Aiming at the issue of gas model selection of DC gas-insulated device in electric-field analysis and design
a model for electric-field evaluation is established for an epoxy cast insulator installed in HVDC gas-insulated wall bushing. Ion-drift model and linear model are considered for gas domain respectively. Calculating and analyzing the surface electric fields under DC voltage
the influences of two models on calculated results for different gas ionization rate
applied voltage level
bulk conductivity as well as the alternative conditions under DC voltage are investigated and the suggestions for gas model selection are proposed. The results show that the calculated results of ion-drift model depend on electric-field strength and are affected by the uneven space charges with gas nonlinearity. The gas conductivity in linear model matching ion-drift model is proportional to gas ionization rate and inversely proportional to applied voltage level. In the case of higher voltage level and larger bulk conductivity of insulator
the bulk current dominates the surface charge accumulation and calculated result for ion-drift model slightly differs from that for linear model. The linear model is more applicable to optimal design for epoxy cast insulator with shorter calculating time.
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