Hurricane causes grid damage across Florida, Georgia, Carolinas, Tennessee, Virginia

What happened

In late September 2024 a Category 4 hurricane made landfall on the northern Gulf coast of Florida and tracked several hundred miles inland through Georgia, South Carolina, North Carolina, Tennessee and Virginia, including areas of the southern Appalachian mountains. At peak the storm caused approximately 4.7 million customer outages across these states. Reported transmission damage in one affected state exceeded 370 high voltage structures and line sections across three transmission owners.

Reported distribution and substation damage included submerged substations, thousands of poles down and fallen transmission towers in mountainous terrain. One large utility reported damage to more than 8,000 poles, more than 21,000 spans of conductor (about 1,000 miles of line), more than 1,500 transformers and thousands of trees on lines. Mobile substations were trucked in to give temporary supply to communities while damaged fixed equipment was repaired or replaced, and some local networks required complete rebuild rather than repair.

Customer hours lost across the affected states made 2024 the worst year for outage hours in the United States in the previous decade, and one affected state averaged nearly 53 hours of interruption per customer during 2024, mainly attributed to this storm. Restoration involved more than 50,000 utility workers from 41 states and Canada. By mid October approximately 99.4% of customers had been restored, although isolated mountain communities remained without supply more than two weeks after landfall, and distribution restoration in the worst affected areas continued for several weeks longer.

Contributing factors

Reported by the source and subsequent public analysis: (1) the storm reached several hundred miles inland while retaining high wind speeds, and the affected mountain areas of Tennessee, North Carolina and Virginia had not generally been treated as hurricane exposed in utility planning frameworks; (2) severe flooding accompanied the wind damage, with substations submerged and access routes destroyed by floodwater and mudslides; (3) the affected networks in these states included long, dispersed distribution circuits through forested and mountainous terrain, which increased exposure to tree fall and made repair access difficult; (4) vegetation damage was reported to be widespread across whole circuits rather than the scattered tree falls assumed in local planning baselines; (5) flooded substations required extensive de-watering, drying and inspection before equipment could be re-energised, a slower process than wind damage repair; (6) reconnection in flooded areas required electrical inspection of each affected building before re-energisation, which added restoration time independent of network repair; (7) commentary in the source placed the severity of inland damage within a broader pattern of weather extremes exceeding historical planning baselines rather than treating it as a single event anomaly.

Lessons learned

1. Inland mountain areas treated as low hurricane risk suffered severe wind and flood damage, so operators should update planning baselines for current weather extremes.
2. Submerged substations needed de-watering, drying and inspection before re-energisation, so operators should install elevated equipment and improved drainage in flood zones.
3. Dispersed distribution circuits through forested mountainous terrain caused widespread tree damage and slow access, so operators should review options such as undergrounding or microgrids.

More lessons on weather and external hazards, from every incident on the register.

Not yet known

• Exact cost of damage and restoration
• Number of days of full supply loss per customer
• Specific models and ages of damaged equipment

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Source

web.archive.org