QUENCH CURRENT DEGRADATION IN SUPERCONDUCTING COIL FOR 6.6KV 2KA FAULT CURRENT LIMITER/

A 6.6 kV/2 kA class fault current limiter that consists of non-inducti ve superconducting windings was developed and tested, The limiter can deliver continuous power at 2 kArms and limit fault current of more th an 20 kA to 4 kA in 6 kV, The limiter recovers to the superconducting state within a few seconds and can perform a fault current limiting op eration in 60 seconds after the last limiting operation. After high-vo ltage operation, however, the quench current of the limiter dropped si gnificantly. This quench current degradation is related to the coil bo bbin strain due-to helium pressure raised by large ohmic heating in qu enching, The degradation is a fatal problem for a fault current limite r if the quench current falls below the operating current because the limiter cannot revert to the normal operation. High Young's modulus bo bbin is effective to remove the coil degradation. We have obtained a f ault current limiter without any degradation after repeated limiting o perations.