Experiments and simulation of helium breakdown at high pressure and temperature in a non-uniform electric field

Abstract Breakdown voltages of helium between needle-plane copper electrodes were measured to obtain the base data for insulation design of the electrical equipment working in high temperature and pressure helium gas in the High Temperature Gas-cooled Reactor (HTGR). The measurements were performed at a gap length between 1.02 mm and 5.30 mm, temperature and pressure varying from 0.01 to 7 MPa and 25–180 °C, respectively. Some abnormal “U-shapes” were found to appear especially at pressure over 3 MPa, which can be explained by the effects of space charge on the corona layer. COMSOL Multiphysics was used to simulate the discharge with a two-dimensional drift–diffusion model. The results agree well with the experimental data on the whole, but the errors rise when the pressure and gap length become very large. Evolutions of the current and particle number densities were also obtained. These breakdown voltages and characteristics of helium discharge is considered much valuable to the insulation design in HTGR.