COLUMN-Phasors and blackouts on the U.S. power grid: John Kemp

Thu Apr 5, 2012 9:04am EDT

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By John Kemp

LONDON, April 5 (Reuters) - Smart meters are the most visible part of the power industry's attempt to upgrade the electricity network to cope with rising consumption and the integration of renewable sources of generation such as wind and solar.

The U.S. federal government is spending hundreds of millions of dollars to support the roll out of smart meters that will enable more variable power pricing linked to time of use (TOU) or peak demand to encourage ordinary households and small businesses to limit their electricity use when demand is greatest and help manage pressure on the grid.

Increasing the amount of "demand-side response" is crucial to improving flexibility and ensuring the grid can cope with the unpredictable output of intermittent power sources such as wind and solar, as well as small-scale distributed generation by households and businesses themselves selling power back into the network at irregular times.

But the smart grid is about much more than just smart meters. The Smart Grid Investment Grant (SGIG) programme established by the American Recovery and Reinvestment Act (ARRA) is also funding the deployment of 877 high-frequency phasor monitoring units (PMUs) linked to satellite communications and the global positioning system.

The aim is to improve the robustness and reliability of the transmission grid and prevent a repeat of the cascading power failures that rolled across the north-eastern United States and parts of Canada in 2003.

TRANSMISSION STRESS

In less than five minutes on the afternoon of Aug. 14, 2003, a local problem in the Cleveland-Akron area of Ohio that had been rumbling all afternoon spread like a tidal wave across the network, shutting down 508 generating units at 265 power plants, including emergency stoppages of 10 nuclear stations, as power surged uncontrollably around the grid. It left 50 million people without electricity, some for as long as four days.

The official report blamed tree growth for failure on five transmission lines, coupled with a computer system failure and poor communications and operating practices by grid managers for starting a power failure that then spiralled as grid managers lost control ("Final Report on the August 14 2003 Blackout" April 2004).

But it was only the largest and most recent in a series of massive outages, including another blackout in the north-east in 1965 which left 30 million people without power for 13 hours; an outage affecting 9 million in New York City in 1977; and disturbances on the West Coast in 1982 and twice in 1996 leaving millions without power each time.

North America's power network, built by a patchwork of local utilities, has always been less robust and more prone to wide-area failures than the more centralised networks common in the United Kingdom and Western Europe.

But the official report into the 2003 incident identified a series of developments that have increased stress on the grid and risked undermining reliability. Marketisation has led to the proliferation of many more short-term power contracts, the entry of a host of smaller generators, often with less experience of interconnected operations.

The report also blamed the erosion of unused transmission capacity, rising system throughput, moving (wheeling) power over long distances, and the declining willingness of utilities to make investments in transmission reliability that do not increase revenues. (See page 104 for a list of the changing industry conditions that have affected reliability).

The report ended with 46 recommendations for improving the system's resilience against cascading failures, as well as cyber-attacks by terrorists or foreign powers. The industry has since made significant progress implementing some of them, especially those linked to operating procedures.

But integration of a substantial share of renewables will make the challenge harder. Grid controllers will have to deal with an increased share of intermittent, unpredictable generation; the need to move power across even longer greater distances (from the windy Midwest to the power hungry north-east for example); and back it up with gas-fired generation at short notice; all the while preventing congestion.

The grid is only as strong as its weakest link and its capacity to react to failures once they happen in an orderly way.

Intermittent and distributed generation will make grid management far more complex. Monitoring power flows across the network and detecting disturbances and failures quickly enough to react will become even more essential to prevent cascading failures.

BEAM ME UP, SCOTTY

The hoped-for solution to grid instability is something called the North American SynchroPhasor Initiative (NASPI), which sounds like something out of Star Trek but is in fact a collaboration between the federal government and industry to improve grid monitoring and control by using modern communications technology.

More than 500 phasor monitoring units have so far been installed across the transmission network to take precise measurements of frequency, voltage and other aspects of power quality on the grid up to 30 times per second (compared with once every four seconds using conventional technology).

Units are synchronised using GPS to enable users to build up a comprehensive real-time picture of how power is flowing across the grid (www.naspi.org/Home.aspx and).

It is a scaled-up version of the monitoring system developed by the University of Tennessee's Power Information Technology Laboratory using inexpensive frequency monitors that plug into ordinary wall sockets.

Tennessee's FNET project provides highly aggregated data to the public via its website.

The systems being developed under NASPI provide a much finer level of detail that will reveal congestion and disturbances on individual transmission lines and particular zones so that grid managers can act quickly to restore balance or isolate failures ().

Data on its own will not ensure greater stability. Better grid operations and practices will be essential to make use of it. But it is a vital first step and is essential if the system is going to integrate more renewables - and maybe eventually plug-in electric vehicles - without increasing chaos on the system and more blackouts.

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