Analysis and Preventive Measures of the Impact of Excitation Inrush Current on Transformer Differential Protection
Due to the variability and uncertainty of transformer excitation inrush current,its value can reach 6-8 times the rated current.It usually occurs during voltage recovery when there is a fault outside the protection device cut-off area or when the transformer is airdropped,which may cause incorrect operation of differential protection,especially for transformer differential protection based on the second harmonic braking principle.Due to differences in setting values and braking mode selection,protection misoperation may occur.This article focuses on the problem of differential protection misoperation during the operation of the contact transformer in the booster station of Lanzhou Aluminum Industry Co.,Ltd.'s self owned power plant.Based on the on-site fault recording waveform and relevant data,the reasons for the misoperation of the protection device are analyzed.By analyzing the waveform characteristics of the transformer excitation inrush current,the impact of excitation inrush current on transformer differential protection is explained and preventive measures are proposed,in order to provide reference for solving related problems of excitation inrush current in the future.
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