Novel scheme of travelling wave based differential protection for bipolar HVDC transmission lines

In this paper, the traveling wave based differential protection for HVDC transmission line is proposed, in which the backward traveling waves in mode 1 are employed to establish the traveling wave based protection, at the same time the zero-mode current detector is utilized to determine that which is the faulty line for bipolar HVDC lines. The operating traveling wave is the differential of the backward traveling wave between two terminals, at the same time the sum of the two traveling waves multiplied a factor as the restraint wave. The entire protection scheme is simulated in PSCAD/EMTDC associated with the typical ±500kV HVDC transmission system supplied by Cigre. The simulating results show that the new protection has the advantages of higher sensitivity, reliability and security. The maximum fault resistance can be overcame by the new differential protection increases to 500 Ohm, in addition, the discriminative results are correct in arbitrary conditions, such as, various fault location of internal fault, the DC bus fault, the AC system fault, etc.