Fire safety and electrical properties of mineral oil/synthetic ester mixtures

The paper presents research results of mineral oil/synthetic ester mixtures comprising: flash point (open and closed cup), fire point (open cup), net calorific value, breakdown voltage, relative permittivity, dissipation factor, conductivity and dielectric losses. Mineral oil/synthetic ester mixtures for the following concentrations: 95/5, 90/10, 80/20, 60/40, 50/50, 40/60, 20/80, 10/90 and 5/95 were tested. In order to compare properties (especially electrical), prepared mixtures and base liquids were conditioned at uniform climatic conditions (temperature 25 °C, relative humidity 9%). This allowed to obtain mixtures with the same relative humidity. Obtained results were referenced to the properties of the base liquids. Furthermore, the results were analyzed in terms of fire safety and changes of electrical properties, in the context of the use of mixtures as insulation liquids in power transformers.