The electrical insulation design is important for high-Tc superconducting (HTS) cable because the cable is operated in a medium voltage environment. For the insulation design of HTS cable, it is necessary to investigate the ac, impulse breakdown, and partial discharge inception stress of a liquid nitrogen/polypropylene laminated paper composite insulation system. These results were used to design the electrical insulation of 22.9-kV-class HTS cable in Korea and cable was manufactured. A manufactured mini-model HTS cable was evaluated for ac withstand voltage, impulse withstand voltage, breakdown and dielectric tangent loss (tan [delta]). From these tests, the cable has satisfied the standard technical specification of KEPCO in Korea. The breakdown voltage was 110 kV. Index Terms--AC withstand voltage, dielectric tangent loss, high-Tc superconducting (HTS) cable, partial discharge inception stress.