Study of Method of Measuring and Determining HTS Coil's Critical Current With $V$ – $I$ Properties Between Different Parts of the Coil

An electric field criterion of 1 μV/cm is often used to measure and determine the critical current of high-temperature superconducting (HTS) tapes, whereas there are no standard criteria to determine the critical current of HTS coils. The voltage between different parts of the tapes in an HTS coil is different, and each part of the tapes reaches critical current at a different time; therefore, the total voltage of the coil is not suitable for determining the critical current. This paper presents a method of measuring and determining the critical current of HTS coils. Second-generation coils (YBCO) cooled by liquid nitrogen are used in our study. HTS coils with seven pairs of voltage lead are wound. V -I properties between innermost, middle, and outermost turns of the coil are measured. V -I properties between straight and bending segments are also measured. Regularity of voltage distribution in the HTS coil is analyzed. A finite-element method model of the HTS coil is built. The distribution of the magnetic field of the coil is calculated. The method presented in this paper and the analysis of the voltage distribution regularities can be referred to when measuring HTS coil's critical current with an electrical method.