Aging and Degradation Studies in Crosslinked Polyethylene (XLPE)

Abstract

Crosslinked polyethylene (XLPE) is widely used in power cable insulation because of its excellent dielectric characteristics, physical properties, thermal stability and chemical resistance. In spite of its advantageous features, the chemical and physical properties of XPLE change irreversibly changes with time as well as with exposure to electrical, thermal, mechanical or chemical stress conditions. These changes eventually lead to degradation and eventually failure of insulation cables. This chapter discusses the thermal, mechanical, electrical and environmental factors that influence aging and degradation in XLPE. The causes, mechanism and consequence of degradation and breakdown due to electrical and water treeing and its dependence on influencing factors like partial discharge, charge carriers, electrical and mechanical stress, temperature, impurities, etc. are discussed. The chemical degradation and thermal degradation in XLPE due chain scission, depolymerization, crosslinking oxidation and/or hydrolysis are explained along with the influencing factors. Aging, the irreversible change in properties of XPLE arising from changes in its physicochemical structure under the influence of various environment affects the operational life of cable insulation. The effect of thermal and radiation aging on dielectric and structural properties of XLPE is reviewed.