Superconducting technology for overcurrent limiting in a 25 kA current injectionsystem

Abstract

Current injection transformer (CIT) systems are within the major group of thestandard type test of high current equipment in the electrical industry, so theirperformance becomes very important. When designing high current systems, thereare many factors to be considered from which their overcurrent protection mustbe ensured. The output of a CIT is wholly dependent on the impedance of theequipment under test (EUT). Therefore current flow beyond the allowable limit canoccur. The present state of the art provides an important guide to developingcurrent limiters not only for the grid application but also in industrial equipment.This paper reports the state of the art in the technology available that could be developedinto an application of superconductivity for high current equipment (CIT) protection withno test disruption. This will result in a greater market choice and lower costs for equipmentprotection solutions, reduced costs and improved system reliability. The paper willalso push the state of the art by using two distinctive circuits, closed-core andopen-core, for overcurrent protection of a 25 kA CIT system, based on a flux-lock-typesuperconducting fault current limiter (SFCL) and magnetic properties of hightemperature superconducting (HTS) elements. An appropriate location of the HTSelement will enhance the rate of limitation with the help of the magnetic fieldgenerated by the CIT output busbars. The calculation of the HTS parameters forovercurrent limiting is also performed to suit the required current levels of the CIT.