•マイカ•アルミナ複合絶縁の高温課電寿命に関する検討

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タイトル別名
  • Investigation on Voltage Life of Mica-Alumina Combined Insulation at High Temperatures
  • マイカ・アルミナ複合絶縁の高温課電寿命に関する検討
  • マイカ アルミナ フクゴウ ゼツエン ノ コウオン カデン ジュミョウ ニ カ

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Experiments and investigations were carried out on voltage life of a bar coil model with a nickel plated copper conductor covered with mica-alumina combined insulation at a temperature range of 550-850°C.<br>Diffusion of copper into the insulation layer was observed on the specimens aged for a long period. The insulation with mica paper was faster in the diffusion speed and shorter in the voltage life than the insulation with mica splitting. The diffusion speed became higher with the increase of temperature. Ac current gradually increased with the aging time, and increased rapidly just before the breakdown time. Betxeen ac current I and applied stress E, there was the relationship of I=aE n (a, n: constants). and n was approximately equal to one in the region where the thermal unballance did not occur. The Arrhenius s law held good in the relation between ac current and aging time. Therefore, breakdown mechanism might be that the effective insulation thickness decreased due to the copper diffusion into the insulation layer and the ac current increased gradually until the thermal breakdown at the last stage. If the diffusion of copper into the insulation layer occurs, even in the case with no voltage application, the aging time required to decrease the breakdown voltage to a certain level (the time is called as life here), obeys the Arrhenius s law. If the life is dominated by the diffusion into the insulation layer, the activation energy for the life in the aging test becomes twice that for the diffusion, irrespective of with or without voltage application.

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