Experimental research and analysis of AC critical current in YBCO tapes

High temperature superconductor (HTS) has found its way into both AC and DC transmission. Since modeling for critical characteristic parameters of HTS in DC circumstance is a hotspot in recent years, research on the critical current of the AC condition is still scarce; a new AC critical current criterion should be established prior to further studies. In this paper, we adopt different DC critical current measurement methods to AC analysis. In alternating current the E-I curve is obtained by four-probe method when the frequency ranges from 30Hz to 810 Hz. The AC current carrying capacity of the superconductors is discussed and analyzed by the RMS method, virtual n value method and the loss concept method. We find that the methods of RMS and virtual n value are no longer applicable in the selected frequency band, while the loss concept method is applied to explain theory of critical current which varies with frequency, therefore an AC critical current calculation method is obtained and the calculative equation at different frequencies is established.