China’s HVDC gearbox is made in China.
On November 27th, the first converter transformer with domestic on-load tap changer independently developed by China was installed in the key project of West-to-East Power Transmission in Conghua, Guangzhou — — Xiluodu DC project has been successfully put into operation from West Converter Station.
The picture shows the Xiluodu DC project from the west converter station. (Photo courtesy of the interviewee)
"The on-load tap-changer of converter transformer has achieved a technical breakthrough from scratch and realized the complete localization of industrial chains such as components, which indicates that China has broken through the constraints of this key core technology of high-end power equipment." Feng Wei, deputy general manager of Biotechnology Department of China Southern Power Grid EHV Company, said.
China’s eastern and western parts span thousands of kilometers, and the power transmission from west to east needs a long-distance, large-capacity and high-voltage DC project for power transmission. The converter transformer, which weighs more than 300 tons, is used in both the power transmission end and the power reception end of the project. The on-load tap-changer of converter transformer is like an automatic gearbox of a car, and it is used to adjust the voltage, load and current.
On-load tap changer is a highly complex and precise equipment. According to Deng Jun, a senior technical expert of China Southern Power Grid EHV Company, the on-load tap changer of converter transformer has more than 1,000 parts, and the switching times are very frequent, reaching more than 6,000 times a year. One switching includes nine processes, each of which involves the precise coordination of more than 400 parts, and the timing coordination of each process is millisecond, and the multi-field coupling of electricity, heat and force is involved in the action process.
The picture shows the installation site of on-load tap changer of converter transformer. (Photo courtesy of the interviewee)
Due to the extremely high reliability requirements and difficult manufacturing, this technology has always been in the hands of a few foreign manufacturers, and equipment maintenance is also limited. In case of failure, only imported products of the same model can be replaced, and the order cycle takes 3 to 4 months, which brings challenges to the safety of power operation.
Liu Xiangqiang, deputy general manager of China Southern Power Grid EHV Company, told the reporter that after more than two years of hard work, the research team jointly established by China Southern Power Grid EHV Company and upstream and downstream enterprises in the industrial chain has successfully developed a large-capacity converter transformer on-load tap changer with rated capacity of 6000kVA, maximum voltage of 6,000 V and maximum rated current of 1,300 A, and realized the domestic manufacturing of the whole chain of "raw materials-components-complete machine".
The picture shows the installation site of on-load tap changer of converter transformer. (Photo courtesy of the interviewee)
The successful operation of this product will not only help to upgrade the industrial chain of high-end electrical equipment in China, but also save costs for engineering construction. According to Liu Xiangqiang, only from the equipment cost estimation, the on-load tap-changer of domestic converter transformer can save nearly 40 million yuan for a new UHVDC transmission project. (Reporter Wu Tao)