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 kilometres 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. 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.
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. 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.
Ordinary fuses and circuit breakers are not capable of dealing with lightning-induced transients. Lightning protection equipment may shunt current, block energy from traveling down the wire, filter certain frequencies, clamp voltage levels, or perform a combination of these tasks. Voltage clamping devices capable of handling extremely high amperages of the surge, as well as reducing the extremely fast rising edge (dv/dt and di/dt) of the transient are recommended. The grounding system must address low earth impedance as well as low resistance so as to reduce the consequences of burning . A spectral study of lightning's typical impulse reveals both a high and a low frequency content. The high frequency is associated with an extremely fast rising "front" on the order of 10 microseconds to peak current. The arrester element consists of the main component of ZnO as it blocks are very reliable apparatus with a low failure rate and several kinds of additives, which are mixed, granulated, formed and sintered into a complete block with electrodes on the both surfaces. At normal voltages it act as an insulator and will not conduct current. But at higher voltages caused by lightning it becomes a conductor. Their junctions are the Electronic Switches(in case of microcontroller based) that turn on and off to divert the lightning around the equipment by making different paths of minimum resistance.
Figure shows a typical internal view of the TNR element under a scanning electron microscope. The boundary layer has a very high impedance for a small current region, so the normal operating voltage is almost all applied to its boundary layer.
Surge Suppressor: This is also a surge diverter, but generally for voltages well below 1000 volts.