Analyses of the impact of connections' layout on the coil transient voltage at the Quench Protection Circuit intervention in JT-60SA

JT-60SAにおけるクエンチ保護回路動作時のコイル過渡電圧に対する結線レイアウトの影響解析

Maistrello, A.*; Gaio, E.*; Novello, L.*; 松川 誠; 山内 邦仁

Maistrello, A.*; Gaio, E.*; Novello, L.*; Matsukawa, Makoto; Yamauchi, Kunihito

The interruption of high direct currents, required in fusion experiments, is a challenging task. Depending on the technology of the circuit breakers the resulting current derivative may be high, leading to dangerous transient overvoltages. This aspect has been analyzed for JT-60SA Quench Protection Circuits (QPC) devoted to the protection of superconducting coils. The QPC adopts edge technology solutions: a Hybrid mechanical-static Circuit Breaker (HCB) as main circuit breaker in series with a PyroBreaker (PB) as backup protection. Snubbers or clamp networks can be provided in parallel to the breakers to smooth the voltage waveform. Dedicated clamp networks for the HCB have been designed and tested during the qualification of the QPC prototypes. On the contrary, it was preferred not to apply any component in parallel to the PB, the ultimate protection, to avoid reducing its reliability. For PB a different approach has been worked out, based on the optimization of the layout of the QPC connections. Analyses have been performed to highlight the impact of different busbar routes on the transient voltage across the toroidal field coils at the PB intervention. The results indeed showed a variation of the peak voltage in between 30% of the maximum allowed value. The paper will present the analyses and will discuss the results.