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About

Salvador Carvalhosa was born in Porto in 1992. He completed his Master's Degree in 2019 at the Faculty of Engineering of the University of Porto (FEUP) and began his PhD in Sustainable Energy Systems in 2021 at FEUP in partnership with MIT Portugal. He has been a Researcher at INESC TEC since 2021 at the Center for Energy Systems where he participates in projects related to Energy Communities. His R&D interests are related to Electric Vehicles, Renewable Energies and Energy Communities. He has published 3 articles in international conferences.

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Publications

2022

Ester-based Dielectric Fluid for Power Transformers: Design and Test Experience under the GreenEst Project

Authors
Carvalhosa, S; Leite, H; Soares, M; Branco, F; Sá, CA; Lopes, RC; Santo, JE;

Publication
Journal of Physics: Conference Series

Abstract
Abstract Ester-based dielectric fluids have now been on the market for several decades, providing fire-safe and environmentally friendly alternatives to mineral oils, which have traditionally been used in transformers and other electrical equipment. This opens the door to innovation in power transformers. However, the use of esters-based dielectrics in power transformers is still very limited, especially for the higher voltage levels. The usage of these esters-based dielectrics in higher voltage power transformers is not yet consensual. this work present results with the use of natural esters in power distribution transformers. Tests carried out on mineral oil and natural ester oil found that the ester-based dielectric can withstand higher voltage thresholds for AC and Impulses tests, mainly within the specs of destructive tests, e.g., the natural ester was able to withstand a 185kV impulse without registering dielectric rupture while the natural oil registered a dielectric rupture with a 160kV impulse. Heating and mechanical tests demonstrated that ester-based dielectric oils for power transformers lead to a flow reduction between 16,8% and 18,2% in the cooling system that was design for mineral oils but they achieve a higher heat transfer coefficient, between 0,5% to 5% depending on the location of measurement.

2022

Renewable Energy Community Pairing Methodology Using Statistical Learning Applied to Georeferenced Energy Profiles

Authors
Lucas, A; Carvalhosa, S;

Publication
ENERGIES

Abstract
Renewable energy communities (REC) are bound to play a crucial role in the energy transition, as their role, activities, and legal forms become clearer, and their dissemination becomes larger. Even though their mass grid integration, is regarded with high expectations, their diffusion, however, has not been an easy task. Its legal form and success, entail responsibilities, prospects, trust, and synergies to be explored between its members, whose collective dynamics should aim for optimal operation. In this regard, the pairing methodology of potential participants ahead of asset dimensioning seems to have been overlooked. This article presents a methodology for pairing consumers, based on their georeferenced load consumptions. A case study in an area of Porto (Asprela) was used to test the methodology. QGIS is used as a geo-representation tool and its PlanHeat plugin for district characterization support. A supervised statistical learning approach is used to identify the feature importance of an overall district energy consumption profile. With the main variables identified, the methodology applies standard K-means and Dynamic Time Warping clustering, from which, users from different clusters should be paired to explore PV as the main generation asset. To validate the assumption that this complementarity of load diagrams could decrease the total surplus of a typical PV generation, 18 pairings were tested. Results show that, even though it is not true that all pairings from different clusters lead to lower surplus, on average, this seems to be the trend. From the sample analyzed a maximum of 36% and an average of 12% less PV surplus generation is observed.

2021

Survey on the advancements of dielectric fluids and experiment studies for distribution power transformers

Authors
Carvalhosa, S; Leite, H; Branco, F; Sá, CA; Moura, AM; Lopes, RC; Soares, M;

Publication
Renewable Energy and Power Quality Journal

Abstract
—The main objective of this work is to summarize the most commonly used dielectric fluids in the power distribution transformers, as well as to discuss what are the latest and the rationale behind those trends. The favorable and unfavorable reasons for any choice behind each of those dielectric fluids will be discussed. Additionally, this work also advances the power distribution transformers health index most commonly used to assess the condition of the transformer.