1,721,015 research outputs found
Single PEM fuel cell analysis for the evaluation of current ripple effects
No full textIn this paper, the results of an experimental analysis performed on a polymer electrolyte membrane fuel cell (FC) for the evaluation of the current ripple effects are reported. The polarization curve (PC) and the impedance spectrum measured for a single FC with a Nafion membrane are presented discussing some advantages and disadvantages of the two adopted techniques from the measurement point of view. The ohmic and activation resistance values provided by the PC are compared to the frequency limits of the equivalent resistance estimated by the spectroscopic analysis to evaluate the additional losses and the system efficiency reduction introduced by the current ripple. The presence of a voltage–current hysteretic behavior is discussed throughout the paper, and some comments on how such a relationship can impact on the identification of the indicated parameters are included
Current distribution measurements in rail launcher multibrush armatures during launch
No full textThe problem of measuring current distribution in multiple-brush armatures for electromagnetic rail launchers is reapproached here to study the dynamic measurement during armature motion on a two-brush armature. The measurement method is based on an array of loops magnetically coupled to the brushes, placed along the rails. From the theoretical point of view, the measured voltages on all the loops should make possible to reconstruct the current distribution between the brushes as a function of time and armature position. This has been experimentally verified on a launcher prototype
Caratterizzazione di alte correnti impulsive e loro distribuzione in armature multispazzola
No full textIn questo articolo viene descritto un metodo per la misura della corrente in un lanciatore elettromagnetico (railgun) e della sua distribuzione tra le spazzole di un’armatura solida. La tecnica di misura è basata sull’utilizzo di spire di ricerca mutuamente accoppiate al circuito. Dalla misura del flusso concatenato è possibile ricavare le correnti nelle spazzole.
Per la misura della corrente totale viene descritto un prototipo di shunt realizzato presso i laboratori dell’Unità di Pisa. Le tecniche di misura descritte sono state sviluppate sulla base del metodo delle induttanze parziali
Misure per l'analisi del comportamento di sorgenti di energia
No full textAmong energy source units, batteries, supercapacitors and fuel cells are the subject of increasing interest and development for several industrial applications. In particular, they represent an important challenge in the field of transportation as an alternative to traditional fuels. As a consequence of the complexity and multiphysical nature of such devices, the characterization of their energetic behavior opens to interesting measurement aspects. In this paper, a few basic concepts related to the frequency dispersion of the electrical permittivity and to the hysteresis phenomena formation are shortly recalled, and the results of an experimental analysis performed on a supercapacitor and two fuel cells are presented
Analytical study of high pulse current shunts
No full textIn this paper we reapproach the study of current shunts via analytical way, focusing on high pulse current applications such as electromagnetic rail launchers. Through the use of the partial mutual inductance method we revisit some design aspects in order to increase the shunt bandwidth and the bandwidth of the measurement circuit. The inductance expression of a `squirrel cage' shunt is derived and tested on a homemade prototype. The experimental results confirm the validity of the model and its robustness with respect to the geometrical parameter uncertainty
Dynamic experiments of current distribution in rail launcher multi-brush armatures
No full textThe problem of measuring current distribution in multiple-brush armatures for electromagnetic rail launchers is reapproached here to study the dynamic measurement during armature motion; in particular the analysis is focused on a two-brush armature. The measurement method is based on an array of loops magnetically coupled to the brushes, placed along the rails. From the theoretical point of view the measured voltages on all the loops should make possible to reconstruct the current distribution between the brushes as a function of time and armature position
Impedance spectroscopy on a single PEM fuel cell for the evaluation of current ripple effects
No full textThe use of fuel cells for powering AC loads requires to employ power converters and in particular inverters. The efficiency of these devices is usually very high, but they add a current ripple on the fuel cell side that might affect the fuel cell performance and decrease the overall system efficiency more than expected. Previous studies revealed that this performance decrease depends on the impedance spectrum of the fuel cell and in particular on the cut-off frequency of the RC equivalent circuit associated with the charge double layer, which is usually in the typical current ripple frequency range. Therefore, accurate measurements of the fuel cell impedance up to high frequencies (kHz) are necessary. In this paper the high-frequency behavior of a single PEM fuel cell is investigated via impedance spectroscopy and some critical issues concerning the effects of current ripple are discussed
Accurate magnetic flux measurements in electromagnetic rail launchers
No full textThis paper deals with the measurement of the magnetic flux generated by the armature of electromagnetic rail launchers linked with external pick-up loops. In particular we discuss possible methods to experimentally evaluate measurement uncertainty when the magnetic flux is obtained by numerical voltage integration. These methods aim at an approximate identification of the correlation among voltage samples introduced by the analog-to-digital converter, only based on the available measurements without requiring additional tests and instruments. An estimate of this correlation allows to better evaluate the overall measurement uncertainty, thus providing the applicability limits of the proposed inductive technique and contributing to a better understanding of the current and force distribution in the armature
Defect Identification by Eddy Current Inspection Data Classification Through Probabilistic Neural Networks with Elliptical Kernels
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