应用等效瞬时电感对称特征判别变压器励磁涌流新方法

Discrimination of transformer inrush current based on symmetry character of equivalent instantaneous inductance

根据变压器在空投和内部故障情况下等效瞬时励磁电感的波形差异性,提出一种利用波形相关性判别励磁涌流和故障电流的新方法。涌流时变压器铁芯必然经历饱和与非饱和过程,瞬时励磁电感是时变且交替变化的。内部故障时,变压器铁芯工作于线性区域,瞬时励磁电感恒为常数。在此基础上,提出利用波形对称度分析等效瞬时电感前后半个周期波形的对称性。通过涌流和故障时等效瞬时电感波形对称度的大小判别涌流和故障。动模试验分析结果表明,新方法能有效区分励磁涌流和故障电流,对轻微匝间故障也有足够的灵敏度。

A new waveform symmetry algorithm for distinguishing the inrush and fault currents of power transformers was introduced based on the waveform differences of equivalent instantaneous inductance between unloading and internal faults. The cause of the inrush currents is that the saturation of core in the transformer and the equivalent instantaneous inductance varies alternately. When the transformer operates in the linear section of the magnetizing curve for the internal fault, the equivalent instantaneous inductance is constant. On this basis, a protective scheme was presented for distinguishing the inrush and fault currents by analyzing the symmetry degrees of pre and post half-waves of equivalent instantaneous inductance. The experimental results indicate that the proposed principle is also reliable and sensitive to slight turn-to-turn faults.