Transient overvoltages on a three terminal DC transmission system due to monopolar ground faults

Transient overvoltages were investigated using the Electromagnetic Transients Program (EMTP) for a three-terminal DC transmission system. Pole-to-ground faults on a DC line were studied to investigate overvoltages on the healthy pole and also on the electrode lines. The effect of providing a metallic neutral conductor in one section of the three-terminal system was also studied, as was the sensitivity of the results to DC filter configuration and to neutral bus capacitance. It was found that the peak overvoltages for the DC line, especially near the converter stations, are sensitive to the DC filter configuration. The overvoltages near the converter stations were also found to be affected by the neutral bus capacitance