Testing of Surface Mounted Superconducting Stacks as Trapped-Flux Magnets in a Synchronous Machine

Abstract

Stacks of high temperature superconducting tapes may offer a technically affordable solution for the application of superconducting materials as trapped-flux magnets in the rotor of synchronous electrical machines. Nevertheless, several concerns must be first addressed, among others, the optimal procedure to induce the current vortexes previously to operation (magnetization), the survivability of these vortexes in the electromagnetic environment present in an electrical machine and the accuracy of recently developed numerical models. With the aim of exploring such practicalities, this paper presents a modified synchronous machine to test under liquid nitrogen conditions thin stacks of superconducting tapes. The machine is run under realistic conditions: currents in the stacks are induced from the stator, then the shaft is rotated and finally the machine is connected to a load, working as a generator. The results confirm previous numerical and experimental studies and establish a procedure for assessing the behavior of stacks in their actual operational environment.

Magnetic flux in stacks of superconducting tapes of different architecture

“…Then, maintaining and protecting the trapped flux is more important than a high initial value for reliable operation. The need for such protection is confirmed by experimental research of application of stacks in electric motors [31]. Even sectioned stacks, which appear to perform poorly can find their use, when an available magnetising flux is low and only narrow tapes are needed.…”

Experimental system for testing a superconducting motor at temperatures close to 15 K

“…By employing the presented system, measurements can be performed at temperatures as low as 15 K, which reects the expected conditions of an actual motor cooled by hydrogen. Previous research on a superconducting motor with stacks of tapes working as trapped-ux magnets were performed with setups cooled in liquid nitrogen [29,30]. An analysis of possibility of application of cryocooler and gaseous heat transfer medium was to cool an HTS motor down to 40 K was also performed [31].…”