HVDC transmission lines have been used to exchange bulk power across long distances. A future dc network or meshed grid can be imagined from the benefit found with the HVDC lines. The development of the future dc grid will require additional devices capable to adapt the voltage level or grounding strategies between portions of the aforementioned grid. These devices are dc-dc converters. This paper presents the flexible dc-MMC interconnecting a bipole and a symmetric monopole. The converter is tested in a detailed simulation including the cable, average ac-dc converters models, fault detection strategy, and detailed converter sizing. The simulations include normal and fault operation to evaluate their impact on the system. The simulation results show that the flexible dc-MMC can isolate a fault without triggering the healthy parts of the system, providing also the possibility to exchange power after the fault clearance.