Design aspects of an inductive type superconducting fault current limiter

An inductive (transformer) type HTS FCL for the protection of a synchronous generator unit was designed, constructed and tested. The hysteresis of the steady-state characteristics (V-I curve) of the FCL was measured. Different cases of the normal and fault currents related to the FCL V-I curve have been determined. In the normal mode of the FCL, the input impedance can be approximated within a few percent by the leakage reactance of the FCL. In the limitation mode the input impedance can be approximated within a few percent by the main field reactance indicating that the normal state resistance of the HTS ring is much higher than the main field reactance of the FCL. A duration test revealed that the steady state limited current tends to decrease as the FCL activation number increases. In our case the rate of decrease was less than 10% after 2000 activations. No further decrease was observed after 3000 activations. In all investigated cases the experimental HTS FCL has shown outstanding fault current limiting properties.