Charge transport and accumulation around a spancer insulator for application in HVDC wall bushing

• Published in: IEEE transactions on dielectrics and electrical insulation Vol. 25; no. 1; pp. 281 - 293
• Main Authors: Liu, Qingying, Yan, Jiu Dun, Hao, Liucheng, Zhang, Bo, Liu, Shan
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.02.2018; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Charge density; Charge distribution; Charge transport; Conductivity; Electric fields; Electric potential; Electrical resistivity; Electron affinity; epoxy insulator; Gases; HVDC insulation; HVDC spacer; HVDC transmission; Insulators; Ions; Mathematical model; Mathematical models; Parameters; Polarity; Shielding; Sulfur hexafluoride; Surface charge; surface charge accumulation
• ISSN: 1070-9878; 1558-4135
• DOI: 10.1109/TDEI.2018.006683

A charge transport model based on ion drift in gases of strong electron affinity has been studied in details and validated against experimental results in air and SF6 at different pressure and voltage levels. The size of the insulators also differs significantly. The choice of the model parameters, i.e. the solid and gas material properties, is carefully examined with information from existing literature. Results show that using the selected parameters, satisfactory agreement between predicted and measured potential distribution and surface charge density along the insulator surface can be obtained. Computational results for an 1100 kV epoxy spacer for use in HVDC wall bushing show that the concept of electrical conductivity as a material property is no longer valid in strong electric field for the gas surrounding the insulator. The polarity and density of the accumulated surface charge depend on the relative largeness of the electrical conductivity of the insulator material and the effective conductivity of the gas. The nonlinear effect due to ion generation and recombination becomes significant at very high voltage. The metallic cap providing shielding to the triple junction at the high voltage end of the insulator can induce much stronger local electric field near the insulator surface, by a factor of 1.48, if its shape is not optimized against the insulator geometry.