This paper is devoted to the study of the most suitable protocols needed
to verify the lightning protection and ground resistance quality in a
large-scale scientific facility located on a site with high risk of lightning
strikes. We illustrate this work by reviewing a case study: the largest
telescopes of the Northern Hemisphere Cherenkov Telescope Array, CTA-N. This
array hosts sensitive and high-speed optoelectronics instrumentation and sits
on a clear, free from obstacle terrain at around 2400 m above sea level. The
site offers a top-quality sky but also features challenging conditions for a
lightning protection system: the terrain is volcanic and has electrical
resistivities well above 1 kOhm·m. In addition, the environment often exhibits
humidities well below 5%, and strong winds pose challenging conditions. On the
other hand, the high complexity of a
Cherenkov telescope structure does not allow a straightforward application of lightning protection standards. We describe here how the risk
assessment of direct strike impacts was made and how contact voltages and
ground system were both tested. Finite Element Simulation (COMSOL Multiphysics)
has been used to estimate the current flowing through the parts of the earthing
system designed for the telescopes in the case of a direct strike impact. This
work is intended to provide assistance to scientists and managers involved in
the construction of scientific installations, particularly those in charge of
defining verifiable reliability and safety requirements for lightning
protection.
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