{"id":1082,"date":"2026-06-24T03:23:03","date_gmt":"2026-06-24T03:23:03","guid":{"rendered":"https:\/\/planetary-gearboxes.com\/?p=1082"},"modified":"2026-06-24T03:23:03","modified_gmt":"2026-06-24T03:23:03","slug":"slewing-drive-planetary-gearbox-for-wind-turbines","status":"publish","type":"post","link":"https:\/\/planetary-gearboxes.com\/th\/slewing-drive-planetary-gearbox-for-wind-turbines\/","title":{"rendered":"\u0e40\u0e01\u0e35\u0e22\u0e23\u0e4c\u0e17\u0e14\u0e23\u0e2d\u0e1a\u0e41\u0e1a\u0e1a\u0e14\u0e32\u0e27\u0e40\u0e04\u0e23\u0e32\u0e30\u0e2b\u0e4c\u0e2a\u0e33\u0e2b\u0e23\u0e31\u0e1a\u0e01\u0e31\u0e07\u0e2b\u0e31\u0e19\u0e25\u0e21"},"content":{"rendered":"
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Korea Ever-Power \u00b7 Application Engineering \u00b7 Wind Energy<\/p>\n

Slewing Drive Planetary Gearbox for Wind Turbines \u2014 25 Years, 100 Metres Up, Zero Unplanned Stops<\/h1>\n

Two slewing drives keep every wind turbine producing power: the yaw drive<\/strong> that rotates the nacelle to face the wind, and the pitch drive<\/strong> that angles the blades to control rotor speed. Together, they determine whether a USD 3 to 8 million turbine generates revenue or sits idle \u2014 for a quarter of a century.<\/p>\n

\u0e40\u0e23\u0e35\u0e22\u0e01\u0e14\u0e39\u0e0a\u0e38\u0e14\u0e40\u0e01\u0e35\u0e22\u0e23\u0e4c\u0e14\u0e32\u0e27\u0e40\u0e04\u0e23\u0e32\u0e30\u0e2b\u0e4c\u0e41\u0e1a\u0e1a\u0e2b\u0e21\u0e38\u0e19 \u2192<\/a><\/p>\n<\/div>\n<\/section>\n

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Two Slewing Drives, Two Completely Different Engineering Problems<\/h2>\n

A wind turbine uses two types of \u0e0a\u0e38\u0e14\u0e40\u0e01\u0e35\u0e22\u0e23\u0e4c\u0e14\u0e32\u0e27\u0e40\u0e04\u0e23\u0e32\u0e30\u0e2b\u0e4c\u0e02\u0e31\u0e1a\u0e40\u0e04\u0e25\u0e37\u0e48\u0e2d\u0e19\u0e01\u0e32\u0e23\u0e2b\u0e21\u0e38\u0e19<\/a> \u2014 and despite sharing the same fundamental gear architecture, they solve fundamentally different engineering problems. Understanding the distinction is essential for specification, because a gearbox designed for the yaw application will fail in the pitch application (and vice versa) even if the torque ratings appear compatible.<\/p>\n

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Yaw Drive \u2014 Nacelle Rotation<\/div>\n

Rotates the entire nacelle (generator, gearbox, rotor \u2014 150 to 400 tonnes total) around the vertical tower axis to face the wind. Operates 20 to 80 times per day, rotating 5 to 180 degrees per event. Must hold the nacelle against wind-induced yaw moments of 3 to 8 MN\u00b7m between movements. Speed: 0.3 to 0.6 degrees per second. Typical configuration: 4 to 8 yaw drives around the tower top bearing, each meshing with an internal ring gear.<\/p>\n<\/div>\n

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Pitch Drive \u2014 Blade Angle Control<\/div>\n

Rotates each individual blade (10 to 30 tonnes, 50 to 80 metres long) around its longitudinal axis to change the angle of attack. Operates continuously during power production, adjusting 0.1 to 5 degrees per second. Must feather the blade to 90 degrees within 5 to 10 seconds during emergency shutdown. Three independent pitch drives per turbine (one per blade). Safety-critical: failure to feather a single blade in a storm can destroy the rotor.<\/p>\n<\/div>\n<\/div>\n<\/div>\n

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\"Slewing<\/p>\n

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Slewing drive planetary gearbox. In wind turbines, 4 to 8 yaw drives and 3 pitch drives work continuously for a 25-year design life \u2014 the longest service requirement of any slewing drive application.<\/p>\n<\/div>\n<\/div>\n<\/div>\n<\/section>\n

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Yaw Drive Engineering \u2014 Holding 200 Tonnes Against the Wind<\/h2>\n
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The yaw system on a modern 3 to 6 MW wind turbine consists of 4 to 8 slewing drive planetary gearboxes mounted around the tower top flange, each driving a pinion gear that meshes with a large internal ring gear (yaw bearing). When the wind direction changes, the yaw controller commands some or all drives to rotate the nacelle. When the nacelle reaches the target angle, the drives stop and the yaw brakes engage to hold the position.<\/p>\n

\n\n\n\n\n\n\n\n
Turbine Class<\/th>\nNacelle (t)<\/th>\nYaw Drives<\/th>\nYaw Moment (MN\u00b7m)<\/th>\nTorque\/Drive<\/th>\n<\/tr>\n<\/thead>\n
2 \u2013 3 MW onshore<\/td>\n80 \u2013 130<\/td>\n4<\/td>\n2 \u2013 4<\/td>\n8,000 \u2013 15,000 Nm<\/td>\n<\/tr>\n
4 \u2013 6 MW onshore<\/td>\n150 \u2013 250<\/td>\n6<\/td>\n4 \u2013 8<\/td>\n12,000 \u2013 22,000 Nm<\/td>\n<\/tr>\n
8 \u2013 15 MW offshore<\/td>\n300 \u2013 600<\/td>\n8<\/td>\n6 \u2013 15<\/td>\n18,000 \u2013 35,000 Nm<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n
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Why multiple drives, not one large one:<\/strong> Using 4 to 8 smaller slewing drives instead of a single large one provides redundancy (the nacelle can still yaw if one drive fails), distributes the pinion load around the yaw ring gear for even tooth wear, and allows each drive to be replaced individually without removing the nacelle \u2014 a critical logistics advantage at 100+ metre hub heights where crane access costs USD 50,000 per day.<\/p>\n<\/div>\n<\/div>\n

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\"Planetary<\/p>\n

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Planetary gear operational mechanics. Wind turbine yaw drives use 2 to 3 stage planetary reductions at ratios of 600:1 to 1,800:1 \u2014 the highest ratios in any slewing drive application.<\/p>\n<\/div>\n<\/div>\n<\/div>\n<\/section>\n

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Pitch Drive Engineering \u2014 The Safety-Critical Slewing Drive That Prevents Turbine Destruction<\/h2>\n

The pitch drive rotates each blade around its longitudinal axis. During normal power production, the pitch system adjusts the blade angle continuously \u2014 fine-tuning the rotor speed to maintain rated power output as wind speed fluctuates. During emergency shutdown (triggered by grid loss, over-speed, or extreme gust), the pitch system must feather all three blades to 90 degrees within 5 to 10 seconds \u2014 rotating each 10 to 30-tonne blade through 90 degrees against aerodynamic and centrifugal forces.<\/p>\n

This emergency feathering function makes the pitch drive the only safety-critical<\/strong> slewing drive in the wind turbine \u2014 and one of the few safety-critical planetary gearboxes in any industry. If the pitch drive cannot feather the blade, the rotor continues to accelerate in high wind until mechanical limits are exceeded. The consequences range from blade damage to complete structural failure of the tower.<\/p>\n

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Redundancy requirement:<\/strong> Modern turbine standards (IEC 61400) require independent power supply for each pitch drive \u2014 typically battery-backed electric motors or hydraulic accumulators \u2014 so that emergency feathering can proceed even if the main electrical supply is lost. Each of the three pitch drives must be capable of feathering its blade independently. The slewing drive planetary gearbox must function under battery power (reduced voltage, reduced speed) with the same reliability as under main power.<\/p>\n<\/div>\n<\/div>\n

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\"Slewing<\/p>\n

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Slewing drive application. Pitch drives must operate in the rotating hub \u2014 exposed to lightning, vibration, and temperature extremes for 25 years without scheduled replacement.<\/p>\n<\/div>\n<\/div>\n<\/div>\n<\/section>\n

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\"Slewing<\/p>\n

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Wind turbine yaw system. 4 to 8 slewing drive units are mounted around the tower top flange, each driving a pinion that meshes with the yaw bearing ring gear to rotate the nacelle.<\/p>\n<\/div>\n<\/div>\n

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\"Planetary<\/p>\n

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Precision CNC gear manufacturing. Wind turbine yaw drives require DIN Class 5 gears with superfinished flanks to achieve 25-year tooth contact fatigue life at 1.25 million stress cycles.<\/p>\n<\/div>\n<\/div>\n<\/div>\n

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25-Year Design Life \u2014 The Engineering Challenge That Separates Wind Turbine Drives from All Others<\/h2>\n

A construction crane slewing drive is designed for 10,000 to 20,000 hours. An excavator track drive targets 8,000 to 12,000 hours. A wind turbine yaw drive must operate reliably for 150,000 to 220,000 hours<\/strong> \u2014 25 years at 70 to 100% availability \u2014 without scheduled gearbox replacement. This 10 to 20 times longer design life compared to construction equipment drives every engineering decision in the gearbox specification.<\/p>\n

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Bearing L10 Life Requirement<\/div>\n

Standard L10 bearing life for construction gearboxes: 10,000 to 20,000 hours. Wind turbine yaw drive L10 requirement: minimum 175,000 hours (25 years at 80% availability). This means the bearing size, grade, and lubricant must deliver an L10 life 9 to 17 times longer than construction equivalents \u2014 often requiring bearings 1 to 2 sizes larger than the torque alone would dictate.<\/p>\n<\/div>\n

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Gear Tooth Contact Fatigue<\/div>\n

At 50,000 yaw movements per year over 25 years, each planet gear tooth endures 1.25 million contact stress cycles. The gear material and heat treatment must place the tooth surface stress below the infinite-life endurance limit of the case-hardened 20CrMnTi or 18CrNiMo7-6 steel \u2014 not merely below the 10,000-hour fatigue limit used for construction drives. This typically requires DIN Class 5 gears with superfinished flanks.<\/p>\n<\/div>\n

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Grease Life and Re-Lubrication<\/div>\n

No sealed-for-life grease can last 25 years. Wind turbine slewing drives use automatic re-lubrication systems that meter fresh grease into the gearbox at programmed intervals \u2014 typically every 2,000 to 4,000 hours. The gearbox must be designed for grease re-lubrication (not oil bath) because the mounting orientation changes as the nacelle yaws. The grease specification must tolerate -40 to +80 degrees C operating range and resist water washout from condensation at hub height.<\/p>\n<\/div>\n<\/div>\n<\/section>\n

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Environmental Extremes \u2014 Operating at the Intersection of Every Climate Challenge<\/h2>\n

At 100+ metres above ground, the wind turbine nacelle is exposed to environmental conditions that no ground-level machine encounters. The slewing drive must function across the full range simultaneously \u2014 a single gearbox must survive -40 degrees C winter nights and +50 degrees C summer afternoons, salt spray and ice accretion, lightning strikes and UV radiation, all at the same installation for 25 years.<\/p>\n

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-40<\/div>\n
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to +80 degrees C operating range<\/div>\n

Cold-climate onshore turbines in Scandinavia, Canada, and northern China operate to -40 degrees C. Desert turbines in the Middle East and Australia reach +50 degrees C ambient with nacelle internal temperatures exceeding 80 degrees C. The grease must maintain lubricity across this 120-degree span.<\/p>\n<\/div>\n<\/div>\n

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Salt<\/div>\n
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Offshore and coastal corrosion<\/div>\n

Offshore turbines operate in continuous salt spray. The slewing drive housing, fasteners, and seal interfaces must resist marine corrosion for 25 years. Marine-grade coatings, stainless fasteners, and sacrificial anodes are mandatory for offshore and coastal installations within 5 km of the shoreline.<\/p>\n<\/div>\n<\/div>\n

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Ice<\/div>\n
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Icing on the yaw ring gear and pinion<\/div>\n

Ice accretion on the yaw ring gear teeth increases the meshing force and can prevent rotation entirely if the ice bond exceeds the available yaw torque. Anti-icing heaters on the yaw ring gear and ice-resistant grease formulations are standard for cold-climate installations. The \u0e0a\u0e38\u0e14\u0e40\u0e01\u0e35\u0e22\u0e23\u0e4c\u0e14\u0e32\u0e27\u0e40\u0e04\u0e23\u0e32\u0e30\u0e2b\u0e4c\u0e02\u0e31\u0e1a\u0e40\u0e04\u0e25\u0e37\u0e48\u0e2d\u0e19\u0e01\u0e32\u0e23\u0e2b\u0e21\u0e38\u0e19<\/a> must deliver breakaway torque 1.5 to 2.0 times the steady-state yaw torque to overcome ice bonding after overnight standstill in freezing conditions.<\/p>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n

\"ZR45
\n\"Korea<\/p>\n
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Top: ZR-series slewing drive unit. Bottom: Korea Ever-Power testing centre \u2014 every wind turbine drive undergoes full torque and endurance verification before delivery.<\/p>\n<\/div>\n<\/div>\n<\/div>\n<\/section>\n

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Three Failure Modes That Drive Wind Turbine Slewing Drive Engineering<\/h2>\n
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1<\/div>\n
Yaw bearing and pinion wear from micro-oscillation (fretting)<\/div>\n<\/div>\n

The yaw system makes thousands of small angular corrections per day \u2014 0.5 to 3 degree movements to track gradual wind direction changes. These micro-oscillations cause the pinion teeth to rock back and forth on the same contact zone of the yaw ring gear without completing a full revolution. This fretting removes the grease film from a narrow band and produces accelerated surface pitting on both the pinion and the ring gear. After 10 to 15 years, the accumulated fretting wear can consume the ring gear tooth profile at the most-used yaw positions \u2014 typically the prevailing wind direction sectors.<\/p>\n

Prevention: Programmed “yaw exercises” \u2014 full 360-degree rotations at monthly intervals \u2014 redistribute wear across the entire ring gear. Automatic greasing at the pinion-ring mesh. DIN Class 5 pinion with superfinished flanks.<\/div>\n<\/div>\n
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2<\/div>\n
Pitch drive motor failure preventing emergency blade feathering<\/div>\n<\/div>\n

The pitch drive motor must respond to an emergency feathering command within 200 milliseconds. If the motor fails, the blade cannot feather. On a 3-blade turbine, the remaining two blades may feather successfully \u2014 but the aerodynamic imbalance from one un-feathered blade generates extreme loads on the hub, main shaft, and tower. The slewing drive planetary gearbox must transmit the emergency feathering torque under battery-backup voltage conditions (70 to 80% of nominal) at the required speed \u2014 a verification that must be performed annually.<\/p>\n

Prevention: Annual pitch function test under battery power. Verify feathering time (less than 10 seconds from 0 to 90 degrees). Replace pitch drive motor and gearbox as a set if feathering time exceeds 12 seconds.<\/div>\n<\/div>\n
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3<\/div>\n
Grease degradation from condensation cycling over multi-year service<\/div>\n<\/div>\n

At hub height, day-night temperature cycling produces condensation inside the yaw drive housing \u2014 the same mechanism that affects stored agricultural track drives, but occurring 365 times per year for 25 years. Even with automatic re-lubrication, the water-contaminated old grease at the bottom of the housing is not fully displaced by fresh grease \u2014 it accumulates as a water-laden sludge that corrodes the lowest bearing surfaces. After 8 to 12 years, the sludge layer can reach the planet bearings and initiate corrosion pitting that was not present at the 5-year inspection.<\/p>\n

Prevention: Specify grease with high water-washout resistance (below 5% loss in ASTM D1264). Programme auto-lubrication to purge old grease. At the 10-year major inspection, drain and flush the yaw drive housing completely.<\/div>\n<\/div>\n<\/div>\n<\/div>\n
\"Korea
\n\"Korea<\/p>\n
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Top: Korea Ever-Power manufacturing facility. Bottom: Assembly workshop with dedicated quality control for wind energy slewing drives.<\/p>\n<\/div>\n<\/div>\n<\/div>\n<\/section>\n

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Slewing Drive Planetary Gearbox for Wind Turbines \u2014 Frequently Asked Questions<\/h2>\n
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What gear ratio does a wind turbine yaw drive use?<\/h3>\n

600:1 to 1,800:1 \u2014 far higher than any construction slewing drive (typically 50:1 to 200:1). The high ratio converts the motor speed (1,000 to 1,500 rpm) to the very slow yaw speed (0.3 to 0.6 degrees per second at the nacelle). This high ratio also multiplies the motor braking torque to help hold the nacelle against wind yaw moments. A 2-stage planetary reduction provides ratios up to approximately 100:1; a 3-stage provides up to 1,000:1; and the additional reduction from the pinion-to-ring-gear mesh brings the total system ratio to the 600 to 1,800 range.<\/p>\n<\/div>\n

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How many slewing drives does a wind turbine require in total?<\/h3>\n

7 to 11 per turbine. The yaw system uses 4 to 8 drives (depending on turbine size and manufacturer). The pitch system uses 3 drives (one per blade). A 100-turbine wind farm therefore contains 700 to 1,100 slewing drive planetary gearboxes \u2014 making wind energy one of the largest single-application markets for slewing drives by installed unit count. The volume and the 25-year reliability requirement together drive the demand for consistent manufacturing quality and full traceability of every gearbox.<\/p>\n<\/div>\n

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Can construction crane slewing drives be used as wind turbine yaw drives?<\/h3>\n

Not for production turbines. Construction crane slewing drives are designed for 10,000 to 20,000-hour service life \u2014 they would reach their bearing L10 life within 1 to 2 years of continuous wind turbine operation. Additionally, crane drives are designed for frequent full-rotation duty (360+ degrees per cycle), while wind yaw drives are optimised for the micro-oscillation fretting resistance that dominates the yaw duty cycle. A crane drive would develop accelerated yaw-ring wear at the prevailing-wind contact positions within 3 to 5 years. Crane-class drives are acceptable only for temporary prototype testing, not for production installations.<\/p>\n<\/div>\n

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What is the typical replacement interval for wind turbine slewing drives?<\/h3>\n

The design target is 25 years (no scheduled replacement). In practice, yaw drives on well-maintained turbines achieve 18 to 25 years before requiring replacement \u2014 typically triggered by pinion tooth wear exceeding the backlash limit. Pitch drives, which operate more frequently and under higher dynamic loads, may require motor replacement at 12 to 15 years, but the planetary gearbox itself typically survives the full 25-year life. The key maintenance interventions that protect the 25-year life are: automatic greasing (continuous), yaw exercise (monthly), pitch function test (annual), and full inspection with grease flush at the 10-year major service.<\/p>\n<\/div>\n

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How does an offshore wind turbine slewing drive differ from an onshore specification?<\/h3>\n

Three principal differences: (1) corrosion protection \u2014 offshore drives require marine-grade coating systems (C5-M class per ISO 12944), stainless steel fasteners, and sacrificial anodes; (2) accessibility \u2014 offshore maintenance windows are weather-dependent and far more expensive than onshore, so the drive must be designed for even longer maintenance-free intervals (5,000 to 8,000 hours between service visits versus 2,000 to 4,000 hours onshore); and (3) yaw moment \u2014 offshore turbines are typically larger (8 to 15 MW versus 2 to 6 MW onshore) and experience combined wind and wave-induced yaw loading, increasing the yaw moment to 6 to 15 MN\u00b7m versus 2 to 8 MN\u00b7m for onshore equivalents.<\/p>\n<\/div>\n

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Does Korea Ever-Power supply slewing drives for wind turbine yaw and pitch applications?<\/h3>\n

Yes. Korea Ever-Power manufactures slewing drive planetary gearboxes for wind turbine yaw and pitch systems with L10 bearing life rated for 175,000+ hours, DIN Class 5 gears with superfinished flanks, automatic greasing provisions, and marine-grade corrosion protection options for offshore installations. Available for turbines from 2 MW to 15 MW. Yaw drives: 8,000 to 35,000 Nm per unit at ratios up to 1,200:1. Pitch drives: 5,000 to 15,000 Nm with emergency feathering speed verification. Provide the turbine manufacturer, model, and installation environment (onshore\/offshore\/cold climate) for a specification matched to the yaw moment and pitch feathering requirement.<\/p>\n<\/div>\n<\/div>\n<\/section>\n

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Wind Turbine Slewing Drives \u2014 25-Year Reliability, From 2 MW to 15 MW<\/div>\n

Korea Ever-Power provides wind turbine yaw and pitch slewing drive planetary gearboxes with 175,000-hour L10 bearing life, IEC 61400 compliance provisions, and marine-grade options for offshore. Provide your turbine platform and site conditions for a specification recommendation.<\/p>\n<\/div>\n

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sales@planetary-gearboxes.com<\/div>\n<\/div>\n<\/div>\n<\/section>\n

\u0e1a\u0e23\u0e23\u0e13\u0e32\u0e18\u0e34\u0e01\u0e32\u0e23: Cxm<\/p>\n<\/div>","protected":false},"excerpt":{"rendered":"

Korea Ever-Power \u00b7 Application Engineering \u00b7 Wind Energy Slewing Drive Planetary Gearbox for Wind Turbines \u2014 25 Years, 100 Metres Up, Zero Unplanned Stops Two slewing drives keep every wind turbine producing power: the yaw drive that rotates the nacelle to face the wind, and the pitch drive that angles the blades to control rotor […]<\/p>","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_et_pb_use_builder":"","_et_pb_old_content":"","_et_gb_content_width":"","footnotes":""},"categories":[965],"tags":[],"class_list":["post-1082","post","type-post","status-publish","format-standard","hentry","category-application-and-technical-guid"],"_links":{"self":[{"href":"https:\/\/planetary-gearboxes.com\/th\/wp-json\/wp\/v2\/posts\/1082","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/planetary-gearboxes.com\/th\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/planetary-gearboxes.com\/th\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/planetary-gearboxes.com\/th\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/planetary-gearboxes.com\/th\/wp-json\/wp\/v2\/comments?post=1082"}],"version-history":[{"count":2,"href":"https:\/\/planetary-gearboxes.com\/th\/wp-json\/wp\/v2\/posts\/1082\/revisions"}],"predecessor-version":[{"id":1085,"href":"https:\/\/planetary-gearboxes.com\/th\/wp-json\/wp\/v2\/posts\/1082\/revisions\/1085"}],"wp:attachment":[{"href":"https:\/\/planetary-gearboxes.com\/th\/wp-json\/wp\/v2\/media?parent=1082"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/planetary-gearboxes.com\/th\/wp-json\/wp\/v2\/categories?post=1082"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/planetary-gearboxes.com\/th\/wp-json\/wp\/v2\/tags?post=1082"}],"curies":[{"name":"\u0e14\u0e31\u0e1a\u0e40\u0e1a\u0e34\u0e25\u0e22\u0e39\u0e1e\u0e35","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}