Further Testing of an “Iron-Cored” HTS Synchronous Generator Cooled by Liquid Air

The systematic performance test program of the 100 kW iron-core HTS synchronous generator has been underway since 2007 at the University of Southampton. The early measurements were conducted at liquid nitrogen temperatures (77 K) and sub-cooled liquid nitrogen close to its triple point (63 K). Further measurements at these operating temperatures for both open circuit and loaded configurations have enabled us to confirm the machine's synchronous reactance. Circulating liquid air through the closed loop cooling system enabled us to lower the rotor temperature down to 61.7 K and boost the critical current I c of the HTS winding up to 144 A. A number of transient tests were carried out to assess the impact on the machine, in particular the current in the HTS field winding when the stator circuit was suddenly shorted. The results show that the peak current can be almost 3 times the initial operating field current in the first cycle of the response. No `thermal quench' of HTS winding was witnessed, despite the occurrence of large over currents. The recovery of the HTS winding back to the initial operating current occurred in several seconds and depended on the initial operating current and the reaction of the power supply.