Grzegorz Dombek

Thermal properties of a mixture of mineral oil and synthetic ester in terms of its application in the transformer

The article presents an analysis of thermal properties of a mixture of mineral oil and synthetic ester used in transformers. The oil/ester rate was as follows: 100%/0%, 95%/5%, 80%/20%, 50%/50%, 20%/80%, 5%/95%, and 0%/100% The measured thermal properties were: thermal conductivity, specific heat, viscosity, density, and the thermal expansion factor. On the basis of measurement results, the authors calculated the heat transfer factor α. This factor determines the ability of a liquid and it has the key influence in transformer cooling. The measurements were done for a wide temperature range from 25 to 80°C.

Thermal properties of mineral oil admixed with C 60 and TiO 2 nanoparticles

Work on modification of insulating liquids with different nanoparticles to improve their electric properties has been done for many years. However, possible changes of thermal properties of such liquids have not been in focus. The article presents an analysis of nanoparticle influence on thermal properties of mineral oil used in transformers. The investigated nanoparticles were fullerenes C60 and barium oxide TiO2. The measured thermal properties were thermal conductivity, specific heat, viscosity, density, and the thermal expansion. On the basis of measurement results of the mentioned thermal properties, the authors calculated the heat transfer factor α. This factor determines the ability of a liquid to carry away heat and it has the key influence in transformer cooling. The measurements were done for a wide temperature range from 25 to 80°C.

The study of thermal properties of mineral oil and synthetic ester modified by nanoparticles TiO 2 and C 60

The paper presents results of investigations of nanoliquids. Mineral oil and synthetic ester were used as base liquid, which was modified using nanoparticles C60 and TiO2. Possibility of the obtaining of stable nanoliquids was tested. Selected properties, which have influence on thermal properties of nanoliquids, were investigated. The influence of modification of mineral oil and synthetic ester by nanoparticles TiO2 on thermal conductivity, was proved.

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.

Cooling properties of natural ester modified by nanopowders fullerene C 60 and TiO 2 for high voltage insulation applications

The paper presents analysis of thermal properties of natural ester modified by nanoparticles C<inf>60</inf> and TiO<inf>2</inf>, used in power transformers. The measurements of thermal properties, such as thermal conductivity, kinematic viscosity, specific heat, density, and thermal expansion were carried out. Measurements were carried out at a temperature of 25 °C, 40 °C, 60 °C and 80 °C. On the basis of measurement results, the heat transfer coefficient α of natural ester admixed with nanoparticles was calculated. Coefficient α of pure natural ester and the coefficient of natural ester modified by nanoparticle C<inf>60</inf> and TiO<inf>2</inf> were compared.