Electric characterization of films peeled from the insulation of extruded HVDC cables

During the manufacture of cross-linked polyethylene cables the insulation material experiences temperature protocols which vary with the radial position. The time-temperature scheme has, however, a major influence on microstructure of the insulation and chemical composition of the peroxide by-products. Thus it could be expected that the electrical properties of the insulation would vary with the spatial position within the cable. The purpose of the present work is to identify if there is a difference in the DC-electric properties at different radial depths of an extruded high voltage direct current (HVDC) cable insulation. In this study, DC electrical resistivity and DC breakdown strength measurements were carried out on samples taken from the insulation regions close to the inner and outer the semi-conductive screens. The obtained results show no significant difference of the investigated electric properties between the two regions. Hence, the DC-electric properties of the bulk insulation are constant within the accuracy of measurements.