Preliminary Experimental Investigation of the Effect of Superimposed Switching Impulses on XLPE-insulated HVDC Cables

Switching impulses superimposed onto rated DC voltage are a particularly-challenging kind of overvoltage which is applied to HVDC cable systems both in service and during qualification tests in the laboratory. This paper aims at a preliminary experimental study of the effect of Superimposed Switching Impulses on XLPE-insulated HVDC cables. It studies the effect of aging 0.15-mm XLPE specimens by applying a sequence of Superimposed Switching Impulses, defined according to CIGRÉ technical Brochure 496. As illustrated in this paper, only preliminary results have been obtained so far from these tests. Such results show an increase in the conductivity in the aged specimens compared to non-aged specimens. An interfacial relaxation phenomenon is also noticed at low frequencies; however, no significant dipolar polarization can be noticed under the above-mentioned aging conditions.