High-Voltage Direct Current#Back to back. High-voltage direct current (HVDC) system is an efficient and low-cost method for long-distance power transmission. Its main characteristics are long single-return sending distance, large output capacity, ultra-high voltage class. It can be used not only for single point long distance transmission, but also for power grid synchronous connection. 

Our UHVDC system began with the Three Gorges Dam project. What needs to be mentioned again here is the completion and commissioning of the Three Gorges Power transmission and transformation project that year, it has a far-reaching influence on promoting the optimal allocation of resources, achieving the goal of energy-saving and emission-reduction, and promoting the coordinated development of economy, society and ecological environment in the areas where the project is located. On the one hand, greatly ease the energy tension in east China, Guangdong and other regions; on the other hand, reduce the pressure of railway coal transport and reduce a lot of carbon emissions. It not only promotes the localization and technical level of transmission and transformation equipment of our country to a new level, but also gradually forms the energy transmission system with UHV AC and DC transmission as framework network.