Influence of Humidity on the Dielectric Breakdown Properties of Nitrogen Switchgears

Abstract

Nitrogen is an environmentally friendly insulating medium gas most commonly used in medium-voltage (MV) gas switchgear. In this paper, the effect of humidity on the insulating property of nitrogen switchgears, namely, a small amount of water impurities mixed in N2 on dielectric breakdown characteristics of gas mixtures for a temperature range from 300 K to 4000 K at pressure of 0.1 MPa is analyzed. First of all, based on the Gibbs minimum free energy, the equilibrium composition of hot humid N2 with different water impurities fractions is calculated. Then, by solving the 2-term Boltzmann equation, the electron energy distribution functions is devoted to computing. The reduced ionization coefficient (α/N), the reduced attachment coefficient (IJ/N), and the reduced effective ionization coefficient (αeffIN) are then obtained based on the electron energy distribution functions. Eventually, the critical reduced electric field ($E$/$N$)cr is calculated. The result shows that the ($E$/$N$)cr of the humid N2 vary with the concentration of water impurities. Additionally, it is important fundamental data for the evaluation of the dielectric breakdown characteristics of N2 insulated switchgears with a small amount of water impurities.