Anomalous Distorsion of Travelling Waves in Helical Transformar Windings

Setting up the milti-conductor transmission line model of a helical winding for an analysis of the very fast electromagnetic transients shows that experimentally fond anomalous distorsion of the trawelling waves come from reflections of the guided waves on the voltage jump between the edges of the open electrostatic screen. These reflections produce a dispersion of the velocities of the aksial travelling waves. Taking the voltage jump distributed over the screen, the guided waves reflections are replaced by an equivalent velocity dispersion. Results of the modal analysis and the method of characteristics are in good agreement with the experiments.