Anti-saturation algorithm in differential protection based on the phaselet

Current-transformer (CT) is prone to get into transient saturated during the fault in the power system. The transient saturation of CTs will cause serious distortion in the secondary side, operation performance of differential protection based on the traditional algorithm is seriously influenced. The phaselet algorithm can accurately obtain the basic frequency component of the fault current with the unsaturated data segment of CTs´ distorted secondary current in a relatively short time window. This paper researches the principle and features of the phaselet algorithm, eliminates the influence of the decaying DC component with the first order difference compensation, gives out the calculation process of the phaselet algorithm, proposes the scheme for the CT´s anti-saturation of the differential protection based on the phaselet algorithm. Finally, the accuracy of the phaselet algorithm is verified by CTs´ transient experiment data, and the validity of the scheme applying in the line differential protection is tested by the simulation in PACAD.