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In recent years, the emerging fear of an energy crisis in central Europe has caused an increased demand for distributed energy resources (DER), especially small photovoltaic rooftop installations up to 10 kWp. From a technical point of view, distributed PV in low-voltage networks is associated with the risk of power quality violation, overvoltage, voltage unbalance, harmonics, and violation of the thermal limit of phase conductors, neutral conductors, and transformers. Distribution system operators (DSO) are currently in a position to determine the amount of installed PV power for which reliable and safe network operation is ensured, also known as the photovoltaic hosting capacity (PVHC). The presented study describes a stochastic methodology for PVHC estimation and uses it to analyze a typical LV rural network in the Slovak Republic. Detailed and precise calculations are performed on the 4-wire LV model with accurate results. In this study, we, thus, profoundly analyze the problems with voltage violation, unbalanced voltage energy losses, and the thermal loading effect of increasing PV penetration. The results show that overvoltage events are the main factor limiting the PVHC in LV systems. This conclusion is in accordance with the experience of the DSO in the Slovak and Czech Republic. Subsequently, the study focuses on the possibilities of increasing PVHC using those tools typically available for DSO, such as changes in PV inverter power factors and no-load tap changer transformers. The results are compared with those derived from similar analyses, but we ultimately find that the proposed solution is problematic due to the high variability of approaches and boundary conditions. In conclusion, the paper discusses the issue of the acceptable risk of overvoltage violation in the context of PVHC and lowering losses in LV networks.

This paper studies the voltage stability of the Slovak Republic’s power system (PS) based on an assessment of the PV curves. The PV curve is a tool for assessing voltage stability, and based on its shape, it is possible to determine weak and strong voltage nodes with the possibility of voltage stability reserve quantification. We present an analysis of the influence of transformers with an automatic voltage regulator (AVR) on the shape of the PV curves and on the magnitude of voltage in the PS. In general, the 400 kV/110 kV transformers equipped with AVRs are critical assets for the PS as they address voltage control in the DS. However, in the case of voltage problems in the TS, the AVR function may worsen the voltage situation across the entire PS. Therefore, we closely analyze the negative effects of the AVR on the PS operation. This impact is clearly proved, and recommendations are given for the transmission system operator (TSO) in order to maintain voltage stability. In addition, the PV curves of the pilot nodes are analyzed very accurately, thereby confirming their importance in the TS in terms of a sufficient reserve of reactive power. The study was conducted in cooperation with the TSO, Slovenská elektrizačná prenosová sústava, a.s.

The problem of electromagnetic fields produced by overhead power lines is still a widely discussed topic. These concerns itself are coming not only from the power line designers, but also from general public sector. Therefore, the topic can be separated into two different areas of interest: health concerns and technical problems. Conducted discussion and research regarding electromagnetic field’s health risks to general public led to creation of legislative time restrictions and absolute value limits for low-frequency electromagnetic fields. On the other hand, technical side of problem is mostly connected with electromagnetic induction in connection with surrounding objects around power lines. Still, precise calculations are needed for both of these areas of interest. The aim of this article is to carry an analysis comparing various electromagnetic fields emitted from basic types of power lines in 2D space. Comparison is made for the worst-case scenarios and for different sets of boundary conditions. The paper also shows the marginal difference of EMF generally emitted by EHV and HV systems. To achieve the most precise results, an integral–differential EMF calculation methodology is introduced and implemented into software interface. Final results are applicable in overhead lines design and planning process and are also suitable for future research of overhead power lines.

This article presents a superposition method in combination with the Coulomb’s law and the Method of image charges for calculation of the electric field distribution generated by high voltage overhead power lines above a flat surface in every dimension. Such calculations are required to ensure the operational safety of people exposed to the action of external electric field as well as to reduce the cost of people protection. The method provides options for calculation of the field around the wire of a general shape. This substantial improvement of the method could be applied to eliminate the usual error in the calculation created using approximation of catenary shape conductors by infinite straight conductors. The method has been extensively tested on a set of shapes with known analytical solutions. It has been shown that the numerical solution converges uniformly to the analytical solution and the accuracy depends only on the number of finite elements.

This paper analyses the impact of asymmetry of over-head power line parameters on short circuit currents when three-phase fault and phase-to-ground fault occur. The calculation results with consideration of an asymmetry of the power line parameters are confronted with the calculation in accordance with the Slovak standard STN EN 60909 which does not consider asymmetry of equipment parameters in the power system. The calculation of short-circuit conditions was carried out for two types of 400 kV power line towers on which is a considerably different arrangement of phase conductors.

The paper presents simulation results of transients during the power system restoration. The Defence plan and Restoration plan development is a part of transmission system operator’s responsibilities and requires thorough calculations, simulations and publication of instructions. The plans focus on extensive failures that have a heavy impact on the system operation and could lead to a blackout. The Restoration plan of power system has to contain procedures for start-up without outside help. TSO regularly checks some part of the Restoration plan.

This paper is aimed on the calculation of the electrical parameters of the overhead transmission lines. Standard trans- position and untransposed calculations are presented, also with results on the existing power line on 110 kV voltage level and known measured values of the electrical parameters. These measured parameters are used as the reference values. A presumption is made, that through more complex calculation one can achieve better results. The real results achieved are presented and compared with an ideal presumption

This paper deals with the 22 kV distribution grid with higher penetration of distributed generation and the possibility of loss of this generation in case of fault. In the first part the reasons of distributed generation growth are shortly explained. For simulation of faults of different parts of distribution grid the model of such distribution grid with substantial amount of distributed generation was created. The second part contents the simulations of two-phase faults in two different power lines of model in order to evaluate and analyze the impact of these faults on distributed generation. The second part focuses on the impacts of short circuit occurred in different feeders of distribution grid on individual power sources and on the feeder with higher penetration of distributed generation.