AC and Impulse Dielectric Strength of Polymer Materials Under Tensile Stress at 77 K

The performance of dielectric materials has an important effect on influencing the service life of the electric equipments. The dielectric sheets used for superconducting devices usually endure several lapping tension when lapped on the conductor, so the AC and impulse dielectric strengths of polymer sheets under tensile status are important to dielectric design. In this paper, a special electrode system was designed to measure the AC and impulse breakdown voltages of polyimide and poly tetra fluoro ethylene (PTFE) sheets under tensile status both in air at normal temperature and in liquid nitrogen at 77 K. The test data are processed by the method of Weibull plot. As a result, the AC dielectric strengths of polyimide sheets in liquid nitrogen at 77 K increase significantly as the tensile stresses increasing, the most amplitude achieves 29.16%. The impulse dielectric strengths of two polymer sheets all decrease little as the tensile stresses increasing. The AC and impulse dielectric strengths of polyimide under tensile stress are significantly higher than PTFE in liquid nitrogen at 77 K, Polyimide has good dielectric characteristics under tensile status in liquid nitrogen at 77 K.