132. Fast Unrestrained Differential Protection Based on Phaselet Algorithm

The misoperation of differential protection caused by saturation of CT would take place during external fault of transformer. In order to solve this problem, this paper describes a fast unrestrained differential current protection algorithm based on phaselet algorithm, which relies only on sampling data of one-fourth circle. Based on the relationship between phaselet algorithm and full circle Fourier algorithm, this paper induces the linear relationship between the two algorithms. The magnitude-frequency characteristics of phaselet are analyzed and the fast protection criteria is proposed. The feasibility of the proposed algorithm is validated by the static testing and dynamic testing. The relay based on the proposed algorithm has been applied in field. The algorithm proposed has fast operation time and can be influenced by CT saturation.