Study on Electric Field Variation of Bubble within Transformer Oil under Various Electrode Geometries Using COMSOL Multiphysics

Bubbles form in liquid insulation systems as a result of the effects of many thermal, mechanical and environmental factors. The researchers proved that bubbles pose a risk to the transformer insulation system. The geometry of the internal parts of the transformer controls the electric field distribution, the bubbles in the transformer oil are subject to this field. Any alteration in this field leads to a change in the local field of the bubble, potentially resulting in the occurrence of partial discharge. Transformer oil contains bubbles of varying shapes, sizes, and quantities, which can interact with one another. This paper presents a study of electric field variation using the finite element method (FEM) based COMSOL multi-physics simulation tool to determine the effects of the size and shape of an air bubble and its position concerning three types of electric fields (uniform, quasi-uniform, non-uniform) on the distribution of the electric field inside it, as well as the reciprocal effect of two air bubbles if they are close to each other. The results reveal that the bubble size and shape have an impact on the electric field inside it. Moreover, a mutual interaction between two nearby bubbles is noticed. In addition, the electrode geometry and the location of the bubble relative to the high-voltage electrode are two significant factors that influence the local electric field of the bubble.