Isolated vs. Interconnected Wind Turbine Grounding Systems: Effect on the Harmonic Grounding Impedance, Ground Potential Rise and Step Voltage (original) (raw)
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Electric Power Systems Research, 2019
The impact of frequency-dependent soil electrical parameters on the lightning response of typical wind turbine grounding systems is investigated. It is shown that the frequency dependence of soil parameters is responsible for decreasing the ground potential rise and, thus, the impulse impedance and impulse coefficient of the grounding systems. This effect is more pronounced for high-resistivity soils and fast current pulses. It is also shown that, considering typical dimensions of actual wind turbine grounding systems and soils with resistivity higher than 300 Ωm, the impulse impedance seen by each single wind turbine is expected to be lower than the low-frequency grounding resistance.
IEEE Access
A safe and cost-effective design of a wind turbine generator (WTG) grounding system requires accurate modelling of local soil resistivity, particularly when wind turbines are spatially distributed across a wide area with different soil types and features. In this article, three locations at an Australian wind farm were modelled based on measured data. Four soil resistivity models were considered: uniform, multilayer horizontal, vertical, and exponential variation with depth. Full-wave electromagnetic simulations were performed at different lightning discharge current frequencies to find the expected ground potential rise and WTG earthing impedance in the event of a lightning strike. Further, the effect of frequency dependent soil parameters on the WTG earthing was analysed, along with the effect of foundation rebar on the grounding impedance. Our results show that an accurate soil resistivity model is critical in the design of a WTG earthing system. INDEX TERMS Wind turbine generator, lightning protection, soil resistivity, grounding system, grounding impedance, ground potential rise.
Transient response of grounding systems of wind turbines under lightning strikes
The paper focuses on the transient analysis of grounding systems of wind turbines. The analysis is carried out in the frequency domain and it uses a recently proposed hybrid approach based on circuit theory and Method of Moments, in order to fully account for resistive, inductive and capacitive couplings. The corresponding transient response is obtained by means of the Inverse Fourier Transform. A typical wind turbine grounding system arrangement based on ring electrodes is analyzed.
Analysis of ground potential distribution under lightning current condition
2017
The grounding system of a lightning protection scheme is designed basically to avoid arcing and dangerous step potentials. The grounding impedance of the system varies depending on soil structure and frequency. This paper describes the effect of harmonic impedance (also called frequency dependence of soil) on potential distribution under lightning strike to a metal tower with single grounding path, for different soil types. The results show that the peak value of ground potential rise (GPR) and step voltage (SP) may reach extremely hazardous values even at distances in the order of 90 m from the tower footing, especially when soil resistivity is high. Hence, we emphasise that, in contrast to power grounding, when designing of grounding systems that are meant to handle transient or high frequency currents as well, the frequency dependent soil parameters should be considered to avoid hazardous situations, especially at locations with a high probability of lightning strikes such as met...
Wind farm grounding systems design regarding the maximum permissible touch & step voltage
2012 11th International Conference on Environment and Electrical Engineering, 2012
Nowadays Wind turbines are used over a wide area as they are environmentally favorably means to product energy without emissions and moreover the fuel is wind which is free for use. Wind turbines are often installed in mountainous area where the soil resistivity and isokeraunic level is high. When the soil resistance is high, the potential rise caused by lightning strike to a wind turbine is more remarkable at the wave tail than at the wave front. On the other hand, the potential rise at the wave tail depends on the steady-state grounding resistance. In this condition the steady-state grounding resistance becomes more important than the transient grounding resistance. In this paper a comprehensive steady-state study on grounding system of wind turbines is presented. Different grounding system configuration will be analyzed. At first a single wind turbine ground system will be considered and the configuration which decrease the step voltage, touch voltage and equivalent grounding resistance of wind turbine grounding system more than other will be selected, then simulations expanded to wind farm which their grounding systems connected to each other. Different grounding methods are analyzed using CYMEGRD which is well known grounding system analysis software.
IEEE Transactions on Electromagnetic Compatibility
In spite of the contemporary interest in renewable power plants, thermal power plants are still inevitable. Various electric equipment and apparatus are grounded via a large-scale grounding system in thermal power plants. In this paper, the three-dimensional finite-difference time-domain method has been employed to study the performance of such a large-scale grounding system against a lightning strike to a nearby transmission tower. The study has emphasized how a nearby sea, which is utilized for cooling purposes in thermal power plants, influences the ground potential rise on the large-scale grounding system considering soil ionization. The results show that the distribution of the ground potential rise on the large-scale grounding system is quite dependent on the alignment of sea with the large-scale grounding system. In addition, the extent that soil ionization affects the ground potential rise is dependent on the distance between the struck tower and the large-scale grounding system. Index Terms-Electromagnetic fields, finite-difference timedomain (FDTD) method, grounding systems (GSs), lightning strikes. I. INTRODUCTION T HE GLOBAL interest in renewable energy is currently increasing due to environmental considerations. However, the majority of the contemporaneous electric energy consumed all over the world is actually produced from thermal power plants owing to the intermittent nature of renewable resources and their associated technical challenges [1]. Power system apparatus, equipment, and electric circuits inside a thermal power plant are grounded by a large-scale grounding system (LSGS) to protect them against power system electromagnetic transients such as lightning and switching surges. Therefore, a considerable research has been devoted to study grounding systems Manuscript
Frequency and Time Response of Power Plant Grounding System Exposed to Lightning Strike
International Journal of Electrical and Computer Engineering (IJECE), 2016
This paper examines the frequency response of power plant grounding system exposed to the lightning current. Large amount of current generated by the stroke flow in the grounding system of power plant and dissipate in the soil. The electric and magnetic field generated by such high voltages and currents may cause damage of equipment and may be dangerous for the personnel in power plant. For the every given frequency obtained using Fast Fourier Transformation (FFT) of lightning current impulse, electromagnetic field theory approach is used to solve Maxell’s equation and compute scalar potential, electric and magnetic field. Also, the influence of the point in which lightning current is diffused in the grounding system is presented. Three dimensional plots of spatial distribution of scalar potential, electric and magnetic field are presented. The time domain response of scalar potential, electric and magnetic field on one profile is also presented.
Frequency response of grounding system of wind turbine generators
This paper examines the frequency response of several grounding systems of wind turbine generators, as they are currently used in wind parks in Greece. Several cases were studied depending on the grounding system and the soil structure. For every given frequency of the fault current the following magnitude have been calculated: the complex grounding resistance, the step and the touch voltages on the ground surface. Also, the effect of the point from which the fault current is diffused in the grounding system of several connected wind turbine generators has been examined. Furthermore, cases for the grounding system, which was energized each time from a different wind turbine, have been separately studied. The effect of the soil structure on the response of a grounding system has been also investigated. Cases of uniform soil model and two-layer soil model with different specific resistivity values for the first and second soil layers, in combination with altering the thickness of the first layer, have been studied. Moreover, the frequency response of a grounding system in each of the above cases has been examined. The soil structure has been computed using soil resistivity measurements and specialized genetic algorithm software, which has been developed in our lab.