This paper deals with the analysis of a 1-D magneto-dynamic model (MDM) of soft magnetic steel sheets (SMSSs) under arbitrary excitation conditions. In the presented analysis, the MDM is coupled with the static hysteresis model proposed by Tellinen. The coupled model of SMSSs is evaluated using measured excitation voltages as well as measured excitation currents directly as the model input variables, where both excitation cases are compared and evaluated versus measurements. The calculated results show a good agreement with the measurements. Based on the presented analysis properties, advantages, and flexibility of the MDM model as well as the limitations of the presented coupled model are pointed out, where guidelines for an improved coupling are also given.
COBISS.SI-ID: 18413334
This paper deals with the evaluation of various dynamic models for modeling of three-limb core power transformers. Due to the specific construction of such transformers, the magnetic fluxes in individual core limbs are interdependent. For applications, such as simulations and testing protection devices and algorithms, adequate prediction of inrush currents waveforms is crucial and indispensable. In this paper, various different dynamic models are tested where the limitations of standard models that are available in commercial program packages are pointed out. Two groups of models are evaluated separately: standard three-phase models composed of three-single phase transformer models and advanced three-phase models, where the topology of the magnetic circuit is considered. Furthermore, in both transformer model groups, three different material descriptions are evaluated, where linear, non-linear, and hysteretic material properties are considered. The comparison between measured and calculated waveforms of inrush currents is used to evaluate individual models. The comparison of evaluated models shows that standard dynamic models cannot provide proper waveforms of inrush currents regardless of which magnetically non-linear behavior of the iron core is considered. For adequate modeling of discussed transformers the consideration of the topology of the magnetic circuit is crucial.
COBISS.SI-ID: 18413846
Magnetic properties can vary significantly inside soft magnetic steel sheets (SMSSs), both due to mechanical stresses and structural changes originating from different manufacturing processes. The integral consideration, i.e. averaging these effects over the SMSS, leads to a strong simplification of the underlying mechanisms. Such simplification is often inadequate when considering the influence of the varying magnetic properties on the hysteresis loop shape and its dynamic behavior. This paper presents a new approach to model irregular hysteresis loops of non-oriented SMSSs using the flux tube approach, where the SMSS is divided into several flux tubes having different magnetic properties. This enables to model non-homogeneous distributions of the magnetic flux and irregular hysteresis loops subject to varying magnetic properties.
COBISS.SI-ID: 18422038
This work compares the energy production of different types and orientations of photovoltaic systems under the equal outdoor conditions over the 4-yr period in Slovenia. The following photovoltaic systems were analyzed: the fixed photovoltaic system oriented to the south tilted at 30 deg, the fixed photovoltaic system oriented to the east tilted at 30 deg, the single axis photovoltaic tracking system tilted at 30 deg, and the fixed photovoltaic system oriented to the south tilted at 15 deg. The same monocrystalline silicon (mc-Si) solar modules are used in the compared systems. The systems are installed in a radius of 20 m. This provides the same meteorological parameters during the measured period. The impact of orientation and inclination on energy production are evaluated. The analysis of the data obtained shows that the energy production of the photovoltaic systems depends on the solar irradiation, temperature of solar modules, efficiency of solar modules, and efficiency of dc-ac inverters. Based on the analysis and measurements for different photovoltaic systems, the optimal orientation and inclination are presented. The results for Slovenia show that the optimal orientation and inclination facing south tilted at 45 deg.
COBISS.SI-ID: 81541633
This paper deals with the impact of a gas discharge arrester%s electrodes% shapes on its performance. When after the extinguishing of the electric arc between the electrodes of the gas discharge arrester and the electric field strength between the electrodes exceeds the critical value, re-ignition occurs. Computation of electric field strength between the electrodes of the existing gas discharge arresters using the Finite Elements Method (FEM) shows that electric field strength reaches its highest values at the edges of the electrodes. It therefore makes sense to reduce the electric field strength E at the edges of the electrodes by changing the electrodesʼ shapes. This also reduces the risk of re-igniting the electric arc between the electrodes and improves the arresterʼs ability to self-extinguish. The electrodes can be geometrically shaped in such a way that ensures much uniform distribution of the electric field strength E as possible. This paper describes the model of a gas discharge arrester and the use of a differential evolution optimization algorithm for computation of the more adequate shapes of electrodes. Thus uniform distribution of electric field strength is ensured between the gas discharge arrester electrodes.
COBISS.SI-ID: 18180630