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 electrical 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 arresters can form part of large electrical transformers and can fragment during transformer ruptures. High-voltage transformer fire barriers are required to defeat ballistics from small arms as well as projectiles from transformer bushings and lightning arresters.
The following are the damages that are caused by the travelling wave on the substation equipment.
1. The high peak or crest voltage of the surge may cause flash-over in the internal winding thereby spoil the winding insulation.
2. The steep wave fronts of the surges may cause external flashover between the terminals of the transformer.
3. The highest peak voltage of the surge may cause external flashover, between the terminals of the electrical equipment which may result in damage to the insulator.