The Cabora Bassa D.C. Transmission System: Overvoltage Protection and Insulation Coordination

The Cabora Bassa-Apollo HVDC Transmission is the first UHV dc long distance transmission system using thyristor valves. The overvoltage protection and insulation co-ordination for the terminal stations of this systemaredescribed. It is shown, how the specific requirements of the thyristor valves for strict and reliable overvoltage protection have been solved by direct surge arrester protection with reasonable insulation levels of the valves and the other HVDC station equipment. The selection of post and suspension insulators used in the d.c. section of the HVDC station, which is fully outdoor, is described as well.