A New Fuzzy-logic-based Extended Blocking Scheme for Differential Protection of Power Transformers

In this article, the design aspects of a new digital differential relay for power transformer protection to recognize inrush currents are proposed. The relay design is based on a percentage differential characteristic combined with an extended magnetizing inrush restraint module, which is implemented by a fuzzy inference system. The extended magnetizing inrush restraint technique used in this article considers the angular relationship as well as the magnitude of the transformer currents. The developed method is evaluated using simulated data that is obtained using a new, detailed three-phase transformer model. The obtained study results illustrate the abilities of the algorithms and feasibility of the whole protection scheme. According to the obtained results, a fast operating relay is obtained that has enough security during energizing the transformer.