684 Int. J. Energy Technology and Policy, Vol. 5, No. 6, 2007 Online condition monitoring of electrical power system imbalance Saleh Al-Jufout Faculty of Engineering Tafila Technical University P.O. Box (92), 66110, Tafila, Jordan E-mail: drjufout@yahoo.com Abstract: Symmetrical components are of great importance in many applications in electrical power systems, such as power protection and condition monitoring. This paper presents a computer-based algorithm for online symmetrical components estimation. The proposed algorithm uses the samples of the phase variables (currents or voltages) to estimate the magnitude and phase angle of each phase phasor at each sampling instant, and then these estimated phase phasors are used to formulate the symmetrical components as phasors and time-domain functions as well. Then the identified symmetrical components are used for condition monitoring of the electrical power system. Test examples of different power-system unbalanced conditions are computed to validate the developed algorithm. Keywords: unbalanced condition; power system; protection system; digital filter; symmetrical components. Reference to this paper should be made as follows: Al-Jufout, S. (2007) ‘Online condition monitoring of electrical power system imbalance’, Int. J. Energy Technology and Policy, Vol. 5, No. 6, pp.684–691. Biographical notes: Saleh Abdel-Hamid Al-Jufout received his PhD in Electrical Power Engineering in 1997 from Donetsk National Technical University. In the same year he joined Al-Balqa’ Applied University; then in 2005 he joined Tafila Technical University in Tafila, Jordan. Currently, he is an Associate Professor at the Electrical Engineering Department of the Faculty of Engineering at Tafila Technical University. His research interests are in the mathematical modelling of electrical power systems, electrical machines and drives and their protection and control. 1 Introduction Computers initially used in electrical power systems for offline calculations (Alyyan et al., 2005), statistics, planning and forecasting (Al-Jufout, 2005) have quickly found their way into online applications. These applications involved time-critical processing and safety control tasks and proved the reliability of industrial digital-engineering techniques in the power system environment. The use of microprocessors enabled ever-simpler tasks to be performed at distributed locations and their use for protection and control was logically the next step (Ungrad and Wiszniewski, 1995). Copyright © 2007 Inderscience Enterprises Ltd.