Experimental study on breakdown voltage of high pressure and high temperature helium gas between parallel electrodes

Abstract

The DC and 50Hz AC breakdown voltage of helium between two parallel copper electrodes were measured to obtain the base data for insulation design of the electrical equipment working in the high pressure and high temperature helium gas in High Temperature Reactor (HTR). The measurements were performed in the distance of 0.25–0.53mm, the temperature of 15–180°C, and the pressure of 0.05–7MPa. It has been proved that, for both DC and 50Hz AC, the breakdown voltage increases with the increasing of the pressure, with the increasing of the distance, and with the decreasing of the temperature. The DC breakdown voltage is about 1.4 times of the value of 50Hz AC or, in other words, is similar to the peak value of 50Hz AC. The Paschen law, describing the relationship between the breakdown voltage of helium (Ub) and the product of gas density and electrode distance (ρd), was presented for DC and 50Hz AC respectively, based on the experimental data at high pressure and high temperature. Good linearity is shown in the data. Furthermore, the linear fitting equation was also presented. The slope of Paschen curve about Ub-ρd at the range of large ρd is influenced by the collision cross section and the ionization energy of helium atom, and not influenced by the temperature, for DC. Both for DC and 50Hz AC, the slope of Paschen curve about Ub-ρd is about 6×105 times of the slope of Paschen curve about Ub-Pd, where Pd is the product of gas pressure and electrode distance. Both for DC and 50Hz AC, the breakdown voltage of helium is less than one fifth of the value of air, at 0.1MPa and room temperature. However, the breakdown voltage of helium at 180°C and 7MPa is larger than the value of air at 0.1MPa and room temperature.