Alexander Smorgonskiy

In this paper, we report the results of wind turbine grounding system impedance measurements performed at the Mont-Crosin wind park in Switzerland. Experiments were carried out twice: (1) when only the construction of the wind turbine foundation had been completed, and (2) once the installation of the rest of the wind turbine was finished: tower, nacelle and blades. The transient grounding impedance was evaluated directly in the time domain by solving Duhamel's integral equation. The influence of the presence of the wind turbine is found to be negligible on the grounding impedance at low frequencies. However, at frequencies beyond 150 kHz or so, the measurement of the grounding impedance is significantly affected by the presence of the wind turbine.

In this paper we present a numerical analysis of lightning current distribution in the conductive elements of a wind turbine blade. They include lightning down conductor, blades spar caps made of carbon fiber reinforced polymers (CFRP) and protective copper mesh placed on the spar caps. The problem is solved in frequency domain by using the finite element method. Anisotropic electrical conductivity of CFRP laminates was considered in the modeling. We have analyzed two cases when CFRP elements are covered by the copper mesh and without such protection. In the first case due to the skin-effect the most of the current flows through the external highly-conductive surface of the copper mesh. However the thin mesh can be easily damaged by lightning. In the second case an extreme result of such failure is modeled. It was found that even the placement of additional down conductors will not prevent lightning current from flowing through CFRP elements leading to delamination of the laminates.

In this paper, we present analytical calculations and numerical simulations of the vertical component of the electric field close to a rocket-triggered lightning site during the ascent of the rocket and prior to the lightning initiation, taking into account the corona layer around the wire. In the analysis, the background electric field was modeled according to the available experimental data. The influence of the space charge layer extending upwards from the ground level was modeled and analyzed. The obtained values of the electric field reduction are shown to be consistent with experimental observations. The presented model can also be used to estimate the charge distribution in the rocket wire and the current flowing into the wire from the ground.

In this paper, we present the calculation of the effective height of the Gaisberg tower using several models in which the Gaisberg Mountain is represented by either simplified geometrical shapes (hemisphere and hemiellipsoid), or by using the actual 3D topography. The procedure to estimate the effective height based on the comparison of the electric field at the top of the tower located on flat and mountainous terrains is studied in detail for the three considered representations of the mountain. For each case, the electric field is computed numerically using the finite element method. We show that the use of the actual 3D topography of the mountain surface results in a very low value of the effective height in the range of 200 - 300 m, which results in an underestimation of the total number of flashes to the tower. The obtained results give some concerns about the applicability of this method of estimation for the effective height.

We compare in this paper direct measurements obtained at the Towers on Mount San Salvatore (Switzerland) and the Gaisberg Tower (Austria). They are situated in similar topographical environments but in different lightning activity zones. Direct measurements of lightning currents on these towers have revealed a major difference in terms of the number of downward flashes. While Berger and co-workers obtained a significant number of downward flashes, more recent observations on the Gaisberg and Peissenberg Towers were essentially composed of upward flashes. We use in this paper a new method to estimate the proportion of upward/downward flashes to a given tower, based on the data from lightning location systems. The analysis using the proposed method explains the discrepancy in terms of the measured number of downward flashes in Gaisberg Tower and in Monte San Salvatore Tower.

A new method to estimate the number of upward flashes from tall structures is presented. The method is based on the analysis of the data provided by lightning location systems (LLS) and thus could be applied for any tall structure located in the region covered by a LLS. About 80 tall objects in Europe with heights ranging from 100 m to 300 m were selected for the analysis. LLS data for a period of 10 years on flashes within circles of 8 km around each object were exported from the EUCLID network database and analyzed. The number of upward flashes for each considered structure was estimated and the obtained results were compared with those calculated using the empirical formula of Eriksson. For towers located on hilly terrain, the physical height of the structure was replaced by its effective height determined according to the IEC recommendation. The obtained results follow the trend predicted by Eriksson's formula. However, significant dispersion is observed. This dispersion might be attributed essentially to meteorological and geological factors associated with different objects.