A power transformer protection technique with stability during current transformer saturation and ratio-mismatch conditions

This paper describes a digital technique for protecting power transformers. The technique uses positive- and negativesequence models of the power system in a fault-detection algorithm. While phase voltages and currents at the transformer terminals are used to detect fault, no information concerning parameters of the transformer and power system is required. The performance of the proposed technique was studied for a variety of operating conditions using data generated by emtp simulations. The impact of ratiomismatch and saturation of cts on the performance of the technique was also examined. Results indicate that the proposed technique is stable during these conditions.