Ultra high voltage AC transmission refers to AC transmission of 1000 kV and above, which has outstanding advantages such as large transmission capacity, long distance, low losses, and less land occupation. The expansion of the power system and transmission scale, as well as the development of high-tech in the world, has promoted the research of ultra-high voltage transmission technology. Since the 1960s, countries such as the former Soviet Union, the United States, Japan, and Italy have successively conducted basic research, practical technology research, and equipment development, and have achieved breakthrough research results, manufacturing complete sets of ultra-high voltage transmission equipment. The former Soviet Union has built over 1900 kilometers of AC transmission lines with a rated voltage of 1150kV (with a maximum operating voltage of 1200kV), and 900 kilometers have been operated at the designed voltage; Japan has built 426 kilometers of double circuit transmission lines on the same tower with a rated voltage of 1000kV (maximum operating voltage of ll00kV). The transmission capacity of a single circuit of a million volt AC line exceeds 5000MW, and it has obvious economic benefits and reliability. As a backbone line for medium and long-distance transmission, it will play an important role in the construction and development of the power grid. Calculated based on natural transmission power, the transmission power of one ultra-high voltage line is equivalent to the transmission power of 4-5 500kV ultra-high voltage lines (approximately 4000-5000MVA), which will save valuable transmission corridors and greatly enhance the sustainable development capacity of China's power industry. From a technical perspective, adopting ultra-high voltage transmission technology is one of the main means to improve the transmission capacity of the power grid, and can also achieve advantages in reducing the occupation of transmission corridors and improving the power grid structure; From an economic perspective, according to research results, under the condition of transmitting 10GW of hydropower, compared to other transmission methods, the competitive transmission range of ultra-high voltage AC transmission can reach 1000-1500 kilometers. If the conveying distance is short and the conveying capacity is large, the competitive advantage of ultra-high voltage AC is more obvious. Since 2004, State Grid Corporation of China has been brewing and demonstrating ultra-high voltage projects. In August 2006, China's first ultra-high voltage AC transmission and transformation project - the Jindongnan Henan Nanyang Hubei Jingmen 1000 kV ultra-high voltage AC test demonstration project, was approved by the National Development and Reform Commission before construction began. It was completed and put into trial operation on December 30, 2008, and officially put into operation on January 6, 2009. The project has been in safe operation for nearly a year, with stable system operation and normal equipment status. The cumulative power transmission is 8 billion kilowatt hours, equivalent to transporting approximately 3.5 million tons of coal. The Jindongnan to Jingmen Ultra High Voltage AC Test Demonstration Project is an AC transmission and transformation project with the highest operating voltage and the most advanced technical level in the world, and China has fully independent intellectual property rights. The total length of the project is about 640 kilometers, with a dynamic investment of 5.736 billion yuan, of which equipment investment accounts for about half, and the equipment localization rate reaches 90%