中文摘要：

现代化大型机组采用数字电液控制（DEH），普遍具有电超速保护控制系统（OPC），其中一个很重要的方面是防止汽轮机超速。但如果OPC的控制策略不当，不仅起不到应有的超速保护作用，而且造成汽门频繁启闭，产生“乒乓”现象。通过对OPC振荡机理的分析，发现在电网侧发生扰动时，OPC的控制参数不合理及与其他保护措施不配合是引起系统振荡的根本原因。对OPC的动作时限及阀门开度提出相应的修改，针对2006年7月7日贵阳南部电网事故，根据实际系统，用NETOMAC程序建立了原动机、调速器和汽轮发电机过速保护的详细模型，根据理论分析的结果提出了3种OPC的动作方案并仿真证明了分析结果的正确性。最后提出相应的改进建议。

英文摘要：

Modern large - scale unit adopts digital electro - hydraulic （DEH） control, which generally has overspeed protection control （ OPC）, and one of its main functions is to prevent steam turbine overspeeding. But if the control strategy of OPC is not appropriate, it will not only fail to execute the overspeed protection, but also cause the valves to open and close frequently, resulting in ＂ping - pong＂ phenomenon. Through the analysis of OPC oscillation mechanism, the basic reason which causes system oscillation is the unreasonable control parameters of OPC which is incoordinated with other protective measures. Some modifications are proposed for OPC action time limit and valve opening. For the accident on 7th July, 2006 in Guiyang Southern Grid, the detailed overspeed protection models of prime mover, speed governing device and turbo - generator are established by using NETOMAC based on the real network data, the testing data of the field measurements, and the supplement data of classic values. According to the theoretical analysis of the results, three kinds of OPC action schemes are put forward and the simulation proves the correctness of the theoretical analysis. At last, the suggestions for improvement are presented.