Temperature and Voltage Analysis of a Protection Scheme for Large Energy Storage Coils

Large superconducting energy storage coils, typically 5000 MWh, require a method of internally dumping their stored energy in an emergency situation. The present scenario envisages: a dump situation is detected; large switch is activated which shorts all conductor turns and shorts the cold structure; liquid helium dump valve is activated; pressurized room temperature helium gas forces liquid helium from cryostat into a reservoir in 5 to 10 seconds; as the turns are uncovered, they go normal but much of the energy is coupled to the other turns still covered with liquid helium and the structure. The system tends to warm up uniformly because of the coupling. Results are presented for the temperature and voltage distribution for the coil with and without the switch. The analysis improves on previous work in accounting for the imperfect coupling between conductor turns and the beneficial effects of having the conductor in electrical contact with the structure, yet electrically insulated from the other turns.