Due to the small system inertia and fast fault growing speed of DC transmission system, and there is no zero cross point for DC current, demands from DC transmission system on the breaker’s ability are rigorous. Based on the upcoming DC circuit breaker installation project for the Nan’ao three-terminal VSC-HVDC system, the world’s first mechanical DC circuit breaker for engineering application is researched. New control and protection strategies for the VSC system with DC circuit breaker are analyzed, some functions such as online opening/closing operation and fault isolation are added. Real-time simulation test is conducted by connecting the physical controller and protection devices to the simulation testing platform, and a series of tests on system characteristics and control-protection strategies are carried out. Typical faults in Qing’ao station are analyzed. Results show that by installing the DC circuit breaker, faults on Qing’ao station and Qinghui line (from Qing’ao station to Jinniu station) can be effectively isolated and tripped, while the other two stations are not affected. The paper provides a theoretical and experimental basis for drafting on-site project commissioning scheme. Futuremore,artificial negative pole to ground fault is also tested on site during commissioning, which fully verifies the reliability of DC circuit breaker in tripping a DC fault.