What causes a power system blackout?

Blackouts occur when power system disturbances cascade beyond the system's ability to compensate. Common causes include: equipment failures, extreme weather damage, generation-load imbalance (frequency deviation), voltage collapse, transmission overloads, and protection system misoperations. The 2003 Northeast blackout started from tree contact on a transmission line. Prevention involves redundancy (N-1 criterion), proper protection coordination, load shedding schemes, and grid interconnections.