QUENCH PROTECTION AND STAGNANT NORMAL ZONES IN A LARGE CRYOSTABLE SMES

The quench protection System for a 30MW SMES built by Babcock & Wilcox is discussed. The magnet uses a cryostable conductor with an aluminum stabilizer cooled by pool boiling helium. A general approach to prote ction of a cryostable magnet is presented. The phenomenon of stagnant zones is identified as a catastrophic process,which can raise the cond uctor temperature in a localized area to hundreds of K in several minu tes and has been selected as the target for quench protection system. A stagnant zone can appear in an area covered by vapor and is characte rized by uncontrollably growing temperature In the center, while its f ronts slowly advance in cryostable regions. Stagnant zones are difficu lt to detect because of the cryostable nature of the conductor and the existence of other types of normal zones analyzed in the paper, such as steady zones or traveling normal zones, each with its unique behavi or. The complexity of quench detection for cryostable magnet and our a pproach to the problem are discussed.