CT compensation of numerical distance relaying algorithm

Abstract

In this paper a prototype algorithm for Numerical Distance relay is developed in order to prevent maloperation of relays when Current Transformer (CT) saturation occurs. Saturation of CT causes errors in reproduction of the current fundamental harmonic. The design of CT(s), which never saturate would end in bulky and expensive units. Therefore most of the protective CTs that are in service saturate during severe transients. Distorted secondary current due to CT saturation is detected and compensated by the algorithm in order to obtain correct operation of Distance relay in saturation area. Thirddifference function and Auto Regressive (AR) model are employed in developing the saturation detection and compensation algorithm. The algorithm is developed using C++ language. Then the performance of the algorithm is evaluated through simulation of case studies in Alternative Transient Program (ATP) simulator. Finally, the Numerical Distance Relaying algorithm with CT saturation compensation is successfully developed