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| Index | Technical solutions in use | |
Technical solutions in useICINGSites with icing events require turbines with heated
wind sensors. A variety of heated wind sensors are
available, tested and used at sites with frequent icing
conditions [1]. Blade heating may be necessary or
profitable on sites having frequent icing or on sites
with high safety requirements. The break-even cost of
such a system depends on many turbine and location
parameters
A simple approach to estimate the break-even conditions has been developed by Peltola et. at. [2]. A number of different approaches for the blade heating have been presented, developed and tested. Current practice indicates that in heavy icing conditions the outer surfaces of the blades need to be heated in order to achieve satisfactory results. There have been a number of other proposed solutions, like blade-heating systems based on microwave technology but to date they have not been successfully implemented. At the present moment there are some commercially available solutions. The Finnish blade heating system, where carbon fiber elements are mounted to the blades near there surface, has the widest operating experience, from 18 turbines at various sites, with a total of nearly 100 operating winters [2]. In sites where icing is slight, infrequent and the icing periods are most likely followed by temperature rising above 0°C, blades coated with black paint may be sufficient, making use of the eventual solar radiation. Stopping the turbine and circulating heated air inside the blades may be adequate in slight icing conditions. Stopping the wind turbine when icing starts may also be a sufficient solution in such environments, although ice detectors are then required. COLD CLIMATELittle specific information is available about material properties and lubricants for cold climates in specific relation to their application in wind energy systems. Most available information comes in the form of reports cit ing field experiences from projects in cold climates. There are however some common areas of concern that are expressed repeatedly in the area of turbine materials and lubricants. Most turbine manufactures offer products or upgrades to products for cold environments. All information indicates that the use of these upgrades is required for successful unit operation in these climates. The use of cold resistant steel in all structural members with welds does not increase the costs significantly. Standard hot-dip galvanized bolts have proven adequate in low temperatures. Recent testing at the National Wind Technology Center has looked at the cyclic loading of wind turbine blade root studs at ambient and extreme cold temperatures, -45° to -51°C (-50° to -60 F). Testing considered 4140 steel root studs, a Vinyl Ester / E-glass laminate with an epoxy annulus to pot the root stud inserts into the fiberglass. In the limited tests "All of the cold temperature samples tested exceeded the life of the room temperature control group, though none of the cold temperature samples exhibited any evidence of superior construction over the room temperature samples" [3]. These tests, one of the few being conducted specifically to look at issues related to wind turbine construction, show that operation in cold temperatures do not always result in damage, but may actually improve the performance of the system. In the area of lubrication, similar practical work has been conducted though few scientifically based reports are avai lable. In all cases synthetic lubricants that are rated for cold temperatures should be used. All manufactures recommend specific lubricants based on their particular turbine design. At the present moment surface heated gearboxes are used to avoid the cold starts after a standstill of turbines. A thermostatic controller heater is also needed at some sites [4].
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Index | Technical solutions in use |
Mail: Tomas Wallenius |
