ABSTRACT
This chapter presents a new current-based technique to discriminate transformer inrush from transformer internal faults. The proposed technique relies on converting the three phase transformer currents on both sides into modal current components using Clarke's transformation to produce three current modes, namely, ground mode, aerial mode 1 and aerial mode 2. As transformer inrush current comprises a large second order harmonic component when compared to that of the typical fault current, conventional transformer protection systems are designed to restrain during inrush transient phenomenon by sensing this large second harmonic. Power transformers are vital links and one of the most critical and expensive assets in electrical power systems. Differential protective relays based on the comparison of transformer input and output are widely accepted as the principal protection scheme for power transformers. In rush current may lead to a false operation of the power transformer differential protection relay.
