STUDY OF ELECTRICAL INSULATION CONDITION FOR GAS INSULATED CUBICLE (C-GIS) BY <SF_6> AND FLUOROCABON MIXTURES

气体绝缘柜（C-GIS）是传统<SF_6>绝缘开关柜的推广版本。通过使用C-GIS将气体压力降低到大气压力或大气压左右，从而使容器结构更简单，从而追求经济性。由于气体压力降低，C-GIS击穿场强较低，但也可继承GIS的其他优点。本项目的目的是寻找利用<SF_6>和氟碳气体混合物的协同作用来提高击穿强度的可能性。利用气雾介质达到这一目的的可能性也进行了实验测试。主要结果如下：1)实验证实了<SF_6>与c- <C_4F_8>、<SF_6>与1- <C_3F_6>气体混合物击穿强度的协同作用。击穿强度比两种单一气体的击穿强度高30%左右。2)实验首次阐明了增效作用的原因：由于混合物的有效电离系数< α >降低。3)首次发现了c- <C_4> <F_8>气体击穿场强的压力依赖性。气体压力越高，击穿强度越大。其原因是有效电离系数随压力的增大而减小。4)常压空气+ < c_4f_0 <F_(14)>蒸汽雾的击穿强度是空气的4倍以上，空气+ <(C_4F_9)_3> N雾在停止产生雾后持续时间超过50分钟，大大降低了发电机的工作负荷，这两者都是首次出现。这些结果有力地说明了气雾介质绝缘在C-GIS中的有效性。

Gas Insulated Cubicle (C-GIS) is a popularized version of the conventional <SF_6> insulated switchgears. Economy is pursured by reducing the gas pressure to or around that of atmospheric air and thus by making the structure of container simpler with C-GIS. Since the gas pressure is reduced the breakdown field strength would be low with C-GIS, although other merits may be inherited from GIS. The purpose of the present project is to find possibilities of improving the breakdown strength by utilizing the synergism of <SF_6> and fluorocarbon gas mixtures. A possibility of attining the purpose by using vapor-mist dielectrics is also tested experimentally.The main results are as follows.1) Synergism in breakdown strength of <SF_6> and c- <C_4F_8> and <SF_6> and 1- <C_3F_6> gas mixtures is confirmed experimentally. The breakdown strength is about 30 % higher than that of either of the single gases.2) The cause of the synergism is clarified experimentally for the first time : it is due to the reduction of the effective ionization coefficient <alpha> of the mixture. 3) The pressure dependence of the breakdown field strength of c- <C_4> <F_8> gas is discovered for the first time. The breakdown strength is larger with higher gas pressure. The cause is found due to the decrease of the effective ionization coefficient with increasing pressure.4) Atmospheric pressure air plus <C_6> <F_(14)> vapor-mist is found to have more than 4 times larger breakdown strength of the air, and the air plus <(C_4F_9)_3> N mist is found to endure more than 50 minutes after the mist generation is ceased, reducing greatly the duty of the generator, both for the first time. These results strongly suggest the effectiveness of vapor-mist dielectric insulation for C-GIS.