A numerical technique based on symmetrical components for protecting three-winding transformers

This paper describes a digital technique for protecting three-winding transformers. The technique uses positive- and negative-sequence 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 simulations on an electromagnetic transient program. The impact of changes in tap-settings, ct ratio-mismatch and saturation of current transformers on the performance of the technique was also studied. Results indicate that the technique is stable during these conditions. (C) 2000 Elsevier Science S.A. All rights reserved.