Forward Fault Identification Element based Transient Power for DC line Protection in UHVDC System

DC line fault is a major threat to the Ultra High-Voltage Direct-Current (UHVDC) system in terms of reliability, since the long-distance bulk-power is involved. This paper proposes a forward fault identification element for DC line protection in the UHVDC system. The forward fault identification element is based on transient power (TP), which is defined as the product of transient voltage and transient current within specific frequency band. Since the DC line attenuation characteristics is fully considered, the forward fault identification element is able to detect the fault along the whole long line from forward external fault. A fault pole selection criterion based on transient power is also proposed. If a directional element is employed, a quick and reliable protection scheme can be formed. The proposed forward fault identification element is able overcome the problem of attenuation effect of long DC line suffered by the some conventional protection methods. Simulation studies carried out in PSCAD/EMTDC and the test with field fault-recording data have validated the effectiveness of the proposed forward fault identification element and fault pole selection criterion.