And that is the problem with an integrated system which resulted in a massive blackout across North-Eastern North America on August 14, 2003.

In order to cope with changing power demands changing by the second, more than 2GW of power were flowing one way and then switched to the opposite direction on the same HV transmission lines.

I remember that one well. What's interesting in your link is that it was "The Perfect Storm". The series of events and the timeline are classic.

• 12:15 p.m. Incorrect telemetry data renders inoperative the state estimator, a power flow monitoring tool operated by the Indiana-based Midwest Independent Transmission System Operator (MISO). An operator corrects the telemetry problem, but forgets to restart the monitoring tool.
• 1:31 p.m. The Eastlake, Ohio generating plant shuts down. The plant is owned by FirstEnergy, an Akron, Ohio-based company.
• 2:02 p.m. The first of several 345 kV overhead transmission lines in northeast Ohio fails due to contact with a tree in Walton Hills, Ohio.[15]
  
  41°21′22″N 81°34′10″W[citation needed]
• 2:14 p.m. An alarm system fails at FirstEnergy's control room and is not repaired.
• 3:05 p.m. A 345 kV transmission line known as the Chamberlin-Harding line sags into a tree and trips in Parma, south of Cleveland.
• 3:17 p.m. Voltage dips temporarily on the Ohio portion of the grid. Controllers take no action.
• 3:32 p.m. Power shifted by the first failure onto another 345 kV power line, the Hanna-Juniper interconnection, causes it to sag into a tree, bringing it offline as well. While MISO and FirstEnergy controllers concentrate on understanding the failures, they fail to inform system controllers in nearby states.
• 3:39 p.m. A FirstEnergy 138 kV line trips in northern Ohio.[16]
• 3:41 p.m. A circuit breaker connecting FirstEnergy's grid with that of American Electric Power is tripped as a 345 kV power line (Star-South Canton interconnection) and fifteen 138 kV lines fail in rapid succession in northern Ohio.
• 3:46 p.m. A fifth 345 kV line, the Tidd-Canton Central line, trips offline.
• 4:05:57 p.m. The Sammis-Star 345 kV line trips due to under voltage and over current interpreted as a short circuit. Later analysis suggests that the blackout could have been averted before this failure by cutting 1.5 GW of load in the Cleveland–Akron area.
• 4:06–4:08 p.m. A sustained power surge north toward Cleveland overloads three 138 kV lines.
• 4:09:02 p.m. Voltage sags deeply as Ohio draws 2 GW of power from Michigan, creating simultaneous under voltage and over current conditions as power attempts to flow in such a way as to rebalance the system's voltage.
• 4:10:34 p.m. Many transmission lines trip out, first in Michigan and then in Ohio, blocking the eastward flow of power around the south shore of Lake Erie from Toledo, Ohio, east through Erie, Pennsylvania, and into southern Erie county, but not most of the Buffalo, New York, metropolitan area. Suddenly bereft of demand, generating stations go offline, creating a huge power deficit. In seconds, power surges in from the east, overloading east-coast power plants whose generators go offline as a protective measure, and the blackout is on.
• 4:10:37 p.m. The eastern and western Michigan power grids disconnect from each other. Two 345 kV lines in Michigan trip. A line that runs from Grand Ledge to Ann Arbor known as the Oneida-Majestic interconnection trips. A short time later, a line running from Bay City south to Flint in Consumers Energy's system known as the Hampton-Thetford line also trips.
• 4:10:38 p.m. Cleveland separates from the Pennsylvania grid.
• 4:10:39 p.m. 3.7 GW power flows from the east along the north shore of Lake Erie, through Ontario to southern Michigan and northern Ohio, a flow more than ten times greater than the condition 30 seconds earlier, causing a voltage drop across the system.
• 4:10:40 p.m. Flow flips to 2 GW eastward from Michigan through Ontario (a net reversal of 5.7 GW of power), then reverses back westward again within a half second.
• 4:10:43 p.m. International connections between the United States and Canada start to fail.
• 4:10:45 p.m. Northwestern Ontario separates from the east when the Wawa-Marathon 230 kV line north of Lake Superior disconnects. The first Ontario power plants go offline in response to the unstable voltage and current demand on the system.
• 4:10:46 p.m. New York separates from the New England grid.
• 4:10:50 p.m. Ontario separates from the western New York grid.
• 4:11:57 p.m. The Keith-Waterman, Bunce Creek-Scott 230 kV lines and the St. Clair–Lambton #1 230 kV line and #2 345 kV line between Michigan and Ontario fail.
• 4:12:03 p.m. Windsor, Ontario, and surrounding areas drop off the grid.
• 4:12:58 p.m. Northern New Jersey separates its power-grids from New York and the Philadelphia area, causing a cascade of failing secondary generator plants along the New Jersey coast and throughout the inland regions west.
• 4:13 p.m. End of cascading failure. 256 power plants are off-line, 85% of which went offline after the grid separations occurred, most due to the action of automatic protective controls.

I knew it was a big deal as I was filling a water bowl for the dogs and saw the pressure drop. My backup generator was online in 30 seconds but the water supply reduced to a trickle. Neighbor walked over and we were chatting. Got out a bottle of Jack and he and his wife came over and we watched movies and enjoyed the air conditioning. Pretty cool being all lit up.

Anyway think of everything that needed to go wrong for that to happen. Normally grid loads are shifted all the time and not even a burp, then this. The perfect storm. Our power was restored around midnight and the generator shut down.

Ron

 

Good stuff. Poor operator.