Performance of HVDC converter protection during internal faults

In this paper, an evaluation study of the behaviour of the overcurrent and differential relays of the HVDC converter during common internal faults is presented. The study is conducted via simulation of an HVDC converter using the electromagnetic transient program (EMTP). Rectifier misfire and backfire in addition to the inverter fire-through and different types of commutation failure are considered. Under these faults, the converter overcurrent and differential relay performances are computed. In addition, the computed results are corroborated using a laboratory scaled down model in conjunction with a DSP board-based overcurrent and differential relays. Delayed detection or complete blindness of these relays in detecting typical converter internal faults are recorded. Modification of the principle of the converter differential and overcurrent relays is a must