利用动态阻抗特性识别变压器的励磁涌流

为更有效地辨别变压器的励磁涌流和内部故障电流,提出了基于动态阻抗特性物理意义明确的识别策略。理论分析表明,变压器发生励磁涌流时和内部故障时表现的特征不同,即动态阻抗前者变化幅度大,且含有各次谐波;后者变化幅度小,且50Hz及其奇数次谐波含量较少。EMTP数值仿真与动模实验证明了利用动态阻抗特性识别励磁涌流的有效性,其具体判别方法容易实现,计算量小。因时、频两域设定阈值的裕度大,可显著提高变压器差动保护动作的可靠性与正确性。

Identification of Transformer Magnetizing Inrush Current by Use of Dynamic Impedance Characteristics

To distinguish magnetizing inrush currents more effectively from internal faults in transformers,an identification strategy was proposed on the basis of dynamic impedance characteristics,which possesses very straightforward physical meaning.Theoretical analysis indicates that,the dynamic impedance presents unique features in extremely different style while inrush currents or internal faults occur in a transformer.In the case of inrush currents,the amplitude variation of the dynamic impedance is large together with average power density of each order harmonics.However,the internal faults are with relatively small amplitude variation in the dynamic impedance,and the power density of the odd-order harmonics is of very small values.The effectiveness to identify inrush currents through specific dynamic impedance features is verified by both numerical simulations and physical modeling tests,and concrete identification methodology of convenient implementation and easy computation is thereby given.Due to large tolerance ranges of the set valve values in both the time and frequency domains,high reliability and accuracy of transformer differential protection scheme are achieved.