Grzegorz Karnas

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.

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.

Power spectrum density analysis of intra-cloud lightning discharge components from electric field recordings in Poland

The aim of this paper was to show usefulness of Power Spectrum Density analysis for identification of different components of IC lightning. We have presented some exemplary pulse train electric field recordings characterized for the specific time development of intra-cloud lightning discharges observed during summer thunderstorms in Poland. These data were gathered by two detection stations working independently in Warsaw and Rzeszow. Both stations are based on triggered electric field acquisition in the ELF-MF frequency range. Such recorded electric field courses of intra-cloud lightning were then analyzed both in the time domain and in the time-frequency domain with application of the short-time Fourier transform (STFT). On the basis of the used STFT procedure the Power Spectrum Density (PSD) spectrograms were computed. This whole computer procedure was performed by using the Matlab platform. Due to that we were able to distinguish some different intra-cloud lightning components as the preliminary breakdown stages including sequences of initial pulse bursts, K- and J-type electric field changes and sometimes even a trace of the Narrow Bipolar Pulses (NBPs). We have obtained different shape/pattern of the particular PSD stripes related/corresponding to the considered components of intra-cloud lightning. Summarizing of our PSD analysis of the recorded intra-cloud lightning incidents we have noticed that the PSD stripe structure of the initial breakdown processes for in-cloud and cloud-to-ground lightning is similar. But, the characteristic and different shape of the PSD stripe was obtained for the K-type electric field changes occurring during intra-cloud lightning. For these cases the PSD stripes were of the same height and width as for the return stroke incidents from the cloud-to-ground flash, but their intensity for the frequencies above 500 Hz was much lower. On the other hand, the PSD stripe obtained for the NBP was very often the strongest one and therefore it was hard to be properly distinguished in contrast to the return stroke stage from the cloud-to-ground flash.

Calibration of electric field antennae operating in the ELF-MF frequency range at the lightning research station in Rzeszow

The purpose of this paper is to find calibration coefficients for antennae operating at the Lightning Research Station in Rzeszow. Two types of antennae used for acquisition of lightning electric field were examined. The first sensor was the ELF electric field mill registering slow electric field variations originated in the thunderstorm cloud. The second antenna was designed to recording relatively fast ELF-MF components of lightning as return stroke, continuing current and preliminary breakdown. In order to create uniform distribution of electric field during the calibration a dedicated setup was made in the high voltage laboratory. Different generators were used to create adequate field waveforms. Due to significant difference in amplification and bandwidth for each sensor. Devices were calibrated together with 10 meter cables dedicated for wiring signal from antenna to the A/D converter. Estimated calibration coefficients were 47.5 mV/kV and -334 mV/kV for the slow and fast electric field sensor, respectively. Small variation of those coefficients was observed when the signal transmission line was terminated by the characteristic impedance. Cable length does not affect the measured signals in this configuration.

Estimation of Building Form Factor and Calibration of ELF-MF Electric Field Antenna Dedicated to Lightning Measurements

This paper is aimed to obtain a calibration coefficient for lightning electric field antenna operating at the Lightning Research System of Rzeszow University of Technology. The measurement showed that the electric field at the antenna location was significantly increased in respect to the flat terrain. Verification of the calibration coefficient was done with application of the commercial lightning location system data. Comparison with previous research from high voltage laboratory showed that an open test site calibration is in better agreement with empirical formulas. Streszczenie. Celem artykułu było wyznaczenie współczynnika kalibracji anten piorunowego pola elektrycznego pracujących w systemie rejestracji wyładowań atmosferycznych Politechniki Rzeszowskiej. Pomiar uwidocznił, że pole elektryczne w docelowej lokalizacji było znacząco zwiększone w odniesieniu do pomiaru na otwartej przestrzeni. Dokonano weryfikacji współczynnika kalibracji z wykorzystaniem danych komercyjnego systemu lokalizacji wyładowań. Metoda pomiaru w terenie okazała się być w większej zgodności z teorią niż w przypadku pomiaru laboratoryjnego. (Pomiar i analiza współczynnika odkształcenia budynku oraz współczynnika kalibracji dla anten piorunowego pola elektrycznego wykorzystywanych w systemie rejestracji wyładowań atmosferycznych Politechniki Rzeszowskiej).

The time and power spectrum density analysis of different lightning components based on electric field waveforms from 2014 thunderstorm season recorded in the south-eastern part of Poland

This paper is focused on the Power Spectrum Density analysis of the lightning electric field signatures collected in Subcarpathian part of Poland, in 2014. Lightning records were carried out in two different ways. The slow electric field sensor (TLF-ELF), the mill, was used for observation of lightning activity during entire thunderstorm lifetime. The second recording mode was the acquisition of fast electric field changes (0.3 Hz to 3 MHz) associated with different types of cloud-to-ground (CG) and inter-, intra-cloud (IC) type discharges. The registration process was synchronized with microsecond time precision. This allowed to relate lightning stroke detections to these reported by the LINET, the commercial lightning location system. Different lightning stroke components, as e.g. the preliminary breakdown (PB), the return stroke (RS) and the continuing current (CC) were identified with application of the Short-Time Fourier Transform. The spectral analysis might be adapted to improve in future some detection algorithms used in lightning location systems. Such lightning CG stroke discrimination is not applied as yet by any lightning location system routinely operated in Europe. Streszczenie.W artykule skupiono sie na analizie spektrogramow widmowej gestości mocy wyznaczonych dla roznych przebiegow piorunowego pola elektrycznego zebranych w poludniowo-wschodniej cześci Polski w 2014 roku. Dane zostaly zebrane z wykorzystaniem dwoch sensorow pola elektrycznego. Sensor pola elektrycznego pracujący w zakresie TLF-ELF umozliwil obserwacje aktywności burzowej w dlugofalowym okresie czasu. Drugi typ rejestracji obejmowal akwizycje szybkich zmian pola elektrycznego (0.3 Hz do 3 MHz) pochodzących of roznych typow wyladowan doziemnych oraz wewnątrz-, miedzy-chmurowych. Proces rejestracji zostal zsynchronizowany z mikrosekundową precyzją. Pozwolilo to na porownanie wlasnych rejestracji z detekcjami LINET-u - komercyjnego systemu lokalizacji wyladowan. Rozne skladowe wyladowania takie jak wyladowania wstepne, udar glowny oraz prąd dlugotrwaly zostaly zidentyfikowane z wykorzystaniem krotkoczasowej transformaty Fouriera. Analiza spektralna moze w przyszlości zostac wykorzystana w usprawnieniu algorytmow detekcji wyladowan. Taki rodzaj identyfikacji wyladowan doziemnych nie zostal jak dotąd zaimplementowany w zadnym systemie lokalizacji wyladowan atmosferycznych pracującym regularnie w obszarze Europy. (Czasowa oraz widmowa analiza roznych skladowych wyladowania atmosferycznego w oparciu o przebiegi pola elektrycznego zebrane w poludniowo-wschodniej cześci Polski w 2014 roku).

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.

Surge current distribution in the lightning protection system of a test house equppied in electrical and electronic appliances

Open air experiments were conducted of surge current distribution in the lightning protection system, supplying cable and electrical installation of a test house equipped in household appliances. Surge currents were injected from the generator into the installation. Current distributions in elements of tested system were measured with multi-channel electro-optical system. To verify the experimental results the simulations of surge current in the test house modeled in ATP-EMTP were conducted. The results indicated a significant influence of frequency dependent parameters of the test house elements on both the amplitude and the shape of current waveforms.