Improved Relay Algorithm for Detection and Classification of Transmission Line Faults in Monopolar HVDC Transmission System Using Signum Function of Transient Energy

Based on the signum function (sign of magnitudes) of transient energy, this paper proposes a fault classification approach and algorithm for a monopolar HVDC system. The analytical study here shows that the signum function of variation in transient energy has a zero value individually at both ends on no-fault conditions. Moreover, the summation of the signum functions computed for internal DC faults is zero, whereas the same has a non-zero value for external AC faults. The performance of the proposed algorithm has been extensively evaluated by simulating faults on a CIGRE benchmark system for HVDC monopolar configuration using EMTDC/PSCAD software. Three locations of DC line fault, and AC fault at the two ends of the system have been considered for this evaluation. Five fault resistance values (0, 10, 100, 1000, and 2000 ohms) have been simulated for each fault location. The results conform with the theoretical analysis, and the fault classification by the algorithm is 100% accurate. The time taken to detect and classify a DC fault at the mid-point of the 800-km line is 1.5 ms, and that for line-end faults on the DC line is 3 ms for all values of fault resistance. These results show a marked improvement over those reported earlier in the literature using other techniques. A comparison table is given in the last section to corroborate it.