Pitch control

Each blade on a modern turbine sits on a large slewing bearing at the hub and can be rotated (pitched) independently by hydraulic or electric actuators. Changing the pitch angle alters the blade's angle of attack, and with it lift and torque.

Pitch control serves three functions:

• Power limitation: above rated wind speed, blades pitch toward feather (leading edge into the wind) to hold output at nameplate. Pitch rates of 5–10° per second allow response to gusts within a second or two.
• Start-up and shutdown: blades sit at about 90° (feathered) when parked and are pitched toward 0° at start; feathering is the primary aerodynamic brake and is required to operate on each blade independently so that one failed actuator cannot cause an overspeed.
• Load reduction: individual pitch control (IPC) adjusts each blade cyclically through every rotation to counteract wind shear, tower shadow and yaw misalignment, cutting blade-root fatigue loads by roughly 10–20% in published studies.

Earlier fixed-pitch, stall-regulated turbines, common in the Danish designs of the 1980s and 1990s, relied on the blade profile stalling at high wind. They were simpler but less precise and could not offer grid services. Pitch-regulated variable-speed turbines can curtail output on command, provide fast frequency response, and ramp gently into storms instead of a hard cut-out. Pitch bearings and actuators are nonetheless among the most frequent failure sources in reliability databases.