According to most definitions, a Lightning arrester is a device used on Power systems above 1000V to Protect other Equipment from lightning and switching surges.
It is not a Lightning Rod. Although Lightning rods are devices that divert lightning surges to ground, they are simple conductive terminals that are always at ground potential and are never energized.
If the system without arrester, when lightning strikes the system, equipment is damaged and the lights go out.
However, if the system with an arrester, when lightning strikes the system, equipment is well protected and the lights still work.
It does not absorb the lightning.
It does not stop the lightning.
It does divert the lightning to ground.
It does dlamp (limit) the voltage produced by the lightning.
It only protects equipment electrically in parallel with it.
The MOV disk is a semiconductor that is sensitive to voltage. At normal voltage the MOV disk is an insulator and will not conduct current. But at higher voltages caused by lightning it becomes a conductor.
The MOV disk is very fast acting electronic switch. It is an open switch to standard system AC voltages and a closed switch to lightning voltages.
By magnifying the MOV materil 5000 times, metal oxide grains and dopants in the material can be discerned. MOV disk with a 35mm diameter and a 35mm height contains about 28 Billion MOV grains.
The MOV grains and their junctions are the electronic switches that turn on and off in unison to divert the lightning around the equipment.
A lightning arrester is essentially a collection of billons of microscopic junctions of metal oxide grains that turn on and off in microseconds to form a current path from the top terminal to the ground terminal of the arrester.
So there you have it. A lightning arrester is a device, used on powersystems, that contains billions of electronic switches that divert lightning currents around sensitive equipment and saves them from damage.
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