Effects of nanoparticle charging on streamer development in transformer oil-based nanofluids
Effects of nanoparticle charging on streamer development in transformer oil-based nanofluids
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DOI：
10.1063/1.3267474
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发表时间：
2010-01-01
影响因子：
3.2
通讯作者：
Liu, Rongsheng
中科院分区：
文献类型：
--
作者：
Hwang, J. George;Zahn, Markus;Liu, Rongsheng
具有导电纳米颗粒悬浮液的变压器油基纳米流体打破了传统观点，因为过去的实验工作表明，这种纳米流体比纯变压器油具有更高的正电压击穿水平和更慢的正流光速度。与纯石油相比，这种矛盾的优越电击穿性能是由于纳米粒子的电子充电，将快电子从场电离转换为慢速负电荷纳米粒子电荷载流子，有效迁移率降低约1x10(5)倍。纳米粒子在无限电导率和有限电导率的变压器油中的充电动力学表明，这种电子捕获是正流光速度降低的原因，从而导致更高的电击穿强度。分析得到了纳米颗粒附近的电场、给纳米颗粒充电的电场线上的电子轨迹，以及纳米颗粒充电特性随时间的变化以及纳米颗粒和周围变压器油的介电常数和电导率的表达式。利用这种带电纳米粒子模型，对正负离子、电子和带电纳米粒子在正高压尖针电极和大型球形接地电极之间的电荷产生、复合和传输进行了全面的电动力学分析。案例研究表明，没有纳米颗粒的变压器油分子电离会导致电场和空间电荷波在电极之间传播，产生的热量会导致变压器油蒸发，产生正流光。使用纳米粒子作为电子清除剂，可以降低流光的速度，从而提高高压设备的性能和可靠性。
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 1x10(5). 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 show that transformer oil molecular ionization without nanoparticles cause an electric field and space charge wave to propagate between electrodes, generating heat that can cause transformer oil to vaporize, creating the positive streamer. With nanoparticles as electron scavengers, the speed of the streamer is reduced, offering improved high voltage equipment performance and reliability.