Dielectric Characteristics of Laminated Paper and Polymer Sheets Used for Lapping Dielectric Structure at 77 K

110 kV cold dielectric high temperature superconducting (HTS) cable has been developing in China. Generally, the lapped dielectric structure is adapted for cable body, so dielectric characteristics of dielectric sheets are very important. Polyimide, Polypropylene laminated paper (PPLP) and polyimide and poly tetra fluoro ethylene (PTFE) are widespread dielectric sheet materials for HTS equipments with lapped structure. In this paper, the lightning impulse dielectric strengths of three materials under tensile statuses are tested by a special electrode system. The experimental results are processed by method of Weibull plot. As a result, the impulse dielectric strengths of all three materials have good adaptive capacity for tensile stresses in liquid nitrogen. The impulse dielectric strengths of polyimide are highest of three materials under normal using stresses. The AC dielectric strengths of three materials are also concluded from previous papers. Combining experimental results, data in previous papers and design methods related, the multi-layered dielectric thickness and layers of PPLP used for 110 kV cold dielectric HTS cable body are designed.