Misura UHF (Ultra High Frequency) delle scariche parziali nei sistemi isolati a gas: metodologie per la verifica della sensibilità di misura

Le apparecchiature di manovra tramite isolamento a gas (GIS) sono in funzione da più di 45 anni e hanno dimostrato un alto livello di affidabilità, con tassi di difetto molto bassi. Tuttavia, il riscontro pratico indica che alcuni dei guasti che si verificano durante il servizio sono legati a difetti del sistema di isolamento. Molti di questi difetti possono essere rilevati tramite diagnostica con scariche parziali (PD). Per la rilevazione PD, viene utilizzato il metodo UHF perché meno sensibile ai disturbi e quindi più facile da gestire in confronto al metodo convenzionale secondo IEC 60270. Un rapporto di Electra pubblicato nel 1999 dal CIGRE Task Force 15/33.03.05 descrive la procedura in due fasi per la verifica della sensibilità del sistema UHF in modo molto generale. Dopo 15 anni dalla sua applicazione, è diventata necessaria una descrizione più dettagliata, sia su misure necessarie al test di laboratorio (Passaggio 1) che sul test in loco (Passaggio 2).

Analisi evolutiva delle radiosorgenti tramite indagine su “compact steep spectrum" (CSS) e “high frequency peakers” (HFP)

in questo lavoro di tesi verrà fornita dapprima una descrizione degli oggetti che andremo a studiare, e cioè i nuclei galattici attivi (AGN), con un richiamo alle strutture più importanti di cui si costituiscono i loro sottogruppi: Quasar e radiosorgenti. Saranno forniti i segni distintivi con cui poter riconoscere queste forme di sorgenti radio e verrà fornito un modello che consenta di concepire il ciclo vitale radiativo a cui sono destinati tali classi di radiogalassie. Si vedrà che il tipo di radiazione emessa è prevalentemente non termico, anch’essa vista come una loro caratteristica peculiare. Si darà quindi una descrizione di questo meccanismo di radiazione ,che corrisponde all’emissione di sincrotrone, e si analizzeranno, facendo riferimento a questa base teorica, dati provenienti da una particolare tipologia di radiosorgenti: le “High Frequency Peakers” (HFP) che, come si evince dal nome stesso, rappresentano delle sorgenti con uno spettro di radiazione con picco riscontrabile alle alte frequenze. Si studieranno i dati raccolti dal catalogo TGSS a 150MHz con la speranza di avere riscontri tali da poter confermare o rigettare il modello evolutivo che prendiamo in considerazione per descrivere il ciclo vitale di questa classe di oggetti astronomici e di cui daremo spiegazione nelle prossime pagine.

Modeling and Design of Phase Shifted Full Bridge Isolated DC-DC ZVS Converter with Peak Current Mode Control

Nowadays, there is a boom in the use of electrification. Electric vehicles are gaining interest worldwide due to various factors, including climate and environmental awareness. In this thesis, a step-down isolated power supply for electric tractors is investigated, specifically the phase-shifted full-bridge (PSFB) DC-DC with synchronous rectification and zero-voltage switching (ZVS). This converter was selected for its high-power capacity with high efficiency. A 3500 W PSFB converter with peak current control (PCCM) is designed and modeled in MATLAB. The input voltage range is from 550 V to 820 V and the output voltage range is limited to 9 V to 16 V with a maximum output current of 250 A. All components were commercially designed and selected, including magnetics for the high-frequency transformer and inductors, taking into account loss calculations. Zero voltage switching for the lagging leg is achieved at 13% to 100% load. The proven efficiency of the converter is around 90

Low Power instrument Transformer: technologies and applications

Instrument transformers serve an important role in the protection and isolation of AC electrical systems for measurements of different electrical parameters like voltage, current, power factor, frequency, and energy. As suggested by name these transformers are used in connection with suitable measuring instruments like an ammeter, wattmeter, voltmeter, and energy meters. We have seen how higher voltages and currents are transformed into lower magnitudes to provide isolation between power networks, relays, and other instruments. Reducing transient, suppressing electrical noises in sensitive devices, standardization of instruments and relays up to a few volts and current. Transformer performance directly affects the accuracy of power system measurements and the reliability of relay protection. We classified transformers in terms of purpose, insulating medium, Voltage ranges, temperature ranges, humidity or environmental effect, indoor and outdoor use, performance, Features, specification, efficiency, cost analysis, application, benefits, and limitations which enabled us to comprehend their correct use and selection criteria based on our desired requirements. We also discussed modern Low power instrument transformer products that are recently launched or offered by renowned companies like Schneider Electric, Siemens, ABB, ZIV, G&W etc. These new products are innovations and problem solvers in the domain of measurement, protection, digital communication, advance, and commercial energy metering. Since there is always some space for improvements to explore new advantages of Low power instrument transformers in the domain of their wide linearity, high-frequency range, miniaturization, structural and technological modification, integration, smart frequency modeling, and output prediction of low-power voltage transformers.

Development of a novel heat treatment for high performances L-PBF Ti6Al4V alloy: microstructural and mechanical characterization

This work presents the experimental development of a novel heat treatment for a high performance Laser Powder Bed Fusion Ti6Al4V alloy. Additive manufacturing production processes for titanium alloys are particularly of interest in cutting-edge engineering fields, however, high frequency laser induced thermal cycles generate a brittle as built microstructure. For this reason, heat treatments compliant with near net shape components are needed before their homologation and usage. The experimental campaign focused on the development of a multi-step heat treatment leading to a bilamellar microstructure. In fact, according to literature, such a microstructure should be promising in terms of mechanical properties both under static and cyclic loads. The heat treatment development has asked for the preliminary analyses of samples annealed and aged in laboratory, implementing several cycles, differing for what concerns temperatures, times and cooling rates. Such a characterization has been carried out through optical and electron microscopy analyses, image analyses, hardness and tensile tests. As a result, the most suitable thermal cycle has been selected and performed using industrial equipment on mini bending fatigue samples with different surface conditions. The same tests have been performed on a batch of traditionally treated samples, to provide with a comparison. This master thesis activity has finally led to the definition of a heat treatment resulting into a bilamellar microstructure, promising in terms of fatigue performances with respect to the traditionally treated alloy ones. The industrial implementation of such a heat treatment will require further improvements, particularly for what concerns the post annealing water quench, in order to prevent any surface alteration potentially responsible for the fatigue performances drop. Further development of the research may also include push-pull fatigue tests, crack grow propagation and residual stresses analyses.