R. Ziemba

Experimental Investigation and Numerical Modeling of Surge Currents in Lightning Protection System of a Small Residential Structure

The distribution of lightning current in the lightning protection system (LPS) and the electrical circuit of two test structures simulating residential buildings was experimentally studied at two research facilities in Florida and in Poland. In Florida, the experiments were conducted using rocket-triggered lightning, and in Poland a mobile current surge generator was employed. The soil in Florida was sandy, while in Poland it was mostly clay. Simulations of lightning current in the LPS and the electrical circuit of each of the test structures were also performed. In this paper, we present results of experiments and numerical modeling of lightning current distribution in different configurations of LPS installed on the test structures at the two sites.

Current Impulses in the Lightning Protection System of a Test House in Poland

The full scale test house was equipped with the lightning protection system and connected to the 15 kV/400 V transformer station. The simulated stroke current was injected into the installation with a current surge generator. Distribution of current in the lightning protection system and connected power supply installation is presented. Measurements were done for several configurations of the LPS, and for current amplitudes ranging from 1 to 10 kA. The results indicated variation with both the amplitude and the shape of the waveforms. The resistance was measured for several groundings individually and for entire grounding system with respect to the surge generator location. Measured waveforms showed frequency-dependent behavior of the circuit. Therefore, in order to improve current simulation accuracy the grounding system impedance should be considered rather than pure resistance. The vertical ground rods of the test house have capacitive impedances, while the long underground cable connected to the grounding system of the transformer has inductive impedance.

Experimental investigation and modeling of surge currents in lightning protection system

The paper presents results of the lightning protection system (LPS) tests for a small residential structure with the connected home appliances and electronics conducted in 2013 at the new test site in Poland using the mobile surge current generator. The primary objective was the same as in the previous studies, that is, to examine the current waveshapes in different parts of the circuit and the division of the injected surge current between the grounding system of the LPS and remote ground. The current waveshapes in the vertical ground electrodes differed from the injected current waveshapes and from the current waveshapes in other parts of the test system. Computer simulation using ATP-EMTP carried out in order to verify the measurements. Vertical and horizontal ground electrodes are modeled for specified parameter resulting from the geometrical configuration of the system and the measured soil conductivity. Computed results show a good agreement with the experimental data. A significant influence of frequency dependent components of the system impedances on current waveshapes has been noticed.

Frequency characteristics of supplying transformer and electrical appliances of residential building in modeling of lightning current distribution

Investigations were conducted aimed on examination of frequency characteristics of middle to low voltage distribution transformer used to supply residential buildings. Two methods were used for the investigations. First, the impedances (absolute values and angles) of transformer middle and low voltage windings were measured and registered using precision LCR meter for frequency range from 20 Hz to 10 MHz. These impedance characteristics were also examined using voltage surge generator and digital oscilloscope. Registered voltage and current waveforms were denoised and transformed to frequency domain. Apart from investigation of distribution transformer the frequency characteristic of input impedances of typical household electrical appliances were examined using the LCR meter. The conducted measurements are significant part of investigations concerning the lightning and overvoltage protection of residential buildings, which are conducted at the test site belonging to Rzeszow University of Technology.

Distribution of lightning current in the grounding grid for different multilayer soil models

The paper presents computer results of current distribution for two different lightning current waveforms injected in the central part of a typical substation grounding grid buried in an uniform soil and two different two-layered soils with positive and negative reflection factors, respectively. Obtained results show that the modules of the input impedance of the grounding systems differ significantly and are almost constant in the low-frequency range being practically the same as dc grounding resistances. The computed input impedances increase rapidly above 10 kHz and reach at 1 MHz similar values for both two-layered soils. The lightning current flowing in the horizontal conductors of the analysed grounding grid with vertical rods is slightly greater in the outer edges than current for the same grounding system and soil but without the vertical rods for both injected current waveforms with relatively slow and very fast rising wavefronts.

Influence of different multilayer soil models on grounding system resistance

The aim of the paper is to compare different multilayer soil models in computer estimation of grounding system resistance as an alternative conception to typical uniform and two-layer soil models. Experimental tests of a simple grounding system are described. Preliminary measurements were conducted at the new open-air laboratory belonging to the Rzeszow University of Technology (RUT), Poland. Finally, measurements of soil resistivity by use of different methods, and at the same time, the ground resistance measurements of simple grounding system were performed. Using the experimental data, a different multilayer soil models were proposed and the grounding resistances of the same grounding system were computed. In case of impact excitations characteristic for lightning currents the potential distributions around the analyzed grounding system are shown for the selected multilayer soil, and then, the obtained simulation results are compared with the case of the corresponding uniform soil.

Modeling of Nonlinear Elements during Lightning Overvoltage Simulations

The paper presents some problems of lightning overvoltage modeling in transmission lines with nonlinear elements. The presented results were obtained mostly for fast front transients of subsequent lightning return stroke currents. The effectiveness of numerical algorithms of nonlinear models and possibilities of their development for such transients are analyzed. Computer simulations carried out by application of EMTP show that nonlinear models of back-flashover and ZnO arresters work properly, while the implemented corona model can not be used for relatively large peak values of subsequent lightning return-stroke currents.

High-frequency grounding impedance measurements at test site in Huta Poreby, Poland

High frequency grounding impedance measurements were conducted at the test site in Huta Poreby during the summer season in 2015. The impedances seen from different locations were measured with the impedance meter AES 1002 at frequencies ranging from 100 Hz to 1 MHz. The obtained impedance vs. frequency characteristics have similar shapes. In the low-frequency range impedance values are almost constant while above tens of kilohertz their values begin to rise and reach a peak at about 200 kHz. Above this frequency impedance values begin to decrease. Additionally, the grounding resistances and surge grounding impedances were measured and analyzed.

Measurements and modeling of electromagnetic disturbances in the lightning protection system of the residential building

The paper presents measurements and computational results of the impulse current distribution in lightning protection system (LPS) obtained based on a circuit approach and a frequency-domain full-wave approach. There is a good agreement between computed and measured currents at the test site using the mobile impulse current generator and small residential structure. Small differences in the current waveshapes result mainly from the adopted mathematical approximation which does not perfectly match the current waveshape injected from the generator. Streszczenie. W artykule zaprezentowano wyniki pomiarow i obliczen rozplywu prądu udarowego w instalacji odgromowej budynku. Obliczenia wykonano dla modeli obwodowego i polowego. Otrzymano dobrą zgodnośc wynikow obliczeniowymi z pomiarami. Male roznice w ksztaltach prądow wynikają glownie z przyjetej do obliczen matematycznej aproksymacji prądu udarowego, ktora nie odwzorowuje dokladnie prądu z generatora. (Pomiary i modelowanie zaburzen elektromagnetycznych w instalacji odgromowej budynku mieszkalnego).

Experimental investigation of the effectiveness of lightning protection system

The preliminary laboratory experiments were carried out of impulse current distribution in a laboratory model of the lightning protection system. The tested system is a model in a scale of 1:5 based on the full size test house equipped with the lightning protection system and connected to a supplying electrical installation used for an open air experiments conducted for the few years. The simulated lightning current was injected into the laboratory model of installation with a surge current generator. Distribution of current in the tested system is presented. Measurements were done for varied shapes and peak levels of the injected current. The results indicated an influence of frequency depended parameters of the laboratory model on both the peak level and the shape of the current waveforms, recorded in measuring points. The results obtained during the laboratory and the open air experiments are comparable.