A novel method to determine leakage inductance for internal fault analysis in power transformer

Inductance calculation is essential for internal fault analysis and protective relay of a power transformer. A new model, including several important factors neglected in the previous ones is proposed to calculate the inductance of power transformers. One of the key factors involves the difference between leakage magnetic field distribution under normal operating condition and the one under fault conditions. We have shown that such a difference affects significantly the short circuit reactance or leakage inductance and other parameters of a power transformer. In the proposed model, the inductance of a faulty transformer is firstly calculated by an axially symmetric magnetic field and then modified according to the constraint of the ampere-turn balance. The comparisons between measured impedance and calculated impedance of a faulty transformer model show that our method, while flexible and convenient to use, provides sufficiently precise results in the internal fault analysis of the power transformer