1,720,978 research outputs found
Efficient Methods for the Study of Eddy-Currents Effects in Medium-Voltage Rotating Electrical Machines
Get PDFLo scopo di questa tesi è presentare alcuni metodi efficienti (dal punto di vista computazionale) per il calcolo degli effetti dovuti alle correnti parassite (eddy currents) in macchine elettriche rotanti in media tensione. Due applicazioni in particolare sono state considerate nel dettaglio.
Inizialmente viene analizzato il fenomeno delle correnti parassite indotte nell'albero di motori asincroni a due poli e il conseguente effetto sulle prestazioni della macchina, focalizzandosi in particolare sul fattore di potenza. La seconda parte della tesi concentra la sua attenzione sullo studio dell'avviamento da rete di motori sincroni con rotore massiccio.
Per ciascuna applicazione vengono introdotte alcune procedure di calcolo, facenti uso di opportuni modelli numerici basati sul metodo degli elementi finiti, per mezzo delle quali vengono adeguatamente calcolati i parametri dei circuiti equivalenti di macchina, tenendo conto degli effetti legati alle correnti parassite. I modelli numerici sono opportunamente definiti, in modo tale da ridurre al massimo la complessità delle geometrie e il conseguente onere computazionale.
I risultati delle procedure innovative qui proposte sono confrontati con i dati provenienti da prove sperimentali sulle macchine oggetto di studio e con analoghi risultati di calcolo dedotti tramite le procedure comunemente utilizzate. Il confronto fra questi dati ha dimostrato che gli approcci di calcolo introdotti in questa tesi permettono di ottenere risultati con un elevato livello di accuratezza e una netta riduzione dell'onere computazionale.The efficient computation of eddy-current effects in medium voltage electric machines is discussed in this dissertation. Two particular cases are considered.
Firstly, the effects of shaft eddy-currents on two-pole induction motor performance is addressed, with special focus on the power factor. In the second part of the thesis the start-up calculation of a large synchronous motor with solid rotor is analyzed.
For each application a special calculation procedure is introduced. These procedures adopt a set of suitable finite-element models to properly compute the machine equivalent circuit parameters that are mainly influenced by eddy-current-related phenomena. By suitably choosing finite-element models boundary conditions and excitations their geometry is simplified to the maximum possible extent, in order to reduce the computational burden.
The results of the new calculation methods are compared with experimental data and with analogous results obtained from commonly-adopted calculation procedures. The comparison proves that the proposed approaches can lead to high accuracy levels with very remarkable computational savings
Pareto Fronts in the Optimization of Fractional Slot Concentrated Windings for Rotor Loss Reduction in Surface Permanent Magnet Machines
No full textFractional-Slot Concentrated Windings (FSCWs) are an attractive option for the stator winding of synchronous permanent-magnet machines. However, they suffer from the drawback of large armature magneto-motive force (MMF) harmonics and consequent rotor losses. The use of a multi-layer design is a well-known method to synthetize FSCWs in which rotor losses are reduced compared to the usual dual-layer layout at the expense of a decreased MMF amplitude. This paper explores the effectiveness of the multi-layer FSCW design optimization for a variety of slot-pole combinations of practical interest. The optimization potential is presented in terms of Pareto fronts featuring rotor loss reduction versus MMF fundamental. Such potential is shown to strongly vary from one case to another, fading away for some well-defined slot-pole combinations
Starting Performance of Large Grid-Fed Solid-Rotor Salient-Pole Synchronous Motors for the Oil&Gas Industry: Simulation Challenges and Factory Test Experiences
No full textIn the Oil&Gas Industry, the use of large medium-voltage salient-pole synchronous motors (SMs) directly fed from the mains with power ratings in the multi-MW range is still of great importance. These motors have to drive gas compressor, either directly or through a gearbox, at a fixed speed so that power electronics converters with relevant cost, reliability and control issues can be removed. In absence of a variable-frequency supply, the start-up process for these machines is critical and usually requires a solid-steel rotor. The starting torque is produced by the currents induced in the solid rotor as well as in the short-circuited excitation winding. The prediction of the starting performance for this kind of machines is a challenge that power engineers have been facing for decades. State-of-the-art simulation tools, based on 2D and 3D Finite Element Analysis (FEA), have brought advances but the problem of a reliable, computationally affordable prediction of the start-up-process is still an open and timely issue. This paper attempts to provide a contribution reporting on computation and testing experiences on a multi-MW SM. The impact of the various possible uncertainties in material properties and the need to model various details of the machine design are investigated in depth through sensitivity analyses in comparison with measured data. It is shown that acceptably accurate results in the starting performance prediction can be obtained through a set of 2D FEA simulations suitably combined with some analytical formulas and simple considerations
A new method for the analytical determination of the complex relative permeance function in linear electric machines with slotted air gap
No full textThe complex relative permeance function is a useful mathematical tool to study the magnetic field of electric machines with slotted air gap. In the literature, the complex permeance function is usually identified by means of numerical techniques based on conformal mapping. In this paper an alternative analytical approach is proposed. The method is based on solving the magnetostatic differential field equation over a portion of the slotted air gap by imposing suitable boundary conditions in the slot opening region. Such boundary conditions exploit the mathematical law which governs the divergence of the magnetic field in the neighborhood of corner-shaped ferromagnetic regions. Furthermore, the results of Carter theory on slot fringing effects on the air gap field are used. A simple easy-to-compute formula is obtained for the complex permeance function. Its accuracy is assessed by comparison with Finite Element Analysis (FEA)
A New Method for the Accurate Prediction of On-Load Power Factor in Two-Pole Induction Motors Considering Shaft Eddy Currents
Get PDFAn accurate prediction of medium-voltage induction motor (IM) power factor in rated conditions is important in the design stage to verify the machine compliance with specifications according to international testing standards. Laboratory and industrial experiences suggest that significant errors in full-load power factor calculation can result for two-pole IMs in particular, due to the eddy currents induced in the solid-steel shaft at rated slip. Such eddy currents are responsible for rejecting the main flux into rotor laminated yokes causing an increase in their saturation and, hence, in the required magnetizing current with respect to no-load conditions. This article proposes a method to study the phenomenon through a combination of analytical and simplified Finite Element (FE) calculations as a computationally-efficient alternative to conventional FE simulations. The results of the proposed approach are experimentally assessed by comparison with measurements on a set of built and tested medium-voltage two-pole IMs of different sizes, showing very good accuracy and computational performance
Benefits of Selecting PMASR Machines as Traction Motors in Battery Electric Forklift Trucks
Get PDFThe advantages of using PM-assisted synchronous reluctance motors as traction devices for electric forklift vehicles are investigated in this paper. Motor energy consumption and drive overall performance are analytically estimated through a simulation of a standard VDI-based driving cycle and compared with the corresponding results from a reference system driven using induction motors
Curvature Effects on Permanent Magnet Harmonic Losses of Surface-Mounted Permanent Magnet Machines
No full textPermanent magnets mounted on the rotor (or mover) of surface-mounted permanent magnet (SPM) rotating (or linear) synchronous machines are exposed to armature reaction field magneto-motive force (MMF) space harmonics, which cause eddy currents and losses. Magnet losses in rotating machines are sometimes studied through simplified models where the air-gap geometry is linearized. This may lead to suppose that curvature plays a minor role. In order to verify the extent to which such assumption holds, explicit formulas are derived and assessed in this paper for magnet loss estimation in case of both linear and circular air-gap geometry. Then, magnet losses in rotating and linear machines having equal MMF harmonics, air-gap width and magnet height and material are compared and conclusions about curvature effects on permanent magnet losses are drawn
On the use of conformal mapping in the analysis of electric machines
No full textConformai mapping is a widespread mathematical technique to approach the electromagnetic study of electric machines. In its practical application, however, it is relatively easy to incur in errors which make results unreliable. In this paper, some fundamental but possibly deceitful facts in conformal mapping application are described, focusing in particular on: energy conservation in magnetostatic and time-harmonic problems; current source assignment in the transformed domain; transformation of the flux density components through conformal mapping. The addressed topics are first investigated from a theoretical point of view; then some application examples, based on Finite Element Analysis are provided for illustration and validation purposes
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
- …
