A Phase-Shifting Transformer Protection Technique Based on Directional Comparison Approach

This paper presents a new directional comparison-based internal/external fault detection and discrimination technique for the protection of all commonly used phase-shifting transformer (PST) types. Similar to traditional differential protection, the proposed solution offers features, such as speed and selectivity. However, unlike PST differential techniques, the proposed technique offers great reliability. It provides secure operation during conditions, such as current-transformer (CT) saturation, magnetizing inrush current, core saturation, any mismatch between CTs and zero-sequence current, etc. Moreover, unlike the differential solutions, the proposed technique solves the problem of nonstandard varying phase shift without tracking the tap-changer position. Performance evaluation of the proposed technique shows that it provides the best overall protection solution for commonly used single/two-core symmetrical/asymmetrical PSTs. This paper also addresses and solves various challenges that can influence the overall performance of the algorithm.