Superconducting technology for power and energy management

Babak Gholizad - Ciclo XXVIII - 2016

Abstract - In this thesis integration of high temperature superconductor technology in the future advanced power system will be investigated. In particular, superconducting magnetic energy storage system (SMES) for power quality of distribution grid and customer protection will be discussed. The complete design method, including the magnet and power electronic interface design will be discussed in more details. The method will be applied to the design of an industrial scale SMES system. Commercially available high temperature superconductor (HTS) material (YBCO) and magnesium diboride (MgB2) tapes will be considered for the design of the magnet. A multifunctional control algorithm for compensating voltage sag and improving power quality will be implemented, and the advantages of the SMES system and utilized control algorithm for this application will be illustrated. As a second part of the thesis, high temperature superconducting DC (HTS-DC) cables for transmission and distribution will be introduced. A method for both electromagnetic and thermo fluid-dynamic design of power cable will be developed. As a first case study superconducting DC collector grid for offshore wind-park will be technically and economically evaluated and the cost and loss model of the system will be discussed. Also, the transient behavior of the high temperature superconducting DC cable in high voltage DC (HVDC) system, which is crucial for stability, will be evaluated. Both line commutated converters (LCC) and voltage source converters (VSC) will be considered.

Continuous-flow magnetic separation with permanents magnets for water treatment

Chiara Caterina Borghi - Ciclo XXVI - 2014

Abstract - More efficient water treatment technologies would decrease the water bodies' pollution and the actual intake of water resource. The aim of this thesis is an in-depth analysis of the magnetic separation of pollutants from water by means of a continuous-flow magnetic filter subjected to a field gradient produced by permanent magnets. This technique has the potential to improve times and efficiencies of both urban wastewater treatment plants and drinking water treatment plants. It might also substitute industrial wastewater treatments. This technique combines a physico-chemical phase of adsorption and a magnetic phase of filtration, having the potential to bond magnetite with any conventional adsorbent powder. The removal of both Magnetic Activated Carbons (MACs) and zeolite-magnetite mix with the addition of a coagulant was investigated. Adsorption tests of different pollutants (surfactants, endocrine disruptors, Fe(III), Mn(II), Ca(II)) on these adsorbents were also performed achieving good results. The numerical results concerning the adsorbent removals well reproduced the experimental ones obtained from two different experimental setups. In real situations the treatable flow rates are up to 90 m3/h (about 2000 m3/d).

Experimental Analysis and Numerical Simulation of Quench in Superconducting HTS Tapes and Coils

Marco Casali - Ciclo XXVI - 2014

Abstract - The quench characteristics of second generation (2 G) YBCO Coated Conductor (CC) tapes are of fundamental importance for the design and safe operation of superconducting cables and magnets based on this material. Their ability to transport high current densities at high temperature, up to 77 K, and at very high fields, over 20 T, together with the increasing knowledge in their manufacturing, which is reducing their cost, are pushing the use of this innovative material in numerous system applications, from high field magnets for research to motors and generators as well as for cables. The aim of this Ph. D. thesis is the experimental analysis and numerical simulations of quench in superconducting HTS tapes and coils. A measurements facility for the characterization of superconducting tapes and coils was designed, assembled and tested. The facility consist of a cryostat, a cryocooler, a vacuum system, resistive and superconducting current leads and signal feedthrough. Moreover, the data acquisition system and the software for critical current and quench measurements were developed. A 2D model was developed using the finite element code COMSOL Multiphysics. The problem of modeling the high aspect ratio of the tape is tackled by multiplying the tape thickness by a constant factor, compensating the heat and electrical balance equations by introducing a material anisotropy. The model was then validated both with the results of a 1D quench model based on a non-linear electric circuit coupled to a thermal model of the tape, to literature measurements and to critical current and quench measurements made in the cryogenic facility. Finally the model was extended to the study of coils and windings with the definition of the tape and stack homogenized properties. The procedure allows the definition of a multi-scale hierarchical model, able to simulate the windings with different degrees of detail.

Sviluppo e Caratterizzazione di Bulk Superconduttori in MgB2 per Sistemi di Levitazione

Elena Perini - Ciclo XXV - 2014

Abstract - Superconduttori bulk in MgB2, ottenuti con tecnologia Mg-RLI brevettata da Edison Spa, sono stati oggetto di un'approfondita analisi in termini di forze di levitazione. Questo studio è stato preliminare per la progettazione di un innovativo sistema di levitazione lineare. I risultati ottenuti sperimentalmente sono stati validati attraverso modelli numerici sviluppati ad hoc. I campioni oggetto dello studio sono tre bulk in MgB2 rappresentativi delle tipiche forme usate nelle applicazioni reali: un disco, un cilindro, una piastra. I bulk sono stati misurati con un sistema di misura per le forze di levitazione realizzato a tale scopo. Un protocollo sperimentale è stato seguito per la caratterizzazione di base, sia in condizioni Field Cooling sia Zero Field Cooling, al quale sono state affiancate prove specifiche come la possibilità di mantenere inalterate le proprietà superconduttive attraverso la giunzione di più campioni con la tecnologia Mg-RLI. Un modello numerico è stato sviluppato per convalidare i risultati sperimentali e per studiare l'elettrodinamica della levitazione. Diverse configurazioni di rotori magnetici sono state accoppiate con un cilindro in MgB2 con lo scopo di valutare la soluzione ottimale; questo tema è stato apporofondito attraverso lo sviluppo di un software di simulazione che può tenere conto sia del numero di magneti sia della presenza di anelli in materiale magneti intercalati fra di essi. Studi analoghi sono stati portati avanti su una piastra di MgB2 per simulare il comportamento di una geometria piana. Un sistema di raffreddamento innovativo basato sull'azoto solido è stato studiato per poterlo accoppiare con un sistema di levitazione. Il criostato progettato è costituito da due dewar, uno dentro l'altro; quello interno ha lo scopo di raffreddare l'MgB2 mentre quello esterno di limitare delle perdite verso l'esterno. Il criopattino così ottenuto è accoppiato in condizioni FC ad una rotaia formata da magneti permanenti in NdFeB.

Un Concetto Innovativo di Limitatore di Corrente di Guasto Superconduttivo

Salvatore Imparato - Ciclo XXIII - 2011

Abstract - The thesis topic concerns the limitation of fault current high temperature superconducting (HTS), reported in scientific literature by the acronym HTSFCL (High Temperature Superconducting Fault Current Limiter) or more commonly with SFCL. These devices, at least in their ideal concept, turn on limiting short-circuit current only when the event of failure occurs, and are transparent to the network during normal operating conditions. The thesis is therefore focused on the study of dierent types of SFCL and results in the production of a new and original concept of superconducting limiter, called "DC Resistive SFCL". It has designed and patented in the Department of Electrical Engineering University of Bologna. The author and ing. Antonio Morandi (tutor) are the inventors. The objective of the thesis is therefore to propose a type of SFCL which may have the potential to be a viable economic solution as well as technique. The innovative concept of DC Resistive SFCL device, in fact, provides a DC operating conditions for the used superconducting (SC). It allows the use of cryogen-free solutions for cooling system and the exploitation of cheap SC materials (MgB2), both of reality are already commercially existing and indeed precluded by the types of SFCL which provides an AC operating conditions for the used SC material.

Theoretical and Experimental Study of the Magnetic Separation of Pollutants from Wastewater

Giacomo Mariani - Ciclo XXI - 2009

Abstract - Obiettivo della tesi è fornire indicazioni relativamente all’influenza dei parametri progettuali sull’efficienza di separazione in un filtro HGMS (High Gradient Magnetic Separator). Il processo di separazione  magnetica è generalmente basato sulla forza che agisce su di una particella magnetizzabile quando è immersa in un campo magnetico non uniforme. Tale forza è proporzionale sia al volume ed alla suscettività magnetica della particella, sia all’intensità del campo di induzione magnetica ed al suo gradiente. L’elemento filtrante è costituito da filamenti ferromagnetici (lana di ferro) a sezione tendenzialmente triangolare che, saturando in presenza del campo magnetico esterno, generano un elevato gradiente di campo nelle loro immediate prossimità. Il modello di calcolo sviluppato è in grado di simulare il moto delle particelle ed analizzare la loro interazione con i filamenti dell’elemento filtrante e con il campo magnetico. Data la differenza di ordini di grandezza tra le dimensioni micrometriche dei filamenti della lana che forma l’elemento filtrante, la cui geometria è incognita ed irregolare, e quelle macroscopiche del dispositivo, si è impostato uno studio statistico dell’interazione particella - filamenti su un volume di controllo al centro del filtro (cella), con condizioni di periodicità. Le soluzioni del problema magnetostatico e della fluidodinamica nella cella sono ottenute con un approccio integrale. L’analisi di una porzione piccola, ma statisticamente rappresentativa, del filtro elimina la necessità di modellare l’intero dispositivo su scala micrometrica, con oneri computazionali inaccettabili, e costituisce la base per l’analisi dell’efficienza del processo di filtrazione magnetica. Il modello proposto è stato validato attraverso un dispositivo di laboratorio.

Antonio Morandi - Ciclo XVI - 2004

Abstract - Superconductivity is becoming a key technology in many fields of engineering. The use of superconducting materials brings remarkable improvements to the performance of existing electrical devices and allows the conception of new ones which are able to carry out functions which cannot not be achieved by using conventional materials. Superconductors greatly reduce the consumption of electrical power with respect to normal conductors. A DC current can flow in a superconducting wire without generating losses at all. Moreover, the magnetic properties of these materials are very peculiar. Superconducting materials can be used in large scale applications, i.e. in the field of large currents and power, as well as in signal processing, digital circuits, ultra sensitive magnetometers, detectors and microwave devices, which are referred to as small scale applications. Concerning the large scale applications of superconductivity, very intense magnetic fields needed for particle accelerators, nuclear fusion or even material processing can only be conveniently produced by means of superconducting magnets. Magnetic energy which is permanently stored in superconducting coils with a DC current flowing through (SMES), can be exchanged with an external system by means of static electronic converters; nowadays small scale SMES (micro-SMES) are used for the local and short term control of power quality for critical loads. Bulk superconductors are used for superconducting levitation and flywheels and also for trapping high magnetic fields in cryo-permanent magnets. Superconducting fault current limiters (SFCL) are regarded as crucial components for modern electric power systems as they offer ideal performances: negligible impedance in normal conditions and passive (i.e. reliable) switch to high impedance state in case of fault. Moreover, combined used of new emerging superconducting materials (MgB2) and technology of hydrogen for transmitting and storing energy produced by renewable sources, is foreseen as a possible future application of superconductivity. In all these applications the materials used are type II superconductors. As the number of applications of superconductors increases, the demand for robust and reliable modeling, both on the microscopic and the macroscopic scale, increases as well. Microscopic models aim to explain the fundamental physical properties; macroscopic models use simplified description of these properties and are application oriented. This thesis is a contribution to the three dimensional macroscopic modeling of type II superconductors for large scale applications.

Thesis_PhD_Morandi_Introduction.pdf  Thesis_PhD_Morandi_Chapter1.pdf  

Thesis_PhD_Morandi_Chapter2.pdf     Thesis_PhD_Morandi_Chapter3.pdf 

Thesis_PhD_Morandi_Chapter4.pdf  Thesis_PhD_Morandi_Conclusion.pdf

Thesis_PhD_Morandi_References.pdf

Current distribution in multistrand superconducting cables

Breschi Marco - Ciclo XIII - 2001

Abstract - The scope of this work is the analysis of current distribution among the strands in multistrand superconducting cables through the development of an appropriate electromagnetic model. The model must be suitable to be applied to all the main configurations of multistrand cables, and to be able to describe current diffusion process in real long cables used in magnets.

Thesis_PhD_Breschi_part1.pdf    Thesis_PhD_Breschi_part2.pdf

Abstract -  La tesi documenta una attività di ricerca sia sperimentale che teorica sulle perdite in regime di corrente alternata nei materiali superconduttori aventi una elevata temperatura di transizione. L’attività di ricerca è stata svolta, per quanto riguarda la parte sperimentale, presso la Divisione superconduttività del CISE (adesso ENEL SpA Struttura Ricerca) a Milano, nell’ambito di una convenzione tra il Dipartimento di Ingegneria Elettrica e tale Struttura. L'obiettivo principale dell'attività era la formulazione e validazione sperimentale di un modello per il calcolo delle perdite negli avvolgimenti superconduttivi realizzati con nastri di BSCCO durante le fasi di carica e scarica e in un regime comunque variabile, quale quello che si presenta nei dispositivi per l’accumulo dell’energia sotto forma magnetica (SMES), aventi applicazioni di particolare interesse nel settore della «power quality».