Drives for wind power: main gearboxes, generators, brakes and pitch/yaw systems
A wind turbine generator (WTG) is a multi-ton mechanical assembly mounted 80–150 m above ground that has to run for 20+ years under reversing shock loads, rotor vibration, icing and salt fog (for offshore sites). Replacing the main gearbox or generator on a 5 MW turbine costs millions of dollars and weeks of downtime, including a jack-up installation vessel. The choice of drive components — main multiplicator with a 100–150 gear ratio, generator, pitch and yaw systems, high-speed shaft brake and yaw brake — therefore defines project LCOE over its full service life.
Industry-typical tasks
- Main gearbox/multiplicator for a 1.5–6 MW WTG with 100–150 gear ratio and a service factor ≥ 1.4 per IEC 61400-4
- Pitch system — individual 5.5–22 kW drives on each of the three blades for power regulation and emergency feathering
- Yaw system (nacelle azimuth) — 4–6 gear motors of 1.5–15 kW each that rotate the nacelle into the wind
- Main generator — direct-drive PMSG or DFIG with wound rotor in a hybrid configuration, 1.5–12 MW
- High-speed shaft brake — emergency rotor stop with up to 30,000 N·m braking torque and parking mode for service
- Yaw brakes — holding the nacelle at the commanded azimuth after positioning (4–8 friction brakes around the yaw bearing)
- Main rotor bearing and a 1–10 t service crane inside the nacelle for component replacement without removing the turbine
- Installation of 8–15 MW offshore turbines from jack-up vessels — crane winch drives, jacking-leg drives, hydraulic power units
Gearboxes
In wind power the main gearbox/multiplicator is the most critical mechanical assembly of the WTG: it steps the 10–20 rpm rotor up to 1,500–1,800 rpm at the generator through a 100–150 gear ratio and operates under reversing wind loads for 20+ years without overhaul. Yaw gear motors (4–6 units around the nacelle yaw bearing) and pitch drives on the blades complete the drivetrain. The flagship main-gearbox supplier in the SDS portfolio is CGC: more than 30,000 wind gearboxes delivered in total, making it the world's second-largest manufacturer after CSSC.
Main turbine gearbox (multiplicator) 1.5–6 MW
Combined planetary-helical gearbox: 1–2 planetary stages on the input (high ratio and compactness) plus 1–2 helical stages on the output (high pitch-line velocity, convenient location of the brake disc and the coupling to the generator). CGC is the flagship in this segment: the Wind/CGC WG series covers 1.5/2.0/2.5/3.0/4.5/6.0 MW WTGs, with 30,000+ wind gearboxes delivered — the world's second-largest volume after CSSC. SG iron housing, ground double-helical gears to ISO grade 5, TIMKEN/SKF bearings, forced lubrication with 6 µm filtration and oil-temperature conditioning.
- — Gear ratio 100–150
- — Design life 20 years (175,200 h) per IEC 61400-4
- — Service factor ≥ 1.4 at rated torque
- — Forced lubrication, air- or water-cooled oil cooler
- — DNV GL / TÜV / Germanischer Lloyd certification
Yaw drives — azimuth gear motors
4–6 planetary gear motors — BONENG K/HB series or dedicated yaw drives — are mounted around the nacelle yaw bearing and rotate it into the wind at 0.3–0.5°/s through pinion-and-ring engagement. They run in sync on commands from the turbine controller fed by the wind-direction sensor. Once positioned, the nacelle is locked by yaw brakes and the gear motors are unloaded. BONENG is a core yaw-drive supplier in the SDS portfolio, repeatedly endorsed by customers in metallurgy and general industry.
- — 1.5–15 kW per drive
- — Gear ratio 1,500–2,500
- — Self-locking stage or integrated electromagnetic brake
- — IP65 protection; offshore version — IP66 + C5-M anti-corrosion coating
- — Flange compatible with the yaw-bearing standard of the turbine OEM
Pitch drives — blade pitch actuators
An individual planetary gear motor on each blade rotates it around the hub axis over 0–90°. It regulates turbine output above rated wind speed and feathers the blade (90°, minimum load) on a fault or storm wind. Emergency travel time is no more than 4–6 seconds — safety-critical. BONENG supplies compact planetary gearboxes for pitch systems; INOVANCE supplies the variable-frequency drives for pitch control with battery backup power.
- — 5.5–22 kW per blade
- — Gear ratio 1,000–2,000
- — Backup power from a Li-ion or ultracapacitor battery for 3 feathering cycles
- — Emergency 0°→90° blade travel time ≤ 4 s
- — Absolute SSI/EnDat encoder for angle feedback
Nacelle service crane winches
A 1–10 t service crane is built into the nacelle ceiling and is used to lift spares and tools from the ground through a floor hatch, or to replace individual components (generator, coupling, controller) without removing the whole nacelle. The winch drive is a worm-helical or planetary gear motor with integrated brake and load limiter.
- — 1–10 t SWL, rope length matched to tower height
- — Two-speed mode (coarse/fine positioning)
- — Load limiter and upper/lower limit switches
- — Compliance with EN 14492-1, DNV GL certificate
- — Electromagnetic brake, fail-safe on power loss
Jack-up vessel drives for offshore installation
Offshore 8–15 MW turbines are installed from jack-up vessels with 4–6 legs up to 120 m long. Jacking drives are high-power planetary gear motors with rack-and-pinion or pin-rack engagement; they operate synchronously to lift the entire hull above sea level for the duration of installation. After the lift the vessel jacks back down and moves to the next turbine.
- — Per-leg capacity 5,000–15,000 t
- — Jacking speed 0.3–0.8 m/min
- — Height synchronization across all legs within ± 50 mm
- — C5-M marine execution, stainless fasteners and shafts
- — N+1 drive redundancy per leg
Motors and generators
In wind power, electrical machines play two roles: main turbine generators (1.5–12 MW) and auxiliary motors for service systems (yaw, pitch, hydraulics, cooling). Three competing main-generator architectures are in use: PMSG (direct-drive, no gearbox), DFIG with wound rotor (hybrid with a gearbox), and full-converter induction machines with squirrel-cage rotor. The flagship generator supplier in the SDS portfolio is Wolong: the YHTM series is purpose-built for renewable generation, rated 1.5–12 MW and explicitly positioned by the manufacturer as its number-one wind solution.
Permanent magnet synchronous generators (PMSG) 1.5–12 MW
Multi-pole low-speed direct-drive generators without a gearbox — the rotor is coupled directly to the blade hub, speed 8–20 rpm, stator diameter 4–7 m. The advantage is removing the main gearbox as a single point of failure; the drawback is greater mass and footprint, especially offshore. Wolong YHTM is the flagship series for renewable-energy generators, rated 1.5–12 MW, with 96–98% efficiency at rated load, specifically optimized for wind power and concentrated solar generation.
- — 1.5–12 MW, 690 V – 6.6 kV
- — NdFeB permanent magnets with demagnetization protection on short circuit
- — Forced air or water cooling, IC81W
- — Insulation class H, operating range −40 °C to +50 °C
- — Offshore execution — sealed enclosure, C5-M anti-corrosion coating
Doubly-fed induction generators (DFIG) 1.5–6 MW
A doubly-fed machine: the stator is connected directly to the 690 V grid, while the rotor is fed through a converter rated at ±30% of nominal power. This allows ±30% rotor-speed control around synchronous with a much smaller converter than a full-converter scheme. It is used in the hybrid architecture together with the main gearbox (multiplicator). Wolong's YHTM series covers this niche as well — wound-rotor induction machines up to 6 MW.
- — 1.5–6 MW
- — Long-life slip rings (graphite brushes, replaced every 3–5 years)
- — Operating speed range ±30% around synchronous
- — Insulation class F with class B thermal margin
- — Low-voltage ride-through (LVRT) compliance per grid code
Hybrid medium-speed configurations
A compromise between direct-drive PMSG and classic three-stage DFIG: a permanent-magnet generator plus a one- or two-stage planetary multiplicator with a 30–60 gear ratio. It cuts mass versus direct drive and improves reliability versus a three-stage gearbox. Wolong supplies generators for this architecture as well; the medium-speed main gearbox is CGC's competence.
- — Speed 100–500 rpm (between direct drive and high-speed)
- — Permanent magnets and minimal slip-ring count
- — Flange-compatible with the CGC medium-speed gearbox
- — Full-converter scheme rated for 100% of power
Main and auxiliary variable-frequency drives
The main converter handles the full turbine power (PMSG full-converter) or ±30% (DFIG), synchronizes the generator with the grid and provides LVRT/HVRT. The turbine also carries auxiliary converters for pitch and yaw. INOVANCE supplies medium- and low-voltage VFDs of the MD/HD series for pitch and yaw control, as well as packaged main-line converter cabinets. INVT supplies auxiliary VFDs for hydraulic power units, cooling systems and nacelle ventilation.
- — Main converter: 1.5–12 MW, 690 V – 6.6 kV
- — Low THD < 3% per IEEE 519
- — LVRT per grid code — ride-through up to 0.15 s at 0% voltage
- — Pitch converters with backup power for emergency feathering
- — EN 50178 / IEC 61800-3 certification
Industrial brakes
A WTG carries three independent braking systems: aerodynamic braking via blade feathering (the primary stop method), a mechanical high-speed shaft brake between the gearbox and the generator (emergency stop and parking), and yaw brakes on the nacelle yaw bearing (holding the azimuth after positioning). The lead mechanical-brake supplier in the SDS portfolio is HUAWU: dedicated lines for high-speed shaft brakes and yaw brakes, with marine versions for offshore turbines.
High-speed shaft brake
The HUAWU YPZ/SBD disc brake is installed between the main gearbox and the generator on the high-speed shaft. It provides emergency rotor stops when protections trip (overspeed, grid loss, pitch fault) and a parking mode for maintenance. Braking torque up to 30,000 N·m, hydraulic clamp with spring closure — the brake closes automatically on pressure loss.
- — Braking torque up to 30,000 N·m
- — Hydraulic clamp with fail-safe spring closure
- — Emergency response time ≤ 0.3 s
- — Pad wear and pad-position monitoring
- — Offshore execution — stainless springs, salt-fog protection
Yaw (azimuth) brakes
The HUAWU YDP series consists of friction caliper brakes mounted around the yaw bearing (8–16 units around the circumference). Once the yaw gear motors have turned the nacelle to the commanded azimuth, the brakes clamp and hold it in place across ±5–8° wind shifts. This unloads the yaw drives and reduces gear-rim wear. A subset of brakes operates in continuous passive-damping mode to suppress nacelle self-oscillation.
- — Aggregate braking torque up to 5–10 MN·m (around the bearing)
- — Hydraulic clamp, 150–210 bar
- — Passive-damping mode on several brakes simultaneously
- — Pad-wear monitoring (limit switch on each brake)
- — C5-M marine execution for offshore turbines
Emergency mechanical rotor brake
On many turbines the high-speed shaft brake covers both parking and emergency duties, but on large offshore machines an additional low-speed shaft brake is fitted on the slow shaft or directly on the rotor hub. It is sized for the full rotor breakaway torque under emergency conditions and serves as a backup if the high-speed brake fails. Braking torque 0.5–3 MN·m.
- — Braking torque 0.5–3 MN·m
- — Hydraulic clamp, fail-safe spring closure
- — Response time ≤ 0.5 s
- — Redundant hydraulic power unit (main + emergency)
- — Compatibility with the turbine PLC system
Brakes for service-crane winches and offshore hoists
A band or disc brake on the nacelle service-crane winch holds the load on power loss and provides controlled emergency lowering. On jack-up vessels used for offshore installation, disc brakes on each jacking drive hold the loaded leg. HUAWU and Jingu (for port-crane applications) are the suppliers in this class.
- — Braking torque with 1.5–2× safety factor on drive rated torque
- — Fail-safe closure on power loss
- — Compatibility with the integrated worm or planetary winch gearbox
- — C5-M marine execution
Couplings and bearings
Dedicated couplings are used in the WTG drivetrain between the main gearbox and the generator: they must accommodate radial and angular misalignment caused by nacelle bedplate deflection under wind load, damp torsional shocks, provide electrical isolation to protect the generator bearings from shaft currents, and act as the flexible element in hybrid drivetrains. The main rotor bearing is a separate class of component with its own requirements.
High-speed shaft flexible couplings (gearbox to generator)
Longxuan LMS/LMD couplings use a steel disc pack or a composite toroidal membrane. They transmit 5–80 kN·m with 1–3 mm radial and up to 1° angular misalignment compensation. They are electrically isolated (a dielectric insert between the flange halves), which protects the generator bearings from converter-induced shaft currents. They damp torsional vibrations at rated speed of 1,500–1,800 rpm.
- — Torque 5–80 kN·m
- — Radial offset compensation 1–3 mm, angular up to 1°
- — Electrical isolation ≥ 5 kV DC
- — Balancing grade G2.5 (high-speed zone)
- — Flexible-element service life of at least 175,000 h
Compact pitch-system couplings
Yongjing LX/LMC compact pin-and-bushing flexible couplings sit between the pitch gear motor and the pitch-bearing pinion. Small envelope is critical — the pitch drive is housed inside the hub, where space is tight. They compensate for small post-installation misalignment and damp shock loads during emergency feathering.
- — Torque 0.5–5 kN·m
- — Compact axial envelope
- — Flange-compatible with the pitch gear motor
- — Elastomer service life 100,000 h+
Hybrid flexible couplings for medium-speed drivetrains
In hybrid drivetrains (PMSG plus a single-stage planetary multiplicator) a special-version Longxuan flexible coupling sits between the gearbox and the generator — it compensates thermal misalignment and acts as a flexible element that suppresses torsional resonance. It is more compact than classic high-speed couplings thanks to medium speed (100–500 rpm) and higher torque density.
- — Torque 50–500 kN·m (medium-speed)
- — Misalignment compensation after bedplate deflection
- — Electrical isolation to protect generator bearings
- — Flange-compatible with CGC medium-speed gearbox and Wolong PMSG
Main rotor bearing
A double-row spherical or tapered roller main rotor bearing carries the full load from the rotor and blades (60–250 t) and transmits torque directly into the main gearbox or PMSG rotor. Service life is 20+ years and replacement requires removing the whole drivetrain. SDS does not list a dedicated bearing brand as a standalone product, but we participate in bearing selection for CGC main gearboxes (TIMKEN/SKF/FAG are supplied integrated) and for Wolong generators.
- — Design L10 life ≥ 175,000 h
- — Double-row spherical or tapered execution
- — Seals with salt-fog protection for offshore
- — Automatic lubrication on a 1–4 h cycle
- — Vibration and temperature monitoring (SKF/Schaeffler sensors)
Applications gallery
Our solutions for this industry
SDS portfolio brands that cover typical applications in this industry.
- CGCmain gearboxes/multiplicators for 1.5–6 MW WTGs. 30,000+ wind gearboxes delivered — the world's second-largest volume after CSSC, CGC's flagship competence in wind power
- WOLONGYHTM-series generators for wind power and concentrated solar generation, 1.5–12 MW. Flagship renewables series — direct-drive PMSG and wound-rotor DFIG
- HUAWUhigh-speed shaft brakes (up to 30,000 N·m) and yaw brakes for the azimuth system. C5-M marine execution for offshore sites
- BONENGyaw drives — azimuth gear motors, 4–6 per turbine, 1.5–15 kW. Pitch drives — compact planetary actuators 5.5–22 kW for blade pitch
- YONGJINGcompact LX/LMC pin-and-bushing flexible couplings for the pitch system, between the blade gear motor and the pitch bearing
- LONGXUANhigh-speed shaft flexible couplings between the main gearbox and the generator, with electrical isolation to protect the generator bearings from shaft currents
- INOVANCEpitch-drive VFDs with backup power for emergency feathering, yaw-system VFDs and main turbine converter
- INVTauxiliary VFDs for hydraulic power units, generator and gearbox cooling, and nacelle ventilation
- DONLYhydraulic power units for the pitch system, high-speed shaft brake and yaw brakes, and for jack-up installation vessels
- DEOoil coolers for main gearboxes and drivetrain lubrication, plate heat exchangers for liquid cooling of the generator
Image credits: U.S. Fish and Wildlife Service - Midwest Region (Public domain) · michael marston (CC BY 2.0) · North Charleston (CC BY-SA 2.0) · Eileen at OE (CC BY-SA 4.0) · Wikimedia Commons (Public domain)