**IEEE C37.118.1**-2011 IEEE Standard for Synchrophasor Measurements for Power Systems.

3.1 Definitions anti-aliasing: The process of filtering a signal before sampling to remove components of that signal whose frequency is equal to or greater than the Nyquist frequency (one-half the sample rate). If not removed, these signal components would appear as a lower frequency component (an alias). Coordinated Universal Time (UTC): (Initials are ordered based on French language.) The time of day at the Earth’s prime meridian (0° longitude). It is distributed by various media, including the Global Positioning System (GPS) system. data concentrator (DC): A device that combines data from several measurement devices. frequency error (FE): The measure of error between the theoretical frequency and the measured frequency for the given instant of time. Global Positioning System (GPS): A U.S. Department of Defense (DoD) navigation system that uses a constellation of 24 satellites broadcasting a precision signal for location and time synchronization. Basic time synchronization accuracy is ± 0.2 microseconds (μs). IEEE floating point: A 32-bit representation of a real number. NOTE—This definition is in accordance with IEEE Std 754-1985. 5 leap second: A positive or negative one-second adjustment to the Coordinated Universal Time (UTC) that keeps it close to mean solar time. Nyquist frequency: A frequency that is one-half the sampling frequency of a discrete signal processing system. Nyquist rate: A sampling rate that is twice the bandwidth of a band-limited signal. It is the minimum sample rate that will result in an alias-free representation of a signal. It must therefore be greater than twice the highest frequency component in the signal.

phasor: A complex equivalent of a sinusoidal wave quantity such that the complex modulus is the cosine wave amplitude, and the complex angle (in polar form) is the cosine wave phase angle. phasor data concentrator (PDC): A data concentrator (DC) used in phasor measurement systems. rate of change of frequency (ROCOF) error (RFE): The measure of error between the theoretical ROCOF and the measured ROCOF for the given instant of time. synchronism: The state in which connected alternating-current systems, machines, or a combination operate at the same frequency, and in which the phase angle displacements between voltages in them are constant or vary about a steady and stable average value. synchronized phasor or synchrophasor: A phasor calculated from data samples using a standard time signal as the reference for the measurement. NOTE— In this standard, the phasors from remote sites have a defined common phase relationship. total vector error (TVE): The measure of error between the theoretical phasor value of the signal being measured and the phasor estimate.IEEE C37.118.1 pdf download.