Economic optimization of the backflashover outage rate in HVDC transmission systems

HVDC transmission lines are capable to deliver much more electric power than HVAC lines built upon similar structures. Thus, the expected outage rates associated to lightning activity should be more exigent in HVDC lines. This paper studies the cost implications of the mitigation measures -grounding electrodes and additional insulation- required to reduce line tripouts due to backflashover phenomenon in HVDC networks. We apply the Hileman's methodology to find optimal total and incremental costs curves of grounding and insulation infrastructure for a desired backflashover outage rate (BFOR). Four well-known standard procedures are applied to assess the BFOR: EPRI, IEEE1243, CIGRE and Montecarlo-EMTP-ATP. The method was applied on 700km long 500kV HVDC line between Colectora 2 and Cerromatoso, considered in the National Transmission Expansion Plan of Colombia 2015-2029. The resultant cost vs. BFOR curves allow us to determine the optimal investment cost according to a desired reliability level.