System Reduces Lightning Damage From $1 Million To $50,000
Lee Ayers of South Carolina used to live in dread of the region's frequent electrical storms. When the phone rang during these events, chances were that it concerned a report of damage—yet another lighting strike on yet another substation.A system engineer for the Mid-Carolina Electric Cooperative, Lexington, S.
Lee Ayers of South Carolina used to live in dread of the region's frequent electrical storms. When the phone rang during these events, chances were that it concerned a report of damage—yet another lighting strike on yet another substation.
A system engineer for the Mid-Carolina Electric Cooperative, Lexington, S.C., Ayers notes that, worse yet, were the times the phone didn't ring—which led him to speculate that a communications tower had been hit, severing the co-op's radio and microwave links. "We were experiencing tremendous losses due to lightning, specifically transformer in five substations," says Ayers. "If a single substation was hit, we would lose as many as 4,000 to 5,000 customers.
"If a communications tower was damaged, we wouldn't necessarily lose power to any customers, but we wouldn't have the radios and data communications to support restoration, maintenance and all the other necessary efforts to get people back on line."
Mid-Carolina serves 42,000 customers in the greater Columbia area. Its service area is second only to central Florida in terms of the number of lighting strikes per year. Compounding that is the sandy soil in the area, "which makes the earth less conductive than usual," Ayers notes. "We think that was a big factor in the number of hits we were getting. The lightning rods we had installed were not protecting our equipment."
At some point, losses at the co-op were so bad, and so repetitive, that Mid-Carolina's insurance company demanded that something be done. Over a five-year period, the replacement cost of damaged equipment was between $1.25 to $1.5 million. Premiums, the insurance carrier said, would go sky-high.
Ayers went looking for a solution and found one—during a presentation at an Institute of Electrical and Electronics Engineers conference—in a system that uses the point discharge principle. The idea: a sharp point in a strong electrostatic field will leak off electrons by ionizing adjacent air molecules, providing the point's potential is raised 10,000 volts above that of its surrounding.
In the system that Ayers heard about, thousands of points are provided. These simultaneously produce ions over a large area, thus preventing the formation of a "streamer," the precursor to a lightning strike. The voltage differential between the ground and the charged cloud is lowered to well below the lightning potential, even in the midst of the worst summer storm.
After a survey, the system was installed on Mid-Carolina's substations and communications towers. "Over the five-year period after the installation, our losses to collateral lightning damage on the protected facilities probably amounted to no more than $50,000."
As a result, Mid-Carolina has made the system standard on all of its installations. "As we build new substations and communications towers, we budget them in," says Ayers. "We don't wait to have a lightning strike to decide the new site needs protecting, we just protect it from the beginning."
From Pure Power, Summer 2001.