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Secondary arc is more severe in the ultra-high voltage (UHV) power grid. However, the mechanism for the generation process of secondary arc at the extinction moment of a short-circuit arc is not yet clear. It is of great theoretical significance and technological application value to study the generation mechanism and dynamic physical characteristics of secondary arc, and further to develop effective suppression technology. In this article, an arc numerical simulation model based on the coefficient partial differential equations combining with classical drift-diffusion model was established, and the implementation method based on the finite element software COMSOL (COMSOL Multiphysics 5.2a, COMSOL Inc., Stockholm, Sweden) was given. Then, the transient analysis method was applied to simulate the generation, diffusion and dissipation phenomena of the short-circuit arc strike, and further to explore the electric field, microscopic particle spatial distribution and reaction process during the arc discharge process. The simulation results show that the development of short-circuit arc mainly includes two processes: corona discharge and arc discharge, of which the former has a very short duration and the latter is caused by short-circuit. During the discharge process, the electron density first increases and then decreases, which is different from the general characteristics of streamer discharge. Although the concentration distribution curve of the positive ions and negative ions has the same trend, there are subtle differences. The diffusion effect of space ions in the initial discharge stage is almost zero, while radial diffusion direction in the peak discharge stage and axial direction in the late discharge stage. The electric field intensity in space has an S-shaped upward trend during discharge. The time relationship of the ion source generated by the neutralization reaction and by the short-circuit arc discharge are basically the same, and the rate of neutralization reaction is lowest near the electrode. When the ionic reaction is approaching the end of the simulation, the ionic concentration is higher than the initial level, which proves that the space ionic concentration is increased due to the short-circuit discharge, and providing the necessary environmental conditions for the subsequent generation of the secondary arc.

Tel: 33 4 76 82 64 40 Fax: 33 4 76 82 63 00 Abstract -In the framework of live working in a rVIV network, a cable-transformer system can be switched-off or switched-on. The ferroresonance phenomenon can occur during this procedure with very dangerous overvoltages. The metal oxide varistor (MOV) can fail during this phenomenon. The paper investigates the determination of the critical feeder length of cable, which will damage MOVs. A transformer model taking into account both the saturation and the hysteresis is proposed. The digital simulation concerning de-energhation of the real configuration of the cable-transformer system is studied and the results obtained are verified by field tests.