Extreme cold is being blamed for equipment failure that caused a brief outage Tuesday for more than 9,600 city of Poplar Bluff electric customers.
Repairs were completed Wednesday afternoon and all equipment is now back online, according to Mike Wech, acting administrator for the Southwestern Power Administration.
SWPA provides electricity to the city utility and is the owner of the damaged equipment.
A breaker at the Morrison Road substation suffered a leak that caused the loss of a non-toxic vapor gas used to insulate the system.
"The cold weather has an impact on these devises and the rubber seals and the O rings that seal the gas in," said Wech. "That ended up being the problem. We had a seal that because of the cold weather caused the leak."
The rubber seal and the sulphur hexaflouride gas have been replaced, Wech said.
The breaker was brought back online at 2:05 p.m. Wednesday. It is less than 10 years old, Wech said.
"We have this problem very rarely. It probably occurs three to four times in a five or six year period," said Wech. "I think the colder than normal temperatures definitely had an impact on this. There are many breakers we have throughout the system that are of this same design."
SWPA markets hydroelectric power from 24 dams to rural electric cooperatives and municipal utilities serving more than 8 million customers.
SWPA was first alerted to the leak at 7:30 a.m. Tuesday.
The breaker normally holds between 90 and 175 psi, Wech said. It had dropped to 70 psi by the time crews de-energized the breaker at 1 p.m. Tuesday, after city residents were alerted to the planned outage.
The substation was de-energized to allow crews to take the breaker offline safely, officials have said.
"The gas is an insulating medium between the energized parts and the grounded portion of the system," Wech said. "When that insulating gas is lost, there's a potential hazard to both the equipment and any personnel in the area. If we would ignore that problem, we could have catastrophic equipment failure."
The breaker serves one of three transformers that bring outside electricity to the transmission lines for local customers.
Although the transformer was initially reported as being offline until the breaker was repaired, Wech said its operations were transferred to an auxiliary circuit breaker.
"We put the transformer that was fed by that circuit breaker with the gas leak back in service within 13 minutes," he said.
Wech extended his thanks to the city utility for their assistance in notifying the public, and to residents for their patience.