Accelerated Life Test Fitting of Bi-Layer Insulations for HVDC Cable Accessories

Abstract

This paper is a first step to validate the IPM-Arrhenius life model put forward in the NEWGEN project from cable insulation to the insulation of accessories. Indeed, here the preliminary fitting of the model is trialed by means of Accelerated Life Test (ALTs) data obtained from bi-layer flat insulating specimens for the accessories of HVDC cables, prepared in the framework of the NEWGEN project. The bi-layer specimens consist of cross-linked Polyethylene (XLPE)/Ethylene Propylene Diene Monomer (EPDM), which aim at reproducing the behavior of the critical interface between the insulation of the cable and that of the accessories. Aim of the paper is to assess the performance of these dielectrics as a function of aging time in the presence of electrical and thermal stresses. This performance is essential for improving the reliability of HVDC cable system accessories. The outcomes of the paper denote a significant scatter of failure times, but 63.2th and 50th percentiles of failure times are strongly correlated with test fields and temperatures. Apart from one case, life exponent values are far greater than 10 (the reference value taken by Cigré Technical Brochure 852) which indicates a good ability of the tested cable accessory dielectrics to endure voltage, including the interface with cable insulation.