Numerical modelling of lightning strikes to wind turbine blades: analysis of equipotential bonding for CFRP spars

Abstract

Modern wind turbine blades are equipped with a lightning protection system to intercept the lightning and conduct its current, preventing the direct attachment to internal conductors. In such conditions, resin thermal degradation develops at the equipotential bonding (EB) connections between down conductors (DCs) and carbon fibre reinforced polymer (CFRP) spars. This problem was investigated in this work by combining experimental studies and finite element method (FEM) simulations. The experimental work focused on the characterisation of the input material properties to be used in the FEM models. An experimental-numerical procedure was established to determine the electrical contact resistivity of EB joints. Besides, the thermal degradation of a commercial epoxy was studied to determine its reaction kinetics. The developed FEM models solve a weakly coupled formulation of the electromagnetic-thermal problem to predict lightning current paths and thermal damage at the bonding interfaces. The validation of the models against conducted current test data showed that they can assist in the design of EB joints. High current densities and temperatures were predicted at the sparking locations found during the test, which allowed a qualitative prediction of potential thermal degradation areas upon the solution of the Arrhenius equation. In addition, such models can be used to assess the potential risk of flashover between the blade conductors due to high electric fields. Finally, typical EB materials were compared using the developed FEM models to provide guidelines and suggestions for the implementation of EB joints. It was seen that materials with high in-plane electrical conductivities, such as ECF and BIAX CFRP, can reduce the electric field below the insulation breakdown strength and prevent flashovers. Besides, hot spots at the bonding interfaces can be controlled by changing the arrangement of the EB layers, or by using a material with low contact resistivity and high thermal diffusivity like ECF.

More information

Identifiers

ORCID for Antonio, Andrea Maria Laudani: orcid.org/0000-0002-0423-5363

Catalogue record

Export record