Detection and Correction of Saturated Current Transformer Measurements Using Decaying DC Components

When fault currents contain decaying dc components, current transformers (CTs) face the risk of becoming saturated. Traditionally, fault current waveform or CT model analyses were used to detect CT saturation. This paper analyzes the decaying dc components in fault currents to detect CT saturation. The decaying dc component in fault currents is first estimated using phasor-based computations. Such a component is then used to define a detection index. The proposed detection index can be easily used to detect CT saturation because its value in an unsaturated period is within a pre-known range. After CT saturation has been detected, the current samples and phasors in the latest unsaturated period are used to correct the saturated current samples. The proposed algorithm was tested using MATLAB/SIMULINK simulator and realized on a DSP Starter Kit to demonstrate its effectiveness and applicability.