Evaluating the Non-sinusoidal and Non-symmetric Regimes from a Railway Supplying Substation

Single phase currents and voltages were acquired from a substation used to supply power lines for railway transport. Different operational contexts were addressed (variable types of locomotives and trains, some of them being simultaneously nearby the substation). Firstly an evaluation of the background noise was performed by using either the mean signal or a thrashing tree. Fast Fourier and Wavelet Packet Transforms were used to evaluate the harmonic spectra and the major types of Root Mean Square quantities. The computed THD revealed significant distortions of the analyzed waveforms. The results yielded by different methods were compared. A good convergence of methods was reached in most of the cases and explanations for the differences recorded for the rest are proposed. Instantaneous values of the fundamental harmonic and global distortions were evaluated with the Stationary Wavelet Transform, allowing the evaluation of maximum/RMS values for currents/voltages to be injected when using active filtering.