• Energy Research

This paper deals with the development of a procedural approach for analysing the compatibility between high voltage alternating current/high voltage direct current power cables and existing/future structures by taking advantage of railway and highway transports. Several critical issues have been deeply analysed in order to ensure a reliable and safe operation of power cables hosted in railway/highway structures. The paper offers a perspective synergy that will have to be considered more and more in future electric networks due to the reduction of energy corridors. After a first assessment of the geometrical compatibility between insulated cables and hosting structures, the paper focuses on the fire behaviour of high voltage cables inside structures, some notes on the maximum length of high voltage alternating current cable links without the use of shunt reactive compensation and on the electromagnetic compatibility.

This paper deals with the reliability analysis of gas-insulated transmission lines (GIL). Two scheme alternatives of a GIL system have been investigated from a reliability standpoint. These configurations are of basic interest since they recognize how reliability performance may be improved by introducing redundancies at either the system level or at the unit level. Of course, reliability can only be increased with higher investment costs: these can be justified when a high level of transmission-line reliability is required. For the connection of a new powerplant to a node of the existing electric grid, the cost of undelivered energy can play a key role. Therefore, in the context of an electric energy market where the transmission grid ensures the efficient matching of demand and supply, a tool for evaluating the availability of a transmission line may be extremely important.

The paper presents a novel configuration of an axial hybrid magnetic bearing (AHMB) for the suspension of steel flywheels applied in power-intensive energy storage systems. The combination of a permanent magnet (PM) with excited coil enables one to reduce the power consumption, to limit the system volume, and to apply an effective control in the presence of several types of disturbances. The electromagnetic design of the AHMB parts is carried out by parametric finite element analyses with the purpose to optimize the force performances as well as the winding inductance affecting the electrical supply rating and control capability. Such investigation considers both the temperature dependence of the PM properties and the magnetic saturation effects. The electrical parameters and the force characteristics are then implemented in a control scheme, reproducing the electromechanical behavior of the AHMB-flywheel system. The parameter tuning of the controllers is executed by a Matlab/Simulink code, examining the instantaneous profiles of both the air-gap length and the winding ampere-turns. The results of different dynamic tests are presented, evidencing the smooth air-gap changes and the optimized coil utilization, which are desirable features for a safe and efficient flywheel energy storage.

Il settore elettrico è investito, in quasi tutti i paesi industrializzati, da una profonda crisi strutturale, iniziata negli anni ‘90 [1]. Essa segna il passaggio dalla fase di diffusione dell’elettrificazione, contrassegnata dal primato della fornitura di energia e dal conseguente affermarsi di monopoli statali, alla fase del libero mercato e della ricerca di efficienza. Questo quadro di grandi mutamenti è caratterizzato anche da rilevanti innovazioni tecnologiche, che si rivelano sempre più essenziali al suo sviluppo. Si pensi, ad esempio, al ruolo giocato dall’elaborazione delle informazioni in un contesto di mercato dominato dalla borsa elettrica, o alle tecnologie innovative nel settore della generazione atte a consentire tempi di ritorno molto contenuti per gli investimenti. In questo contesto è naturale che gli investitori siano spinti a ricercare soluzioni favorevoli allo sfruttamento anche di minimi vantaggi competitivi. Limitandoci al segmento della produzione di energia elettrica, è ben noto il collo di bottiglia, costituito dalle difficoltà burocratiche, che ostacolano l’ingresso nel mercato di nuovi soggetti: trattasi di un processo che richiede almeno venti diverse autorizzazioni, che coinvolgono circa 80 Enti, con tempi stimati in 950 giorni. La stessa Legge Bassanini, trasferendo alle Regioni le competenze autorizzative degli impianti fino a 300 MW termici (che richiedono nuovi adeguati strumenti strutturali e valutativi) ha finito per incrementare, anziché diminuire com’era nelle intenzioni, tempi e costi. Ostacoli anche maggiori si profilano sul versante dei fattori ambientali legati alle emissioni al camino, all’impatto sul territorio, ai campi elettrici e magnetici associati alle linee di trasmissione. E tuttavia gli ostacoli non sembrano ancora scoraggiare i potenziali nuovi attori del mercato della produzione, considerato che le richieste di connessione alla rete di trasmissione e gli studi di fattibilità hanno superato, in un solo anno e in termini di potenza, i 60 GW! Lo scenario si presenta dunque contrassegnato da alti rischi ma potrebbe anche fruttare elevati premi laddove gli operatori riescano ad individuare soluzioni tecnologiche che accelerino i tempi senza rinunciare a fornire elevate prestazioni e garanzie. È abbastanza singolare, a tale proposito, che impianti di generazione di elevato impegno, autorizzati e finanziati, non riescano a decollare per la difficoltà di ottenere i permessi alla costruzione di pochi chilometri di linea necessari per raggiungere il più vicino nodo della RTN. Infatti, la normativa sull’esposizione ai campi elettrici e magnetici che si va profilando all’orizzonte renderà, ancor più di quella vigente, in molti casi pressoché impossibile la realizzazione di tali tratte di linea. È con riferimento a questo aspetto che il presente lavoro intende fornire un utile contributo prospettando l’impiego di elettrodotti innovativi di tipo blindato (EBLI) in grado di rendere insignificanti i campi elettrico e magnetico sul territorio. Obiettivo principale dell’articolo è quello di mostrare, tramite un confronto tra linee aeree e linee blindate, la possibile convenienza di queste ultime laddove vengano correttamente computati prestazioni e oneri complessivi. I risultati ottenuti mostrano l’effettiva competitività della tecnologia EBLI quando le potenze da trasmettere siano rilevanti e la valorizzazione del territorio sia importante.

This paper deals with the simulation and the experimental confirmation of electromagnetic events that could interfere with the successful formation of the restoration path during the power system restoration procedure. The studied phenomena are more relevant for bulk power systems characterized by a low short circuit power as the restoration backbone. In particular, two case studies have been simulated and analyzed: one related to a transformer energization during the formation of the restoration path, and the other one occurred after the de-energization of some transmission lines and one autotransformer belonging to the restoration path. From the simulation results, it emerged that such events are related to the resonant effects between the supplying transformer and the restored network. Such resonances could have negative effects on the restoration if they are not effectively managed. In order to evaluate the impact of such phenomena in real networks, the measurement recordings of on-field tests were compared with the simulation results. It is worth noting that the performed analyses require the knowledge of several parameters that were not always available in practice. Hence, the exact magnitude of the described resonant phenomena was not easy to foresee for the restoration of real networks. The performed comparison confirms the preliminary simulation results and highlights that detailed electromagnetic models are particularly important to support the power system restoration management, in particular the planning of recovery procedures.

The paper deals with the possibility of using the distribution line carrier (DLC) in order to prevent dispersed generation islanding. The feasibility of this technology applied to MV networks has been investigated from a theoretical as well as experimental point of view. A multiconductor matrix procedure based on bus admittance matrix allows us to predict the high frequency behaviour of MV lines (overhead and cable): the signal strength can be verified at any section of MV networks. Moreover two measurement campaigns have been performed on real MV networks in order to validate the theoretical results.

The possibility of installing a double-circuit Gas Insulated transmission Line (GIL) in the pilot tunnel of the planned new railway galleries Fortezza-Innsbruck has been throughout described in a previous paper [1]. The importance of this topic has driven the European Community to co-finance a feasibility study in the frame of Trans-European Energy Networks (TEN-Energy Programme). The study will last three years and will be completed at the end of 2005. The Italian (GRTN) and Austrian (TIRAG) TSOs are involved in this study together with the University of Padova. The work is in progress and this paper reports the studies that have been already finished: it is completely focused on the technical feasibility whereas the integration into the EHV Austrian and Italian networks, a comparison with other transmission technologies and the environmental impact will be set out in a next paper.

Gas-insulated high-voltage and extra high-voltage transmission lines are a new technology for transmitting high-power ratings over long distances. A previous paper was devoted to predict the current distribution along with the external flux density in this multiconductor system, highlighting its proximity effect. It served as the vehicle for the present further research taking into account the thermal problems coupled to the electromagnetic field. The aim of the present paper, therefore, is to show the concordance between literature analytical formulas and the finite-element method (FEM) approach considering the concrete tunnel installations. The FEM model is able to study the precise thermal distribution inside the phase and enclosure thickness both in the steady-state regime and transient condition due to the phase-to-ground short circuit.