Stefano Quaia

Reducing voltage sags through fault current limitation

Short circuit current limitation in distribution utilities can be an effective way to improve power quality, since the expected voltage sag amplitude during faults can be dramatically reduced. A simple series LC circuit tuned at the net frequency, with the capacitor shunted by a metal oxide varistor (MOV), proves to be a well suited limiter to reach the goal. In the paper, the properties of such a circuit are analyzed and its operation is investigated through computer simulation. The relevant pro and con aspects are outlined and discussed.

Economical analysis and innovative solutions for grid connected PV plants

The world total photovoltaic (PV) installed capacity is growing very quickly, due to both government incentives and increased environmental concerns. This situation calls for the realization of large, grid-connected ldquoindustrialrdquo PV plants, aimed at delivering energy to the grid. However, the cost/kWh of PV energy is still quite high. This paper reports some of the most promising research approaches currently in progress on new PV materials and devices, focusing on the reduction of PV generation cost expected from the technological implementation of such research. Because of their large size, industrial PV plants could have different characteristics compared to the small ones that, with few exceptions, have been realised until now. This problem is analyzed with the aim of providing a set of recommendations and guidelines for proper design of industrial PV plants, mainly concerning the choice of the power electronic conditioning systems and the use of simulation-aided design tools.

Four-Phase AC Connections: An Alternative Possibility for the Expansion of Transmission Grids

This paper investigates the economical feasibility of four-phase (4P) overhead transmission lines, considered as a possible alternative to the traditional three-phase (3P) connections. The paper performs an economical comparison between innovative 4P transmission lines and traditional 3P lines, with the goal of evaluating the contests where a 4P connection could become convenient, accounting for different reliability, land occupation, visual impact, energy losses and investment costs.

The Loadability of Overhead Transmission Lines—Part I: Analysis of Single Circuits

This paper provides a methodology for a thorough technical comparison between traditional three-phase ac lines, on the one hand, and possible (in some cases unconventional) alternative solutions that include HVDC lines, four-phase ac lines, and combined ac-dc lines, on the other. The comparison is based on the loadability curves, which are calculated here for all of the considered lines taking into account thermal limits, voltage drop, power losses, and-when feasible-steady-state and transient stability. The focus is on four-phase ac and combined ac-dc lines, for which the loadability curves are derived for the first time, whereas the loadability curves of three-phase ac lines-well-known in the literature-are derived and used here just as the natural reference for the comparison. Due to the great deal of theoretical and numerical developments, the study is split in two. Part I analyzes single-circuit lines of comparable loadability at the thermal limit (three phase, four phase, and monopolar HVDC). Part II broadens the analysis to double-circuit lines of comparable loadability at the thermal limit (three-phase, bipolar HVDC, and combined ac-dc) and performs an overall comparison among the different systems in single-circuit and double-circuit configuration.

The Loadability of Overhead Transmission Lines—Part II: Analysis of Double-Circuits and Overall Comparison

This is the second part of an investigation aimed at providing a thorough technical comparison between traditional and alternative overhead power transmission lines based on the loadability characteristics. The previous Part I outlined and applied the fundamentals of the loadability analysis to three comparable single-circuit lines. In Part II, the analysis is broadened to three comparable double-circuit lines: traditional three-phase ac double-circuit lines (assumed as the reference system for the comparison) and bipolar HVDC lines and nonconventional combined ac-dc lines. As in Part I, the loadability analysis takes into account thermal limits, voltage drop, power losses, and - when feasible - steady state and transient stability. Part II also performs an overall comparison among the different systems in single-circuit and double-circuit configuration to draw final conclusions.

Technical comparison among different solutions for overhead power transmission lines

The goal of this paper is to develop a technical comparison among different possible solutions for overhead transmission lines. These include both traditional and innovative solutions: the former are usual three-phase AC lines and HVDC lines, the latter are four-phase AC lines and combined AC-DC lines. A technical-economical comparison between aerial standard three-phase AC and innovative four-phase AC lines has been already developed in, where the possible scope of convenience of the four-phase solution has been individuated. This paper first illustrates the main characteristics of the four considered solutions, pointing out the technical advantages provided by each one. Secondly, the paper performs a more detailed comparison based on a probabilistic analysis of the transient stability performances of the considered alternatives.

Using pumped storage loads in restoration paths: a field test in the Italian national grid

This paper deals with power system restoration and discusses the connection of pumped storage loads to restoration paths. This new strategy allows avoiding any disturbance to customers during field tests of restoration paths and improves as well the reliability of restoration plans. The first application of the new strategy concerned the field test of a new path in central Italy. This paper reports the test and analyzes the main novel features of the considered path: complete separation from subtransmission and distribution networks and use of pumped storage loads during its energization. These aspects and their consequences are discussed with reference to both field testing of restoration paths and effectiveness of system restoration.

Surveying PQ aspects in Italian industrial customers

The paper has the objective to identify levels of power quality (PQ) at industrial customers in the various areas of Italian electric system. To this aim, the results of two different questionnaire based surveys performed so far in different Italian Districts have been analyzed in comparison in order to derive general rules and guidelines concerning PQ aspects. The surveys have involved, as a whole, a sample of about 200 industrial customers located in central and northern areas of the country. The surveys have concerned even some aspects relevant to costs of PQ problems. The main results as obtained from either the surveys are reported and discussed.

All-electric Mega-Yachts: Integrated power system operation and its interaction with propulsion converters

More and more commercial and pleasure modern ships are equipped with electric propulsion system, which is the most important and power-consuming electric apparatus onboard. The significant increase in the power required onboard by the adoption of electric propulsion causes a great evolution in onboard power systems and poses the need for a proper development of design techniques and tools. At the same time, the traditional approach for onboard power system design based on experience and rules of thumb is becoming no longer adequate. This paper deals with this evolving scenery, and mainly concerns power system design and power quality aspects. Real data and measurements are provided with reference to a new-built mega-yacht. The work, in progress, aims to set up a complete electric model of the all-electric ship to allow simulation of different operating conditions and to predict the main power quality issues and the fulfillment of the relevant technical rules

Technical-economic evaluation of a Combined Heat And Power Solar (CHAPS) generator based on concentrated photovoltaics

Combined Heat And Power Solar (CHAPS) generators are becoming increasingly popular due to the capability of providing, with high overall conversion efficiency, both electrical and thermal power: a feature that makes them very interesting not only for large-scale but also for domestic- and commercial-scale applications. The object of this study is one specific implementation of the CHAPS technology based on concentrated photovoltaics (also reported as CPVT, Concentrated PhotoVoltaics and Thermal). First of all, this paper reports on the state of the art of such concentration-based CHAPS; the specific system under investigation is then described and critically analyzed from a technical point of view. Finally, an economic analysis is performed, demonstrating the viability of such approach.