Breakdown Characteristics under Metallic Particle Contaminated Conditions in Vacuum Gap

Abstract

An experimentwas carried out to investigate the influence of metallic particles on vacuum breakdown characteristics. By laser scattering method, the movement of particles, the lifting voltage of particles and the velocity of impact to the opposite electrode were measured. The particles were made of pure copper, and the particle diameter was 0.1 to 300 µm. The electrodes were parallel plane, 40 mm diameter, and two sets of electrodes (pure copper and stainless steel)were examined.Experimental results showed that breakdown voltage was reduced by the presence of metallic particles. This breakdown voltage reduction depended on the number of particles between elec trodes. The effect of electrodes material on breakdown characteristics was not apparently obser ved. The observation results of the paticle movement showed that the lifting voltage of particles decreased with decreasing particle size. The electrical breakdown of the gap occurred that when the impact velocity of the particles at the opposite electrode exceeded the critical value. We found microparticle-induced breakdown phenomena that could explain the phenomena of long delayed restrikes that is occasionally observed in vacuum circuit breakers.

Monte Carlo simulation of microparticle motion in vacuum gap

“…Finally, in each of the three cases, the degree of freedom adjusted determination coefficient (Adj. R ) was 0.93 or greater. Therefore, we can say that the regression curves satisfactorily explain the influence of each of the parameters.…”

“…For example, Kamikawaji et al . and Shioiri et al . demonstrated that the breakdown voltage in a gap may decline 30% or less due to the presence of electrically conductive microparticles.…”

Effect of contact surface on non-sustained disruptive discharge phenomena after current interruption in vacuum

“…① Growth of protrusion on the contact surface by applying voltage ② Melting of protrusion by emission current and emission of vapor and gas ③ Movement of particle between contact ( [6] suggests that dielectric breakdown occurs late after current interruption when metallic particles are poured onto the electrode surface.) Therefore we decided to examine the contact surface after current interruption to clarify these points [3,4].…”

“…Insulation breakdown occurs late as shown in Figure 22 when the collision energy of metallic particles is large because the metallic particles repeatedly collide on the electrode surface. In addition, the condition of electrode surface influences on dielectric breakdown [6]. The main reason for the later occurrence of NSDD after current interruption may be due to the above mentioned phenomenon.…”

Relation between breakdown voltage and prebreakdown current in vacuum gap

“…Therefore, the relation between breakdown and the prebreakdown current for an unconditioned electrode surface at currents of less than 10 6 A is not clear. Papers on the relation between electrode conditioning and the prebreakdown current [10,11] note that breakdown occurred suddenly on unconditioned electrodes despite the fact that no prebreakdown current was detectable by a pico-ammeter, suggesting that the sudden breakdown was related to lower current levels.…”