中文摘要：

随着大型发电机组大量投运，失磁故障对系统的危害日益增大。在厂网分开的背景下，如何同时确保发电机和电网的安全稳定运行是一个值得关注的研究课题。针对发电机失磁保护在系统振荡时容易误动或拒动的问题，研究了失磁和振荡两种情况下系统电气量变化规律的不同特征，并结合不同失磁类型的特点，提出了电压、无功和时间三种新型判据，进而设计了计及机网协调的新型失磁保护方案，并给出了相应动作参数的整定方法。计算机仿真实验表明，新型方案可有效区分失磁和振荡现象，具有动作速度快、可靠性高的优点。

英文摘要：

As large capacity units is playing an increasily important role, loss of excitation failure has become more and more dangerous to the power system stability. Especially when the power plants and grid are seperated, it is a main concern to guarantee the security operation of both generators and grid. This paper concentrates on the mal-operation or misoperation problems of loss of excitation protection, which happen frequently in system swings. Based on the different generator performances in the two scenarioes and different kinds of loss of excitation failures, three innovative criterions including voltage, reactive power and timer criterions are proposed. Further, a new loss of excitation protection scheme based on the presented criterions is designed, and the scheme parameters tuning method is also introduced. The computer simulation results show that the new scheme can accurately distinguish the phenomena of loss of excitation from power system swings, and shows the advantages of high action speed and high reliability.