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A superconducting power cable is a prospective application of high-temperature superconductors. Even though superconducting power cables have been developed worldwide mainly for the grid application, we focus on railway application of superconducting power cables. We have studied the fault current of DC electric railway feeding systems using superconducting power cables. MATLAB-Simulink electric circuit models based on a model railway line are constructed for numerical analysis of short-circuit and grounding faults. Influence of introducing superconducting power cables under different fault conditions is studied. Then the protections in an electric power system of railway are taken into account, and the feasibility for detaching the fault and protecting the system including the superconducting power cables are studied. Application of a superconducting fault current limiter is also studied and its potential is discussed.

Abstract.A resistive type superconducting fault current limiter (SFCL) using REBCO tapes has shown its advantages in power applications. However, the hotspot problem, which can be caused by the uniformity of critical current density JC over long-length of REBCO tapes, is still a threat to the SFCL safety. In this paper, we have studied the limiting performance and transient temperature rise distribution of a nonintersecting type non-inductive solenoidal SFCL REBCO coil using three-dimensional electromagnetic and thermal coupled FEM analysis. Firstly, we modelled a local degradation of JC and studied its influence on the transient temperature rise distribution during the over current. The results indicated that a narrow and severe JC degradation leads to the concentration of current and heat generation in the normal JC area, which is opposite to the case of a relatively wider and slighter JC degradation area. Furthermore, REBCO tapes with different thickness of substrate and Ag over-layer were analysed to study the influence on limiting performance and temperature rise. A thicker substrate leaded to a slower temperature rise because of its higher heat capacity, and the Ag over-layer of 4 μm showed better limiting performance and thermal stability because of its better thermal conductivity as well as uniform temperature rise and SN transition. IntroductionA resistive type superconducting fault current limiter (SFCL) using REBCO tapes has shown its advantages in limiting fault currents and improving the reliability of a power system for its compactness and rapid increase in resistance [1]- [4]. However, critical current density (JC) uniformity over longlength of REBCO tapes may lead to a local overheating and burning of the tapes, which are called as the hotspot phenomenon. In the previous research, two types of non-inductance solenoidal coils for resistive type SFCL were studied on their current limiting properties and recovery characteristics [5]. In addition, the electrical and thermal behaviours of several types of REBCO tapes during the fault current limitation were analysed and evaluated with a simulation model, consequently, tapes with no stabilizer were considered more suitable for constructing SFCLs [6]. In reference [7], a 2D JC distribution map of such REBCO tape with no stabilizer was measured using the scanning hall probe microscopy (SHPM).In this paper, we have studied the thermal characteristics of an REBCO coil for SFCL use during the fault current limitation with the electromagnetic and thermal coupled FEM analysis. The nonintersecting type non-inductive solenoidal winding [5] consisting of the stabilizer free REBCO tape was assumed for the REBCO coil, which concept is shown in figure 1. This coil consists of an inner and an outer winding that are wounded bifilarly and connected in series to reduce the inductance of the coil. A local

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