Feasibility Study of Fiber Bragg Grating Sensor for Quench Detection of High Temperature Superconductors

The energy stored in a 2 MW motor coil, or a generator field winding, may be as high as 25 kJ (for a 5 H field windings with 100 A current) and this energy release would be catastrophic if rapidly released. Therefore quench detection and protection in large machine coils is a significant concern. In this work, the feasibility of uncoated Fiber Bragg Grating (FBG) sensors for high temperature superconductor (HTS) magnet quench detection has been studied by studying the thermal distribution of a vertical HTS tape stack without applying current. The ceramic heater and PT100 platinum resistance sensors were employed to trigger the hotspot and provide a temperature reference. A proposed thermal-mechanical model was used to predict the response of the attached FBG sensors. The measured results agreed well with the prediction results, and the temperature sensitivity of uncoated FBG can be improved significantly by the thermal expansion of HTS tape and epoxy at the operating temperature of HTS. The thermal distribution results were studied by the attached FBG sensors. Finally, a mechanical stress test was carried out to simulate the effect of magnetic force on the FBG temperature sensor. The result shows that the slow change of stress can be ignored in comparison with the rapid temperature change in the ramping process, the FBG sensor can work properly for quench detection on HTS coil operation state. This paper provides the feasibility of the application of bare FBG sensors for the quench detection of HTS magnets. Our purpose is to monitor the temperature in real time, and give a quick feedback for any possible heat disturbance.