Configurations and earthing of HVDC grids

HVDC grids are considered to be essential building blocks for the future upgrade of the existing AC power system and as a means to transport the expected massive amounts of renewable energy from remote sources to the load centers. HVDC systems exist for over 50 years, yet meshed DC grids do not exist so far. For point-to-point HVDC connections, there is a certain freedom in choosing the configuration and earthing scheme. For a grid, different converter arrangements and earthing schemes can be considered. The choices made will influence how the grid will look like, the components in the grid and their rating, the operating principles, the protection philosophy, the degree to which the grid is extensible and the overall reliability and inherent redundancy. Clearly, it will influence investment and operating costs as well. This paper provides an qualitative overview of potential grid configurations for DC grids (symmetrical monopole, asymmetrical monopole, bipolar schemes, with and without metallic return and combined systems). The possible earthing options for a meshed HVDC grid are part of this discussion. The extensibility and reliability of the HVDC grid are specifically dealt with.