Almost everything we use in the form of appliances and machines runs on electricity. You have two faces of electricity – the conducting part and the insulating part. Without the insulation on the conductors we could not handle the conductors and we would have accidents every day. The insulators help us from another potential danger – the surge in the conductors when a lightning strikes the conducting wires.
Two fold manifestation in protection
The use of lightning arresters is two-fold. One is in the use of the actual arrester to prevent damage from direct lightning hits and the second is the surge arrester that prevents indirect surges when lightning occurs in the vicinity of a conductor. The lightning strike sends thousands of kilovolts of power in the wires bringing electricity to your house. This can damage the wires, the insulators, the appliances using the electric power, and even cause death.
Construction of the arrester
The fundamental part of the lightning arrester is the spark gap. This may sometimes have a filling of any semiconductor material such as zinc oxide or silicon carbide. Air is a perfect insulator and is used in most of the arresters. But, in some the gap is filled with semiconductor gas that ionizes when the voltage reaches a preset value. This increases the conducting value of the gap and helps to divert the huge surge in the current.
Operation of the arrester
The huge surge is invariably directed to the earth. When the voltage returns to the normal value, the gap opens and the bypass does not conduct current anymore. The normal grid voltage passes through the regular channels to the house appliances. Though the arresters are of normal size for domestic applications, you need huge lightning arresters for substations and power distribution centres. These have a porcelain tube having zinc oxide discs. They have dimensions of several feet length and their diameter is a couple of inches.
Extra provisions provided
You have occasional explosions in the cylinder. To accommodate this, the arresters have vents in their sides. Rating for the lightning arresters considers factors such as energy they can absorb, their capacity to withstand peak current, along with their breakover voltage. The breakover voltage is needed to begin conduction again.
Use of surge protection devices
The surge protectors are also protection devices for electrical installations against lightning strikes. When the lightning strikes in the vicinity of the conducting wire, you have an induced voltage in the wires. The current travels to the ends of the wire and if there are any electrical appliances connected, it will damage them.
The surge protectors are not connected to prevent the direct strikes but will prevent any surge currents from flowing through the domestic circuit. The excess current is grounded or sent to the ground. They have another name, the surge protection device. People also refer to them as the transient voltage surge suppressor. One can use scaled down versions of this in domestic circuit electrical panel service entrance to give protection to household equipment. An indication light will show when the current is excess.
The principle of operation of these protectors is either in diverting the current away from the primary circuit or blocking the excess unwanted energy. Either way, they add to the safety of the electrical network. Use of protectors and arresters is mandatory in all electrical circuits.