三峡工程水轮发电机组灭磁方案研究

Study on field suppression scheme for hydropower generator unit in Three Gorges Project

三峡水轮发电机组单机达700MW,是目前世界上最大的水轮发电机组,采用传统的直流灭磁方式,其灭磁开关及碳化硅(SiC)灭磁电阻在国际市场上的生产厂家越来越少,备品比较困难。尽管灭磁开关采用8断口串联、超大型结构,但误强励时仍不能保证足够的弧压,断口存在不同期性、跳跃问题。交流侧的真空开关不能保证可靠灭磁,灭磁元件采用的进口SiC电阻阀片没有国家标准和成熟的试验方法、价格较高。推荐三峡机组采用结构简单、维护量小、可靠性高的交流电压灭磁加熔丝换流后备灭磁的方案。该方案用交流电压灭磁新理论和在300MW机组运行5a多证明的成熟技术、市场普及的小型开关、国产氧化锌(ZnO)灭磁电阻元件解决上述问题。

Along with the unceasing increase of the capacity of generator unit, the field discharge switch is also more and more big, especially under the extreme condition (as false forced excitation under no load of generator unit), the working parameters of switch equipment are greater more than the normal, and the project practice is more difficult, and it is not reasonable from point of view of technology and economy. The manufacturers in international market for the field discharge switch and its field discharge resistance of carbonization silicon (SiC) are more and more less, and the spare parts are difficult to get, if Three Gorges generator units adopt traditional DC field suppression. Though the field discharge switch adopts the 8 series of fracture and large scale of structure, the arc pressure cannot be enough under the false forced excitation, and the fractures exist the problems of asynchronous and jump. AC side vacuum breaker cannot guarantee the reliable field suppression, and there is no national standard and testing method for the imported SiC resistor of field discharge elements. According to the above-mentioned problem, the paper recommends the field suppression scheme of AC voltage and backup fuse converting for Three Gorges generator units. The scheme is with simple structure, less maintenance and high reliability, and uses new theory of AC voltage field suppression, the mature technology operated in 300 MW generator units for more than 5 years, the popular small-sized switch and the field discharge elements of the zinc oxide (ZnO) made in China.