**7. Conclusions**

The new modeling approach allows integration of the grounding system into the transmission system when analyzing the lightning surge performance of the transmission system. By using the more detailed Matlab/Simulink model presented in this work, large data-sets are processed to extract overall measured values in EMI analysis. Different functions and parameters may be processed by the simulation log of the grounding system and parameters such as the effective length and the electric field distribution. Moreover, by taking advantage of the newly developed FMI interface, the grounding grid model itself is integrated as an element in the transmission system modeling and analysis by EMTP-RV. Lastly, the surge arrester performance is better assessed when the grounding system is included and consequently, the corresponding effects of all parts in the transmission system could be more accurately analyzed.

The grounding system model presented in this work is simplified and neglect significant factors of a physical system. Moreover, with the implementation of the grounding system in Matlab/Simulink features flexibility and significant potential for further development so that the accuracy could be improved.

**Author Contributions:** V.S. developed the method, performed simulation/data analysis and prepared the manuscript as the first author. L.H.S., S.Z. and E.C. assisted the project with insights in the method development phase and review process. All authors discussed the results and approved the publication.

**Funding:** This research received no external funding

**Acknowledgments:** The authors thank for the support given by Western Norway University of Applied Sciences and the University of Bergen to carry out this work. A special thank to International Conference on High Voltage Engineering and Application (ICHVE) 2018 for the invitation to publish in this special issue entitled "Selected Papers from 2018 IEEE International Conference on High Voltage Engineering".

**Conflicts of Interest:** The authors declare no conflict of interest.
