Electrical Insulation of HTS Coils in Saturated Iron Core Superconducting Fault Current Limiter

HTS coil is a key component for saturated iron core superconducting fault current limiter (SISFCL), which does not quench during all kinds of operation conditions of SISFCL. Voltages of the HTS coils have big differences among different operation conditions of SISFCL. During the normal operation, large dc current loaded on the HTS coils magnetize the iron core to saturated, and voltage on the HTS coils is very low. When a short-circuit fault occurs in the grid, dc current is cut off in milliseconds, resulting in high induced voltage on the HTS coils. After the fault is clear, a dc voltage is applied on the HTS coils for rapid magnetization of iron core. Design of electrical insulation for HTS coils is based on the above working conditions. In this paper, a dc breakdown test results of HTS tapes wrapped with Kapton as turn insulation, and the insulation structure, and the electrical test results of the HTS coils in 220 kV SISFCL are introduced in detail. Now, in-live operation of the 220 kV SISFCL also shows that the electric insulation of HTS coils is satisfied, reliable, and safe.