PERFORMANCE OF DIGITAL DISTANCE RELAY ALGORITHMS FOR PROTECTING TRANSFORMER TERMINATED LINES

Abstract

Recent advances in microelectronics has enabled the use of micro-processors in distance protection of transmission lines. This area has drawn much attention of power system researchers. Different algorithms for use in digital distance relays are reported in the literature. The performance of these algorithms can be evaluated off-line before actual implementation in power systems. Frequency response and effects of decaying d.c. which is normally present in transient currents are among some of the characteristics of the algorithms that can be examined. Their performance can also be examined using fault data or data of transients like inrush currents which occur during switching-on of transformers. This thesis is concerned with the simulation of inrush current and the assessment of the performance of digital algorithms for distance protection during the presence of inrush current. Initially,the modelling of transformers is examined so as to simulate and analyze in rush current. Some of the simulation studies of inrush current are reported in the thesis. The ability of each algorithm for detecting faults in the presence of inrush current is checked by using simulated data. The faultson transformer terminated lines are simulated using an electromagnetic transients program, EMTDC. Development and assessment of a fault direction discriminating algorithm for protection of transformer terminated lines is also presented. Results reported in the thesis demonstrate that this algorithm performs satisfactorily.