In order to deal with the problems of long-distance large-scale offshore wind power transmission, VSC-HVDC transmission system has been gradually applied to the integration of renewable energy power plants. In the case of an AC fault occurring at the sending end of the VSC-HVDC system, the short-circuit current on both sides of the AC line is provided by the power electronic converter. There is a fundamental change in the fault characteristics of the system. The change of fault characteristics will directly lead to the degradation of traditional protection performance, or even incorrect operation. The security of transmission system operation is thus challenged. Therefore, this paper studies the topology of the VSC-HVDC transmission system connected to the inverter-interfaced wind farms. To confirm the applicability of the linear analysis method, the characteristics of the AC side fault at the sending end are analyzed. Combined with different fault-ride-through control strategies, the analytical expression method of the converter short-circuit current is derived. Theoretical analysis shows that the short-circuit current is only provided by the flexible DC converter, and the short-circuit current has limited amplitude, even lower than the rated current. In the case of the normal output of wind farms, both the flexible DC converter and the wind farm provide short-circuit current, and their control objectives are different. Therefore, there must be a phase angle difference between the two sides of the same phase short-circuit current. Based on the study of fault characteristics, a performance analysis of common protection is carried out. It is known that the performance of line distance protection and differential protection will decline. The refined model of a VSC-HVDC transmission system connected to wind farms is established in PSCAD. The simulation results verify the correctness of the analysis. It provides a theoretical basis for protection configuration and novel protection research. This work is supported by the National Natural Science Foundation of China (No. 51725702 and No. 51777071) and “Special Project on Offshore Wind Power and Smart Energy System Technology (Phase I)” of Science and Technology Project of the Headquarters of China Huaneng Group Co., Ltd. (No. HNKJ20-H88).