基于特征电流波宽判据的变压器差动保护方法

变压器差动电流波形在区内故障后第一周期内由于非周期分量和高次谐波的影响而存在较大偏移,导致保护容易出现误判。为解决该问题,在PSCAD中建立变压器差动保护仿真模型,对三相差流瞬时值取绝对值后求和得到特征电流。研究发现励磁涌流与内部故障电流的特征电流在波形间断角和纵向偏移上存在明显差异,可以通过在时间轴上方设置合理的门槛值,取特征电流波形在该门槛值以下的波宽作为识别涌流与内部故障电流的判据,由此提出一种基于特征电流波宽判据的变压器差动保护方法。仿真表明该方案能有效提高保护动作速度,维持在20 ms左右,弥补了波形对称性原理的差动保护在可靠性和速动性上的不足。

The transformer differential protection method based on characteristic current waveform width criterion

The differential current waveform of the transformer has a large offset due to the influence of non-periodic components and higher harmonics in the first period after the internal fault, which causes the protection to be misjudged. In order to solve this problem, a transformer differential protection simulation model is established in PSCAD. The absolute value of the three-phase differential current is summed as the characteristic current. It is found that there is a significant difference in the waveform discontinuity angle and longitudinal offset of the characteristic current between the magnetizing inrush current and the internal fault current, which can be measured by setting a reasonable threshold above the time axis, and the width of the waveform whose characteristic current waveform is below the threshold is taken as the identification of inrush current and internal fault current. Therefore, a new method based on characteristic current waveform width criterion of Transformer Differential Protection is proposed. The simulation shows that the scheme can effectively improve the speed of protection action and maintain it at around 20ms, which makes up for the lack of reliability and quickness of differential protection based on the principle of waveform symmetry.