Numerical analysis on coupled magneto-thermal properties of high temperature superconducting cables subjected to fault currents

In the power grid, a cold dielectric high temperature superconducting (CD HTS) cable usually subjects to the impact of fault currents in the transmission system. During the fault, a large amount of Joule heat is generated, causing the temperature of HTS cable rise and leading a transformation of HTS elements therein from a superconducting state to a normal state which would deteriorate the current carrying capacity of HTS cables. This paper proposes a new method for calculating transient currents and temperature distributions in CD HTS cables by coupling an equivalent circuit mathematical model with a thermal conduction model of HTS cables considering the impact of fault currents. The proposed method is applied to an 110 kV/ 3 kA CD HTS cable consisted of YBCO coated conductor with a fault current of 25 kA rms lasting 3 s. The obtained current and temperature distributions in the HTS cable show that there is a serious current diversion effect in the CD HTS cable and the currents of the superconducting layers decrease along with the rise of the temperature in the HTS cable which has different rate of change after reaching 92 K. Therefore the copper former becomes the main path for the fault current and withstands about 96% of the fault current. This analytical method provides the theoretical basis for the protection strategy of superconducting cables which is significant for the stable operation of HTS cables.