Following the recent developments in renewable energy sources, wind turbines have been one of the primary devices focussed on. Basically, wind turbines are devices that convert the kinetic energy from the wind into electrical power for human usage. “Wind farms” are created in very windy places to harness this energy.
It is however impossible to harness the entire power potential from the wind. Only 59% of the total kinetic energy of the wind flowing in the turbine can be harnessed. Efficiency greatly depends on the maintenance of the wind turbine and its components.
A variety of tests can be applied to test the material and structures.
In-Depth analysis and NDT tests done.
The lifecycle of wind turbines, the blades are a very important component. The lifespan of equipment due to spinning and exposure to surrounding cause thermal stresses, corrosion, oxidation and erosion. These aspects reduce the lifespan of the wind turbine. The lifespan can vary in usage, due to many unforeseen incidents occurring in the environment of the blades are. Also some type in production or in repair can deteriorate the constituents and in same time curtail the lifespan of the modules.
DYE PENETRANT TEST
Dye penetrant test is the NDT method most often used for inspecting wind turbine blades and vanes. It is recommended to use fluorescent dye penetrants for examination. After some time in overhaul, the blade surface is often corroded. In these circumstances, fluorescent dye penetrant is not endorsed and normal dye penetrant is more practical. The disadvantage of dye penetrant testing is its appropriateness only for surface opening cracks. Subsurface defects cannot be detected. As soon a crack is found, it is not possible to estimate its depth, and here other methods are needed. There are several methods which can be used for revealing of cracks, ageing and degradation of a layer, and for thickness depth. Thermal methods is used for dimension of wall thickness and revealing of near surface irregularities like delaminations.
EDDY CURRENT TECHNIQUES
Eddy current technique is used for detecting crack. It is usually best to calibrate with a calibration block made from the same material as the real component. Althought this results in higher costs but it gives certainly most reliable results. Open cracks and tight cracks can be separated from each other with eddy current technique.
However a crack which goes through grain boundary is clearly more difficult to estimate. Figure 1 shows eddy current signals from three cracks that were found with dye penetrant testing.
a) 3 surface breaking cracks on a turbine blade b) Eddy current signals from cracks.
Fig 1: Eddy current signals from the three cracks shown in the blade .
Measuring the width of a layer is simple with eddy current technique, if there are no strong changes in permeability. In addition, the geometry of a turbine blade can complicate the dimension. Figure 2 shows the width dimension from a first...