Novello, L.*; Cara, P.*; Coletti, A.*; Gaio, E.*; Maistrello, A.*; 松川 誠; Philipps, G.*; Tomarchio, V.*; 山内 邦仁
IEEE Transactions on Applied Superconductivity, 26(2), p.4700507_1 - 4700507_7, 2016/03
The voltage transient appearing across and inside the toroidal field (TF) coils of JT-60SA in case of fast voltage variation, such as a safety discharge operated by the quench protection circuit (QPC), can be significantly high. In fact, the voltage distribution between coils and inside the winding can be not uniform during fast transient, being influenced by the presence of parasitic capacitances. A simplified electrical model of the TF coils has been developed to investigate this aspect. The obtained model has been used in conjunction with an electrical model of the TF circuit elements, including a simplified model of the QPC. The worst case in terms of transient voltage applied to the winding has been identified, corresponding to a fault to ground occurring just after QPC operation. It has been verified that the resulting voltage is largely inside the coil insulation capability defined by performed insulation voltage tests.
Maistrello, A.*; Gaio, E.*; Novello, L.*; 松川 誠; 山内 邦仁
Fusion Engineering and Design, 98-99, p.1109 - 1112, 2015/10
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.
Novello, L.*; Baulaigue, O.*; Coletti, A.*; Dumas, N.*; Ferro, A.*; Gaio, E.*; Lampasi, A.*; Maistrello, A.*; 松川 誠; 島田 勝弘; et al.
Fusion Engineering and Design, 98-99, p.1122 - 1126, 2015/10
JT-60SA, the superconducting tokamak under construction in Japan, will be equipped with a mix of new and reused Power Supplies (PS). Most of the new PS are procured by European Voluntary Contributors under the framework of Broader Approach agreement between F4E and JAEA. For the toroidal circuit, the 6 pulses ac/dc converter will be procured by CEA. It is rated 25.7 kA and 80 V dc, and will work in steady state condition. For the poloidal circuits the procurement of ten ac/dc converters, rated 20 kA and about 1 kV is shared between CEA and ENEA. They are 24 pulses four quadrant converters, with back to back thyristor bridges. Plasma initiation requires a fast variation of current in the Central Solenoids, obtained with the insertion of a settable resistor in series to the coils. This is achieved with the operation of four Switching Network Units procured by ENEA, producing up to 5 kV at the nominal 20 kA. The protection of superconducting magnets, both toroidal and poloidal, is assured by 13 Quench Protection Circuits procured by Consorzio RFX, rated 20 kA and 3.8 kV for poloidal QPCs and 25.7 kA and 2.8 kV for toroidal ones. The present status of the aforementioned PS is described in the paper: their detailed design has been completed and some systems have been already manufactured and tested.
Maistrello, A.*; Gaio, E.*; Ferro, A.*; Perna, M.*; Panizza, C.*; Soso, F.*; Novello, L.*; 松川 誠; 山内 邦仁
IEEE Transactions on Applied Superconductivity, 24(3), p.3801505_1 - 3801505_5, 2014/06
This paper deals with the qualification process of the full scale prototypes of the Hybrid mechanical-static dc Circuit Breaker (HCB) for the Quench Protection Circuits (QPC) of the Toroidal Field (TF) and Poloidal Field (PF) superconducting coils of the Satellite Tokamak JT-60SA. The HCB developed for JT-60SA QPC is the first dc circuit breaker based on hybrid mechanical-static design at this level of power (25.7 kA - 1.93 kV, 20 kA - 3.8 kV). Special type tests have been designed to verify the performance of the device up to the nominal ratings and beyond, thus proving the suitability of the technology, the design margins and the reliability; the results of the most significant tests are presented and discussed. The qualification program also includes the validation of the electrical models developed during the design phase, which are described in the paper too.
Gaio, E.*; Maistrello, A.*; Barp, M.*; Perna, M.*; Coffetti, A.*; Soso, F.*; Novello, L.*; 松川 誠; 山内 邦仁
Fusion Engineering and Design, 88(6-8), p.563 - 567, 2013/10
This paper deals with the development, manufacturing and testing of the full scale prototype of the Quench Protection Circuit (QPC) for the superconducting magnets of the JT-60SA Satellite Tokamak, which will operate in Naka, Japan. After the completion of the system detailed design in summer 2011, the manufacture of the poloidal and toroidal prototypes was launched and completed at the beginning of 2012. Several factory type tests on the main components have been done at the manufacturers' premises and are described in this paper. Then, two main campaigns have been performed to test the operation of the overall poloidal and toroidal QPC prototypes; the main results are reported in the paper too.
Gaio, E.*; Maistrello, A.*; Coffetti, A.*; Gargano, T.*; Perna, M.*; Novello, L.*; Coletti, A.*; 松川 誠; 山内 邦仁
IEEE Transactions on Plasma Science, 40(3), p.557 - 563, 2012/03
This paper describes the detailed design of the quench protection circuits (QPC) for the superconducting toroidal field (TF) and poloidal field (PF) magnets of the Satellite Tokamak JT-60SA, which will be installed in Naka, Japan. The nominal currents to be interrupted and the maximum reapplied voltages are 25.7 kA and 2.8 kV for the TF QPCs and 20 kA and 5 kV for PF QPCs. The innovative solution proposed in the QPC design is based on a hybrid circuit breaker (CB) composed of a mechanical Bypass Switch for conducting the continuous current, in parallel to a static CB for current interruption. The main choices of the final design are presented and discussed, either to confirm or to update and complete the study performed at the conceptual design level.