With the extended use of very sensitive electronic components, in modern systems, the danger represented by a lightning stroke becomes something not to be neglected. The composite structures housing the components require protection not only against direct strike, but also against the indirect effects. The formulations from the standards (civil and military) confirm this need. The peak currents of the discharges are between 50 and 200 kA, for the A pulse, 2 kA for the B pulse and 200 to 800 Amps for the C pulse.
Due to a nearby lightning stroke the electromagnetic pulse generates a high intensity magnetic field. Thin metal layers as applied in composite structures cannot shield such a magnetic field. Electronic equipment inside such structures will suffer from high-induced voltages and damage and interference will occur. If a lightning stroke hits the composite structure directly the material will be damaged due to the heat generated in the composite material.
A direct lightning stroke is even more complex. The current path for the fast transient and the long tail, with the largest portion of the energy, is different, and different protection measures have to be developed. The levels of protection start from avoiding local destruction of the composite encasing and prevent the mechanical fatigue along the tail of the current path.
In order to provide the required protection measures for these situations we must focus at three main targets:
- The probability of a lightning strike in that area;
- The maximum current induced in the protection system;
- And last but not least the analysis of current protection situation.
Starting from the current models that apply only to the continental areas, we develop new models adapted to the costal and littoral areas. And also according to the position of the composite structure, with the help of the Rolling Sphere Method, the effective protective area is determined. All this to determine the probability of a lightning strike.
A future model that takes in consideration the use of new shielding materials and methods (mono or dual layer), for the lightning current distribution, together with the tolerated risk of service loss will assure a reliable protection system.
In the end the analysis of current protection situation will be used to verify these two models. Also, the future measurements at the test facility in Hengelo will provide an extra certification.
- prof.dr.ir.ing. F.B.J. Leferink
- Ir. M.A. Blaj