利用电流变化率极值特征的变压器涌流识别研究

A method to detect inrush currents in power transformer using current derivation characteristics

为进一步提高电力变压器差动保护性能,提出一种利用电流变化率极值特征的励磁涌流识别的方法。变压器发生涌流时,三相电流波形至少存在一相以上有间断及尖顶波特性,一个工频周期内电流变化率的极大值与极小值的时间间隔小于半个周期,且不具备周期性特点。而内部故障时,故障电流变化率波形近似呈正弦特征,一个工频周期内极大值与极小值的时间间隔近似为半个周期,且具有周期性特征。利用电流变化率一方面可以削弱非周期直流分量的影响,另一方面可以凸显幅值较小的间断变化临界点的特征,构造了利用电流变化率特征的涌流识别判据及实现方案。最后利用动模试验进行验证,不同情况下的计算分析结果表明该算法原理清晰、判据简单、计算量小,在一个周波内能可靠识别出涌流与内部故障,为进一步提升和优化变压器保护性能提供了有益的理论基础。

To further improve the performance of differential protection for power transformers, this paper presents a new method for distinguishing inrush currents from internal faults using the extreme values of current derivation rate. In the condition of inrush currents, there are at least one phase whose current waveforms have the characteristics of discontinuity and steeple wave and the time span between the maximum value and the minimum one of the derivation rate in a power frequency cycle is less than half a cycle. While in the case of internal faults, its derivation rate curve is close to sine waveform and the time span between the maximum value and the minimum one is approximately near to half a cycle. Using the current derivation rate, on the one hand, can weaken the impact of DC component. On the other hand, it can also highlight characteristics of the intermittent critical point. Thus, a criterion using the features of current derivation rate is developed and the corresponding realization flow is presented. At last, the results of dynamic tests under different conditions suggest that the proposed algorithm can identify inrush currents from internal faults in a power frequency period accurately and quickly, with clear principle, simple criterion, and a small amount of calculation. It also provides a helpful theoretical basis for improving the performance and optimization of differential protection in power transformers.