2168-6777 (c) 2016 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information. This article has been accepted for publication in a future issue of this journal, but has not been fully edited. Content may change prior to final publication. Citation information: DOI 10.1109/JESTPE.2016.2581986, IEEE Journal of Emerging and Selected Topics in Power Electronics Abstract— Decentralization of electric power is possible with penetration of Distributed Generators (DG’s) in the microgrid (MG) network. Reconfiguration of microgrid poses a key challenge in identifying suitable protection schemes for varying topology of the network. In this paper, a central protection centre (CPC) is incorporated whose function is to monitor the microgrid continuously, identify fault occurrence and locate the exact faulted branch. The proposed Prims aided Dijkstras algorithm executed continuously in CPC is responsible for identifying the current topology of the network and aids in identifying the shortest route from the faulted point to the nearest operating source. The CPC is also responsible for adaptively varying the settings of the relays existing in the shortest path identified based on their selectivity levels. This heuristic algorithm is validated on an IEEE 21-bus and 40-bus microgrid test systems for all possible topologies and faults. The proposed algorithm is capable of clearing the fault by disconnecting minimum portion of the network and ensuring continuity of supply to majority of the loads. Index Terms—Microgrids; Protection of microgrid; Power System Protection; Graph Theory; NOMENCLATURE der I Rated Distributed Energy Resources (DER) current F I Fault current E System voltage s Z Source impedance l Z Total line impedance th V Thevenin voltage, which is the voltage at the fault point before the occurrence of the fault th Z Series impedance, the impedance seen from the location of the fault looking back into the network FL Fault Level al no V min Nominal Voltage b V Base Voltage b I Base Current Manuscript received January 6, 2016; accepted June 11, 2016; O.V.Gnana Swathika is with the VIT University Chennai, Chennai, Tamilnadu 6000127 India (e-mail: gnanaswathika.ov@ vit.ac.in). S. Hemamalini, is with the VIT University Chennai, Chennai, Tamilnadu 6000127 India (e-mail: gnanaswathika.ov@ vit.ac.in). b MVA Base Mega Volt Ampere FT I Actual fault current at faulted line FG I Fault current contribution from grid FDG I Fault current contribution from individual DG rl Z Impedance measured at relay location sl Z Impedance setting at the fault location rl U Voltage measured by the relay at the fault location r upstream Z _ Impedance between relay location and point of common coupling (PCC) r downsteam Z _ Impedance between PCC and fault point ‘f’ min k I DER current contribution to short circuit current K Fault current contribution coefficient rder I Rated output current of a particular DER kder I Fault current contribution by a particular DER max t Maximum time to clear the fault comm t Communication delay base t Base time of operation relay t Estimated operating time of relay assigned t Assigned operating time of relay d Distance from the faulted point to the nearest operating source n Total number of nodes of the network I. INTRODUCTION ROTECTIVE relay technologies are evolving to eliminate the faults in distribution networks. A good protection scheme ensures that minimum portion of a network is disconnected, while clearing the fault. The increasing popularity of DG penetrated microgrid forces the distribution network to be no longer radial in nature. Dynamic behavior of a microgrid is due to the addition of new DG or load, occurrence of fault in the network, islanded operation and reconfiguration for reasons such as maintenance. It is a challenge for the protection engineers to design a suitable protection scheme for a dynamic microgrid. The impact of DGs connected to or disconnected from the microgrid causes protection issues like variation of fault current levels [1], blind Prims Aided Dijkstra Algorithm for Adaptive Protection in Microgrids O.V. Gnana Swathika, and S. Hemamalini, Member, IEEE P