Breakdown Characteristics and Electrical Life Time Evaluation of 525 kV EHVDC Cable Insulation at Different Temperatures

The extensive deployment of remote offshore wind power has gained considerable traction, wherein cross-linked polyethylene(XLPE) cables are preferred for their benefits, including straightforward structure, significant transmission capacity, and high temperature resistance. However, due to the harsh environment and operating conditions of submarine cable laying, the safe operation of HVDC submarine cables faces serious challenges. Hence, it is imperative to undertake studies focused on the breakdown properties and life index of ±525 kV DC submarine cables at different temperatures and thicknesses, in order to provide support for promoting the development of long-distance and high-capacity power transmission at sea. DC breakdown, impulse voltage breakdown, and DC step-stress tests were carried out on samples of different temperatures and thicknesses. The results indicate that as the temperature increases, The sample's DC breakdown strength and impulse voltage breakdown strength exhibit a declining trend, and an inverse power law describes the functional link between breakdown strength and thickness. The breakdown characteristics and electrical aging life index of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\pm 525$</tex> kV DC submarine cables were obtained through DC breakdown, impact breakdown, and gradient withstand voltage tests. The insulation of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\pm 525$</tex> kV DC underwater cables has aging life indices of 22, 20, 15, and 13 at 30, 50, 70, and 90°C, respectively. The test findings can offer support for the design of insulation structure and the lifespan evaluation of high-voltage direct current (HVDC) submarine cables.