Short circuit faults are one of the most common disturbances in power systems that occur because of insulation failure due to a sudden overvoltage condition caused by lightning, switching operations, insulation contamination, etc. Medium voltage power distribution networks use different methods for grounding the neutral point. Influences of these grounding methods on the characteristics of single-phase short circuit fault are discussed in this paper on the example of substation “Bugojno”. Modeling and simulation are implemented in EMTP-RV (Electromagnetic Transient Program-Restructured Version) software. Data recorded by protection system during normal operation and three-phase short circuit fault in the substation are analyzed and used for comparison with simulation results to validate developed model of the observed part of power system. This validated model was then used to analyze the effects of neutral point grounding methods on the characteristics of single-phase short circuit fault.

Transient events, especially those related to the short circuit faults, are the main causes of power distribution lines outages. This paper is dedicated to the analysis of three-phase short circuit fault and its impact to the real 20 kV power distribution lines. One of the most important parts of Bosnia and Herzegovina's power system was monitored and analyzed. Short circuit currents and voltages were obtained by using the power distribution lines numerical protection system measurements from the moment of fault occurrence to the moment when the faulty line was switched off. Part of the power system of interest was modeled in EMTP-RV (Electromagnetic Transient Program - Restructured Version) software which is standardized software for transient analyses. Several simulations were conducted to perform fault analysis. Measured data and simulation results were compared.

Climate problems, the increasingly robust European emissions policy and falling prices of solar and wind have led to the shutdown of many thermal power plants and increased installation of renewable energy power plants. The installed capacity of wind and solar power plants in our country is not yet significant, but small hydropower plants are often considered as a good solution for the power supply to remote areas despite the problems that sometimes arise after the installation of these power plants. This paper describes a power quality problem of high voltages occurs after the installation of a small hydropower plant of 800 kVA in an area with predominantly industrial consumers. Many industries use high technology for manufacturing and require high power quality and reliability of power supply. Even modest power quality problems can have significant technical and economic effects on these consumers. Therefore, it was necessary to precisely monitor power quality to adequately address all related problem recorded during the plant performance test phase. Also, the observed problem has led to power plant outage on several occasions in a short period of time which resulted in a reduction in power generation. Techniques for mitigation the observed power quality issue are also considered in this paper. The implemented solution of the problem is verified by power quality monitoring and SCADA system measurements.

The aim of this paper is to analyze the lightning protection model of a photovoltaic power plant, which is of great importance, in order to guarantee the smooth work of the system and avoid errors and damage to the equipment. Atmospheric discharges affect the proper operation of photovoltaic sources and their installation, including sensitive equipment. Determining the need for lightning protection and assessing the success of risk analysis are the first steps to adopt appropriate lightning protection measures. The paper assesses surges due to lightning strikes and the required protection measures based on the results of risk analysis and protection costs. Also, external and internal lightning protection systems, selection of equipment characteristics, and earthing systems are discussed. The lightning protection model was analyzed using the SCIT (Shield) software, and the risk analysis was processed in the Sparkta software.

The steady increase in electricity demand has led to more installed generation capacity in wind farms, which, due to the stochastic nature of their production, may have characteristic and non-standard responses to some occurrences in the grid. The power output from the wind farm changes constantly, depending on the wind speed, so the impact of the network on the wind farm will inversely vary depending on the moment of the short circuit and the wind farm operating mode, since the values of currents and voltages in these fault systems depend on the power flows. Although wind power is known to contribute to the short circuit current / power at the point of its connection, this paper focuses on the response of the wind farm to short circuits in the network and the impact of these phenomena on the grid-wind relation. The aim of the paper is to determine the worst type of short circuit for wind turbine operation in the distribution system.

Depending on actual load profiles connected to grid containing a PV system, losses and power quality disturbances vary during the day due to the power unbalance in the connection node. With the increase in size of PV power plants this problem becomes more important. Different load profiles have different correlation with the daily power generation from the PV system. Therefore, economic and technical impact of different daily load curves on grid connected PV systems should be considered. This paper gives an analysis of aforementioned problems. After the description and comparison between different load profiles and daily load curves, a simulation model is described and different situations of occurring problems are tested and analyzed. Simulations were carried out with real load profiles. Finally, this paper gives an overview of problems and gives few proposes for their solution.

The advancement of LED technology in the last 10 years has completely put other light technologies into the fore-ground. LED has almost entered all spheres of life. When it comes to products that use LED technology, one of the most important issues is lifetime. This paper contains a detailed overview of the research in the field of lifetime testing of LED components and products which have an LED element. Mathematical models for accelerated LED ageing tests are given in this paper. Ageing tests with constant temperature and constant current were analyzed. In this paper a simplified model of the lifetime of LEDs in products is proposed. The results of testing several samples for a product with an LED based technology are given.

Analysis of harmonic propagation in transmission network represents an important factor in exploitation of the power system. These analyses are conducted in time and frequency domains. In a case of a robust power system, analyses are usually conducted in frequency domain and usually carried out in the Three-phase system (TPS), so that all effects of interest in the frequency spectrum are taken in consideration. Transmission line (TL) modeling in TPS and frequency domain, with the usage of Kron Matrix Reduction (KMR), can be found in this paper. The model is created for frequency values between 0.05 (Hz) and 10 (kHz), which represent the frequency spectrum of interest. Mathematical procedure for implementing the KMR can also be found in this paper. Usage of KMR for voltage profile analysis on a TL is shown on a plain example. The proposed model is compared with tested mathematical models from EMTP-RV.

Phasor estimation is an essential task in power system since the voltage angle and voltage RMS determine the available active power and its flow. This paper proposes fast and simple algorithm for harmonic phasor estimation in a three-phase system. Harmonics are considered the most serious power quality (PQ) problem in the emerging scenario with a growing proportion of power electronic based devices in the power system. The algorithm is based on well-known mathematical transform and recommendations given in relevant IEC and IEEE standards. The presented algorithm can be used to generate input data for Harmonic State Estimation.

The paper describes a photovoltaic system (PVS) composed of a group of photovoltaic (PV) panels and presents the initial evaluation of power quality (PQ) in the low-power microgrid connected to these PV panels. This PVS is called solar tree and it is built as a research platform at our faculty to conduct teaching and research on renewable energy sources. The solar tree can operate in two modes: on-grid and off-grid (autonomous operation). An off-grid mode was analysed and experiments were carried out in order to determine the maximum power that can be delivered to the load connected to this autonomous photovoltaic system (APVS). Also, the various consumer's responses to a sudden load changes in this APVS were analysed. The experiments were carried out by using modern power quality monitoring devices and PQ of this single-phase APVS with energy storage is examined in terms of compatibility with the relevant international standards.