The GPS receiver provides the 1 pulse-per-second (pps)
signal, and a time tag consisting of the year, day, hour, minute, and second. The l-pps
signal is usually divided by a phase-locked oscillator into the number of pulses per
second required for the sampling of the analogue signals. The analogue signals are
derived from three-phase voltage and current transformers with appropriate anti-aliasing
filtering. The microprocessor calculates the positive sequence voltage and current
phasors, and determines the timing message from the GPS, along with the sample
number at the beginning of a window