Electrical tests on a fully superconducting synchronous machine

The emergence of ultrafine multifilamentary superconducting wires with very low losses under varying magnetic fields allowed the testing in 1987 of a three-phase 50-Hz superconducting stationary winding with a classical copper/iron rotor. A superconducting field rotor was constructed and mounted into the previous stator to form a fully superconducting machine. The rotating part is rather simple: a helium vessel rotates into a low-pressure vessel to avoid thermal losses by turbulence. There is no thermal shielding due to the cryogenic environment of the stator, and the electromagnetic shield, present in classical superconducting generators, has been avoided with the low loss superconductors used. The combined 900-mm-long, 320-mm-diameter, rotor-stator cryostat uses fiberglass composites in the central parts due to the rotating fields under permanent or transient operations. The first electrical tests of this small-scale 18-kVA machine under permanent and sudden-short-circuit tests are reported.