An Energy Variation-Based Method for Discrimination Between the Internal Fault and Inrush Current in Power Transformers

Inrush currents are over currents that occur during the switching of power transformers. Differential relays can misidentify these currents as a fault and needlessly disconnect a healthy transformer. The typical methods for detecting inrush currents and blocking the function of differential relays are the second harmonic and zero-crossing methods, which are widely used in differential relays. However, these methods have several weaknesses that limit their applicability. This paper presents a new inrush current detection method based on the rate of change in the signal energy. The proposed method has been tested on a 230/63kV network with Ynd11 current transformer and compared with conventional industrial methods for different inrush currents and transformer internal faults.