A superconductor has zero resistance at the superconducting state. This unique property creates many exceptional phenomena, of which some are known and the others are not. Our experiments with multilayer high temperature superconductor (HTS) cable samples revealed a new phenomenon that alternating current had a tendency to flow in the inner and outer layers of the cables. We attribute the cause of this phenomenon to the electromagnetic interaction in an infinite electrical conductivity medium and term it "super-proximity-effect". This effect will greatly affect the performance of a multilayer superconducting cable and other superconducting devices which are involved with alternating current transportation. HTS cables, proximity-effect, superconductivity, electromagnetic interaction Citation:Xin Y, Gong W Z, Zhang J Y. A nontrivial factor in determining current distribution in an ac HTS cable-proximity effect. Sci China Tech Sci, 2010, 53: 922−928,

Saturated Iron-core Superconducting Fault Current Limiter (SISFCL) has superior properties as a fault current limiting device. DC excitation system plays a key role during the operation of SISFCL. Besides its basic function, outputting dc excitation current to keepIron-core saturated, its field suppression unit absorbs magnetic energy stored in superconducting coil and suppresses the reverse voltage applied to superconducting coil, high speed switch IGBT, and dc excitation circuit elements to a safe level instantly when a fault happens. In this paper, SISFCL device and its dc excitation system will be briefly introduced, then the field suppression unit will be analyzed, calculated and discussed in detail based on the researching of 220kV 1300MV A SISFCL, which has been developed and run in power grid in China.I.