Oil Impregnation in Transformer Boards (2) Theoretical Analysis of Changes in Impregnation Depth

A theoretical analysis of the oil impregnation process is given. Assuming that transformer boards consist of parallel capillaries and that oil impregnation obeys the Hagen-Poiseuille´s law, the oil impregnation depth in transformer boards was calculated. To estimate oil impregnation depth several coefficients were needed. These coefficients were the average capillary radius of transformer boards, surface tension of the insulating oil and the contact angle of the oil to the transformer boards. Using these coefficients, changes in oil impregnation depth were calculated. These values were compared with measured values. Calculated values showed relatively good agreement with published values [1], and clearly showed the effects of insulating oil viscosity and external pressure of oil impregnation, as in the case of measured values.