Methods of Time Synchronization

Time synchronization is critical to modern electrical power systems. Based on the lessons learned from the postdisturbance analysis of the August 14, 2003, northeast blackout, NERC (North American Electric Reliability Corporation) recommendations place a high priority on implementing time synchronization in data-recording devices. This eliminates or reduces the effort involved in comparing event information from distributed intelligent disturbance recording devices. Accurate device time is required for disturbance analysis in order to correlate individual device event reports and is also essential for synchronized system control and synchrophasor applications. Many different time-synchronization methods currently in use provide time using different physical dissemination methods and deliver varying levels of accuracy. In many cases, these time-synchronization methods are untested, yet they are assumed to be sufficiently accurate. This paper explores some of the most commonly used synchronization methods, identifying the strengths and weaknesses of each. Measured accuracy for each method is identified, and a determination is made regarding the suitability of each method for event correlation, synchronized system control, and synchrophasor applications. Methods tested include: • Direct IRIG-B to an intelligent electronic device (IED). • DNP3 to an IED via a communications processor receiving IRIG-B. • DNP3 over radio via a communications processor receiving IRIG-B. Conclusions are presented regarding which timing method is preferred for different applications. Tables are provided to allow direct comparisons of application methods to assist in applying the best method of this important technology.