Abstract
Oak Ridge National Laboratory (ORNL) is collaborating with Waukesha Electric
Systems (WES) to develop a high-temperature superconducting (HTSC) utility power
transformer with primary and secondary coils cooled by liquid nitrogen. Since the vacuuminsulated
cryogenic coil dewar surrounds the magnetic core limb and cannot form a shorted
turn, non-conductive materials are required. Two test vessels and a small prototype dewar
have been fabricated by Scorpius Space Launch Company with epoxy/fiberglass
composites, using their proprietary PRESSURMAXX vessel technology. The effects of
pumping time, bakeout temperature, and cryogenic vessel temperature on vacuum
outgassing rates have been investigated. Outgassing rates of the individual materials used
in vessel construction have also been measured. The results will be scaled up to determine
the required pumping capacity for a full-size 25-MVA commercial transformer dewar.