Yiliang Lv

Design and Experiments of a High Field Electromagnetic Forming System

The concept of capacity coefficient is introduced to evaluate the processing capacity of electromagnetic forming (EMF). An EMF system design method, including capacity coefficient design, inductance design and strength design, is developed by a finite element method. The geometry and size of the driving coil are optimized by the capacity coefficient design. The inductance design is aimed at obtaining a reasonable pulse width of EMF. Finally, the strength design of the driving coil is presented with respect to the reinforcement. With this design method, a high strength driving coil is designed and wound. The height, inner radius, and outer radius of the driving coil are 25 mm, 5 mm, and 50 mm respectively. The number of turns is 40, resulting in reasonable pulse width of 380 . Experiments with different driving coils and pulse width were carried out. The results show that the processing capability of EMF is improved due to the high strength driving coil.

Development of a High-Stability Flat-Top Pulsed Magnetic Field Facility

A high stability flat-top pulsed magnetic field has both high field strength and high field stability simultaneously, which can be used for the high precision scientific experiments. In this paper, we present such a high stability flat-top pulsed magnetic field facility developed in the Wuhan National High Magnetic Field Center. A passive bypass circuit is developed to regulate current up to tens of thousands amperes, as well as a 25 T/200 ms flat-top pulsed magnetic field with a ripple of 250 ppm (0.025%). The main circuit scheme of the facility as well as the preliminary experimental results will be presented in this paper.

Magnet Development Program at the WHMFC

In 2008, the Wuhan National High Magnetic Field Center (WHMFC) was set up at the Huazhong University of Science and Technology, Wuhan, China. The objective of the pulsed magnet program is to produce pulsed magnetic fields in the range of 50 to 80 T. The following pulsed magnets were initially conceived: 1) 50-80 T monolithic magnets energized by one or a few modules of the 1 MJ capacitor bank, 2) a 50 T/100 ms flattop long pulse magnet energized by the 100 MJ/100 MVA pulse generator, 3) a 60 T/200 ms long pulse magnet energized by the 12 MJ capacitor bank, and 4) an 80 T dual coil system energized by two capacitor bank modules. In addition, a 16 T PPMS and a 7 T SQUID-VSM systems were acquired. Currently, work on a 40 T long pulse magnet energized by lead acid battery units and the acquisition of a 400 MHz NMR spectrometer are in progress.

Short and Long Pulse High Magnetic Field Facility at the Wuhan National High Magnetic Field Center

The pulsed high magnetic field facility funded by the Chinese National Development and Reformation Committee has been developed at the Wuhan National High Magnetic Field Center (WHMFC). Magnets of short pulse, long pulse and the combination of both with bore sizes from 12 to 34 mm have been developed and are operational for electric transport, magnetization, magneto-optics and electron spin resonance at temperatures in the range from 100 mK to 350 K. The power supplies for these magnets consist of a capacitor bank with 12 modules of 1 MJ/25 kV each and 2 modules of 0.8 MJ/25 kV each, a 100 MVA/100 MJ flywheel pulse generator and a 771 V/180 kAh battery bank. A dual-coil magnet driven by the capacitor banks has successfully generated 86.3 T field with a total pulse duration over 350 ms in a 12-mm bore. A dual-coil long pulse magnet wound from soft copper wire energized by the flywheel generator produces 50 T peak field with a 100 ms flat-top and a total 1.1 s pulse duration in a 22 mm bore. A battery bank driven long pulse magnet composed by the series connection of two nested coils generates 32 T peak field with the pulse duration of 1.5 s in a 21-mm bore.

The Development of High Performance Pulsed Magnets of the Prototype Facility of WHMFC

Coils for pulsed magnets in the range of 50-75 T are developed with optimized combinations of conductors and reinforcement for the prototype laboratory of the Wuhan High Magnetic Field Center (WHMFC). The basic design tool is a Pulsed Magnet Design Software package (PMDS) for calculating the capacitor discharge, conductor heating, mechanical stresses and the residual stress, including plastic deformation and winding tension. A 1 MJ capacitor bank is equipped with a thyristor switch, a mechanical switch, polarity reversal switches, a current limiting inductor and a diode crowbar. The design and the test results of the magnets, of the protection inductance and of the capacitor bank are presented and discussed in this paper.

Design and Experimental Validation of a Pulsed Electromagnetic Sheet Shearing System

A pulsed electromagnetic shearing system consisting of a pulsed magnet driven by a capacitor bank and a conductive plate as a driver has been proposed, designed, and developed for thick plate cutting. The interaction of the pulsed magnetic field with the eddy current induced on the copper driver produces a huge Lorentz force that pushes a blade to cut off the steel sheet of heavy thickness. To validate the effectiveness of the system, magnetic force acting on the driver plate in the shearing process was analyzed and a series of experiments were carried out. Results show that the maximum of generated electromagnetic force reaches about 100 tons in the simulations and a steel plate with a thickness of 10 mm can be effectively cut without any burrs and slivers in the experiments.

Post-assembly magnetization of a 100 kW high speed permanent magnet rotor

A post-assembly magnetizing fixture has been designed and successfully used to magnetize the rotor of a 100 kW high speed permanent magnet synchronous motor. The rotor is a solid cylinder with outer diameter of 80 mm and total length of 515 mm. The permanent magnet material is samarium-cobalt (Sm2Co17) with saturation magnetizing field of 6 T. The mechanical stability of the magnetizing fixture has been studied as well as the general design methodology. The magnetizing coil is subdivided in order to reduce the electromagnetic force, and the coils are separately reinforced in different ways. The electromagnetic and structural optimization is performed by finite element analysis and verified by experiments.

Fabrication and Test of a 40 T Long-Pulse Magnet Driven by Battery Bank

A 40 T long-pulse magnet has been constructed and tested to 32 T with total pulse width of 1.5 s at the Wuhan National High Magnetic Field Center (WHMFC). The magnet is energized by a battery bank power source consisting of 900 12 V/200 Ah lead-acid battery cells. The magnet consists of a polyhelix inner coil and an outer coil wound with copper foil. We made some improvements by adding axial slots on the helices due to the eddy current electromagnetic force, and each layer of helices is reinforced by Zylon-epoxy composite. The copper foil coil is insulated with polyimide film extending over the sides of the foil. The copper bar electrode is silver brazed on the ends of copper foil and has been proved to be quite feasible. In this paper, the calculated results of the electromagnetic force caused by eddy current will be presented. The magnet manufacture techniques will be described and the magnet test results will be listed and analyzed.

Finite Element Analysis for Stress and Magnetic Field of a 40 kA Protection Inductor

The protection inductor serves for limiting the peak current in order to protect the thyristor switch of the pulsed magnetic field facility in case of a short circuit. Because of the high current and strong magnetic field, the Lorentz force in the protection inductor is large. This paper describes the calculation of the inductance and the optimization of the stresses in the protection inductor. A finite element analysis with the ANSYS software is used to calculate the magnetic field and stresses in the protection inductor. A three-dimensional static finite element analysis model of the inductor has been built for calculating the stresses in the copper coils and stainless steel rings as well as the static inductance. Furthermore, a harmonic finite element analysis model has been built to analyse effects such as the influence of eddy currents in the copper wires and induced current in the stainless steel rings on stress and inductance. Eddy currents cause an uneven distribution of stresses; induced current can decrease the stresses in the copper coils but increase those in the stainless steel rings. Both effects reduce the inductance. The typical maximum stresses in our design are 70 MPa in the copper coils and 210 MPa in the stainless steel rings; these are both below the yield strength of these materials. The inductance is 1.05 mH at the frequency of 50 Hz. The protection inductor has been manufactured according to the design and the performance testing has been successfully completed.

25 kV/40 kA Protection Inductor for Capacitor Bank of the Wuhan Pulsed High Magnetic Field Facility

A 25 kV/40 kA protection inductor with low stray field was designed and the first prototype was fabricated. The protection inductor protected the thyristor switch in the capacitor bank, limit the current at 40 kA in case of a short circuit. It was designed as a toroidal system consisting of 12 coils evenly distributed in the perimeter of a circle. The inductance could be changed easily by adjusting the number of coils. The structure of coils was optimized to withstand the great electromagnetic force produced by the 40 kA current. The coils were wound by a 4 45 mm copper strip standing on edge. Each coil was externally reinforced by a stainless steel ring tightly enclosing the coil. The first prototype was fabricated. Its inductance and magnetic field were tested. The prototype has been mounted in the 1 MJ module and is now in operation. In this paper, the structure design, fabrication and testing of a new protection inductor are presented. The testing results are discussed. Tested inductance was 1.05 mH and direct resistance was 16 . The first prototype was proved to be successful and 13 more protection inductors will be made after some improvements.