DIgSILENT.