Background: High Voltage Direct Current (HVDC) is preferred to High Voltage Alternating Current for bulk transmission of power over long distances due to lower capital costs and reduction in transmission losses. The electric power transmission industry has been working to facilitate reliable transmission of HVDC by converting existing HVAC lines. Tripole HVDC is ideally suited for conversion of existing ac transmission lines to HVDC. It can make use of all three phase conductors substantially increasing the line capability. It eliminates the need to build new transmission towers conductors and related switchgear equipment. However with a conventional tri-pole HVDC system there is scope for improvement in transmission efficiency. Additionally current tri-pole designs entail substantial investment of power semiconductors to adapt existing infrastructure. Technology Description: Researchers at NC State University have proposed a novel design to create a tripole HVDC system by including a switched conductor as the third pole in the bi-pole system. This design allows optimum utilization of the third conductor by optimizing the current modulation flowing through it. The Switched Conductor (SC)-HVDC when compared with conventional tri-polar HVDC transmission designs has been observed to provide higher power transfer capability higher semiconductor and transformer utilization and simple control. This design can be readily implemented with minimal changes to the existing infrastructure.
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