Every electrical distribution network and transmission line needs protection from the lightning strikes. Since we cannot predict with any degree of accuracy as to where the lightning strike will occur, the wise thing to do is to provide arresters.
Work of the surge arrester
The work of the lightning arrester is different from that of a surge arrester. While the lightning arrester stops the flow of the current due to a lightning strike out of the network, the surge arrester waits for the surge current and diverts it to the ground. It does not arrest the current due to the lightning strike.
Installing break off gaps
Now, the various appliances we use today that run on electricity need to have a constant range of voltage and current. If this is not so, then it could result in damage to the electrical appliances such as the fan, the light, and the television. The way to make sure that the current stays within the prescribed range is by using cut off insulators within the circuit.
These come into operation when the current in the wires reach a high value. This is not the case in the normal course of events. However, whenlightning strikes the wires, the excess current close the insulting gap in the lightning arresters and thus establish a safe passage direct to the ground. Thus, we prevent the high current from reaching our televisions and refrigerators.
Induced current due to lightning
The work of the surge arrester is similar to that of the lightning arrester. When huge current flows near a conductor, it produces enormous induced current in the conductor. This travels along the conductor to the ends and damages the appliances placed there. The surge arrester prevents this from happening by providing a safe passage for the excess unwanted current down to the earth.
Working of an arrester
The arrester has a spark gap filled with air but may also use semiconducting material such as zinc oxide. The semiconducting gas ionizes when large current passes through it. So, the spark that until now was non-conducting becomes conducting and the current is passed down to the earth.
Once the current reaches the earth, the gap opens out again and it becomes non-conducting. The current now passes through the normal circuit and since it has only the normal flow it does not harm the circuits or appliances. In this way, the surge arresters protect the instruments, machines, and appliances we use in our daily life.
For domestic applications, one uses standard size arresters. However, when we consider huge applications such as substations and power distribution centres, the size of the surge arresters is several feet in length and the diameter is a couple of inches across.
At times, you get explosions in the cylinder of the surge arrester. To make room for this, you see vents in the sides of the arrester. The considerations for the design and use of these arresters consists of capacity to withstand peak current, break over voltage for the same, and energy they can absorb. The arresters work by either blocking the excess energy or diverting it to the ground. This improves the safety of the network.