New Algorithm for current transformer saturation detection and compensation based on derivatives of secondary currents and Newton´s backward difference formulae

This study presents a new current transformer (CT) saturation detection and compensation algorithm. The proposed algorithm depends on a saturation detection index (D_n) which is derived by using the derivatives of the current signals and Newton´s backward difference formulae. The calculated index is continuously compared with an adaptive threshold (T_h) to estimate the start and the end point of CT saturation. A low-pass first-order Butterworth filter is used to suppress noise and harmonics which may be present in CT secondary current. The proposed saturation detection algorithm has been tested by considering different values of remanent flux, fault type, fault inception angle, burden resistance, decaying DC component of fault current and noise. At the same time, modified discrete Fourier transforms-based compensating algorithm has also been proposed to reconstruct the saturated samples. Validation of the proposed scheme is also performed on a developed laboratory prototype. A comparative evaluation of the proposed algorithm is also performed with the existing schemes. A series of test results from the simulation software and the laboratory prototype show the effectiveness of the proposed scheme.