Research the late discharge in VCB using point-to-plane electrodes

In order to investigate the behavior of protrusions in VCB, the point-to-plane insulation structure is constructed in vacuum. The high speed video camera is synchronized with the high voltage and used to visualize the phenomena. Particles are observed with supplementary laser. But, the vapor is recorded through the excitation emission with the projection of the field emission electron. It is observed that successive current pulse cascades during the conditioning process of the needle with the generation of the craters on the needle´s tip. Meanwhile, the tip explosion generally occurs at the peak of the pulse current. Through the frames in the video of the explosion, the speed of the particle is estimated within 150m/s. Through the computation of the Fowler-Nordheim (F-N) Curve, two patterns of field emission are revealed on the F-N plot, which are current rising pattern and current falling pattern. In the current rising pattern, the field enhancement factor is 10 times larger than that in the current falling pattern. Moreover, the two patterns are enclosed with the non-field emission cooling part to form a cycle on F-N plot.