Design of a DC Resistive SFCL for Application to the 20 kV Distribution System

A DC-operating resistive-type superconducting fault current limiter for AC applications (in short a DC Resistive SFCL) is based on the synergistic use of the "resistive" and the "rectifier" fault current limiter concepts, and allows the superconductor to operate in nearly DC current conditions. This regime of operation drastically reduces the AC losses and therefore opens up completely new perspectives with regard to the materials, the architecture of the cable, the layout of the windings and the cryogenics. In this paper the design of a DC resistive SFCL for application to the 20 kV distribution system is presented. A bus tie position with nominal rate of 25 MVA is considered as case study. The resistance and the inductance of the superconducting winding are arrived at by means of the parametric analysis of voltage transients, harmonic distortion and peak fault current. The design of the windings of the real scale device is carried based on a optimized MgB2 cable. The detailed design of the bridge rectifier is carried out and the power losses due to diodes are evaluated.