| Abstract |
Frequency content of line currents due to electrical traction must meet predefmed limits. Generic criterias are signal frequency bands, amplitude and time limits. The most common analysis methods for demonstration of compliance are the Fast Fourier Transform (FFT) and bandpass filtering. While achieving good analysis results at steady. state conditions, both methods fail in the case of transient phenomena. Particularly on DC-lines, load or line voltage jumps that occur frequently require analysis methods v.hlch are better adapted to transients. Using synthetic data and real measurement data of a DC-line vehicle, the Berlin 8-Bahn, three different analysis approaches for line interference currents, FOURIER, BANDPASS and the new WAVELET analysis are compared. Gaining at least three different analysis
results for the same measurement data a comparison and evaluation of the methods is performed. It is obvious that FFT is not suited for investigation of transients due to averaging and poor time or vice versa frequency information. Bandpass filtering shows better time and selective frequency information but reacts on every big transient with oscillations which could be misinterpreted as a disturbing current Wavelet analysis combines time and frequency information, but frequency
resolution of the Morlet Wavelets used here is found to be poor. The comparison shows that further investigations in the
field of combined methods and more advanced Wavelet methods is necessary. |
