Bifilar coil is one of the most appliable structure used for resistive type superconducting fault current limiter (SFCL). However, the turn-to-turn (longitudinal) insulation of the bifilar coil under lightning and switching impulse is rather different from the conventional pancake coil. The longitudinal insulation is characterized as the distributed circuit of the coil under high-frequency excitation, and the capacitance, inductance and resistance parameters are solved by finite element model. The influence of those RLC parameters on the accuracy of the model is analyzed, and two samples of one bifilar pancake coil and two series connected bifilar coils are fabricated for high-frequency impulse voltage testing. The experimental results are consistent with the simulation results. The initial voltage distribution and impulse response of two samples are calculated under standard lightning impulse. The maximum voltage of inter-turn channel is 1 and 0.5 lightning voltage amplitudes for one bifilar coil and two series connected bifilar coils in initial voltage distribution.

The longitudinal insulation analysis method is developed for the solenoid type windings. The distributed lumped model is proposed to calculate the response under high frequency transient impulse for the solenoid type superconducting fault current limiter (SFCL). Various simulation results according to the proposed model are consistent with the experimental results, which indicates that developed model is effective for describing such kind of “non-inductive” type solenoid windings. Therefore, the longitudinal insulation of the 20 kV/400 A SFCL has been analyzed by this method. The initial voltage distribution and the standard lightning impulse response for different turn-to-turn distances of the superconducting coils are calculated. According to the simulation results, the most severe impact moment is the moment when the lightning impulse wave enters the SFCL, the first and last turn coil of the windings undergoes a very high voltage drop at this moment. Considering the factors of insulation margin and size, the turn-to-turn distance of 4.5 mm is taken as the longitudinal insulation distance of the SFCL.

High-temperature superconducting (HTS) cable has the merits of high capacity and small volume in the normal operation condition. However, the fault current, which could be 10–30 times of the nominal current, gives a great challenge to its thermal stability. Due to the overcurrent, the HTS tapes will quench to resistive state and result in generating large amount of heat, which may degrade or even damage the HTS tapes. Therefore, it is of great significance to study the thermal stability of superconducting tapes. This article studies the thermal characteristics of different HTS tapes under dc overcurrent. The testing tapes are made of YBCO produced by Shanghai Superconductor (SHSC) and Samri advanced material (SAM). The thermal stability is defined as the maximum overcurrent and impact duration that a tape can withstand before getting its properties degraded. According to the testing results, the thermal stability of the HTS tape with copper reinforced layer is better than brass and stainless steel. The thicker the thickness of the tape, the better the stability. But the thermal stability of 25 $\mu \text{m}$ copper reinforced YBCO is close to 50 $\mu \text{m}$ . Owing to the resistivity and specific heat capacity, with the same pulse lengths, the 150 $\mu \text{m}$ copper reinforced YBCO can be pulsed to twice the current of 25 $\mu \text{m}$ .

Resistive type superconducting fault current limiter (R-SFCL), based on REBCO coated conductor, is of great help to enhance the safety and stability of power system. When the fault current appears, the current is transferred from the superconducting layer to the metal layers with large resistance in the REBCO coated conductor, so as to limit the current. However, the interface resistance affects the current distribution between different metal layers. What’s more, the inhomogeneity effect of REBCO coated conductor has great influence on the quench characteristics of R-SFCL. In this article, the current transfer model of REBCO coated conductor is established, and the influence of interface resistance on current distribution is analyzed. The inhomogeneity effect of resistivity parameters and critical current of REBCO coated conductor is analyzed. One non-inductive bifilar coil is fabricated for DC impulse current test, and the influence of inhomogeneity effect of REBCO coated conductor on quench characteristics is verified.