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Two-punch storm may hit underground power systems

The second punch from Hurricane Florence may hit some electric cooperative members served by underground systems, as heavy rain accumulates and flows into portions of South Carolina this week. As the storm winds die down, the calm provides only partial relief from potential damage to the power supply.

Wires buried underground and transformers that sit on the ground usually give members confidence that their electricity supply will be protected during hurricanes or tornadoes.

“That’s true only to a limited degree,” said Rob Ardis of Santee Electric Cooperative in Kingstree. “Underground systems are not directly affected by toppled trees.”

On overhead electric systems, cross arms with attached wires sit near the top of power poles. Transformers that look like round buckets are bolted to the poles. All are vulnerable to falling trees or even wind if its speed is high enough. In the winter ice can accumulate on wires and break their attachments to poles.

Underground systems, however, are protected from windy conditions.

“Hurricane winds. Check. Tornados. Check. But, when the rains come, and the flooding follows, we worry about underground systems, too,” said Ardis, an electrical engineer and the cooperative’s CEO.

Cooperative members feel an extra layer of security with underground service, but in a flood the security can be fleeting.

“The buried wires are heavily insulated for years of safe, dependable service, and the transformers sit above ground, covered from rain but in unsealed cabinets,” said Ardis, whose cooperative serves about 44,000 members in Clarendon, Florence, Georgetown and Williamsburg counties. 

Flood waters have easy access to the inside of the transformers and the switch gear where connections are made between overhead supply lines and the lines that go underground.

“We can’t seal the transformer cabinets because the heat they generate needs a way to get out,” Ardis said.

In coastal areas, a hurricane’s storm surge can push salty water inland, damaging switch gear and transformers. Often, the flood water shorts out the electric system. Sometimes, the cooperative will de-energize flooded areas with underground service to protect other parts of the system. That can be the source of misleading rumors that far exaggerate the frequency of such action. No utility would ever de-energize any area unless it was absolutely necessary.

Water, whether salty or fresh, causes problems for underground and ground-mounted equipment.

“The unfortunate fact,” said Ardis, “is that no system is completed protected from Mother Nature.”

Not when she punches like she’s doing this week.


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The Electric Cooperatives of South Carolina, Inc. is the state association of electric cooperatives. More than 1.3 million South Carolinians in all 46 counties use power provided by 20 independent, member-owned electric co-ops.  Together, the co-ops operate the state’s largest electric power system with 75,000 miles of power lines across 70 percent of the state.

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