Insulation Coordination of ±1 000 kV/± 100 kV UHVDC Converter Stations

The study result on insulation coordination of ± 1 000 kV and higher voltage grade ultra-high voltage (UHV) DC converter stations is presented. Aiming at the ± 1 000 kV UHVDC system, influences on arrester configuration and converter transformers insulation levels of converters 'connections are discussed based on three schemes of serial converters structure: 500 kV+500 kV scheme, 667 kVq-333 kV scheme and 400 kV+400 kV+200 kV scheme. Comparing with the 500 kV+500 kV scheme, the 667 kV+333 kV scheme cannot reduce the maximum insulation level significantly and would bring problems to valve hall layout and operation controlling. The 400 kV+ 400 kV--200 kV scheme has no economic advantage as it increases land occupation and amount of equipments. According to comprehensive comparison, the 500 kV + 500 kV scheme is recommended for ±1 000 kV UHVDC projects, and it is also suitable for higher voltage grade DC systems. According to system conditions of 1 100 kV, the switching impulse withstanding level (SIWL) of 2 100 kV and the lightning impulse withstanding level (LIWL) of 2 350 kV are feasible for ± 1 100 kV UHVDC project, judging from the insulation levels. Meanwhile, arresters with higher performance are needed.