The Research Of Inrush Current And CT Saturation In Transformer Differential Protection

This paper simulated and analyzed four situations for causing inrush current of the transformer,which included:1)The condition for the breaker switching-on asynchronously without load;2)The condition for various of external faults in the near districts of the transformer;3) sympathetic inrush current;4)The condition for the non-linear load putting into the power system.It proposed the clustering analysis theory of the pattern recognition to discriminate between the inrush current and internal fault current of the transformer,and compared the undetermined current waveform with the given current waveform of the normal sine waveform,the inrush current waveform and the fault waveform,by similarity measure to distinguish the inrush current of the transformer.Meanwhile it also proposed a new thought for avoiding the transformer differential protection mal-operation when CT saturation,which restored the dead angle of the current waveform before CT saturation,and discerned the fault current,thus making transformer differential protection act correctly.