How the U.S. Power Grid Is Like a Big Pile of Sand

How the U.S. Power Grid Is Like a Big Pile of Sand - NationalJournal.com
Last month, The Wall Street Journal gave us quite a scare.
"The U.S. could suffer a coast-to-coast blackout if saboteurs knocked out just nine of the country's 55,000 electric-transmission substations on a scorching summer day," Rebecca Smith wrote.
"It's no secret that North America's three massive power grids, the interconnected systems that transmit electricity from power plants to consumers, are not invincible.
The U.S. power grid is, in fact, big enough to fail."
In other words, the grid may be not be the "right" size—big enough to distribute power efficiently, but small enough to prevent widespread blackouts, such as the 2003 blackout that cut power to 50 million people in the U.S. and Canada for two days.

....The bigger the grid gets, the greater the risk of failures.
Need help visualizing the problem?
Just think of a sandpile, Newman says.
"Sandpiles are stable until you get to a certain height. 
Then you add one more grain and the whole thing starts to avalanche," Newman said. 
"This is because the pile's grains are already close to the critical angle where they will start rolling down the pile. 
All it takes is one grain to trigger a cascade."