On May 17, in Zhoushan, Zhejiang Province, the world’s first five-terminal flexible DC transmission project, Zhoushan five-terminal VSC-HVDC transmission project, is undergoing a complete overhaul for the first time after it was put into operation. Aeroamphibious intelligent equipment and advanced technology are used in this overhaul, in order to greatly enhance working efficiency by decreasing the overhaul duration in the converter station to 9 days, which took 15 days in the past.
It is reported that the overhaul is the largest after 10 years’ running. For example, in the Zhoudai converter station, the hub of 5 converter stations, the staff need to conduct an overall test on electrical equipment, like sub-modules, water cooling systems, wall bushings, and transformers, involving 8 working surfaces and over 210 items of inspection test in total.
Black technologies used by State Grid Zhoushan Power Supply Company help improve the quality and efficiency of this overhaul, such as the X-ray inspection device to check the integrity of the water electrode inside the water cooling system on the valve tower, the intelligent inspection UAV to check and accept the maintenance of the equipment in the high place of the valve hall, and the underwater robot to check the wear condition of the submarine cable in the intertidal zone and diagnose the health of the protective insulation layer outside the submarine cable.
Upon completion of the overhaul, the power supply reliability of the island grid in the north of Zhoushan will be significantly improved. At the same time, it will also provide an overhaul demonstration for other multi-terminal flexible DC projects in China.
Zhoushan five-terminal VSC-HVDC transmission project is the world’s first five-terminal flexible DC transmission project, as well as the flexible DC transmission project with the most terminals in the world.
The project was put into operation in 2014, including 5 converter stations called Zhouding, Zhoudai, Zhouqu, Zhouyang and Zhousi, with a DC interconnection network set up among the islands of Zhoushan through 283km DC submarine cables, realizing DC interconnection and energy interconnection among the power grids of several islands in the north of Zhoushan.
