Aspects interpreting PILC cables' diagnostic parameters measured at different test voltage frequencies

Abstract

Medium voltage cables with oil impregnated paper insulation are still to be found numerously in many distribution grids. Many of these cable lines have been installed dozens of years ago, so there is a strong interest in getting an overview on the condition of the insulation of these cables. For this purpose, a long lasting aging experiment has been performed in the laboratory, where multiple cables of all kinds of different service histories have been artificially aged in an accelerated way by means of thermal and electrical stresses and combinations of these. During this process, the diagnostic parameters like dissipation factor and partial discharges have been continuously recorded at power frequency (50 Hz). The gathered data from the laboratory experiment serves as basis for field measurements, which are being carried out. The necessary measurement equipment has been engineered and integrated in a cable test van. This consists of two different voltage sources (50 Hz and 0.1 Hz), a measurement unit on top of a high voltage divider and a computer based control and data acquisition system. A correlation of these two measurements promises enhanced diagnostic relevance for the condition assessment of medium voltage networks. Based on numerous field measurements carried out in the local distribution network, new approaches in the correlation of measurements at two different frequencies of test voltages are to be created. This includes a reference to other already well established methods. However, the reference to other methods needs to be verified in a more detailed way.