By 2010, the GAO predicts that the probability of maintaining at least 24 satellites may dip below 95%, the service quality standard set by the Air Force. Due to development delays, the current constellation of GPS satellites may begin to fail before new satellites are ready for launch. Normally, this news might be of interest to national defense and navigation system buffs, but the U.S. electricity grid is slowly developing its own dependence on the GPS system.

Syncrophasors are highly accurate measurement devices that are now being deployed to monitor the grid’s health. As half of the smart grid’s “monitor and control” mentality, syncrophasor data will be critical for system operators to anticipate and locate problems in advance of catastrophic outages. Now here’s the dependency: syncrophasors get their time from the GPS signal (part of the origin of the “synchro” name).

When grid operators base their decisions on data from syncrophasors, an interruption of the GPS signal could shut off useful data from the new smart grid devices. The grid will now be vulnerable to interruptions caused by natural or hostile actions not only on the wires themselves, but also on the GPS satellites. Certainly, having grid status data most of the time is better than having no data at all, and there are ways to provide time accuracy without using GPS (although more costly). However, like environmental mitigation measures, grid architects need to consciously avoid swapping one reliability problem for another.

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