Performance evaluation of XLPE materials for 90°C HVDC applications

The aim of this study is to understand present limitations of current extruded XLPE materials for HVDC applications and develop a new XLPE to meet higher operation temperature requirements. Measurement of DC conductivity of several XLPE compositions (including standard XLPE, commercially available HVDC insulation and a newly developed XLPE for DC application) was performed on hot pressed plaques. The impact of crosslinking byproducts on the apparent conductivity has been investigated through samples with different levels of peroxide subjected to 24-hour conductivity tests before and after degassing. It was confirmed the retention of the majority of byproducts during this 24-hr evaluation, while over 90% are removed by a degassing protocol. It was also confirmed a degassing treatment does reduce the apparent conductivity. Additional data compared properties of a new fully crosslinked material solution targeting 90 °C HVDC applications and the commercially available solutions. Improved breakdown strength at elevated temperatures and desirable conductivity are demonstrated. Successful evaluations of full-size cables tested at 90 °C with joints is discussed.