Experimental Qualification of the Hybrid Circuit Breaker Developed for JT-60SA Quench Protection Circuit

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). Moreover, the JT-60SA QPC represents the first application of protection for superconducting magnets based on this hybrid technology. 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.