Analysis Model for VFT Considering the Effect of Nonuniform Distribution of Residual Charge

The magnitude and distribution of residual charge have a significant effect on very fast transients (VFTs) in gas-insulated substations (GISs). So far, as we know, references for researching the effect of a nonuniform distribution of a residual charge on VFT have not been found. Considering the effect of a nonuniform distribution of a residual charge, a hybrid method is presented in this manuscript by combining the finite-element method (FEM) and finite-difference time domain (FDTD) for analyzing VFT. In this method, the distribution of residual charge along a no-load line may be first analyzed at the moment before the arc starts by using the FEM. And then, based on transmission-line theory and considering the residual charge as an initial value, VFT is analyzed by using FDTD. The validation of the method was performed in comparison with the 3-D-Maxwell model-based transient simulation. On the point of setting initial voltage, the proposed analysis process is more practical to actual VFTs than the Electromagnetic Transients Program and COMSOL analysis in references, and it is better to deeply research the mechanism of VFT generation, especially the effect of the initial phase of operation on VFTs and the suppression of VFT overvoltage in GIS.