Reduction of current carrying capacity in multistrand superconducting cables at changing current

Results of an experimental investigation of current carrying capacity of two-strand cable with insulated strands, at linearly changing transport current, are presented. The experimental procedure permits to exclude completely a reduction of the cable current carrying capacity due to uneven distribution of the current throughout the strands. It enables to study separately an influence of the non-uniform; magnetic field from one strand on the quench current value of another strand as the one of possible causes of the quench current degradation in multistrand cables as compared with the sum of quench currents of strands at the same rate of current change. It is shown that due to the mutual effect of the strands, the reduction of quench current of each strand in the two-strand cable (and the reduction of the cable quench current, relatively) can reach 10 percents. In the considered range of the transport current change rate (1 A/s divided by 10 kA/s), the cable quench current degradation is connected mainly with a decrease of critical parameters of strands situated in the magnetic field of each other. Considerable dependence of the cable quench current on the transport current change rate is not observed. Theoretical analysis of the results is given. It is demonstrated that the smoothness of I-V characteristic of strands can give a substantial reduction of the cable quench current degradation connected with some difference in resistances of the strands joints with current leads.