New Approach to SF6 Gas Insulated HVDC Converter Station

Compressed SF6 gas insulation will give a promising way to obtain a reliable, compact, and economical converter station for HVDC transmission. Some of the outcomes of a project in which we have developed a metal enclosed converter station are presented in the paper. Thyristor valves, metal oxide surge arresters, DCCT, PT´s, switchgears, connecting-buses, and other components in a converter station have been developed. All of these equipment have been subjected to a long term voltage endurance test at 1.3 pu of their rated voltage at ±125 kV. A control and protection system has also been developed. Fundamental control function has been digitalized to secure reliability, accuracy and flexibility of the dc plant control. A 9.6 MW back-to-back miniplant rated at 16 kV, 600 A has been constructed to gain an operational experience of the new gas insulated converter station. In spite of the rated voltage of the system, all the equipment in the system is rated at 125 kV line to ground voltage and stressed at the voltage using a separate dc bias voltage source. Based on the experiences obtained in the project, a conceptional design of a ±500 kV 5 GW converter station will also be discussed. Technical feasibility and benefits of introducing the gas insulation, metal oxide dc arresters and digitalized control have been investigated through the development of the full scale dc equipment rated at 125 kV and a 9.6 MW back-to-back miniplant which is fully gas insulated and controlled by the digitalized scheme.