Aportación al análisis de la distribución de corriente del rayo en palas de aerogenerador equipadas con fibra de carbono
- Autores: José Antonio Rey Fernández
- Directores de la Tesis: Joan Montañá Puig (dir. tes.)
- Lectura: En la Universitat Politècnica de Catalunya (UPC) ( España ) en 2021
- Idioma: español
- Materias:
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- Resumen
This doctoral thesis investigates the current distribution in a wind turbine blade when it is struck by lightning. The thesis focuses on the problem of current distribution in blades with carbon fiber spar caps. In the first part of this thesis, a code is developed for the simulation of the current distribution from the resolution of Maxwell's equations using the method of finite differences the time domain (FDTD). In order to be able to model a wind turbine blade with a 25 meter carbon fiber (CFRP) spar cap, the standar FDTD method has been modified. In particular, the non-uniform meshing of the geometry to be simulated and the possibility of simulating materials with anisotropic electrical properties have been implemented. The code has been implemented combining the Matlab and Fortran programming languages, taking advantage of the facilities that Matlab provides for creating 3D geometries, assigning properties and post-processing. The resolution of the electromagnetic problem is carried out in Fortran, significantly reducing the simulation time. With the code carried out, the current distribution between the down-conductor of the lightning protection system and a CFRP laminate of the beam has been studied. Also the differences in electrical potential that occur between various points of the lightning protection system and the CFRP. The results have been published in the journal Electric Power Systems Research (EPSR).
The results obtained from the current distribution show the significant effect due to the contact resistance between the elements that are part of the path of the lightning currents. In particular, those contacts between metallic conductors of the protection system and the CFRP components. The second part of the thesis deals with the modeling of these contacts. First, it is checked whether the analytical contact resistance formulas can be applied when one of the electrodes is made of CFRP. For this, experiments have been carried out with electrodes simulating point contacts to a CFRP laminate. The case of one and two point contacts in the same direction of the carbon fibers and in the perpendicular direction have been studied. From the experiments it is concluded that the Holm expression can be applied to a point contact but not to the total of a conventional electrode. In this case, the resistivity of the CFRP between the point contact points that form the global contact must be taken into account.
After the analytical and experimental study, it has been verified that methods such as the finite element method (FEM) or FDTD produce very significant errors in the simulation of the contact between a medium with high conductivity (eg copper) and one with low conductivity. like the CFRP. To solve this problem, two electrical contact models are proposed where the first one identifies the contact areas between the electrode and the CFRP material by using thermography to subsequently discretize the contact area. In the discretization, each of the point contacts that form the connection is modeled with the resistance obtained from the Holm expression. This methodology is applied to methods such as FEM and FDTD. The second connection model is for application to a circuit theory model formed by a network of resistors. The model, in addition to representing the connection, allows to obtain in a simple way the total resistive value of the CFRP specimen as well as to be able to investigate the effect of the electrical conductivities of the CFRP in the longitudinal and perpendicular axes to the fibers.
