Important key technologies of high-$T_c$ superconducting (HTS) transformer may include the HTS wire technology, bushing technology, cooling technology, AC loss, reduction technology, large current technology, and cryogenic temperature insulation technology. From among others, the cryogenic temperature insulation technology may be specifically a core technology for ensuring reliability for the smaller size, stability, economic efficiency, and power supply of a transformer. Therefore, the electric insulation technology of a superconducting transformer should be prerequisite. Such relevant studies are ongoing, but still, they are very insufficient for establishing the cryogenic insulation technology as of yet. Therefore, this paper simulated HTS transformer applied with continuous transposed conductor (CTC), which has been studied as a way of reducing AC loss. Also, the paper analyzed the insulation configuration of HTS transformer and bushing, and, accordingly, reviewed various characteristics of insulation breakdown out of liquid nitrogen. Thus, the paper constituted insulation database, and it is going to design the insulation of a transmission class HTS transformer and bushing.