In this study, the insulating properties on DC voltage in hydrogen atmosphere at high temperatures (600-850°C) were evaluated for alumina (Al2O3), magnesia (MgO), silicon nitride (Si 3N4) and mica (KMg3 (Si3Al) O 10 (OH) 2) to comprehend the difference in insulating properties of oxide, nitride and mineral. The activation energies of electrical conductivity of alumina and magnesia in hydrogen were larger than those in air. On the other hand, at silicon nitride and mica electrical conduction in hydrogen were same as those in air. Therefore low oxygen partial pressure would have some influence on electrical conduction of oxide. And increasing temperature didn't bring a huge change of electrical conduction mechanism in all materials and both of the atmospheres. The maximum amounts of partial discharge in hydrogen tended to increase compared to those in air at high voltage. Applied voltage, in which the maximum amounts of partial discharge started to increase rapidly, became lower with increasing temperature in all materials and both of the atmospheres. The total amounts of partial discharge tended to decrease with increasing temperature in all materials and both of the atmospheres. However, at exceeding certain temperatures, the total amounts of partial discharge increased or slightly decreased.
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