Last edit: 16/05/2023
In 1752 the American inventor Benjamin Franklin discovered, during a very dangerous experiment with a kite, that lightning is an electrical discharge.
Today we know that lightning can discharge between a cloud and the ground (ground lightning, descending lightning), between ground and cloud (ascending lightning) or between cloud and cloud. Most atmospheric discharges detected are so-called “negative descending lightning”: this type of discharge is caused by the difference between the negative polarity of the cloud and the positive polarity of the ground. With this discharge, current flow occurs from the ground to the cloud.
The random nature of lightning, which is defined only by statistical values, forces the protection system to be designed and sized in a technically correct manner, otherwise the danger of damage may be aggravated.
The effective solution against the effects of lightning consists of both external protection by lightning rod (external LPS) and internal protection (internal LPS), according to IEC 62305 (class. IEC 81-10).
The purpose of the internal LPS is to avoid potential differences between the various points of the installation by systematically equipotentiating all metal bodies and active conductors by means of arresters.
However, the insertion of SPDs in the various distribution systems must take into account the measures taken to protect against indirect contacts of persons and the requirements to ensure, as far as possible, continuity of operation. It should be noted that in TT networks, differential relaying is commonly deployed to achieve adequate safety, but with the insertion of SPDs there are often untimely openings that no longer guarantee continuity of operation.
In detail, the normative body consists of the following parts:
– EN 62305-1: “Lightning protection. General principles.” Contains information on lightning hazard, lightning characteristics and significant parameters for simulating the effects produced by lightning.
– EN 62305-2: “Lightning protection. Risk assessment.” The assessment is based on an analysis of the risks themselves in order to first establish the need for lightning protection. The technically and economically optimal protection measure is determined. Finally, the remaining residual risk is determined.
– EN62305-3: “Lightning protection. Material damage to structures and danger to people.” Deals with the protection of buildings and people from material damage and danger of death, which could be caused by the effect of lightning current or dangerous discharges.
– EN 62305-4: “Lightning protection. Electrical and electronic systems in structures.” Covers the protection of buildings containing electrical and electronic systems from the effects of electromagnetic interference (EMF) produced by lightning.