Reminders about spark gaps
Medium voltage HTA and high voltage HTB lightning arresters

The spark gap is the simplest, oldest, sturdiest and cheapest means of protection. It generally consists of two electrodes, one connected to the element to be protected, the other to earth. The air gap between the two electrodes constitutes a weak point in the network installation, preventing an ignition from occurring at a point in the network where it could have serious consequences. The distance between these two electrodes is adjustable and determines the ignition voltage.

The shape and nature of the electrodes vary widely, but are generally the result of dielectric test campaigns to give them well-defined ignition properties for given environmental conditions (temperature, humidity, atmospheric pressure of ambient air).