The currently high energy efficiency demands and control requirements impose an extensive usage of power electronic devices and circuits in both domestic and industrial applications. These intrinsic nonlinear loads generate prominent level distortion of the electric current waveforms, which lead to additional losses and thermal stress within the power supply distribution system. Thus, due to the supplementary harmonic losses, the power transformer, experience an increase of its hot-spot temperature that may cause the machine insulation failure and ultimately the transformer lifetime expectancy reduction. In order to overcome these undesirable consequences, the reduction of the apparent power rating of the transformer (derating) is commonly adopted. This paper quantitatively investigates the nonsinusoidal steady state of the transformer by evaluating the losses distribution within the machine, its hot-spot temperature rise and the corresponding transformer loss of life. The computation procedure is exemplified on a 250 kVA liquid filled three-phase power distribution transformer that supplies both linear and nonlinear industrial loads.

Soft magnetic materials are at the core of electromagnetic devices. Planar transformers are essential pieces of equipment working at high frequency. Usually, their magnetic core is made of various types of ferrites or iron-based alloys. An upcoming alternative might be the replacement the ferrites with FINEMET-type alloys, of nominal composition of Fe_73.5Si_13.5B₉Cu₃Nb₁ (at. %). FINEMET is a nanocrystalline material exhibiting excellent magnetic properties at high frequencies, a soft magnetic alloy that has been in the focus of interest in the last years thanks to its high saturation magnetization, high permeability, and low core loss. Here, we present and discuss the measured and modelled properties of this material. Owing to the limits of the experimental set-up, an estimate of the total magnetic losses within this magnetic material is made, for values greater than the measurement limits of the magnetic flux density and frequency, with reasonable results for potential applications of FINMET-type alloys and thin films in high frequency planar transformer cores.

Hysteresis phenomenon is currently met in magnetic materials characterization. From many years this hysteresis had been modeled with different approaches. The aim of this paper is to present a comparison between few sigmoid functions used more often in other research areas. The functions were updated according to the requirements of the magnetic hysteresis and there comparisons for three different magnetic materials were performed. In the last part, hysteresis losses are evaluated using relative errors between experimental loop area and modeled loop area.

The actual energy efficiency requirements generated a large usage of the power electronic converters for driving asynchronous motors in numerous industrial facilities. The associated power quality issues of these adjustable speed drives, especially harmonic currents, adversely affect the power distribution transformers by increasing their losses and decreasing their life time expectancy. Accordingly, the intentional reduction of the transformers apparent power rating (derating) becomes mandatory in order to preserve their rated losses and the equivalent admissible thermal stress. The paper investigates both theoretically and experimentally the transformers harmonic behavior by evaluating the additional losses and the corresponding maximal permissible supplied power. The transformer derating factors, according to different international standards, are also computed and critically analyzed in terms of their suitable usage. The study is illustrated on 160 kVA oil-type three-phase power distribution transformer that mainly supplies induction pump motors controlled by frequency converters. The transformer operating parameters are acquired at its low-voltage secondary windings by a portable power quality analyzer.

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.

For different sorts of electrical sheets, the magnetic losses separation using Bertotti method was performed. Using a fitting procedure, the Steinmetz coefficients were approximated. For each parameter, an analytical expression regarding the measured values was determinated. Finally, a comparison between the measured data and the predicted losses was made. The modeled losses are quite close to the experimental one and the modeled might be validated on other sort of sheets.