Although fascinating to watch, lightning strikes can cause a lot of problems. They are a leading cause throughout the world of power-line disruptions, utility outages, and fires, and other damage. In the second week of this year, for example, lightning sparked a fire at a chemical plant in Australia’s New South Wales Hunter Valley, hit a substation and disrupted train service in Gauteng, South Africa, and struck a TV transmitter in Greenville, S.C., taking the station off the air for several hours. More than a thousand lightning strikes hit Sydney, Australia, on 8 January.
If facilities are not properly equipped, lightning can cause millions of dollars in damage and downtime of critical equipment. But businesses can protect themselves against the violent force of nature, according to several IEEE experts.
A single spark of lightning can be over 8 kilometers long, soar to temperatures of 27 800 degrees Celsius, and harbor currents of 100 000 amperes.
In considering protection against a lightning strike, think of a voltage divider, says IEEE Senior Member David Brender, national program manager for the Copper Development Association’s Electrical Program, which is headquartered in New York City. Brender’s organization is the market development, engineering, and information services arm of the copper industry in North America. One side of the divider is your structure, and the other side is the lightning protection system, with collection points, down conductors and, hopefully, low-impedance grounding
“A robust low-impedance grounding path is essential to safety,” Brender says. “A lightning protection system without this may be worse than no lightning system at all.
“Lightning is a tremendous source of energy in the sky that wants to get to earth as quickly and as easily as possible. You want the conduction path to earth to be easy and robust so as to conduct the maximum amount of the lightning strike. If the lightning should flow into a building, there is a fairly significant danger of damaging the structure or equipment and injuring people.”
Adds IEEE Fellow Vladimir Rakov, “As countries become more industrialized, man-made structures are built which include power and communication lines. That means more lightning strikes will be intercepted by those structures.” Rakov is co-director of the International Center for Lightning Research and Testing, and a professor in the department of electrical and computer engineering at the University of Florida, in Gainesville. He notes that Florida has about 10 strikes per square kilometer per year—the highest rate in the United States.
Lightning affects buildings both directly and indirectly. Direct effects include the burnout or even explosion of electrical power and distribution equipment. Indirect effects are caused by increases in ground voltage when lightning hits the earth, generating high electromagnetic fields. That can induce voltage and current surges in electric power and signal circuits in the area—which might in turn burn out electrical equipment. Power, telephone, data, and even underground plumbing might transfer damaging lightning surges into a building.
About one third of power-line outages are lightning related, according to Rakov. Outages are also caused by trees falling across the lines, high winds, or a vehicle hitting a utility pole. “Consumers are very unhappy when they lose their electricity,” Rakov notes, “so lightning protection is a must for power lines.”
One of the most common hazards power engineers must protect against are flashovers, which can lead to an interruption of service, says IEEE Senior Member John McDaniel, chair of the IEEE Power & Energy Working Group on Lightning Performance of Overhead Lines. He is a lead engineer with the electric utility National Grid in North Syracuse, N.Y.
A flashover is a fault on an electric power line caused by an arc across an insulator. Faults on power lines can involve tremendous levels of current and cause bright arcing, showers of sparks, and loud bangs and buzzing sounds. Flashovers also can be induced when lightning strikes close enough to an overhead line to cause a sharp increase in voltage.
Lines may be protected in three ways, according to McDaniel: by adding shielding, surge arresters, or insulation. Static wires are normally placed above transmission and distribution lines to shield them from a direct stroke. These wires intercept most such strokes and conduct them harmlessly to ground. Nearby objects such as trees, buildings, and fences can act as natural shields.
A surge arrester is similar to a big diode. It protects against both direct strokes and induced flashovers. When it senses a lightning surge on the line, it limits the voltage by shunting the surge to ground and clamping the voltage there to prevent a flashover. Surge arresters can be installed on just about any piece of equipment including cables, transformers, regulators, and capacitors. The insulation layer used in fabricating the power line also helps prevent lightning damage.
TYING IT TOGETHER
Brender urges building owners and facility managers to check their electrical grounding systems and to take a “total systems approach” when evaluating their lightning protection. “The building must be considered as a whole,” he says, “with all the grounding electrodes tied together in one robust grounding system, as opposed to individual ground paths for each service.” For example, electric service grounding should not be electrically separate from the lightning-protection grounding. “Such separation is not permitted by codes and presents a danger for personnel and equipment,” he adds.
Buildings are typically grounded by several methods. The Franklin rod system is often used on roofs to gather the energy from a stroke and guide it to earth by a series of down conductors. Several elements go into a grounding system, sometimes including a ring ground around the building. Another might be the reinforced steel within the building’s concrete footings. That should also be part of the grounding system, Brender says.
“Structural steel rods are often used as the down conductors, as are separate copper down conductors,” he says. “The idea is to have multiple, parallel paths for the lightning to follow.
“An ill-placed lightning strike can seriously compromise any facility, leaving lost equipment and damaged electronics in its wake. While the equipment may be very expensive, the downtime can be even more significant.”
IEEE offers several lightning-related standards and conferences. They include IEEE 998, Guide for Direct Lightning Stroke Shielding of Substations, IEEE 1243 Guide for Improving the Lightning Performance of Transmission Lines, and IEEE 1410, Guide for Improving the Lightning Performance of Electric Power Overhead Distribution Lines. Conferences dealing with lightning protection include the IEEE PES Transmission and Distribution Conference and Exposition (7 to 10 May), the Asia-Pacific Symposium on Electromagnetic Compatibility (21 to 24 May), the International Beijing Symposium on Electromagnetic Compatibility (22 to 25 May), and the International Symposium on Electromagnetic Compatibility—Europe (17 to 21 September).