Mixed Monoesters derived from non-edible Natural Esters as an Alternative dielectric fluid for Oil-filled Transformers

This research explores a new eco-friendly insulating oil for transformers, Mixed Insulating Oil (MIO). MIO is formed by blending methyl esters of Pongamia Oil (PO) and Neem Oil (NO), PE and NE created from non-edible oils. The study compares a specific blend 75% of NE, 25% of PE that was given a name MIO-C where C stands for scheme-C, with the base oil blend (PO+NO). MIO-C demonstrates lower dielectric loss and Ohmic conductance, which remains unaffected by frequency, preventing electrode polarization due to alternating current. Over the 0–288-hour period, the change in streaming current for MIO-C is approximately 200 pA with a conductivity of 0.9x10-9 S/m, representing an 88% reduction in conductivity compared to PO+NO. MIO-C exhibits a high breakdown voltage (BDV) of 61 kV with an 80% probability, surpassing the 48 kV BDV of PO+NO under the same conditions. MIO-C shows minimal thermal aging (1.53% fire point drop), suggesting good stability for transformers indicating the stabilization of OH sites in Fourier Transform Infrared (FTIR) peaks in oil and OH sites in pressboard to control H+ ions. Thermogravimetric analysis (TGA) shows minimal decomposition before and after aging. X-ray diffraction (XRD) measurements reveal that the relative crystallinity (% Crel) of MIO-C after 288 hours is 86.03%, indicating that crystalline sites in pressboard remain unaffected and closely resemble virgin pressboard. Overall, this study suggests mixed monoester-based insulation fluids like MIO-C are a viable and sustainable alternative to Mineral Oil (MO) for transformers and potentially other oil-filled electrical equipment.