Inductive Sensor for measuring partial discharges in electrical machines

The research group 'Diagnosis of Electrical Machines and Insulation Materials (DIAMAT) of the University Carlos III of Madrid, has developed an inductive sensor that can detect and measure partial discharge that are characteristic in electrical machines (its analysis allows to estimate the aging degree of the internal insulation)

Hydrogen as a fuel. some aspects of its combustion processes

The possibility of utilizing hydrogen as a fuel in air breathing power plants or in other energy conversion systems in a near future has been extensively studied and discussed, as for example, in the First World Hydrogen Energy Conference, including the associated problems of energy storage and energy transportation. Research on combustion of hydrogen has been mainly pionered through aerospace programs, due to the fact of the high interest of hydrogen both as a propellant for liquid fueled rocket motors, and as a fuel of excellent characteristics for air breathing engines, for the propulsion of subsonic, supersonic and hypersonic vehicles

Processing ambiguous fault signals with three models of feedforward neural networks

In the industrial technological field, running equipment or processes usually is monitored through automatic diagnosis systems. Within several Technologies for implementing such systems, the artificial neuronal networks are the most successful and widely spread. The data signals coming from the equipments or processes under supervision are interpreted by the neuronal networks so as to diagnose the presence of any fault. In this work three models of artificial neural networks and two methods of training are analyzed so as to establish, based on real experiences, the best combination of the neuronal model and the training method for recognizing in an efficient way the ambiguous patterns of faults.Presentado en el I Workshop Procesamiento de señales y Sistemas de Tiempo Real (WPSTR)Red de Universidades con Carreras en Informática (RedUNCI

A theoretical model for the combustion of droplets in supercritical conditions and gas pockets

Supercritical combustion of droplets is studied by means of a physical model which assumes spherical symmetry, laminar conditions, constant pressure and a zero-thickness flame. Boundary conditions at the infinity state that temperature and composition of the mixture are given and constant. Initial distributions of temperature and mass fractions of the species are given, as well as the initial conditions at the droplet surface. As combustion proceeds, droplet surface is not considered to exist as a physical boundary allowing unrestricted diffusion of species through it. With some additional simplifications for the density and t r ansport coefficients, a numerical solution of the problem is obtained. An analytical solution of the problem is also obtained by means of an asymptotic analysis. This solution applies when the initial temperature of the droplet is small as compared with the temperature of the sourounding atmosphere. It is shown that this is the most impor t ant case from the technological point of view. For this case results show that an apparent droplet exists throughout most of the process, in which its surface is characterized by an abrupt change in temperature and composition of the chemical species. Results show burning rates, combustion times, flame radius and temperature at the droplet center as function of the principal variables of the process. In particular, the square of the apparent droplet radius is a linear function of time as occurs in subcritical combustion. It is shown that combustion times are faster in supercritical conditions than in subcritical conditions with the minimum value existing at critical conditions. A numerical application is carried out for the case of oxygen droplets burning in hydrogen and a comparison is carried out between the theoretical results obtained numerically and analytically as well as with those experimentally obtained

Transport and Combustion of Firebrands. Final Report of Grants FG-SP-114 and FG-SP-146 Vol. II

A theoretical and experimental study has been carried out on the combustion properties and flight paths of firebrands when they are carried upwards by convective currents and then forwards by the winds. The study has shown that the flight paths of firebrands can be fall decreases continuously as the firebrand burns. Several types of wind tunnels have been developed especially designed to study combustion of firebrands at their final velocity of fall. The study has also show that combustion of firebrands at constant wind speed. The influence of the initial size and initial shape of the firebrands, kind of wood and initial moisture content has been studied, as well as the influence of several types convection columns configurations. Results of these studies enable the calculation of the maximum range of possible fire spread by firebrands of given initial characteristics, once the convective currents above the fire are known as vell as the horizontal wind conditions

Multiple Partial Discharge Source Localization in Power Cables through Power Spectral Separation and Time-Domain Reflectometry

Insulated power cables are becoming increasingly popular in today's developing distribution and transportation networks. However, due to aging, deterioration, and various operational and environmental stresses, insulation defects may appear and so the cable needs to be monitored in a timely manner to avoid unexpected failures. Many of these defects are responsible for partial discharge (PD) activity. The localization of the sources of these discharges is a highly decisive facet in the condition-based monitoring of power cables. The techniques for the localization of single-PD defects in insulated power cables are well presented in the current bibliography. However, when several simultaneous PD sources are active, the localization of the sources becomes quite complex. This paper develops an efficient technique for the separation and localization of multiple PD sources in a medium voltage cable. The experimental results are obtained with single-end-based measurements using a high-frequency current transformer in a laboratory environment. The data processing based on the spectral characteristics of the signals is carried out by using the power ratios technique in order to determine the presence of different types of PD. Once the signals are separated, the PD sources can be localized with an individualized analysis of each source through time-domain reflectometry. The proposed methodology can be very valuable to improve the location diagnostic capability of the condition-based monitoring solutions, especially for underground cables.This work was supported in part by the Ministry of Economy and Competitiveness of Spain (MINECO), in part by the European Regional Development Fund (ERDF) under Contract DPI2015-66478-C2-1-R (MINECO/FEDER, European Union), and in part by the Academy of Finland under Grant 30941

Sensor inductivo para la medida de descargas parciales en máquinas eléctricas

El grupo de investigación “Diagnóstico de Máquinas Eléctricas y Materiales Aislantes (DIAMAT)” de la Universidad Carlos III de Madrid, ha desarrollado un sensor inductivo que permite detectar y medir las descargas parciales características en máquinas eléctricas (cuyo análisis permite estimar el grado de envejecimiento del aislamiento interno)

Shielding effect of power transformers tanks in the ultra-high-frequency detection of partial discharges

Partial discharges (PD) measurement is a well-known technique for judgment of the condition of power transformer offline. Phase-resolved PD measurement is a normalized technique for PD tests, but noise, especially by PD-measurements onsite is sometimes difficult to reject, and a post-processing of a pattern is necessary to separate different sources. Higher-frequency-detection devices and processing strategies are useful for PD classification and identification. Recently, ultra-high-frequency (UHF) detection by means of antennas has been shown to be a promising detection system for both offline and online PD-measurements. However, it is necessary to assess whether PD source separation and classification is possible by means of pulse analysis because some additional UHF noise sources are coupled to the detected signals, and it is not clear whether different sources produce different pulses. In this study, the attenuation effect of the metallic tank of a power transformer on the inner PD activity when measured outside the tank was studied. Additionally, experiments were conducted to detect and characterize two different PD sources (internal and external discharges) using two antennas measuring the same phenomenon inside and outside of a transformer. It will also be shown that broadband UHF signals are useful for PD recognition and that a deep study of frequencies below 500 MHz can separate PD occurring inside from those occurring outside when measured with an antenna outside the tank.This research has been supported by the Spanish Science and Technology Ministry under contract DPI 2009-14628- C03-02 and by the Madrid Regional Government and Universidad Carlos III de Madrid under contract CCG10- UC3M/DPI-4627. Tests have been made in the High Voltage Research and Tests Laboratory of Universidad Carlos III de Madrid (LINEALT).Publicad

On the structure of premixed and diffusion laminar spherico symmetrical flames

Premixed and diffusion laminar spherico-symmetrical flames are studied by means of a non-adiabatic model which considers variable temperature at infinity. The flame is supposed to be maintained by a porous sphere through which the gaseous mixture or one of the reactant gases is injected. Stationary conditions are assumed and chemical kinetics of the process is approximated by means of an overall reaction rate. Solution of the problem is achieved by means of an approximate analytical method. Flame temperature, mass flow per unit area at the flame surface, thickness and radius of the flame and temperature at the sphere surface are given as functions of the mass flow. The influence of the main parameters of the process: temperature at infinity, dimensionless ratio of the activation energy to the heat of reaction and sphere radius is also considered. Some experimental results for diffusion flames are also given in the paper