Iosif Vasile Nemoianu

Theoretical and Experimental Investigation of Multiple Horizontal Diamagnetically Stabilized Levitation With Permanent Magnets

This paper reports the study of a multiple horizontal diamagnetically stabilized levitation setup with two or more free floating permanent magnets. In a first step, the authors present the development of a fast and accurate analytical calculation method for the equilibrium point determination and stability check of the floating magnets. The proposed method uses equivalent magnetic charges for modeling the permanent magnets yielding compact analytical formulas for the flux density. Furthermore, demagnetization in open-loop of the used NdFeB magnets is analytically taken into account by determining their operating point on the BH curve. Compared to sole numerical approaches, the developed calculation method offers a significant reduction of computation time and is especially suitable when performing parameter variations. Finally, the calculation results are validated against several experimental levitation setups including one to three floating magnets.

Theoretical and experimental evaluation on a counterintuitive diamagnetically stabilized levitation setup with permanent magnets

We report a novel counterintuitive vertical levitation structure involving permanent magnets and at least one stabilizing diamagnetic piece. The setup consists of two permanent NdFeB magnets in a vertical inline configuration. A strong lifter magnet attracts a smaller magnet and compensates its weight. Stability at the equilibrium point is ensured by a diamagnetic pyrolytic graphite plate placed either above or below the levitated magnet. Compared to the classical vertical diamagnetic levitation cases, the magnetic moments of the magnets are antiparallel. Accepted tolerances during the magnetizing process lead to a visible anomaly of the levitated magnet equilibrium point position that apparently defies symmetry. First experiments and calculation results are presented. The proposed setup could find application as a highly sensitive tilt meter or in sensing magnetization angle errors.

Influence of increase mechanical cutting degradation on 50 Hz magnetic properties of non-oriented electrical steels

In this paper is point out the influence of the classical mechanical cutting on the magnetic properties of three industrial non-oriented electrical steels M400-50A, M400-65A and, M700-50A. The selected materials were magnetically characterized and analyzed at 50 Hz and at a peak magnetic polarization JP ∈ {50, 100, 250, 500, 800, 1000, 1100, 1200, 1300, 1400, 1500} mT. Based on the complex permeability concept, in which the total permeability is divided into two parts, the real and the imaginary component, the measured values are presented. All the investigated strips have a length of 300 mm and, to magnify the degradation, a decreasing width of 30, 15, 10, 7.5 and 5 mm were chosen. The magnetic characterization was performed on a laboratory single strip tester (SST) set-up, which can make standardized measurements on samples with an area of 300 mm × 30 mm. To reassemble the standard width of 30 mm, there were put together side by side 2, 3, 4 and 6 pieces.

Active and reactive power flow in distorting three-phase unbalanced circuits without neutral

A groundbreaking discovery made by Professor Andrei Ţugulea in mid 1980s led to a new approach concerning the power flow analysis in three-phase circuits. The present study is devoted to provide a further insight into the possibilities opened by this new theory, when a three phase circuit has two different unbalanced and distorting consumers powered through a balanced line. Symmetry, non-symmetry and residual (distortion) active and reactive powers are the conceptual quantities introduced by Professor Ţugulea capable to assess the nonlinearity and unbalance effects on power circulation. Correspondingly, three normalized coefficients were defined to allow a more compact representation of the phenomena: symmetry, non-symmetry and distortion power factors. Initially formulated for two balanced linear receptors and a single unbalanced distorting one, the present study considers a single balanced linear receptor and two unbalanced nonlinear (distorting) consumers. All possible cases concerning the active and reactive powers flow directions are put in evidence through different parameter circuits simulated in PSpice. Finally, interpretation of the obtained results is presented and discussed.

Thermal treatment of ferromagnetic pieces at medium frequency

The paper is a continuation of the research reported by the authors regarding the eddy-current heating analysis of a ferromagnetic piece heating equipment. The previous results were dedicated to circular conductors, whereas, in the present paper bars of any the cross-section shape are considered. The electromagnetic field depth of penetration being sufficiently small in comparison with the other geometrical dimensions of the bar, we will take into account only a zone in the vicinity of the bar surface, having a thickness of five times the depth of penetration. Along this depth, the problem is one-dimensional and a combined numerical and analytical approach will result in an extremely efficient procedure for the analysis of the electromagnetic field problem coupled with the thermal diffusion one.

Analytical calculation of the constriction resistance for a switchgear pole of particular shape

The paper provides a better evaluation of the electrical resistance in the case of a particular pole shape, common in many different power switchgears (circuit breakers, contactors, and isolators etc.), used for both low and high voltage installations use. Currently, the dimensioning, design and optimization of these devices relies mostly on empirical procedures and determinations. Our proposed analytical approach provides a more accurate relationship for the constriction resistance, method based on the solution of Laplaces equation verified by the electric field inside the poles conductive domain, in the steady-state regime formulation. Separations of variables method was used, leading to an accurate expression for poles electric resistance which takes into consideration the electric current constriction phenomenon. This precise relationship becomes particularly useful in various important design and dimensioning computations, e. g., the prospective value of short-circuit current, at a the specific level of the electric net, where these electrical apparatus are placed.

Magnetic measurements from low to high frequency on amorphous ribbon of Co 67 Fe 4 B 14.5 Si 14.5 and prediction of excess losses with the statistical loss model based on magnetic objects (OM) theory

We report an investigation and theoretical assessment of power losses prediction in toroidal samples made of Co67Fe4B14.5Si14.5 amorphous alloy. The loss behavior of this material was studied as function of frequency, within the range of 5 Hz – 5 MHz, at a given 20 mT magnetic flux density. Using the concept of loss separation for the data analysis, in the approximation of linear magnetization law and arbitrary frequency, it can be considered that excess losses can be quantitatively assessed within the theoretical framework of the statistical loss model based on magnetic object theory.

Analysis of direct current flowing inside a linear increasing conductivity half-space

The paper analyses the injection of a direct current through an above-ground circular plate earth electrode. The assumed medium in which the current flows, filling a half-space, has a nonuniform linear increasing conductivity. A parameter having the dimension of length is considered, in order to describe the in-depth linear increase of conductivity inside the half-space. Solving the steady-state electromagnetic field equations describing the phenomena, a homogenous second order partial differential equation (PDE) for the electric potential is obtained. The analytical solution of the PDE, based on the separation of variables method, allows an accurate computation of both the electric field strength and Poyntings vector in the considered area. Thus, an exact analytical relationship of the earth electrode resistance is derived, whose calculated limit gives the already reported formula of the same quantity in the constant conductivity medium case, and hence validating the obtained results.