Generació, transport i distribució d'energia : problemes

Descripció del recurs: 2 de maig de 2012Aquest llibre és presenta, en deu temes, problemes resolts dels principals elements dels sistemes elèctrics, i analitza les instal·lacions elèctriques en què hi ha diferents components connectats. La segona part del llibre recull, en nou annexos, problemes bàsics dels sistemes trifàsics i del mètode per unitat, i inclou una recopilació de taules, de manera que l'estudiant pot treballar amb les dades obtingudes de les taules per tal d'analitzar amb més profunditat el funcionament dels sistemes elèctrics. Moltes vegades, els càlculs matemàtics dificulten que l'estudiant pugui assolir la capacitació adequada per afrontar l'anàlisi i el disseny de sistemes d'energia elèctrica. Per aquest motiu, en aquest llibre, a més de presentar un conjunt de problemes completament resolts, es proporcionen dues eines matemàtiques -el MATLAB i l'Excel- per tal de facilitar-ne els càlculs als estudiants i ajudar-los a centrar-se en els coneixements dels sistemes d'energia elèctrica

Advanced quiz development for students’ self-learning in power generation, transmission and distribution

Students’ learning can be improved by using online quizzes with a valuable feedback, especially in large groups, making it very interesting for engineering subjects which are based on mathematics. This paper presents the evaluation of an online quiz experience based on a case study in two university subjects. Quizzes were created by using Wiris Quizzes (WQ) that can register the complete solution with all the steps involved. WQ has a calculator that allows us to solve the mathematical part of the quiz. The first aim of the online WQ experience is to provide feedback to students through automatic grading and clues to find the correct answers. The second aim is to promote autonomous student learning. The teachers also have excellent feedback about faulty interpretations or weaknesses in the students’ understanding. Consequently, teachers can provide corrective information to clarify ideas about what they want to be understood and what is understood by students. WQ allows teachers to develop algorithms for the quizzes by using random data, figures realized through programming, and multiple solutions that depend on the values of a table. The teaching experience of using WQ has shown that this tool can be useful in university technological subjects with large groups that require advanced and customized quizzes.Peer ReviewedPostprint (author's final draft

New methodology to calculate DC voltage signature in n-phases TRUs under supply voltage sags

A new methodology based on the shadow projection has been developed to study any multipulse rectifier's dynamic behavior under balanced and unbalanced conditions. The proposed methodology calculates the DC average voltage and instantaneous values under balanced and unbalanced supply voltage conditions for multiphase Transformer Rectifier Units (TRUs). The calculation of the developed algorithms is more practical than the classical methods and other approaches based on Fourier series or symmetrical components that are difficult to apply under unbalanced conditions. Furthermore, classical methods are not simple to determine the limits of the integrals and calculate them to obtain the average value, so a more friendly and practical methodology has been developed to analyze rectifiers operating under supply voltage sags. This new methodology has been validated by simulation for a 12-pulse TRU in series and parallel connections, and it has also been validated for a 36-pulse TRU in parallel connection using interphase inductors. The accuracy of the calculations is validated by the experimental results for 12-pulse TRUs, series, and parallel connection, and 18-pulse TRU in series connection.This work was supported by the research project ‘‘Estabilidad de redes MVDC integrando tecnologías de energías renovables, almacenamiento de energía y convertidores de fuente de impedancia,’’ by the Ministerio de Ciencia, Innovación y Universidades and European Union, under Grant RTI2018-095720-B-C33.Peer ReviewedPostprint (published version

Open-circuit fault diagnosis and maintenance in multi-pulse parallel and series TRU topologies

©2020 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.Transformer Rectifier Units (TRUs) are a reliable way for DC generation in several electric applications. These units are formed by multiple three-phase uncontrolled bridge rectifiers connected according to two main topologies (parallel and series), and fed by a phase-shifting transformer, which can have different configurations. Fault diagnosis of the uncontrolled bridge rectifier diodes is one of the most important concerns on the electronic devices, nonetheless, rectifier units are inherently not protected in front of Open-Circuit (O/C) faults, which cause malfunction and performance deterioration. In order to solve this drawback, the proposed fault diagnosis method is based on the O/C fault signature observed in the DC-link output voltage of TRUs rectifier. It allows detecting the O/C diodes of parallel and series TRUs with different phase-shifting transformer configurations and for the most usual fault scenarios. Moreover, it also helps the prediction of diodes that could be exposed to failure after the fault, which provides corrective maintenance for the TRU development. The proposed method is illustrated from MATLABTM numerical simulations of a 12-pulse TRU, and is validated with experimental tests.This work supported in part by the Research Project Estabilidad de Redes MVdc Integrando Tecnologias de Energias Renovables, Almacenamiento de Energia y Convertidores de Fuente de Impedancia, RTI2018-095720-B-C33, in part by the Ministerio de Ciencia, Innovación y Universidades, and in part by the European Union.Peer ReviewedPostprint (author's final draft

Arc tracking control in insulation systems for aeronautic applications: challenges, opportunities, and research needs

Next generation aircrafts will use more electrical power to reduce weight, fuel consumption, system complexity and greenhouse gas emissions. However, new failure modes and challenges arise related to the required voltage increase and consequent rise of electrical stress on wiring insulation materials, thus increasing the risk of electrical arc appearance. This work performs a critical and comprehensive review concerning arc tracking effects in wiring insulation systems, underlying mechanisms, role of materials and possible mitigation strategies, with a special focus on aircraft applications. To this end an evaluation of the scientific and technological state of the art is carried out from the analysis of theses, research articles, technical reports, international standards and white papers. This review paper also reports the limitations of existing insulation materials, standard test methods and mitigation approaches, while identifying the research needs to comply with the future demands of the aircraft industryPeer ReviewedPostprint (published version

New smart sensor for voltage unbalance measurements in electrical power systems

This paper deals with voltage unbalances and how they can be quantified according to the standards. Firstly, a comparison between the different unbalance voltage factors is conducted in order to remark on their divergences. Secondly, according to the standard that better represents the phenomenon, i.e., EN 50160, a new methodology is proposed to quantify the voltage unbalance factor (VUF). In order to do so, it is recommended to measure the voltage unbalance in three-phase installations by means of a new smart sensor based on a single voltage sensor, which measures the direct-current (DC) voltage at the output of a three-phase diode bridge rectifier, while current methods make use of three voltage sensors (which can measure either phase-to-neutral voltages or phase-to-phase voltages). Furthermore, both simulation and experimental results have been carried out to validate the proposed methodology. Finally, a new voltage unbalance factor (and the corresponding methodology to obtain it from the measured DC voltage) is proposed.This research was funded by the Spanish Ministry of Science and Innovation, grant number PID2021-123633OB-C33.Peer ReviewedPostprint (published version

Actividad formativa mediante cuestionarios de autoevaluación

La promoción del aprendizaje autónomo se puede realizar utilizando diferentes medios, en este trabajo se expone la actividad formativa desarrollada en la asignatura de Circuitos Eléctricos de la ETSEIAT con el objetivo de promover el aprendizaje autónomo. Se han desarrollado cuestionarios de autoevaluación online personalizados. Para ello se ha utilizado la aplicación WIRIS quizzes que permite generar cuestionarios e incopora una calculadora para la realización de todos los cálculos. Wiris es una aplicación de la compañia Maths for More [1]. En este trabajo se muestra cómo se han integrado los cuestionarios de autoevaluación en la asignatura de Circuitos Eléctricos de la ETSEIAT y las lecciones aprendidas en esta experiencia docente. Los cuestionarios de autoevaluación creados utilizan datos aleatorios e instrucciones condicionales para conseguir que cada estudiante tenga un cuestionario personalizado. Los cuestionarios creados, además de promover el aprendizaje autónomo, permiten que los profesores conozcan el grado de aprendizaje alcanzado y por consiguiente poder realizar los ajustes necesarios en el desarrollo de la asignatura. Esta es una de las características significativas de la aplicación Wiris. La experiencia en la enseñanza de Circuitos Eléctricos muestra que los estudiantes necesitan un tiempo excesivo para realizar los cálculos que conducen a la resolución de los problemas planteados, lo que retrasa el aprendizaje de los conceptos claves de la materia. Wiris incorpora una calculadora que permite hacer los cálculos a medida que se contestan los cuestionarios [2]. Concretamente en este trabajo se han utilizado cuestionarios con la calculadora incorporada para solucionar el inconveniente comentado. Los resultados obtenidos en la aplicación de esta actividad formativa permiten concluir que con una inversión de tiempo significativa, esta herramienta es útil tanto para el aprendizaje del alumno como para el seguimiento de dicho aprendizaje por parte del profesor. JORNADA INNOVACIÓN DOCENTE – RIMA 2012 5-6 Julio 2012, UPF ~ 388 ~ La percepción de los estudiantes ha sido que mejora su aprendizaje, les da más seguridad y manifiestan que se consideran mejor preparados para la realización de los exámenes.Peer Reviewe

Power control strategies during voltage sags according to Spanish grid code

In order to connect any power converters into the grid there are some grid requirements to insure the safe operation of the grid. So, the control of the converters especially during abnormal condition e.g. during voltage sags is a very important key to guarantee the good behavior of the distributed generation system. In this paper four control strategies, will be stated in the literature, are discussed in order to ensure their ability to match the grid requirements when unsymmetrical voltage sags are produced in the network. The Spanish grid code did not give any information about the negative sequence, and it only represents the positive sequence components. Therefore, the main contribution of this paper is to verify the grid code with not only the positive sequence but also with the negative sequence. Moreover, the system is tested by simulation to show that the results cope well with the analytical equations.Postprint (published version

Energy harvesting methods for transmission lines: a comprehensive review

Humanity faces important challenges concerning the optimal use, security, and availability of energy systems, particularly electrical power systems and transmission lines. In this context, data-driven predictive maintenance plans make it possible to increase the safety, stability, reliability, and availability of electrical power systems. In contrast, strategies such as dynamic line rating (DLR) make it possible to optimize the use of power lines. However, these approaches require developing monitoring plans based on acquiring electrical data in real-time using different types of wireless sensors placed in strategic locations. Due to the specific conditions of the transmission lines, e.g., high electric and magnetic fields, this a challenging problem, aggravated by the harsh outdoor environments where power lines are built. Such sensors must also incorporate an energy harvesting (EH) unit that supplies the necessary electronics. Therefore, the EH unit plays a key role, so when designing such electronic systems, care must be taken to select the most suitable EH technology, which is currently evolving rapidly. This work reviews and analyzes the state-of-the-art technology for EH focused on transmission lines, as it is an area with enormous potential for expansion. In addition to recent advances, it also discusses the research needs and challenges that need to be addressed. Despite the importance of this topic, there is still much to investigate, as this area is still in its infancy. Although EH systems for transmission lines are reviewed, many other applications could potentially benefit from introducing wireless sensors with EH capabilities, such as power transformers, distribution switches, or low- and medium-voltage power lines, among others.This research was funded by Ministerio de Ciencia e Innovación de España, grant number PID2020-114240RB-I00 and by the Generalitat de Catalunya, grant number 2017 SGR 967.Peer ReviewedPostprint (author's final draft

Smart switching in single-phase grid-connected photovoltaic power systems for inrush current elimination

Grid-connected photovoltaic (PV) power systems are one of the most promising tech- nologies to address growing energy demand and ecological challenges. This paper proposes smart switching to mitigate inrush currents during the connection of single-phase transformers used in PV systems. An effective inrush current mitigation contributes to the reliability of PV systems. The inrush current severity is influenced by the pseudorandom residual flux at the transformer core and the energization point-on-wave. The most common approach to avoid inrush currents is controlled connection, which requires prior knowledge of the residual flux. However, the residual flux can differ in each case, and its measurement or estimation can be impractical. The proposed smart switching is based on a comprehensive analysis of the residual flux and the de-energization trajectories, and only requires two pieces of data (fRM and f0, flux values of the static and dynamic loops when the respective currents are null), calculated from two simple no-load tests. It has a clear advantage over common approaches: no need to estimate or measure the residual flux before each connection, avoiding the need for expensive equipment or complex setups. Smart switching can be easily im- plemented in practical settings, as it considers different circuit breakers with distinctive aperture features, making it cost-effective for PV systems.Peer ReviewedPostprint (published version