S. Wyderka

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]).

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.

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.

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.