A Review of Current Issues in Lightning Protection of New-Generation Wind-Turbine Blades

The salient issues related to lightning protection of long wind-turbine blades are discussed in this paper. We show that the lightning protection of modern wind turbines presents a number of new challenges due to the geometrical, electrical, and mechanical particularities of the turbines. The risk assessment for the lightning-protection-system design is solely based today on downward flashes. We show in this paper that the majority of the strikes to modern turbines are expected to be upward lightning. Neglecting upward flashes, as implicitly done by the International Electrotechnical Commission, might result in an important underestimation of the actual number of strikes to a tall wind turbine. In addition, we show that the rotation of the blades may have a considerable influence on the number of strikes to modern wind turbines as these may be triggering their own lightning. Because wind turbines are tall structures, the lightning currents that are injected by return strokes into the turbines will be affected by reflections at the top, bottom, and junction of the blades with the static base of the turbine. This is of capital importance when calculating the protection of internal circuitry that may be affected by magnetically induced electromotive forces that depend directly on the characteristics of the current in the turbine. The presence of carbon-reinforced plastics (CRP) in the blades introduces a new set of problems to be dealt with in the design of the turbines' lightning protection system. One problem is the mechanical stress resulting from the energy dissipation in CRP laminates due to the circulation of eddy currents. We evaluate in this paper the dissipated energy and propose recommendations as to the number of down conductors and their orientation with respect to the CRP laminates so that the dissipated energy is minimized. It is also emphasized that the high static fields under thunderclouds might have an influence on the moving carbon-fiber parts. This issue needs to be addressed by lightning protection researchers and engineers. Representative full-scale blade tests are still complex because lightning currents from an impulse current generator are conditioned to the electrical characteristics of the element under test and return paths. It is therefore desirable to complement laboratory tests with theoretical and computer modeling for the estimation of fields, currents, and voltages within the blades.