Study on the Overvoltage and Insulation Coordination of Yunnan-Guangdong ±800 kV UHVDC Transmission System

The overvoltage and insulation coordination of Yunnan-Guangdong ±800 kV UHVDC transmission system are studied with focus on the following subjects:the overvoltage in the island operation mode, the influence of different smoothing reactors arrangement, and the insulation coordination method for the UHVDC transmission system.Two schemes of arrester configuration are put forward in order to reduce the insulation requirement of the highest potential valve side of converter transformer.Meanwhile it is suggested that the switch impulse overvoltage level could be adopted as 1.85 p.u.for the middle section of the 10 km transmission line, and 1.70 p.u.for the other.By adopting appropriate configuration, the equipment insulation level of ±800 kV UHVDC pole line side can be limited to about 75% of the extrapolated value from 500 kV to 800 kV based on the linear relationship between the insulation level and the DC voltage.