IEEE C37.118.1a-2014 IEEE Standard for Synchrophasor Measurements for Power Systems Amendment 1: Modification of Selected Performance Requirements.
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4. Synchrophasor measurement 4.3 Measurement time synchronization Change first paragraph in 4.3 as shown below: The PMU shall be capable of receiving time from a reliable and accurate source, such as the Global Positioning System (GPS), that can provide time traceable to UTC with sufficient accuracy to keep the total vector error (TVE), the frequency error (FE), and the rate of change of frequency (ROCOF) error (RFE) within the required limits. All measurements shall be synchronized to UTC time with accuracy sufficient to meet the requirements of this standard. Note that a time error of 1 µs corresponds to a synchrophasor phase error of 0.022 degrees for a 60 Hz system and 0.018 degrees for a 50 Hz system. A phase error of 0.57 degrees (0.01 radian) will by itself cause 1% TVE as defined in Equation 12. This corresponds to a time error of ±26 µs for a 60 Hz system and ±31 µs for a 50 Hz system. A time source FE of 0.083 MHz in a 60 Hz system or 0.1 MHz in a 50 Hz system will cause the maximum allowed steady-state FE of 0.005 Hz. Similarly, a time source with a varying frequency will cause a corresponding error in ROCOF (the relationship is not as direct as those above). A time source that reliably provides time, frequency, and frequency stability at least 10 times better than these values corresponding to 1% TVE is highly recommended. The time source shall also provide an indication of traceability to UTC and leap second changes.
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