International Journal of Smart Electrical Engineering, Vol.7, No.3, Summer 2018 ISSN: 2251-9246 EISSN: 2345-6221 109 An Overview on Microgrid Concept with Special Focus on Islanding Protection Issues Ferinar Moaidi*, Masoud Aliakbar Golkar Faculty of Electrical Engineering, K. N. Toosi University of Technology, Tehran, Iran. Ferinar_moaidi@yahoo.com, Golkar@eetd.kntu.ac.ir Abstract Subscriber service is not feasible in the construction of large-scale traditional networks with the aim of providing more services. The high distance between production and consumption requires the definition of a transmission network as a challenging intermediary. The cost of transmission network and the risk associated with it cannot be ignored at all. The idea of a microgrid, which began with the local feeding of loads, can improve the reliability of the previous power system and, in addition, deliver the power to customers with more quality. Microgrids are the key to achieve low carbon networks by collecting distributed generation (DG) resources. Power management in the form of a microgrid causes other sensitivities. The need for storage systems besides the power intermittency of DGs, unintended islanding, and the protection of microgrids, especially in the island state, are the main issues discussed in this paper in a coherent format. This research work is a detailed reference for microgrids mainly in protection issues related to the islanded ones. Keywords: Distributed Generation (DG), Islanding, Island protection, Low carbon networks, Microgrid. Article history: Received 01-Sep-2018; Revised 23-Sep-2018; Accepted 14-Oct-2018. © 2018 IAUCTB-IJSEE Science. All rights reserved 1. Introduction Microgrids are a set of small sources of energy that connect to the main network. Microgrids are designed as combined heat and power (CHP) systems for small-scale low voltage (LV) networks, which provide thermal and electrical loads to a limited number of subscribers. With the connection of multiple microgrids to each other can provide additional heat and electricity needs. Effective operation of the heat consumed in CHP systems is one of the most important advantages of microgrids. Distribution sources used in microgrids can include various types of production technologies with a small carbon emission in the air. Typically, microgrids are exploited in two modes: interconnected to the network and island, in both operating modes, microgrids will have an impact on subscribers as well as on the main network. In this chapter, the sources of distributed generation (DG) used in microgrids, energy storage systems, the technical, economic and environmental impacts of microgrids and their protective issues are presented [1, 2 and 3]. In Fig. 1, a microgrid consisting of renewable and non-renewable energy sources with battery storage in interconnected mode is illustrated [24]. Fig. 1. Components containing a microgrid [4] pp. 109:117