Effects of nanoparticle charging on streamer development in transformer oil-based nanofluids

作者：J. George Hwang, Markus Zahn, Francis O’Sullivan, Leif A. A. Pettersson, Olof Hjortstam, Rongsheng Liu · 发表于：Journal of Applied Physics · 年份：2010 · DOI：10.1063/1.3267474 · 被引用次数：361 · 研究领域：Power Transformer Diagnostics and Insulation、High voltage insulation and dielectric phenomena、Electrohydrodynamics and Fluid Dynamics

Transformer oil-based nanofluids with conductive nanoparticle suspensions defy conventional wisdom as past experimental work showed that such nanofluids have substantially higher positive voltage breakdown levels with slower positive streamer velocities than that of pure transformer oil. This paradoxical superior electrical breakdown performance compared to that of pure oil is due to the electron charging of the nanoparticles to convert fast electrons from field ionization to slow negatively charged nanoparticle charge carriers with effective mobility reduction by a factor of about 1×105. The charging dynamics of a nanoparticle in transformer oil with both infinite and finite conductivities shows that this electron trapping is the cause of the decrease in positive streamer velocity, resulting in higher electrical breakdown strength. Analysis derives the electric field in the vicinity of the nanoparticles, electron trajectories on electric field lines that charge nanoparticles, and expressions for the charging characteristics of the nanoparticles as a function of time and dielectric permittivity and conductivity of nanoparticles and the surrounding transformer oil. This charged nanoparticle model is used with a comprehensive electrodynamic analysis for the charge generation, recombination, and transport of positive and negative ions, electrons, and charged nanoparticles between a positive high voltage sharp needle electrode and a large spherical ground electrode. Case studies ...