In east China's Suzhou, there is a new type of Ultra High Voltage (UHV) called UHV AC, which connects it with surrounding cities including Nantong, Nanjing, Hefei, Hangzhou and Shanghai. They form one of the world's most important city groups and manufacturing hubs. UHA helps to build a giant energy loop among them and reduce the number of local power plants.

The difference between the long-distance power transmission UHV Direct Current and UHV Alternative Current is the quantity of landing points. UHV DC only has one starting point and one landing point, while in the case of UHV AC, there can be a landing point in the middle of the power line at any time. So, cities along the AC line starting from Suzhou can get the electricity directly.

In this case, since all cities are along a section of the Yangtze River, a 1000-kilovolt AC line needs to cross the river to complete a UHV loop.

But how to transmit AC line along the Yangtze River? Because there is the relatively busy section of the Yangtze River, the way adopted by engineer Wang Zhongqiu and his team from State Grid GIL project is building a tunnel under the river. 

The total length of the tunnel is 5468.5 meters with an expansion joint every few hundred meters. The tunnel has 503 expansion joints in the entire pipe gallery. 

According to Wang, the main function of the expansion joint is to absorb some thermal expansion and contraction, including the settlement of the tunnel, and it also absorbs some of the forces. Inside the insulated pipeline filled with dielectric gas, energy flows safely through the Yangtze River.

Eastern China has been the load center in China for many years. Without electricity from outside the area, this area needs a lot of local coal-fired power plants. 

After using clean energy like UHV, people can reduce the number of local power plants and save a lot of energy.

To know more stories about carbon neutrality, check out the rest of CGTN's documentary Human Carbon Footprint.