Comparison of VLF and power frequency measurements for diagnostic analysis of medium voltage PILC cables

Summary

Medium voltage cables with oil impregnated paper insulation are still to find numerously in many distribution networks. As many of these cables have been installed partially multiple decades ago, there is a strong need to get an overview on the condition of the insulation of these cable lines. To this end, a long term aging experiment has been performed in the laboratory, wherein dozens of single cables 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 discharge behaviour were continuously recorded at power frequency (50 Hz). This built-up database is to serve as basis for field measurements, which are to be carried out. The necessary measurement equipment has been developed and integrated in a cable test van. This includes two voltage sources (0.1 Hz and 50 Hz), a mobile measurement unit together with a high voltage divider and a computer-based control and data acquisition system. The dissipation factor measurement at very low test voltage frequencies (VLF, in this case 0.1 Hz) is a well-established method for cable diagnostics. The next step will be the establishment of a correlation between the field-measured values (0.1/50 Hz) and the recordings in the laboratory experiment (50 Hz). The 50 Hz measurements thereby fulfil two purposes: they may allow a direct interpretation by analysing the behaviour over different voltage steps and they may also be seen as a link between the field-measured VLF-measurements and the results of the laboratory experiment. The general feasibility of this correlation will be discussed based on exemplary results of the field measurements.

Additional informations

Authors

BRKANIC

Keywords

Diagnostic method, dissipation factor, PILC, VLF, asset management