Effect of CT transient characteristics on transfer of inrush

During the inrush period, multiple misoperation accidents of differential protection of transformers happened, which seriously threatened the safe and stable operation of power grid. In the traditional malfunction analysis, only the inrush current process is considered, and the electromagnetic transient interaction between the transformer and other non-linear ferromagnetic components such as CT is hardly considered. Here, the variation rule of inrush current waveform characteristic is analysed, and the influence rule of secondary load and type of CT on inrush current second harmonic proportion and dead angle is simulated by using the simulation Lucas model of industrial practical CT (P/PR). The results show that the second harmonic proportion of the inrush current and the dead angle of the waveform depend on the saturation angle of the transformer core. The larger the saturation angle is, the smaller the second harmonic proportion is, and the larger the dead angle of the waveform is. The second harmonic proportion of the inrush current becomes larger, and the dead angle of sympathetic inrush becomes smaller after CT transfer. The dead angle of magnetising inrush waveform depends on the secondary load resistance. It may increase or decrease.