Development of superconducting DC machines using bulk YBCO

An investigation is being made into building superconducting machines using YBCO bulks as quasi-permanent magnets. To investigate the performance of t he superconductors in motor applications a test rig has been built in which a moving or vibrating magnetic field can be applied to the superconductor, The test rig allows two-dimensional motion of a magnet relative to a superc onductor, in order that two-dimensional vibration modes can be investigated . This allows more accurate simulation of the conditions in a motor, and al lows values of the absolute forces between magnet and superconductor during the motion to be inferred. The vibration methods used in the paper are suitable for measuring long-ter m behaviour of the superconductor-magnet interaction, including long-term d ecay of the trapped field when exposed to oscillations, The shorter tests r eported here measure force/torque characteristics, and the stable limits of operation. Beyond these limits, a superconductor will be de-magnetised, re sulting in a sudden loss of torque and machine damage.