Wind Turbine Yaw Drive

Overview

The yaw drive is what keeps a wind turbine pointed into the wind. A horizontal-axis turbine only makes full power when its rotor faces the wind squarely, but the wind shifts direction constantly, so the entire nacelle, weighing many tonnes with the rotor on its nose, has to be slowly swung around the top of the tower to track it. The yaw drive does this with several geared electric motors that grip a large toothed ring and walk the nacelle around, plus brakes that lock it in place once it is aligned so gusts cannot push it off heading.

The system is a set of cooperating parts. Several Yaw Drive Unit actuators provide the muscle, meshing the Yaw Bearing slewing ring that both supports and turns the nacelle. The Yaw Brake System holds the heading, the Yaw Control System decides when to move, the Wind Sensing tells it where the wind is, the Lubrication System keeps the teeth greased, and the Cable Management stops the cables from twisting apart as the nacelle turns.

Drive units

The force to swing the nacelle comes from four to eight Yaw Drive Unit actuators spaced around the ring, working together so no single unit is overloaded. Each starts with a Yaw Motor, an electric motor that spins fast at low torque. That feeds a Planetary Gearbox, a high-ratio planetary reducer often close to a thousand to one, built from stacked Planet Set stages around a Sun Pinion inside a Internal Ring Gear ring. The reduction trades the motor's speed for the enormous torque needed to move the nacelle, delivered through the Output Pinion that meshes the yaw ring. A Holding Brake on each motor lets the drives rest without the load creeping back.

Yaw bearing

The Yaw Bearing is the single large interface between the fixed tower and the turning nacelle. It is a Slewing Ring, a roller bearing two to three metres across running on Bearing Roller elements, that carries the full weight and tipping load of the nacelle while letting it rotate freely. The clever part is that the ring also carries Yaw Ring Gear, gear teeth cut directly into it, so the same component that supports the nacelle is also the gear the drives push against. Bearing Seal lip seals keep grease in and the weather out of the raceway, and a heavy Fastener Set bolts the ring between the tower top and the nacelle bedplate.

Holding the heading

Once aligned, the nacelle must hold still against gusts that would otherwise hammer the gear teeth back and forth, which is the job of the Yaw Brake System. A ring of Yaw Brake Caliper hydraulic calipers, each built from a Caliper Body and Caliper Piston set, clamps the steel Yaw Brake Disc through Yaw Brake Pad friction pads. Pressure comes from the Hydraulic Power Unit, where a Hydraulic Pump and gas-charged Hydraulic Accumulator feed the calipers through Brake Hose lines. During a yaw move the calipers release just enough to let the nacelle turn under a residual drag, which keeps the motion smooth and stops the teeth from rattling.

Sensing and control

The decision to yaw is made by the Yaw Control System. A Yaw Controller reads the wind and compares it to the nacelle heading reported by a Position Encoder, then commands the motors through a Motor Drive for each unit. Those drives, built around a Power Switch and Gate Driver, soft-start the motors so they ramp up gently instead of slamming the gear teeth, and Relay contactors switch them on and off. The wind information itself comes from the Wind Sensing pack on the nacelle roof: a Wind Vane gives direction and an Anemometer gives speed, both kept clear by a Sensor Heater. The controller deliberately tolerates small misalignment rather than chasing every gust, because constant yawing wears the drive and gives little extra energy.

Lubrication and cable handling

The open ring teeth and the slewing raceway sit exposed to weather under heavy, slow load, so the Lubrication System system greases them automatically: a Grease Pump meters Lubricating Grease through a Grease Distributor and Grease Line feeds to each point on a schedule. Finally, because the nacelle can rotate many full turns over time, the power and signal cables running up from the fixed tower would twist off if nothing managed them. The Cable Management handles this with a hanging Cable Loop of slack that absorbs several turns, supported by Cable Clamp clamps on a Cable Ladder. A Twist Counter keeps a running tally of net turns, and when the cable has wound up to its limit the controller deliberately yaws the nacelle back the other way to untwist it, even at the cost of a brief misalignment.