**7. Conclusions**

Radio interference lateral profiles in HVDC lines were computed using a method that considers a transmission line model which includes the skin e ffect in the conductors and in the ground plane. The attenuation constants were determined from the line parameters, and the bipolar system is decoupled using modal decomposition theory. As application cases, two HVDC bipolar transmission lines were analyzed, one of ±500 kV and the other of ±600 kV. The parametric sweeps of five prospective parameters revealed that, as expected, the RI levels decrease when increasing the sub-conductor radius. However, in the case of bundle spacing and the number of sub-conductors, the results show that these parameters should be carefully selected because these present a more complicated relationship with the magnitude of the RI level. Finally, vector optimization was applied to minimize RI levels and the feasibility of the obtained optimal designs discussed. This kind of electromagnetic compatibility study (EMC) can be used to estimate the magnitude of the impact on the environment in the vicinity of a transmission line during the design stage.

**Author Contributions:** Investigation, C.T.-M., F.P.E.-C., S.I. and A.O.; Methodology, C.T.-M. and F.P.E.-C.; Project administration, F.P.E.-C. and A.O.; Software, C.T.-M.; Validation, S.I. and A.O.

**Funding:** This research was funded by "The Scientific and Technological Research Council of Turkey TUBITAK" and "The National Council of Science and Technology-CONACYT of Mexico".

**Acknowledgments:** This research is funded as a part of "215E262/263956 Corona discharge characterization and electromagnetic e ffects of HVDC transmission lines" project under the framework of the "Bilateral Research and Technology Cooperation Turkey-Mexico" organized by "The Scientific and Technological Research Council of Turkey TUBITAK" and "The National Council of Science and Technology-CONACYT of Mexico".

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