Fundamental Research of Vapor-Mist Dielectrics for Insulation of Electric Power Apparatus

通过在缓冲气体中产生介电液体的蒸气和雾来制备蒸气-雾介质，并且已经表明少量的液体足以为缓冲气体提供额外的高介电强度。本计画的目的是探讨将蒸气雾状绝缘材料应用于电力设备绝缘的可能性，以达到小型化及改善性能的目的。在1987年，我们对C_8F_0<18>、C_8F_0<16>和（C_4F_9）_3N介质液体作为气雾剂的气雾绝缘特性进行了实验研究。主要结果如下。(1)每种液体都显示出清晰的汽雾效果。(2)由液体制备的所有蒸气-雾介质在4 mm的间隙长度下显示出两倍于大气的介电强度。(3)在关闭雾发生器后的1小时内，介电强度仅下降了10%。这表明可以显著地降低雾发生器的负荷。(4)在C_8F_2<18>和C_8F_0<16>的雾中，大部分雾粒子的直径在0.3 ~ 0.5 μ m之间。对于（C_4F_9）_3N雾，最常见的粒径为1.0 ~ 2.0 μ m。(5)除超声波振子外，其他方法产生的雾也具有类似的提高介电强度的效果。在1988财政年度，通过用脉冲高度分析仪观察平行板之间电子雪崩尺寸的分布，对在缓冲气体中产生蒸气雾而增加高介电强度的机理进行了研究。结果表明，在缓冲气体中产生水蒸气可以降低大尺度雪崩的发生频率，当同时产生水蒸气和薄雾时，这种作用似乎有所加强。结果表明，气雾的产生提高了介质的介电强度，这至少是由于缓冲气体的有效电离系数降低所致。

Vapor-mist dielectrics are prepared by generating vapor and mist of dielectric liquids in buffer gases, and small amounts of the liquid have been shown to suffice for giving additional high dielectric strength to the buffer gases. The objective of the present project is to find the possibility of applying vapor-mist dielectrics to the insulation of electric power apparatus for minimizing the size and improving the performance. In the fiscal year 1987, the insulation charac teristics of vapor-mist dielectrics was experimentally studied for C_8F_<18>, C_8F_<16>O and (C_4F_9)_3N dielectric liquids as vapor-mist. Main results are as follows.(1) Each of the liquids shows clear vapor-mist effect.(2) All of the vapor-mist dielectrics prepared from the liquids showed a dielectric strength twice as much as that of the atmospheric air at a gap length of 4 mm.(3) The dielectric strength decreased only by 10 % in 1 hour after the mist generator was turned off. This suggests that the duty of the mist generator may be reduced considerably.(4) In mists from C_8F_<18> and C_8F_<16>O, most of the mist particles had diameters ranging from 0.3 to 0.5 m. With (C_4F_9)_3N mist, the most frequent particles size was from 1.0 to 2.0 m.(5) Mists generated by other means than ultrasonic vibrator have similar effects of raising dielectric strength. In the fiscal year 1988, an investigation into the mechanism of the additional high dielectric strength by generating vapor-mist in buffer gases was done by observing the distribution of the size of electron avalanches between parallel plates by a pulse hight analyzer. It was found that the frequency of large size avalanche decreased by generating vapor in buffer gases, and this effect seemed to strengthen when both vapor and mist were generated. It may be concluded that the increases of dielectric strength by generation of vapor-mist is caused at lease by decrease of the effective ionization coefficient of the buffer gas.