Effect of converter DC fault on the transient stability of a Multi-Machine Power System with HVDC transmission lines

This paper deals with the effect of DC faults on the transient stability of a multi-machine power system with two transmission line configurations; HVDC and a hybrid HVAC-HVDC transmission line. The faults are located at the DC terminals of the HVDC converter station. In order to carry out this study, two case studies are presented. In the first case study a double HVDC transmission line is used to transmit 2000 MW to an area of the power system called Pookland which has a total load demand of 2440 MW. In case two, a parallel hybrid HVAC-HVDC transmission line is used to transmit the same amount of power to Pookland. In both cases, the impact of a short term converter DC fault on the transient stability of the entire system was investigated. This was done by studying the response of the rotor angle of G2 in Pookland, G3 in the Bing Coal plant and the voltage profile at the terminals of the generators to the DC fault at the HVDC converter station. Amongst other results, it was established that in case 1 which has a double HVDC transmission line, the rectifier side (in the Bing coal plant) has less rotor angle oscillations when compared to the inverter side (in Pookland), but the rectifier side took longer than the inverter side for the rotor angle of the generators to stabilize. In case 2, the voltage at G2 in Pookland took six times the amount of time it took G3 in the Bing coal plant to stabilize while the voltage in the Bing Coal plant dipped by 0.35 pu (smaller than case 1 which dipped by 0.4 pu). In conclusion, the converter DC fault had a smaller impact on the transient stability of the multi-machine power system when the hybrid HVAC-HVDC transmission line was adopted.