Why is time synchronization important?
Through the use of integral GPS receiver-clocks, PMUs sample synchronously at selected locations throughout the power system. This provides a system-wide snapshot of the electrical system. The GPS not only provides time tagging for all the measurements but also ensures that all phase angle measurements are synchronized to the same time as well. Figure 6 shows how time skews in the measurement and analysis process can induce errors in the phase angle difference computations. Here, the phase angle difference between two sets of measurements was approximately 10 degrees. However, when one of these two phase angle signals was skewed by 1 second and then the phase angle difference was computed, then the resulting answer incorrectly indicated a phase angle difference of approximately 5 degrees between those two data sets. Phasor calculations demand greater than 1 millisecond accuracy.
