• Energy Research

IN QUESTO LAVORO VIENE PRESENTATA UNA METODOLOGIA SEMPLIFICATAPER IL CALCOLO ELETTRICO DEI SISTEMI DI TRASPORTO FERROVIARIO ELETTRIFICATI IN CORRENTE ALTERNATA MONOFASE ALLA TENSIONE DI 2X 25 KV, 50 HZ, CON AUTOTRASFORMATORI. I RISULTATI OTTENUTI MEDIANTE UNA PROCEDURA DI CALCOLO AUTOMATICO SONO STATI CONFRONTATI CON QUELLI RICAVATI A PARTIRE DA MODELLI PIU’ RIGOROSI, RICONOSCIUTI COME RIFERIMENTO A LIVELLO INTERNAZIONALE. ATTRAVERSO ALCUNI ESEMPI DI APPLICAZIONE E’ STATA INFINE ILLUSTRATA L’IDONEITA’ DELLA METODOLOGIA PROPOSTA PER UNA SIMULAZIONE RAPIDA E SUFFICIENTEMENTE PRECISA DEL FUNZIONAMENTO DEL SISTEMA ELETTRICODI POTENZA IN REGIME PERMANENTE.

Abstract The transmission expansion planning has to guarantee the increase of competitiveness of market participants ensuring high standards of reliability and the safety of system operation. The congestion occurrences limit the competitiveness and cause an increase of costs for the final users. In the present paper a new deterministic methodology is proposed in order to support the static transmission system planning in deregulated electricity markets, which are characterized by high levels of uncertainties. The concept of criticality in transmission system planning is introduced: congestion cases and bottlenecks represent critical cases of the transmission system from a point of view of planners. The proposed approach allows individuating these critical states by solving specific optimization problems and performing reliability analyses based on the N − 1 criterion. A comparison of different transmission expansion plans is performed assessing the indices of criticality, whose evaluation is based on measuring the exploitation of the margin capabilities of transmission lines. The indices have been used to measure the reduction of criticality associated to expansion plans. The proposed approaches have been applied on two different test systems in order to demonstrate the effectiveness of the methodology in transmission system planning applications.

In a free-market scenario, power system planning is affected by a significant degree of uncertainty about time and location of generating assets expansion. The paper contains a methodology for the evaluation of the flexibility, defined as the attitude of the transmission system to adapt, quickly and with limited costs, to every change, from the initial planning conditions, with a particular regard to the changes in generation. The method provides new global and local flexibility indices, based on technical and economical parameters, defined as Technical Uncertainty Scenarios Flexibility Index (T-USFI) and Technical Economical Uncertainty Scenarios Flexibility Index (TE-USFI). The T-USFI computation segment of methodology has been tested on simple networks.

The paper describes the design and implementation of a new protection system consisting of a permissive overreach (PO) pilot relaying scheme with directional overcurrent relays for both phase and ground faults supporting closed-loop operation in MV network; attention is focused on ground fault relaying of loop networks operated with ungrounded or compensated neutral. Relevant zero-sequence quantities are studied and changes to relay settings are proposed and verified by detailed simulations. The system, developed within the framework of “Piano Operativo Interregionale” (POI) funded by Italian Government, will soon enter service in an Enel Distribuzione (hence:Enel-D) network.

Abstract The present paper reviews the concept of flexibility for an application to power systems for operational planning of transmission grid in market environment. The background that makes useful the application of the flexibility notion to power systems is explained. Some general definitions concerning the concept of flexibility in more recent scientific literature are reported. A specific and unique definition of transmission system flexibility in respect of the generation changes is proposed. The mathematical model and the calculation methodology of some bulk system flexibility indices are presented. A dedicated tool in Matlab for their computation is briefly shown in its features. The tool is owned by the Italian Transmission System Operator (TERNA) and is in testing for the flexibility evaluation of parts of the Italian National Transmission Grid. An application of the procedure to a real case is presented and the main results are discussed with the aim of test the validity of the proposed indices.

In a free-market scenario, power system planning has to deal with a significant degree of uncertainty about time and location of generating assets expansion. A methodology for the evaluation of the attitude of the transmission system to keep up a desired standard of reliability under such uncertainty (that is, flexibility) is presented. The method, relying on the Monte Carlo simulation approach, is applied to check the effectiveness of a flexibility index, based on structural as well as operational network parameters. The results of tests carried out on simple networks and on IEEE RTS are reported showing the encouraging agreement between the probabilistic simulations and the proposed index.

Abstract The paper reports some experimental measurement results concerning harmonic content of current absorbed by Personal Computers (PC). The measurements provided different samples of PC's being monitored at short time interval lengths (2 s). The relatively large quantity of measurement results has permitted a statistical characterization of the harmonic content with both different modes of operation and various upstream system characteristics. Curves obtained from the measurement results processing have been proposed which give a parametrical estimate of the mutual influence between harmonics produced by PCs and the supply system characteristics at the point of common coupling.

A model of electric residential end-use is proposed for establishing the load diagram of an area by a process of synthesis. The model follows a "bottom-up" approach, allowing construction of the relative load shape of the area, starting from knowledge of its most relevant socioeconomic and demographic characteristics, unitary energy consumption and the load profiles of individual household appliances. Several probability functions have been introduced in order to cover the close relationship existing between the demand of residential customers and the psychological and behavioral factors typical of the household; the model makes frequent use of the latter through a Monte Carlo extraction process. The model has been applied for the simulation of a residential area where field measurements of power demand had been made at 15-minute intervals and a combined mail survey had been conducted to investigate household energy usage. The paper reports the results of a comparison between recorded and predicted load profiles. >

A simulation model developed for prediction of the electric load profile of a residential area is briefly outlined in the paper. The model based on a "bottom-up" approach in order to reproduce customers' daily behaviour concerning elcctricity usage, has been applied for validation to reproduce load diagrams of a sample residential area where field measurements of power demand arid a combined mail survey had been previously conducted. Since the residential electric load was almost exclusively of the discretionary, weather-independent type, the survey ques tionnairc regarded mainly thc lifestyle of customers, thus evidencing the need for probabilistic processing of the data collected by the survey. To this end customers' presence at home and appliance usage have been considered as normal distributions around a incan value as ensued from the survey data. In the paper, a sensitivity analysis is performed on standard deviation values of the above distributions, which allows quite good matching of recorded data with simulation risults. A heuristic approach is proposed for correcting the dispersions of normal distributions to compensate for the averaging inherent in the questionnaire replies compared with actual random behaviour of the persons concerned