Quench protection for the 21 MWh ETM coil

An emergency internal dump procedure and analysis are presented for the 21-MWh engineering test model (ETM) of a full-scale superconductive magnetic energy storage (SMES) coil. The coil is arranged into four modules which can be connected in parallel using cryogenic switches. The first step in the energy dump procedure is to close all switches. The second step is to expel the liquid helium in about 20 to 40 s. As the liquid helium level drops, the current transfers inductively from the uncovered top modules to the other modules. The conductor and parallel structure pieces tend to warm up uniformly with tolerant voltage levels. Two cases are considered: the case where all turns are connected in series (no parallel switching) and the case of the parallel connection of the four modules. A safety analysis of the consequences of a faulty switch is also presented.