Search

Large-scale deployment of renewable energy sources in power systems is basically motivated by two universally recognized challenges: the need to reduce as far as possible the environmental impact of the massive increase of energy request and the dependency on fossil-fuel. Renewable energy sources are interfaced to the network by means of interfacing power converters which inherently exhibit zero inertia differently from the conventional synchronous generators. This matter jointly to the high level of time variability of the renewable resources involve dramatically frequency changes, recurrent frequency oscillations and high variability of frequency profile in general. The need of a fast estimation of time variability of the power system inertia arises at the aim of predicting critical conditions. Based on the analysis of some actual data of the Italian Transmission Network, in this paper the authors propose an autoregressive model which is able to describe the dynamic evolution of the power system inertia. More specifically, the inertia is modeled as the sum of a periodic component and a noise stochastic process distributed according a non-Gaussian model. The numerical results reported in the last part of the paper, demonstrating the efficiency and precision of estimation of inertia, allow justifying the assumptions of the above modeling.

A framework for simulating wide area measurement system (WAMS) of electrical transmission networks to test measurement algorithms is proposed in the paper. The framework has been implemented by a joint team involving the Italian transmission system operator (TSO), Terna S.p.A, and the University of Naples Federico II, and is essential to assess the performance of algorithms estimating network variables before making them operational on the real WAMS. On the other hand, the algorithm performance must be evaluated on a system that reproduces as faithfully as possible the problems characterizing an actual monitoring system. The authors propose a mixed solution including open-source software for managing timestamped data streams and Matlab script for both emulating PMUs and measurement algorithm. In the paper also preliminary tests carried out in order to assess the framework reliability are described.

This paper deals with the inertia estimation of power systems in presence of significant contribution provided by renewable energy sources. The efforts to decommission conventional power plants and replace them with renewable resources could affect the robust and reliable operation of future power systems. The main issue related to the integration of renewable-based generation in the networks deals with the substitution of conventional synchronous generators connected to the grid and equipped by rotating masses, with converter-based generator which have not rotating masses, or they are decoupled by the grid due to the presence of interfacing power converters. Since the system inertia is the inherent ability of the online synchronous machines to oppose sudden changes in generation or load, the increasing share of renewable generators, such as wind and solar, the overall system inertia could decrease. This leading network operators to introduce new tools for monitoring the system inertia values, to contain them within admissible values, and to better prepare for different kinds of operational scenarios with undesired reduction of the system inertia. At this purpose, in this paper a tool for the analysis and prediction of inertia is proposed. The proposed method is based on a minimum variance harmonic finite impulse response and can consider the actual penetration of renewable energy sources. The proposed approach is tailored for online monitoring and exploits the real time measurements of relevant features of the network. The method is tested with actual data of the Italian Transmission Network and its effectiveness is studied by comparisons with some popular and well-established method of analysis and prediction.

Large-scale penetration of renewable energy sources in power systems is essentially related to the need of reducing the environmental impact caused by the fossil-fuel. As well known, the interface between the power grid and this kind of energy resource is achieved by power converters, with a consequent dynamic behavior quite different from the synchronous generators. This matter involves negative impacts on the operating conditions of power systems. In this context, it is crucial to individuate estimation techniques able to predict promptly critical conditions which could, in extreme cases, compromise the stability of whole system. In this paper the authors employ an auto-regressive model which can describe the dynamic evolution of the power system inertia. The core of the procedure relies on an inertia model conceived as the sum of a periodic component and a noise stochastic process distributed according a Logistic model. The robustness of a novel estimation procedure, able to capture the dynamic evolution of the inertia, is investigated by testing two scenarios of Italian Transmission Network. The assumptions in terms of the obtained numerical results show the validity of the estimation technique and of the probabilistic characterization of the noise.

Wide-Area Monitoring Systems play a key role in ensuring reliability and security of modern electric power system operation. Phasor Measurement Units are the enabling technology for WAMS, since they provide synchronized measurements in spread points of the system characterized by higher data flow rate compared to traditional SCADA systems. An interesting application of WAMSs is the Dynamic Thermal Rating assessment of power lines, that allows fully exploit the benefits deriving by massive penetration of Renewable Power Generators by dynamically evaluating the interconnections’ transfer capabilities, reducing congestions in the system.Despite these benefits, these systems are vulnerable to Time Synchronization Attacks, since the majority of PMUs uses GPS signals as time reference for the synchronization procedure.In this paper the impact of TSAs on the reliability of DTR assessment will be discussed by analyzing the first results obtained on a realistic case study.

Two types of concretes were prepared in order to build thermal storage units for solar plants having as primary aim to improve thermal conductivity. The first type consists of concrete for casting on site (A), whereas the second for moulding upon vibration (B). Samples of both typologies were prepared changing type of additions or aggregates. The use of recycled materials into concrete (e.g. polyamide fibres from post-consumer textile carpet waste, metallic powders or shavings and steel fibres) was investigated. Fibre-reinforced concretes were tougher (up to 300%) than ordinary ones. All the concretes show high thermal conductivity and are good candidates for an efficient thermal storage unit, but the performances of type B concretes are better than those of type A. Moreover, the morphology of type B concretes appears compact and less cracked, even after thermal treatment at temperature higher than 300 °C. The thermal conductivity of the mix containing polyamide fibres and metallic shavings was 2.74 and 2.13 W/m °C, before and after a thermal treatment of 4 h at 300 °C, respectively. © 2017 Elsevier Ltd

The present paper presents a Cyber Physical Power System (CPPS) framework based on the Service-Oriented Architecture for proactive transmission grids control, modeling and monitoring. CPPS paradigm aims at integrating and coordinating computation, networking, and physical processes according to a holistic vision of the transmission system. The key feature of the proposed framework is the ability of multiple entities to process, manage and share massive heterogeneous information. More specifically, the idea is to conceptualize a holistic architecture that enables the computing resources to deliver much more automation that the sum of its individually self-managed components, allowing the Transmission System Operator to improve the interoperability and the integration level of monolithic and hard to customize power system control and monitoring functions. Moreover, it allows TSO to develop content-based data extraction and aggregation from a host of pervasive sensors network and to exploit distributed embedded computing resources aimed at solving large-scale problems. To assess the benefits of the CPPS framework, the first experimental results obtained on a real test bed are presented and discussed.

The paper deals with the issue of achieving a dynamic equivalent for large scale power systems with particular reference to the European Network of Transmission System Operators for Electricity (ENTSO-E) Continental Synchronous European Area (CESA). In this paper some essential aspects of the dynamic reduction process are deepened while others are faced according some practical considerations, in some cases derived from other studies in ENSTO-E community. Broadly speaking therefore, it deals with a preliminary study which leads to the deployment of a reduced order model able to describe the electromechanical phenomena occurring on the European Continental Synchronous network.

Guidelines for designing a concrete storage module and for its integration into a solar plant, respecting constraints linked both to an adequate solar field operation and to the production system based on ORC, are described. A series of simplified procedures are developed to be used for a first module design and more sophisticated (even if more expensive) simulation techniques via the Finite Element Method are checked and upgraded. Once the ongoing experimental phase on a scaled storage prototype at the ENEA site of Casaccia has been concluded, the obtained data will be used for completing both the setup of the calculation instruments and the R&D activity dealing with the development of an appropriate concrete mixing, optimising its chemical-physical and durability performances, and with the module integration within a CSP system. ﾩ 2014 Elsevier Ltd.

The use of recycled materials in new concrete production is very appealing because of the low cost of the raw materials and the landfill space saving, as well as the enhancement of the resulting concrete's properties. This paper focuses on the production of concrete for thermal energy storage systems using polyamide fibres from post-consumer textile carpet waste. We investigated the influence of a fibre content of 5kg/m3 on the mechanical and thermal properties of fresh and hardened concrete with a w/c ratio of 0.35, comparing it with plain concrete. The nylon fibre-reinforced concrete was slightly more ductile and tougher than the plain concrete because the fibres have an important role after failure. The tensile strength, maximum load-bearing capacity and modulus of elasticity decreased slightly with the addition of nylon fibres, but drying shrinkage was lower than for plain concrete. Given that heat capacity and thermal conductivity are the most important parameters for thermal energy storage purposes, we measured these parameters for all the samples at 25°C, and after a thermal treatment at 300°C. The heat capacity values were 0.63 and 0.81Jg-1K-1 for fibre-reinforced concrete (FC) and plain concrete (C), respectively, and the thermal conductivity values were 1.16 and 1.02Wm-1 K-1. © 2013 Elsevier Ltd.