Qualitative analysis of PEA and TSM techniques on a 200kV extruded cable during a VSC ageing program

This paper presents results from GE Grid solutions' Cable Ageing Facility where two complementary, state-of-the-art, on-line space-charge monitoring techniques are deployed to assess the health of a full size HVDC extruded cable. The bespoke on-line space charge probes are installed on the same cable length that is subjected to identical electrical and thermal stress profiles during the ageing programme. The cable is rated at 200kV and is subjected to a VSC ageing programme according to CIGRE TB 496. One of the probes uses the Thermal-Step-Method (TSM) and the other probe uses the Pulse-Electro-Acoustic (PEA) technique. The TSM technique provides the average charge distribution along a cylindrical section of the cable of around 50 cm while the PEA technique provides the charge distribution of a hair thin cable insulation section. The data obtained from the two techniques is compared qualitatively in order to understand charge distribution characteristics of different sections of the cable under test. Despite the fundamental difference in methodology of the TSM and PEA techniques qualitative analysis of the results suggests that there is an agreement in space charge distribution.