Adaptive Braking Ratio Based On Waveform Recognition Transformer Differential Protection Principle And The Secondary Current Compensation Algorithm

Due to capacity increase or structure change of the power system, an extra-high current possibly 100 times of the rated current may appear in some circuits of the power system when a short-circuit happens nearby, which will cause the current transformer iron core into saturation for the nonlinear magnetic curve characteristic of the current transformer. In the network of large capacity and over-voltage, direct current component reduces slowly, and it may deteriorate the flux transmissibility severely of the current transformer winding. In some situations, there is large residual flux in the current transformer iron core, which well force the current transformer trend into saturation easily. The differential protection of transformer may operate delay or error because of current transformer saturation, which was discussed in references [11]-[15]. In this paper, major factors that affect on current transformer saturation have been analyzed, and methods of detecting transformer saturation and compensation approach of secondary current have been discussed. An applied algorithm of detecting current transformer saturation and an improved compensation arithmetic of secondary current have been presented, and a compensation algorithm of ANN(artificial neural network) based on Matlab also has been debated. By analyzing the affection of current transformer on the transformer differential protection, the relationship between current transformer error and waveform correlation coefficient of secondary current has been established, then, a principle of self-adaptive restraint ratio coefficient transformer differential protection based on waveform correlation coefficient is presented.