A Tabu-search-based Algorithm for Distribution Network Restoration to Improve Reliability and Resiliency

Fault restoration techniques have always been crucial for distribution system operators (DSOs). In the last decade, it started to gain more and more importance due to the introduction of output-based regulations where DSO performances are evaluated according to frequency and duration of energy supply interruptions. The paper presents a tabu-search-based algorithm able to assist distribution network operational engineers in identifying solutions to restore the energy supply after permanent faults. According to the network property, two objective functions are considered to optimize either reliability or resiliency. The mathematical formulation includes the traditional feeders, number of switching operation limit, and radiality constraints. Thanks to the DSO of Milan, Unareti, the proposed algorithm has been tested on a real distribution network to investigate its effectiveness

Reconfigurable radar transmitter based on photonic microwave signal generation

In this paper we propose a photonic technique for a reconfigurable microwave signal generation based on the beating in a photodiode of two laser modes from a regenerative Fiber Mode-Locked Laser (FMLL). The excellent performance of this kind of pulsed laser guarantees high stability to the generated microwave signal even at ultra high frequencies (up to W band). Therefore, by using the proposed architecture, the performance of a reconfigurable full digital coherent radar system can be enhanced in terms of Moving Target Indicator (MTI) improvement factor. Moreover, thanks to the achievable high repetition rates and the coherence properties of the FMLL, this laser scheme has also been proposed for digitizing the received signal by electro-optical sampling. Thus the advantage of using just one device for signal generation in both the transmitter and receiver chain, makes the proposed solution a cost effective architecture for microwave signal generation. Differently from the microwave synthesizers, whose performance strongly deteriorate with increasing frequencies, the photonic radio frequency generation always shows an excellent spectral purity. The results show excellent spectral purity above 5 KHz for the proposed technique compared to a state of the art Agilent synthesizer even though the timing jitter increases for integration time greater than 10 msec. In order to achieve the same stability performance at both high and low frequencies a Phase Locked Loop between the laser and a synthesizer could be used

Assortativity Decreases the Robustness of Interdependent Networks

It was recently recognized that interdependencies among different networks can play a crucial role in triggering cascading failures and hence system-wide disasters. A recent model shows how pairs of interdependent networks can exhibit an abrupt percolation transition as failures accumulate. We report on the effects of topology on failure propagation for a model system consisting of two interdependent networks. We find that the internal node correlations in each of the two interdependent networks significantly changes the critical density of failures that triggers the total disruption of the two-network system. Specifically, we find that the assortativity (i.e. the likelihood of nodes with similar degree to be connected) within a single network decreases the robustness of the entire system. The results of this study on the influence of assortativity may provide insights into ways of improving the robustness of network architecture, and thus enhances the level of protection of critical infrastructures

Power System Stability Analysis of the Sicilian Network in the 2050 OSMOSE Project Scenario †

This paper summarizes the results of a power system stability analysis realized for the EU project OSMOSE. The case study is the electrical network of Sicily, one of the two main islands of Italy, in a scenario forecasted for 2050, with a large penetration of renewable generation. The objective is to establish if angle and voltage stabilities can be guaranteed despite the loss of the inertia and the regulation services provided today by traditional thermal power plants. To replace these resources, new flexibility services, potentially provided by renewable energy power plants, battery energy storage systems, and flexible loads, are taken into account. A highly detailed dynamical model of the electrical grid, provided by the same transmission system operator who manages the system, is modified to fit with the 2050 scenario and integrated with the models of the mentioned flexibility services. Thanks to this dynamic model, an extensive simulation analysis on large and small perturbation angle stability and voltage stability is carried out. Results show that stability can be guaranteed, but the use of a suitable combination of the new flexibility services is mandatory

OPTIMAL MANAGEMENT OF FLEXIBILITY SERVICES IN LV DISTRIBUTION GRIDS

With the increase of intermittent and not programmable generation from clean resources and of new demand tech-nologies characterized by high coincident peaks (like heat pumps, induction cookers, etc.) the management of avail-able flexibility in distribution grids to provide network ser-vices has become very important. The paper proposes an optimization model to manage the flexibility in the LV net-work to both solve local network problems and aggregate the available flexibility for use at higher levels while sat-isfying LV network constraints. The model is a tool for the LV DSOs to optimally manage the flexibilities and its fea-tures are illustrated on the IEEE 123 test feeder

CLEAN technique for polarimetric ISAR

Inverse synthetic aperture radar (ISAR) images are often used for classifying and recognising targets. To reduce the amount of data processed by the classifier, scattering centres are extracted from the ISAR image and used for classifying and recognising targets. This paper addresses the problem of estimating the position and the scattering vector of target scattering centres from polarimetric ISAR images. The proposed technique is obtained by extending the CLEAN technique, which was introduced in radar imaging for extracting scattering centres from single-polarisation ISAR images. The effectiveness of the proposed algorithm, namely, the Polarimetric CLEAN (Pol-CLEAN) is tested on simulated and real dataM. Martorella, A. Cacciamano, E. Giusti, F. Berizzi, B. Haywood, and B. Bate

The effects of new 2030 scenario: Reduction of short-circuit power and widening of voltage dips

In Italy, 80% of PV installations are at MV and LV levels, which makes it particularly challenging to control them from the national dispatch centre; this leads to an increase of the reverse power flow in the primary and secondary substations, increasing pressure on the existing measuring and protection systems and on voltage control. The National Strategic Plan, approved on November 10 th , 2017 by the Ministry of Economic Development and the Ministry of the Environment, has launched an ambitious challenge, e.g., phasing-out of coal and the increase of electricity from renewable sources: more than 55% by 2030 of gross final consumption. The power system must be able to withstand unplanned events and manage their impacts on the network, thus reducing the risk of cascading effects and maintaining suitable quality of supply. During operation with a high percentage of RES connected to the network through inverters, the system is weaker (lower short circuit power) and, with currently adopted controls, less able to react to emerging faults. With the increase of PV installations, also due to reduction of rotating synchronous machines connected to transmission grid, there is lower Short-circuit-Power available and therefore voltage dips generated at transmission level have larger impact (c.g. area impacting supply quality widens hundreds of kilometers away from the event). This paper summarizes the main challenges in terms of impacting supply quality for the Italian Power system in a new scenario with more than 50% RES by 2030 of gross final consumption and suggests some computation procedures to investigate the phenomenon