Arduous Advance Actions Launch World's First ±800kV Multi-Terminal VSC-UHVDC Project for China Southern Power Grid

Lines of the Project over Bei River in Guangdong

The ±800kV Longmen Converter Station

Evening light tests at the ±800kV Kunbei Converter Station

The low-terminal converter valve hall at the Kunbei Converter Station

Debugging before operational at the control room of the Longmen Converter Station

“The debugging of the VSC-UHVDC line from Yunnan to Guangdong has been  completed and today the is placed into full operation,” so said the senior managers of the Wudongde Project (also the Kunliulong DC Project) in late July for this national key project for West-East Power Transmission, heavily invested by China Southern Power Grid which has exceeded all expectations by completing the bulk of the operation efforts in advance of looming deadlines.

This marks the first international “highway” for ±800kV multi-terminal VSC-UHVDC transmission … spanning more than 1,450 kilometers (in total) and covering the growing metropolitan areas of Yunnan, Guizhou, Guangxi and Guangdong.

This unique multi-terminal transmits abundant hydroelectricity from the Wudongde Hydropower Station - the world's seventh largest such facility - to the electric load center of the Greater Bay Area, significantly enhancing the economic development of this region while flushing it with green, renewable energy.

With an investment of more than 24.2 billion yuan, the project was launched in December 2018 and was slated to be placed into operation before the annual flood season (usually each April) of 2021.

It was the bi-polar low-terminal VSC-UHVDC from Yunnan to Guangdong that was placed into operation some 30 days ahead of schedule.

Speeding up the optimization of energy structure in five southern provinces

As part of the macro Kunliulong DC project, the Wudongde Hydropower Station, and other such similar stations, combine to play a unique joint effort in the transmission of electrical power from Yunnan to Guangdong and Guangxi. In total, CSG has built transmission lines from Kunbei Converter Station in Yunnan to Liubei Converter Station in Guangxi and Longmen Converter Station in Guangdong … and is thus correctly named “Kunliulong DC Project”.

This is significant as its operation will further optimize the energy structure of the five southern provinces and make significant contributions to building a stable and safe grid using renewable hydroelectric green energy for west-east power transmission.

Expanding the scale of this West-East Electricity Transmission Project Power Transmission Capacity (PTC) is like adding additional traffic lanes onto a superhighway which dramatically increases its capacity. The overall PTC is expected to reach 8GWh when the project is completed. By then, China Southern Power Grid's overall participation in the PTC for the West-East Electricity Transmission Project will exceed 58GWh as well as increasing the power capacity of 5GWh and 3GWh for Guangdong and Guangxi (respectively).

- Increasing the proportion of clean energy consumption

In Year 2019, the amount of power transmitted in the West-East Electricity Transmission Project was 226.5TWh … of which more than 80% was generated by clean renewable energy sources. When the project is complete, an additional 33TWh of clean hydropower-originated electricity will be transmitted from west China each year where it is also expected to reduce standard coal consumption by a substantial 10 million tons and eliminate carbon dioxide emissions by 26.6 million tons.

Among that total, some 20TWh will be transmitted to Guangdong, accounting for one fifth of Shenzhen's overall power consumption per annum. This will go a long way to help in the proper use of Yunnan hydropower and contribute to cleaner air and substantial reduction in air-pollution, aiding in energy conservation and lower emission pollutants throughout Guangdong and Guangxi, thus making the sky bluer, water cleaner and an overall improved environment quality.

- Promoting coordinated regional development opportunities

The project is also expected to lay a firm foundation for needed power supplies for the economic development of the Greater Bay Area and Guangxi throughout the 14th  Five-Year Plan period (2021 to 2025) and beyond. It will also serve to take advantage of Yunnan's numerous advantages in resources to boost its economy with the further development of clean, renewable green energy industries.

CSG breakthroughs in the untapped territory of VSC-UHVDC transmission with key technologies in hand

“This is a super important project which set new standards throughout the world and across the international community.” said Li Licheng, one of the academicians at the Chinese Academy of Engineering, adding “that it is put into operation in advance of its timeline indicates a huge cutting edge science advancement in China's HVDC power transmission technology. It creates a new mode of power transmission and provides experience for the world.”

To transmit power in massive large volumes over long distances with high utilization rates, and ensure the stability of the receiver system in Guangdong and Guangxi, in this project, CSG senior managers and engineers utilized the world's first multi-terminal LCC/VSC-UHVDC system, with LCC in the sender end and VSC in the receiver ends.

Mr. Li explained that when the project is completed, it will win more than 10 FIRSTs throughout the international community, including the first ±800kV multi-terminal VSC-UHVDC project, the VSC-UHVDC with the largest capacity in one single station and the first VSC-UHVDC project which can clear faults in aerial lines and restart automatically.

Rao Hong, Chief Technical Expert of China Southern Power Grid and Board Chairman of SEPRI said, “We are the first to develop the VSC-UHVDC and multi-terminal LCC/VSC-UHVDC system, which will significantly improve the safety and stability of the macro power grid, utilizing the latest technologies will make the grid more flexible and reliable with substantial contributions to the West-East Electricity Transmission Project”.

However, behind the FIRSTs are the lack of equipment sets and many other challenges to the operation mode as all CSG engineers and researchers have been diligent in the fight to make breakthroughs in key technologies for several years in this unknown territory.

Engineers from China Southern Power Grid have also met a series of challenges head on regarding the development of key equipment and technologies including the topological structure of VSC-UHVDC, power system control and protection, IGBT components and VSC-UHVDC transformers by integrating the technical force of SEPRI and CSG EHV Power Transmission Company and cooperating with China's research institutes, universities and equipment manufacturers.

Since the proposal of the project, the research and engineering teams have made several breakthroughs in the VSC-UHVDC, multi-terminal UHVDC system, equipment manufacture, testing, installation and operation … combing to solve a set of very detained challenges using cutting-edge solutions at the highest international standards.

For example: The VSC-UHVDC converter valve is among the most crucial equipment, known as the “heart” of the project. Today, the world's first “heart” that can carry an ultra-high voltage of ±800kV has been exclusively developed by CSG engineers and “beats” powerfully within the center of the Longmen Converter Station.

Some of the most advanced technologies will be applied to the construction of CSV-HVDC international projects and become showpieces for the electrical industry worldwide.

While racing against time, both the supply and industrial chains made significant contributions

The construction of the Kunliulong DC Project was extremely challenging. The average elevation of the transmission lines is 1,300 meters. 54.6% of the area that the lines has to span are mountainous with another 10.5% experience heavy ice during fridge winter months.

In total, the lines spans across railways, navigable rivers, roads and important power lines more than 2,690 times.

For a project of this magnitude, China Southern Power Grid engineers constructed  a large-span converter valve hall for VSC-UHVDC, with the largest roof grid in the history of power construction. In addition, CSG senior managers and staff had to overcome numerous setbacks occurring from natural disasters such as continuous heavy rain along the lines.

“The sudden COVID-19 outbreak was a serious pause to the construction, making it more difficult to advance the project along our set timelines.” said Tang Shouquan, president of CSG Infrastructure Department. Upon resuming work in March, CSG engineers set up a “Project Headquarters” to confront important issues and serve to manage the projects' progress via "cloud monitoring".

Engineers from the CSG EHV Power Transmission Company sped up many key  elements of the project; Yunnan Power Grid Company partly put into operation the supporting project for AC transmission from the Wudongde Hydropower Station in advance of schedule, thus enabling the testing and advanced operation of its first batch of generation sets; engineers from the Guangdong and Guangxi Power Grid Company constructed the supporting AC project and power receiving lines; and engineers from the Guizhou Power Grid Company coordinated allocated resources along the lines.

Driven by immensity of the project, companies up and down the power industry chain reached the target output after work resumed from the COVID-19 shutdown, including those companies who provide raw materials, power equipment, power electronic devices, design, construction, monitoring and testing.

The number of suppliers for the converter station alone was more than 165.

During the busiest period, more than 11,000 staff and engineers were dedicated to work on the project, an increase of more than 20% than originally scheduled. It also employed a large number of people along the lines, giving vital employment and work benefits from impoverished households.

After a five-month construction period with the combined efforts of more than 10,000 staff, during the middle of a global pandemic, the project was partly put into operation in advance of schedule.

“We will continue to make persistent efforts to appropriately speed up our construction to fully put the project into operation, on time, before the flood season arrives next year.” said Mr. Tang.