Lightning parameters are needed in different engineering applications. For the prediction of the severity of transient voltages in power systems, an accurate knowledge of the parameters of lightning ...currents is essential. All relevant standards and technical brochures recommend that lightning characteristics should be classified according to geographical regions instead of assuming that these characteristics are globally uniform. Many engineers and scientists suggest that better methods for lightning current measurements and analyses need to be developed. A system for direct lightning current measurements installed on Mount Lovćen is described in this paper. Observed data were analyzed, and statistical data on parameters that are of interest for engineering applications were obtained, as well as correlations between various lightning parameters. Furthermore, a novel approach for classifying and analyzing lightning data from direct measurements based on empirical mode decomposition (EMD) is proposed. Matlab was used as a tool for signal processing and statistical analysis. The methodology implemented in this work opens possibilities for automated analysis of large data sets and expressing lightning parameters in probabilistic terms from the data measured on site.
In this paper, a new high-frequency black-box model of the power transformer is presented for the calculation of transferred lightning overvoltages. The model is based on frequency-response analysis ...measurements and the application of four-terminal network theory. The computational verification of the presented model was successfully performed on a white-box transformer model in Electromagnetic Transients Program-Restructured Version software. The experimental verification was carried out on 130-kVA and 36-MVA three-phase power transformers. The presented calculation and measurement results confirm the validity of the proposed model for full and chopped lightning impulse voltages.
•Transients during controlled switching of 123kV shunt reactor are investigated.•Results of field measurements and computer simulations are presented.•Effects of different values of chopping-current ...during switching-off are considered.•Inrush currents strictly depend on accuracy of circuit breaker (CB) drive mechanics.•Overvoltages were lower for motor-driven CB than for hydraulically operated CB.
This article deals with results of performed studies of transient phenomena in application of controlled switching technique by switching high voltage 123kV, 100MVAr shunt reactor. First, for switching a single-pole hydraulically operated SF6 circuit breaker has been selected and after that, one with electric motor-drive. In preparing of experimental part of studies the EMTP-ATP software has been used in computer simulations, further for analyses the cases of optimal controlled switching and switching within time deviation limits. For simulation of uncontrolled switching with current chopping and arc-reignition dynamic model of arc behavior has been implemented. The field tests with both circuit breakers have been repeated in similar network conditions for further statistical analyses. During some tests, the transient phenomena of uncontrolled switching have been observed. The achieved experimental results were compared with the computer simulations.
•Grounding impedance of the overhead line tower is frequency-dependent.•Flashover occurrence on the insulator string depends on the grounding impedance.•Model of the grounding is based on the impulse ...impedance measurements up to 410 kHz.•Grounding impedance is modeled in EMPT-type tool.•State space equations and rational approximation are used to model impedance.
The paper demonstrates the importance of taking the frequency-dependence of the tower grounding impedance into account when studying the lightning performance of an overhead line located in an area with high soil resistivity. Towers’ impulse grounding impedance measurements and their rational approximations are used to construct a wideband model of the towers’ grounding electrodes in an EMTP-type software program.
In order to examine the impact of tower grounding impedances, simulations of lightning strokes to the overhead line tower were performed using an EMTP-type tool in the following three different cases: constant grounding impedance of the tower hit by a lightning stroke, frequency-dependent tower grounding impedance and frequency-dependent tower grounding impedance for the tower equipped with a Line Surge Arrester (LSA) installed at the lowest phase.
The simulations have shown the influence of the frequency-dependence of the tower grounding impedance on the level of the build-up voltage across the tower’s insulator string and consequently on the flashover occurrence in the observed configuration with a high soil resistivity.
•Development of experimental real-time monitoring system for line surge arresters.•Accurate measurements of the transient currents.•Successful functional and communication testing in high voltage ...laboratory.•Match between measured and simulated waveshapes.•Proposal of implementation of the developed system on site.
Power systems are exposed to different types of electromagnetic transients, which involve a large spectrum of signals whose duration can range from several nanoseconds to several milliseconds, and whose peak values can also cover a wide range of values. Therefore, measuring electromagnetic transients in power systems is a challenging task. Fast front transients caused by lightning events are especially dangerous, and improved knowledge about them is essential for better protection design. The development of measuring systems for such phenomenon is important. This paper is dedicated to the development of a measuring system for lightning and line surge arrester currents. Modern electronic tools and equipment, as well as cutting-edge communication and information technologies, constitute the foundation of the proposed system. This includes the most recent models of acquisition units and GPS devices that are now available on the market, as well as communication networks including 4 G, 5 G, and WiFi. Software and hardware components of the system are described. The paper presents laboratory tests conceived to prove that the system operates correctly and provides accurate results. The measurements are compared to EMTP and MATLAB simulations. Both are in agreement.
•Low frequency signal injection can be used for fault location in isolated MV networks.•Comparison of conventional earth-fault protection and signal injection method.•Induction voltage transformers ...can be used for sinusoidal signal injection.•Saturation of inductive voltage transformer depends on injected signal parameters.•Injection method is more efficient for high resistance fault detection.
Neutral earthing directly affects systems' behaviour regarding the maximum level of earth-fault current and overvoltages. Isolated neutral is used where continuity of power supply is essential, which is often the case in industrial power utilities. Although the system can remain in service during a single-phase earth-fault, locating the fault should be done as quickly as possible, without disrupting the operation of the loads. Directional earth-fault protection (67N) can be used to indicate the faulty feeder. An alternative method is low-frequency (LF) current injection combined with sensors for detecting the injected signal, which is a known technique used in LV systems. In this paper, the application of 67N protection and the LF current injection method are tested on the same MV system with inaccessible neutral point. Inductive voltage transformers (IVTs) are used for signal injection. Both methods are discussed, and their limitations are compared based on simulation results obtained using the model of an isolated MV industrial plant. The model includes relay protection devices and IVTs for signal injection.
•Interaction of electric power system and railway system.•Modeling of electric traction system 25kV, 50Hz and the traction vehicle with 3f induction motors.•Monitoring of power quality parameters at ...the point of electric railway system connection to transmission system.•Measurements and analysis of power quality parameters.
Three-phase induction motors are widely used in electric traction systems. The impacts of the traction vehicles equipped with three-phase induction motors on power quality are much different from the impacts of vehicles with DC traction motors. In this paper, the effects of the traction vehicle operation with three-phase induction motors on power quality in a 110kV transmission network are investigated.
The electric traction system 25kV, 50Hz and the traction vehicle with three-phase induction motors were modeled including AC/DC rectifier and DC/AC inverter based on IGBT technology. The parameters of those power electronic elements directly determine the current and voltage waveforms, and consequently power quality parameters.
Measurements and calculations of power quality parameters were presented. Three operation modes of traction vehicle were considered including acceleration, constant drive and regenerative breaking. During the test drives, the values of total harmonic distortion, unbalance, flicker and power factor were obtained.
•Application of LSAs for the reduction of SOVs on voltage uprated transmission lines.•The method for selection of optimum LSA installation locations was developed.•An algorithm that estimates the ...risk of flashover due to SOVs was developed.•Overvoltage protection of the transmission line uprated from 220kV to 400kV.•Compacting of 400kV transmission line by installing LSAs.
This paper discusses the possibility of using line surge arresters (LSAs) for the reduction of switching overvoltages (SOVs) on voltage uprated transmission lines. The method for the selection of LSA energy class and determination of optimum installation locations was proposed. The method was applied in case of improving the overvoltage protection of the transmission line uprated from 220kV to 400kV.
The possibility of compacting a 400kV transmission line by installing LSAs was considered. Since a risk of flashover increases due to the reduction of insulation clearances, an algorithm that estimates the risk of flashover was developed and applied in case of compacting a 400kV transmission line.
This paper presents the method for the shape optimization of the DC solenoid electromagnetic actuator using a genetic algorithm. Numerical simulation of its transient response includes simultaneously ...solving differential equations of magnetic, electrical and mechanical subsystems. The magnetic subsystem is analyzed by finite element method (FEM), while the electrical and mechanical subsystems are modeled separately and mutually coupled. A modified genetic algorithm is programmed in MATLAB software package. The shape optimization has been performed on two-dimensional (2D) axial-symmetric model of electromagnetic actuator. The measurement results obtained after the production and testing of electromagnetic actuator are compared with results of numerical simulation.
