Study Regarding the Harmonic Currents Reducing in Electric Traction System Supply by Connecting Active Filters Using PSCAD-EMTDC Tool IOAN BACIU*, CORINA DANIELA CUNTAN*, RALUCA ROB * , CAIUS PANOIU * * Electrical Engineering and Industrial Informatics Department, Timisoara Polytechnical University, Faculty of Engineering Hunedoara, Revolutiei Street, no. 5, Hunedoara, cod 331115, Romania,{baciu.ioan, corina_c, raluca.rob, c.panoiu,}@fih.upt.ro Abstract: - This paper analyzes the effects that are obtained after connecting an active filter in a traction substation. The active filter command is made in function of the active and reactive power obtained using Clarke transformation. The active filter simulated in PSCAD is connected at 110kV three phase system using power transformers. The authors present in this paper the currents and voltages variation waveforms for the mono phased an three phased circuits of a DC traction locomotive. Key-Words: Active filter, active power, reactive power, voltage and current harmonics, harmonic distortion factor. 1. Introduction Active filters are power static converters that can accomplish various functions. Present filtering schemes permit the synthesizing of any current waveform that contains harmonic components of high orders at high power levels [1]. The electric energy consumer can choose in principle for one of the following solutions: abandons the equipments that absorb distorted current and invests in new equipments that contains circuits that makes the power system currents sinusoidal or invests in electric devices that keep the distortion level between imposed limits: active, passive or hybrid filters. Term active power filter is applying to many categories of electric power circuits that contain power semiconductors and passive elements for energy stockage – inductivities or capacitors. The filters functions can be various, depending on the application [2]. There are two possible configurations: balanced and non balanced loads. For balanced loads there are used three phase filter for harmonic elimination. For non balanced loads, there are used three mono phased compensator, but there are four arms structures (three phases and null). The disadvantage consists in the following: nul arm loading is harder the the other three. 2. Theoretical Issue In order to solve the problems of the proliferation of the harmonic generation equipments, the electric energy dealers tries to stimulate the important industrials consumers to act in conformity with the present standards. The tendency is strong enough to determine some equipment producers to include active filters in harmonics generation installations in order to improve power quality generation [3]. Parallel structure, presented in figure 1, of the filter connection has the largest distribution [4]. The active filter compensates the load harmonic currents that in other way would be injected in power system. Nonlinear load Shunt active filter Figure 1. Active filter in parallel connection. Depending on the structure and the command system, this topology has the possibility to compensate the reactive power and to equilibrate the power system. The filter conducts only the compensation current. This is an important advantage of parallel connection. In the same time there can be connected more filter unities in order to Proceedings of the European Computing Conference ISBN: 978-960-474-297-4 170