International Journal on Electrical Engineering and Informatics - Volume 2, Number 3, 2010 204 An Improved Method for Determining Contribution of Utility and Customer Harmonic Distortions In A Power Distribution System M. Farhoodnea 1 , Azah Mohamed 2 , H. Shareef 3 , and R. A. Jabbar Khan 4 1,2,3 Department of Electrical, Electronic and Systems Engineering, University Kebangsaan, Malaysia 4 Rachna College of Engineering and Technology, Gujranwala, Pakistan masoud702001@yahoo.com Abstract: This paper presents an improved method for determining the share of harmonic distortion generated by utility and customer in a distribution system. The method is based on a Norton equivalent circuit to represent the whole system, modeling the customer side with RLC components by using measured voltage and current at the point of common coupling (PCC). The proposed method evaluates the contribution of harmonic voltage and current distortion, which may appear from utility and customer sides of the system. Several case studies have been made to verify the accuracy of the method in determining the share of utility and customer harmonic distortions. Results showed that the proposed method can accurately determine harmonic contributions of utility and customer sides for measurement made at the PCC. Keywords: Harmonic distortion, harmonic source location, power quality. 1. Introduction The proliferation of electronic nonlinear devices such as adjustable speed drives, inverters and personal computers in the past three decades has caused severe harmonic distortion in power distribution systems. These harmonics distort fundamental voltage and current waveforms and have many negative effects on power systems. It may cause resonance problems, overheating in capacitor banks and transformers, false operation of protection device and reduction of power quality which eventually increases the maintenance costs of the system. Before taking the necessary harmonic control measures, it is important to know who is responsible for the cause of harmonic distortion. Several methods have been proposed to identify the location of harmonic sources so as to determine whether the source is from the utility and customer side. One of the earlier methods for harmonic source localization is based on the real power direction in which the side that produces greater harmonic power is responsible for harmonic distortion [1]. However, the accuracy of the real power direction method is less than 50% and therefore the reliability of the method is questionable. An incentive-based method for harmonic source localization is presented in which the method is found to be impractical because it requires knowledge of actual impedances of the system for its calculation [2-3]. Other methods for harmonic source localization are such as the critical impedance method [4]and voltage magnitude comparison method [5] which requires implementation of switching tests for obtaining the harmonic impedance. Hence, the switching tests do not allow its application in practical power systems. A recent method for harmonic source localization which is called as the harmonic vector method (HVM) [6] uses resistance as the reference impedance for modeling the customer side and uses the equations in [2-3] for determining the harmonic contribution of utility and customer. However, modeling the customer side by an equivalent resistance may introduce inaccuracy in calculating the harmonic contribution factors especially in cases where loads contain inductive elements such as motors. In [7], the total harmonic distortion (THD) is used for finding the share of harmonic distortion from utility and customer sides. The disadvantage of this method is that the THD value cannot show the variation of contributions caused by changes in phase angle of harmonic Received: March 25, 2010. Accepted: July 24, 2010