On December 27, 2024, China's first high-altitude ultra-high voltage (UHV) alternating current (AC) project – the Sichuan-Chongqing 1000 kV Ultra-High Voltage AC Project (hereinafter referred to as the Sichuan-Chongqing UHV project) – was officially put into operation. Regarded as a "star project" for the Sichuan-Chongqing region, it is gaining widespread interest at every stage, from initiation and groundbreaking to construction, testing and operation. It is also a "dream-fulfilling project". After over ten years of planning, the vision for the interconnection of the Sichuan-Chongqing UHV AC grid has finally come to fruition.

Keyword 1: AC Project

Sichuan's First Ultra-High Voltage AC Project Following Several Previous UHV Lines

In recent years, Sichuan, as a key hub for the State Grid's UHV construction, has successively put into operation six UHV projects: Xiangjiaba-Shanghai, Xiluodu-Zhejiang, Jinping-Jiangsu, Yachong-Jiangxi, Baihetan-Jiangsu, and Baihetan-Zhejiang. However, these six projects are all direct current (DC) projects. The Sichuan-Chongqing UHV project marks the first UHV AC project in the southwest region.

What is the difference between DC and AC? Jiang Zhenchao, Director of the System Technology Center at the Electric Power Research Institute of the State Grid Sichuan Electric Power Company, explains that these are two different methods of power transmission. DC transmission, or point-to-point transmission, is like a direct train with no stops at intermediate stations. It can transmit power over distances ranging from 2,000 to 3,000 kilometers. In contrast, AC projects operate like highways, enabling extension and expansion. They provide flexible access and exit points, allowing for the addition of new entrances and exits. Typically, AC transmission covers distances within 1,000 kilometers.

As the first UHV AC project in the southwestern region, the Sichuan-Chongqing UHV project not only connects the power and load centers of Sichuan and Chongqing but also continually extends and expands, aiming to achieve greater effectiveness. Recently, the Chengdudong-Suining 500 kV line project is about to be put into operation. This is a dedicated line for Suining to connect to the Sichuan-Chongqing UHV project on a point-to-point basis, boosting Suining's power supply capacity by three million kilowatts. Zeng Xiaohui, Executive Manager of the Owner Project Department for Newly Constructed Projects at the Chengdudong 1000 kV substation, introduces that three 500 kV transmission channels connecting to the Sichuan-Chongqing UHV project are under construction at the Chengdudong site. These include the Chengdudong-Suining, Chengdudong-Shiling, and Chengdudong-Huaizhou 500 kV line projects. Upon completion, these lines will significantly enhance the power supply capacity of the Longquanyi and Jintang areas.

Keyword 2: Integrated Project

Supporting the Chengdu-Chongqing Economic Circle and Enhancing Power Supply Security in Sichuan and Chongqing

The implementation of the Sichuan-Chongqing UHV project is closely linked to two significant backgrounds: the construction of the Chengdu-Chongqing Economic Circle and the integrated development of the Sichuan-Chongqing power grid.

The concept of the Sichuan-Chongqing UHV AC grid interconnection was first proposed over a decade ago. In 2017, the Sichuan Provincial Bureau of Energy organized research to determine the UHV AC scheme. At that time, the Sichuan-Chongqing power grid had only three main transmission corridors with a total of six 500 kV transmission lines, and all these lines were already operating at full capacity. Chongqing anxiously sought more Sichuan electricity, while Sichuan worried annually about hydropower curtailment and absorption challenges.

In July 2020, Sichuan and Chongqing signed a cooperation agreement on jointly promoting the integrated and high-quality development of the energy sector in the Chengdu-Chongqing Economic Circle. The agreement encompassed 20 major energy projects, with the Sichuan-Chongqing UHV interconnection project being the most significant.

In September 2022, construction of the Sichuan-Chongqing UHV project officially started. This project connects the power and load centers of Sichuan and Chongqing, effectively breaking through the bottlenecks in the power transmission channels between Sichuan and Chongqing, as well as within Sichuan Province. Upon the project's operation, it will boost Sichuan's hydropower outward transmission capacity by 4.8 million kilowatts, increase the maximum transmission capacity of the Sichuan-Chongqing section by four million kilowatts, enhance Chongqing's power supply security, and promote the optimization of the energy consumption structure. Once completed, the Sichuan-Chongqing UHV project will elevate the main grid voltage level of China's southwest power grid from 500 kV to 1000 kV, markedly bolstering the overall power supply security of the Chengdu-Chongqing Economic Circle.

Once operational, the Sichuan-Chongqing UHV project will facilitate the annual transmission of 35 billion kilowatt-hours of clean electricity from western Sichuan to the load centers of Sichuan and Chongqing, equivalent to the annual residential electricity consumption of nearly ten million households. Industry experts evaluate this project as a "key project" to support the power supply security in Sichuan and Chongqing. In the coming years, it will significantly boost confidence in meeting the Sichuan-Chongqing region's peak summer power demand and greatly alleviate the pressure on power supply security in this area.

Keyword 3: Initial Project

The UHV AC Backbone Grid Starts with This Project

The State Grid Corporation of China positions the Sichuan-Chongqing UHV project as the initial project for constructing the UHV AC backbone grid in the southwest region. How do we understand the concept of an initial project?

Tang Gang, Director of the UHV Construction Management Division of the Construction Department at the State Grid Sichuan Electric Power Company, introduces that the Sichuan-Chongqing UHV project consists of three sections: Ganzi-Tianfunan-Chengdudong, Tianfunan-Tongliang, and Aba-Chengdudong.

In September 2022, construction commenced on the Ganzi-Tianfunan-Chengdudong section. In April 2023, the construction of the Tianfunan-Tongliang section began. These two sections were synchronized for operation during this interconnection phase. After reaching Tianfunan from Ganzi, the grid splits into two branches: one extending to eastern Chengdu and the other to Chongqing's Tongliang, completing the "Y-shaped" grid framework of the Sichuan-Chongqing UHV project.

In July 2024, construction began on the third section of the Sichuan-Chongqing UHV project – the Aba-Chengdudong project – with a targeted completion date of December 2026. This development will extend the left branch of the "Y-shaped" grid to Aba, transforming the Sichuan-Chongqing UHV project into a "Z-shaped" grid framework.

What does this transformation imply? According to Tang Gang, upon the completion of the Aba-Chengdudong project, which boasts an annual transmission capacity exceeding 15 billion kilowatt-hours, it will, together with the Ganzi-Tianfunan-Chengdudong project, form a new pattern of "dual sending-end" joint power supply pattern for bolstering the province's power security. For the Sichuan-Chongqing power grid, the transition to a "Z-shaped" grid framework enhances both its power supply and grid support capabilities. This enhancement creates the necessary conditions to further optimize and adjust the Sichuan-Chongqing 500 kV power grid and to solve the problem of local grid overloading.

The Sichuan-Chongqing 1000 kV UHV AC ring network project is currently moving forward quickly with its engineering justification. The Sichuan-Chongqing UHV AC project is set to progress beyond the "Z-shaped" grid framework. The next phase envisions "forming a ring".

In the subsequent phase of establishing a ring, Sichuan will focus on planning and constructing the Panxi-Sichuannan-Tianfunan 1000 kV UHV AC project, which will further integrate Panxi as a sending point. The development of a "three sending-end locations (Ganzi, Aba, Panxi) and three receiving-end locations (Chengdu, Sichuan South, Sichuan North)" network framework for the Sichuan-Chongqing UHV AC project will further optimize power distribution in southwest China, establish a clearer structure of sending and receiving ends, and promote the coordinated development of DC and AC in the power grid.