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

蒸汽雾电介质是通过在缓冲气体中产生介电液体的蒸汽和雾来制备的，并且少量的液体已被证明足以给缓冲气体提供额外的高介电强度。本项目的目的是寻找将蒸汽雾介质应用于电力设备绝缘的可能性，以减小尺寸并提高性能。1987年，对C_8F_<18>、C_8F_<16>和（C_4F_9）_3N介质液体作为气雾介质的绝缘特性进行了实验研究。主要结果如下：(1)每一种液体都表现出明显的汽雾效果。(2)在间隙长度为4 mm时，液体制备的蒸汽雾介质的介电强度是大气介质的两倍。(3)在雾发生器关闭后1小时内，介电强度仅下降10%。这表明，雾发生器的职责可以大大减少。(4)在C_8F_<18>和C_8F_<16 >o的雾中，大部分雾粒的粒径在0.3 ~ 0.5 m之间。在（C_4F_9）_3N雾中，最常见的粒径为1.0 ~ 2.0 m。(5)除超声波振子外，其他方法产生的水雾也有类似的提高介电强度的效果。在1988财政年度，通过脉冲高度分析仪观察平行板间电子雪崩大小的分布，对缓冲气体中产生蒸汽雾而产生额外高介电强度的机理进行了研究。研究发现，在缓冲气体中产生蒸汽可以减少大型雪崩发生的频率，而在同时产生蒸汽和雾的情况下，这种作用似乎更强。由此可以得出结论，气雾的产生使介质的介电强度增加，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.