Power quality disturbances due to interaction between AC and DC traction systems

The growing complexity of the AC and DC traction systems in terms of both new technologies and automation requires a careful control of the power quality disturbances they cause. In some cases-as in Italy-both traction systems operate in the same transmission network area, so that the power quality problems have become much more complex because of the interactions between the two systems. In this paper the problem of a careful evaluation of these interactions is analyzed. The study is performed with reference to a mixed (2×25 kV-50 Hz) and 3 kV DC traction system, similar to the one adopted for the Italian railways, and by using computer simulations developed by means of Matlab power system blockset. Waveform distortions and voltage unbalances are assessed and suggestions are given to solve the interaction problems. (6 pages)