Research On The Accurate Simulation Model Of VFTO Considering Non-uniform Distribution Of Residual Charge

GIS is the core component of the electric power system. The gap between contacts will strike when disconnector operation happens in gas insulated substation, and the overvoltage wave will refract and reflect as result of wave impedance’s sudden change. Therefore a very fast transient voltage (VFTO) in GIS is initiated by superposition of travel waves. Residual charge is left on the no-load bus after the arc extinction between contacts. Residual charge releasing may lead to a more severe VFTO in GIS. And it’s well known that charge is distributed nonuniformly on the bus. Above all, it’s essensial to research on the voltage response produced by residual charge releasing. Based on 252kV GIS model two methods are used to analyze the effect of non-uniform distribution of residual charge.Firstly, non-uniform distribution of residual charge is simulated. Based on transmission line model, a new line model based on charge density is proposed to solve the voltage response produced by residual charge. And the comparsions are made between the result obtained with the FDTD and the EMTP. When insulator is equivalent with lumped capacitance in EMTP and the source line don’t have initial value,the results obtained with both the two case is not accurate enough.Secondly, based on 3D full-maxwell model, FEM (Finite Element Method) method is used to simulate the effect of non-uniform distribution of residual charge. The electromagnetic field of GIS and characteristics of very fast transient are obtained.3-D electromagnetic FEM method is regarded as accurate method. VFTOs were analyzed based on electromagnetic FEM method with not only considering the structure of conductors and contacts but also considering the non-uniformity of residual charge along the conductor at initial time. From simulation results we can see that VFTOs within early time are largely affected by the initial charge distribution. And the initial potential of no-load line is significantly determined by the distribution of charge. Comparisons of simulation results were made between circuit-based model and field-based model. The discussions about the key use of field based model were taken.Finally, two methods mentioned above are compared, and their advantages and disadvantages are analysed. A lot of time can be saved by FDTD, but the result between 3D fields is not considered.3D full-maxwell is more accurate but it is hard to split grid precisely.