Selection of fault discriminators for unit protection of monopolar HVDC transmission system

Abstract

For bulk power transmission over longer distances, line commutated converter based HVDC technology is widely used. Protection systems currently used for HVDC line protection need further improvement in terms of sensitivity, speed and reliability. This paper presents a study of the response of HVDC system on occurrence of faults at different locations along the length of the line. The response has been analyzed in terms of change in voltage, current, power, impedance and transient energy measured at both the ends of the line. The study has been done by simulating a 500 kV LCC based monopolar HVDC system using PSCAD/EMTDC. Critical analysis of these variables shows that the changes in current, power and transient energy measured at the two ends of the dc transmission line are well suited as fault discriminators for unit protection of monopolar HVDC transmission system.