DEVELOPMENT OF DIGITAL DISTANCE PROTEC flON ALGORITHM FOR SERIES COMPENSATED TRANSMISSION LINES

Abstract

In this thesis, a digital distance protection algorithm for series compensated transmission lines is presented. In a series compensated line, the presence of non-linear MOV elements (which are placed in parallel across series capacitor to protect them from overvoltages), alters the impedance seen by the distance relay. Consequently, the existing digital distance relaying algorithms, which rely on the assumption of constant impedance of the protected zone, may fail to work satisfactorily. In this thesis, a relaying algorithm, which is based on a technique called voltage compensation technique, has been used. In this technique, the voltage across the series capacitor and overvoltage protective device (MOV) is calculated in the relay and subsequently, this calculated voltage is subtracted from the voltage measured at the relaying point. The new compensation technique makes the impedance measurement immune to MOV operation, thus enhancing accuracy of impedance measurement. The presented algorithm completely integrates three aspects of a digital distance protection system i.e. fault direction discrimination, fault classification and fault impedance calculation. The algorithm has been tested using PSCAD/EMTDC model of 400kv 300 km transmission lines. The enclosed results demonstrate dependability of the developed technique.