Lightning protection of 500-kV DC gas-insulated lines (GIL) with integrated surge arresters

A 500-kV dc hybrid transmission line consisting of a gas-insulated line (GIL) with lengths up to 10 km connected at both ends to long overhead lines is applied for lightning overvoltage studies. For this system, the conventional application of external surge arresters results in high electrical stress on the insulation of GIL. Therefore and because of the modular structure of GIL, the application of internal surge arresters and two combinations of external and integrated surge arresters are investigated. The influence on the voltage buildup in GIL of variation in the position of integrated surge arresters is explained and the best positions are calculated by a sensitivity study. All variants of the application of integrated surge arresters result in a reduction of voltage stress within the GIL compared to the conventional application of external surge arresters.