复杂电磁暂态下变压器差动保护异常动作行为分析及对策

随着电力系统结构与组成的复杂性增加,变压器差动保护发生原因不明的误、拒动作几率明显上升,给电网安全带来隐患,也影响工业生产的正常运行.分析变压器经历外部故障切除、有载合闸、非线性负荷投入、换流变合闸等复杂电磁暂态过程时基于二次谐波制动的差动保护误动的机理,指出TA局部暂态饱和、非线性特性元件的相互作用是造成上述保护误动的根本原因.并对换流变压器差动保护在故障情况下长延时动作的原因进行分析,基于相电压突变量和差流突变量的时差,提出一种能有效解决上述问题的变压器差动保护判据。在任何非故障的异常情况下,该时差总是存在,而内部故障时该时差很小,可以将变压器故障和其经历的异常运行状态相区分.通过大量的试验对该判据的可行性和有效性进行验证.

Analysis and countermeasure of abnormal operation behaviors for transformer differential protection during complex electromagnetic transient courses

With the increase of the complexity of power system structure and components, the abnormal operation probability of transformer differential protection is obviously rising, and the sequent accident analyses are frequently unclear. It is adverse for power system security and will have negative impact on industrial productions. The real-operation mechanisms of the 2nd harmonic restraint based differential protection are analyzed in this paper, while experiencing complex electromagnetic transient courses （such as the external fault removal, loaded transformer switching-in, the non-linear load inception, the converter transformer energization ）. It is pointed out that local TA transient saturation and the interaction between non-linear characteristic elements are the reasons leading to the above real-operations. Meanwhile, the reason of long time delay operation for the converter transformer differential protection is also analyzed. Based on ahove investigations, a new criterion of transformer differential protection that can solve the above problems is put forward, which is based on the time interval between superimposed phase voltage and superimposed differential current. In the case of abnormal scenario without faults, this time interval always exists. However, this time interval is very small when a real internal fault occurs. Therefore, the transformer fault can be identified from abnormal operation states. The proposed criterion is verified with amounts of test results.