Influence of Natural Ester Admixture to Mineral Oil on the Transformer Bubbling Inception Temperature

• Published in: Electrical Insulation Conference and Electrical Manufacturing Expo pp. 1 - 4
• Main Authors: Gmati, Ghada, Picher, Patrick, Arroyo-Fernandez, Oscar, Fofana, Issouf, Rebaine, Djamal, Rao, U. Mohan
• Format: Conference Proceeding
• Language: English
• Published: IEEE 18.06.2023
• Subjects: bubbling; Liquids; Loading; Mineral oil; Minerals; Mixed oil; Moisture; Oil insulation; Oils; Paper insulation; transformer; Windings
• ISSN: 2576-6791
• DOI: 10.1109/EIC55835.2023.10177370

In the present study, the influence of natural ester admixture to mineral oil on the bubbling inception temperature is investigated. First, the thermal model of the IEC 60076-7 standard is adjusted by recalculating the oil and winding parameters of a 66-MVA transformer. This is performed by simulation using software based on the Thermal Hydraulic Network Model. The scenario simulates various loadings in steady state (K=0.7,1.0,1.7 pu) using thermal characteristics of mineral oil and the mixed fluids containing 80% of mineral oil and 20% of natural esters. Then, a moisture model is used to understand the behavior of the relative moisture saturation of these liquids and to estimate the bubble inception temperature for pure and mixed liquid. Simulations are performed to predict the temperature at which bubbles are formed under certain loading profiles. The maximum load that can be applied prior to bubble generation is also predicted. Importantly, it was found that adding 20% of natural esters to mineral oil improve the bubbling inception temperature and the emergency overloading of the transformer, without degrading the thermal performance significantly.