# Evaluating the High Frequency Behavior of the Modified Grounding Scheme in Wind Farms
## 5 Conclusions  
Grounding in electrical systems is necessary to ensure the protective device's performance, and the wind turbine is no exception. Due to the importance of wind turbines in providing sufficient clean energy, their earthing system should be designed carefully considering all range of frequencies in various types of grounds particularly during lightning to constrain the lightning current and prevent excessive overvoltages. This research studied the impacts on high-frequency models of wind turbines, including transformers, grounding systems and underground cables, that are associated with soil ionization effects during temporary transitions associated with lightning strikes in order to design a proper grounding scheme, the PMGS. The analysis examined different states, such as an indirect lightning strike on a single wind turbine and a pair of turbines. The main objective in introducing the PMGS was to reduce the peak values of transient voltages and have the least equipment failure. Compared to prevalent models, the PMGS is more reliable in real conditions for limiting surge propagation to an acceptable range and making the voltage reach an acceptable value at the HV terminal with a nonlinear load. The following conclusions may be derived from this study:  
* The combination of the PMGS with a high-frequency SA and FD cables can greatly reduce the maximum transient overvoltages. This result can be used to smooth the lightning current path in rocky lands with high soil resistivity.
* Maximum overvoltages can be decreased on the LV side of the power transformer by using FD cable.
* Due to the large magnitude of lightning overvoltages that occur during the working of turbines, the PMGS is needed to reduce the rate of equipment failure.
* Integrating the PMGS in a pair of turbines will be helpful in terms of noticeably reducing the peak voltages.
* Regardless of which type of lightning hits a pair of turbines, the rate of transient response is considerable only in the exposed wind turbine, and the other turbines do not suffer much from such strikes.  
**Acknowledgments:** [PERSON] is supported by a Marie Curie Fellowship funded by the European Commission (Agreement PCIG11-GA-2012-321980). This work is also partially supported by the EU TagItSmart! Project (Agreement H2020-ICT30-2015-688061), the EU-India REACHProject (Agreement ICI+/2014/342-896) and by the projects \"Physical-Layer Security for Wireless Communication\" and \"Content Centric Networking: Security and Privacy Issues\" funded by the University of Padua.  
**Author Contributions:** All authors together proposed, discussed and finalized the main idea of this work. [PERSON] and [PERSON] proposed the idea, calculated and plotted the feasible regions, and implemented the algorithm and their comparisons. [PERSON] and [PERSON] helped in the paper preparations, English corrections and submission.  
**Conflicts of Interest:** The authors declare no conflicts of interest.  
\begin{table}
\begin{tabular}{c c c c} \hline
**Direct Strike** & **LV Side** & **HV Side** & **Control System** \\
**(200 kA)** & **(kV)** & **(kV)** & **(kV)** \\ \hline In service single wind turbine & 20 & 19 & 26 \\ In service a pair of turbines with separated PMGS & 80 & 40 & 26 \\ In service a pair of turbines with connected PMGS & 78 & 34 & 18 \\ \hline Out of service single wind turbine & 20 & 18 & 26 \\ Out of service a pair of turbines with separated PMGS & 90 & 20 & 27 \\ Out of service a pair of turbines with connected PMGS & 80 & 15 & 18.5 \\ \hline \end{tabular}
\end{table}
Table 2: Peak voltage values of \(\mathrm{LV/HV}\) sides of boost transformer and control circuit with direct strike.