A. Arroyo

Study on the cooling capacity of alternative liquids in power transformers

This work focuses on the thermal behavior of natural esters on power transformers. For this purpose a model of the windings is presented. These are considered as a set of rectangular blocks representing the cross section of the different turns of copper. The model is implemented in a finite element method tool and it is considered as a two-dimensional problem. It serves to study how the dielectric liquid flows between the channels of a disc-type power transformer. The results of this study are compared to the thermal behavior of the conventional mineral oil. It seems that natural esters produce a positive effect in the solid insulation. It is also shown that windings suffer higher temperatures in the case of mineral oil, this leading to a faster speed on insulation deterioration. On the other hand, a wrong design of the horizontal channel size can lead to hot-spots in natural ester-cooled transformers.

Methodology for the Low-Cost Optimisation of Small-Wind Turbines

The increasing use of small-wind energy has made it necessary to develop new methods that improve the efficiency of this technology. This is best done by considering the interaction between the various components, such as wind rotors, electrical generators, rectifiers and inverters, as opposed to studying the individual components in isolation. Hence, this chapter describes a methodology to increase the efficiency of small-wind turbines (SWTs) equipped with an electrical machine, rectifier and inverter. To achieve this objective, capacitor banks will be connected between the electrical machine and the rectifier. This methodology is motivated by two clear aims. The first one is to operate the SWT with its maximum power coefficient (Cp). The second one is to select the most suitable capacitor bank for each wind speed in order to optimise the energy supplied to the grid.