Effect of Carrier Mobility on Corona Discharge of Transformer Oil Under DC Voltage

The insulation performance improvement of transformer oil under dc voltage is of great significance in reducing the fault of the converter transformer. The nano-modified transformer oil has excellent electrical properties, but the research on corona discharge characteristics under dc voltage is insufficient. This article studied the corona discharge characteristics of SiO2 and TiO2 nanofluids (NFs, transformer oil with SiO2 and TiO2 nanoparticles addition, respectively) and pure oil by combining experiments with simulation. A series of dc corona discharge tests were carried out under the needle-plate electrode, and the pulse current was used to characterize the corona discharge level. The electron mobility was obtained through the surface potential decay method, and positive and negative ions' mobility was measured using the polarity reversal method. Then, the effects of the mobility of electrons, negative, and positive ions on the distribution of space charge and electric field in transformer oil were analyzed, respectively. The mechanism of nanoparticles regulating carrier mobility to improve the insulation performance of transformer oil was revealed. The result is of great theoretical significance and practical value for promoting and applying in advanced insulating liquids in power transformers.