Ramp-Rate limitation due to current imbalance in a large cable-in-conduit conductor consisting of chrome-plated strands

Abstract

The current distribution in the conductor, consisting of chrome-plated strands, was analysed assuming asymmetric strand transposition. The results show the circulation current is induced through the electrical joints at both ends of the conductor and electrical contact among the strands in the conductor. The current imbalance is produced as a result of the superimposition of the circulation and transport currents and becomes larger as the ramping rate increases. It was also found that the large current induced in the strands during a pulse charge cannot sufficiently be reduced at normal generation because of the induced voltage on these strands. The current flowing in the normal-state strands becomes larger for faster ramping. In addition, the effect of the non-uniform current distribution on the stability was experimentally investigated. The stability margin deteriorated when the current distribution in the conductor was not uniform. Moreover, the quench process in the ramp-rate limitation was considered. Since the coolant temperature is locally raised around the normal-state strands in the laminar-state coolant flow, the generation of the laminar flow region affects the ramp-rate limitation as a result of the current imbalance. From these results, it can be concluded that the current imbalance in the conductor has a very strong influence on the ramp-rate limitation.