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.

The manuscript presents a model of partial discharge activity taking place in the protrusion defect inside the cable system. Through such approach COMSOL MPh provides the capacitance values obtained from the model of power cable containing defect, while conventional capacitive equivalent circuit built in MATLAB, uses these values in order to describe partial discharge activity. Having in mind that real protrusions represent non-regular shaped cavities whose analytical capacitance computation is very complex, use of COMSOL Mph facilitates capacitance computation and then provides convenient platform for the MATLAB capacitive circuit use for non-regular shaped cavities.

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.

Abstract Line surge arresters are mainly used for transmission line lightning performance improvement. Calculation of energy stresses of lines surge arrester is of extreme importance for the selection of the arrester class. Energy stresses of transmission line surge arresters due to multicomponent lightning flashes are analysed in this paper. To obtain lightning data two approaches were used: direct measurements using instrumented towers and lightning location systems. Both lightning monitoring systems are described. Data obtained from lightning monitoring systems are compared and used in simulations. Detailed modelling procedure for a transient analysis of the transmission lines is also described. Multicomponent lightning flash and 110 kV transmission line were modelled using Electromagnetic Transient Program -Restructured Version (EMTP – RV). The arrester current shapes and arrester energy duties are presented in order to clearly show influence of lightning current parameters to arrester energy duty.

For measuring lightning strokes, it is necessary to select the appropriate sensor. The nominal sensor parameters (lightning current peak and frequency range) should be selected taking into account that the lightning current peak which strikes the tower top can be up to 400 kA. In addition, sensors should be able to store all the components in one flash. This paper presents the system of testing and sensor calibration.

The paper presents the analytics of lightning data collected by monitoring system in real - time for the measurement of the direct lightning current (LAMS) and the lightning location system (LINET). The both systems and their operation mode are shortly described. A great number of collected data are analyzed, explained and compared. The data analyses showed the Lovćen mountain has the overall highest number of registered lightning strokes in the whole analyzed area.

Analysis of electric power system reliability presented in this paper, refers to complex (composite) systems. General issue of assessment of complex electric power system reliability is how to implement and solve mathematical system equivalents and their possible states, taking into account as many possible effects, impacts and conditions of their real functions. Number of possible states of the system in real conditions can be very big, so it is extremely difficult to explore all cases of assessing the reliability of such systems. In this paper, the methods of determining possible states of the system, as well as the methods of determining system deficit, are presented and analysed. For calculations of electric power system reliability, in order to carry out a complete analysis and calculation of characteristic system reliability parameters, it is necessary to determine deficit of electricity. The paper also presents the concrete results obtained using the developed mathematical model and software program developed on its basis.

Monitoring of lightning discharges has become an indispensable activity, in order to improve protection systems. To select the appropriate lightning protection systems, it is necessary to know the lightning current parameters: shape of lightning current (lightning current peak, duration of front), polarity, frequencies, number of components during the stroke. The systems for locating lightning discharges are today's modern tool for monitoring lightning discharges. To establish a better relation between the lightning current parameters, it is necessary to provide a significant number of statistical data, especially data which are obtained by measuring direct lightning current strokes. Thanks to the progress in developing measuring, information and communication technologies, today we have an opportunity for the development of new models and methods for measuring the parameters of the lightning current. This paper presents a system of links and characters that are used for the operation of the station for the direct measurement of of atmospheric discharges.

This paper introduces a new monitoring system in real-time for measurement of the direct lightning current. Its application on a broadcasting tower in Montenegro is described, and some field measurements are presented. For the selection of this monitoring location, a new approach was used, based on data provided by a Lightning Location System (LINET).