Optimization of new and thermally aged natural monoesters blends for a sustainable management of power transformers

The depletion of the worldwide reserves of petroleum resources combined with the environmental concerns incited researchers and industrials to seek for new appropriate available electroinsulating liquids. The perspective of using mixtures of insulating liquids in power transformers can help to improve the overall performance of these static electrical machines. Natural monoesters represent good candidates for this issue. This paper presents the performance evaluation of eleven proportions of castor and palm kernel oil monoesters blends. Samples were consecutively aged with Nomex-910 papers at 120°C, then 140°C, and finally 150°C for 168 h each. Both the unaged and aged samples undergone dielectric and physicochemical characterization. The dielectric dissipation factor, relative permittivity, acidity, and viscosity increased with aging. However, the electroinsulating and cooling properties were not significantly degraded. Polynomial relationships were proposed to predict these quantities. A simplex lattice design was applied to both new and aged samples to determine the optimal blend formulation. An approximative ratio of 79:21 v/v COME: PKOME was determined. Hence, blending natural monoesters is a significant contribution to the sustainable management of power transformers. • 11 proportions of blends of castor and palm kernel oils monoesters prepared. • Blends aged with Nomex-910 paper consecutively at 120, 140, and 150°C during 168 h each. • Proposed polynomial equations to predict blends properties depending on castor content. • Simplex lattice design used to predict optimal ratio at 40°C and each aging temperature. • A global optimal ratio of 79:21 v/v castor oil monoester: palm kernel oil monoester was obtained.