OREANDA-NEWS. August 22, 2014. Flexible DC Transmission Project with the World's Highest Voltage, Most Terminals and Largest Single-terminal Capacity.
 
On July 4, the science and technology demonstration project of Zhejiang Zhoushan ±200kV five-terminal flexible DC transmission was officially put into operation, which featured the highest level of voltage, largest number of terminals and biggest capacity for single terminal among world's multi-terminal flexible DC transmission projects. It represents China's leading position in the field of flexible DC transmission technology in the world and ensures strong power supply for the rapid development of the new district in Zhoushan Islands, the first national new district with the theme of marine economy.

This project was officially approved by Zhejiang Development and Reform Commission on December 14, 2012 and began construction on March 15, 2013. Five convertor stations of Zhouding, Zhoudai, Zhouqu, Zhousi and Zhouyang were constructed with a total capacity of 1GW. A 141.5km ±200kV DC transmission line was newly built, among which, undersea cable reached a length of 129km. A 31.8km AC transmission line was newly built and an auxiliary marine power transmission test and inspection base was built. The project owner is SGCC Zhejiang Electric Power Company, and the chief contractor is the combo of China Electric Power Equipment and Technology Co., Ltd and Beijing Grid Connection Direct Current Engineering and Technology Co., Ltd.

At 10:06 on July 4, after the five-terminal system had been operating for 168 hours' trial at a transmission capacity of 200MW, SGCC Deputy Chief Engineer Wang Yimin announced the official launch of the project in the central control of Zhoudai convertor station. The completion and operation of Zhoushan flexible DC project has brought the technological advantage of flexible DC transmission in island power supply into full play, demonstrating SGCC's technological innovation ability, signifying a new stage for SGCC's R&D capacity in high-end smart grid equipment and realizing the dream of "Made in China" and "Led by China"

Flexible DC transmission technology is a new-type DC technology based on gate-turn-off semiconductor device IGBT (insulated gate bipolar transistor). It has strong technological advantages in improving power system stability, dynamic reactive power repertory, power quality, system's accommodating capability of clean energy, and distribution grid's reliability and flexibility. It is also environmental friendly with less land use and little environmental impact. As an important technology to construct the smart grid, it can be applied to grid connection for clean energy such as solar power, power supply for isolated islands (passive load), and power supply for large cities. The multi-terminal flexible DC transmission is a significant technological breakthrough on the basis of double-terminal flexible DC transmission technology. It can get power from multiple sources and supply power to multiple places by constructing a multi-terminal flexible DC system, adopting 3 convertor stations or more and connecting them using various methods.

Flexible DC transmission technology is an important direction for the future power and electric technology development and is highly emphasized by countries around the world. European and American countries are actively promoting the key technology research on flexible DC transmission and project construction. SGCC is the first corporation in China that acquires key technologies of flexible DC transmission. Through the construction of Zhoushan multi-terminal flexible DC Demonstration Project, SGCC has comprehensively acquired the set design for system digital simulation, convertor electrical design, equipment parameter selection, and coordination control protection strategy. Breakthroughs have been achieved in HV large-capacity convertor valve and HVDC submarine cable. The company successfully developed flexible DC convertor valve with the largest capacity and DC submarine cable with the highest voltage in China, and accomplished system test despite of many core technical difficulties in dynamic simulation experiment and joint operation and commissioning of the multi-terminal flexible DC control protection system. 

Based on the advantage of multi-terminal flexible DC transmission technology in island power supply, SGCC decided to implement the demonstration project in Zhoushan to actively serve the development of the new district in Zhoushan Islands. As the project owner, SGCC Zhejiang Electric Power Company has taken full advantage of its successful experience in UHV project, overcome many difficulties such as complicated environment in construction area and twists and turns in equipment commissioning, and accomplished the project construction with high quality after keeping fighting for 10 months together with the chief project contractor and many participating companies.

The successful operation of Zhoushan Multi-terminal Flexible DC Transmission Project has realized the flexible conversion and inter-allocation of power among islands in north Zhoushan and provided strong power guarantee for the development of new district in Zhoushan Islands. Meanwhile, this project will remarkably increase the overall technological content in China's power grid, improve the international competitiveness of China's DC transmission industry, and produce great demonstration effects on the large-scale popularization of flexible DC and marine power transmission technology in China.