“Didattica acquisizionale” e cortesia linguistica in italiano L2

Le norme pragmalinguistiche e sociopragmatiche che regolano l’uso dell’allocuzione pronominale e la modulazione della forza illocutoria degli atti linguistici in italiano sono particolarmente complesse, acquisite in stadi molto avanzati dai parlanti non nativi e difficili da dominare anche per apprendenti con una buona padronanza complessiva della lingua obiettivo. Alle difficoltà acquisizionali delle strutture si unisce l’atteggiamento dei parlanti nativi, che tendono a rivolgersi ai non nativi con una lingua semplificata anche sul piano pragmatico. Il mancato rispetto delle norme che regolano l’espressione linguistica della cortesia può rappresentare un ostacolo alla serena accettazione degli stranieri da parte dei membri della comunità ospitante. Inoltre, la semplificazione del sistema presente nell’input rischia di instaurare una forma basilare di discriminazione e l’adozione di questa semplificazione da parte dei non nativi potrebbe corrispondere a una strategia di adattamento culturale o addirittura a una implicita legittimazione di tale discriminazione. A partire da queste considerazioni e confortati dai nostri dati, sosteniamo che un sillabo informato ai principi della “didattica acquisizionale” dovrebbe addestrare all’uso degli esponenti linguistici della cortesia fin dalle primissime unità didattiche, anche se ciò va contro ogni evidenza di insegnabilità.Handling the pragmalinguistic and sociopragmatic rules governing the use of address forms and the modulation of illocutionary force is extremely demanding for Italian L2 learners. Most of these rules are acquired very late, and even proficient learners of the target language can hardly cope with them. Not only are the linguistic forms intrinsically difficult, but also the input is not of help, as native speakers tend to present non-native speakers with a pragmatically simplified variety of the target language. Violating the rules governing the linguistic expression of politeness can become a source of hindrance to learners’ smooth participation in the L2 community. Furthermore, a basic form of discrimination could stem from native speakers’ use of simplified input, and the adoption of the simplified variety by non-native speakers could result in a strategy of cultural accommodation but even in an implicit legitimization of that discrimination. On these bases, and supported by our data, we argue that a syllabus designed according to the principles of the so called “didattica acquisizionale” should train in using linguistic forms of politeness from the very beginning of the instructional program, even against any evidence of teachability.Le norme pragmalinguistiche e sociopragmatiche che regolano l’uso dell’allocuzione pronominale e la modulazione della forza illocutoria degli atti linguistici in italiano sono particolarmente complesse, acquisite in stadi molto avanzati dai parlanti non nativi e difficili da dominare anche per apprendenti con una buona padronanza complessiva della lingua obiettivo. Alle difficoltà acquisizionali delle strutture si unisce l’atteggiamento dei parlanti nativi, che tendono a rivolgersi ai non nativi con una lingua semplificata anche sul piano pragmatico. Il mancato rispetto delle norme che regolano l’espressione linguistica della cortesia può rappresentare un ostacolo alla serena accettazione degli stranieri da parte dei membri della comunità ospitante. Inoltre, la semplificazione del sistema presente nell’input rischia di instaurare una forma basilare di discriminazione e l’adozione di questa semplificazione da parte dei non nativi potrebbe corrispondere a una strategia di adattamento culturale o addirittura a una implicita legittimazione di tale discriminazione. A partire da queste considerazioni e confortati dai nostri dati, sosteniamo che un sillabo informato ai principi della “didattica acquisizionale” dovrebbe addestrare all’uso degli esponenti linguistici della cortesia fin dalle primissime unità didattiche, anche se ciò va contro ogni evidenza di insegnabilità

Electromagnetic and thermal modelling, sizing and design refinement of a permanent magnet synchronous motor

This work copes with electromagnetic and thermal design of a permanent magnet synchronous motor. In the first part of my thesis, a standard sizing procedure starting from rated parameters is introduced in order to get the geometry of the machine. Moreover, a concentrated parameters model for the estimation of the temperatures in the main parts of the machine is presented. Secondly, a comparison between the analytical results and a finite element method (FEM) approach is shown in order to validate the analytical model presented in the first part. In this section, different structures of winding have been tested with a FEM based software and different percentages of error about some main quantities have been found. Finally, some combined simulations have been used with the purpose of obtaining the best combination of the magnet span and slot opening for the minimization of the torque oscillations at no-load conditions. The obtained magnet span and slot opening have been entered in the analytical model and the results have shown a further decrease of error between analytical and Fem based models

Harmonic reduction methods for electrical generation: a review

This paper provides a comprehensive literature review of techniques for harmonic related power quality improvement of electrical generation systems. An increasing interest in these aspects is due to the ever more stringent power quality requirements, deriving from new grid codes and compliancy standards, aimed at limiting waveform harmonic distortion at all points of the distribution network. Although a wealth of literature is available for such techniques, it has never been compiled into a handbook incorporating all the solutions aimed at both electrical machine and power systems engineers

A fast method for modelling skew and its effects in salient-pole synchronous generators

The general effects of implementing skewing techniques in electrical machines are well known and have been extensively studied over the years. An important aspect of such techniques is related to the identification of optimal methods for analyzing and modelling any skewed components. This paper presents a fast, finite-element-based method, able to accurately analyze the effects of skew on wound-field, salient-pole synchronous generators in a relatively shorter time than the more traditional methods. As vessel for studying the proposed technique, a 400kVA alternator is considered. Analytical and theoretical considerations on the benefits of skewing the stator in the generator under analysis are preliminary carried out. A finite-element model of the machine is built and the proposed method is then implemented to investigate the effects of the skewed stator. Comparisons against more traditional techniques are presented, with focus on the analysis of the voltage total harmonic distortion and the damper bars’ currents. Finally, experimental tests are performed at no-load and on-load operations for validation purposes, with excellent results being achieved

Analysis, modelling and design considerations for the excitation systems of synchronous generators

The traditional generating set is usually comprised of a classical, wound-field, salient-pole or cylindrical rotor synchronous generator, excited by a separate smaller machine, via a rotating, uncontrolled diode rectifier. The effects of the commutation processes of the diode bridge are often overlooked and neglected. However due to the uncontrolled nature of this process, the rectified voltage available at the main generator’s rotor terminals can be significantly lower than the expected value. This is especially true for low-to-medium power rated systems. In this paper, a detailed investigation of these aspects is done and an accurate voltage drop prediction model is then proposed. The model is validated with finite element analysis and with experimental results for a particular low-medium rated generating system in the 400kVA power range. The validated tool is then integrated into an innovative design tool, which first performs an analytical pre-sizing procedure and then utilizes a genetic algorithm approach to identify an optimal excitation system design, aimed at minimizing the voltage drop ensuing from the diode commutations, with minimum impact on the overall efficiency

Power quality improvement by pre-computed modulated field current for synchronous generators

Although power quality aspects of electrical machines have been extensively studied and investigated for a large number of years, room for improvement still exists in the field of classic, wound-field, synchronous generators. This paper proposes an innovative method of power quality improvement for single-phase synchronous generators in which the usual DC field current is replaced by a calculated current waveform. The optimised field current waveform is designed in such a way that harmonics created by the machine geometry and the winding configuration are significantly reduced

Analysis of Voltage Distribution and Connections within a High-Frequency Hairpin Winding Model

In the last years the adoption of hairpin windings is increasing, especially in the automotive sector, mainly due to their inherently high fill factor and electric loading capability. A critical aspect related to the reliability and lifetime of every winding typology is the voltage stress due to the uneven voltage distribution. This phenomenon has already been largely analyzed in conventional stranded conductors, while a few studies are available for hairpin windings. With the spreading of wide bandgap devices, the investigation on voltage distribution becomes an ever-timely topic due to their short rise times. This paper presents an analysis of the uneven voltage distribution triggered within hairpin windings by a low rise time waveform, using a complete high-frequency winding model. The different options to series-connect different paths are investigated, providing simple but essential guidelines to reduce the electrical stress within hairpin windings. © 20XX 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 worksThis paper reflects only the author's view. JU is not responsible for any use that may be made of the information it contains

Moving Toward a Reliability-Oriented Design Approach of Low-Voltage Electrical Machines by Including Insulation Thermal Aging Considerations

© 2020 IEEE. Electrical machines (EMs) are required to consistently perform their intended mission over a specified timeframe. The move toward transportation electrification made the EMs' reliability an even stringent and predominant requirement, since a failure might cause severe economic losses, as well as endanger human lives. Traditionally, the design procedure of motors conceived for safety-critical applications mainly relies on over-engineering approaches. However, a paradigm shift is recently taking place and physics of failure approaches/methodologies are employed to meet the reliability figures, while delivering an optimal design. This article proposes and outlines a reliability-oriented design for low-voltage EMs. Thermal accelerated aging tests are preliminarily carried out on custom-built specimens. Once the aging trend of the turn-to-turn insulation system is assessed, the thermal endurance graph at several percentile values is determined and lifetime models are developed, for both constant and variable temperature operations. Finally, these models are used to predict the turn-to-turn insulation lifetime of motors meant for aerospace and automotive applications

Simplified Damper Cage Circuital Model and Fast Analytical–Numerical Approach for the Analysis of Synchronous Generators

The long and enduring history of utilization of the wound-field synchronous generator in a large number of applications makes it one of the most known and consolidated electrical machine technologies. Thus, its design, modeling, and analysis processes have been widely exploited and implemented through various and different methods, including the equivalent circuit approach. When a damper cage is embedded within the rotor of the synchronous generator, its theoretical analysis becomes quite complicated. Thus, today numerical tools are being used. In this paper, an alternative way of modeling symmetric damper cages of salient-pole synchronous generators is presented. The proposed approach is embedded in the circuital model of the generator. A hybrid analytical-numerical model is implemented, permitting to accurately predict the voltage waveforms of the generator with excellent accuracy, however, at a lower cost of computational resources than the pure numerical method. A case study of an off-the-shelf 400 kVA machine is considered to develop and validate the proposed technique. The results are compared with the corresponding finite-element and experimental evaluations for validation purposes

On the damper cage of salient-pole synchronous generators

In the field of power generation, the wound-field synchronous generator has a well consolidated history of utilisation, mainly due to its proven and excellent performance. Nevertheless, due to the ever-increasing requirements in terms of power quality, efficiency, grid compliance and manufacturing costs, there is interest in renewing the design of this electrical machine, also allowed by the recent advancements in the computational resources. In this thesis, an unconventional, modulated damper cage topology for salient-pole synchronous generators is proposed in order to address the requirements inherent to the power quality (by improving the total harmonic distortion of the output voltage), the efficiency (by reducing the damper cage associated losses) and the manufacturing costs and times (by achieving an un-skewed stator core structure). In order to achieve these objectives, a suite of innovative modelling techniques are proposed and validated in this work, including hybrid numerical/analytical models, a new methodology to model skewing in an accurate and fast manner and specific optimisation methodologies for synchronous generators. In this work, these tools are then used to propose improvements to synchronous generators through new configurations of the damper winding. The thesis focuses on two main platforms, namely 1) a 4MVA generator, where the modulated damper bars are shown to improve the losses and the THD of the system and 2) a 400kVA generator, where it is shown how through a new damper winding configuration, the traditional skewing of the stator can be removed without compromising the machine performance in any way