Luxi Back-to-Back DC Asynchronous Interconnection between YPG and CSG Main Grid Starts Operation

On June 30, the conventional DC unit of the project of Luxi back-to-back DC asynchronous interconnection between Yunnan Power Grid (YPG) and CSG main grid (hereafter referred to as Luxi back-to-back DC project) was completed and put into operation, marking the first successful asynchronous interconnection between provincial and regional power grids. Once in operation, the project can efficiently improve the stable and safety operation of CSG’s main grid, promote the consumption of clean energy and reduce the electricity loss caused by water releasing by more than 2 billion kWh annually during the flood season in Yunnan Province. In order to accomplish such a heavy task in a tight schedule, CSG organized scientific construction and put it into operation in just 11 months, breaking the record of shortest DC project construction period. This project is also a special tribute for the 95th anniversary of the founding of the Communist Party of China.

New “Firewall” Helps Safeguard Grid Security

The back-to-back DC project combines together two convertor stations, a rectifier and an inverter, without DC lines in between. Xu Shukai, Deputy Director of the DC Transmission Division of CSG Electric Power Research Institute, said, “Imagine when a military camp is on fire. If a “firewall” is added between barracks, the fire in one camp will not spread to another. Thus, the security of grid operation can be improved.”

Standing in the Luxi convertor station, one can see clearly that it connects CSG main grid on one end and YPG main grid on the other end. This is the “firewall”.

By building two convertor stations into one, the back-to-back DC project is aimed to improve the security and reliability of the grids. “To date, CSG has completed 17 west-east electricity transmission channels, among which the maximum transmission capacity reaches 39.5 GW. The larger the transmission volume, the longer the distance, the more complicated the grids will be. Faults emerging at any part may affect the rest.”

Lead and Improve China’s VSC-HVDC Equipment Manufacturing

Though it’s just a convertor station, without precedent all the technologies are developed independently, creating many “firsts” in the world.

Ren Chenglin, Manager of Asynchronous Interconnection Project at CSG EHV Power Transmission Company, said, “One of the firsts is that it operates the conventional and VSC-HVDC units in parallel connection for the first time. Another is that the capacity of a VSC-HVDC unit reaches 1000 MW and its DC voltage is as high as ±350 KV. Both the capacity and voltage are the highest in the world. It is reported that Luxi back-to-back DC project is the first one that adopts the mode combining high-capacity VSC-HVDC and conventional DC. And the VSC-HVDC part, planned to be put into operation on August 30, is right under installation and debugging.”

“When I heard that Europe had developed asynchronous interconnection technology, I was amazed. But just a few years from then we also have our own. The VSC-HVDC technology is the most advanced, and all the technologies and equipment are developed and manufactured in China. Even visiting foreign experts are surprised at our fast speed. I am extremely proud of that.” Ren Chenglin introduced.

Because the high-capacity VSC-HVDC technology is adopted for the first time and the major equipment such as VSC-HVDC converter valve and valve controller are first developed domestically, there is no previous experience to follow. Besides, faced with such a short production period, a mount of technical problems are to be tackled. To ensure the equipment quality and project progress, CSG managed the entire process and every step comprehensively, from the compilation of technical specifications, tender and procurement, quality control contract to transportation of bulky items. During the process it monitored the quality strictly from the source of raw materials to the control of production techniques.

The project director observed that the project can not only promote the development and innovation of the packaged design, experiment of high-capacity VSC-HVDC technology and equipment manufacturing but also enhance China’s capabilities in this sector. It is leading the development direction of the world’s DC transmission field.”