Synchronized phasor measurements (synchrophasors) provide a real-time measurement of electrical quantities from across a power system. These measurements can be used to validate system models, measure stability margin, and maximize stable system loading. Reduce cost and complexity of wide-area measurement and event recording using SEL Synchrophasor technology. Improve power system reliability by operating within measured stability limits. Check phasing and connections of current and voltage transformers. Use automatic or manual comparison of phasors for real-time control.
Any interconnected system will have phase shifts in voltages and currents at various points on the system. These phase shifts are caused by load flows and can be used to measure the state of the system.		Many SEL relays and meters include built-in synchronized phasor measurements. SEL-421 and SEL-451 Relays provide synchrophasor data in IEEE C37.118 format. SEL substation-rated computers provide complete data concentration and display formatting.

In each SEL device being used for synchrophasor measurement, a reference wave is created based on the satellite clock. This puts all the devices on the same standard reference (Vref (t) shown above). With an absolute reference for all locations, it is possible to compare voltages and currents from anywhere on a system.

The voltage and current sine waves are converted to a phasor using the formulas shown. The value α is the difference between the signal being measured and the reference wave. A synchrophasor message provides the magnitude and angle for each measured quantity along with a timestamp. Messages from different locations taken at the same time can be compared to each other with errors of less than 1/4 of an electrical degree.

By convention, the phasor is a counterclockwise rotating vector. Its rotational frequency is the system synchronous frequency (50 or 60 Hz).

In a simple system, phasors from different locations can be compared by using calculations based on local voltages and currents. On more complex systems, instantaneous power transmission calculations are extremely difficult, if not impossible. This is where synchrophasors become important. System angles at different points can be viewed instead of calculated.

Use displayed and recorded synchrophasor information from across the power system to improve transmission and generation dispatching. Use measured system load angles to maximize line loading without exceeding stability limits. SEL Synchrophasor technology provides a new tool to economically get more from the power system.

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