Sichuan power transmission "new three direct" ultra-high voltage is accelerating

So far, the main channels for hydropower transmission in Sichuan include the ±800 kV Fufeng, Jinsu and Binjin UHV DC transmission lines, plus the ±500 kV Debao DC, the Sichuan-Chongqing 6-circuit 500 kV AC lines and the Sichuan-Tibet interconnection project (2-circuit), Sichuan's hydropower transmission capacity is about 30 million kilowatts. With the Yalong River Middle Reaches Hydropower Station, Baihetan Hydropower Station and other power stations coming into operation in the future, Sichuan's hydropower transmission urgently needs new transmission channels.

In this regard, the State Grid Sichuan Electric Power Company recently held a press conference to meet the peak summer demand and revealed that from the second half of this year to the beginning of next year, the construction of the ±800 kV UHV DC transmission projects of Yazhong-Jiangxi, Baihetan-Jiangsu, and Baihetan-Zhejiang will start. Currently, the preliminary work of the "new three direct" UHV is underway. It is also reported that with the recent commissioning of the Chongqing-Hubei DC back-to-back interconnection project, the structural risks brought by the "strong direct current and weak alternating current" of the UHV power grid will be effectively reduced, and Sichuan's hydropower transmission capacity will be improved.

Baihetan-Jiangsu UHV

Supporting line relocation completed

On June 14, with the resumption of power transmission of the 500 kV Douchang 5267 and Shanchang 5232 double lines, the "hard battle" of the Baihetan-Jiangsu UHV DC receiving-end supporting line relocation project was completed. This is a microcosm of the early work of the Baihetan-Jiangsu UHV DC project accelerated by various regions.

The Baihetan-Jiangsu UHV DC project is a key project listed in the national "13th Five-Year Plan for Energy Development" and "13th Five-Year Plan for Electricity Development", and is scheduled to be completed and put into operation in June 2021. Since the receiving end Changshu converter station is located close to the east side of the Changshu 500 kV substation, it will occupy the existing 220 kV Shanghu-Changshu North double-circuit, 500 kV Zhangjiagang-Changshu North double-circuit, Dousan-Changshu South double-circuit and Luqiao-Changshu South single-circuit line corridors, so the line must be relocated.

It is understood that as the world's second largest hydropower station after the Three Gorges Project, the Baihetan Power Station with an installed capacity of 16 million kilowatts was approved for construction in July 2017. The first unit is scheduled to be put into operation in June 2021, and all units will be completed and put into operation by the end of 2022. Therefore, in order to ensure the transmission and consumption of the power station, the National Energy Administration issued the "Notice on Accelerating the Planning and Construction of a Batch of Key Transmission and Transformation Projects" (hereinafter referred to as the "Notice") in September last year, which clearly stated that two ±800 kV UHV DC transmission projects will be built, and the left and right bank hydropower of Baihetan will be sent to Jiangsu and Zhejiang respectively.

It is also reported that the Baihetan-Jiangsu UHV will innovatively adopt hybrid cascade multi-terminal flexible DC technology. Among them, the hybrid cascade means that the sending end adopts traditional DC and flexible DC technology based on voltage source control, and the multi-terminal flexible DC means that the receiving end applies multi-terminal flexible DC technology, which has the advantages of good compatibility and high reliability.

In addition, all feasibility study work for the Baihetan-Zhejiang UHV DC project is also being actively promoted.

Ya'an-Jiangxi UHV DC

Landing place: Fuzhou, Jiangxi

Recently, the preliminary approval and reporting work of the Guizhou section of the ±800 kV Yazhong-Jiangxi UHV DC transmission project, which is undertaken by Sichuan Electric Power, has been completed. All 373 documents involving the governments and land departments above the county, city and prefecture level in Guizhou have been received and funded, marking that the project has fully completed the approval and reporting of the five provinces along the line (Sichuan, Yunnan, Guizhou, Hunan, and Jiangxi) and entered the national approval procedure. This shows that this is the fastest-progressing project among the "new three direct" UHV transmission projects of Sichuan hydropower.

The project has a transmission distance of 1,711 kilometers and a total investment of 24.8 billion yuan. In order to meet the electricity demand of Sichuan hydropower transmission and Jiangxi and other central China regions, and optimize the national energy layout, according to the "Notice", the project will be located in Nanchang, and supporting the construction of Nanchang-Wuhan and Nanchang-Changsha ultra-high voltage AC projects. According to the "Yazhong-Jiangxi ±800 kV UHV DC Project Environmental Impact Report (Draft for Approval)" recently announced by State Grid Corporation of China, the sending-end converter station of the project is located in Yanyuan County, Liangshan Prefecture, Sichuan Province, and the receiving-end converter station is located in Dongxiang District, Fuzhou City, Jiangxi Province. In this regard, industry insiders said that the two million-kilowatt units of Datang International Fuzhou Power Generation Company will play an important role in the future safe and stable operation of UHV into Jiangxi and UHV interconnection in Central China.

Chongqing-Hubei DC back-to-back interconnection

Effectively solve the problem of abandoned water in Sichuan

On June 12, the National Energy Administration held a special meeting in Beijing on the safety of the Chongqing-Hubei DC back-to-back interconnected operation, requiring that the project be put into operation smoothly and that the power system operate safely and stably after the project is put into operation.

It is understood that the Chongqing-Hubei back-to-back project has built two new DC back-to-back converter stations in Yichang and Enshi. The Yichang converter station is located on the northern channel of the 500 kV interconnection line between Chongqing and Hubei, in Yiling District, Yichang City, Hubei Province, and is equipped with 2×1.25 million kW flexible DC units with a rated DC voltage of ±420 kV and a current of 1,500 A; the Enshi converter station is located on the southern channel of the 500 kV interconnection line between Chongqing and Hubei, in Xianfeng County, Enshi Prefecture, Hubei Province, and is equipped with 2×1.25 million kW flexible DC units with a rated DC voltage of ±420 kV and a current of 1,500 A.

The Sichuan Power Grid's press conference on peak summer demand revealed that after the Chongqing-Hubei DC interconnection, the transmission capacity of Sichuan's major hydropower channels will be effectively released. It is expected that after the Shujing third line and the Ya'an transmission reinforcement project are put into operation, the overall transmission capacity of the hydropower channels will be increased by about 6 million kilowatts. At the same time, the maximum transmission capacity of the Sichuan-Chongqing section can be increased by about 1 million kilowatts.

In addition, the back-to-back direct current between Chongqing and Hubei will realize asynchronous interconnection between the power grids of Sichuan and Chongqing and the power grids of the four provinces in central China. Especially with the start of the "new three direct" ultra-high voltage, it can fundamentally solve the stability problems existing in the 500 kV cross-regional long-chain power grid, effectively reduce the structural risks brought about by the "strong direct current and weak alternating current" of the ultra-high voltage power grid, simplify the power grid safety and stability control strategy, and improve the flexibility and reliability of power grid operation.