PC BASED PROTECTIVE RELAYING FOR TRANSFORMERS

Abstract

The present, work aims at development of a percentage biased harmonic restrained- differential- protection using PC for a single phase power transformer. - The -protective Scheme, differential protection of power transformers consists in converting the primary and secondary line currents to a common base using appropriately connected CTs- of Suitable ratios and comparing these currents. During, normal • operating conditions, the difference between._these currents is small, resulting from normal magnetizing current. and small ' CT errors. This difference during external faults can be. quite -large because of a difference in the dynamic behaviours of CTs on the two sides of the transformer.. On the contrary, during a. winding (internal) fault, the difference current may not be very large.- If only a small portion of the .winding is short circuited.