Progressive Fault Isolation and Grid Restoration Strategy for MTDC Networks

A multiterminal de (MTDC) grid has a number of advantages over traditional ac transmission. However, de protection is still one of the main technical issues holding hack the expansion of point-to-point de links to MTDC networks. Most de protection strategies are based on de circuit breakers; however, DCCBs are still under development and their arrival to the market will come at an unclear time and cost. Conversely, ac circuit breakers (ACCBs) are readily available and represent a more economic alternative to protect dc networks. Following this line, a protection strategy for MTDC grids is proposed in this paper. This uses ACCBs for de fault current clearing and fast de disconnectors for fault isolation. The faulty link is correctly discriminated and isolated while communication links are not required. This strategy contributes to a reduced network outage period as the nonfaulty links are out of operation for a relatively short period of time and are restored in a progressive manner. The effectiveness of the proposed strategy is tested in PSCAD/EMTDC for pole-to-ground and pole-to-pole faults.