Transmission Model of Partial Discharges on Medium Voltage Cables

Medium voltage cables are poor transmitters of signals with high frequency spectrum such as partial discharges. The propagating signals are strongly attenuated and distorted depending on the transmitted distance. In order to understand this process, this article provides a model to simulate the transmission of such signals on medium voltage cables. Compared to earlier approaches, this model does not neglect the wave character of the high frequency signals. Therefore, to describe the signal transmission, a comprehensible solution of the telegrapher's equations is provided. To work with this solution, the propagation constant of the medium voltage cable used must also be known. This propagation constant is calculated on the basis of the individual cable layers, considering all ohmic and dielectric losses. In contrast to previous methods, all primary line constants are modeled frequency dependent. The final transmission model is able to predict the spectrum of a transmitted signal at any distance from its origin. Validation measurements show that prediction and measurement agree with good accuracy. A possible application of the developed model is the investigation of the transmission of partial discharges on medium voltage cables. This model is probably also suitable for high voltage cables.