Use of Rogowski Coil as Current Transducer for Distance Relay Reach Correction

Abstract

Conventional iron core CT gets saturated with increase in system X/R ratio, burden connected across it under normal condition and presence of DC component in symmetrical current waveform under faulty condition. CT saturation causes distance relay (DR) to under reach and operate it with certain time delay. The problem becomes more critical when fault takes place near to the boundary of first zone of DR. RC has become more popular for measurement of normal and complex transient current due to its inherent linearity, wide operating current range, reduced size, cost and its flexibility in operation. With the development of today's microprocessor/numerical relay, Rogowski coil (RC) has become more suitable for protective relaying applications. This paper presents use of RC for measurement of current in distance protection scheme (DPS). Case study for validation of use of RC is carried out on Electric furnace system. The simulation results of DPS used for protection of part of 220kV IEEE 9 Bus system shows excellent performance of RC over conventional CT during normal and abnormal conditions.