同步发电机失磁保护的改进方案

在电力系统继电保护中,同步发电机失磁保护是最为重要的保护之一.励磁故障涉及发电机的大干扰稳定性,也是一个较为复杂并难以解决的问题.目前所用的励磁保护的动作效果并不理想,尚需进一步改进.分析了目前所用的3种励磁保护判据存在的不足,指出这些保护判据或基于小干扰稳定性原理而未考虑发电机动态功角特性的严重变形,或未考虑发电机完全失磁后的测量阻抗与正常励磁下扰动后的测量阻抗具有较大的公共区间,从而可能使保护误动或拒动.基于对同步发电机失磁后动态行为的仿真分析,提出了同步发电机失磁保护的改进方案,通过直接测量功率角判断同步发电机的失磁故障,提出了其整定条件和计算方法.仿真计算证明该方案能可靠、快速地反映各种励磁故障,动作稳定且整定灵活、方便.

Improvement on Loss-of-excitation Protection of Synchronous Generators

The loss-of-excitation protection of synchronous generators is one of important protections in the power system relay protection.The excitation protection is a complex problem because the excitation faults are related to the large-disturbance stability of generators.The operational situation of the current excitation protection hasn't been ideal and so needs further study on.The shortage of three excitation protection criterions applied currently is analyzed,which based on small-disturbance stability analysis principle without considering the changes of dynamic power-angle character of the generator,or without considering a rather large common area between measuring impedance circle after complete loss-of-excitation and measuring impedance circle after a disturbance at normal excitation operation.So the maloperation or misoperation is difficultly avoided.Based on the simulation analysis of dynamic varying process of synchronous generators after losing excitation,an improved scheme based on direct power-angle measurement is put forward,including setting conditions and calculation method of loss-of-excitation protection of synchronous generators.Simulation results show that the presented protection scheme can judge excitation fault reliably and rapidly,and at the same time,its operation is stable with flexible and easy setting mode.