PHASE AND AMPLITUDE COMPARATORS FOR TRANSMISSION LINE PROTECTION

Abstract

There are four different types of faults which are usually experienced on a transmission line: phase-to-ground, phase-to-phase, double phase to ground and three phase faults. Therefore, it is essential to protect the transmission lines. Transmission lines have been protected using electromagnetic distance relays. There are two categories of distance relays - the single phase and polyphase. These relays use the principle of either phase or amplitude comparison techniques in their designs. Polyphase relays, however, have some advantages than single phase relays. The main objective of this research is to evaluate the performance of polyphase amplitude and phase comparison techniques. Both of these techniques are implemented for protecting a transmission line against phaseto- phase, three-phase and phase-to-ground faults. The characteristics of the proposed amplitude comparator and conventional phase comparator are examined. Extensive testing was done to study the tripping times. Two and six bus test systems were used to study the behavior of these relays. Several situations were simulated which led to the conclusion that the phase and amplitude comparator took practically same time to generate a trip command. This finding is likely to have a significant savings in the cost of digital distance relays.