An experimental generator using high temperature superconducting quasi-permanent magnets

An experimental axial gap generator, with a 6 inch diameter rotor and quasi-permanent HTS magnets, was tested. A variable speed motor was used to rotate the rotor above a stator composed of copper wire wound in an 8 pole 3 phase configuration. The rotor and stator were both run in liquid nitrogen. A 3 phase variable resistor bank was the generator load. The HTS magnets were YBCO, each 2 cm in diameter and 1 cm thick, melt textured using a SmBCO seed, containing 60% excess Y, and about 1%Pt. They were not irradiated, and could trap maximum fields of 3500-4000 G. First, the HTS magnets were field cooled in a field of approximately 2200 G, provided by the stator while carrying 25 Amperes. The HTS magnets trapped about 1800 G. In this configuration, the generator was run for about one hour at speeds up to 2000 RPM, and developed a maximum power output of 33 Watts. Next the HTS magnets were warmed, and then zero field cooled. In this case, activation was accomplished by a /spl sim/15 ms pulse on the stator, providing 5000 G of pulsed field. The HTS magnets trapped about 2600 G. The generator was then run for about 1 hour at speeds up to 2265 RPM, and developed a maximum power output of just under 100 Watts.<>