Testing of protection schemes is important before it can be used for an actual topology. Nowadays, DC protection has not readily been designed and implemented in power systems. Therefore, due to high requirements on DC fault interruption, the designing and testing the corresponding DC protection with the use of a DC circuit breaker (DCCB) becomes a challenge. In this thesis, a four-terminal meshed VSC-MMC HVDC system is developed in RTDS environment. Diverse fault tests, concerning different fault types, fault locations and fault impedances are conducted in a remote testing way. The MATLAB-based testing controller by a remote computer will command the local computer and the RTDS-modelled system through the communication network, in order to automatically run all test scenarios and do data processing. The related testing results demonstrate the DC fault dynamics in an effective way in order to test DC protection. In order to do this a refined DCCB model has been developed.