• Energy Research

The rapid increase of electric vehicles (EVs) penetration represents an important challenge for the distribution system operator (DSO). The main issues arise not only from an optimal grid expansion planning point of view but also for managing the system in the near future. The paper focuses on a short-term period EV penetration scenario and proposes a mechanism of EV charging sessions rescheduling in order to mitigate grid congestions. The collaboration between three actors, namely the DSO, the fleet manager and the end user, allows the DSO to identify rescheduling programs in order to face overload events, that represent the most important issue for the grid caused by the widespread penetration of EVs. The IEEE 33-bus test system is used to check the potential of the proposed mechanism. Load flow simulations show that more than 50% of congestions are avoided by means of this approach. The promising results constitute a base case for a future work in which the optimal rescheduling program would be investigated.

In order to increase network resilience, Distribution System Operators are evaluating different remedial actions against extreme events that lead to long interruptions. This paper evaluates the technical solutions for deploying an emergency generator (EG) supplying an islanded Medium Voltage (MV) network. The paper identifies the minimum technical requirements and different neutral grounding arrangements that can be adopted. Taking into account the maximum size of the mobile generators available in the market, evaluation results show that supplying a section of a distribution network could be done only if cable length is lower than 5 km and maximum load is less than 0.5 MW.

Abstract A 3D thermal model of underground power cable is presented in this paper. A detailed representation of the cable and its joints, the laying condition, the soil and the heat exchanges between soil upper surface and air, considering different weather conditions, is given. The model solves the thermal problem by means of an equivalent electric circuit and has been validated against field measurements, showing its applicability both for steady state and transient studies. In order to verify if any correlation between the occurrence of overheatings and the anomalous increase of failures, observed by Italian Distribution System Operators (DSOs) during summer 2015, exists, the model has been applied to simulate one-year operation of an existing underground cable. The cable is located in the MV distribution network owned by A.S.M. Terni S.p.A., the DSO in Terni, a city placed in the Central Italy. Ambient temperature and relative humidity trends have been taken from registrations made by a weather station, whereas the current profile along the cable has been assumed equal to that measured in 2015 by A.S.M., sampled every ten minutes. A second current profile has been also used, derived from the measured one in order to have the cable loaded at ampacity for a considerable time span during the year. In all cases, results show that no overheating occurred and, moreover, that the joint is the coldest part of the underground power cable.

Abstract Simulation of direct lightning strokes to overhead line towers requires accurate modeling of tower grounding systems. When large-scale statistical simulations are needed (e.g. in backflashover rate assessment), detailed but computationally intensive models are not suitable. This paper presents a genetic algorithm-based procedure to synthesize a generalized pi-circuit model, aimed at simulating the impulse response of complex grounding systems, including non-linear soil ionization, for backflashover studies. The equivalent electrical parameters of the pi-circuit model are determined as functions of soil resistivity for some commonly used grounding systems; the pi-circuit model is then validated by time-domain ATP-EMTP comparison with a complete circuit model, obtaining very good results (worst-case errors do not exceed 3–4%). ATP-EMTP time-domain simulations of direct lightning strokes to overhead lines equipped with the pi-circuit model are also reported, showing an excellent agreement with results yielded by the complete circuit model as well as drastically decreased computation times (up to 3 orders of magnitude).

The paper describes a project dealing with the deployment of an e-mobility service for persons with disabilities. The service is focused on the movements of people with disabilities within and between buildings of Sapienza University of Rome, dislocated in different areas of the city. A methodology suited to design correctly the service is explained. For each connection, different routes and electric vehicles are analyzed in terms of travel time, energy consumption and battery state of charge by a software developed by the authors; the most suited routes and electric vehicles can be thus chosen. Amongst the numerous connections analyzed in the project, the paper reports and discusses results of a single case study, in order to show the effectiveness of the proposed methodological approach.

Technical improvements in the construction of EHV cables have made possible the installation of very long EHV AC cable lines; with a sufficient degree of voltage control such lines can retain a large part of their theoretical power transmission capability. Quick, accurate expressions for the evaluation of cable length-loading relationships are given to that purpose. Appropriate choice of shunt compensation by standard, fixed-type shunt reactors, aimed at solving most steady-state constraints on the operation of very long EHV cable lines as well as temporary overvoltages, is discussed. Analysis of the operating envelopes of very long EHV AC cable lines shows that line losses play a very limited role. A simple criterion for optimal utilization of real, lossy cable lines is also proposed.

For several years, the increase of extreme meteorological events due to climate change, especially in unusual areas, has focused authorities and stakeholders attention on electric power systems’ resilience. In this context, the authors have developed a simulation model for managing the resilience of electricity distribution grids with respect to the main threats to which these infrastructures may be exposed (i.e., ice sleeves, heat waves, water bombs, floods, tree falls). The simulator identifies the more vulnerable network assets by means of probabilistic indexes, thus suggesting the best corrective actions to be implemented for resilience improvement. The fulfillment of grid constraints, i.e., loading limits for branches and voltage limits for buses, under actual operating conditions, is taken into account. Load scenarios extracted from available measurements are evaluated by means of load flow analyses in order to choose, among the best solutions identified, those compatible with the constraints. The proposed tool can assist Distribution System Operators (DSOs) in drawing up the Action Plan to improve, on one hand, the resilience of the network and, on the other hand, to remove any possible limitation for the adoption of the best solutions to ensure maximum operational continuity during extreme weather events.

The paper presents a methodology which can be used to improve the static adequacy of high-voltage (HV) transmission systems under contingency. In this case the most suitable actions to be taken for bringing the power system back to acceptable operation conditions are identified by means of a power system management software. The proposed software combines a micro-genetic algorithm (μGA) optimization procedure with a load-flow program based on the fringing current correction (FCC) method. The foreseen control actions consist in transformer tap setting, insertion and/or regulation (if variable) of shunt reactor and capacitor banks, change of network configuration, power re-dispatching and load shedding. The performance of the proposed procedure is tested with respect to the main parameters both of electrical power systems and of genetic algorithms (GAs). An application to existing HV transmission systems is presented and discussed in order to evaluate its possible use in a System Control Center.