In order to improve the reliability and rapidity of single-end protection for bipolar HVDC transmission line

we proposed a transverse differential protection method. Firstly

the specific frequency harmonic current was selected based on the impedance characteristics of DC filter. Based on the equivalent harmonic calculation circuit for DC transmission system

the features of specific frequency harmonic currents and their transverse differential values during internal and external faults were analyzed subsequently. The results show that the minimum transverse differential value for internal fault is obviously higher than that of external fault

which is employed as a fault criterion to identify external fault from internal fault in this paper. In addition

the harmonic current on faulted line is significantly larger than that on non-faulted line

by which a pole selection method is proposed. Since 600 Hz current is used as fault criterion

a sample frequency of 2 k Hz will meet the requirements of the proposed protection. By employing the transverse differential method to achieve fault detection

the shortages that fault at DC line terminal and external fault cannot be identified by the traditional protections based on sing-end harmonic current are overcome. The simulation results show that the proposed protection scheme can identify internal and external faults reliably

and it is able to select the faulted pole. Moreover

the proposed protection scheme can also be applied in the situations with asymmetric operation modes.