Particle-Initiated Breakdown Characteristics of Conical Insulator in N2 GAS and N2/02 Mixture under DC Voltage

Particle-initiated breakdown characteristics of conical spacers were investigated experimentally in N2 and 79% N2/21% 02 gas mixture to provide fundamental parameters determining the breakdown voltage of a dielectric spacer contaminated by metallic particles. Experimental results show that the breakdown voltage of a particle-contaminated spacer increases with the value of |90-¿|, while in contrary that of the clean spacer decreases with the value of |90-¿| in the region of ¿ of 0|90-¿|60 degrees where the spacer angle ¿ is defined as the angle between the spacer surface and the anode plane electrode. With a given spacer the breakdown voltage reveals the minimum value (MBDV) when a particle was placed very near the anode in N2/02 mixture, and on or very near the electrodes in N2 gas. At the particle conditions giving the MBDV, the corona stabilization effect is less effective. The MBDV decreases with decreasing in the gas pressure and the wire particle diameter. The critical particle length beyond which the breakdown voltage is lowered by the particle depends on the spacer shape. Analysis of the MBDV to include a minimum electric field necessary for discharge propagation along the spacer surface and the effect of the field enhancements due to particle on a cylindrical spacer shows fairly good agreement with the experimental results.