HARMONIC FILTER FOR POWER QUALITY IMPROVEMENT Liana CIPCIGAN, Mircea CHINDRIS, Adrian RUSU, Khalid RASHED Technical University of Cluj-Napoca, Romania Electrical Power Systems Department Gulf Extrusions Co (L.L.C) Dubai – Jebel Ali, United Arab Emirates Abstract: Harmonic currents in particular are receiving more attention as a critical power quality concern, with an estimated 60 percent of electricity now passing through nonlinear loads. This paper shows the principles of how the harmonic filter can be used in radial medium voltage distribution system as a solution to solve harmonic current problems. The well-developed graphic facilities available in an industry standard power system package, namely PSCAD/EMTDC, are used to conduct all aspects of model implementation and to carry out extensive simulation studies. Keywords: Power system, Non-linear load, Harmonic distortion , Harmonic filter, Power quality, PSCAD/EMTDC simulation. 1. INTRODUCTION The last decade has seen a marked increase on the deployment of end -user equipment that is highly sensitive to poor quality control electricity supply. Several large industrial users are reported to have experienced large financial losses as a result of even minor lapses in the quality of electricity supply. Harmonic distortion is today present in almost all power systems and the distortion level varies much from system to system and at different voltage levels. The main source of the distortion is formed by non- linear loads connected at low voltage; mainly rectifiers. The large decrease of the total current distortion, at higher voltage levels, is due to the fact that nonlinear loads are mixed with linear loads (the fundamental total current increases), also that zero sequence harmonics are blocked by delta connected transformers. There is also an interaction between non-linear loads, mainly single and three phase connected at the same voltage level, which reduces the total current distortion. The decrease of the total voltage distortion is of course due to the decrease of the current distortion but it also depends on the higher ratio of the short circuit power and the rated power at higher voltage levels, compared to lower voltage levels. The voltage and the current distortion cause additional losses in power system components and in linear loads. The flow of the harmonic active power components supplying these losses, between different parts of the power system or different loads, depends on the configuration of the power system and the mix of loads. This power flow, at a certain point, can be positive, negative and sometimes it is not seen at all. Harmonic filters have been used as a solution to solve harmonic current problems and can be subdivided into two types: passive and active. Passive filtering is based on the series resonance principle (recall that low impedance at a specific frequency is a series -resonant characteristic) and can be easily implemented. Even with the potential cost of new capacitors, passive filtering still appears to offer the most cost effective solution to the harmonic problem at this time. 2. GENERAL CHARACTERISTICS OF THE HARMONIC DISTORSION IN POWER SYSTEMS 2.1. Voltage and current The first important characteristic of harmonic distortion in power systems is that the fundamental