Abstract-- Network reconfiguration is a switching action process for altering the distribution network structure. It is an efficient method for line loss reduction in power systems and though uncommon, it can also be employed for voltage sag mitigation. In this paper, a method for improving bus voltage magnitude during voltage sag is presented. It is done by applying network reconfiguration to the exposed weak area in distribution systems. In the process of reconfiguration, genetic algorithm with a new encoding method is used to maintain the radial structure of distribution network while reaching the optimal solution. The simulation results show that the proposed method is efficient and feasible for improving the bus voltage profile during voltage sag. The proposed method may assist utility engineers in taking the right decision for network reconfiguration. Index Terms—Voltage sag, distribution system and power quality. I. NOMENCLATURE A nomenclature list is: N bus System buses number V source Main source voltage V pcc Voltage magnitude of substation bus as point of common coupling between source and fault location. V pcc1 Voltage magnitude of substation bus after reconfiguration. Z s Theveninn’s impedance behind the source Z f is Fault impedance Z i Line impedance of the feeder i II. INTRODUCTION OLTAGE sag is defined as a decrease in rms voltage magnitude between 0.1 and 0.9 pu. at the power frequency for durations of 0.5 cycle to 1 min. [1]. Voltage sag, similar to other power quality phenomena, should be treated as a compatibility problem between equipment and power supply. When installing a new piece of equipment, a customer needs to compare the equipment sensitivity with the performance of the supply. Currently, a lot of research is under way to solve the problem of voltage sag in distribution systems. Most of these research works focus on installing voltage sag mitigation devices [2]. Other research works focus on improving the immunity of customer equipment by custom devices developed to improve the voltage sag ride through capability [3]. Some researchers deal with utility efforts in finding feasible solutions to mitigate voltage sag problem. Since power system faults are considered as the main cause of voltage sags, utilities try to prevent faults and modify the available fault clearing practices in power systems. Network reconfiguration was proposed in [4] as a voltage sag mitigation method by using feeder transfer switches in power distribution systems. Switches at sectionalizing points of a distribution network are used to find the weak points during voltage sags and transfer the weak customers to other sources areas [4]. Actually, voltage sag assessment at a particular site in the network consists of determining the frequency of sags of specified sag magnitude and duration over a period of interest [5]. It is also dependent on the utility fault performances, the way the fault effects propagation of disturbance in the system, and the customer’s service quality requirements [6]. For the assessment, voltage sag characteristics can be accurately reproduced by means of a time-domain simulation tool, and stochastic prediction. The random nature of the voltage sag causes [7, 8, 9 and 10] could be incorporated in the mitigation process. A voltage sag mitigation method was developed by means of a series of utility strategies implemented for a period of 10 years and upgraded on the basis of actual data during that period [11]. In this paper, a new network reconfiguration strategy is presented for voltage sag mitigation. Based on voltage sag propagation analysis, the exposed weak area in a distribution network is initially identified. Then the size of the exposed weak area to a specific voltage sag is reduced by network reconfiguration using the genetic algorithm (GA) optimization tool. A new encoding technique to generate switching string for radial structure restoration is developed to improve the GA process. Based on the new network reconfiguration strategy, the weak areas in distribution systems can be placed as far away as possible from the main source while maintaining the main properties of the distribution system operation. III. OPTIMAL NETWORK RECONFIGURATION Since the idea of this work is to utilize optimal network reconfiguration for voltage sag mitigation, a brief review of the network reconfiguration principles is first presented. It is Voltage Sag Mitigation in Distribution Systems by Using Genetically Optimized Switching Actions Nesrallh Salman, Azah Mohamed, Hussain Shareef Department of Electrical, University kebangsaan Malaysia, Selangor, Malaysia nesrullahsalman@yahoo.com, azah@eng.ukm.my, hussain_ln@yahoo.com V The 5th International Power Engineering and Optimization Conference (PEOCO2011), Shah Alam, Selangor, Malaysia : 6-7 June 2011 978-1-4577-0353-9/11/$26.00 ©2011 IEEE 329 978-1-4577-0354-6/11/$26.00 ©2011 IEEE Downloaded from http://iranpaper.ir http://www.itrans24.com/landing1.html