Fault-Type Discrimination in HVDC Transmission Lines Using Rate of Change of Local Currents

A simple and yet dependable technique for fault-type identification in HVDC transmission systems is presented in this paper. A set of indices is defined for pairs of rate of change of current measurements to identify the pole(s) involved in the fault to discriminate the ground faults from those involved with the dedicated metallic return conductor. The proposed fault discrimination method will identify the faulty pole within a 1-ms window, and therefore, it can be used to improve the sensitivity and reliability of DC fault protection. Furthermore, the knowledge-whether or not the dedicated return conductor is involved in the fault-is useful for determining the post-fault configuration of bipole grids. Considerable discrimination margins are observed during the rigorous evaluation of the technique for two-conductor and three-conductor HVDC systems under various fault scenarios, for both considerably long overhead transmission lines and cables. The indices can be computed using local current measurements made using low-bandwidth sensors. They are independent of the fault resistance, and therefore, settings can be found easily.