Highly dynamic and distorting loads like electrified trains have complex power flow schemes, with active power not exclusively assigned to the fundamental (either dc or ac). The estimate of energy consumption shall thus cover the most relevant power spectral terms, in order to adequately track and quantify the active power flow. This work investigates the dynamic behaviour of two distortion power indexes calculated with the pantograph quantities, voltage and current, using experimental recordings performed over some European railway networks (3 kV dc, 2x25 kV 50 Hz and 15 kV 16.7 Hz). The results show the relevance of a reduced set of components and the strong correlation with train operating conditions. The relevance is significant for ac systems, and in particular 16.7 Hz systems.