Research on the erosion characteristics of air arc on contacts under harmonic current

In new energy generation systems, grid-connected inverters generate a large amount of harmonic currents during operation due to inherent factors, such as modulation effects and deadband characteristics. The injection of harmonic currents leads to the distortion of the grid-connected current waveform, which affects the breaking arc characteristics of the inverter-side circuit breaker, resulting in a higher incidence of post-arc re-breakdown accidents and exacerbating the erosion of the circuit breaker contacts. In order to study the above phenomenon in depth, first, the change rule of electrode erosion quality under the action of harmonic current is analyzed by building an electrode erosion experimental platform. Second, the arc was equated to a Gaussian distributed heat source, and the melting phase change process of the contact was simulated based on the heat conduction theory and fluid theory combined with the melting-solidification model, while the evaporation and sublimation effects of the material were considered comprehensively. Based on this model, the effects of harmonic content and harmonic frequency on the ablation characteristics of the anode contact were deeply analyzed. The results show that the role of harmonic frequency on the anode ablation process is obvious, and when the harmonic current frequency increases, the surface temperature of the anode, the size of the melting pool, and the ablation quality also increase; when adding different contents of fifth harmonic currents in the short-circuit current, with the increase in the harmonic current content, the onset of the erosion time of the material is then shifted forward, the maximum rate of ablation is significantly elevated, the duration of material evaporation is prolonged at the same time, and the process of material evaporation is intensified.