Lieu d’installation : Plate-forme DIMM et bâtiment TDF
Discipline : Protection contre la foudre
Domaine de recherche : Phénomènes d’attachement de la foudre sur une structure au sol
Context
The aim of the Pic du Midi experiments is to estimate the risk of a structure or site being struck by lightning.
More specifically, the aim is to gather data on the phenomenon of lightning strikes in the specific conditions of a high-altitude site and the presence of a high-rise structure (a TDF antenna).
In addition to its high lightning frequency, the Pic du Midi has other advantages that make it ideal for long-term experimentation. In particular, the presence of a cable car provides easy access to the summit compared with other mountain ranges, which are generally accessible on foot. In addition, the presence of an electrical network and Internet access means that certain equipment can be powered without the need for batteries or solar panels, and that all instruments can be remotely controlled at all times.
The data collected are being used to develop a computer simulation method that not only designates the vulnerable zones of a structure, but also estimates impact probability values for each of the structure’s more or less vulnerable zones. This initial approach, which provides probabilities without considering the actual lightning strike at the site, is then supplemented by a statistical analysis of data from the METEORAGE detection network. An estimate of the number of impacts likely to strike each zone of the structure in question can then be calculated on a global basis, i.e. taking into account downward or upward strikes and not being limited to a single current value.
Installation method and operation
In order to study the phenomenon of lightning attachment to a complex structure, the Pic du Midi site was instrumented with various diagnostic tools. Although lightning strikes are observed throughout the site, particular attention is paid to two specific locations: the DIMM platform lightning conductor and the TDF antenna.
Instrumentation is therefore spread over several locations. Firstly, the DIMM platform houses a 5 m high lightning conductor, the various sensors associated with it, and the entire data acquisition system. Cameras are also installed throughout the site, including behind glass in a room in the TDF building, providing a 150 m view of the lightning conductor and the DIMM platform.
High-speed and video surveillance cameras are installed to record lightning strikes anywhere on the site. Similarly, a field mill and capacitive antennae are placed near the DIMM platform to record fluctuations in the electric field associated with the presence of a thundercloud and lightning strikes occurring on or near the Pic du Midi. As no instruments could be placed near the TDF antenna, only the DIMM platform’s lightning conductor was fitted with current probes, placed around its mast, to measure the currents flowing through it. The various acquisition devices used to record, digitize and store all sensor signals are located in the room beneath the DIMM platform.
As all devices are connected to the network, they can be consulted, configured or controlled remotely. What’s more, all the equipment has a common clock, enabling measurements to be synchronized and correlated. This GPS synchronization also facilitates the identification and correlation of lightning strikes with data supplied by the METEORAGE detection network.
Expected results
Experiments at the Pic du Midi have enabled us to gain a better understanding of the physics of lightning attachment to structures.
These data are essential to our field of activity.
They also enable us to develop computer models for simulating lightning attachment, so as to improve site protection in the long term.
Laboratories and partners involved
- ABB Pôle Foudre in Bagnères de Bigorre
- SIAME Laboratory, University of Pau and Pays de l’Adour.
- METEORAGE in Pau.
