In this paper, a numerical model of bubble evolution is established by studying the microstructure of pressboard and the physical process of bubble generation. In the model, the porous structure of fibers is equivalent to microtubules, the gases in the bubbles are classified into two categories, and the ideal gas state equation is used to describe the bubble state. Then the pressure conditions at the bubble boundary and the evaporation rate of water are taken as solution conditions to solve the physical quantities in the state equation. The numerical model provides a new way to calculate the initial temperature of bubble escape (ITBE). And the bubble evolution inside the pressboard is obtained which is hard to be observed in experiment. After that, the influences of moisture content of pressboard and cellulose aging on ITBE in the numerical model are discussed. The model results show that the expansion rate of bubble is not uniform. Bubble growth is slow in the early stage of temperature rise, when the temperature reaches a certain threshold the growth rate of bubble radius increases significantly, which is of great significance to the temperature limit on oil-immersed power transformers.

中文翻译：

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基于微管模型的油纸绝缘气泡效应机理及数值模型


本文通过研究纸板的微观结构和气泡产生的物理过程，建立了气泡演化的数值模型。模型中，纤维的多孔结构相当于微管，气泡中的气体分为两类，并采用理想气体状态方程来描述气泡状态。然后以气泡边界处的压力条件和水的蒸发速率为求解条件来求解状态方程中的物理量。该数值模型为计算气泡逸出初始温度（ITBE）提供了一种新方法。并获得了纸板内部气泡的演变过程，这是实验中难以观察到的。然后，在数值模型中讨论了纸板含水率和纤维素老化对ITBE的影响。模型结果表明气泡的膨胀速率并不均匀。升温初期气泡生长缓慢，当温度达到一定阈值时，气泡半径生长速率显着增大，这对油浸式电力变压器的温度限制具有重要意义。