4.1 Air-termination systems

Air-termination systems are used to capture lightning strikes in a targeted manner. Placing them on, at or next to a structure to be protected determines defined possible points of strike for the lightning discharge. These are the first point of contact between an external lightning protection system and the lightning discharge and are therefore subject to complex electrical and mechanical stress. Correct dimensioning of the air-termination systems reduces the effects of a lightning strike to a structure in a controlled manner.
In case of cloud-to-earth flashes, a downward leader of lightning discharge grows step-by-step in a series of jerks from the cloud towards the earth (chapter 1.2). When the downward leader has got close to the earth within a few tens, to a few hundreds of metres, the electrical insulation strength of the air near the ground is exceeded. A further “leader” discharge similar to the downward leader begins to grow towards the head of the downward leader: The upward leader (Figure 1.5.1). This determines the point of strike of the lightning (chapter 1.5). The electrogeometric model (chapter 1.5) was derived from the relationship between the electrical parameters and the length of the striking distance of a lightning stroke. This model forms the basis of all methods used to design air-termination systems.