A Numerical Analysis of the Harmonic Impedance in a Medium Voltage AC Network

Under the current conditions of the increasing harmonic pollution of three-phase distribution networks, the correct determination of the harmonic impedance of a network in a section or in a consumer bus becomes more and more important. This is due to the importance of harmonic impedance used as a tool of analysis and basing of the solutions required to increase the network performance, including the power quality delivered to consumers. The article uses the results of the numerical analysis applied in a case study performed for a medium voltage distribution network, like a real one, in order to demonstrate that the underground electrical lines of relatively long lengths significantly influence the harmonic modelling of the network and the correctness of the harmonic impedance values. In addition, the model of such a line must consider the distributed equivalent parameters, which becomes an imperative requirement when seeking to obtain the correct values for the equivalent harmonic impedance of the network.