A lightning arrester is a protective device used in electrical power systems, buildings, communication systems, and other infrastructure to safely divert high-voltage surges caused by lightning strikes or switching events to the ground for preventing damage to equipment.
Actually, a lightning arrester is a device connected between the line and ground. It remains non-conductive under normal conditions, but during a voltage surge above its threshold level, it becomes a highly conductive path between the line and earth, thereby passing the surge energy to the ground. After the surge is over, the arrester again becomes non-conductive to withstand the normal system voltage.
Purposes of Lightning Arrester
Surge protection is vital in power systems. A lightning arrester plays a crucial role in safeguarding electrical equipment. Mainly during lightning and some switching surges, the system voltage gets disturbed with high peak voltage surges. The insulation of the equipment connected to the system may fail to withstand these high-voltage surges. As a result, the insulation can get punctured and become permanently damaged along with the equipment.
A lightning arrester diverts these overvoltage surges to the ground, so the equipment remains safe from insulation breakdown and damage. Therefore, an arrester extends the lifespan of transformers and other equipment in the power system.
Types of Lightning Arrester
There are various types of lightning arresters used in electrical systems. This section briefly covers their basic construction, working principle, and applications. The Rod Gap Lightning Arrester was among the first developed types. However, it is now considered obsolete and is rarely used today, typically limited to early or temporary installations. Design-wise, it is simple and cost-effective.
This arrester consists of two metal rods with a defined air gap between their heads, known as the spark gap. One rod is connected to the line conductor, while the other is connected to the ground. The spacing between the rod heads is determined by the voltage rating of the system.
When a voltage surge appears on the line, the electric field across the spark gap increases. If this field exceeds the dielectric strength of air, the air in the gap becomes ionized, initiating an arc. This arc provides a low-resistance path, allowing the surge energy to be diverted safely to ground, thereby protecting the connected equipment from overvoltage damage.