The Living Power Grid

Your power grid is the largest machine ever built. In the US alone, it spans over 160,000 miles of high-voltage transmission lines and serves more than 145 million customers. It also has to balance supply and demand in real time — electricity can't be easily stored, so generation must match consumption every second.

• Grid frequency (50 or 60 Hz) is watched closely — if it drops, demand is outrunning supply
• Blackouts cascade because overloaded lines heat up, sag, and short out on trees, tripping more lines
• The 2003 Northeast blackout cut power to 55 million people, set off by a software bug and untrimmed trees.