A Novel Algorithm for Discrimination Between Inrush Currents and Internal Faults Based on Equivalent Instantaneous Leakage Inductance

A novel scheme based on equivalent instantaneous leakage inductance (EILI) to distinguish inrush currents from internal fault currents in power transformers is proposed, which is derived from the circuit differential equation. First, the EILI that represents different characteristics between the inrush current and an internal fault is defined, and its calculation methods and the criteria of two-winding and three-winding transformers are derived. This method does not require B-H curve data and the parameters of leakage inductances obtained from the transformer manufacturer. A total of 147 experimental cases verify that the EILI calculated in real time is able to clear internal fault even light fault rapidly and correctly.