International Journal of Advances in Engineering & Technology, Nov 2011. ©IJAET ISSN: 2231-1963 89 Vol. 1, Issue 5, pp. 89-95 A NOVEL DESIGN FOR ADAPTIVE HARMONIC FILTER TO IMPROVE THE PERFORMANCE OF OVER CURRENT RELAYS A. Abu-Siada Department of Electrical and Computer Engineering, Curtin University, Perth, Australia ABSTRACT Due to the ever-increasing in non linear loads and the worldwide trend to establish smart grids, harmonic level in the electricity grids is significantly increased. In addition to their impact on power quality, harmonic current can have a devastating effect on the operation of over current relays as they are designed to operate efficiently at the fundamental frequency. The distorted waveform will affect the operation of the over current rely and may cause the relay to trip under normal operating conditions. To solve this problem, power passive and active filters are employed to eliminate the harmonics and purify the relay operational signal. Passive filters are not cost effective choice to solve this issue. On the other hand, active filters are more complex and need proper and complicated controller. This paper introduces a new and simple approach for adaptive filter design. This approach is economic, compact and very effective in eliminating harmonics in the grid. It can be easily attached with any protective relay to improve its performance. Application of this design to improve the performance of over current relays in the IEEE-30 bus system with heavy penetration of non-linear loads is investigated. KEYWORDS: Over current relay, harmonic filters, IEEE-30 bus system I. INTRODUCTION Most of the litratures reveal that the performance of relays in presence of harmonic currents is not significantly affected for total harmonic distortion (THD) less than 20% [1]. As there has been a tremendous increase in harmonic sources in the last few decades, harmonic levels of 20 % and higher are expected. Moreover overcurrent relays have to operate with current transformers which may saturate and distort the current waveform causing a relay to trip under conditions which would normally incur smooth running of the system without interruption [1-5]. Current transformer saturation may occur due to the presence of harmonics which may cause a current transformer failure to devliver a true reproduction of the primary current to the relay during fault conditions and thus may cause undesirable operations [6-8]. Electromechanical relays are nowadays considered obsolete in most of developing countries, however they are still used in some places. Electromechanical relays time delay characteristics are altered in the presence of harmonics. Another type of relays that is affected by harmonics is the negative-sequence overcurrent relay which is designed to specifically function with the negative sequence current component and it cannot perform upto its standard when there is a significant waveform distortion. Digital and numerical relays usually have built-in filters to filter out harmonics and thus are less prone to maloperation [9]. Active power filters which are more flexible and viable than passive filters have become popular nowadays [10]. However, active power filters configuration is more complex and require appropriate control devices to operate [11]. This paper introduces a novel active filter design that is compact, simple and reliable. Application of this design to improve the performance of over current relays in the IEEE-30 bus system with heavy penetration of non-linear loads is investigated.