Quench Protection Characteristics of Coil Wound of Bi/Ag-Sheathed Wire

The most probable cause of quenches of a coil wound of Bi/Ag-sheathed wires is the appearance of a long resistive zone caused by the temperature rise of the long part of the conductor due to, for example, ac losses and the malfunction of the cryogenic system. Protection characteristics of quenches by this cause are experimentally and analytically investigated. In the experiment, the operating temperature of a coil wound of a Bi/Ag-sheathed wire is gradually increased until the resistive voltage of the coil exceeds a given threshold to start a quench dump sequence. Damages in the test coils are examined by changing the decay time constant of the coil current. Based on those results, conditions to protect coils from damages are investigated. Analysis is conducted to simulate quench events, and conditions for quench protection are obtained. The analytical results well explain the quench behaviors of the test coils.