Emil Cazacu

Correction of Measured Magnetization Curves Using Finite Element Method

Magnetic measurement accuracy for open samples is analyzed using numerical simulations. The finite element method is used for the complete numerical correction of experimental data which are measured with a vibrating sample magnetometer. The magnetization curves are recalculated taking into account the demagnetizing field, the shape of the open magnetic circuit, and the field probe position.

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.

An improved method for the inrush current evaluation in single phase power transformers

The paper presents an automatic procedure for quantitative evaluation of energizing inrush current of a specific range of single phase power transformers: 1.2-25 kVA. Starting from transformer main rated data and core magnetic H-B characterization, the first peak value of inrush current is accurately estimated. Additionally, the harmonic content of its waveform is also investigated offering valuable indicators of this transient phenomenon. The predetermination of the main inrush current characteristics becomes very useful in avoiding its countless undesirable effects on both the transformer and the installation where the device operates. The proposed method offers a fast and flexible solution of the energizing inrush current problem for the main general purpose single phase transformers.

Derating the three-phase power distribution transformers under nonsinusoidal operating conditions: A case study

The paper quantitatively investigates the problem of derating the in-service distribution power transformers that supply heavy nonlinear balanced loads. The adopted computation method basis on the international standards and only requires the basic power quality parameters measured at the secondary winding of the transformer and its certified test report. Hence, by computing the major transformer harmonic factors, an on-site derating report is generated, which provides the additional power losses generated by the harmonic currents and the corresponding transformer maximum permissible current (reduction in apparent power rating). The paper also critically analyzes other solutions that could avoid or minimize the harmonics detrimental effects on the transformers steady-state operation. The study is carried out on a 1600 kVA oil-filled type distribution transformer that serves both linear and nonlinear industrial loads.

A simple and low-cost method for miniature power transformers' hysteresis losses evaluation

Our study proposes a method that evaluates the core hysteresis losses for a large variety of miniature power transformers or inductors with minimal resources and computation effort. After the visualization of hysteresis loop, using a basic integrator circuit, the collected data are analyzed using a numerical code developed with a general purpose computation software. Thus, one can better appreciate this important efficiency parameter of such low-power supply devices commonly used in electronic applications.

An efficient method for investigating the ferroresonance of single-phase iron core devices

The paper presents a fast and efficient method for determining the solutions of the ferroresonant circuits generated at the switching of different single-phase low-voltage iron-core devices. These are widely encountered in modern electric installations as no-loaded power transformers, magnetic choke or shunt reactors. The here suggested procedure basically relies on the solutions of the nonlinear and non-autonomous differential equations systems that model the commutation (dynamic) process. Starting from the devices manufacturer data, the energy supply installation specification and adopting an adequate description of their magnetic characteristics, the time evolution of the major electrical parameters is numerically predicted and critically analyzed. The power spectrum, phase portraits and Poincaré map of some relevant electrical quantities variation complete the analysis of the ferroresonance phenomenon. Additionally, mitigations strategies for the common undesirable power quality issues associated with the ferroresonace occurrence are proposed and discussed.

Magnetising inrush current of low-voltage iron core three phase power reactors

The paper presents the quantitative evaluation of the magnetizing inrush current initiated at the connection instant of various three phase iron core reactors to a low-voltage power network. An analytical approach is adopted, which bases on the ferromagnetic coils circuit model and its time domain transient characterization. Thus, the solutions of the corresponding nonlinear differential equation system allow extracting the main inrush current features: waveform signature, amplitude and duration. The major power quality issues generated by the three phase reactors energizing process are also investigated and additionally some inrush current mitigation techniques are suggested.

Fundamentals of Reactive Power in AC Power Systems

The fundamentals of reactive power in AC power systems are discussed in the second chapter. The chapter presents basic theory of AC circuits including two-ports linear elements, basic equations and definition of powers in AC circuits. The phasor diagrams and power measurement techniques in AC networks are also presented. The chapter also investigates the effects of reactive power as well as power factor compensation in consumers. The end part of the chapter is related to minimum active and reactive absorbed power in linear AC circuits and also non-sinusoidal conditions. All of the parts include some practical examples and case studies. The chapter is closed with a large list of bibliographic references.

Influence of harmonics' initial phases on magnetic losses in non-oriented grains FeSi sheets

The estimation of magnetic losses in a non-oriented grains FeSi sheet by a time-dependent method is used in the paper for underlining the influence of each harmonic initial phase. The initial phase of the first harmonic, usually indicated by a power analyzer to be zero, is very important for the signal shape, the losses being dependent on this parameter. The paper proves that THD and the harmonic amplitudes of the magnetic flux density are not sufficient for the magnetic losses predetermination in distorted regime, the initial phases of the harmonics being of great importance for any computation involving a truncated Fourier series.

Numerical and experimental investigations on the energizing of miniature iron core transformers

The paper analysis both numerically and experimentally the no-load miniature power transformer energizing process. The transient state characterization targets the predetermination of the main inrush current features: amplitude, duration and waveform signature. The whole quantitative investigation is carried out on a particular core-shaped devices (E+I), widely used in small power applications. The here suggested analytical computation method bases on the solution of the nonlinear differential equations that model the commutation phenomenon. Supplementary, a simple and low-cost experimental set-up platform is proposed to validate the theoretical results.