A transformer protection technique with immunity to CT saturation and ratio-mismatch conditions

This paper describes a digital technique for protecting power transformers. The technique uses positive- and negative-sequence models of the power system in a fault-detection algorithm. The phase voltages and currents at the transformer terminals are used to detect faults. The performance of the proposed technique was studied for a variety of operating conditions using simulated data. The impact of ratio-mismatch and saturation of CTs on the performance of the technique was also examined