| In 2011 our country built Ningdong-Shandong ±660kV high-voltage direct current (HVDC) power transmission project, and in February 28,2011 formally put it into operation. As the world’s first ±660kV voltage class for HVDC project, east Ningxia-Shandong ±660kV high-voltage direct current transmission project adopted with double towers HVDC project, began in the Ningxia Yinchuan east converter station, and stopped at the Shandong Qingdao converter station. Since the 21st century, in response to the central party committee called for state grid company, realize the complementary advantages between the east region, to carry out the scientific concept of development, energy conservation and emissions reduction work, promote social harmony, multiple transmission project have been completed and put into operation. Put into operation in early 2011 east Ningxia-Shandong ±660kVhigh-voltage direct current transmission project for HVDC project not only makes the implementation of the strategy of standardization, serialization construction, but also provides a solid foundation and the guarantee for the implementation of the strategy of sustainable development in our country, which has an exemplary role and far-reaching influence.High-voltage direct current transmission system runtime will usually produce a large number of harmonics.The harmonic once in power grid can cause pollution to power grid. And it is more serious that the harmonic may cause serious damage to the safety of electrical equipment, such as generator, transformer and so on. Eventually the harmonic could make the electrical equipmentcan’t run safely and effectively. Harmonic will not only cause serious damage to the normal operation of power grid, and improve power grid maintenance costs, but also can bring electricity to residents of trouble, serious cases, and can bring threat to the personal safety of maintenance personnel. Therefore, it is necessary to suppress the harmonic. Although the high-voltage direct current transmission system operation during a large part of harmonic filter will be out of the grid, but there is still part of harmonic current into the grid.So, the harmonic should be analyzed theoretically and practically.First of all, based on the steady running of Ningdong-Shandong ±660kV high-voltage direct current transmission system,this paperestablished the Ningdong-Shandong ±660kV high-voltage direct current transmission system simulation model, by using software PSCAD/EMTDC simulation experiments analysis. In order to get the ac/dc characteristic harmonic high-voltage direct current transmission system, we simulated andcalculated the Ningdong-Shandong ±660kV ac harmonic characteristics of HVDC transmission system. Secondly, by using the software PSCAD/EMTDC, the east Ningxia-Shandong ±660kV high-voltage direct current transmission, dc line fault simulation and analysis of high voltage direct current transmission harmonic characteristics of dc line fault. In view of the failure every harmonic change, impact on the dc line protection is analyzed. At the same time, use the software PSCAD/EMTDC, exchange converter transformer internal fault simulation, and analyze the harmonic characteristic. Through the above simulation analysis, make analysis of high voltage direct current transmission dc line harmonic of relay protection and the impact of system operation.Through theory deduction and experience summary, based on the east Ningxia-Shandong ±660kV for every harmonic switch converter transformer, electric equipment such as rotary motor, capacitor, reactor, temperature rise, loss, and vibration may cause electrical effects, such as to determine the influence degree of the harmonic of electric equipment, for Ningdong-Shandong dc power transmission project in the choice of equipment to provide the reference. Finally, through software simulation, summarize the harmonics in HVDC project to adopt different algorithms of relay protection device, and the influence of refusing action will happen whether to protect or malfunction, and make analysis of the impact on system operation. |
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