Abstract: The saturation of CT when it was faulted often causes the relay protection incorrect tripping. The saturation mechanism of CT and the secondary current characteristics of saturated CT were analyzed. According to the wavelet Mallat algorithm, a CT saturation detection method based on the wavelet theory was put forward. In this method, the wavelet Mallat algorithm was used to extract the low frequency energy and the high frequency energy of the secondary current, and their ratio is used as criterion for CT saturation detection. PSCAD/EMTDC simulation result shows that under various faults, the method can correctly detect whether the CT is saturated; the method has stable performance, and only lesser data were needed for the detection.

Key words: current transformer (CT), saturation, wavelet, Mallat algorithm