To develop a sodium immersed type electromagnetic pump which is expected to contribute to the realization of the FBR plant in the near future, the establishment of an electrical insulating technique at temperatures exceeding 500°C is indispensable. Also, the mechanism of the dielectric deterioration has to be understood.
Using mica-alumina combined insulation, an ageing test was performed by applying high voltage in nitrogen at high temperatures. As a result, all the specimens with high voltage applied at 750°C caused dielectric breakdown around 1000 hours, but an emergency signal could be detected before dielectric breakdown by monitoring the a. c. current. Mica splittings insulation is superior in dielectric performance to mica paper. The deterioration mechanism was found to be mainly subject to thermal influence.
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