How hurricane-force winds caused a wind turbine to explode

In December 2011, a wind turbine exploded during a storm, triggering claims that turbines cannot cope with extreme weather. A new report details what happened.

In December 2011, a wind turbine in Ardrossan, U.K., exploded during a storm, triggering claims that turbines can’t cope with extreme weather.

Now, a report from Infinis, the operator of the wind farm (pictured), claims that the turbines should be able to withstand such conditions if new safety measures are put in place. New Scientist reports.

When wind speeds reach 88 kilometers per hour, turbine blades are twisted (or “feathered”) so they no longer intercept airflow properly, and stop turning. This helps protect people on-site and protects the turbine from structural stress. But for this blade-stalling process to work, the turbine head must be rotated horizontally (or "yawed”) and pointed into the wind.

So on that day, winds reached 176 km/hour, forcing the blades to turn against their brake pads, and the friction resulted in extremely high temperatures. The Vestas Wind Systems turbine suffered two major heat-producing problems, which sent debris flying:

  1. First, yaw control on the turbine was lost, due to gear failure, so the feathered blades weren’t pointed into the wind.
  2. The turbine head swung back and forth, generating frictional heat and sparking a fire in the generator enclosure.
  3. Second, since the turbine was configured to apply a brake to the blades when no power is available, this fixed the blades in a stationary position.
  4. But the strong winds forced the blades to turn anyways, dragging the brake pads around a metal disc, generating heat and causing a second flashpoint, possibly by igniting hydraulic oil.

Infinis and Vestas disagree on the key initial cause of the fire: Infinis believes it was loss of yaw control, Vestas thinks it was brake drag.

Vestas has since fixed the brake problem. Future feathered rotors will not have the brake applied in high winds, and a slip clutch should ensure that loss of yaw control won’t generate excessive heat.

Infinis's report recommends that turbine-makers improve fire detection and prevention, by using more fire retardant materials in construction and developing automatic fire extinguishing systems.

Meanwhile, Vestas has produced their own report, and the Health and Safety Executive, which polices workplace safety, will take both reports into consideration for their own assessment.

[Via New Scientist]

Image: Vincent van Zeijst via Wikimedia

This post was originally published on Smartplanet.com

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