Summary:

DC transmission superiority

The State Grid Corporation of China UHV DC test site was started construction in Beijing's Zhongguancun recently. After the base is completed, it will meet the scientific research needs of the UHV DC transmission project construction and provide good conditions for domestic enterprises to occupy the commanding heights in the world power science and technology field.

With the further development of western water and thermal power bases, surplus power will be sent to the eastern provinces and cities where energy is in short supply and the economy is developed. Selecting direct current transmission has extraordinary advantages.

According to the plan of the National Development and Reform Commission, the UHV DC project will directly assume the tasks of the planned West-to-East power transmission.

At present, the State Grid Corporation of China has arranged a ±500kV DC project from Baozhou, Lanzhou to Tianjin, and is expected to be ready for operation in 2010. This line can send thermal power from the upper reaches of the Yellow River to the hydropower station and the Ningdong Energy Base to the tightly-charged Jingjintang area; the other line is the ±500kV DC project from Baoji to Deyang and is expected to be put into operation in 2010. This line will enable Sichuan hydropower to interoperate with Shaanxi thermal power to reduce reserve capacity. At the same time, it will also link the Northwest Power Grid with Central China Power Grid. China Southern Power Grid Corporation has arranged a ±800kV UHV DC transmission project from Kunming, Yunnan to Zengcheng, Guangdong. It is expected that unipolar operation will be completed in June 2009 and bipolar operation will be launched in June 2010. According to the plan, the line's equipment autonomy rate should reach 60%.

In addition, there are also brewing in the northeastern Liaoning power grid connected with the North China power grid in Liaoning Gaozhong back to back project, and Inner Mongolia Hulunbeier thermal power group sent to the Liaoning load center of the DC project. At the same time, there are ±800kV UHV projects from Yunnan Lufeng to Guangdong Suidong. In the ten years from 2011 to 2020, China will also construct 12 DC lines with a transmission capacity of 37 million kW.

The key to success is to achieve localization

According to the State Grid Corporation of China, whether or not localization can be fully realized is the key to the success of the HVDC transmission business and also relates to the future development of the power industry. In recent years, many successful experiences have been obtained in the construction of DC transmission projects in China, and there has also been a major breakthrough in the localization rate of equipment. Many experiences are worth learning from.

The Sanchang ±500kV DC transmission project uses the largest section conductor. The ±500kV DC transmission project from Sanxia to Changzhou has a total length of 890km and was put into operation in 2003. The DC line adopts ASCR-720/50 four-split wire, which is the largest conductor in China. The OPGW composite ground cable installed along the line not only improves the high-level communication function, but also sets up an information superhighway between the eastern and western regions of China.

During the tendering process of the project, due to the relatively high technical conditions for bidding, the only companies qualified to undertake the construction are Siemens, ABB and GEC-Alstom (now France AREVA Transmission and Distribution Co., Ltd.). Although the project finally determined that ABB and Siemens won the bid, it also signed a DC technology transfer agreement and a cooperative production contract. Fortunately, the technology transfer has yielded results. Xi'an Xidian Transformer Co., Ltd. has manufactured one flat wave reactor and two converter transformers. Xi'an Power Electronics Technology Institute has introduced ABB technology and launched its own production line. The Three Gorges Project delivered 72 thyristors.

Lingbao ±120kV DC transmission project to achieve complete independent property rights. Lingbao Project is the first back-to-back networking project in China. The first time domestically completed the compilation of functional specifications, system research, and complete set of design tasks. It is also the first medium-sized project in China to use domestic equipment. Its construction has opened up a precedent for the independent design and independent construction of medium-sized DC transmission projects in China. Not long ago, with the successful completion of the State Grid Corporation of China Northwest-Huazhong Lingbao back-to-back HVDC project, Nanrui and Xu Ji’s 168-hour trial run of the control protection system were formally put into production, marking China’s first national The large-scale DC networking project of the company has been successfully completed.

This line can connect the northwest power grid with the central China power grid, with a transmission capacity of 360 MW and 100% localization of major equipment. The project also uses two transformer technologies of West and Shen change, two control and protection technologies of Xu Ji and Nanrui, and two valve manufacturing technologies introduced by West Whole Plant, which solved the problem of control protection and valve technology binding. . Since the characteristics of back-to-back DC networking are that there is no DC transmission line, and the rectification and inversion are in a back-to-back converter station, the technical difficulty is relatively small. Selecting Lingbao Engineering as a "training" operation for the further implementation of large-scale HVDC transmission project is of significance. Extraordinary. These successful practices are the first in the field of international HVDC transmission.

In this project, the State Grid Corporation of China also encourages the use of domestically produced raw materials, such as thyristor components, valve components, magnet wire, casing, and insulation molded parts, as well as the first domestic use of converter transformers. (PetroChina) transformer oil. These practices have laid a solid foundation for the complete localization of the next major project. Full localization is still difficult

China’s current installed capacity for electric power has ranked second in the world and it has become a major country for DC transmission, but it is not yet a strong country for DC transmission. The realization of localization of DC transmission is the development direction of the power industry, and it is also an important way to improve the level of China's equipment manufacturing.

Because DC transmission has the advantages of long transmission distance, good regulation performance, low over-voltage level, and small line loss, it is particularly suitable for occasions such as long-distance high-power transmission, large-scale power grid interconnection and peaking, and cable transmission, which is very suitable for China’s national conditions. However, there are many difficulties and problems in implementation. In general, in terms of design, there are problems with the harmonics of the converter transformers, DC biasing problems, and the optimization of the DC composite electric field for insulating materials. In terms of transportation, there are problems with the size and quality of the change of flow. In terms of technology, there are problems with insulation saturation and partial discharge levels. In addition, there are certain problems in the elimination of board defects, the linearity and accuracy of analog inputs, and the smoothness of information channels in control and protection equipment.

Statistics show that the Three Gorges Power Transmission Project has accumulated a total of 1,865km of DC transmission lines, 5 converter stations, 12.72 million kW of converter capacity, and 1075km of DC lines under construction, creating the largest and most technologically advanced DC transmission project in the world. The world's highest, single largest transformer capacity in the world, the shortest construction period in the world, and the world's best operating economic indicators, etc., have accumulated experience for the construction of UHV projects in the future.

Although the Three Gorges Project used the market-for-technique to enable multinational companies to transfer some of their core technologies, the prospects for the localization of DC transmission equipment are still worrying: First, although multinational companies have transferred core technologies, domestic companies cannot yet independently develop them. There is still a certain dependence on foreign companies. Second, domestic HVDC enterprises have a low level of integrated integration, and they are often single-armed and cannot be turned into a rope. Therefore, they cannot compete with multinational companies such as ABB, Siemens, and AREVA. Third, multinational corporations have increased technical input in the field of DC transmission, and the improvement of relevant technical standards will also set a higher threshold for domestic equipment manufacturers.

(The author of this article is an expert of China International Engineering Consulting and Design Institute)

Source: China Industry News Publisher: China Electric Equipment Network