Study on Creeping Partial Discharge and its Influence for Inorganic Insulating Materials at High Temperatures

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Various fundamental studies on partial discharge of inorganic insulating materials at high temperatures, performance improvement investigation of an electric motor applied with heat-resist insulation, dielectric properties of direct current high voltage, and dielectric constant characteristics for condenser materials have been carried out. The schematic results are summarized below.(1) Partial discharge generation phenomena have been measured with several kinds of ceramics. Discharge quantity increases with temperature rise but saturates above a threshold value because of local enhancement of conductance. It has been hinted that the threshold temperature rises as a function of thermal conductivity of specimen.(2) Increase effect of power density on heat-resist motor has been evaluated by computer simulation. It has been clarified that the power density improves up to 400℃ but significant effect cannot be obtained higher than it.(3) Insulating properties of disc shape alumina ceramics have been measured with applying DC voltage in nitrogen atmosphere up to over 500℃. The partial discharge inception voltage decreases with temperature rise and saturates at temperatures higher than 500℃.(4) The dielectric constant of BaTiO_3 ceramics follows the Curie-Weiss theory from 150℃ to 300℃ However, the characteristics changes like a resistance. It has been considered that the reason is due to a reduction of the apparent resistance value with leak current enhancement including partial discharge.