EDP - Energias de Portugal ranks among Europe's major electricity operators, as well as being one of Portugal's largest business groups.In December 2011, China Three Gorges Corporation acquired a 21.35% Portuguese government's stake in Energias de Portugal for €2.69 billion. Wikipedia.
Martins M.A.G.,EDP Energias de Portugal |
Gomes A.R.,Institute Biologia Experimental e Tecnologica IBET
IEEE Electrical Insulation Magazine | Year: 2012
Insulating oil plays a fundamental role in power transformers, providing both the electrical insulation and the means for transferring the thermal losses to the cooling system. In addition, insulating oil is an important information carrier. It can provide information about the degradation of insulating paper, by depolymerization, which is very important in transformer diagnostics . © 2006 IEEE.
Pinto De Sa J.L.,University of Lisbon |
Louro M.,EDP Energias de Portugal
IEEE Transactions on Power Delivery | Year: 2010
The minimum phase-to-ground fault current required to be sensed by protection systems in medium-voltage (MV) networks can be as low as 0.7 A in a few countries, leading to a lot of undesired relay trips and poor service quality to costumers. However, these settings raise the protection threshold above the minimum fault current that concerns network operators regarding human safety, although they cannot be practiced when grounding is distributed. The purpose of this paper is to present a risk assessment foundation to determine the required protection sensitivity to ensure human safety in MV distribution networks. The proposed approach is based on a biophysical model included in IEC standards, the consideration of current paths models for typical faults and Monte Carlo methods to deal with nonlinearity, and the many involved random variables. Downed conductors and line-to-concrete pole faults are investigated and sensitivity analysis performed to highlight some important determinants of the results. © 2010 IEEE.
Diaz G.,University of Oviedo |
Gonzalez-Moran C.,University of Oviedo |
Viescas C.,EDP Energias de Portugal
IET Renewable Power Generation | Year: 2013
This study shows a methodology for state-space representation of large wind power plants, through models that include the dynamics of the internal grid. The methodology presented fundamentally separates plant and controls at the stage of formation of the model. It is shown then that most of the plant can be built up from elementary RL branches - with special clarification about the reduction of the induction machine to an RL network - that are put together by means of a incidence matrix. The problems and solutions of reference frame dynamics - complex because of the existence of two control frames for the doubly-fed induction generator and different frames in the grid, one for each generator - are also discussed. The control is separately formulated into a gain matrix, and control and plant are put together by simple matrix algebra. As a result, detailed, large systems can be easily formed. The study shows an example in which ten generators are considered and shows that there may appear particular dynamic features when multi-machine systems (rather than single, aggregated machine systems) are represented. © The Institution of Engineering and Technology 2013.
Edge P.,EDP Energias de Portugal
International Conference on the European Energy Market, EEM | Year: 2015
A power purchase agreement (PPA) is a contractual mechanism used by energy suppliers and consumers to manage long term price and volume risk. The contract has value once an agreement on price and volume has been made. The value of the contact is stochastic and based on the current and future expectations of the underlying electricity price. The total contract value can be positive for the producer if realized market prices are lower than originally expected or positive for the purchaser if prices are higher than expected. These contracts typically are uncollateralized and therefore pose a credit risk to both counterparties. Assessing the value of this credit risk can be slow and computationally burdensome requiring Monte Carlo calculations, so this paper proposes an approximation to the problem that yields a closed form solution. © 2015 IEEE.
Martins M.A.G.,EDP Energias de Portugal
IEEE Electrical Insulation Magazine | Year: 2014
In recent years, several documented cases of transformer failures have been attributed to the presence of corrosive sulfur species in the insulating oil , . However, all sources of corrosive sulfur in oil have not been completely identified, yet. They can be residuals from the refining process, or they are formed under favorable operating conditions, such as high ambient and operating temperature and low oxygen concentration. It has been recently shown that noncorrosive sulfur compounds can become corrosive in oil with dissolved oxygen in the range of a few hundreds to a few thousands of parts per million, producing, for example, metal sulfides, after being exposed to high temperatures, electrical stresses, transient phenomena, DC fields, and hot metal surfaces. This has been quite commonly found in closed-type transformers (rubber bag or nitrogen blanketed) but can also occur in open breathing transformers, that work under more-or-less constant load, and in this case they breath very little , . © 2014 IEEE.