DISTANCE RELAYING SCHEME WITH MOV PROTECTED SERIES CAPACITOR

Abstract

Continuous increase in power demand leads the fast development in transmission line system. In order to meet
the high demand for power transmission capacity, some power companies have installed series capacitor on power
transmission line. This allows reduction in line impedance, thus resulting increased power transmission capacity. The series
capacitor make sense because it is simple and could be installed 15 to 30% of the cost of installing a new line and provide
the benefits of increased system capacity, reduced system losses and voltage regulation. Integration of the series capacitor in
transmission line reactance adds certain complexities to the effective application of impedance based distance relays. The
protective distance relays use impedance measurement in order to determine the location and presence of faults. The
protective distance relays are fooled by series capacitor on the line when the presence or absence of capacitor in fault loop is
unknown. In such condition distance relay overreach if fault in second zone or it may be reverse reach if fault in first zone.