Lab testing of external gas pressure cables and determination of different ageing states

In the last century external gas pressure cable systems with 64/110 kV operating voltage have proven to be a reliable way for the transportation of electrical energy in urban areas all over the world. The beginning of their development reaches back to the 1930s. The dielectric used in these thermally stable cables consists of a mass impregnated paper insulation that requires the absence of partial discharges as a prerequisite for continuous operation. In this contribution two test set-ups for advanced lab testing of external gas pressure cable specimens were established. Two specimens of different aging state were subjected to various electrical voltage levels and frequencies as well as different temperatures. Both dissipation factor measurement and partial discharge detection were applied simultaneously. Finally the specimens’ relationships between dissipation factor, partial discharge level, temperature, impregnation mass to paper ratio, water content and external gas pressure were discussed.