Insulation Characteristics of Polyimide as Insulation Material Used in Pancake Tape Coil Structure for Resistive-Type SFCL

Space utilization is very important for the application of a superconducting fault current limiter (SFCL) in a high-voltage power system. Accordingly, for efficient space utilization, a pancake structure in which superconducting tapes are wound into coils should be adopted. However, because neighboring windings are in direct contact with each other in a pancake structure, special measures must be taken to overcome high-voltage insulation safety problems. This paper proposes two methods: 1) lapping polyimide adhesive tapes on superconducting tapes; and 2) coating a very thin layer of polyimide on the surface of superconducting tapes. A comparison is made between the two methods. A special breakdown strength testing platform is manufactured. Using the platform, the breakdown strength and surface flashover voltage are tested. Considering that the edges of superconducting tapes are very sharp, the influence of pre-breakdown partial discharge on insulation is explored. The results will be used to design and optimize the geometrical structure of the SFCL pancake component.