A high quality factor (Q-factor) is most desirable for resonant mass sensors because their sensitivity greatly depends on the detectable frequency shift after mass adsorption. The authors fabricated lead zirconate titanate (PZT) thin film transduced micro cantilevers and studied the energy dissipation mechanisms to better understand the essential aspects affecting the Qfactor. It was found that energy dissipation induced by the multi-layered device structure and the PZT thin film was noteworthy even under atmospheric pressure conditions. The effects of the PZT film on the energy dissipation became dominant under reduced pressure. Accordingly, the Q-factors of cantilevers without PZT film became larger than those with PZT film when pressure was reduced into the molecular flow region. The single-layered SiO 2 cantilever exhibited the largest intrinsic Q-factor. The electro-mechanical conversion in the PZT film and the thermoelastic damping caused by the property difference between each layer contributed significantly to the energy dissipation.
In order to identify the long span reliability of vacuum gap insulation under continuous AC voltage application, characteristics of breakdown strength versus breakdown time (long time E-t characteristics) were measured for a uniform and a non-uniform field gap. The breakdown strength of these gaps before the discharge conditioning treatments did not depend on breakdown time. However, after the discharge conditioning treatments, the breakdown strength became describable as an experimental formula E = A ・ t -1 / n . The value of drop index (life index) n in the formula was a maximum of 75 for the uniform field gap, while a maximum of 25 for the non-uniform field gap. In addition, with repeating the discharge conditioning treatment, the long time E-t characteristics of both gaps shifted to higher electric field. In particular, the value of n for the uniform field gap became larger. Breakdown modes (failure modes) of these gaps before and after the discharge conditioning treatments, evaluated by the value of shape parameter m in Weibull probability distribution function, were classified into decreasing failure rate mode and constant failure rate mode, respectively. キーワード:真空,絶縁破壊,長時間 E-t 特性,放電コンディショニング Keywords:vacuum, breakdown, long time E-t characteristic, discharge conditioning 1. はじめに SF6 ガスが温室効果ガスに指定されたことを背景に, 開閉 装置では真空絶縁の適用範囲が拡大している。真空絶縁は 真空遮断器の接点間絶縁だけでなく,断路器や接地開閉器 の接点間や対地間絶縁にも適用され始めている (1)~(3) 。これ らの新たな真空絶縁では,交流電圧の連続印加時間が真空 遮断器の接点間絶縁よりも長くなる。すなわち真空遮断器 接点は常時閉の状態で運用されることが多く,その場合電 流遮断のため接点を開極した後に絶縁が必要になる。これ に対し,対地間絶縁および常時開極状態で用いられる接地 開閉器の接点間絶縁では,その機能上,長期間の連続的な 絶縁が必要になる。このような背景から,真空絶縁の長期 信頼性に対する検討が必要になっている。 真空絶縁の長期信頼性を検討するには,交流課電時間に 対する破壊電圧または破壊電界の特性(本論文では長時間 V-t 特性または長時間 E-t 特性と呼び,印加電圧波形の影響 検討のために測定するµs~ms 領域の V-t,E-t 特性と区別 した)を取得し,その特性に基づいて長時間課電時の破壊電 圧を見積もる必要がある。しかしこの点を検討した報告は 少ない。長時間課電に伴う破壊電圧の低下は知られている が (4)~(6) ,その低下割合を表し絶縁裕度見積もりに重要な垂 下係数(または寿命係数)の値は不明確である。実用面では, 短時間破壊特性の向上に効果がある放電コンディショニン グの,長時間破壊特性に対する効果の検討も必要と思われ る。さらに,長時間課電に伴う破壊電圧の低下が,電極表 面状態の劣化に起因するかの検討も必要である。これらに * 三菱電機 (株) 先端技術総合研究所 〒661-8661 尼崎市塚口本町 8-1-1 Advanced Technology R&D Center, Mitsubishi Electric Corporation 8-1-1, Tsukaguchi-honmachi, Amagasaki 661-8661 ** 三菱電機 (株) 受配電システム事業所 〒763-8516 丸亀市蓬莱町8番地 Power Distribution Systems Center, Mitsubishi Electric Corporation 8, Horai-cho, Marugame 763-8516 論 文
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