A Multi Objective Genetic Algorithm for Weighted Load Shedding M. Tarafdar Hagh Electrical and Computer Engineering Faculty University of Tabriz Tabriz, Iran tarafdar@tabrizu.ac.ir S. Galvani Electrical and Computer Engineering Faculty University of Tabriz Tabriz, Iran s-galvani@tabrizu.ac.ir Abstract— Load shedding during contingency conditions is an efficient solution to alleviate transmission lines over loadings. Minimization of total load shedding considering loads importance has great significance in these situations. This problem requires simultaneous optimization of two or more conflicting objectives, such as minimization of the total load shedding, minimization of transmission lines over loadings and voltage violations minimization. The objectives are in conflict since the improvement of one of them leads to the deterioration of another. A modified version of Non-Dominated Sorting Genetic Algorithm (NSGA-II) is used as an effective optimization tools for solving the minimum weighted load shedding problem during contingency conditions. Also relation between transmission lines overloading and amount of load shedding is surveyed. IEEE 14 bus test system is used as a study case and results are discussed. Keywords-: Contingency, energy not supplied, generation rescheduling, load shedding, NSGA-II. I. NOMENCLATURE BUS N number of buses, G N number of generators, 0 normal state indicator (superscript), p contingency state indicator (superscript), i bus index (subscript), i α importance factor of load in i th bus, 0 Di P load active power demand in normal state, p Di P load active power demand in contingency state, 0 Gi P active power generation in normal state, p Gi P active power generation in contingency state, p L P active power losses in contingency state, 0 Di Q load reactive power demand in normal state, p Di Q load reactive power demand in contingency state, 0 Gi Q reactive power generation in normal state, p Gi Q reactive power generation in contingency state, p L Q reactive power losses in contingency state, min Gi P minimum active power generation, max Gi P maximum active power generation, min Gi Q minimum reactive power generation, max Gi Q maximum reactive power generation, min Di P minimum amount of load which must be supplied, ij S apparent power flow from bus i to j, max ij S apparent power limit of line, min i V voltage low limit, i V i th bus voltage, max i V voltage up limit. II. INTRODUCTION The emergency states may occur in a power system as a consequence of a sudden increase of system load, the unexpected outage of a transmission line, a generator or failure in any of the system components. This state may result in some problems such as lines overloading, under frequency, voltage collapse and angle instability [1]. Generation rescheduling and/or load shedding can be used to overcome the mentioned problems, effectively. Load shedding schemes have become quite important in present day systems, where there is a lack of adequate spinning reserve margin or a shortage of tie line capacity to make up the lost generation [2]. Optimal load shedding has been taken into consideration from various aspects and by means of various techniques in many papers. It is a common practice for utility companies to perform load shedding by using under frequency relays to disconnect the predetermined load when the frequency drops below set values [3]. A load shedding method which considers the frequency decay rate is also applied for utilities in [4]. Proceedings of ICEE 2010, May 11-13, 2010 978-1-4244-6760-0/10/$26.00 ©2010 IEEE