Impact of the DC technology on transmission grids

This paper summarises some of the important challenges power transmission networks will be facing in the near future. Special focus has been laid on the operation of High Voltage Direct Current (HVDC) overhead transmission lines, which are expected to be used for extended parts of newly built HVDC transmission systems. As one of the most promising and emerging DC technologies, a Modular Multilevel Converter (MMC) based on Full Bridge technology has been described. Reference is made to the Trans Bay Cable project where the first pioneering Voltage Sourced Converter (VSC) realised as MMC HVDC technology has demonstrated its excellent performance of power transmission and power system strengthening. From a similar perspective, simulation results are presented showing the effects HVDC connections on the transmission grid of Germany. The simulations were carried out on the German transmission network modelled with an operation scenario for 2030. The paper concludes with an outlook on possible scenarios for the future HVDC Grid system developments in Europe, where protection philosophies and fault clearing mechanisms are expected to play a key role.