Agustín Santisteban

Numerical analysis of the hot-spot temperature of a power transformer with alternative dielectric liquids

The assessment of two vegetal oils as coolant in Low Voltage Winding of a power transformer with zigzag cooling have been analyzed. These dielectric fluids cooling performance has been compared with a typical mineral oil. To make the study, a 2D-axisymmetrical model of a power transformer has been developed to perform a numerical analysis using a Finite Element Method based software, COMSOL Multiphysics®. Some values are obtained in order to establish the comparison, such as hot-spot temperature or hot-spot factor. Moreover, the influence of the increase of the number of passes of the cooling circuit on the hot-spot temperature has been evaluated for all liquids and compared with the initial design. Results obtained in this work show that the hot-spot temperature is lower for the vegetal oils in the initial design. Furthermore, an increase in the number of passes affect more positively to the mineral oil since similar values of the hot-spot temperature for all liquids are obtained. Values of the hot-spot factor indicates that higher number of passes leads to lower efficient cooling circuits owing to the increase of the pressure drop although the hot-spot temperature decreases.

Effect of TiO 2 nanoparticles on the performance of a natural ester dielectric fluid

Mineral oil has been frequently used in most of high voltage transformers. However, this oil has started to be replaced by vegetable oils. Additionally, different authors have found that mineral oil-based nanofluids have a potential in improving insulating properties of transformer oil. In order to improve the characteristics of a commercial vegetal oil, this work has used TiO2 nanoparticles to obtain a nanofluid whose ageing behavior at 150°C for 300 hours has been studied.

Transformer health indices calculation considering hot-spot temperature and load index

The state of a transformer depends on many parameters, which should be taken into account to determine its actual condition. In recent years what is known as health indices of transformers has been defined, which is a practical tool to assess the overall status of these electrical devices. Data from field inspection, laboratory tests, and observations during operation of the transformer are combined. All of these result in an index that provides fairly objective and quantitative information as to the condition of the transformer [1].