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Abstract: Distributed generation (DG) using renewable energy resources, is intended to reduce the impact of power generation from fossil fuels on climate change. Microgrids (MGs) represent a method of interconnecting several low voltage (LV) renewable energy sources and loads to the distribution system. Multi-microgrids (MMGs) integrate distributed generators (DGs) and MGs with medium voltage (MV) distribution systems. Protection system design for MGs pose significant challenges due to bi-directional flow from DGs as well as lower fault current levels due to the inverter connected DG sources in islanded MGs. This paper reviews the coordination strategies and protection schemes that have been proposed for MGs to address these challenges. The protection coordination strategies based on communication and time grading including their relative performance are described. The advantages and limitations of existing MG protection schemes are discussed. As most of these protection schemes apply to relatively small MGs, they may need to be extended for larger MG configurations in practical power systems. Some future directions for research in the protection system design for both MGs and MMGs are also outlined in this paper. [Copyright &y& Elsevier]

Abstract: Electricity generation in different countries is based on a variety of fuel mixes compromising solid fossil fuels, oil, natural gas, nuclear and renewable energy sources. While in the past, national energy agendas have directed the optimal utilisation of domestic resources as a means to achieve supply security, today''s environmental debates are influencing the electricity fuel mix in new directions. In this paper we examine the electricity sectors of Germany, Greece, Poland and the UK in an attempt to identify the policy and technology choices implemented in each country. The country selection is deliberately made to facilitate an extended overview of national agendas, varying domestic energy resources and industrialisation levels but still within the common EU framework. The focus is placed on policies related to two objectives, climate change mitigation and improving electricity supply security. The theoretical framework developed provides the possibility to assess the electricity sector independence at a national level using a multi-parametric analysis of the fuel mix data. Through a comparative assessment of the knowledge gained in different countries the authors provide insights and suggestions that allow for an improved understanding of the trade-offs and synergies that various policy options may introduce. [Copyright &y& Elsevier]