Sensitivity and Stability of GPS Synchronised Differential Protection
Current differential relays are now widely used for §the protection of transmission lines. Simplicity of §operation and the ability to clearly discriminate §internal and external faults ensures their §popularity, particulary when digital communication §systems are available. Increasing availability of §digital communication systems creates tremendous §opportunities for protection but recent move to §switched hierarchical communication networks has §created problems for phasor synchronisation. The §solution is GPS. GPS provides time synchronisation §to an accuracy of +/- 1.0 microsecond. Although the §phasor error at +/- 1.0 microsecond is §insignificant, concerns remain about temporary loss §of the GPS signal.§§This thesis presents a technique using symmetrical §component analysis to cope for the loss of the GPS §signal, a robust method in detecting signal §distortion caused by current transformer core §saturation and an adaptive bias technique that §provides improvements in relay sensitivity.