CT Saturation Detection Based on Waveform Analysis Using a Variable-Length Window

Saturation of current transformers (CTs) can lead to maloperation of protective relays. Using the waveshape differences between the distorted and undistorted sections of fault current, this paper introduces a novel method to quickly detect CT saturation. First, a symmetrical variable-length window is defined for the current waveform. The least error squares technique is employed to process the current inside this window and make two estimations for the current samples exactly before and after the window. CT saturation can be identified based on the difference between these two estimations. The accurate performance of this method is independent of the CT parameters, such as CT remanence and its magnetization curve. Moreover, the proposed method is not influenced by the fault current characteristics, noise, etc., since it is based on the significant differences between the distorted and undistorted fault currents. Extensive simulation studies were performed using PSCAD/EMTDC software and the fast and reliable response of the proposed method for various conditions, including very fast and mild saturation events, was demonstrated.