Synchrophasors: An Opportunity Wrapped in an Enigma

The Western Interconnection’s shiny new synchrophasor grid – 450+ shoebox-sized phasor measurement units (PMUs), each giving system operators 30 to 60 snapshots of voltage, current, angle and frequency per second – has radically transformed system operators’ ability to understand real-time system conditions. Until about a year ago, transmission system monitoring technology could produce about one measurement every two to four seconds -- good enough for the average home alarm system, but a geological epoch in the microsecond world of high-voltage transmission control.

This incremental leap in transmission system diagnostic capability is on par with someone handing a Renaissance anatomist an electron microscope instead of a magnifying glass. Synchrophasors arm operators with a degree of “actionable visibility” unprecedented in the history of grid management, potentially leading to tools that respond to deteriorating system conditions in nanoseconds, rerouting power flows away from pinch-points and making rolling blackouts a memory.

But at least for now, translating the terabytes of data the Western Interconnection’s synchrophasors are producing into real-world control systems remains more promise than reality. The problem, in talking with experts such as Brett Wangen, Peak Reliability’s Director of Engineering, isn’t data quantity – it’s data quality.

“Even in the huge volume of data we’re now producing, there are gaps,” Wangen says “– data packets drop, data frequency varies, we wonder ‘Why are we only getting 27 signals per second rather than 30?’ It’s a new system and obviously there are going to be issues that need to be resolved – the next phase of the project will target data quality.”

At the heart of the issue is data verification in real-time -- for control systems to work, the data that triggers them has to be accurate. “Currently there’s really no way to verify the signal-based data from the PMUs in real-time,” Wangen said. “At 30 signals per second, we just don’t have a way to say, yep, that’s a good data point. We can validate the data after the fact, but that doesn’t help us in real-time.”

Worldwide, multiple utilities, including Scottish Power, are researching the Holy Grail: distribution system synchrophasor-based control systems. The technology’s real-time data verification issues will eventually be solved, but in the meantime, the tsunami of synchrophasor data is already beginning to reshape crucial transmission modeling tools.

Reliability compliance standards require operators to set system operating limits – essentially, the inventory of available transmission capability – conservatively, in order to leave plenty of margin for unexpected events. Synchrophasors are now giving modelers an unprecedented level of visibility into how accurate their models really are. “We can see minutely how the system responds to an event or disturbance,” Wangen says. “We can see that the system responded this way, but the model predicted that. In most cases the system planning models predict the response perfectly; in others, there are discrepancies that have to be investigated. System operating limits are one output – obviously that has crucial reliability and economic impacts for our clients.”

There’s a lot at stake – better system visibility equals more accurate models, which equals more transmission inventory to sell. It’s an extremely valuable commodity, a fact that will continue to drive technological innovation that exploits the full potential of the synchrophasor array for years to come.

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