A New Method for CT Saturation Detection using Secondary Current Envelope Detector

This paper presents a new Current Transformer (CT) saturation detection scheme which is based on the waveform identification technique. The variation of secondary current at the time of saturation has been carried out using first order system and slope of current waveform envelope. The slope magnitude of current envelope may depend on low to high degree of saturation. Based on characteristic of current envelope and its slope magnitude, level of CT saturation can be estimated. The fault data with CT saturation condition are generated using the PSCAD/EMTDC software package and algorithm is implemented in MATLAB software. A low-pass, first order Butterworth filter with cutoff frequency of 400 Hz is used to smoothen the CT secondary current. Various parameters such as remanent flux, burden resistance and presence of DC offset are considered for the validation of the proposed algorithm. The simulation results show the effectiveness of the proposed method to detect CT saturation under varying system condition.