The frequency characteristics of medium voltage distribution system impedances Liviu Emil Petrean * , Mircea Horgoş ** , Olivian Chiver *** * Department of Electrical Engineering, North University of Baia Mare, Faculty of Engineering, Dr. Victor Babeş str., 62/A, 430083 Baia Mare, Romania, E-Mail: petreanliviu@yahoo.com , * , mhorgos@ubm.ro ** , olich@ubm.ro *** Abstract – In this paper we present the frequency characteristics of impedances involved in the electrical equivalent circuit of a large medium voltage distribution system. These impedances influence harmonics distortions propagation occurring due to the nonsinusoidal loads. We analyse the case of a 10 kV large urban distribution system which supplies industrial, commercial and residential customers. The influence of various parameters of the distribution network on the frequency characteristics are presented, in order to assess the interaction of harmonic distortion and distribution system network. Keywords: frequency characteristics, harmonics distortions. I. INTRODUCTION In recent times there have been considerable progress in the penetration of modern technology that uses power electronics. This led to the appearance of other nonlinear loads, which absorb nonsinusoidal large currents and create harmonic voltages throughout power system. These nonsinusoidal consumers produce poor power quality to both themselves and other consumers . The purpose of harmonic analysis of electric networks is to determine the distribution of nonsinusoidal currents in the network. In harmonic analysis, the interaction between nonsinusoidal currents and network determined by the frequency characteristics of network impedances is extremely important. For a correct harmonic study eight basic rules [3] containing necessary to be met, one being that of that analysis are contained all the load substation fueled by the same transformer substation HV / MV. Usually it is considered that the analysis is good when taking into account 10-12 loads substation for a power feeder. In our case we considered a 10 kV medium voltage distribution system, with simplified equivalent electrical diagram shown in Fig.1. The equivalent circuit contains a number of n = 107 loads substations of 10/0.4 kV supplied by 36 feeder of 10 kV. There are 10 types of loads substations with power transformer rated in range 160 kVA - 2x1000 kVA. Fig. 1 Equivalent circuit of medium voltage distribution system 76