Nitrogen is an environmentally friendly insulating medium gas most commonly used in medium-voltage (MV) gas switchgear. In this paper, the influence of a small amount of water impurities mixed in N₂ on dielectric breakdown properties of gas mixture at pressure of 0.1 MPa for a temperature range of 300 K–4000 K is numerically analyzed. First, the equilibrium composition of hot N₂ with different water impurities fractions is calculated using a method based on the Gibbs minimum free energy. Then, the electron energy distribution functions (EEDF) is devoted to computing by solving the two-term Boltzmann equation. The reduced ionization coefficient, the reduced attachment coefficient, and the reduced effective ionization coefficient are then obtained based on the EEDF. Finally, the critical reduced electric field (E/N)_cr is obtained. The result shows that the (E/N)_cr of the mixtures vary with the concentration of water impurities. Additionally, it is important fundamental data for the evaluation of the dielectric breakdown properties of N₂ insulated switchgears with a small amount of water impurities.
 

gas switchgear,dielectric breakdown properties,water impurities,the Boltzmann equation