Department of Power Engineering

Klinička bolnica Osijek i Elektrotehnički fakultet Osijek Pomoću impedancijskog modela ljudskog tijela u ra du je analizirana defibrilacija srca. Proces defibrilacije simuliranje na personalnom računalu i dobiven je valni oblik strujnog impulsa koji se javlja na srcu pri defibrilaciji. Analiza je provedena za 2 različita položaja elektroda defibrilatora. Vremenska analiza impulsa defibrilatora na ostalim dijelovima tijela upućuje na postojanje znatnih struja i napona u oko lini srca, tako da prilikom rada defibrilacije moramo biti vrlo oprezni. Članak upućuje na nužnost smanje nja prijelaznog otpora između kože i elektroda defi brilatora do najniže moguće granice zbog Džulovih gubitaka koji se tu javljaju.

U članku je istražen utjecaj ograničenja prijenosnih kapaciteta spojnih dalekovoda na pouzdanost
prijenosne mreže. Istraživanje je obavljeno na stvarnom primjeru modela prijenosne mreže Slavonije i
Baranje u programskom paketu DIgSilent Power Factory. U prvom trenutku uspostavljeni su tranziti
električne energije približni stvarnim tranzitima na karakterističnu srijedu mjeseca siječnja 2012. godine.
Analizirani su pokazatelji pouzdanosti kod ovakvih tranzita pri nazivnom i smanjenom prijenosnom
kapacitetu spojnih dalekovoda. Nakon toga uspostavljeni su povećani tranziti električne energije te je
izvršena analiza promjene pokazatelja pouzdanosti u slučaju smanjenja prijenosnih kapaciteta.

By determining the losses in the power system, the aim is to determine the difference between the theoretical values and the actual losses obtained by measuring, to determine the reason for this difference, and to propose a theoretical method for selecting the calculation method that best corresponds to each type of transmission system. It is important to estimate the losses index for the expected level of loads, and thereby provide a basis for planning of system exploitation. The paper deals with the analysis of new methods used for the determination of losses in transmission network. New methods for determining losses that best suit the transmission system are presented, as well as a new method for determining losses in the transmission network, which is based on three elements. In conclusion, a comparison of individual methods tested on the real network model is shown with the aim of comparison of calculation, validation of results and evaluation of the analytical method of choice.

 Abstract—This paper presents a new islanding detection strategy for low-voltage (LV) inverter-interfaced microgrids based on adaptive neuro-fuzzy inference system (ANFIS). The proposed islanding detection method exploits the pattern recognition capability of ANFIS and its nonlinear mapping of relation between inputs. The ANFIS monitors seven inputs measured at point of common coupling (PCC), namely root-mean square (RMS) of voltage and current (RMSU and RMSI), total harmonic distortion (THD) of voltage and current (THDU and THDI), frequency (f), and also active and reactive powers (P, Q) that are experimentally obtained based on practical measurement in a real-life microgrid. The proposed method is composed of passive monitoring of the mentioned inputs and therefore, does not influence power quality (PQ); but considerably decreases non detection zones (NDZs). In order to cover as much situations as possible, minimizing false tripping and still remaining selective, type and number of samples are introduced. Here, one of the main goals is reducing NDZ by still keeping PQ in order. Based on the sampled frequency and number of samples, we find that the proposed method has less detection time and better accuracy, compared to the reported methods. S imulations performed in MATLAB/S imulink software environment and several tests performed based on different active load conditions and multiple distributed generation (DG)s, prove the effectiveness, authenticity, selectivity, accuracy and precision of the proposed method with allowable impact on PQ according to UL1741 standard.

This paper presents an intelligent electronic device (IED) utilized for automatic meter readings (AMR) scheme using "Open-Source" software. This IED is utilized to measure a low-voltage intelligent electronic device) system with a boundless number of sensors, and it is accessible on the Internet of Things (IoT). The utilized equipment for this task is Arduino UNO R3 motherboard and fringe sensors, which are used for measurement of the referenced information. The Arduino motherboard is used not only for sole tranquility of equipment but also for serving as wireless fidelity (Wi-Fi) switch for the sensors. The personal computer is utilized to gather information and perform client-side calculations. The server works based on an open-source program written in Java programming language. The underlying objective of the proposed scheme is to make the meter based on the "Do It Yourself " methodology which requires considerably fewer funds. Also, it is conceivable by keeping easy to understand interface, information legitimacy, precision of measured information and convenience for the conclusive client. The information is measured in just about 1 ms which is superb for custom-designed IED. Furthermore, the measured qualities are calculated based on their RMS values to be used for analyzing and further presentation of data.

The issue of optimal allocation of capacitor banks concerning power losses minimization in distribution networks are considered in this paper. This optimization problem has been recently tackled by application of contemporary soft computing methods such as: genetic algorithms, neural networks, fuzzy logic, simulated annealing, ant colony methods, and hybrid methods. An evolutionaryheuristic method has been proposed for optimal capacitor allocation in radial distribution networks. An evolutionary method based on genetic algorithm is developed. The proposed method has a reduced number of parameters compared to the usual genetic algorithm. A heuristic stage is used for improving the optimal solution given by the evolutionary stage. A new cost-voltage node index is used in the heuristic stage in order to improve the quality of solution. The efficiency of the proposed two-stage method has been tested on different test networks. The quality of solution has been verified by comparison tests with other methods on the same test networks. The proposed method has given significantly better solutions for time dependent load in the 69-bus network than found in references.

Transient behaviour of transmission towers and associated grounding systems exposed to a lightning surge current having a double exponential pulse waveshape is investigated and analyzed. Frequency domain solutions for electromagnetic fields generated by the network of overhead and buried cylindrical conductors subject to the thin-wire approximation are derived based on the field theory approach. Once the scalar potentials and electromagnetic fields in the vicinity of the tower have been computed at selected frequencies, the time domain response is obtained using the inverse Fast Fourier Transform. Simulation models are obtained by the use of HIFREQ and FFTSES modules of the CDEGS (Current Distribution, Electromagnetic Fields, Grounding and Soil Structure Analysis) software package.

In the new open market and economy environment the assessment of reliability of interconnections has become a more complex task, as it involves modeling of the new functions of wheeling and interchange contracts. The classical approach to reliability assessment and classical reliability indices are no longer used in the open electricity market environment. The reliability indices originally conceived and still in use today are those describing the behavior of the vertically integrated (VI) utilities. Now a new set of reliability indices has been defined and computed for power systems operating in the interconnections. This paper will first present the theoretical background of reliability assessment of the interconnected power system in the open electricity market according to the CIGRE Report Task force 38.03.11. After that a new set of defined reliability indices for the open electricity market and system operation in interconnection will be introduced and computed for the Croatian TSO (HEP TSO-Transmissions System Operator). HROTE is the Croatian Energy Market Operator. Currently, there is only one electricity market in Croatia. In the initial phase of market opening, the model of the bilateral market has been chosen and the electricity trading has been carried out through bilateral contracts. HROTE announced the first trading electricity market rule on December 8, 2006 in which all relations between participants in the electricity market are defined. The paper presents the computation of reliability indices of the Croatian electric power system, more precisely of the Croatian HEP TSO in interconnection with all the neighbor countries. The CBT (Cross Border Transactions) agreements with Hungary, Slovenia, Serbia and Bosnia and Herzegovina will be considered and included in the reliability assessment. A set of load point indices for main 110 kV load supply points, system reliability indices and interconnection reliability indices will be computed.

This paper presents calculation and simulation of a three phase short circuit, single line to ground fault and lightning stroke transients on a 110 kV cable-overhead transmission line that connects the new 110/20 kV transformer station Djakovo 3 with the existing TS 400/110 kV Ernestinovo and TS 220/110 kV Djakovo. Calculation and simulation of short-circuit transients are made using the EMT DIgSILENT Power Factory module. Simulations of a lightning stroke are compared using the ATP-EMTP software and EMT DIgSILENT module. Using the composite DSL (DIgSILENT Simulation Language) model, the Direct lighting stroke has been represented as the Double-exponential function and the return stroke as the Heidler function. Using the ATP-EMTP model, the lightning stroke has been represented as the Heidler function. Lighting stroke simulations are made with and without the presence of ZnO polymer-housed surge arrester model in both simulation tools.

Voltage events introduce considerable economic losses and have the high impact on consumers. From an economic point of view the frequency and duration of voltage sags are very important because they can cause huge damage in industrial processes. This paper presents results of voltage dips measurements in several transformer stations in eastern Croatia. Power network analysers (LEM MEMOBOX 800, LEM MEMOBOX 808 and LEM TOPAS 1000, supported by powerful mathematical software) were used for measurements and analysis. The paper presents voltage dip probability functions calculated from the actual measurement data. The intention of the authors is to show a statistical method which could be useful for assessing the total annual event.

Abstract: The electrical power system provides production and delivery of electrical energy in sufficient quantities to areas that need electricity through a grid. The goal of the electrical power system is a secure and reliable electricity supply of costumers at minimum costs. ...

Modern power distribution networks assume the connection of Distributed Generators (DGs) and energy storage systems as well as the application of advanced demand management techniques. After a network fault these technologies and techniques can contribute individually to the supply restoration of the interrupted areas and help improve the network reliability. However, the optimal coordination of control actions between these resources will lead to their most efficient use, maximizing the network reliability improvement. Until now, the effect of such networks with optimal coordination has not been considered in reliability studies. In this paper, DGs, energy storage and demand management techniques are jointly modelled and evaluated for reliability assessment. A novel methodology is proposed for the calculation of the reliability indices. It evaluates the optimal coordination of energy storage and demand management in order to reduce the energy-not-supplied during outages. The formulation proposed for the calculation of the reliability indices (including the modelling of optimal coordination) is described in detail. The methodology is applied to two distribution systems combining DGs, energy storage and demand management. Results demonstrate the capability of the proposed method to assess the reliability of such type of networks and emphasise the impact of the optimal coordination on reliability.

This paper aims at applying the Evolutionary Strategy (ES) to capacitor banks optimal allocation problem in the case of multiobjective optimization. The multiobjective optimization includes several objectives such as power losses, capacitor costs and voltage deviation. The multiobjective optimization problem consists of conflicting objectives which need to be simultaneously optimized. Some other constraints are also considered. In the paper the following is proposed: the ES mutation operator adapted to the optimization problem, individual coding and generating of the initial population and finally,the mutation operator adapted to the optimization problem with discrete variables. The proposed approach has been evaluated on the test radial feeder and simulation results have been compared with those existing in the literature.