AC over-current test results of YBCO conductor for YBCO power transformer with fault current limiting function

We are developing elemental technology for 66 kV/6.9 kV 20 MVA-class YBCO power transformer. The YBCO transformer is considered to have a possibility to stabilize the power system by improving function of fault current limiting. Current limiting behavior functions over critical current flows. There is a possibility that superconducting characteristic may be damaged due to increase in temperature of YBCO tapes. Therefore, we have taken a measure to combine YBCO tape with CuNi tape or Cu Tape. We manufactured model coils using these conductors and conducted the AC over-current tests. The test current was two to seven times larger than the I_c of conductor and it was damped with time from its maximum value according to the generation of conductor resistance. We verified the effectiveness of current limiting characteristics. In these tests, the I_c of model coil did not degrade. We consider this conductor to be able to withstand AC over-current with the function of current limiting.