Grzegorz Maslowski

An Improved Model for Prediction of the Dynamics of Lightning Channel Corona Sheath

We consider dynamics of the lightning-channel corona sheath that is implicitly specified by lumped-current-source lightning return-stroke models. Two slightly different corona models for prediction of charge motion in the corona sheath are proposed. Both models can be viewed as generalizations of the model proposed by Maslowski and Rakov (2006) [2] and are in agreement with measurements of the horizontal (radial) electric field component made in the immediate vicinity of triggered lightning channel.

Testing of Lightning Protective System of a Residential Structure: Comparison of Data Obtained in Rocket-Triggered Lightning and Current Surge Generator Experiments

We present a comparison of data obtained during testing of lightning protective system of a residential structure in rocket-triggered lightning experiment at the International Center for Lightning Research and Testing (ICLRT) at Camp Blanding, Florida, and current surge generator experiment at Rzeszow University of Technology in Poland. Three different configurations of LPS were tested in Poland with the dc grounding resistances of the entire system 4.09 Omega (LPS 1a), 1.65 Omega (LPS 1b), and 2.88 Omega (LPS 2). For LPS 1a with three ground rods the value of the peak current entering the electrical circuit neutral was about 56% of the injected current peak, and for LPS 1b with two additional ground rods, each connected by a buried horizontal conductor 5 m long, was about 16%. For LPS 2 with five ground rods interconnected by a buried loop conductor this ratio was 21%. The current waveshapes in the ground rods differed from the injected current waveshapes and the current waveshapes in other parts of the test system, especially, for poorer LPS 1a. The surge-generator results are consistent with those of triggered-lightning experiments at Camp Blanding, Florida (DeCarlo et al., 2006 [2]).

Equivalency of Lightning Return-Stroke Models Employing Lumped and Distributed Current Sources

We show that any engineering return-stroke model can be expressed, using an appropriate continuity equation, in terms of either lumped or distributed current sources with the resultant longitudinal-current distribution along the channel being the same. This property can be viewed as the duality of engineering models. The conversion alters the actual-corona current (if any) of the model. For lumped-source (LS) models the actual-corona current is unipolar and directed radially out of the channel core, while for distributed-source (DS) models it is unipolar and directed into the channel core. For LS models converted to DS models and for the Diendorfer-Uman (DU) model converted to the equivalent LS model, the corona current is the sum of the negated actual-corona current (if any) and a fictitious-corona current, the latter being bipolar. For the transmission-line (TL) model (no longitudinal current attenuation with height) expressed in terms of DSs, there is only a fictitious bipolar corona current component. Conversion of the traveling-current source (TCS) and Bruce-Golde (BG) models to equivalent LS models involves replacement of the actual, unipolar corona current with a fictitious one, the latter current being bipolar near the channel base and unipolar at higher altitudes

Some Inferences From Radial Electric Fields Measured Inside the Lightning-Channel Corona Sheath

Radial electric field waveforms at a horizontal distance of 10 cm from the triggered lightning channel attachment point (inside the corona sheath) have been measured with a Pockels sensor. The electric field change during the leader stage was often overcompensated by the opposite-polarity electric field change during the return-stroke stage. The opposite polarity overshoot in radial electric field waveforms is consistent with the expected existence (during the return-stroke stage) of two concentric zones within the corona sheath: an inner zone containing net positive charge and an outer one with negative charge. The measured radial electric field waveforms exhibited quasi-exponential decay (very similar for all the waveforms), which was used for estimating the apparent electrical conductivity inside the corona sheath.

Developing of lightning research center in south east part of Poland

A short description of developed open-air laboratory and new test equipment for lightning investigations in south east part of Poland is presented. Experience in the field achieved until now was the basis to build the site for testing of lightning and overvoltage protection of residential buildings, low and medium voltage electrical networks, and electrical and electronic devices. For the experiments two new lightning current generators with energy 50 kJ and 100 kJ, and measuring system based on fiber optic technology were constructed and built in Poland. Additionally, a lightning observation station for investigation of natural lightning is implemented at the Rzeszow University of Technology, Poland. The system is based on electric and magnetic field antennas and fast video camera.

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.