Modeling of the Dielectric Strength of Transformer Oil in Divergent Field with Bakelite and Pressboard Insulating Barriers by Central Composite Face Method (CCF)

The presence of barriers in point-plane oil gaps has an important role on the insulating oil dielectric strength. This latter closely related to the nature (material), the thickness and the diameter of the barrier, its relative position, the distance between electrodes and theirs interactions. The present work is devoted to estimate the dielectric strength of the transformer oil, the Borak 22 under 50 Hz AC voltage, in presence of Bakelite and Pressboard barriers of 2 and 4 mm thicknesses. To achieve this goal, proposal mathematical models have been built via Central Composite Face method (CCF) which is a robust tool introduced by FISHER. It allowed us to estimate the dielectric strength through a mathematical model. For each barrier, the formulation and the verification of the established models are carried out for several inter-electrodes distance (d=4, 6, 8 10 and 12cm) and relative positions of the barrier (a/d=20, 40, 60, 80 and 100%; a being the point-barrier distance). For each configuration, the corresponding model is verified using graphical and statistical analyses. It is validated as long as the relative mean error between the estimated dielectric strength values and the experimental ones.