Characterization of phase and amplitude comparators in UHS directional relays

In this paper, conventional techniques to compute the phase angle between a voltage and a current waveform are applied to assess the directionality as it is necessary in ultra high speed directional relays. It is shown that with this type of relays the main difficulty stems from the fact that in order to compute the angle, a prior knowledge of the amplitudes of the superimposed voltage and current magnitudes is necessary. Therefore very fast algorithms have to be devised that would take into account anticipated values of these magnitudes in order to assure secure trips in the shortest possible time. Keywords: digital relaying, ultra-high speed directional relays, suppression of DC offset effects, protective relays