Using combined characteristics to identify inrush current and internal fault current of traction transformer

Due to weakness of transient second harmonic for large capacity traction transformers, traditional methods of its differential protection are faced with great challenge. For the characteristics that inrush current waveform has dead zone and peak wave, while the internal fault current waveform remains fundamental frequency sine wave, a new approach to identify inrush current and internal fault current of traction power transformer based on three-phase differential current combined characteristics of skewness and kurtosis is presented in this paper. Firstly, according to statistics theory of skewness and kurtosis and the cycle characteristics of sine wave, the data window width of differential current waveform is set and the algorithms of skewness and kurtosis are designed. Secondly, through the definition of skewness and kurtosis combination characteristics of three-phase differential current, new fault criteria are constructed in paper. Finally, it is proved that the new protection methods adopted waveform parameter identification principle that not only has features of clear principles, simple calculation, easy-to-project implementation, but also can quickly and correctly identify the fault current and inrush current in experiment.