The paper presents the load currents of two tram traction substations. These substations power lines with different characteristics of tram traffic. Loads were analysed for one working day and one public holiday. Attention was paid to the differences and similarities in the current waveforms. The demand level was assessed, with respect to the rectifier units in the substations. The time series method was used, inter alia, and chiefly an analysis of the characteristics of autoregression and partial autoregression was carried out, to act as a diversity index with respect to the nature of variability in the analysed traction load currents.