The internal protection against lightning safeguards electrical and electronic equipment against surges caused by the electromagnetic impulses of a lightning bolt.
Transient overvoltages are an increase of voltage on the electrical network, measured between two conductors. It may be due to atmospheric electric discharges (lightning), to switching or faulty processes (grounding or short circuit). The most destructive are those due to lightning.
Protection devices must respond instantly, safeguarding the equipment connected to the power supply lines and the data lines. The application standards in this field are IEC 61643-11 and IEC 61643-21.
How do overvoltages enter the equipment?
Power supply, telephone, TV or data lines often cover long distances, far from any protected areas, and are connected to very sensitive equipment. This condition makes the lines especially receptive to overvoltages, which will then be transmitted by conduction to the connected equipment.
Care must be taken with overhead lines that connect sensitive equipment even in protected environments, as it is likely that dangerous voltages may be induced. It is also important to take into account that lightning and power switching generate high magnitude electromagnetic fields, thus inducing currents in the conductors placed inside the field.
Finally, lightning effects can enter through the earthing system, changing the voltage reference of all the equipment connected to it or to the power supply line itself.
In addition, when there are several buildings in the same area, the risk can increase due to the higher number of possible interconnections.