Thermal Ageing of XLPE Cable Insulation under Operational Temperatures – Does It Exist?

Abstract

Thermal ageing of power cables may cause premature breakdown if the cables are operated at elevated temperatures, a relation usually described by Arrhenius’ law. The purpose of the present study is to investigate if any significant ageing takes place under normal operational temperatures. The investigation shows that thermal degradation at these comparably low temperatures is hardly reported and seems not to be of practical concern to transmission system operators. This may be the result of a conservative mind-set during the dimensioning of power systems, here in the case of power cables, which means that the lines are generally lightly loaded. Based on the literature found or, to be more precise, on the literature not found it seems to be very difficult to determine that thermal ageing should be problematic for operational power cables at all, in particular as compared to laboratory investigations at very high temperatures, where thermal ageing clearly takes place. To this conclusion contributes the fact that failure statistics do not correlate failures with severity of loading, and that the laboratory studies (which mosly conclude thermal ageing to be problematic) exposes the materials to unrealistic conditions.