Electric systems

Postprint (published version

Spectrum of corona discharges and electric arcs in air under aeronautical pressure conditions

Due to the increase in electrical power demand, future more electric and all-electric aircraft designs will operate at higher voltage levels compared to current aircraft. Due to higher voltage levels and reduced operating pressure, insulation systems will be at risk. Air is the main insulating medium, and it is well known that its dielectric strength decreases considerably with operating pressure. Although electrical discharges can be detected by different techniques, optical methods are very attractive due to their sensitivity and immunity to acoustic and electromagnetic noise typical of aeronautical environments. This work analyzes the UV-visible spectrum of corona discharges and electric arcs in the 10–100 kPa pressure range, which covers most of the aeronautical applications, due to the lack of experimental data for this pressure range. The data presented in this work are important to select the most suitable optical sensors to detect electrical discharges at an early stage, before significant damage occurs. This approach will help implement preventive maintenance plans and increase aircraft safety. The results presented in this paper can also be applied to other areas, such as monitoring of discharges in power lines, particularly those located in high-altitude regions.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

Application of image sensors to detect and locate electrical discharges: a review

Today, there are many attempts to introduce the Internet of Things (IoT) in high-voltage systems, where partial discharges are a focus of concern since they degrade the insulation. The idea is to detect such discharges at a very early stage so that corrective actions can be taken before major damage is produced. Electronic image sensors are traditionally based on charge-coupled devices (CCDs) and, next, on complementary metal oxide semiconductor (CMOS) devices. This paper performs a review and analysis of state-of-the-art image sensors for detecting, locating, and quantifying partial discharges in insulation systems and, in particular, corona discharges since it is an area with an important potential for expansion due to the important consequences of discharges and the complexity of their detection. The paper also discusses the recent progress, as well as the research needs and the challenges to be faced, in applying image sensors in this area. Although many of the cited research works focused on high-voltage applications, partial discharges can also occur in medium- and low-voltage applications. Thus, the potential applications that could potentially benefit from the introduction of image sensors to detect electrical discharges include power substations, buried power cables, overhead power lines, and automotive applications, among others.This research was funded by the 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

A model to calculate the current–temperature relationship of insulated and jacketed cables

This paper proposes and validates using experimental data a dynamic model to determine the current–temperature relationship of insulated and jacketed cables in air. The model includes the conductor core, the inner insulation layer, the outer insulating and protective jacket and the air surrounding the cable. To increase its accuracy, the model takes into account the different materials of the cable (conductor, polymeric insulation and jacket) and also considers the temperature dependence of the physical properties, such as electrical resistivity, heat capacity and thermal conductivity. The model discretizes the cable in the radial direction and applies the finite difference method (FDM) to determine the evolution over time of the temperatures of all nodal elements from the temperatures of the two contiguous nodes on the left and right sides. This formulation results in a tri-diagonal matrix, which is solved using the tri-diagonal matrix algorithm (TDMA). Experimental temperature rise tests at different current levels are carried out to validate the proposed model. This model can be used to simulate the temperature rise of the cable when the applied current and ambient temperature are known, even under short-circuit conditions or under changing applied currents or ambient temperatures.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

An educational tool to assist the design process of switched reluctance machines

The design of electric machines is a hot topic in the syllabuses of several undergraduate and graduate courses. With the development of hybrid and electrical vehicles, this subject is gaining more popularity, especially in electrical engineering courses. This paper presents a computeraided educational tool to guide engineering students in the design process of a switched reluctance machine (SRM). A step-by-step design procedure is detailed and a user guide interface (GUI) programmed in the Matlab® environment developed for this purpose is shown. This GUI has been proved a useful tool to help the students to validate the results obtained in their lecture assignments, while aiding to achieve a better understanding of the design process of electric machines. A validation of the educational tool is done by means of finite element method (FEM) simulations.Postprint (author's final draft

Analysis of capacitance to ground formulas for different high-voltage electrodes

Stray capacitance can seriously affect the behavior of high-voltage devices, including voltage dividers, insulator strings, modular power supplies, or measuring instruments, among others. Therefore its effects must be considered when designing high-voltage projects and tests. Due to the difficulty in measuring the effects of stray capacitance, there is a lack of available experimental data. Therefore, for engineers and researchers there is a need to revise and update the available information, as well as to have useful and reliable data to estimate the stray capacitance in the initial designs. Although there are some analytical formulas to calculate the capacitance of some simple geometries, they have a limited scope. However, since such formulas can deal with different geometries and operating conditions, it is necessary to assess their consistency and applicability. This work calculates the stray capacitance to ground for geometries commonly found in high-voltage laboratories and facilities, including wires or rods of different lengths, spheres and circular rings, the latter ones being commonly applied as corona protections. This is carried out by comparing the results provided by the available analytical formulas with those obtained from finite element method (FEM) simulation, since field simulation methods allow solving such problem. The results of this work prove the suitability and flexibility of the FEM approach, because FEM models can deal with wider range of electrodes, configurations and operating conditions.Peer ReviewedPostprint (published version

Paper samples identification by means of IR spectrometry and multivariate

Actualmente en todo el mundo se consume una gran cantidad de papel reciclado. Ello ha provocado la fabricación de papel que contiene muchos tipos de impurezas, por lo que las empresas papeleras se están viendo con la necesidad de desarrollar métodos para controlar la calidad del papel entrante para así garantizar su calidad. Para ello en este trabajo se investiga un método muy rápido y no destructivo para identificar diferentes tipos de papel que permita desechar el papel entrante que no cumpla con unos requisitos mínimos de calidad. De este modo se puede mejorar el comportamiento de la máquina de papel y al mismo tiempo asegurar la calidad del producto final. Ello se hace en base al estudio de los espectros FTIR (espectroscopia del infrarrojo medio por transformada de Fourier)y NIR (espectroscopia del infrarrojo cercano) tratados mediante ICA (análisis de componentes independientes) como técnica multivariable de extracción de características para reducir la cantidad de variables utilizadas y k-NN k vecinos más cercanos) como técnica de clasificación. Los resultados experimentales muestran que es posible identificar con éxito más de un 90% de las muestras estudiadas, de una forma rápida, muy automatizada y de forma no destructivaPostprint (published version

Identificación de muestras de papel mediante espectrometria IR y métodos multivariables

Actualmente en todo el mundo se consume una gran cantidad de papel reciclado. Ello ha provocado la fabricación de papel que contiene muchos tipos de impurezas, por lo que las empresas papeleras se están viendo con la necesidad de desarrollar métodos para controlar la calidad del papel entrante para así garantizar su calidad. Para ello en este trabajo se investiga un método muy rápido y no destructivo para identificar diferentes tipos de papel que permita desechar el papel entrante que no cumpla con unos requisitos mínimos de calidad. De este modo se puede mejorar el comportamiento de la máquina de papel y al mismo tiempo asegurar la calidad del producto final. Ello se hace en base al estudio de los espectros FTIR (espectroscopia del infrarrojo medio por transformada de Fourier) y NIR (espectroscopia del infrarrojo cercano) tratados mediante ICA (análisis de componentes independientes) como técnica multivariable de extracción de características para reducir la cantidad de variables utilizadas y k-NN (k vecinos más cercanos) como técnica de clasificación. Los resultados experimentales muestran que es posible identificar con éxito más de un 90% de las muestras estudiadas, de una forma rápida, muy automatizada y de forma no destructiva.Postprint (published version