Common insulation gas cannot normally work in refrigeration temperature range(153-243 K), especially in extremely cold regions. To solve this problem, this essay uses cubic equation combined with two-parameter model in theorem of corresponding states to estimate dew-point of hybrid gas. The influence of temperature on mixing ratio is studied by using van der Waals equation. The result shows that the mixing ratio is stable during temperature-fall period. Insulation property of CF_4 and CF_4/N_2 in refrigeration temperature range is studied through self-designed low-temperature test system. The result shows when the density of hybrid gas is invariable, temperature changing has less influence on breakdown voltage, and when the mixing ratio is 20%, CF_4/N_2 is the greatest potential hybrid gas.
HOU Meng-xiLI Wei-guoYUAN Chuang-yeYANG Yi-xinOUYANG Jie
Self-organization phenomena on the surface of a metal electrode in low-pressure DC discharge is studied. In this paper, we carry out laboratory investigations of self-organization in a lowpressure test platform for 100–200 mm rod-plane gaps with a needle tip, conical tip and hemispherical tip within 1–10 k Pa. The factors influencing the pattern profile are the pressure value, gap length and shape of the electrode, and a variety of pattern structures are observed by changing these factors. With increasing pressure, first the pattern diameter increases and then decreases. With the needle tip, layer structure, single-ring structure and double-ring structure are displayed successively with increasing pressure. With the conical tip, the ring-like structure gradually forms separate spots with increasing pressure. With the hemispherical tip, there are anode spots inside the ring structure. With the increase of gap length, the diameter of the selforganized pattern increases and the profile of the pattern changes. The development process of the pattern contains three key stages： pattern enlargement, pattern stabilization and pattern shrink.
The mechanism of gas discharge in refrigeration temperature range is still not clear. N2, CF4, 20% CF4＋N2 and 50%CF4＋50%N2 binary gas mixtures were tested under the conditions of –153–25 ℃ and 50–2000 Pa. The experimental results show that the minimum of Paschen curves of all test samples shifts to low pressure, from 500 Pa to 200 Pa. The value of Paschen curve minimum of N2 shows remarkable fluctuation. This fluctuation is explained by molecule agglomeration and electronic mean energy. The fluctuation decreases with the increasing mixing ratio of CF4. What’s more, the value of Paschen curve minimum of CF4 decreases with temperature. This phenomenon is ascribed to attach-radiation and secondary process.
LI Wei-guoHOU Meng-xiYUAN Chuang-yeCHENG Yu-diTU You-ping
为研究低气压下长间隙工频放电击穿电压与气压U_(50%)-P关系曲线饱和特性,利用低气压放电试验平台对2~70 k Pa气压范围内300~600 mm棒-板间隙进行了工频放电试验研究,得到不同间隙距离的U_(50%)-P曲线,并对曲线饱特性以及饱和区击穿前过程进行研究。研究结果表明:在2~70 k Pa气压范围内不同棒-板间隙的U_(50%)-P曲线均存在明显饱和区,随间隙距离减小饱和区向高气压方向移动,饱和范围增大且U_(50%)分散性增大。产生上述现象的的原因为:饱和区内击穿前间断发展的流注放电产生大量空间电荷,影响电子自由行程和碰撞几率,削弱了气压对电子自由行程和碰撞几率的影响。研究结果对研究低气压下长空气间隙放电特性提供参考。
