Transformer Protection Evaluation Following Brazil's National System Operator Recommendations

This paper presents the evaluation of transformer protection functions that have been typically employed by the Agents, according to the report ONS RE 3/200/2012 [1], as well as others that have been made available by the manufacturers but are not reported in [1], such as the negative sequence and REF elements. Therefore, this paper compares the performance of the recommended functions by ONS with the negative sequence and REF functions, in order to demonstrate if there is any sensitivity and reliability gain. In order to do so, the following protection functions were implemented: phase (87T) and negative-sequence differential (87Q) as well as restricted earth fault differential protection (87REF); overcurrent protection (50/51) and restricted earth fault directional protection (67REF). The evaluation of these functions was by parametric sensitivity analyzes (PSAs). The obtained results reveal the performance of these functions for transformer internal short circuits, considering the influence of the following parameters: percentage of short-circuited turns, sources strength and conditions of system loading.