A New Transformer Protection Scheme based on the Numerical Characteristics of Equivalent Excitation Impedance

According to the analysis of the characteristics in equivalent excitation impedance for power transformers under different operating states, a transformer protection scheme based on the numerical characteristics of equivalent excitation impedance is proposed. The research shows that the equivalent excitation impedance of transformers has different characteristics under different states, while the equivalent excitation impedance can only maintain a stable small value when there is internal fault in the transformer. Therefore, an internal fault identification criterion of the transformer is constructed. Simulation result shows that the proposed scheme can identify the internal faults of the transformer quickly and accurately, and it is less affected by remanence and direct current (DC) bias.