Development of a Prototype Hybrid DC Circuit Breaker for Superconducting Magnets Quench Protection

Abstract

A quench protection system for superconducting magnets mainly involves a mechanical dc circuit breaker (CB) and a dump resistor where the entire energy of the inductive magnet is dumped during quench. During the current commutation to the dump resistor, these mechanical CB experiences arcing at their contacts, which causes degradation in the performance as well as life expectancy of the CB, affecting the reliability of the entire quench protection system and appears as threat to the expensive and critical superconductor magnets also. A combination of mechanical and static breakers, which is termed a hybrid dc CB, presents a novel technique for arcless current commutation into the dump resistor. Furthermore, the current commutation time can also be reduced by adopting real-time switching schemes. A series of experiments has been done at the Magnet Technology Development Division Laboratory, Institute for Plasma Research, Gandhinagar, India, for testing the hybrid CB operation and operation at various current levels up to 800 A using a mechanical contactor as the mechanical CB and an insulated gate bipolar transistor as the static switch. A significant improvement in the voltage profile across the dump resistor has been observed using the hybrid CB exhibiting arcless current commutation into the dump resistor. Furthermore, an overall reduction in the current interruption time between a mechanical CB operation and a hybrid CB has been observed. The time for current commutation into the dump resistor with the conventional mechanical breaker is 48 ms, whereas that with the hybrid CB is observed to be 18 ms.