Quench Characteristics in the parallel PCS circuit using two NbTi Mechanical PCS's

Abstract

A persistent current switch (PCS) used in the large-scale SMES system needs to have high OFF resistance as well as zero ON resistance for efficient load-leveling operations. So far, the authors have successfully developed NbTi mechanical PCS, which realizes zero contact resistance, infinite OFF resistance, and switch current capacity over 200 A. Considering practical use of the PCS, the switch current capacity has to be further increased to obtain much larger rated current of 100 kA order for the GWh class SMES system. This paper describes the switch current capacity and quench characteristics in the parallel PCS circuit which consists of two NbTi mechanical PCS's. Effects of current distribution and quench property of each single PCS are especially investigated in detail. To clarify the posterior quench mechanism at the time when both PCS's are quenched, quench characteristics on the time are also investigated by applied pulsed current. It was found that each PCS in the parallel circuit has to obtain identical quench current and distribute current uniformly so as to achieve the theoretical maximum switch current capacity. Additionally, existence of quench time lag is definitely confirmed. Quench time lag is the key property to make clear the succeeding quench mechanism.