An extended magnetizing inrush restraint method applied to digital differential relays for transformer protection

This paper describes the design, computational aspects and results of digital differential relays for transformer protection. Two estimators based on Walsh series and least squares algorithms are developed. The extended magnetization restraining technique, which uses angular relationship as well as magnitude of transformer currents, is applied for inrush current recognition. Inrush trip suppression is checked using real data. Test results illustrate the abilities of the algorithms and feasibility of the whole protection scheme. Obtained results are presented and discussed in the paper.