In this paper, through AC and DC overcurrent tests on second generation high temperature superconducting tape (2G HTS tape), we respectively summarize the typical types of quenching resistance and corresponding quenching degree, in which there are three types under AC overcurrent and two types under DC overcurrent. According to experimental results, a rule was found that, when 2G HTS tape quenches to normal state, the relationship between quenching resistance and joule heat generated from 2G HTS tape presents a fixed trend line, and the influence of liquid nitrogen can be ignored. Then, the characteristics and rules of quenching resistance found in experiments are well explained and confirmed by a detailed 3D finite element model of 2G HTS tape including electromagnetic field and thermal field. Finally, based on above works, our group proposes a new equivalent method to estimate the quenching resistance, where the results of AC and DC overcurrent experiments can be equivalent to each other within a certain range. Compared with FEM, the method has the following advantages: (i) The method is simple and easy to implement. (ii) This method combines precision and computational efficiency. (iii) With superconducting tape quenching to normal state, this method presents a good consistency with experimental results.

With the development of modern power systems, the occurrence of fault current and system sensitivity to fault current have increased. Along with extensive damage to network hardware, considerable consumer losses can result from fault current events. However, with the extensive application of voltage source converter based power systems, large dc fault current becomes an important issue due to the bottleneck of the capacity of the dc breaker. To provide effective dc power system fault protection, a novel dc superconducting current fault limiter (dc SFCL) was designed. Here, the working principles and the mathematical model of the designed SFCL are presented. The simulation test based on SIMULINK and the demonstrator experiment were performed to confirm the correctness of the theoretical analysis. The test results show that the dc SFCL exhibits a rapid response time and good current limiting performance in dc systems.

With the rapid development of the integrated power system (IPS) on shipboard, the medium voltage DC (MVDC) power distribution system has received widely attention. At present, one of the bottlenecks restricting the development of MVDC IPS for ships is the occurrence of short circuit faults. Short circuit faults not only cause extensive damage to the line hardware, but also cause a lot of losses. Therefore, how to protect system from high-amplitude short circuit fault current has become a hot research topic. In order to ensure that the MVDC IPS of the ship can still operate safely in the event of typical faults, a flux-coupling-type superconducting fault current limiter (SFCL) is applied to shipboard MVDC IPS under two typical short circuit faults. In this paper, a flux-coupling-type SFCL is conceptual and electromagnetic designed, with working principle analyzed and mathematical model established. Two typical types of short-circuit fault are selected in the shipboard MVDC IPS, and the flux-coupling-type SFCL is installed at different positions on two fault short platforms to evaluate its performance. The results show that the flux-coupling-type SFCL has effective current limiting performance on protection of shipboard MVDC IPS.

In recent years, high-voltage dc power transmission is widely developed in the world. However, it is difficult for the existing dc breaker to cut off the fault transmission line with large short-circuit fault current. In a short-circuit fault of dc systems, short-circuit fault current is composed of initial transient impulse current and steady-state fault current. Therefore, a hybrid-type dc superconducting fault current limiter (SFCL) is proposed with two-stage current limiting capability. In the early stage of short-circuit fault, initial transient impulse current is limited by inductance and resistance. In the later stage of short-circuit fault, a sustained and steady current-limiting resistance is provided by the dc SFCL. A small-scale prototype of the dc SFCL is developed and the parameter design of the dc SFCL prototype is presented. According to the experimental tests and simulation analysis, the design scheme's effectiveness can be confirmed from high current-limiting ratio. Based on experimental tests and simulation analysis, the current-limiting characteristics and energy loss characteristics of the hybrid-type dc SFCL have been well verified.

Superconducting cables or fault current limiters may encounter short-circuit currents during operation. When experiencing mul-tiple overcurrent cycles, critical current degradation of YBCO tapes may occur. The performance degradation of YBCO tapes under overcurrent is a gradual process. It may take dozens or hundreds of overcurrent or overheating pulses. To get a better understanding of this process, we explored the performance change of YBCO tapes under repeated overcurrent. A life charac-teristics test platform was established. The electromagnetic per-formance degradation of YBCO tape under 50 Hz sinusoidal AC operating conditions was investigated, taking the effect of the overcurrent amplitude and duration into account. Meanwhile, the relationship between the number of overcurrent cycles and the Ic degradation is proposed. The reason for this performance change is analyzed by comparing the 2D current density distribution of the YBCO film before and after experiencing overcurrent. In ad-dition, the U-I property and resistance variations of these tapes are presented. It is inferred that the cracking of the supercon-ducting layer is the main cause of Ic degradation. The experi-mental results provide meaningful references for performance degradation of the YBCO tapes and related devices.