Ground electrode circuit protective system and device of high-voltage DC transmission system

The invention relates to a ground electrode circuit grounding protective system of a high-voltage DC transmission system. The system is provided with two parallel ground electrode circuits respectively connected in series with a high-voltage DC breaker, sets an allowable range of current differences of two ground wires and an allowable range of the subtraction of the line current sum of the two ground wires from the line current difference of the two ground wires and then sequentially executes the following control program: (1), reading currents of the two ground wires; (2), judging and comparing whether an absolute value of the current difference of two ground wires is larger than the allowable range thereof, if the absolute value is not larger than the allowable range, returning to the step (1); if the absolute value is larger than the allowable range, (3) then, judging whether the subtraction of the line current sum of the two ground wires from the line current difference of the two ground wires is smaller