**6. Conclusions**

In this paper, through the combination of AC and DC overcurrent experiment and simulation study, the quenching characteristics and common laws of YBCO superconducting tape applied in R-SFCL are summarized as follows:

(1) Under AC overcurrent, the quenching resistance of the HTS tape can be divided into three types: half-wave type, half-wave and half-incremental curve type and incremental curve type. Under the DC overcurrent, there are two quenching resistance types of the HTS tape: half-wave type and incremental curve type.

(2) The quench resistance type is closely related to the current and the temperature of the HTS tape. When the current exceeds the critical current and the temperature is lower than the critical temperature of the HTS tape, the HTS tape is in partial resistance state. When the temperature exceeds the critical temperature, the HTS tape enters normal state.

(3) In the normal state, the relationship between quenching resistance *R* and joule heat *Q* of HTS tape and coil is independent of current waveform. In essence, there is a fixed correspondence between *R* and *Q*. Therefore, *R-Q* curves are consistent under AC and DC overcurrent.

Based on these, the *R-Q* curve method can be used to estimate and predict the quench resistance and temperature change of HTS tapes in completely quenching stage. Compared with FEM, this method can ensure simulation accuracy, greatly shorten calculation time and improve simulation efficiency. It can be used for simulation modeling, prototype design and quench resistance estimation of resistive type SFCL in complex power systems. Furthermore, this method can realize the equivalent calculation of quenching resistance under AC and DC overcurrent, which can provide theoretical support for large-scale DC current limiters to be tested by AC equivalent experiment.

**Author Contributions:** Conceptualization, S.L. and L.R.; Data curation, J.S.; Formal analysis, S.L. and S.Y.; Funding acquisition, Y.X. and M.S.; Investigation, X.T., Z.L., G.C. and Z.C.; Methodology, S.L. and L.R.; Project administration, T.M. and Y.X.; Resources, T.M. and L.X.; Software, S.L.; Supervision, Y.T.; Validation, X.T., Z.L., G.C., Z.C. and J.S.; Writing—original draft, S.L.; and Writing—review and editing, L.R.

**Funding:** This research was funded by the Project of the National Natural Science Foundation of China under gran<sup>t</sup> number 51707074 and National Key Research and Development Program 2017YFB0902304.

**Conflicts of Interest:** The authors declare no conflict of interest.
