3:06 P.M. The first of three transmission lines that are believed to have triggered the blackout trips off. The outage puts strain on another line, and a domino effect ensues. Cleveland Power’s voltage plummets to zero.
4:08 P.M. Utilities in Canada and the Northeast experience major power swings. The Bruce Nuclear Station in Ontario shuts down and blackouts hit Toronto and southern Ontario, where most of the province’s 10 million residents live.
4:10 P.M. The Campbell No. 3 coal-fired power plant near Grand Haven, Mich., trips off and, at 4:17, the Enrico Fermi nuke plant near Detroit shuts down automatically after losing power. A number of transmission lines trip between 4:17 and 4:21.
4:10 P.M. A 345-kilovolt line known as the Hampton-Thetford, in upstate New York and Vermont trips. Much of New England is spared, however, when the region’s power operator disconnects its system from New York’s after realizing something is terribly wrong.
4:11 P.M. A transmission line that stretches between Pennsylvania and Toledo, Ohio trips. Between 4:10 and 4:25 at least five nuclear power plants in New York state shut down. Parts of nine states - including all of New York City - are affected by the blackout.
Restoring power to the massive area affected by the blackout was no small feat. Utilities must balance electricity coming from the restarted plants with demands from consumers. Any imbalance can trigger more blackouts. Here’s how it’s usually done.
FIRING UP THE GENERATORS: Once they’ve been shut down, power plants need time and coddling to get up and running again. Supplementary power sources called black starters re-engage the generators and get auxiliary systems online.
SENDING IT TO THE SUBSTATIONS: Once the generators get going, they risk flooding the grid with too much electricity (and shutting it down again) if enough substations aren’t online to draw power.
FANNING OUT: By flipping switches and circuits at the substations, operators can control power distribution and gradually funnel more to neighborhoods that need it.
LINKING THE GENERATORS: As new power plants are connected to the grid, those that are already up and running must pull back their output to compensate for the extra power pumped into the system.
PRIORITIZING THE POWER: Essential systems and services are the first to get their electricity back. These include hospitals, police and fire departments, and sewage-treatment plants.
CONNECTING THE GRIDS: Once areas controlled by individual utilities are up and running, they connect with other nearby regions. The merge can be tricky; as it may prompt destabilizing fluctuations.
TURNING THE LIGHTS ON: By 10 p.m. on the day of the blackout, 50% of affected areas in New England had their power restored. By 5 a.m. the next day, 50% of Canadian areas were back online. New York was fully restored by 10:30 p.m.
