Investigation of HTS Power Transmission Lines Stability Conditions in Short-Circuit Mode

Generally in HTS cables, sample test is performed to measure the sample heating when it is more often subjected to a short-time load by a current exceeding the critical value. This test is assumed to determine the HTS line stability against short-circuit modes (SCMs). However, the characteristics of these modes depend not only on the sample properties but also on the HTS line parameters as a whole and the electric power network part under protection as well. In this paper, we aimed at the theoretical analysis of these dependences, technique of analytical calculation of cable heating in SCM, and the results of a more exact numerical calculation of all the SCM characteristics for various designs of HTS ac lines. The results show that taking into account all the electric power network parameters allows not only a more exact determination of conditions of the cable stability against SCM, but can lead to the contrary conclusions concerning the cable design ensuring this stability. In particular, at the parameters, typically for most of the ac HTS lines, extra copper added to the cable materials increases the cable heating rather than decreasing it. The removal of copper or its replacement by another material with higher electric resistance not only diminishes the cable heating in the SCM but also allows an essential decreasing of the surge current and the current reached at the end of SCM. There is also an opportunity to significantly reduce the ac losses in the rated operative mode.