Abstract
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.
Highlights
Specific standards are available to provide guidelines on lightning protection strategies
FEM has been used to estimate the current that will be dissipated during a lightning strike in a LST telescope, as well as to study how a high discharge current pulse is guided through the grounding electrodes to Earth
We are proposing a design and verification protocol for lightning protection systems installed on scientific facilities which addresses critical issues that are common to installations on harsh environments
Summary
Specific standards are available to provide guidelines on lightning protection strategies. In some cases local standards must be considered. While all these standards provide valuable information, they are mostly focused on the analysis of buildings and industrial installations, and some peculiarities of scientific installations are not always well covered by them. We focus this work on the risk and earth quality assessments, and apply this to an example of a large scale scientific installation: the largest telescopes of CTA-N observatory. CTA-N has been conceived as an array of fourteen Cherenkov Telescopes of two different sizes, which will be constructed in La Palma Island, Spain. Cherenkov Telescopes can provide valuable information on different astrophysical sources from the gamma rays reaching the Earth’s atmosphere. The design and construction of the LST Lightning Protection System faced a number of technical difficulties that were addressed with the protocols described in this paper
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