Current differential relay with a power-current spectrum blocking for transformer protection

In this paper, a combined power-current spectrum blocking for current differential protection of power transformer is proposed. The proposed algorithm can exclusively classify the internal faults associated with transformer inrush currents. This combination is assessed based on the individual analysis of differential power and power spectrum releasing functions and second harmonic current blocking considering modern design of power transformer. The investigation involves both theoretical and experimental studies in order to validate the new algorithm. Also, the scheme stability and sensitivity boundaries are obtained covering broad band of operational and fault conditions.