A Model-Based Approach for Improving Power Transformer Differential Protection

In this paper, a new algorithm based on Kalman Filter (KF) is proposed for improving the reliability of power transformer differential protection. The three-phase currents of the transformer at the energization side are first estimated by KF. Three residual signals which are the differences between the measured (by current transformers) and estimated (by KF) are defined and considered as the decision criteria to discriminate the fault and inrush conditions. During the transformer energization, the residual signals are almost zero. However, in fault conditions, the residual signals exceed a determined threshold value and a trip command will be subsequently issued. The performance of the proposed method is verified using simulations in MATLAB and PSCAD software.