高压氦气平行极板击穿电压实验研究

为获得高温气冷堆核电站电气设备绝缘设计所需基础数据, 本文设计了一套测量高压氦气绝缘性能的装置. 利用该装置进行了15-20 ℃, 0.1-7 MPa氦气, 间距0.25, 0.35, 0.5 mm平行极板击穿实验. 实验表明: 氦气的绝缘性能远低于空气; 气压越高, 氦气的击穿电压越大, 3.0 MPa氦气的击穿电压与常压空气基本一致; 根据低气压实验数据和巴申定律推导的公式, 在高气压下计算值偏大, 且偏差随着气压和间距乘积的增大不断增大; 提出了可计算0.1-7 MPa氦气击穿电压的简易公式, 同时修正了高气压氦气的巴申公式, 并进行了理论分析.

Experimental study on breakdown voltage between parallel plates in high-pressure helium

To obtain the base data for insulation design of the electrical equipment used in the high temperature gas cooled reactor nuclear power plant, an experimental apparatus for testing helium insulation property under high pressure is designed. The apparatus is composed of a pressure vessel, a heating system, an electrical penetration assembly, a vacuum pump, a pressure gauge, a safety pressure valve, a release valve, and a helium bottle. The highest pressure that the vessel can hold is 10 MPa, and in this experiment the safety pressure valve is set to be 8 MPa. The temperature inside the vessel can be heated to 200 ℃ by a heating system. The resolution of the pressure gauge is 1 kPa, and the highest pressure that the gauge can measure is 9.999 MPa. The purity of the helium used in this experiment is 99.999%. The breakdown voltage of helium gas between two parallel plane electrodes is measured by the apparatus under the conditions of 15-20 ℃ and 0.1-7 MPa. The electrodes are made of copper, and their diameters are both 100 mm. The distances between the parallel electrodes are 0.25 mm, 0.35 mm and 0.5 mm respectively. The error of the distance is less than 0.01 mm. The DC voltage between the electrodes is supplied by GPI-735A, a withstand voltage and insulation tester produced by GW Instek corporation. The voltage increases slowly from 0 to 6000 V (highest), until the current more than 0.1 mA is detected. The highest voltage recorded is the breakdown voltage. With other researchers’ experimental data under low pressure, the Paschen equation for helium gas is obtained. It is found that the calculated breakdown voltage for this equation is larger than the experimental result in this paper under high pressure. And the deviation becomes larger as the product of the pressure and the distance increases. Firstly, it is because the ionization coefficient γ in the equation is influenced by the gas pressure. Secondly, because of larger areas of electrodes, worse surface roughness and less electrode distance, under the same product of the pressure and the distance, the breakdown voltages in this paper are less than the ones in other researches, which are the base of the calculated values. The Paschen equation is modified to accord with the values under high pressure. Under high pressure, the Paschen curve is almost a straight line. A linear equation is presented for calculating the breakdown voltages of helium gas under 0.1-7 MPa. And an equation is presented to calculate the slope of the line. The slope is influenced by the collision cross section, the ionization energy and the temperature of the helium. The experimental data also show that the breakdown voltage of helium is far lower than that of air under the same condition. As the pressure increases, the breakdown voltage of helium increases. The value of helium under 3 MPa is equal to the one of air under atmosphere, and the value of helium under 7 MPa is about twice as high as that of helium under 3 MPa. So, it is possible to replace some experiments or tests under high pressure helium by the same operations under atmospheric air.