Helium now commonly serves as the coolant in high temperature gas-cooled reactor (HTGR). Some electrical facilities work in helium gas at certain temperature and pressure, such as the helium blower, magnetic bearings and the electrical penetration assemblies. Because the insulation property of helium is much poorer than that of air, especially at high pressure, the insulation design of these electrical facilities is rather important and challenging. So far, national standards of insulation design is only for the air while there exists almost no industrial standard for helium gas. In addition, not many scientific researches on insulation property of helium have been conducted yet and most efforts were made to deal with liquid helium. In this paper, uniform field breakdown strength in millimeter-scale gaps of helium was studied with a streamer model analysis, at from 15°C to 180°C and 0.01MPa to 7MPa. Coefficients of Paschen law are modified to better fit the experimental data under specific conditions and some analysis or explanation was given. The experimental data and rules obtained will be useful for the design of insulation structure in helium gas and promote the study of HTGR.

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