With the increasing integration of renewable energies in the power system a thorough analysis of the adequacy of defence plans is needed. This paper focusses on the impact of a high penetration of photovoltaics in distribution systems on the under frequency load shedding schemes designed by the TSO. First an overview of the issues arising from a higher penetration of embedded renewable energy sources in the current UFLS scheme design is described. It will be shown that neglecting photovoltaics in load shedding scheme design can lead to adverse effects in system stability and can have a disproportional high social impact. Subsequently an overview of different methodologies to improve the UFLS scheme design is given. These methodologies are then applied to the measurements of two feeders in the Belgian power system. From the evaluation of these results, it can be concluded that the proposed methodologies lead to substantial improvements in UFLS scheme adequacy.
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