变压器空充下的励磁涌流二次谐波特性分析

针对近年来变压器空充试验时，电流的二次谐波含量低于保护整定值导致差动保护误动作的问题，首先利用2条不同斜率的直线对变压器磁化特性曲线进行拟合，推导出不同空充电压下励磁涌流二次谐波含量的表达式，进而基于有限元分析软件搭建并验证了一台14 kVA单相变压器以及一台325 MVA三相变压器的仿真模型，然后对验证过的模型进行了变压器空充仿真。研究表明：在考虑铁芯磁化曲线起始部分存在非线性特征的情况下，空充电压小于临界电压时，励磁涌流中含有少量二次谐波；空充电压等于临界电压时，励磁涌流二次谐波含量达到峰值；随着空充电压等级的提高，励磁涌流二次谐波含量呈现先增后减的趋势。

Characteristic Analysis of Second Harmonic of Magnetizing Inrush Current with No-load Transformer Energization

In recent years, the second harmonic content of the transformer current is lower than the protection setting value during the no-load transformer energization test, which leads to the problem of mal-operation of differential protection. Aiming at the problem, two straight lines with different slopes are used to fit the magnetization characteristic curves of transformers. Then, the expressions for the second harmonic content of magnetizing inrush currents with different no-load voltages are derived. Based on the finite element analysis software, this paper develops and verifies the simulation models of a 14 kVA single-phase transformer and a 325 MVA three-phase transformer. The validated model is simulated under the condition of no-load transformer energization. The study shows that: considering the non-linear characteristics of the beginning of the core magnetization curve, the magnetizing inrush current contains a small amount of the second harmonic when the no-load voltage is less than the critical voltage; the second harmonic content of the magnetizing inrush current reaches its peak when the no-load voltage is equal to the critical voltage; with the increasing of no-load voltage level, the second harmonic content of magnetizing inrush current shows an increasing trend before decreasing.