Stressed Oil Volume Theory in Transformer Winding Corner Stress Analysis

The aim of this paper is to demonstrate how stressed oil volume (SOV) theory can be used in experimental research to obtain better reliability of transformer insulation design criteria. For this purpose, combined stress research is taken as an example. In combined stress research winding edge geometry is investigated, where at the same time winding edge is exposed to axial lightning impulse stress due to potential difference between discs/coils and radial LI stress due to potential difference between windings. Transformer designers usually consider this axial and radial stress as two independent manifestations, evaluating each with its own design criteria. Combining the radial and axial stress into a single design criterion should lead to a more reliable insulation design. This paper shows how SOV theory can be used to analyse the influence of radial electric field on axial oil gap LI withstand stress, which is an essential step in combined stress design criteria development.