C I R E D 22 nd International Conference on Electricity Distribution Stockholm, 10-13 June 2013 Paper 0924 CIRED2013 Session 3 Paper No 0924 COMPENSATION OF DGS IMPACT ON OVERCURRENT PROTECTION SYSTEM OF SMART MICRO-GRIDS Rahim. JAFARI *1 , Mehdi. S. NADERI † , Gevorg. B. GHAREHPETIAN *2 , Naghi. MOADDABI *3 * Electrical Engineering Department, Amirkabir University of Technology, Tehran, Iran † Iran Grid Secure Operation Research Institute, Amirkabir University of Technology, Tehran, Iran E-mails: *1 Rhm.Jafari@gmail.com, † mehdi_salaynaderi@yahoo.com, *2 grptian@aut.ac.ir, *3 nimamoaddabi@aut.ac.ir ABSTRACT Traditional distribution networks have radial and unidirectional topology. The protection system of these networks is based on time and current coordination of overcurrent protection devices, which are negatively affected by DGs. The coordination of these devices is the most important issue of the protection system. DGs increase the voltage of faulted feeders at their connection point and cause the underreach in the time inverse characteristic of overcurrent protection devices. In this paper, a self- adaptive method for smart micro-grid is proposed, which compensates the underreached fault current seen by the relay. Therefore, there is no need to change the settings of protection devices for different operation conditions. INTRODUCTION Distributed Generation (DG) alongside the traditional generation is implemented as an appropriate alternative to supply consumers. Usually, DGs are connected directly to distribution feeders and their integration in the distribution network can result in the micro-grids concept [1]. A micro- grid is a part of a distribution system, which contains a few distributed energy resources (DER). The micro-grid can be isolated from the utility and continuous working in an island mode [2]. Traditional distribution networks have a radial and unidirectional topology. The protection system of these networks is based on the time and current coordination of overcurrent protection devices affected by DGs [3]. The protection system of distribution networks contains time inverse overcurrent devices including relays, reclosers and fuses. The coordination of these devices is the most important challenge for the protection system. DGs affect the performance of protection devices and can cause the protection system maloperation as follows:  Undesired trips [4]  Overcurrent protection devices underreach [5]  Undesired islanding [6]  Loss of coordination including relay to relay, fuse to fuse and fuse to recloser  DGs undesired outages In order to overcome these problems, some recent works are presented. Traditional protection will be subjected to a few new developments. The first and simple one is changing all protection devices and their settings which is so costly and economically irrational. There is no tendency to this solution. Also, this proposal is rejected because the protection devices settings should be changed for each generation condition and the replacement of devices is not feasible [7]. Another alternative solution is the application of the Fault Current Limiter (FCL) in series with any DG. Whenever a fault occurs, the FCL impedance increases so that the DG fault current can be limited. Thus, DG has no effect on the short circuit currents and the protection system can operate the same as the traditional one [8]. The fault location is used to fault clearing as discussed in [9]. Finally, as an acceptable and available alternative solution, the adaptive protection schemes are widely noted in recently works [10]. These protection schemes are based on the local or non-local information. The adaptive local protection updates protection devices settings based on the local information, but non-local information based adaptive methods gathers information through the smart grid infrastructures from all over the power grid. In this paper, it is focused on an adaptive method based on wide area measurements. In the proposed method, an adaptive protection scheme compensates the underreached fault currents seen by overcurrent protection relays. In the smart grid based proposed method, there is no need to change the settings of protection relays for different operation conditions because this solution uses an online compensation for the DGs impact on the overcurrent protection system. Actually, the currents seen by relays are increased as much as DGs decrease them. Thus, the fault currents seen by relays are the same as the case with no DG. The compensation depends to fault type which is detected based on available works [11]. The Compensation algorithm is adaptively selected based on the detected fault type and fault location. As will be presented in the following sections, the principles of compensation are mathematically discussed and the analyses is implemented for two most important scenarios (three phase to ground and single phase to ground faults) for different fault location and DGs condition. The effectiveness of the proposed method is presented based on PSCAD/EMTDC simulations. PRINCIPLES AND SIMULATIONS The underreach phenomenonon occurs in grid connected micro-grids. In island mode, utility does not supply the