基于零模涌流波形相似度的零差保护CT极性校验方法

CT polarity checking method of zero-sequence differential protection based on the similarity of inrush

由于变压器正常运行时无零序电流,零差保护回路CT(变压器Y侧)存在极性校验的难题。传统极性校验方法需要利用负荷电流,存在应用局限。为此,提出了基于零模涌流的零差保护CT极性无负荷校验方法。该方法利用变压器空载合闸励磁涌流的零模分量,通过计算Y侧自产与中性点零模涌流的波形相似度,采取“假设-检验”的方式,遍历所有可能的极性错误情况,实现零差保护CT极性正确性的校验,并引入欧氏距离以进一步提高方法对极端涌流情况的适应性。基于PSCAD/EMTDC4.6和Matlab对此方法进行了仿真分析,并利用南方电网某500 kV主变空载合闸涌流录波数据进行了验证,结果表明该方法能在无负荷情况下可靠识别零差保护二次回路CT极性错误类型,有效防止零差保护误动。

The polarity checking of zero-sequence differential protection(Y side CT of transformer)is difficult because there is no zero-sequence current in the normal operation of the power system.Research shows that the traditional method requires load current,which can not be applied to the scene of no load.To solve this problem,a new method is proposed.The method uses the zero-mode component of inrush current generated by no-load closing,and calculates the waveform similarity of self-produced zero-sequence current and neutral point current at the Y side,adopts the“hypothesis-test”method,traverses all possible polarity error cases,and realizes the CT polarity calibration of zero-sequence differential protection.To improve the adaptability of this method in extreme inrush conditions,the Euclidean distance is introduced.The proposed method is simulated with PSCAD/EMTDC4.6 and Matlab,and verified by the on-site recording data of a 500 kV transformer of the China Southern Power Grid.The results show that the proposed method can identify CT polarity error type of zero-sequence differential protection without load current,and can effectively prevent mis-operation.