变压器零模涌流解析分析及其等值电路

Mathematical Analysis for Zero-Mode Inrush Current of Transformer and Its Equivalent Circuit

变压器(尤其是高压绕组内置型高阻抗变压器)空投产生幅值大且衰减缓慢的零模涌流,导致变压器甚至相邻线路零序保护误动现象常有发生。产生零模涌流的主要原因是变压器三相铁芯饱和不一致,目前尚缺乏这一复杂过程的解析方法和零模涌流等值电路。文章推导了能反映不同类型变压器参数差异的零模涌流解析表达式并构建了零模涌流等值电路,分析了参数变化对涌流大小的影响并解释了零模涌流衰减特性。分析表明,对于同一台变压器,前一次的分闸角θ和该次空投的合闸角α共同决定了零模涌流的大小和波形。数学解析复现了4组典型工况的零模涌流波形,并通过现场录波进行了验证。进而提出了减小副方三角绕组自漏感和增加二次谐波比判据的零序保护应对思路。

Transformer,especially the high-impedance transformer with built-in high voltage winding,will generate zero-mode inrush current of large amplitude and slow decay when it is energized under non-load condition.The zero-mode inrush current usually leads to maloperation of zero-sequence protection of the transformer and even nearby lines.The main cause for generation of zero-mode inrush current is inconsistent saturation of the iron cores in three-phases of the transformer. There is still no analytical method and equivalent circuit for this complicated process.In this paper,an analytical expression of the zero-mode inrush current is deduced,and an equivalent circuit is constructed.The impact of the circuit parameters on the magnitude of the inrush current is analyzed and its attenuation characteristics are explained.The analysis shows that for the same transformer,previous opening angle θ and closing angle a jointly determine the waveform of the zero-mode inrush current. Four types of zero-mode inrush current waveforms are reproduced with mathematical analysis,and verified by on-site recorded data.Two coping ideas are proposed:reducing the self-leakage inductance of secondary delta winding and increasing the second harmonic ratio criterion.