Lightning arresters are devices used to stop lightning from damaging electrical power systems. Modern electrical systems tend to be vulnerable to voltage surges of any kind, so arresters have become more necessary. Lightning arresters catch surges in electrical wiring and divert them to grounding cables, which direct the current into the ground. Several popular types of lightning arresters are available.
Horn Gap Arresters
Horn gap arresters are named for their two horn-shaped metal rods. These rods are arranged around a small air gap, and the distance between the two rods increases as they rise from the gap. The rods are placed on porcelain insulators.
The horn is connected to two different wires: One attaches to the electrical line. Between it and the horn is a resistance and a choke coil. The resistance regulates the level of current allowed into the arrester at once, and the choke coil increases the reactivity of the arrester when transient frequency occurs. The other wire is connected to a ground, which siphons the excess electricity to the ground.
Multi-gap arresters are made from a series of metal cylinders. These cylinders are all insulated from one another as well as separated by air gaps. The first cylinder gets connected to the electrical line, while all of the other cylinders are attached to the ground through a series resistance, which gradually wears down the power of the current. Some of the gaps between the later cylinders have a shunt resistance that catches a surge when there is an excess of voltage.
Valve-type arresters are commonly used in more high-powered electrical systems. They consists of two main parts: a series of spark gaps and a series of non-linear resistor discs. Valve-type arresters work when excessive voltage causes the spark gaps to touch, and the non-linear resisters carry the voltage into the ground. Once the surge of excess power ends, the resisters push the spark gaps apart.
Pellet-type arresters are made up of glass tubes filled with lead pellets. The pellets are made from an interior of lead peroxide coated by lead oxide. Lead oxide is not strongly conductive; lead peroxide is. When the lead oxide is heated, it becomes lead peroxide, giving the current a place to flow. After the current is transferred, the lead peroxide changes back to lead oxide. This type of arrester is no longer widely used.
- Photo Credit Lightning image by Mohamed Hayat from Fotolia.com
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