AC Loss and Magnetic Shielding Measurements on 2GHTS Inductive Fault Current Limiter Prototype Modules

A new calorimetric measurement set up based on the measurement of nitrogen gas flow rate that results from the liquid nitrogen boil-off was established to measure ac losses in prototype superconducting modules of an inductive fault current limiter (iSFCL). A copper coil, to serve as the primary winding of iSFCL, was used to induce currents in the superconducting modules and drive them to a quench. The set up is suitable for superconducting devices of up to 360 mm in diameter and 400 mm in height. AC losses and magnetic shielding characteristics of the superconducting modules, made from wide second-generation high-temperature superconducting (2GHTS) tapes, were studied. Measurements were carried out at primary currents up to the quench current at frequencies from 10 Hz to 200 Hz. Dependence of primary quench current and ac losses on the frequency were measured. Implications of the extent of ac losses on the operating costs for maintaining liquid nitrogen in a practical iSFCL are discussed. The sudden change in the inductance of the primary coil and the corresponding change in the voltage during a quench of the superconducting modules were demonstrated.