On July 1, the 2080 kilometer long Baihetan Jiangsu ± 800 kV HVDC project (hereinafter referred to as "Baihetan Jiangsu Project") passed through five provinces and cities including Sichuan, Chongqing, Hubei, Anhui and Jiangsu was completed and put into operation. Since then, the green power generated by the Baihetan Hydropower Station at the junction of Sichuan and Yunnan can reach Jiangsu thousands of miles away in only 7 milliseconds. From the western mountainous areas to the eastern coast, what challenges have more than 30000 builders overcome and what benefits can the project bring? The reporter conducted an interview. The green electric energy that can be transmitted every year is equivalent to the electricity consumption of Nanjing for half a year. UHVDC, known as "electric highway", has the advantages of point-to-point direct access, large transmission capacity, long transmission distance and low line loss. Zhong Zhiyi, deputy director of the UHV Department of the State Grid, said that based on the maximum flow rate of 48 meters per second when the Baihetan Hydropower Station discharges the flood, it takes about 12 hours for the river water to flow from Liangshan Yi Autonomous Prefecture in Sichuan to Suzhou in Jiangsu Province, but the generated hydropower is transmitted through the UHV DC project, which takes only 7 milliseconds. For our country, "electric highway" plays a very important role. China's energy production and consumption are inversely distributed. The energy consumption in the Middle East accounts for more than 70% of the country, but the production accounts for less than 30%. Important energy bases are mainly distributed in the western region, forming a pattern of energy flows such as the transmission of electricity from the west to the East for a long time. This requires the development of UHV to optimize energy allocation and ensure power supply nationwide. The Baihetan Jiangsu project meets this demand. On the one hand, hydropower is a clean, green and renewable energy. Sichuan is rich in hydropower resources, with a technically exploitable capacity of 148 million KW, accounting for about 1/5 of the national total. By the end of last year, the installed capacity of hydropower in Sichuan had reached more than 89 million kilowatts, ranking first in the country. On the other hand, with the economic and social development, the demand for electricity in Jiangsu, a strong economic province, is also increasing day by day. "The transmission capacity of the Baihetan Jiangsu project is 8million kW, accounting for half of the total installed capacity of the Baihetan Hydropower Station. It can send more than 30 billion kwh of electricity to Jiangsu every year, and at the same time, it can send more than 4 billion to 6 billion kwh of surplus hydropower during the wet season in Sichuan, greatly improving the utilization efficiency of hydropower." Hu Guoqiang, executive deputy commander-in-chief of the State Grid Sichuan Electric Power UHV construction headquarters, said that during the "14th five year plan" period, the Baihetan Zhejiang UHV DC project will also be completed, and the construction of the Jinsha River upstream Hubei UHV DC project will be started, further improving the hydropower transmission capacity of Sichuan. Chen Bing, deputy general manager of State Grid Jiangsu electric power construction branch, told reporters that last year, the electricity consumption of the whole society in Jiangsu exceeded 700billion kwh for the first time, and the net electricity input from other provinces exceeded 17%. The annual transmission power of the Baihetan Jiangsu project is equivalent to the power consumption of Nanjing for half a year, which can increase the maximum acceptance capacity of external power in Jiangsu by 32.5%. It can not only better meet the growth demand of local power consumption in Jiangsu, but also cooperate with the existing UHV projects in East China to enhance the mutual economic capacity of hydropower and thermal power in the power grid. With difficult transportation, small space and crossing rivers, the builders have overcome many difficulties. As a key project of China's west to East power transmission, the Baihetan Jiangsu project has obvious benefits, but the construction process is not easy to cross turbulent rivers and pass through steep and uninhabited mountains. With wisdom and sweat, builders have overcome many problems. To deal with transportation problems, "ants move elephants". The Butuo converter station, located in Butuo County, Liangshan Yi Autonomous Prefecture, Sichuan Province, is the starting point of the project. Before the current starts, it must first "change" from AC to DC. The converter transformer is the "heart" of the converter station, with a single weight of 350 tons, equivalent to the weight of 70 or 80 adult Asian elephants. It is conceivable that it is difficult to transport 52 such "Big Macs" in Daliangshan, where the road is narrow and the bends are sharp. "There is a 139 kilometer mountain road from Xichang railway station to Butuo converter station. It takes 215 S-shaped bends and 62 U-shaped sharp turns to cross Erwu mountain, which is 3300 meters above sea level. On average, you have to turn a 180 degree bend every 280 meters." Li Jian, head of the State Grid Sichuan Electric Power UHV heavy cargo transportation technical support group, said that the hydraulic scooter used for transportation is equipped with 180 tires and 4 tractors. The whole vehicle is 70 meters long, almost occupying the whole road width, and the average speed is only 5 kilometers per hour. It is easy to roll over if you don't pay attention. At every turn, Li Jian had to get off in advance to observe the route and walk with the car to remind the driver. Overcome the difficult conditions, "tower on the top of the mountain". "In the no man's land at the junction of Leshan and Liangshan in Sichuan, the maximum drop is 1800 meters. There are cliffs all around, and no equipment can be put down. The foundation pit more than ten meters deep can only be excavated a little manually. Even so, everyone just 'competed' on the top of the mountain!" Yu Jiamin, manager of the construction project Department of the no man's land in the Sichuan section 2 of the Baihetan Jiangsu project, said that the maximum slope of some tower sites is more than 50 degrees, and the working surface is very narrow. Tower materials can only be transported by cableway, one of which can be assembled, and often an iron tower can be erected in 20 days. Across the Yangtze River waterway, the "silver line crosses the river". For the builders of the Anhui section of the Baihetan Jiangsu project, it is undoubtedly the biggest challenge for the conductor to smoothly cross the 2500 meter wide Wuhu section of the Yangtze River. In order to ensure the safe distance between the conductor and the river, the design height of the main crossing tower on both banks is 278.2 meters, close to 100 floors high, and the weight is more than 2200 tons. This is the crossing tower with the largest span, the highest tower body, and the heaviest single foundation of the whole line. Hanzhongrui, the leader of the construction team of the Yangtze River Crossing in Anhui section, said: "the single tower pipe connected with the tower leg section alone weighs 17 tons, and the connection is fixed by 26 bolts, each of which weighs 35 Jin. Such bolts need about 2000 for the whole tower, and must be tightly connected." The Wuhu section of the Yangtze River has been busy with transportation for many years, with an average daily vessel flow of 4500. The project requires the deployment of 22 conductors and ground wires, and the construction volume is not small. How to minimize the impact on the closure? "More than 10 years ago, we used the method of 'one lead one' to lay the conductor. Now it is' two lead three ', like two horses pulling three cars, which can be completed in 20 days, greatly reducing the construction period." Han Zhongrui said. Get rid of the influence of thick fog, "Beidou to navigate". In the Chongqing section of the Baihetan Jiangsu project, the most worrying thing for the builders is the frequent occurrence of dense fog, which will affect the sag observation of the conductor and ground wire. "Excessive sag may not only cause safety hazards such as phase to phase short circuit, but also limit the transmission capacity of the line." Yangguoqiang, the project manager of the Yu3 bid section of the Baihetan Jiangsu project, introduced that they can use Beidou's high-precision positioning radar measurement and control to determine whether the conductor is installed in place under non visual conditions, with an accuracy of plus or minus 2mm, so as to effectively solve the sag observation problems in fog, night and other situations, and improve the project progress by more than 15%. We have strengthened independent technological innovation, developed 20 kinds of new equipment, 19 new technologies, and built iron towers and silver wires. To ensure the safe and stable delivery of green power, we cannot do without many innovative technologies and equipment. In Suzhou, Jiangsu Province, Yucheng converter station, which covers an area equivalent to 47 football fields, is the terminal of the white crane beach Jiangsu project. Here, DC once again "transformed" into AC and distributed to the surrounding area. Yucheng converter station is also the first converter station in the world to adopt "conventional DC + flexible DC" hybrid cascade connection. "This converter station integrates the advantages of large capacity, long distance and low loss of conventional DC transmission, as well as flexible DC transmission control and strong system support." Zhong Zhiyi explained that if conventional DC is compared to a train, it can only run on a flat track. Flexible DC is like an off-road vehicle, which can cope with poor road conditions such as muddy roads and gravel roads, and has no high requirements for the strength of the power grid. "Not only that, flexible DC can in turn support voltage and frequency, support power grid black start, etc. in order to overcome this hybrid cascaded UHV DC transmission technology, nearly 100 enterprises and scientific research institutions spent more than three years." Yucheng converter station is also facing another test: as the conversion end of DC and AC, when the AC system has a serious fault, the DC side will immediately trip and shut down in order to protect the equipment, but at this time, the AC system is still injecting energy. How to quickly consume this part of energy so that the system can quickly return to normal after fault removal? The builders developed a controllable self recovery energy dissipation device equivalent to an "airbag". When the AC system fails, this device can make a millisecond response, absorb excess energy, and prevent the converter valve and other key equipment from being damaged due to high voltage; It can also avoid the restart time of DC system after fault recovery, so as to greatly improve the power receiving capacity of East China power grid. "The controllable self recovery energy dissipation device also integrates high-capacity lightning arresters, ultra-high speed trigger switches, fast mechanical switches and other equipment. Taking the lightning arrester tower with a height of about 14 meters as an example, each floor is composed of 136 lightning arresters, with a total of 680 on five floors, and 1360 are installed on two sets of energy dissipation devices." Yang Jinggang, director of the transmission and transformation technology center of State Grid Jiangsu Electric Power Research Institute, introduced. "Physical examination" is required before the equipment goes on duty, but only about 13 arresters can be completed every day by using the traditional method to conduct high-voltage test on arresters. Based on this calculation, it will take at least 3 months of continuous testing, which is difficult to keep up with the progress of the project construction. Therefore, researchers have studied the overall pressurization test method, which can test 136 arresters on each floor at the same time, so that the detection time can be greatly shortened. In the Baihetan Jiangsu project, there are many similar innovative equipment and methods: to "slim down" the converter transformer, independently develop the world's first single column coil converter transformer, double column to single column, which can reduce the load loss by about 25%, reduce the temperature rise and fall by about 10 degrees Celsius, and extend the service life of the equipment; Research and develop "Super Brain" for the project, upgrade the control and protection system, shorten the fastest control cycle from 75 microseconds to 10 microseconds, and increase the operation mode from more than 40 in the past to 252, increasing the flexibility of the system... "Baihetan Jiangsu Engineering has innovated and developed 20 new equipment and 19 new technologies, which has a strong demonstration significance in strengthening the independent innovation of power grid engineering technology." Zhiyi is very proud. To stabilize growth, benefit people's livelihood and improve the environment, the State Grid will also start eight UHV projects as soon as possible this year. "I have been looking for odd jobs near my home before, and this is the first time I have participated in such a large project." Xi Yongfu, a crane driver from Yichang, Hubei Province, participated in the construction of the Hubei section of the Baihetan Jiangsu project. He earned a considerable monthly income in the project department and was very happy. After the project was put into operation, he followed the construction team to the Baihetan Zhejiang UHV project. For Li Kedashi, a villager in Zhushang village, Mabian Yi Autonomous County, Sichuan Province, the road built by the UHV project for the transportation of materials has opened up the outward transportation channel of bamboo shoots, Gastrodia elata and other mountain goods. "It was not easy to go down the mountain before. It took four or five days to go down the mountain after picking up the mountain goods. After a long time, it couldn't sell at a good price. Now with Panshan Road, you can transport it down the mountain by motorcycle that day. It's very fresh, and sometimes you can earn more than 600 yuan a day." Li Kedashi said happily. According to reports, the total investment of the Baihetan Jiangsu project is 30.7 billion yuan, which can add more than 20000 jobs and increase output