Emergency braking requirements of today’s large wind turbines under maximum wind conditions are comparable to those of a 40-ton mining truck driving down a 25% grade at 87 mph with a cliff just ahead. To meet these demanding requirements, Warner Electric
, South Beloit, Wisc., an Altra Industrial Motion company, modified its ERS series of electrically-released, spring-engaged brakes to serve as pitch brakes for wind turbine applications that require both “static” holding power and to withstand high inertia dynamic stops in an emergency situation.
The electromagnetic brake mounts outboard of an inductive encoder which is mounted to the back of a motor to position the blades to the proper pitch. In normal use, the unit functions as a static brake to hold the blades from rotating in a power-off situation, during routine maintenance and for other reasons.
However, the design spec for one OEM requires the brake to make 1,000 fully loaded dynamic stops during its service life. The largest in the Warner Electric ERS series, the 11.3-pound ERS68, has been tested to a capacity of more than 20,000 fully-loaded dynamic stops, surpassing the design spec 20 fold. The ERS68 brake offers 100 ft. lbs. of static torque, a maximum of 2,000 rpm, and a brake release time of 0.2 sec.
The new blade-pitch brakes also have the advantage of being a one-piece design, fully-enclosed and painted to withstand extreme environmental conditions such as salt-spray, condensation, and water. Previous pitch brakes used two-piece designs that required an adapter plate, extra fasteners, and an external boot to seal a gap between brake and adapter plate.
Warner Electric also developed a series of static holding brakes for controlling yaw when the wind-turbine nacelle is positioned into the wind. For this technically simpler application, the yaw brakes are mounted on the back end of a yaw motor. Typically, each turbine requires three pitch brakes and four to five yaw brakes.
Filed Under: Pitch & yaw