Direct current voltage increment due to ac coupling in a high T-c superconducting coil

The voltage-current characteristics of a superconducting coil, made of mult ifilamentary silver-sheathed Bi2Sr2Ca2Cu3O10+delta tape, are investigated. We find that a small ac current I-ac superimposed on a relatively large dc current I-dc causes a significant increase in the coil dc voltage, approxim ately proportional to I-dc, I-ac(2), and the ac frequency. We attribute thi s effect to the nonlinear magnetoresistance of the coil, and discuss its si gnificance in power applications of high T-c superconducting coils, such as fault current limiters and superconducting magnetic energy storage devices . (C) 1998 American Institute of Physics. [S0003-6951(98)02352-3].