Lightning Arrestor

Lightning Arrestor

A lightning arrester (alternative spelling lightning arrestor) (also called lightning diverter) is a device used on electric power systems and telecommunication systems to protect the insulation and conductors of the system from the damaging effects of lightning. The typical lightning arrester has a high- voltage terminal and a ground terminal. When a lightning surge (or switching surge, which is very similar) travels along the power line to the arrester, the current from the surge is diverted through the arrester, in most cases to earth.

In telegraphy and telephony, a lightning arrester is placed where wires enter a structure, preventing damage to electronic instruments within and ensuring the safety of individuals near them. Smaller versions of lightning arresters, also called surge protectors, are devices that are connected between each electric conductor in power and communications systems and the Earth. These prevent the flow of the normal power or signal currents to ground, but provide a path over which high-voltage lightning current flows, bypassing the connected equipment. Their purpose is to limit the rise in voltage when a communications or power line is struck by lightning or is near to a lightning strike.

If protection fails or is absent, lightning that strikes the electrical system introduces thousands of kilovolts that may damage the transmission lines, and can also cause severe damage to transformers and other electrical or electronic devices. Lightning-produced extreme voltage spikes in incoming power lines can damage electrical home appliances or even produce death.

Lightning arresters are used to protect electric fences. They consist of a spark gap and sometimes a series inductor.

Lightning, is a form of visible discharge of electricity between rain clouds or between a rain cloud and the earth. The electric discharge is seen in the form of a brilliant arc, sometimes several kilometers' long, stretching between the discharge points. How thunderclouds become charged is not fully understood, but most thunderclouds are negatively charged at the base and positively charged at the top. However formed, the negative charge at the base of the cloud induces a positive charge on the earth beneath it, which acts as the second plate of a huge capacitor.

When the electrical potential between two clouds or between a cloud and the earth reaches a sufficiently high value (about 10,000 V per cm or about 25,000 V per in), the air becomes ionized along a narrow path and a lightning flash results.

Many meteorologists believe that this is how a negative charge is carried to the ground and the total negative charge of the surface of the Earth is maintained.

The possibility of discharge is high on tall trees and buildings rather than to ground. Buildings are protected from lightning by metallic lightning rods extending to the ground from a point above the highest part of the roof. The conductor has a pointed edge on one side and the other side is connected to a long thick copper strip which runs down the building. The lower end of the strip is properly earthed. When lightning strikes it hits the rod and current flows down through the copper strip. These rods form a low-resistance path for the lightning discharge and prevent it from travelling through the structure itself.

Arrestors are typically installed on transmission lines and they divert lightning and utility switching surges to ground, clamping (or limiting) the voltage of the surge. Their function is similar to that of a hardwired Surge Protective Device (SPD)that is installed inside a facility.

lightning never strikes in the same place twice …The CN Tower gets hit by lighting on average 75 times a year. It is still standing.. The tall structure has 42 Grounding Rods each 20 inches thick. These grounding rods safely direct lightning strikes to ground. Power Lines, Electrical Substations, buildings and farms are protected against lightning strikes with Lightning Arrestors .