Enhancement Test of Critical Clearing Time of One-Machine Infinite Bus Transmission System by Use of SFCL

Abstract

A transformer type field shielding superconducting fault current limiter (SFCL), which is made of rare-earth barium-copper-oxide (REBCO) for primary and secondary windings, is designed and made for demonstration of not only fault current limiting but also power system stability improvement performance. A lab-scale test power system consists of one machine (18.26 kVA, 200 V) and double transmission route to an infinite bus. The simulated fault occurs at the sending end of one of the transmission route and after a certain time (fault clearing time), the fault route was rejected by circuit breakers. While the clearing time is short, the generator can continue to operate with one healthy transmission route, however, it becomes longer than a certain time critical clearing time (CCT), the generator loses its synchronism and fails into step out. The test SFCL was installed at the generator side bus of the fault route. The peak fault current was reduced to less than half of that without SFCL and the generator terminal voltage did not fall below 20% of rated voltage. It was confirmed experimentally that CCT can be enhanced by introducing the SFCL. It is confirmed that the SFCL cannot only limit the fault current but also improve the system stability.