GC: n
CT: Equipment and buildings can also be protected by raising the effective ground level with a static line or lightning rod. The static line on the utility’s distribution system and the lightning rods on farm buildings are attempts to do just that. Lightning rods, such as those at utility substations, offer a 45-degree cone of protection beneath them. When lightning strikes a lightning rod, the lightning passes directly to the ground without first going through the object shielded below. For this reason some medium-size and larger wind turbines sport lightning rods above the nacelle.
S: WP – http://goo.gl/2S66y5 (last access: 28 February 2015)
N: 1. lightning (n): late 13c., present participle of lightnen “make bright,” extended form of Old English lihting, from leht. Meaning “cheap, raw whiskey” is attested from 1781, also sometimes “gin.” Lightning bug is attested from 1778. Lightning rod from 1790.
rod (n): Old English rodd “a rod, pole,” which is probably cognate with Old Norse rudda “club,” from Proto-Germanic rudd- “stick, club,” from PIE reudh- “to clear land.”
As a unit of measure (5½ yards or 16½ feet, also called perch or pole) first attested mid-15c., from the stick used to measure it off. As a measure of area, “a square perch,” from late 15c., the usual measure in brickwork.
2. Wind Turbine Component Damage.
The following systems, arranged in order from most to least vulnerable, may be damaged by lightning strikes:
- damage to the control system. These include sensors, actuators, and the motors for steering the equipment into the wind. According to the updated National Fire Protection Association handbook: “While physical blade damage is the most expensive and disruptive damage caused by lightning, by far the most common is damage to the control system”;
- damage to electronics. Wind turbines are deceptively complex, housing a transformer station, frequency converter, switchgear elements, and other expensive, sensitive equipment in a relatively small space;
- blade damage. A lightning strike to an unprotected blade will raise its temperature tremendously, perhaps as high as 54,000° F (30,000° C), and result in an explosive expansion of the air within the blade. This expansion can cause delamination, damage to the blade surface, melted glue, and cracking on the leading and trailing edges. Much of the damage may go undetected while significantly shortening the blade’s service life. One study found that wood epoxy blades are more lightning-resistant than GRP/glass epoxy blades;
- damage to generators;
- batteries can be destroyed, or even detonated, by a lightning strike.
3. Lightning rods are not likely to protect the windmill’s electronic equipment. Furthermore, lightning rods may obstruct the flow of wind around the turbine’s blades, reducing the system’s efficiency. This advice contrasts with that offered by Machine Design Magazine, which states that “Franklin-type lightning rods protect [wind turbines] against direct lightning strikes.”
S: 1. OED – http://www.etymonline.com/index.php?allowed_in_frame=0&search=lightning+rod&searchmode=none; http://www.etymonline.com/index.php?allowed_in_frame=0&search=rod&searchmode=none (last access: 28 February 2015). 2 & 3. http://www.nachi.org/wind-turbines-lightning.htm (last access: 28 February 2015).
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S:
CR: nacelle , wind energy, wind turbine (1).
