As power infrastructure was in the path of Hurricane Sandy this past week, AWEA connected with wind project owners and operators to assess the impact on wind power projects in the Northeast. It appears that Hurricane Sandy has had some, but minimal, impact on the wind turbines in its path, according to early reports this week from several operators of East Coast wind farms and manufacturers and owners of smaller turbines, most of which started generating electricity again after the storm passed.
Initial reports were received by e-mail from a number of wind farm operators accounting for 68 percent of the total 3,700 MW of wind generating capacity in the states located in the path of Sandy.
Some companies have yet to inspect all their turbines. The operator of five turbines near the waterfront in Atlantic City, N.J., reports that it will be unable to assess damage for several days. Another company reported yesterday that a project it operates in West Virginia has yet to restart because the neighboring town is without power, and the site is located on a mountain ridge top and the roads are impassable due to snow and downed trees.
Wind turbines are designed to take high winds of 120 to 135 mph, and some manufacturers make turbines that can withstand even higher winds for deployment in hurricane-prone areas. However, wind turbine typically shut down at wind speeds of about 55 mph and rotate to face the wind with their blades feathered, to minimize any risk of damage.
Reports regarding smaller turbines, though very sparse at this time, indicate that the machines operated as designed, shutting down when winds surpassed their cut-off speeds and restarting later.
General background on wind turbines and hurricanes
· Major hurricanes are a risk to all property owners in their way, including all types of power plants. Wind turbines are designed specifically to harness the wind, but they are also designed to withstand it. Modern wind turbines utilize several techniques to reduce the likelihood of harm. Active techniques, such as feathering the turbine’s blades, enable the turbine or turbine operator to protect or stop a turbine and halt electric generation in extreme weather conditions. Other techniques wind turbines utilize can include, but are not limited to:
· Turbine brakes – Most turbines are installed with turbine brakes that automatically engage if winds reach a certain speed – usually around 55 miles per hour. At the rated speed, the turbine brakes are applied and the rotor stops spinning.
· Blade feathering – Wind turbine blades can be tilted (feathered) remotely by an operator or automatically, so that instead of harnessing strong winds, wind is allowed to slip through the blades.
· Active yaw systems – Large turbines have active yaw systems that require a small motor that moves the nacelle (or gearbox, where the generator is housed) to point directly into the wind. By pointing directly into the wind, turbine aerodynamics allow wind to flow past the blades easily.
· Heavy monopole towers – Monopole towers can reach up to 100 meters in height and are meant to hold nacelles and blades that can weigh several tons. Thicker monopoles constructed with more steel and internal structures can support more weight and withstand stronger environmental forces like wind or waves for offshore structures.
· Strong foundations – For onshore wind turbines, most large-scale turbines have a foundation pad constructed from concrete. These foundation pads are usually buried several feet deep to help anchor the turbine to the ground. Offshore turbines in Europe utilize heavy concrete gravity-based structures that are placed on the seabed or monopiles that are driven many feet into the seabed to keep turbines steady in high winds and waves.
Tom Gray, http://www.awea.org/blog
