Basic Study on Electrical Insulation Property in a New Type Cryogenic Gas Insulated Transmission Line

利用高温超导体实现气体绝缘输电线路和电力设备，需要深入研究低温气体空间的电绝缘特性。在低温恒温器提供的-180℃低温气体空间中，首次研究了非均匀场隙中的电击穿特性，如棒-面电极在闪电或开关脉冲电压作用下的击穿特性。其次，利用体积为1m^3的大型低温恒温器，测量了低温均匀场间隙大于100 mm且尚未积累数据的电击穿电压。主要研究结果如下：1)室温下空气中非均匀场隙的击穿电压按雷电冲击、操作冲击和直流电压的顺序依次升高。2)氮气中非均匀场隙的击穿电压几乎不依赖于温度或电压波形。它主要取决于高电位杆电极的尖端半径，并且随着半径的增大而增大。3)电晕放电产生的电荷强烈地依赖于电晕发生电压。对于相同的电晕发生电压，在-180℃下观察到的电荷变得比在室温下观察到的小。4)直径为150 mm的球-球间隙的击穿电压随着间隙长度的增加而线性增加，直到100 mm时，对于所有的直流、交流和脉冲电压波形，击穿电压都趋于饱和。在线性关系范围内，证实了低温下的帕森定律是成立的。

An intensive study on electrical insulation property in a cryogenic gas space is required for realizing a gas insulated transmission line and an electric power equipment using a high temperature super conductor. Electrical breakdown characteristics in a non-uniform field gap such as a rod-to-plane electrode which is stressed by lightning or switching impulse voltage are first investigated in a cryogenic gas space of -180 degrees Celsius provided by a cryostat. Secondly, electrical breakdown voltages of a cryogenic and uniform field gap of more than 100 mm whose data have not been so far accumulated are measured using a large cryostat of 1 m^3 in volume. Main results obtained form these studies are summarized as follows.1) The breakdown voltage of a non-uniform field gap in air at room temperature becomes higher in the order, for lightning impulse, switching impulse and dc voltages. On the other hand, the value at cryogenic temperature becomes in the reverse order.2) The breakdown voltage of a non-uniform field gap in nitrogen gas hardly depends on either temperature or voltage waveform. It mainly depends on the tip radius of a high potential rod electrode and it increases with increasing radius.3) The charge produced due to corona discharge strongly depends on the occurrence voltage of the corona. the charge observed at -180 degrees Celsius becomes smaller than that observed at room temperature for the same corona occurrence voltage.4) The breakdown voltage of a sphere-to-sphere gap of 150 mm in diameter increases linearly with increasing gap length up to 100 mm and tends to saturate over the gap length of 100 mmfor all voltage waveforms of dc, ac and impulse. In the region of the linear relationship, it is confirmed that the Paschen's law holds true for cryogenic temperature.