High voltage breakdown of solid epoxies at room temperature and in liquid nitrogen

With the development of high temperature superconductors (HTS) in flexible tape form, work has rapidly moved toward high voltage power applications such as HTS power cables, transformers, and fault current limiters. Generic to the design of these devices is the use of solid dielectric material that can hold off high voltages in combination with either vacuum or liquid nitrogen. Several types of epoxies have been screened by subjecting them to "dunk" tests in liquid nitrogen to determine which materials would not crack after immersion. Materials that survived the dunk tests were further tested for dielectric strength at room temperature and at 77 K. Stycast^® 2850 FT/24 LV catalyst was found to decrease slightly in strength at 77 K while the Araldite^® CY 5808/HY 5808 hardener and Stycast^® 2850 KT/11 catalyst significantly increased. These materials are found to follow a Weibull distribution.