Partial discharge in power distribution electrical systems: pulse propagation models and detection optimization

Investigation on impulsive signals, originated from Partial Discharge (PD) phenomena, represents an effective tool for preventing electric failures in High Voltage (HV) and Medium Voltage (MV) systems. The determination of both sensors and instruments bandwidths is the key to achieve meaningful measurements, that is to say, obtaining the maximum Signal-To-Noise Ratio (SNR). The optimum bandwidth depends on the characteristics of the system under test, which can be often represented as a transmission line characterized by signal attenuation and dispersion phenomena. It is therefore necessary to develop both models and techniques which can characterize accurately the PD propagation mechanisms in each system and work out the frequency characteristics of the PD pulses at detection point, in order to design proper sensors able to carry out PD measurement on-line with maximum SNR. Analytical models will be devised in order to predict PD propagation in MV apparatuses. Furthermore, simulation tools will be used where complex geometries make analytical models to be unfeasible. In particular, PD propagation in MV cables, transformers and switchgears will be investigated, taking into account both irradiated and conducted signals associated to PD events, in order to design proper sensors.

Discharge characteristics and discharge simulation model of long air gaps containing a floating conductor

Long air gaps containing a floating conductor are common insulation types in power grids. During the transmission line live-line work, the process of lineman entering the transmission line air gap constitutes a live-line work combined air gap, which is a typical long air gap containing a floating conductor. This thesis investigates the discharge characteristics, the discharge mechanism and a discharge simulation model of long air gaps containing a floating conductor in order to address the engineering issues in live-line work. The innovative achievements of the thesis are as follows: (1) The effect of the gap distance, the floating electrode structure, the switching impulse wavefront time, the altitude, and the deviation of the floating conductor from the axis on the breakdown voltage was determined. (2) The physical process of the discharges in long air gaps containing a floating conductor was determined. The reason why the discharge characteristics of long air gaps containing a floating electrode with complex geometrics and sharp protrusions and long air gaps with a rod-shaped floating electrode are similar has been studied. The formation mechanism of the lowest breakdown voltage area of a long air gap containing a floating conductor is explained. (3) A simulation discharge model of long air gaps containing a floating conductor was established, which can describe the physical process and predict the breakdown voltage. The model can realize the accurate prediction of the breakdown voltage of typical long air gaps containing a floating conductor and live-line work combined air gaps in transmission lines. The findings of the study can provide theoretical reference and technical support for improving the safety of live-line work.

Grid Connected Doubly Fed Induction Generator Based Wind Turbine under LVRT

This project concentrates on the Low Voltage Ride Through (LVRT) capability of Doubly Fed Induction Generator (DFIG) wind turbine. The main attention in the project is, therefore, drawn to the control of the DFIG wind turbine and of its power converter and to the ability to protect itself without disconnection during grid faults. It provides also an overview on the interaction between variable speed DFIG wind turbines and the power system subjected to disturbances, such as short circuit faults. The dynamic model of DFIG wind turbine includes models for both mechanical components as well as for all electrical components, controllers and for the protection device of DFIG necessary during grid faults. The viewpoint of this project is to carry out different simulations to provide insight and understanding of the grid fault impact on both DFIG wind turbines and on the power system itself. The dynamic behavior of DFIG wind turbines during grid faults is simulated and assessed by using a transmission power system generic model developed and delivered by Transmission System Operator in the power system simulation toolbox Digsilent, Matlab/Simulink and PLECS.

Essays in the Economics of the Family and Cultural Transmission

My research aims at identifying the role cultural-ethnic traits play in marriage choices and at uncovering the implications of marital sorting on consequent intra-household decisions. From different perspectives, this thesis focuses on intermarriages, within the Italian marriage market. In the first chapter, I explore the role of ethnic endogamy on marital instability. I document the existence of a positive differential in marital instability of interethnic marriages compared to homogeneous ones and I demonstrate that genetic and ethnolinguistic measures of cultural diversity are informative about the incidence of marital dissolution. The second chapter investigates a novel channel, which explains the differential in household stability and investments across family types: cultural socialization of children. I propose a marital matching model along cultural-ethnic lines, to study the process of family formation and intra-household decision making in a context where ethnic differences between spouses potentially matter both in terms of preferences and technologies for household production. The observed intermarriage, fertility, separation and socialization rates are in line with theoretical predictions and they are consistent with strong preferences of parents toward cultural socialization of children to their own ethnic identity. In the third chapter, I propose and estimate a marital matching model along ethnic lines. I argue that gains to intermarriage depend on both cultural preferences and legal status motives. Taking advantage of the exogenous EU enlargements to East European countries in 2004 and 2007, I show that gains to intermarriage of East European migrants significantly decrease in response to the acquisition of the legal status. The final chapter aims to understand whether judicial decisions respond to the ethnic identity of spouses and what incentives those judgments are guided, by looking at separation and divorce sentences. Studying the legal custody assignment of children, I document a significant differential interacting mothers’ ethnicities with the family type.