Quench Detection Criteria for YBa2Cu3O7-delta Coils Monitored via a Distributed Temperature Sensor for 77 K Cases

Distributed temperature sensing (DTS), such as Rayleigh-scattering interrogated optical fiber (RIOF) sensing, is a promising method for detecting quenches in high-temperature superconductor (HTS) magnets. One key for the successful implementation of RIOF-based DTS for quench detection is to identify effective quench detection criteria for the onset of a quench. In this paper, two DTS-based quench detection criteria, and their dependence on the operating current and heat disturbance characteristics, are investigated through numerical simulations of quench behavior in a YBa2Cu3O7-delta (YBCO) HTS helix coil cooled by a liquid nitrogen (LN2) bath and a YBCO HTS pancake coil cooled by conduction at 77 K. One is based on the minimum propagation zone (MPZ). The reference temperature to define the MPZ size is found for different operating currents. The other is based on the equilibrium temperature profile, in which the peak temperature and a characteristic normal zone length are found from a preselected reference temperature. The advantages and disadvantages of the two quench detection criterions are discussed and compared. Simulation results show that both criteria are independent of the nature of unpredictable heat disturbances. Similar to the helix coil, equilibrium temperature profiles independent of unpredictable disturbances are found for the pancake coil with different operating currents.