Threshold value analysis of YBCO tapes under transient DC over-current impulse

Compared to the AC application, different research should be emphasized when the superconducting fault current limiter is used in VSC-HVDC. In the AC application, over-current flowing in the superconducting will last for 45 ms-60 ms before the circuit breaker is shut down. Two or three times of the critical current of the superconducting tapes will be enough. And the heat generation will be absorbed a lot by the liquid N2 during 45 ms-60 ms. However, in HVDC situation, the time will decrease to 4 ms-10 ms and the over current could be ten times of the critical current of the tapes. This paper would explore the threshold value of the YBCO tapes in DC over-current situation and the heat transfer between the tapes and the liquid nitrogen. We obtained the relationships between time and the threshold value of over-current according to the DC over-current impulse experiments under different time conditions. The heat flux of liquid nitrogen with temperature difference was obtained by calculations. Combinations with the experiment results and the temperature-resistance curve, we got the heat transfer law. Finite element simulation model is also established in Comsol to analyze the heat transfer law between the layers during the impulse. The results will be a reference for design of the superconducting fault current limiter (SFCL).