At present, the related research on the internal overvoltage of the power collection system is mostly about the offshore wind farms connected to the grid through high voltage AC transmission lines, but the far-offshore wind farms that are connected to the grid through voltage source converter based high voltage direct current (VSC-HVDC) transmission are not paid enough attention. Therefore, the electromagnetic transient models of the power collection system and the VSC-HVDC transmission system are established, and the characteristics of overvoltage under three typical working conditions of grid connection, load shedding, and three-phase ground short-circuit faults in the power collection system are analyzed. It is found that the overvoltage caused by the three-phase ground short-circuit fault at the bus and its adjacent feeder port is the most serious, which poses a challenge to the insulation of the generator-terminal transformer and the VSC-HVDC transmission line, and triggers the disconnection of all the wind turbine generators from the grid. Therefore, a suppression measure that configures surge arresters at key nodes and improves the control strategy of offshore converter stations during faults is proposed, which reduces the amplitude of transient overvoltage significantly. As a result, the influence of overvoltage is controlled within the wind farm where the fault occurs, and the large-scale disconnection of wind turbine generators from the grid is avoided effectively.