System integration aspects of DC circuit breakers

Currently, most of the voltage sourced converter (VSC) based high voltage direct current (HVDC) projects are point to point cable connections. However the market for VSC based HVDC projects using overhead lines is expected to grow rapidly in the near future. Depending on the requirements for DC fault clearing and grid topology there are different protection concepts for these HVDC applications. The application of full bridge technology or the application of DC circuit breakers (DCCB) are the main approaches being discussed today for providing a fast DC fault clearing with auto-reclosure. The main focus in this study is on the protection of HVDC systems by means of DCCBs and the challenges being faced with this approach. The first part of the study focuses on the description of hybrid DCCBs for the application with half bridge converter technology. The second and main part of the study presents the factors influencing the design of the DCCB: AC network, travelling waves, DC reactor and DC line inductance. The results from the given examples confirm the wide range of the energy to be absorbed (5.3 up to 50 MJ!) and the significant impact that these factors can have on the design of the DCCBs.