Residual current protection system of unipolar direct current power transmission system

The invention provides a residual current protection system of a unipolar direct-current power transmission system. A direct-current bus of the unipolar direct-current power transmission system comprises a positive line and a negative line. The residual current protection system comprises an alternating signal generator and a residual current protection device. And the alternating signal generator is used for injecting an alternating signal to the direct current bus through the capacitor when the direct current bus has insulation failure. And the residual current protection device is connected to a direct current branch of the direct current bus and is used for cutting off the direct current branch due to induction of the alternating signal when the alternating signal generator injects the alternating signal into the direct current bus. According to the invention, direct-current residual current protection can be carried out in time when the direct-current bus of the single-pole direct-current power transmiss