Effect of Dispersion on PD Pulse Propagation in Shielded Power Cable

High frequency attenuation and dispersion affect partial discharge detection and location in shielded power cables. The effect of high frequency attenuation is well understood through both measurement and computation, which cannot be said of dispersion. The electromagnetic propagation velocity as a function of frequency in concentric neural distribution cable has been computed from measured material properties, from which the dispersion deduced. The computed dispersion is in reasonable agreement measurements in the literature. The effect of dispersion on PD pulse propagation has been evaluated, including coupling between dispersion and high frequency attenuation, which are both functions of the same material parameters. The analysis indicates that dispersion causes a Gaussian PD pulse (at the source) to evolve into an asymmetric shape with faster rise than fall. The difference in pulse peak time of arrival with and without dispersion has been computed numerically, and a simple analytical basis for predicting this offset has been developed.