An Adaptive Differential Relay for CT Saturation Based on Wavelet Transform

Differential protection relays may false tripping for external faults due to current transformer saturation (CT). This paper presents an adaptive technique for transformer differential protection against saturation of current transformers, based on differential currents. A Wavelet Index (WI) by wavelet Transform has been devised using extracted feature from differential currents due to saturation currents. In this technique, with beginning of saturation of current transformers, the restrain currents in area zone of the differential relay will increase. The proposed algorithm is evaluated by using various simulated internal fault on a power transformer, saturation current cases and different magnetizing inrush currents that has been modeled using Electromagnetic Transients Program software. Results of evaluation study show that, proposed wavelet based differential protection scheme can stable in CT saturation events. The obtained results demonstrate precise operation of the proposed algorithm in different conditions.