Massimo Fabbri

Experimental and Numerical Analysis of DC Induction Heating of Aluminum Billets

We have analyzed the characteristics of dc-induction heating of aluminium billets both numerically and experimentally and developed a numerical model for the calculation of the power and temperature distributions inside the billet during the heating. We validated the model by comparison with the experimental results from a laboratory-scale prototype using permanent magnets. We studied the heating process of a real scale system by means of the model, taking into account the weakening of the mechanical properties during the heating. We provide an example of design of an industrial scale dc induction heater.

Application of a multiobjective minimization technique for reducing the torque ripple in permanent-magnet motors

The main design parameters of a permanent-magnet motor, which reduce the total torque ripple, are determined. A two-step design procedure is utilized. First the geometry of the permanent-magnet rotor is derived by a one-dimensional field analysis coupled to a multiobjective minimization technique. The objective function of the minimization is defined as a combination of the electromotive force harmonic components induced in the stator and of the harmonic components of the air-gap magnet permeance. As a second step, a two-dimensional numerical model, solved through a finite element method, is adopted to further improve the analysis of the magnetic field. This allows the optimization of the magnet arc width and the minimization of the cogging torque. The method described has been used for the design of a three-phase, six-pole, permanent-magnet synchronous motor. Experimental tests have been carried out to verify the results obtained by the design procedure.

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.

Electromagnetic and thermal analysis of the induction heating of aluminum billets rotating in DC magnetic field

Purpose – The paper aims to deal with the induction heating of metal billets rotating in a DC magnetic field.Design/methodology/approach – The induced power distributions are analysed and the main heating parameters are estimated with reference to an infinitely long Al billet 200u2009mm diameter. The paper refers to the activity developed in the frame of a National Italian Project carried out by research groups of the Universities of Bologna, Padua and Roma “La Sapienza.”Findings – The main process parameters have been evaluated for the heating up to 500°C of an Al billet 200u2009mm diameter.Practical implications – This innovative technology appears to be very promising for improving the efficiency of the through heating of high‐conductivity metals (e.g. copper, aluminum) before hot working, by using superconducting magnets.Originality/value – The paper analyses the induction heating of a infinitely long billet rotating in a uniform DC magnetic field.

A Modified Formulation of the Volume Integral Equations Method for 3-D Magnetostatics

A magnetization-based formulation of the volume integral equations method for 3-D magnetostatics is discussed. The magnetization of each element is related, via the constitutive law of the material, to the average magnetic flux density within the element rather than to the value at the center as is usually done. This assumption leads to more accurate distribution of magnetization and allows a faster convergence of the solution. Moreover, it leads to more symmetric matrix of the coefficients and reduces the numerical instability due to looping patterns of magnetization, which is inherent to integral methods. The formulation is made effective by the use of a hybrid numerical and analytical approach, which allows for the fast and accurate calculation of the coefficients. The proposed model is validated and compared with the usual model both for saturable and linear material with high susceptibility.

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.

Design and Comparison of a 1-MW/5-s HTS SMES with Toroidal and Solenoidal Geometry

The design of a high-temperature superconducting (HTS) Superconducting Magnetic Energy Storage (SMES) coil with solenoidal and toroidal geometry is carried out based on a commercially available second-generation HTS conductor. An SMES system of practical interest (1 MW/5 s) is considered. The comparison between ideal toroidal and solenoidal geometry is first discussed, and the criteria used for choosing the geometrical parameters of the coils bore are explained. The design of the real coil is then carried out, and the final amount of conductor needed is compared. A preliminary comparison of the two coils in terms of ac loss during one charge and discharge cycle is also discussed.

Numerical Analysis and Experimental Measurements of Magnetic Bearings Based on

The levitation performance of a magnetic bearing, based on 48 mm inner diameter, 3 mm thickness and 80 mm height, MgB2 tube is experimentally investigated. A numerical model is developed and validated against the experimental results in order to compare different rotor geometries and to investigate the temperature behavior of the system. Investigation of the effect of the hysteresis on practical superconducting bearings is also carried out by means of the model.

{\rm MgB}_{2}

Purpose – To investigate the feasibility of a novel scheme of high‐efficiency induction heater for nonmagnetic metal billets which use superconducting coils.Design/methodology/approach – The idea is to force the billet to rotate in a static magnetic field produced by a DC superconducting magnet. Since a static superconducting magnet has no losses, the efficiency of the system is the efficiency of the motor used. In order to evaluate the temperature distribution arising from the field profile produced by a given SC coil configuration, a numerical model, based on an equivalent electric network with temperature‐dependent parameters, is developed.Findings – A substantial independence of the shape of the temperature profile on the angular velocity and the value of the uniform magnetic field applied, is observed. A strong temperature gradient is observed in the radial direction in the proximity of the penetration front and in the axial direction at the top and bottom surface of the billet. Small temperature gra...

Hollow Cylinders

The feasibility of a 1 MW-5 s superconducting magnetic energy storage (SMES) system based on state-of-the-art high-temperature superconductor (HTS) materials is investigated in detail. Both YBCO coated conductors and MgB2 are considered. A procedure for the electromagnetic design of the coil is introduced and the final layout is arrived at and compared for the two materials. The choice of the inductance of the coil is carried out as part of the design procedure. Both low-field (3 T) and high-field (8 T) designs are considered for the YBCO. AC losses during a complete charge/discharge cycle at full power are estimated and the cooling power needed for continuous operation is derived. The power conditioning system and control algorithms needed to carry out various operations are discussed in detail. Performances of the SMES system during voltage sag compensation, load leveling and power factor correction are investigated by means of numerical simulation.