Thermal and AC-DC Characterization of 2nd Generation High
Temperature Superconducting Tape for the Development of
Superconducting Fault Current Limiter

Abstract

The aim of the thesis is to present the comprehensive study of Alternating Current (AC) and Direct Current (DC) characterization of 2nd Generation High Temperature Superconducting (2G HTS) tape based laboratory scale Superconducting Fault Current Limiter (SFCL) module. DC characterization of the module assists to identify the feasibility of the HTS tape for SFCL. The V-I characterization has been done to define the critical current of the tape in liquid nitrogen. The critical current of the HTS tape has been found out 98.3 A. Degradation characterization of the tape has also been done to identify the decrement in the critical current by multiple high temperatures thermal cycles up to 500 K. The critical current of the tape has been reduced down to 93.6 A at 500 K thermal cycle from the original value of 98.3 A. The recovery from normal state to superconducting state on fault is one of the most important design aspects for SFCL. Recovery time depends on the heat transfer coefficient between the liquid nitrogen and HTS tape and the structure of SFCL module, which is also calculated analytically and reported in this work. Different types of mounting structure have been designed and developed for SFCL module and explained briefly. A test setup has been designed and developed to identify the behavior of HTS tape in AC current. An 18 kVA step down transformer has been used as an AC current source which is connected in series with electrical load and a shunt resistor (75mV/500A) in order to monitor the current. A thyristor rated 3000 A is also connected which provides bypass path to generate high value of fault current with specific no of cycles. Electrical faults have been generated using fault current generator for different numbers of fault cycle and identify the reduction in fault current using SFCL module. The electro-thermal load for the boil off of the liquid nitrogen for both normal and fault condition has also been analytically calculated and briefly explained in this thesis.