Feasibility study of a high-voltage DC & AC multi-circuit hybrid transmission line

With the ever-growing need for electric power in today´s world, the power industry is being faced with both the realities of limited transmission resources and the high costs of new transmission right-of-way. High-voltage direct current (HVDC) transmission lines are a promising alternative to more traditional AC lines, offering reduced voltage drops over long distances and the possibility of reduced operating costs. With the current limits on right-of-way, however, the most cost-effective method to increase transmission capacity is by building HVDC circuits onto existing right-of-way, alongside AC transmission lines. However, the interaction between these new HVDC circuits and existing AC lines is of great concern, especially when both types of lines are placed on the same towers. Moreover, there is little existing research on the interaction between AC and HVDC transmission lines. This paper presents the outcome of a feasibility study that was undertaken to determine the severity and extent of AC/HVDC line interactions. This study focused on interactions caused by the close proximity of the transmission lines themselves, and not by connections between the circuits at either end. A three-circuit (one 115-kV AC, one 230-kV AC, and a bipolar ±500-kV DC) tower configuration was considered in the study, utilizing a 250-mile long transmission system and nine equivalent sources. Various faults and loading conditions were simulated on both types of lines to determine the effects of the AC circuits on the DC line, as well as the effects of the DC circuit on the AC lines. This paper presents the results of these simulations, which signify the feasibility of hybrid AC/HVDC transmission lines.