IEEE C37.242-2013 pdf download IEEE Guide for Synchronization, Calibration, Testing, and Installation of Phasor Measurement Units (PMUs) for Power System Protection and Control
Universal Time (UTC) time scale and the phase of the reference cosine wave. The required performancecould be realized by either synchronizing the samples directly to the timing reference or by software-basedpost processing of the acqired samples. To achieve a common timing reference for the PMU acauisitionprocess, it is essential to have a source of accurate timing signals (i.e, synchronizing sourcc) that may bcinternal or extermal to the PMU. In the first case the synchronization source is integrated (built-in) into thePMU (external GPS antenna still required) In the latter case. the timing signal is provided to the PMU bymeans of an external source. which may be local or global, and a distribution infrastructure (based onbroadcast or direct connections).
The timing signal gencrated by the synchronizing source must be referenced to UTC and provide cnoughinformation to determine that the time is in agreement with UTC. The synchronization signal must also beavailable without interruption at all measurement locations throughout the interconnected grid. The timingsignal should be characterized by the availability, reliability, and accuracy suitable for power systemrequirements.
The timing signal should be accurate cnough to allow the PMUs to maintain synchronism with an accuracsufficient to keep the total vector error (TVE) within the limits defined in IEEE Std C37.118.1-2011 (scc4.3 of that standard for discussion).
The PMU is required to detect a loss of time synchronization that would cause the TVE to exceed theallowable limit or within 1 min of an actual loss of synchronization, whichever is less(IEEE Std C37.118.2-2011, 4.5). In this case a flag in the PMU data output (STAT word Bit 13) should beasserted until the data acquisition is resynchronized to the required accuracy level.
In addition to the STAT word Bit 13, IEEE Std C37118.1-2011 specifies further signals intended todescribe the time quality of the synchronization source. Each of the PMU output messages defined(Configurations 1, 2, and 3, Header, and Data) have a time quality field of 4 bits. This field allows the PMUto state the quality of the tie source from clock locked, 1 ns to 10 s uncertainty (estimated worst-caseerror), or clock failure. Also, the Data message STAT has two bits to indicate the length of time the clockhas been unlocked. This varies from locked to unlocked for more than 10 s, 100 s, or more than 1000 s.
Even though a clock may be unlocked for over 1000 s, a quality oscillator is able to maintain better thatI us accuracy over this period. Consult the clock manufacturer’s documentation for its drift specification.
IEEE Std C37.118.2-201 adds a 3-bit PMU Time quality field to the status word in place of a previouslyunused security bit field. When used, this field indicates the uncertainty in the easurement time at thctime of measurement and indicates time quality at all times. both when locked and unlocked, and unknownwhen the clock is starting up.
4.3 Satellite-based synchronizing sources
This subclause summarizes the main technologies that could be adopted for PMU synchronization.
The following figures of erit have been considered in assessing the performances of the synchronizationsource technologies (Lilley,Church, Harrison)[B37]):
Accuracy: The degree of conformance between the measured synchronization signal and its trucvalue.
Availability: The capability of the synchronization system to provide usable timing services withinthe specified coverage area.
Continuity: The probability that the synchronization system will be available for the duration of aphase of operation, presuming that the system was available at the beginning of that phase oloperation. The factors that affect availability also affect continuity.