Adaptive Transformer Inrush Current Identification Principle Based on Second Harmonic

In order to prevent the maloperation of the transformer differential protection device affected by transformer magnetizing inrush current and internal short circuit fault current, the device should be able to identify the internal fault current and inrush current. Accordingly, this paper is aimed at adaptive transformer inrush current identification based on the second harmonic. The main idea is to introduce the floating threshold value on the basis of the traditional second harmonic brake and to track the change characteristics of the content of second harmonic and fundamental wave in real time. This method not only inherits the advantage of the original second harmonic braking method, but also helps to identify the internal fault and inrush current quickly, and improve the sensitivity of the magnetizing inrush current.