Application of 50 Hz superconductors close to self field conditions

Abstract

Applications of 50 Hz superconductors like the transformer and the fault current limiter correspond to relatively low magnetic fields, so that AC losses and stability are mainly governed by the conductor self field. AC loss calculations as they are performed in most cases for superconductors, are based on the Bean critical state model which states that everywhere in a superconductor, the current density has a modulus equal the critical current density Jc. This model is applicable when the superconducting transition E(J) is very sharp, but sizeable discrepancies appear for 50 Hz superconductors, as they present a relatively smooth superconducting transition. AC loss calculations have been developed using the Maxwell equations combined with the actual E(J) relationship. The heat generation in the conductor is then used as an input for a numerical calculation of the temperature distribution through the superconductor. The stability limits directly derive from the thermal model.