Pier Luigi Ribani

Design of a DC Resistive SFCL for Application to the 20 kV Distribution System

A DC-operating resistive-type superconducting fault current limiter for AC applications (in short a DC Resistive SFCL) is based on the synergistic use of the resistive and the rectifier fault current limiter concepts, and allows the superconductor to operate in nearly DC current conditions. This regime of operation drastically reduces the AC losses and therefore opens up completely new perspectives with regard to the materials, the architecture of the cable, the layout of the windings and the cryogenics. In this paper the design of a DC resistive SFCL for application to the 20 kV distribution system is presented. A bus tie position with nominal rate of 25 MVA is considered as case study. The resistance and the inductance of the superconducting winding are arrived at by means of the parametric analysis of voltage transients, harmonic distortion and peak fault current. The design of the windings of the real scale device is carried based on a optimized MgB2 cable. The detailed design of the bridge rectifier is carried out and the power losses due to diodes are evaluated.

Modeling of the electro-mechanical behavior of ITER Nb3Sn cable in conduit conductors

The coupling of electrical and mechanical modeling of superconducting cable in conduit conductors (CICCs) can be useful for the understanding of the complex phenomena occurring in cables based on strain-sensitive materials like Nb3Sn. The MULTIFIL model is a detailed mechanical model aimed at computing the strain distribution at the strand level in multistrand superconducting cables. MULTIFIL is a finite element code dealing with the contacts between beam assemblies that includes plasticity and it allows modeling both transverse and longitudinal loads applied to the cable. The electromagnetic part of the THELMA code is based on a distributed parameter electrical circuit model of CICCs and is aimed at computing the current distribution and electrical losses at an arbitrary cabling stage. In this work, the maps of strain have been computed with MULTIFIL for a petal of a relevant conductor for the central solenoid of the ITER magnet system. These strain maps were computed in three main cases, namely applying only a thermal compressive strain due to cable contraction in cool-down, considering thermal strain plus the strain due to Lorentz force in a virgin state, and thermal strain plus Lorentz force after a given number of electromagnetic cycles. These strain maps have been implemented in the THELMA code, in order to compute the E?T curves corresponding to the different cases, such deriving important parameters to be compared with experimental results (Tcs, n value, effective strain). A methodology to account in the electrical model for the inhomogeneous strain on the strand cross section due to bending is described and the corresponding results are compared to the case of a homogeneous strain on the wire cross section. The model is able to explain the experimental difference between the physical strain that can be determined with Tc measurements and the effective strain that can be derived from the Tcs measurements.

Feasibility of Superconducting Magnetic Energy Storage on Board of Ground Vehicles With Present State-of-the-Art Superconductors

Liquid storage of gaseous fuel on board of vehicles as possible alternative to high-pressure storage is receiving an increasing attention because of the higher mileage, the lower cost of the tank, and the faster refill allowable. The research effort devoted to liquid storage is also boosting the advance of cryogenics on board of vehicles, thus opening the way to the synergic use of superconductors. In such a context, superconducting magnetic energy storage (SMES) for regenerative braking may represent a possible alternative to electrochemical batteries or to developing technologies such as supercapacitors or flywheels. In this paper, the feasibility of SMES for regenerative braking on board of hybrid vehicles with cryogenic fuel tank is investigated. Possible application scenarios are discussed. The design of the superconducting magnet based on commercially available superconducting tapes and the cooling are addressed. The performance of the power control system is also investigated by means of a MATLAB/Simulink simulation model.

Experimental Evaluation of AC Losses of a DC Restive SFCL Prototype

A DC resistive SFCL consists of an inductance and a quenching superconducting resistance embedded in diode bridge. The superconductor operates in nearly DC current conditions. This regime of operation drastically reduces the AC losses and makes it possible to implement the device by means of present state of the art superconductors. In this paper the AC losses of a laboratory scale prototype of DC resistive SFCL (a 200 V/60 A) are experimentally investigated. The prototype consists of a non inductive Bi2223 winding series connected with a conventional iron core inductor and embedded in a diode rectifier which is connected to the protected circuit. The AC losses are measured and compared with those occurring in pure AC operation at the same current.

Coupled Electromagnetic-Thermal Model and Equivalent Circuit of a Magnetic Shield Type SFCL

A numerical model of a magnetic shield type superconducting fault current limiter based on an integral formulation of the coupled electromagnetic-thermal problem is presented. A step-by-step linearization of the magnetic problem is introduced in order to solve the system. A simplified equivalent circuit is introduced and implemented inside the Electromagnetic Transient Program power system simulator. The results of the simplified and the full model are compared and the error is evaluated.

Design and Testing of a Magnetically Levitated Conveyor

In this paper, a conveyor device aimed at moving objects placed on a translating chain is studied. Losses, friction, and noise reduction are the main objectives, which are obtained by magnetically levitating the chain with the aid of a system of permanent magnets placed on the chain and on the beam. A stable vertical levitation was obtained, while the horizontal instability was managed reducing the allowed gap between the chain and the beam. A customized three-phase drive unit was also realized in order to reduce the size and the inertia of the conveyor. A prototype was built and tested in order to verify the outcomes of the design.

One- and two-dimensional models for the linear MHD generator channel design

Abstract Mathematical models for the design of the linear channel of an MHD generator, are described. By means of a quasi-one-dimensional optimizations model the main design parameters of the channel, are calculated. The local phenomena effects are analyzed through a steady state two-dimensional model. This model is based on the description both of the fluid dynamic and of the electrodynamic in the plane containing the channel axis and normal to the magnetic induction. The transients caused by variations of the loading and by faults, are studied by means of a time dependent quasi-one-dimensional model.

Electrical insulation for high temperature superconducting fault current limiters

This paper provides an overview of the electrical insulation of high temperature superconducting fault current limiter (HTS FCL) by singling out from the literature a few aspects that are critical for such insulation. The performances of some important insulating materials such as organic polymers with fillers, non-filled ethylene propylene rubber (EPR), polyimide and epoxy nano-composites are reported. The main elements of the electrical design and withstand tests of mini-model coils are described. Moreover, as practical applications of such concepts, the paper illustrates the electrical insulation design of a 13.2 kV/630 A bifilar winding type HTSFCL with YBCO coated conductor (CC) wire and of a cryogenic bushing for superconducting power applications.

Analysis of sudden quench of an ITER superconducting NbTi full-size short sample using the THELMA code

The coupled thermal–hydraulic electromagnetic model, implemented in the THELMA code, is applied to the analysis of the sudden quench in the ITER NbTi poloidal field conductor insert full-size joint sample. The computed results are compared with the measured values, showing that the major experimental features, like the premature and sudden voltage take-off, as well as the presence of precursors of the quench in the form of voltage spikes, can be qualitatively reproduced by the code. A self-consistent explanation of the phenomenon is presented, emphasising the effect of current, magnetic field and temperature non-uniformities on the cable cross section, together with the fundamental role played by coupled electromagnetic and thermal–hydraulic dynamics in the current redistribution associated with the voltage spikes.

Operational constraints on the DC induction heating of aluminum billets

Purpose – The purpose of this paper is to analyse the heating process of an aluminum billet rotating in a static magnetic field produced by optimized supercoducting coils.Design/methodology/approach – In order to meet the technical specifications of industrial heating, many processes with low speed in the given high magnetic field have been simulated. The mechanical stresses in the billet are examined by taking into account the temperature dependence of the mechanical properties.Findings – The main heating parameters, i.e. heating time, average temperature and temperature homogeneity, are evaluated for different values of angular velocity. The simulation results show that an optimal angular speed can be chosen with respect to the heating time.Research limitations/implications – The mechanical stress in the billet due to weight, centrifugal effects, applied torque and resonance is examined by taking into account the weakening of the material properties with the increase of temperature. The practical limits...