Effect of the Bubble on Streamer Discharge of Transformer Oil

As an essential equipment of the High-Voltage Direct Current (HVDC) System, transformers inevitably exist gas inside, and will generate bubbles to accelerate other forms of discharge, and then affect its normal operation, threatening the safe of the power grid. However, the effect law of bubbles on transformer oil stream discharge has not been well clarified. Therefore, by coupling electrohydrodynamic model and Poisson’s equation, we analyze the influence law of bubbles on transformer oil stream discharge. Simulation results show that the presence of bubbles enhances the strength of the electric field in the oil and accelerates the discharge of streamer. In addition, a maximum electric field strength is found at the interface between the transformer oil and the bubbles. Where at the interface between the transformer oil and the air bubble has a maximum strength of $9.46 \times 10^{8} \mathrm{~V} / \mathrm{m}$, and the space charge density also reached the maximum, which was $6.31 \times 10^{3} \mathrm{C} / \mathrm{m} 3$. By exploring the influence law of bubbles on transformer oil stream discharge, it can better understand the mechanism of transformer internal discharge, and then improve the safety and reliability of transformers. Simultaneously, this research also contributes to the reliable and stable operation of high-voltage direct current (HVDC) systems. And the study of bubble effects on the streamer development characteristics in transformers is of significant importance for the analysis and diagnosis of localized discharges within transformers.