Surface potential decay on material samples taken from in-service aged HVDC silicone rubber composite insulators

Surface potential decay characteristics of specimens extracted from in-service aged and reference HVDC composite insulator sheds are reported and analyzed in this paper. In the experiments, surfaces of the insulator samples were charged by dc corona and the decay was recorded utilizing a non-contact technique. In addition, surface and bulk conductivities of the specimens were determined and used for analyzing by means of computer simulations their impact on the potential distribution profiles and its decay. Based on the performed experiments, trap density distributions, mobility of charge carriers and field dependent bulk conductivities are deduced for the investigated samples with the aim to evaluate the ageing severity.