Fault detection and protection of modular multilevel converter high voltage direct current (MMC-HVDC) power grids constitute a critical technology within the domain of electric power systems. When the DC power grid fails, equipment damage is caused and grid stability is jeopardized by the rapid escalation of fault currents. Consequently, extremely high requirements are placed on the rapidity and reliability of the fault protection system. By comparing the changes in the voltage value of the current limiting inductor on the line before and after the fault, a method for identifying line faults using the voltage ratio of the current limiting inductor is proposed. The proposed method is validated using a four-terminal MMC-HVDC power grid model constructed on the PSCAD/EMTDC simulation platform. The validation encompasses fault initiation, type identification, and pole selection. Through accurate fault identification, the appropriate DC circuit breaker (DCCB) is activated to isolate the fault effectively. Additionally, feasibility analysis is conducted on system performance metrics along with four critical factors: fault transition resistance values, post-fault noise interference, fault location variations, and communication error impacts. The final research outcomes demonstrate that the proposed fault protection scheme can accurately detect and rapidly isolate faults, thereby safeguarding the stable operation of the power grid.