Study on degradation of trigger current level of superconducting fault current limiter of transformer type

A superconducting fault current limiter (SCFCL) of a transformer type with adjustable trigger current level was proposed in previous works. Basic tests were performed using the trial SCFCL of proposed type. The degradation of the trigger current level of the SCFCL was observed. It is observed that the trigger current level depends on the frequency of the power source. The measured AC loss is about seven times as large as the calculated hysteresis loss and the coupling loss. It is assumed that an excessive loss generated at the short-circuit contact of the secondary winding causes the degradation. The new trial SCFCLs with the improved contact are made. The degradation of the trigger current level does not appear for the new trial SCFCLs.