Grid Events & Physical Disaster Response

Glossary

Cascading failure

A sequence in which the loss of one grid element shifts its load onto others, causing them to trip in turn, each trip making the next more likely and faster. Cascades accelerate, quickly outpacing human intervention, and can black out wide areas even when total generation exceeds total demand.

Common cause

A single event or condition — a cold front, a heat wave, a flood, a shared fuel supply — that disables multiple supposedly independent components at once. The number of shared common causes, not the number of backups, determines real resilience.

Correlated failure

Failures that share a common cause, so that one occurring makes others more likely or certain. Correlation breaks the probability-multiplication that makes redundancy and reserve margins effective, and is the mechanism behind most wide-area disasters.

Freeze-off

The loss of natural gas production when water in the gas stream or gathering lines freezes during deep cold, cutting supply to power plants at the same moment cold-driven heating demand is peaking on the same pipeline network.

Full-load test

A generator test that applies realistic electrical load — ideally the actual facility load, or a load bank — for a sustained duration, provoking the cooling, fuel-delivery, stability, and transfer failure modes that a no-load test hides. A controlled rehearsal of failure rather than an emergency discovery of it.

N-minus-one (N-1)

The planning principle that a grid should survive the loss of any single component without loss of service. It protects against isolated failures but does not, by itself, guard against common causes that remove many components at once.

Reserve margin

Nameplate generating capacity above expected peak demand, expressed as a percentage. An accounting figure that assumes capacity is available and outages are independent; it can evaporate when a common cause fails many units simultaneously.

Wet stacking

The accumulation of unburned fuel and oil in a diesel engine's exhaust when it runs at light or no load and never reaches proper operating temperature. Ironically caused by the low-load monthly tests meant to ensure reliability, it degrades the engine over time.