An investigation of semiconducting materials at cryogenic temperatures

Summary form only given, as follows. Tests of semiconductive materials have been performed at 77.3 K and 4.2 K to examine the application of these materials to a corona protection system for use in the high voltage stator windings of a turbogenerator operating at cryogenic temperatures. The following low-resistance and high-resistance semiconductive materials have been tested: copper-containing glass fiber tapes, graphite-carbonate fabric, fiberglass reinforced plastic, carbon black filled epoxy compounds, non-linear conductivity epoxy compounds, filled with silicon carbide (SiC) powders, based on various epoxy resins and ternary epoxy compounds. The volt-ampere characteristics (VAC) of these semiconductive materials have been measured at dc and ac (50 Hz) voltages at room temperature, at 77.3 K inside liquid nitrogen, and again after heating to room temperature. The materials and their combinations that remained in the required range of resistance at 77.3 K were tested at 4.2 K. These tests suggest methods to obtain semiconductive materials for cryogenic temperatures. On the basis of these investigations, it is suggested that the corona protection system examined may be tested at high voltage at room temperature during manufacture and successfully operated at cryogenic temperatures.